Abstracts of the 9th International Conference on Durability and Fatigue - Fatigue 2024

Abstracts of the 9th International Conference on

Durability and Fatigue

FATIGUE 2024

Edited by:

E. R. Cawte, S. Stekovic and J.R. Yates

Organised by the Engineering Integrity Society

Abstracts of the 9th International Conference on Durability and Fatigue

FATIGUE 2024

Edited by: E. R. Cawte, S. Stekovic and J. R. Yates

Held at Jesus College, Cambridge, UK 19th - 21st June 2024

Engineering Integrity Society

PUBLISHED IN 2024 BY:

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© 2024 Engineering Integrity Society

ISBN 978-0-9544368-6-5

The full proceedings are available in electronic format from submissions supplied by the various authors. Where formatting alterations to these manuscripts were necessary, the editors cannot accept responsibility for any inaccuracies or for any comments and opinions expressed in the papers.

The following publications of the society are available:

FATIGUE 2021 - FATIGUE & DURABILITY ASSESSMENT OF MATERIALS, COMPONENTS & STRUCTURES - Proceedings of the 8th International Conference of the Engineering Integrity Society, held online, March 29-31, 2021, - Editors: R. Akid, F. Berto, E. R. Cawte, A. Chahardehi, P. Irving, P. Roberts, M. T. Whittaker and J. R. Yates, ISBN 978-0-9544368-5-8 (2021) 461 pages.

FATIGUE 2017 - FATIGUE & DURABILITY ASSESSMENT OF MATERIALS, COMPONENTS & STRUCTURES - Proceedings of the 7th International Conference of the Engineering Integrity Society, Downing College, Cambridge, UK., July 3-5, 2017, - Editors: P. Bailey, E. R. Cawte, P. Roberts, M. T. Whittaker and J. R. Yates, ISBN 978-0-9544368-3-4 (2017) 551 pages.

FATIGUE 2007 - FATIGUE & DURABILITY ASSESSMENT OF MATERIALS, COMPONENTS & STRUCTURES - Proceedings of the 6th International Conference of the Engineering Integrity Society, Queens’ College, Cambridge, UK., March 26-28, 2007, - Editors: M. R. Bache, P. A. Blackmore, E. R. Cawte, P. Roberts and J. R. Yates, ISBN 978-0-9544368-1-0 (2007) 257 pages.

FATIGUE 2003 - FATIGUE & DURABILITY ASSESSMENT OF MATERIALS, COMPONENTS & STRUCTURES - Proceedings of the 5th International Conference of the Engineering Integrity Society, Queens’ College, Cambridge, UK., April 7-9, 2003, - Editors: M. R. Bache, P. A. Blackmore, J. Draper, J. H. Edwards, P. Roberts and J. R. Yates, ISBN 0 9544368 0 6 (2003) 566 pages.

FATIGUE 2000 - FATIGUE & DURABILITY ASSESSMENT OF MATERIALS, COMPONENTS & STRUCTURES - Proceedings of the 4th International Conference of the Engineering Integrity Society, Robinson College, Cambridge, UK., April 10-12, 2000 - Editors: M. R. Bache, P. A. Blackmore, J. Draper, J. H. Edwards, P. Roberts and J. R. Yates, ISBN 1 901537 16 1, 600 pages.

PRODUCT OPTIMISATION FOR INTEGRITY – COMPUTERS: A BOON OR A BURDEN? – Proceedings of the Third International Conference of the Engineering Integrity Society, Sheffield, U.K., April 3-5, 1995 – Editors: E. R. Cawte, J. M. Draper and N. Trigwell, ISBN 0 947817 76 X, 315 pages.

ENGINEERING INTEGRITY IN RAIL TRANSPORT SYSTEMS 1994 –

Proceedings of the Third International Conference on Rail Transport Systems –“Rolling Stock Leasing – The Technical Challenges” organised by the Engineering Integrity Society, Birmingham, U.K., July 11-12, 1994 – Editors: J. H. Edwards, A. Jablonski and R. A. Smith, ISBN 0 947817 72 7 (1994), 260 pages.

ENGINEERING INTEGRITY IN RAIL TRANSPORT SYSTEMS 1993 –

Proceedings of the Second International Conference on Rail Transport Systems organised by the Engineering Integrity Society, Birmingham, U.K. July 12-13, 1993 – Editor: J. M. Tunna, ISBN 0 947817 65 4 (1993), 412 pages.

ENGINEERING INTEGRITY IN RAIL TRANSPORT SYSTEMS –

Proceedings of the First International Conference on Rail Transport Systems organised by the Engineering Integrity Society, Birmingham, U.K., July 13-14, 1992 – Editors: J. M. Tunna and S. J. Hill, ISBN 0 947817 47 6 (1992), 359 pages.

ENGINEERING INTEGRITY THROUGH TESTING – Proceedings of the Second International Conference of the Engineering Integrity Society, Birmingham, U.K., March 20-22, 1990 – Editor: H. G. Morgan, ISBN 0 947817 39 5 (1990), 537 pages.

MEASUREMENT AND FATIGUE – Proceedings of the First International Conference of the Engineering Integrity Society, Bournemouth, U.K., March 1720, 1986 – Editor: J. M. Tunna, ISBN 0 947817 11 5 (1986), 565 pages.

PREFACE

The 9th International Conference on Durability and Fatigue “FATIGUE 2024” was held at Jesus College, Cambridge on 19th - 21st June 2024. This conference series, organised by the Durability & Fatigue Committee of the Engineering Integrity Society, provides a regular interface between leading researchers and practitioners dealing with fatigue issues across the world. The following keynote presentations were given to introduce a number of the major conference sessions:

“Advanced concepts on fatigue and fatigue-crack growth of metallic materials”

Professor James Newman, Mississippi State University, United States

“Design & manufacturing challenges for high pressure disc rotors in aircraft engines”

Dr Mark Hardy, Rolls-Royce Plc., U.K.

“Characterising fatigue crack tip deformation states in nickel base superalloys: slip character, strain accumulation and oxidation effects”

Professor Philippa Reed, University of Southampton, U.K.

The success of any conference depends on many factors, not least an enthusiastic and efficient team of organisers in the background. To this end, we must pay tribute to the following for their commitment, support and in the case of the Local Technical Committee, valuable time and effort spent reviewing the papers submitted for the proceedings:

Conference Secretariat:

Mrs Sara Atkin

Conference Organising Committee:

Dr John Yates

Dr Hollie Cockings

Assoc. Professor Svjetlana Stekovic

Sara Atkin

Local Technical Committee:

Dr Amir Chahardehi

Andrew Blows

Assoc Prof Chris Hyde

Dr Chuanjie Cui

Dr Emilio Martínez-Pañeda

Dr Fabien Lefebvre

Dr Farnoosh Farhad

Prof Filippo Berto

Prof Francisco A Diaz

Prof Hassan Ghadbeigi

Dr Hayder Ahmad

Dr Hollie Cockings

Dr James Rouse

Dr John Yates

Prof Mark Whittaker

Dr Mohamed Bennebach

Naveed Sheikh

Dr Pablo Lopez-Crespo

Paul Roberts

Dr Peter Bailey

Robert Cawte

Dr Spencer Jeffs

Assoc Prof Svjetlana Stekovic

Dr Yi Gao

International Scientific Committee:

Alan Hellier (Australia)

Alberto Campagnolo (Italy)

Alfredo Navarro (Spain)

Ali Fatemi (USA)

André Galtier (France)

Andrea Carpinteri (Italy)

Andrea Spagnoli (Italy)

Barbara Rossi (UK)

Chris Hyde (UK)

Christophe Pinna (UK)

Daolun Chen (Canada)

David Nowell (UK)

Ken Wackermann (Germany)

Fabien Lefebvre (France)

Filippo Berto (Italy)

Francesco Iacoviello (Italy)

Francisco A Diaz (Spain)

Frank Walther (Germany)

Harry Bhadeshia (UK)

Hellmuth Klingelhoeffer (Germany)

Hossein Farrahi (Iran)

James Marrow (UK)

James Newman (USA)

Jan Papuga (Czech Republic)

Johan Moverare (Sweden)

Liviu Marsavina (Romania)

Luca Susmel (UK)

Marc Geers (The Netherlands)

Mark Whittaker (UK)

Martin Bache (UK)

Matteo Benedetti (Italy)

Matteo Luca Facchinetti (France)

Mike Fitzpatrick (UK)

Miloslav Kepka (Czech Republic)

Muhsin J Jweeg (Iraq)

Neil James (UK)

Pablo Lopez-Crespo (Spain)

Paul Bowen (UK)

Phil Withers (UK)

Philippa Reed (UK)

Reinhard Pippan (Austria)

Rob Ritchie (USA)

Robert Akid (UK)

Sabrina Vantadori (Italy)

Shahrum Abdullah (Malaysia)

Svjetlana Stekovic (Sweden)

Takashi Nakamura (Japan)

Thierry Palin-Luc (France)

Veronique Doquet (France)

Wim de Waele (Belgium)

Yee Han Tai (UK)

Yoshihiko Uematsu (Japan)

Youshi Hong (China)

Yukitaka Murakami (Japan)

The organisers wish to record their gratitude to all of the presenters, delegates and sponsors for ensuring the success of this meeting and quality of the Conference Proceedings.

Headline Sponsor:

ZwickRoell

Conference Sponsors:

Altair

Beta CAE Systems

Darvick

Dassault Systèmes Simulia

Hottinger Bruel & Kjaer UK

Instron

Kent

Severn Thermal Solutions

Swansea Materials Research & Testing Ltd (SMaRT)

STEP Lab

TWI

J. R. Yates

Fatigue 2024 Chairman

Front cover image acknowledgements:

Top row L-R: M. Hell (abstract #10.2), J. Nafar Dastgerdi, O. Jaberi & H Remes (abstract #28.2)

Middle row L-R: S. Stekovic, R. Boyd & L. Selegård (abstract #7.3), Y. Yamazaki, K. Okada & K. Yoshida (abstract #24.2)

Bottom row L-R: A. Gonzalez Garcia, J. Jones, R. Lancaster, M. Whittaker, S. John & J. Mason-Flucke (abstract #12.1), K. Wackermann, F. Ebling, T. Michler, F. Schweizer & H. Oesterlin (abstract #26.1), S. Murchio, R. De Biasi, D. Maniglio, A. Rigatti, L. De Nart, V. Luchin & M. Benedetti (paper #7.2)

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CONTENTS

1: KEYNOTE

1.1 Advanced concepts on fatigue and fatigue-crack growth of metallic materials

J. C. Newman Jr.

2: ADDITIVE MANUFACTURING I

2.1 A new additive manufacturing factor dominating fatigue performance of alloys

Y. Hong, Y. Xia, X. Pan & A. Zhao

2.2 Fatigue strength characterisation of wire+arc additively manufactured steel components and the relation with manufacturing imperfections

R. Motte, V. Rappe, R. Nunes, W. Verlinde & W. de Waele

2.3 The high-temperature fatigue properties of additively manufactured nickelcopper alloys with dispersion strengthening particles

I. Šulák, J.P. Roth, M. Gálíková, M. Šmíd & U. Krupp

2.4 Structural integrity of cold spray repaired aluminium alloy 7075 specimens

A. A. Bakir, X. Zhang, M. Dore & P. McNutt

3: TESTING

3.1 Influence of deformation heat on small-scale ultrasonic fatigue tests in 304 stainless steel

J. Gong & A. J. Wilkinson

3.2 Refinement of cyclic R-curve determination on extrinsically short cracks by annealing

L. Walch, T. Klünsner, G. Ressel, A. Hohenwarter & R. Pippan

3.3 Mesoscale cantilever testing of high cycle fatigue crack initiation and short crack growth in Ti-6Al-4V

L. Pujilaksono, J. Gong & A. J. Wilkinson

3.4 Advances in a novel ultrasonic fatigue method on CMSX-4 meso-cantilevers

R. J. Scales, J. Gong & A. J. Wilkinson

4: IMAGING

4.1 Characterisation of the forward and backward plastic zone in the crack tip of a fatigued sample

J. A. Aguilera, P. M. Cerezo, A. S. Cruces, A Garcia-Gonzalez, A. Steuwer, T. Buslaps, P. J. Withers & P. Lopez-Crespo

4.2 In-situ full-field strain mapping by HR-EBSD and J-integral analysis of a short fatigue crack in Ni

X. Su, R. Scales, A. Koko, J. Gong & T. J. Marrow

4.3 Advanced stress intensity factor monitoring in additively manufactured 18Ni300 samples using digital image correlation

P. M. Cerezo, J. A. Aguilera, A. S. Cruces, A. Garcia-Gonzalez, R. Branco, L. Borrego & P. Lopez-Crespo

5: JOINTS

5.1 High temperature fatigue crack growth in nickel-based alloys joined by brazing and additive manufacturing

A. Bhadeliya, B. Rehmer, B. Fedelich, T. Jokisch, B. Skrotzki & J. Olbricht

5.2 A practical approach for the fatigue life estimation of hybrid joints through testing and numerical simulations

C. Bagni, A. Halfpenny, M. Hill & A. Tarasek

5.3 An investigation into fatigue failure and self-loosening of bolted joints subjected to transverse vibration

S. Hashimura & A. Saito

5.4 A practical methodology for the fatigue testing of hybrid joints

A. Pierpoint, M. Hill & C. Bagni

6: PROBABILISTIC MODELLING

6.1 A probabilistic fatigue model using Gaussian processes and its application to additively manufactured metals

M. Schultz, H. Erdelyi, M. Hack, S. Straesser & N. Lammens

6.2 Probabilistic modelling of fatigue behaviour in inhomogeneous metallic materials using physics-based machine learning approaches

E. Salvati, A. Tognan, M. Pelegatti, L. Laurenti & F. De Bona

6.3 3Dprint AM35 wire arc additively manufactured milled specimens under fatigue

B. Karabulut, X. Ruan, S. MacDonald, J. Dobric & B. Rossi

6.4 A comparative investigation on the uniaxial plain and notch fatigue strengths of heavy-section castings made of pearlitic and high-silicon ferritic ductile cast irons

M. Pedranz, V. Fontanari, C. Santus, F. Zanini, S. Carmignato, G. Angella, D. Lusuardi, F. Berto & M. Benedetti

7: TITANIUM ALLOYS I

7.1 Predicting fatigue crack initiation in milled aerospace grade Ti-6Al-4V parts using CPFEM

M. F. Arcidiacono, I. Violatos & S. Rahimi

7.2 Uncovering the role of building orientation and stress ratio on the fatigue behaviour of L-PBF Ti6Al4V miniaturised strut-like lattice specimens

S. Murchio, R. De Biasi, D. Maniglio, A. Rigatti, L. De Nart, V. Luchin & M. Benedetti

7.3 Cracking and damage mechanisms in nitrided Ti64 grade 5 alloy after high cycle fatigue

S. Stekovic, R. Boyd & L. Selegård

8: SURFACE CONDITIONS

8.1 Plenary Lecture: The effect of specimen machining processes on fatigue life of 42CrMo4+QT steel

J. Papuga, T. Vrbata, K. Trojan, A. Trefil, A. Zabala & V. Mára

8.2 Stability of compressive residual stresses in austempered ductile iron (ADI) under cyclic loading

U. Hähnel, E. Müller & P. Hübner

8.3 Impact of laser shock peening on fatigue strength of additively manufactured AlSi10Mg

M. Matušů, O. Stránský, J. Šimota, L. Džuberová, J. Rosenthal, J. Papuga & L. Beránek

8.4 Effect of zinc coating and grease on the fretting fatigue life of crossed steel wire contacts: application to offshore spiral ropes

S. Montalvo, S. Fouvry & M. Martinez

8.5 Hot corrosion fatigue behaviour of a shot peened nickel based superalloy

Y. Li, H. Cockings, M. Whittaker, B. J. Cockings, P. M. Mignanelli, R Buckingham & M. R. Bache

8.6 Fatigue failure mechanisms and life prediction of a laser shock peened disc alloy

R. Jiang, J. Zhang, R. Wang, C. You & Y. Song

8.7 Advantages of laser shock peening over the conventional shot peening of the fatigue lifetime of aluminium 2024 alloy

H. Ahmad & M. Craig

9: HIGH TEMPERATURE

9.1 The effects of H+ fusion plasma loading on the low-cycle thermal fatigue behaviour of tungsten

J. Hargreaves, J. Scholten & T. Morgan

9.2 Effects of temperature measurement and adiabatic heating during strain controlled fatigue tests

P. B. S. Bailey

9.3 Real time structural health prediction for critical industrial application

C. J. Hyde, B. Engel & A. Morris

9.4 Consideration of elastoplasticity and viscoplasticity during thermomechanical fatigue simulations of a pipe bend using the FEM-implemented Prandtl operator approach

D. Šeruga, M. Nagode, J. Klemenc & S. Oman

9.5 Effects of frequency and dwell on the fatigue crack propagation in single crystal Ni-based superalloy CMSX-4 at intermediate service temperature

J. C. Doyle, A. Evangelou, E. A. Saunders, J. M. Woolrich, N. Gao & P. A. S. Reed

9.6 Thermomechanical fatigue properties of additively manufactured nickel-based superalloy IN939

M. Gálíková, I. Šulák & I. Kuběna

9.7 High-temperature viscoelastic-viscoplastic deformation of 316 stainless steel

K. Sithole, W. Lavie, B. Engel, J. P. Rouse & C. J. Hyde

10: DESIGN

10.1 Plenary Lecture: Scale-bridging fatigue assessment of steels – from production to performance

N. Baak, K. Donnerbauer, A. Kalenborn, H. Kanagarajah, L. Lücker, L. Lingnau, J. L. Otto, J. Rozo Vasquez, S. Strodick & F. Walther

10.2 Fatigue design of cast aluminium passenger car wheels with respect to the transfer of cyclic material properties

M. Hell

10.3 Predicting the fatigue life of steel cables

L. Larippe, A. Lecercle, A. Jamoneau, C. Gandiolle, J-Y. Buffière & V. Aubin

10.4 Implementation of fatigue crack growth laws in Abaqus

H. Farid

10.5 Finite element analysis of the MAGEC spinal rod under compressive and shear loading conditions

T. S. Mosley, M. Birkett, T. J. Joyce & F. Farhad

11: KEYNOTE

11.1 Design & manufacturing challenges for high pressure disc rotors in aircraft engines

M. Hardy, C. Argyrakis, P. Bowen, R. Buckingham, H. Cockings, B. Grant, S. Gray, T. Jackson, H. Kitaguchi, H. Li, D. MacLachlan, H. Tai & M. Taylor

12: SUPERALLOYS I

12.1 Phase angle effects on thermo-mechanical fatigue (TMF) in a single crystal nickel superalloy

A. Gonzalez Garcia, J. Jones, R. Lancaster, M. Whittaker, S. John & J. Mason-Flucke

12.2 Coupling effects of temperature and fatigue, creep-fatigue interaction and thermo-mechanical loading conditions on crack growth and dominant failure mechanisms of a nickel-based alloy

V. Shlyannikov, A. Shanyavskiy, A. Sulamanidze & D. Kosov

12.3 Study on thermo-mechanical fatigue crack propagation behaviour of powder metallurgy superalloy

L. Zhang, Y. Z. Wang, Z. W. Yu, R. Jiang, L. G. Zhao & Y. D. Song

12.4 Evaluation of fatigue striations in a nickel-based superalloy

Y. Alyousif, E. A. Saunders, S. Taylor, J. C. Walker & P. A. S. Reed

13: NON-METALLIC MATERIALS

13.1 Crack growth in a piezoelectric ceramic induced by a cyclic electric field

K. Hockauf, F. Poschmann & R. Pleul

13.2 High- and low-cycle tensile fatigue of all-carbon hybrid quasi-isotropic laminate

V. Carvelli, S. B. Sapozhnikov, S. V. Lomov & Y. Swolfs

13.3 Mean stress correction for carbon fibre reinforced polymer composites under fatigue loading

Z. Lu

13.4 Fracture and fatigue characterisation of the shot-earth 772

A. Zanichelli, A. Carpinteri, C. Ronchei, S. Scorza & S. Vantadori

13.5 Investigations on experimental fatigue life and damage of designed hybrid composite laminates with negative and positive Poisson’s ratio

H. Hosseini-Toudeshky, M. Tashayyoee, A. Navaei, J. Nafar Dastgerdi & S. Esmaeili

14: VARIABLE AMPLITUDE

14.1 Fatigue crack growth behaviour of 9310 steel under constant and variable-amplitude loading

T. M. Senhaji & J. C. Newman Jr.

14.2 Plastic CTOD as fatigue crack growth characterising parameter under variable amplitude loading by using DIC

G. L. Gómez-Gonzales, A. Camacho-Reyes, J. M. Vasco-Olmo, F. A. Díaz, D. Neto & F. V. Antunes

14.3 Machine learning based fatigue life prediction of metal components subjected to block loading

K. Hectors, Q. Bouckaert, J. Plets & W. De Waele

15: WELDS I

15.1 Industry-oriented assessment of the fatigue life of thin-walled profile weldments used in the construction of bus bodies

M. Kepka, R. Minich, M. Krizek & M. Kepka Jr.

15.2 Influence factors on fatigue strength of arc-welded joints using ultra-high strength steel sheets and its improving methods

N. Yamaguchi, T. Shiozaki, Y. Tamai, Y. Ichikawa & K. Ogawa

15.3 Fatigue of ultrasonic spot welded joints of lightweight materials

D. Chen

16: CONTACT

16.1 Evaluation of non-proportional multi-axial stress states in drive-train components related to contacts

J. Schanner, A. Hasse & L. Suchý

16.2 Fretting fatigue of shafts under varying contact pressure and creep slip conditions in bearing-shaft contacts

D. Knabner, L. Suchý, S. Busch & A. Hasse

16.3 Influence of microstructure, stress gradient and defect size on the stability of the critical distance method for fretting crack nucleation

H. Lannay, S. Fouvry, B. Berthel & C. Glandiolle

17: MULTI AXIAL

17.1 Cracking behaviour and lifetime predictability of P558 steel in annealed and cold deformed states under mixed complex loading

T. Ngeru & S. Hanke

17.2 Fatigue crack growth in air or in oil, under cyclic mode II + static biaxial compression

M. Zaid, V. Bonnand, D. Pacou, V. Chiaruttini, V. Doquet & P. Depouhon

17.3 The critical distance concept to design notched 3d-printed metals against uniaxial/multiaxial fatigue

L. Susmel

17.4 Experimental and computational investigation of mixed mode fatigue crack propagation

B. Sheen, C. M. Davies & D. Nowell

18: TITANIUM ALLOYS II

18.1 High-cycle and very-high-cycle fatigue behaviour and life prediction of Ti6Al-4V fabricated by laser powder bed fusion

C. Ling & L. Zheng

18.2 Effect of discontinuous printing on the fatigue limit of selective laser melted Ti6Al4V specimens

A. H. Jabbari Mostahsan, F. Farahmand & D. Domitner

18.3 Influence of defect shape and position on the high cycle fatigue behaviour of additively manufactured TA6V alloy

M. Bonneric, N. Saintier, D. El-Khoukhi & J. Bega

19: ENVIRONMENT I

19.1 In vitro short-time testing method for evaluating the long-time corrosion fatigue strength of biomedical magnesium alloys

N. Wegner, K. Donnerbauer, L. Hempel & F. Walther

19.2 Effect of artificial corrosion on retardation of fatigue crack growth –assessment by local cyclic plasticity

H. Shibata, K. Staoh, R. Fincato & S. Tsutsumi

19.3 Experimental validation of a model for predicting the bending fatigue strength of corroded grey cast iron water pipes

E. John, J. Boxall, R. Collins, E. Bowman & L. Susmel

20: SIMULATION

20.1 Plenary Lecture: Predictions of crack growth rates, R-ratio effects and overload behaviour based on smooth specimen LCF test data and using a strip yield-type model

S. J. Williams, M. T. Whittaker & M. C. Hardy

20.2 An investigation of the RSE-M crack closure parameter F(R) on a large ferritic PWR component with negative R-ratio including welding residual stress

M. P. Nielsen

20.3 Fatigue crack growth and crack closure in 304L large compact tension specimens with cyclic crack tip plasticity

M. M. J. Gillet & C. M. Davies

20.4 Numerical approaches in the fatigue damage simulation in quasi-brittle materials

L. Ferreira Friedrich, A. Bordin Colpo, S. Vantadori, F. Soares & I. Iturrioz

20.5 Proposal of a fatigue crack extension mode and its prediction method — damage accumulation mode fatigue crack propagation

S. Hamada, Y. Okawa & Y. Araki

21: ADDITIVE MANUFACTURING II

21.1 The transition of grain boundary in an additively manufactured aluminium alloy under very-high-cycle fatigue

X. Pan & Y. Hong

21.2 Role of columnar β grains on fatigue crack growth behaviour in additive manufactured titanium alloy Ti6Al4V

A. Khadar Syed, A. E. Davis & X. Zhang

21.3 Using fatigue crack growth tests for quality assessment in additive manufacture

P. B. S. Bailey

21.4 Investigation on the fatigue behaviour of stainless steel 316L produced by laser powder bed fusion process

M. Shahriarifar, M. Doré, M. Dodge, K. Khan & X. Zhang

22: ENVIRONMENT II

22.1 Defect-based assessment of mechanical and corrosive loads on the capability of light metal structures

N. Wegner, A. Koch & F. Walther

22.2 Effects of pitting corrosion on fatigue performance of legacy cast iron pipe materials

L. Ronayne, J. A. Wharton & P. A. S. Reed

22.3 Investigating the role of low temperature hot corrosion on crack initiation and propagation in single-crystal nickel alloys under fatigue conditions

M. Elsherkisi, L. Brooking, J. Mason-Flucke & S. Gray

23: KEYNOTE

23.1 Characterising fatigue crack tip deformation states in nickel base superalloys: slip character, strain accumulation and oxidation effects

P. A. S. Reed

24: SUPERALLOYS II

24.1 Fatigue crack propagation behaviour of the grain size transition zone in a dual microstructure turbine disc

Y. C. Wang, R. Jiang, L. C. Zhang & Y. D. Song

24.2 Effects of microstructure and oxidation on fatigue crack initiation behaviour in a titanium aluminide alloy

Y. Yamazaki, K. Okada & K. Yoshida

24.3 Study on fatigue crack propagation mechanism and model of a powder metallurgy superalloy under gas-marine environment

L. C. Zhang, R. Jiang, J. T. Liu, Y. W. Zhang & Y. D. Song

25: LIFING

25.1 Integration of physical and virtual tests for achieving high confidence in fatigue reliability of automotive battery systems

A. Halfpenny, K. Tahera, B. Thumati & C. Wynn-Jones

25.2 Mechanistically based fatigue lifetime predictive model for legacy steam turbine blades

A. Masis Khodavirdi, A. Hamilton & P. A. S. Reed

25.3 Frequency domain fatigue approach for sine swept loadings

G. De Morais

25.4 Key issues with residual fatigue life estimation in steels, highly scattered and non-conservative thresholds, crack closure mechanisms, influencing factors, relevant material properties

T. Vojtek, R. Kubíček, P. Pokorný, M. Jambor, L. Náhlík & P. Hutař

26: HYDROGEN

26.1 Plenary Lecture: Design, usage and safety aspects for tubular specimens for materials qualification with pressurised hydrogen

K. Wackermann, F. Ebling, T. Michler, F. Schweize & H. Oesterlin

26.2 Phase field modelling of hydrogen-assisted fatigue

E. Martínez-Pañeda, A. Golahmar & C. F. Niordson

26.3 Correlation of fatigue behaviour in pressurised hydrogen and electrolytically supplied hydrogen

S. Schönborn & A. Kansy

26.4 Effect of pressurised hydrogen on low cycle fatigue of Inconel 718: modelling and testing

F. Ebling, H. Oesterlin & K. Wackermann

27: MICROSTRUCTURAL INFLUENCES

27.1 Fatigue damage assessment of C45 samples via different experimental measurements and microstructural investigations

A. Saponaro, R. De Finis, G. Renna, P. Leo & R. Nobile

27.2 Cyclic loading induced dynamic refinements of local microstructures in high-strength martensitic steels

S-S. Rui, S. Wei & C. Sun

27.3 A corroborative study on the fatigue mechanisms at room and elevated temperatures of a dual-phase high entropy alloy

Q. Han, Y. T. Tang & R. C. Reed

28: ADDITIVE MANUFACTURING III

28.1 Short fatigue crack behaviour in a new aluminium alloy AlMgSc fabricated by wire based directed energy deposition

J. Ye, A. Khader Syed & X. Zhang

28.2 On the role of the internal and surface defects in the fatigue and structural integrity of additively manufactured 316L stainless steel

J. Nafar Dastgerdi, O. Jaberi & H. Remes

28.3 Continuum damage mechanics approach for SLM-manufactured nickelbased superalloy under multiaxial fatigue loading conditions

H. Yuan, J. Xu & J. Lu

29: WELDS II

29.1 Improved fatigue calculation of attachment welds in offshore wind structures using additive MK factor

J. Taylor

29.2 Fatigue performance of modern submerged arc welds in 85mm grade S355 steel

C. Johnston

29.3 Impact of shot peening on the fatigue strength of arc-welded advanced high strength steel assemblies

A. Nabara, C. Mareau, F. Morel, M-R. Chini, R. Munier, P. Kusakin & M. L. Facchinetti

POSTERS

P1 Effect of environment on fatigue crack growth of polycrystalline nickel-based superalloys at high temperatures

J. Buckley, H. L. Cockings, Y. Li & M. Hardy

P2 Investigations of the GRP beams for dynamic loaded structures behaviour during three-point bending test

M. Fikrle & J. Chvojan

P3 Effects of build orientation on high-temperature fatigue behaviour of laser powder bed fusion Inconel 718

M. Hulbert, P. A. S. Reed & A. Hamilton

P4 Predicting the fatigue limit of lath martensitic steel microstructures

S. Kino, D. Itoh, S. Ueki & S. Hamada

P5 Mechanistic understanding of life extensition of ageing offshore structures

S. Manzoor, K. Khan, X. Sun & N. Larrosa

P6 Investigation into the fatigue performance of aluminium cold spray substrate alloys

R. Reed, P. A. S. Reed, A. A. Bakir, A. W-Y. Tan & A. G. S. Araujo

P7

Notch-stress approach for the fatigue life evaluation of rough wire arc additively manufactured plates

X. Ruan, B. Karabulut, J. Dobric & B. Rossi

1: KEYNOTE

ADVANCED CONCEPTS ON FATIGUE AND FATIGUE-CRACK GROWTH OF METALLIC MATERIALS

J. C. Newman Jr.1

The classic paper by Paris, Gomez and Anderson on “A Rational Analytical Theory of Fatigue” was a major development in the study of fatigue. The newly emerging field of Fracture Mechanics, driven by the works of Griffith and Irwin, began to help engineers characterize fracture of brittle materials; and to provide the stress-intensity factor (K) to correlate fatigue-crackgrowth data on metallic materials for various crack configurations, and to provide a method to predict failure of cracked structural components.

In the early 1970’s, attempts by the author to predict “fatigue” of engineered metallic materials using the stress-intensity-factor concept were unsuccessful. Several things had to be developed before fatigue, especially under spectrum loading, could be predicted using Fracture Mechanics: (a) stress-intensity factors for small surface cracks, (b) crack-closure theory, (c) plasticity effects on the crack-driving parameter, (d) constraint effects on crack growth and crack closure, (e) small- and large-crack data in the “threshold” regime without load-history effects, and (f) understanding micro-structural initiation sites for various materials and micro-machining marks. After several decades of research, these concepts began to merge, and fatigue can now be calculated or predicted on “engineered” metallic materials. These are materials that nucleated cracks at constituent particles, inclusions, grain boundaries, voids, and, also, manufacturing defects (such as machining marks).

The current presentation reviews application of an improved FASTRAN (life-prediction) code, based on the principles of Fracture Mechanics and Elber’s crack-closure theory, to calculate or predict fatigue behavior of notched coupons made of a variety of materials using only crack-growth properties and a micro-structural feature (inclusion-particle size). The approach has been successful applied to aluminium alloys, titanium alloys, and steels.

The presentation reviews some advanced concepts on characterizing fatigue and crack growth in a variety of materials. Low fatigue-crack-growthrate data has been affected by the current ASTM E-647 load-shedding test procedure. Thus, large-crack threshold data is not valid but small-crack data is the appropriate data to use in the low-rate regime. In addition, major differences in fatigue-crack-growth-rate data in terms of the stress-intensity factor range (∆K) on various crack configurations have been observed on a railway steel and a titanium alloy. Cracks in tension-loaded crack configurations grow faster than those in bend-loaded crack configurations at the same ∆K. Future research on fatigue-crack-growth rate behavior should address these issues.

1Department of Aerospace Engineering, Mississippi State University, Mississippi State, Mississippi, USA

2: ADDITIVE MANUFACTURING I

A NEW ADDITIVE MANUFACTURING FACTOR

DOMINATING FATIGUE PERFORMANCE OF ALLOYS

Y. Hong1, Y. Xia1,2, X. Pan1 & A. Zhao2

Additive manufacturing (AM) as an innovative and promising technique has been widely used to produce complex engineering components with high efficiency and relatively low cost. However AM parts inevitably contain intrinsic propensities such as (i) evident internal and surface defects, (ii) fine microstructure with anisotropy, and (iii) large residual stresses. These propensities of AM parts greatly affect the related mechanical properties especially fatigue performance.

The mechanical behaviour is basically attributed to the microstructure and porosity (or defects) of AM materials, which is resulted from the AM process with a set of processing parameters. Thus, the combination of AM processing parameters is a key point to determine the microstructure and porosity, and therefore to result in the given mechanical behaviour.

In the process of selective laser melting (SLM) or laser powder bed fusion (L-PBF) that is the technology frequently used to produce AM alloys, a factor of laser energy density E v=P/(v-h-t) was proposed to characterise AM process, where P is laser power, v is scan speed, h is hatch spacing, and t is layer thickness. In our previous research and other results in the literature, the effects of processing parameters, in terms of E v on the porosity and mechanical properties especially fatigue performance of AM alloys were preliminarily addressed.

Here in this paper, the effects of AM processing parameters on the mechanical behaviour of AM parts are comprehensively investigated. The data of porosity, tensile properties and fatigue strength in high-cycle and very-high-cycle regimes of AM titanium and aluminium alloys as a function of laser energy density (Ev) are collected from our research and from the literature. Based on such data collections, the variation of E v

with porosity, tensile properties and fatigue performance of AM titanium and aluminium alloys is analysed and to evaluate the optimal range of the processing parameters in terms of E v .

More importantly, a new dimensionless factor for AM processing is therefore proposed, which is capable for characterising the AM process with the main target of porosity and the resulted mechanical properties especially high-cycle and very-high-cycle fatigue performance of AM alloys. The dimensionless factor is a combination of E v with the intrinsic quantities of elastic modulus, shear modulus, Burgers vector staking fault energy, melting point and Boltzmann constant for related alloys. This dimensionless factor is intended to be used in AM quality control, and thus to obtain the lowest value of porosity (also in terms of defect volume fraction and the number of pores or lack of fusions) and the highest values of fatigue strength and tensile properties of AM alloys.

1LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China

2College of Civil Engineering, Nanjing Tech University, Nanjing 211816, China

FATIGUE STRENGTH CHARACTERISATION OF

WIRE+ARC ADDITIVELY MANUFACTURED STEEL COMPONENTS AND THE RELATION WITH MANUFACTURING IMPERFECTIONS

R. Motte1, V. Rappe1, R. Nunes2, W. Verlinde2 & W. De Waele1

In this paper, the fatigue performance of two steels (denoted as EMK8 and 1%Ni) produced by wire+arc additive manufacturing (WAAM) is characterised by rotating bending fatigue experiments. Specimens were extracted from thin walls and thick blocks in both X- (deposition) and Z(build) directions. The walls produced from EMK8 showed statistically relevant anisotropy in fatigue performance. No significant anisotropy was observed for the blocks of EMK8 material, nor for the 1%Ni material. The experimentally obtained S-N curves of both materials were also benchmarked against data for conventionally manufactured steel grades. For the EMK8 material, only the endurance curve for the X-direction of the walls was seen to exhibit higher fatigue performance than the reference curves. For the 1%Ni material, the fatigue performance exceeds the references for both directions. The fracture surfaces of all failed specimens were investigated in order to characterise manufacturing imperfections and their impact on the fatigue performance.

1Department of EMSME, Laboratory Soete, Faculty of Engineering and Architecture, Ghent University, Technologiepark 46, BE-9052, Zwijnaarde, Belgium

2Belgian Welding Institute, Technologiepark 48, BE-9052, Zwijnaarde, Belgium

THE HIGH-TEMPERATURE FATIGUE

PROPERTIES OF ADDITIVELY MANUFACTURED NICKEL-COPPER ALLOYS WITH DISPERSION

STRENGTHENING PARTICLES

I. Šulák1*, J-P. Roth2, M. Gálíková1, M. Šmíd1 & U. Krupp3

For the last few years, additive technologies have been at the forefront of research and development, bringing a range of advantages in component design as well as opportunities to create unique microstructures with tailored properties. Associated with these rapid technological advances is intensive research into mechanical properties with a direct link to the unique hierarchical structure. Given the limited choice of commercially available alloys for additive manufacturing, it is also essential to evaluate new alloy compositions to optimise their production and improve overall performance. In this study, the effect of different dispersion strengthening particles (TiN, Y2O3) on high cycle fatigue properties of additively manufactured nickelcopper alloy 400 in as-build conditions was investigated. Force-controlled high-temperature fatigue experiments were performed on miniaturised cylindrical specimens in the temperature range of 400 °C to 750 °C. Direct comparison with conventionally prepared alloy and non-strengthened 3D printed specimens showed the strengths of the dispersion strengthening (Fig. 1). The results of the fatigue tests will be discussed with repect to the manufacturing variables and resulting microstructural features revealed by SEM and TEM analyses.

Fig. 1 S-N curve of TiN modified nickel-copper alloy 400 (MAC-ISIN-400) in comparison with (a) conventionally produced alloy 400 (bulk) (b) 3D printed alloy 400 without strengthening particles (SAC-UN-400).

1Institute of Physics of Materials, Czech Academy of Sciences, 61600 Brno, Czech Republic

2Faculty of Engineering and Computer Science, Osnabrück University for Applied Sciences, 49076 Osnabrück, Germany

3RWTH Aachen University, Steel Institute, D-52072, Aachen, Germany

* Corresponding author: sulak@ipm.cz

STRUCTURAL INTEGRITY OF COLD SPRAY REPAIRED ALUMINIUM ALLOY

7075 SPECIMENS

A. A. Bakir*1,2, X. Zhang1, M. Dore1,3 & P. McNutt3

Aluminium alloy 7075 is widely used in the aerospace industry owing to its high strength-to-weight ratio and durability. Nonetheless, these components are prone to damage during their operational lifespan, such as corrosion pits, and fatigue cracks. Repairing such components becomes crucial to minimise costs, maintenance time, and environmental impact. Cold spray is a promising technique to repair temperature and oxidation sensitive materials because of its solid-state nature. Peng et al. [1, 2] showed that under cyclic loading the cracks originate on the substrate surface and propagate within the substrate. However, further research is needed to understand the causes of crack initiation and the performance of cold spray repaired specimens with different repair geometries under static and cyclic loads.

Tensile test results showed that the cold spray repair patch contributes to the load carrying capacity, but the patch failed at a low strain level (0.7% elongation) and stress level equivalent to 82% of the UTS level of the wrought material. To understand the repair performance under cyclic loading, axial fatigue tests were performed as per ASTM E466 with a stress ratio of R=0.1. Four types of specimens were tested, see Figure 1: undamaged, single-side groove repaired, double-side groove repaired and dent repaired.

FIGURE 1 Schematic of the fatigue specimens and the cross-section view showing the repair ratios. A) undamaged, B) single side groove repaired, C) double side groove repaired, D) dent repaired.

The S-N curve indicated a significant decrease in fatigue life by an order of magnitude for the repaired specimens at higher stress levels (e.g., 70% of the base material yield strength). Notably, among the repaired specimens, centre dent samples exhibit a better fatigue performance reaching 10 million cycles at lower stress levels (50% of the yield strength). This can be attributed to the centre dent specimens having a lower area fraction of the repair and a reduced stress concentration factor compared to the other repaired geometries.

Fractographic analysis showed that the cold spray repaired specimens experienced fatigue fracture as a result of crack initiation on the substrate surface. The main source of the initiation sites is the stress concentration on the substrate surface due to the craters formed as a result of particle impact during the cold spray deposition.

Our ongoing research also aims to explore the influence of repair geometry on fatigue performance in real-life structures. Specifically, numerical modelling is used to model the crack growth from craters under different stress levels. These results can aid repair design and improve the effectiveness of cold spray repair for structural components.

References

(1) Peng, D., Jones, R., Matthews, N. and CaTang, C., Applied Surface Science Advances, 3, 2021, 100044.

(2) Peng, D., Tang, C., Matthews, N., Jones, R., Kundu, S., Raman, R. S., and Alankar, A., Materials, 14, 2021, pp 4451.

1Faculty of Engineering and Computing, Coventry University, Coventry, CV15FB, UK

2NSIRC, TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK

3TWI Ltd., Cambridge CB21 6AL, UK

3: TESTING

INFLUENCE OF DEFORMATION HEAT ON SMALL-SCALE ULTRASONIC FATIGUE TESTS

IN 304 STAINLESS STEEL

J. Gong1* & A. J. Wilkinson1

Fatigue crack initiation (FCI) and short crack growth (SCG) are one of the most important topics in the field of fatigue. Our group developed ultrasonic micro- and meso-cantilever fatigue testing techniques that can assess FCI and SCG in a well controlled small volume of materials. One critical concern in ultrasonic fatigue testing is the deformation heat. The temperature of a specimen can increase significantly due to the ultra-high strain rate up to ~ 103/s. This paper will assess the influence of deformation heat in small-scale ultrasonic fatigue tests.

A thermo-mechanical coupling model was built to simulate the dynamic response of a meso-cantilever with respect to the ultrasonic vibration. Conservative boundary conditions were made to predict the heat generated by the deflection of a beam. The results show that the highest temperature occurs at the front end of a cantilever and the max temperature increase is ~ 30 ˚C. Based on the modelling, an in-situ experiment was conducted by means of an infrared thermal microscope to map the temperature field in 304 stainless steel meso-cantilevers during an ultrasonic fatigue test. The temperature of a specimen increases by a few ˚C before a complete failure. We believe that the marginal temperature increase is due to the high surfaceto-body aspect ratio which can efficiently dissipate the deformation heat into theenvironments and holder.

Meso-scale ultrasonic tests were conducted in 304 stainless steel cantilevers from 104 to 109 cycles. The results show that the SN curve achieved with forced high pressure air cooling is comparable to the fatigue data without cooling, indicating that the deformation heat has imperceptible effect in our meso-scale ultrasonic fatigue tests.

1University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, United Kingdom

*Corresponding Author: jicheng.gong@materials.ox.ac.uk

REFINEMENT OF CYCLIC R-CURVE

DETERMINATION ON EXTRINSICALLY SHORT CRACKS BY ANNEALING

L. Walch1*, T. Klünsner1, G. Ressel1, A. Hohenwarter2 & R. Pippan3

Reliable information on the resistance to fatigue crack propagation is a key parameter for fatigue life predictions. However, an accurate determination of the cyclic R-curve is demanding. One challenge in the involved experimental techniques consists of introducing a pre-crack. When precracks are generated by cyclic compression-compression loading, a zone of tensile residual stresses of up to material yield strength is generated ahead of the crack tip. A small zone of these residual stresses remains even when the sample is subjected to very high numbers of load cycles during pre-cracking. These stresses may affect crack propagation during the actual crack propagation test and should consequently be removed. However, subsequent stress-relief annealing is impractical for numerous metallic material classes due to undesired microstructural alterations at the temperatures required for stress relief. In the present contribution, the above-described issue is addressed for a high speed steel using single-edge notched bending specimens pre-cracked at various stages of a typical high speed steel heat treatment process.

1Materials Center Leoben Forschung GmbH (MCL), Roseggerstraße 12, A-8700, Leoben, Austria

2Department of Materials Science, Chair of Materials Physics, Montanuniversity Leoben, Jahnstraße 12, A-8700 Leoben, Austria

3Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, A-8700 Leoben, Austria

MESOSCALE CANTILEVER TESTING

OF HIGH CYCLE FATIGUE CRACK INITIATION AND SHORT CRACK GROWTH IN Ti-6Al-4V

L. Pujilaksono1*, J. Gong1 & A. J. Wilkinson1

Fatigue crack initiation (FCI) and short crack growth (SCG) consume most of the fatigue life in the very high-cycle regime. The growth rates of short cracks exceed those of long cracks within the same driving force. Additionally, short cracks also provide lower ΔK thresholds than long cracks. These behavioural differences lead to over-predicting the component life when using conventional growth rate models based on long cracks and linear elastic fracture mechanics (LEFM) [1].

Ti-6Al-4V is the primary material assessed due to its stringent fatigue properties in safety-critical jet engines. The ultrasonic fatigue method uses a mesoscale cantilever to overcome the difficulties in assessing fatigue mechanisms using conventional fatigue methods. The small sample size used in this ultrasonic fatigue setup minimises the “needle in a haystack” issue found in common fatigue specimens, which allows for the rapid characterisation of short cracks and their growth. A full set of S-N curve has been achieved in Ti-6Al-4V mesocantilevers from 104 to 109 cycles. Due to a miniature sample size, the fatigue data presents the life of FCI and SCG.

An interrupted ultrasonic fatigue test method was developed based upon the change in deflection angles of a mesocantilever to evaluate the crack tip conditions and propagation rate at different short crack lengths. The interrupted sample with different lengths of short cracks is then characterised using multiple methods. High angular resolution EBSD (HR-EBSD) using the cross-correlation method [2] is performed to evaluate the GND densities and local strain mapping ahead of the crack tip. Besides ΔK, the SCG rate will be related to the crack tip stresses and plastic zone in this study.

References

[1] Ritchie, R. O. and J. Lankford (1986). “Small fatigue cracks: A statement of the problem and potential solutions.” Materials Science and Engineering 84: 11-16.

[2] Wilkinson AJ, Meaden G, Dingley DJ (2006). “High-resolution elastic strain measurement from electron backscatter diffraction patterns: new levels of sensitivity”. Ultramicroscopy.

1University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, United Kingdom

*Corresponding author: lazuardi.pujilaksono@materials.ox.ac.uk

ADVANCES IN A NOVEL ULTRASONIC FATIGUE METHOD

ON CMSX-4 MESO-CANTILEVERS

R. J. Scales1*, J. Gong1 & A .J. Wilkinson1

CMSX-4 is a significant single-crystal nickel superalloy used in the highpressure turbine blades of jet engines. In service, the blades can undergo very high cycle fatigue [1] whilst under harsh environmental conditions. A novel small-scale ultrasonic fatigue method that bends meso-cantilevers is used in this research [2], which has the benefits of: reducing the region to find crack initiation; a larger short-crack:sample dimension ratio aiding the valuable study of short fatigue cracks; enhancing environmental effects from the large area:volume ratio. The samples’ small size allows for appreciable stress amplitudes when driven far away from its resonant frequency, allowing for the same sample design to be used under different temperatures. With the aforementioned benefits, CMSX-4 has been fatigued using this technique under ambient; room temperature vacuum (<10-5 mbar); high-temperature air; and high-temperature vacuum conditions. Developments in the testing capabilities and methodology have also been implemented. The achieved SN data for CMSX-4 shows that it is stronger under vacuum than in air at room temperature, and that in air it is stronger at 450°C than at room temperature.

Intermittent low-power frequency sweeps have been used to find and track the change in sample’s resonant frequency due to short crack growth. The crack length and resonant frequency of a cantilever are correlated by finite element modelling.

High angular-resolution electron back-scattered diffraction (HREBSD) and electron channelling contrast imaging (ECCI) have been used to assess dislocations and stress fields near the fatigue crack tip [3]. Energy dispersive X-ray spectroscopy (EDS) was used to visualise chemical influences. SEM fractography to study the fatal crack’s history and critical defect(s).

References

[1] A. Cervellon, S. Hémery, P. Kürnsteiner, B. Gault, P. Kontis, and J. Cormier, “Crack initiation mechanisms during very high cycle fatigue of Ni-based single crystal superalloys at high temperature,” Acta Mater, vol. 188, pp. 131–144, Apr. 2020, doi: 10.1016/J.ACTAMAT.2020.02.012.

[2] R J Scales, J Gong, and A J Wilkinson, “Mesoscale Ultrasonic Fatigue with Non-Contact Fatigue Crack Detection Method & Environmental Testing Capabilities,” in 16th International Conference on Advances in Experimental Mechanics, Nov. 2022, vol. 104, pp. 251–262. Accessed: Feb. 20, 2023. [Online]. Available: https://www.bssm.org/media/4601/ mesoscale-ultrasonic-fatigue-with-non-contact-fatigue-crack-det ectionmethod-environmental-testing-capabilities.pdf

[3] C. Gammer and D. An, “Conditions near a crack tip: Advanced experiments for dislocation analysis and local strain measurement,” MRS Bulletin, vol. 47, no. 8. Springer Nature, pp. 808–815, Aug. 01, 2022. doi: 10.1557/s43577-022-00377-4.

1University of Oxford, Department of Materials, Parks Road, Oxford OX1 3PH, United Kingdom

*Corresponding author: robert.scales@materials.ox.ac.uk

4: IMAGING

CHARACTERISATION OF THE FORWARD AND BACKWARD PLASTIC ZONE IN THE CRACK TIP OF A FATIGUED SAMPLE

J. A. Aguilera1, P. M. Cerezo1, A. S. Cruces1, A. Garcia-Gonzalez1, A. Steuwer2,3, T. Buslaps4, P. J. Withers5 & P. Lopez-Crespo1

The research about crack-tip stresses and Plastic Zones (PZ) subjected to cyclic and variable amplitude loading represents a fundamental aspect of the discipline of fracture mechanics. Synchrotron X-ray diffraction (S-XRD) is an experimental technique that allows for precise measurement of stress fields and strain distributions at the crack tip while studying the effects of overload on fatigue crack growth. This study aimed to understand fatigue and fracture by analysing the plastic zone surrounding a crack tip. Researchers used X-ray diffraction to obtain data during an in-situ fatigue test on a bainitic steel sample. The experimental plastic zones were in good agreement with the analytical model for the monotonic and cyclic plastic zones. The cyclic plastic zone was characterised, representing a novel achievement based on experimental data.

1Department of Civil and Materials Engineering, University of Malaga, C/Dr Ortiz Ramos s/n, 29071, Malaga, Spain

2EISCAT Scientific Association, Bengt Hultqvists väg 1, SE-981 92 Kiruna, Sweden

3Nelson Mandela University, Gqeberha, 6031, South Africa

4ESRF, 71, avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France

5Henry Royce Institute, Department of Materials, The University of Manchester, M13 9PL, UK

IN-SITU FULL-FIELD STRAIN MAPPING BY HREBSD AND J-INTEGRAL ANALYSIS OF A SHORT FATIGUE CRACK IN Ni

X. Su1, R. Scales1, A. Koko2, J. Gong1 & T. J. Marrow1

The study of short fatigue cracks in structural materials is critical as the propagation of these cracks can be the primary factor determining the total fatigue life. However, predicting their behaviour is complicated by the fact that these cracks typically grow within a changing local crystallographic environment and can interact with features in the microstructure, such as grain boundaries. Understanding the behaviour of short fatigue cracks is essential for improving the durability and reliability of these materials. Direct observations of the local strain fields, which are intimately connected to the crack tip deformations that control the crack propagation, can help develop this understanding. In this paper, we present an in-situ full-field characterisation of a short fatigue crack in nickel using the high-resolution electron backscatter diffraction (HR-EBSD) technique. A J-integral analysis of the stress field was then performed to determine the effect of applied load on the local stress intensity factors.

A fatigue crack was initiated on the (111) plane using flexural ultrasonic loading (R= -1) of a single crystal foil (001) specimen of a Ni alloy (maximum stress parallel to [100]). The specimen was then loaded with a pre-tilted tensile stage for in-situ HR-EBSD. The elastic strain field at the crack tip region was measured and further integrated into a displacement field, which was injected into a finite element model as boundary conditions. This FE-based post-processing method calculated the J-integral of the crack tip field with increasing load. The mixed mode stress intensity factors were then extracted with the interaction integral method. This local evaluation of the crack tip stress was compared with the values expected from the remote loading and crack geometry.

The actual conditions of a short fatigue crack tip have thus been observed and characterised in situ for the first time. This novel method has the

potential to provide valuable insights into the behaviour of short fatigue cracks. Future studies will investigate the effect of overloads on the elastic and plastic strain fields.

REFERENCES

[1] A. Koko, T.H. Becker, E. Elmukashfi, N.M. Pugno, A.J. Wilkinson, T.J. Marrow, “HR-EBSD analysis of in situ stable crack growth at the micron scale”, in Journal of the Mechanics and Physics of Solids, 2023, vol. 172.

[2] J. Gong and A. Wilkinson, “Ultra small scale high cycle fatigue testing by micro-cantilevers” , in Nanomechanical Testing In Materials Research and Development V, 2015, vol. 59, [Online]. Available: http://dc.engconfintl. org/nanomechtest_v.

1Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK

2National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK

ADVANCED STRESS INTENSITY FACTOR

MONITORING IN ADDITIVELY MANUFACTURED 18Ni300 SAMPLES USING DIGITAL IMAGE CORRELATION

P. M. Cerezo1, J. A. Aguilera1, A. S. Cruces1, A. Garcia-Gonzalez1, R. Branco2, L. Borrego2,3 & P. Lopez-Crespo1

Additive manufacturing (AM) offers versatility and minimal material consumption but lacks insurance of component fatigue strength, which is crucial. Digital Image Correlation (DIC) aids in Stress Intensity Factor (SIF) assessment, eliminating the need for prior crack information. Recent advancements in DIC have improved SIF estimation precision for various specimens. This study aims to evaluate the effectiveness of SIF against cyclic loading in an AM-fabricated steel plate using DIC methodology. Experimental analysis reveals discrepancies between experimental and nominal SIF estimations due to crack tip plasticity effects, highlighting the need for further investigation. Through Williams’ and Irwin’s approaches, SIF evolution under cyclic loading is monitored until sudden fracture occurs, emphasising the importance of understanding crack behaviour in AM components.

1Department of Civil and Materials Engineering, University of Malaga, C/Dr Ortiz Ramos, s/n, 29071 Malaga, Spain

2CEMMPRE, Department of mechanical engineering, University of Coímbra, Rua Luís Reis Santos 3030-788 Coímbra, Portugal

3Department of mechanical engineering, Coímbra Polytechnic- ISEC, Rua Pedro Nunes, 3030-199 Coímbra, Portugal

5. JOINTS

HIGH TEMPERATURE FATIGUE CRACK GROWTH IN NICKEL-BASED ALLOYS JOINED BY BRAZING

AND ADDITIVE MANUFACTURING

A. Bhadeliya1*, B. Rehmer1, B. Fedelich1, T. Jokisch2 , B. Skrotzki1 & J. Olbricht1

Nickel-based alloys have been widely used for gas turbine blades owing to their excellent mechanical properties and corrosion resistance at high temperatures. The operating temperatures of modern gas turbines have been increased in pursuit of increased thermal efficiency [1] [2]. Turbine blades are exposed to these high temperatures combined with mechanical stresses, resulting in material damage through creep, fatigue, and other mechanisms. These turbine blades must be regularly inspected and replaced as needed, to prevent the loss of efficiency, breakdown, and catastrophic failure [1]. Repair of the damaged turbine blades is often a more practical and cost-effective option than replacement, as replacement is associated with high costs and loss of material resources [3]. To this end, state-ofthe-art repair technologies including different additive manufacturing and brazing processes are considered to ensure efficient repair and optimum properties of repaired components.

In any repaired part, materials property-mismatches and/or inner defects may facilitate the crack initiation and propagation and thus reduce the number of load cycles to failure. Therefore, a fundamental understanding of the fatigue crack growth and fracture mechanisms in joining zones is required to enable the prediction of the remaining life of repaired components and to further improve and adapt the repair technologies.

Fatigue crack growth experiments have been conducted on SEN (Single Edge Notch) specimens joined via brazing, and pre-sintered Preform (PSP) and multi-materials (casted/printed) specimens layered via additive manufacturing (AM). The experiments were performed at 950 °C and various stress ratios. The crack growth was measured using DCPD (Direct Current Potential Drop) method. The stress intensity factors for joined SEN

specimens were calculated using the finite element method and then used to derive the fatigue crack growth curves. Metallographic and fractographic analyses were conducted to get insight into the fracture mechanism.

Results show that the experimental technique for fatigue crack growth was successfully adapted and applied for testing joined specimens. Furthermore, the initial tests indicate that the investigated braze filler material provides a lower resistance to crack growth, and bonding defects cause a crack to deviate to the interface of the base material and joining zone. In AMsandwich specimens, the crack growth rates are significantly reduced when the crack reaches the interface of printed material and casted material. The obtained crack growth data can be used to calibrate a crack growth model, which will further be utilised to predict the remaining life of repaired components.

References

[1] A.M. Kolagar et el., Failure analysis of gas turbine first stage blade made of nickel-based superalloy, Case studies in Engineering Failure Analysis, 2017, Volume 8, 61-68.

[2] M. Konter, M. Thumann, Materials and manufacturing of advanced industrial gas turbine components, Materials Processing Technology, 2001, Volume 117, 386-390.

[3] Guijun Bi, A.Gasser, Restoration of Nickel-base turbine blade knifeedges with controlled Laser Aided Additive Manufacturing, Physics Procedia, 2011, Volume 12, 402-409.

1Bundesanstalt für Materialforschung und -prüfung (BAM), Department Materials Engineering, 12205 Berlin

2Siemens Energy Global GmbH & Co. KG, Berlin

*Corresponding author: ashok.bhadeliya@bam.de

A PRACTICAL APPROACH FOR THE FATIGUE

LIFE ESTIMATION OF HYBRID JOINTS THROUGH TESTING AND NUMERICAL SIMULATIONS

C. Bagni1, A. Halfpenny1, M. Hill1 & A. Tarasek2

Nowadays, lightweight structures are essential to achieve higher efficiency of battery electric vehicles, and to support the development of greener ways of transportation. Hybrid joints, along with the use of lightweight materials and design optimisation, are one of the possible ways to obtain lightweight components and they are becoming increasingly popular in the transportation industry. The term ‘hybrid joint’ is commonly used to identify a connection where adhesive bonding and traditional joining techniques, such as spot welds and rivets, are used in conjunction with the aim of combining and exploiting the advantages of the individual joining techniques. To optimise the design of hybrid joints and minimise the risk of in-service fatigue failures, the transportation industry needs efficient, robust, and easy-to-use approaches for the modelling and fatigue life estimation of hybrid joints. Furthermore, the fatigue performance of hybrid joints is influenced by several factors, such as material and thickness of the jointed sheets, type of adhesive and surface preparation of the adherends, as well as type, size and quality of the mechanical joints. Therefore, it is strongly recommended to obtain bespoke Stress-Life (SN) curve parameters from testing of hybrid joint specimens, representative of the joints in the production parts.

To answer the needs highlighted above, this work presents a practical approach for estimating the fatigue life of hybrid joints that can be easily adopted by companies in the transportation industry.

1 Hottinger Bruel & Kjaer UK Ltd, Rotherham, S60 5WG, United Kingdom

2 NIO Performance Engineering Ltd, Begbroke Hill, OX5 1PF, United Kingdom

AN INVESTIGATION INTO FATIGUE FAILURE AND

SELF-LOOSENING OF BOLTED JOINTS SUBJECTED TO TRANSVERSE VIBRATION

S. Hashimura1 & A. Saito2

In bolted joints, it has been considered that fatigue failures occur after self-loosening occurs because in many cases the fatigue failures do occur after self-loosening has already occurred. However, self-loosening does not always occur before fatigue crack initiation. In this study focusing on the grip length which is the length between the first thread of bolt engaging with the internal thread and the bearing surface under the bolt head, we have investigated the thresholds of the grip length which determines the occurrence of self-loosening or fatigue failure. The investigations have been conducted using FE analyses based on transverse fatigue tests conducted in this study. Results show that the occurrence of self-loosening or fatigue failure is determined by the grip length. That is determined by whether the stress amplitude at the root of the first thread caused by the transverse vibration force applied to the bolted joint exceeds the fatigue strength of the bolt, or whether slippage occurs at the thread face and bearing surface of the bolt before the stress amplitude surpasses the fatigue strength.

1Department of Engineering Science and Mechanics, Faculty of Engineering, Shibaura Institute of Technology, 3-7-5 Toyosu, Koto-ku, Tokyo, 135-8548

2Graduate School of Shibaura Institute of Technology

A PRACTICAL METHODOLOGY FOR THE FATIGUE TESTING OF HYBRID JOINTS

A. Pierpoint1, M. Hill1 & C. Bagni1

This work presents a practical methodology for the fatigue testing of hybrid joints; a type of load-transferring joint where structural adhesive is used in conjunction with mechanical fasteners. The method was successfully used by HBK’s Advanced Materials Characterisation and Testing (AMCT) facility in the UK. Bespoke specimen geometries were designed to be both representative of in-service joint configurations, whilst permitting the calculation of all the various mathematical parameters used in the fatigue models. Various grades of automotive metals were tested. Defects in the joints can have an effect on the amount of scatter present in the Load-Life data. Identifying these issues early, through a thorough pre-test inspection of the specimens, can help when analysing and understanding the test data. The correlation of images recorded during testing with drops in stiffness of the joint can be used to define alternative failure criteria to specimen separation. This can allow the selection of a more representative failure criterion and can sometimes aid in reducing the amount of scatter in the Load-Life data when compared with using specimen separation as the failure criterion. The testing methodology presented in this paper enables the generation of high quality Load-Life data sets as required to obtain good quality fatigue parameters generated through reverse engineering using Finite Element results.

1Hottinger Brüel & Kjær UK Ltd, Advanced Manufacturing Park Technology Centre, Brunel Way, Rotherham, South Yorkshire, S60 5WG, United Kingdom

6. PROBABILISTIC

MODELLING

A PROBABILISTIC FATIGUE MODEL USING GAUSSIAN

PROCESSES AND ITS APPLICATION TO ADDITIVELY MANUFACTURED METALS

M. Schulz1, H. Erdelyi2, M. Hack1, S. Straesser1 & N. Lammens2

In this contribution, a hybrid modelling approach is taken where the parameters of an established probabilistic fatigue model are predicted by multiple Gaussian processes. The emerging model is trained with uniaxial fatigue data from additively manufactured metal parts. The model can represent the training data and generalises well to new data.

1Siemens Industry Software GmbH, Germany

2Siemens Industry Software NV, Belgium

PROBABILISTIC MODELLING OF FATIGUE

BEHAVIOUR IN INHOMOGENEOUS METALLIC MATERIALS USING PHYSICS-BASED MACHINE

LEARNING APPROACHES

E. Salvati1, A. Tognan1, M. Pelegatti1, L. Laurenti2 & F. De Bona1

The structural integrity of engineering products manufactured via Additive Manufacturing can be severely impaired by the intrinsic presence of defects, especially when post-processing treatments are not a viable route to mitigate this collateral effect. As a consequence, the presence of defects must be taken into account during the design-against-failure process of structural components.

State-of-the-art fatigue design approaches rely on semi-empirical fracture mechanics formulations to consider the presence of crack-like defects. Nevertheless, several other sources of uncertainty play a role in this context, thus making this approach poorly reliable in some cases.

Defect-based fatigue predictive models can be endowed by the intervention of modern Machine Learning techniques, aimed at considering additional geometrical features of defects. Such a new predictive scheme improves the accuracy of the failure prediction and at the same time, it avoids unrealistic results even when dealing with limited fatigue datasets. This novel modelling concept can be applied both to finite fatigue life in high cycle fatigue and to assess the fatigue endurance limit. For design-against-failure approaches, such a framework can be equipped with additional probabilistic features. In this way, the level of reliability of a certain structural problem can be promptly evaluated, thus enabling rational exploitation of the safety margin.

The fatigue modelling framework presented here overcomes the limitations of current predictive methods taking the accuracy to a higher level; a prerequisite to achieving the optimal cost vs. performance trade-off for defective engineering products.

1Polytechnic Department of Engineering and Architecture (DPIA), University of Udine, Via delle Scienze 206, Udine, Italy

2Delft Centre of System and Control (DCSC), TU Delft University, Mekelweg 2, Delft, the Netherlands

3DPRINT AM35 WIRE ARC ADDITIVELY MANUFACTURED MILLED

SPECIMENS

UNDER FATIGUE

B. Karabulut1, X. Ruan1, S. MacDonald2, J. Dobric3 & B. Rossi1,4

Today, wire arc additive manufacturing (WAAM) can be used to fabricate critical structural steel components. The process enables the fabrication of sophisticated shapes, achieving high levels of material capacity utilisation. Key welding parameters inevitably influence the mechanical resistance of WAAM-fabricated components subjected to static or cyclic loading. This study specifically examines the fatigue behaviour of WAAM carbon steel elements. Firstly, samples are produced by cold metal transfer (CMT) welding process using carbon steel 3Dprint AM 35 (S355) grade, following an optimised welding procedure to minimise induced imperfections. A series of microstructural investigations and mechanical experiments, including static tensile and cyclic fatigue tests, are conducted on milled samples, in both transverse and longitudinal directions. The obtained fatigue test results are then assessed for reliability and validated using Weibull models, commonly employed in survival analysis.

1KU Leuven, Faculty of Engineering Technology, Sint-Katelijne-Waver, Belgium

2Whittaker Engineering, Robotic Welding Engineering, Stonehaven, United Kingdom

3University of Belgrade, Department of Civil Engineering, Belgrade, Serbia

4University of Oxford, Department of Engineering Science, Oxford, United Kingdom.

A COMPARATIVE

INVESTIGATION ON THE UNIAXIAL PLAIN AND NOTCH FATIGUE

STRENGTHS OF HEAVY-SECTION CASTINGS MADE OF PEARLITIC AND HIGH-SILICON FERRITIC DUCTILE CAST IRONS

M. Pedranz1, V. Fontanari1, C. Santus2, F. Zanini3, S. Carmignato3, G. Angella4, D. Lusuardi5, F. Berto6 & M. Benedetti1

Ductile cast iron (DCI) finds increasing application in important industrial branches to produce large components. While increasing the component’s dimension, the cooling rate generally decreases, thus leading to the formation of casting defects, such as degenerated graphite and shrinkage pores. Different DCI grades can be characterised by different distributions of pores in the material. A change in the dimension, shape and spatial distribution of pores may lead to different behaviours of the materials, thus requiring a change in the designing approach, especially against fatigue failure. In this work, we analyse the fatigue properties of GJS-600 (pearlitic) and high silicon content, HSi, (ferritic) grades, emphasising the different features that lead to fatigue failure. We propose a statistical approach to assess the size of the expected critical pore in the vicinity of a notch, which is then combined with a strain energy density (SED)-based fatigue approach to carry out fatigue predictions. The effectiveness of the method is validated using specimens of varying geometries, where fatigue failure is induced by either shrinkage pores or graphite nodules. The proposed approach demonstrates the ability to predict this critical feature, offering valuable insights for designing against fatigue failure in DCI components.

1Department of Industrial Engineering, University of Trento, Via Sommarive 9, Trento, Italy

2Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 2, Pisa, Italy

3Department of Management and Engineering, University of Padova, Stradella S. Nicola 3, Vicenza, Italy

4Institute of Condensed Matter Chemistry and Technology for Energy (CNRICMATE), Department of Chemical Science and Materials Technology (DSCTM), Via R. Cozzi 53, Milan, 20125, Italy

5Fonderie Ariotti S.p.A., Adro, Italy

6Department of Chemical Engineering Materials Environment, Sapienza University, Via Eudossiana, 18, Roma, Italy

7. TITANIUM ALLOYS I

PREDICTING FATIGUE CRACK INITIATION IN MILLED AEROSPACE GRADE Ti-6Al-4V PARTS

USING CPFEM

M. F. Arcidiacono1*, I. Violatos1 & S. Rahimi1

A Crystal Plasticity Finite Element Method (CPFEM) model is proposed for determining the likelihood of fatigue crack initiation and its sites in an aerospace-grade Ti-6Al-4V machined part. The methodology is based on a digitally reconstructed Electron Backscatter Diffraction (EBSD) microstructural model that incorporates the previous deformation history, the residual stress distribution and the roughness profile which result from milling. The constitutive model employs the Armstrong-Frederick nonlinear formulation and implements microstructure sensitive fatigue initiation parameters. Findings suggest that fatigue initiation is significantly influenced by the surface topology and the pre-existing strain and stress fields. The simulation predicts the formation of persistent slip bands within the deformed microstructure and ratcheting that causes local plastic strain accumulation. The model indicates that at the surface and near-surface regions fatigue initiation is mainly driven by local topography, while orientation becomes more dominant at higher depths.

1Advanced Forming Research Centre (AFRC), University of Strathclyde 85 Inchinnan Drive, Inchinnan, Renfrewshire

*Corresponding author: mauro.arcidiacono@strath.ac.uk

UNCOVERING

THE ROLE OF

BUILDING

ORIENTATION AND STRESS RATIO ON THE FATIGUE BEHAVIOUR OF L-PBF Ti6Al4V

MINIATURISED STRUT-LIKE LATTICE SPECIMENS

S. Murchio1,2,*, R. De Biasi1, D. Maniglio1,2, A. Rigatti1, L. De Nart1, V. Luchin3 & M. Benedetti1,*

Metal additive manufacturing has revolutionised the production of intricate components for specialised applications, such as prosthetic devices or aircraft components. This innovation also stems from the ability to effortlessly fabricate architected cellular materials, a new class of engineering materials with tailorable mechanical properties. However, challenges in structural integrity and standardisation still persist, impacting latticebased component performances. Fatigue behaviour in lattice structures remains a critical concern, particularly at the millimetre/sub-millimetre scale, an aspect that has not yet received adequate attention. This study examines miniaturised Laser-Powder Bed Fusion (L-PBF) Ti6Al4V thinstrut specimens under diverse loading conditions and building orientations. The impact of the latter on the mean stress sensitivity is assessed by using Haigh diagrams. Additionally, suitable mean stress predictive models and buckling instability regions are explored to enable a more informed lattice design.

1Department of Industrial Engineering- DII, University of Trento, Italy

2BIOTech Research Center, University of Trento, Italy

3Lincotek Medical Trento, Pergine Valsugana, Italy

*Corresponding authors: simonemurchio@unitn.it & matteobenedetti@unitn.it

CRACKING AND DAMAGE MECHANISMS IN NITRIDED Ti64 GRADE 5 ALLOY AFTER HIGH CYCLE FATIGUE

S. Stekovic1, R. Boyd2 & L. Selegård3

The main aim of this study is to evaluate the effect of two nitriding heat treatments on high cycle fatigue of Ti64 (Grade 5) alloy. For this, axial fatigue tests have been performed on untreated and nitrided round bar specimens under constant amplitude load-controlled mode at a frequency of 20 Hz at room temperature and in laboratory air. After the testing, the fractured surfaces and microstructures were investigated by scanning electron microscopy, focused ion beam, transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional studies show that two different layers were formed after the nitriding processes, namely, a top compound layer and a diffusion layer below it. Additionally, a very thin layer rich in aluminium was also detected. The fatigue results show that the nitriding treatments are detrimental to the fatigue life when compared to the untreated and extruded Ti64 alloy. The main conclusion is that the reduction of high cycle fatigue life is a result of the cracking of the nitrided layers.

1Engineering Materials, Department of Management and Engineering, Linköping University, Linköping, Sweden

2Plasma and Coatings Physics, Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden

3Saab Aeronautics AB, Linköping, Sweden

8. SURFACE CONDITIONS

THE EFFECT OF SPECIMEN MACHINING PROCESSES ON FATIGUE LIFE OF 42CrMo4+QT STEEL

J. Papuga1, T. Vrbata1, K. Trojan2, A.Trefil3, A. Zabala4 & V. Mára1

The paper discusses the effect of various turning parameters setups on the fatigue strength of 8mm active diameter specimens manufactured from 42CrMo4+QT steel. In the search for the reasons for the varying fatigue strengths related to individual setups, the surface quality monitored in various surface roughness parameters and in residual stress values measured on the free surface is evaluated. However, the output of the analysis shows that these parameters are not sufficient and that neither each of them nor their combination can be related to the fatigue strengths of the output of the individual manufacturing setups.

1FME, Czech Technical University in Prague, Technická 4, Prague 6, Czech Republic. E-mail: jan.papuga@fs.cvut.cz

2FNSPE, Czech Technical University in Prague, Trojanova 13, Prague 2, Czech Republic.

3FME, VŠB – TU Ostrava, 17. Listopadu 15/2172, Ostrava-Poruba, Czech Republic

4Mondragon Unibertsitatea, Faculty of Engineering, Mechanics and Industrial Production, Loramendi, 4, Mondragon 20500 Gipuzkoa, Spain

STABILITY OF COMPRESSIVE RESIDUAL STRESSES IN AUSTEMPERED DUCTILE IRON (ADI) UNDER CYCLIC LOADING

U. Hähnel1, E. Müller2 & P. Hübner3

Compressive residual stresses induced by deep rolling can effectively reduce crack initiation and crack growth in the surface layer of high strength cast components. The result is an intended increase in fatigue strength. In this study, compressive residual stresses were induced in the austempered ductile iron GJS 800-8 by deep rolling. The influence of the residual stresses was investigated on notched round specimens under cyclic loading at constant load amplitudes and R-ratio. In the deep-rolled notch radius depth profiles of the near surface residual stresses were mapped using the cosα method. The test results show a relaxation of the compressive residual stress depending on the stress amplitude. The applicability of the cosα method for ADI was confirmed by reference measurements using the holedrilling method.

1University of Applied Sciences Mittweida, Faculty of Engineering Sciences, Technikumplatz 17, 09648 Mittweida, Germany

2Bochum University of Applied Sciences, Am Hochschulcampus 1, 44801 Bochum, Germany

309600 Weißenborn, Germany

IMPACT OF LASER SHOCK PEENING ON FATIGUE STRENGTH OF ADDITIVELY MANUFACTURED AlSi10Mg

M. Matušů1,2*, O. Stránský1,3, J. Šimota1, L. Džuberová1, J. Rosenthal2 , J. Papuga1 & L. Beránek1

This study investigates the fatigue strength of additively manufactured AlSi10Mg under cyclic loading, focusing on the high cycle fatigue domain (HCF). Specimens were produced using Laser Powder Bed Fusion (LPBF), with the main objective of analysing fatigue strength concerning various post-processing surface treatments. The hourglass-shaped specimens were printed in a single batch, and six distinct groups of specimens were tested. Three series were left as-built, while three series were machined to achieve specific dimensions and surface roughness. Two setups of Laser Shock Peening (LSP) were applied for two groups of as-built specimens and two groups of machined specimens. Fatigue testing was conducted using a resonant pulsator. Surface roughness and residual stress depth profiles were analysed. Thermal response on the sample surface was monitored with an infrared thermal camera, enabling fatigue life prediction with fewer samples.

1Faculty of Mechanical Engineering, Czech Technical University in Prague. Technická 4, Praha 6, Czech Republic

2Department of Mechanical and Environmental Engineering, OTH Amberg-Weiden, Kaiser-Wilhelm-Ring 23, Amberg 92224, Germany

3HiLASE Centre, Institute of Physics of the Czech Academy of Sciences, Czech Republic

*Corresponding author: martin.matusu@fs.cvut.cz

EFFECT OF ZINC COATING AND GREASE ON THE FRETTING FATIGUE LIFE OF CROSSED STEEL WIRE

CONTACTS: APPLICATION TO OFFSHORE SPIRAL ROPES

S. Montalvo1,2, S. Fouvry1* & M. Martinez2

Spiral steel ropes are often used as mooring lines in offshore industry. These ropes are intended to be used in tension only. Cyclic bending must be limited as it can produce fretting fatigue damages between the steel wires. The fretting fatigue of such assembly is little known, in peculiar when zinc coating and grease are present. Using a dedicated double actuator fretting fatigue experiment, the fetting fatigue endurance of a reference bright steel crossed wires contact is investigated keeping constant the fatigue stress and the normal force but varying the contact displacement amplitude. As expected the fretting fatigue endurance decreases under partial slip until a minimum value at sliding transition (Fig. 1). Then, under gross slip regime, the endurance rises again up to the material fatigue limit. Indeed, under gross slip surface wear is activated which extending the contact area decreases the contact stressing. The reference bright steel wire contact is then compared versus the zinc coated steel whereas the effect of grease is investigated for (zinc) coated) and (bright) uncoated steel wires. The zinc coating and grease lubricant reduce the partial slip damaging domain, but without eliminating it. A complete investigation is developed to quantify how tribological processes involving grease and soft zinc coating can influence the contact stressing and finally the fretting fatigue cracking process. This experimental investigation is supported by an original 3D “hybrid” analytical – FEM simulation of the fretting fatigue damage combining a SWT multiaxial fatigue stress analysis, a surface wear simulation and a cumulative damage strategy [1]. It is shown that as long as the fretting fatigue process is controlled by mechanical parameters the given SWT fatigue model provides reliable endurance predictions. However it fails when complex tribo-chemistry process are occurring underlying the necessity to develop alternative multiphysics strategies to capture the complexity of fretting fatigue processes.

Reference:

[1] S. Montalvo, S. Fouvry, M. Martinez, A hybrid analytical-FEM 3D approach including wear effects to simulate fretting fatigue endurance: Application to steel wires in crossed contact, Tribology International 187 (2023) 108713.

Fig. 1 : Evolution of the fretting fatigue endurance for constant fatigue stress and the normal force varying the fretting displacement amplitude δ (θ wires = 30°, σmean = 320 MPa, σa = 320 MPa, normal force P = 1400N)): (a) Illustration of the benefit effect of combined zinc coating and grease (experiments) ; (b) comparison between experiments and hybrid 3D fretting fatigue modelling for greased contact.

1LTDS, Ecole Centrale de Lyon, France

2IFP Energies Nouvelles (IFPEN), France

*Corresponding author: siegfried.fouvry@ec-lyon.fr

HOT CORROSION FATIGUE BEHAVIOUR OF A SHOT PEENED NICKEL BASED SUPERALLOY

Y. Li1, H. Cockings1, M. Whittaker1, B. J. Cockings1, P. M. Mignanelli2 , R. Buckingham2 & M. R. Bache1

As turbine entry temperatures (TET) in modern gas turbine engines continue to increase to improve engine efficiency, turbine disc rim temperatures approach 700°C. This reaches the optimum temperature region for Type II hot corrosion in nickel based superalloys whereby typical corrosion pit damage is recognised as a significant risk in the disc rim, combined with high centrifugal stress exerted by the attached blades. Therefore, under service conditions, understanding the hot corrosion fatigue resistance of alloys is critical in terms of component lifing.

In the current research, low cycle fatigue behaviour of a newly developed polycrystalline nickel disc superalloy was investigated. The testing program involved consideration of the variations in fatigue life brought about by changes in surface condition when tested at 700°C in a salt and SO2based environment. The hot corrosion fatigue resistance behaviour has been compared to a previous generation alloy, and detailed fractography has been conducted to identify the mechanisms of fatigue crack initiation. Hot corrosion fatigue behaviour has also been correlated to the shot peened work hardened layer. Overall, a comprehensive understanding of the next generation turbine disc alloy, with an optimised surface treatment has been established under hot corrosion fatigue conditions.

1Institute of Structural Materials, Swansea University, SA1 8EN, United Kingdom

2Rolls–Royce plc, P.O. Box 31, Derby, DE24 8BJ, United Kingdom

FATIGUE FAILURE MECHANISMS AND LIFE

PREDICTION OF A LASER SHOCK PEENED DISC

ALLOY

R. Jiang1*, J. Zhang1, R. Wang1, C. You1 & Y. Song1

Aeroengine turbine discs often suffer from fatigue failure due to the combined thermal and mechanical loads during service, and surface strengthening treatments such as laser shock peening (LSP) are usually employed to process the turbine disc to improve its fatigue performance. Therefore, a disc alloy (i.e. powder metallurgy Ni-based superalloy FGH4098) was strengthened by LSP in this study, the residual stress relaxation and microstructure evolution of the surface strengthened layer under the cyclic loading were evaluated by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). Fatigue crack initiation and small crack propagation behaviours were investigated at room temperature and 650oC via three point-bending test using replication procedure. The results indicate that residual stress filed brought about by LSP can be up to 1 mm in depth. The microstructures and residual stress filed in the strengthening layer show good stability under the cyclic loading, and the surface residual stress is approximately relaxed by 25% at room temperature and 50% at 650oC respectively. The fatigue life of the LSP samples is significantly increased especially at the relatively lower load due to the compressive residual stress which delays the crack initiation and suppresses the fatigue crack propagation. Based on the experimental work, an finite element model which considers the residual stress distribution was established via the inverse eigenstrain method, and a calibrated Chaboche viscoplasticity model was used to simulate the stress relaxation and cyclic deformation. The Smith–Watson–Topper criterion was calculated and then used to predict the fatigue life of the LSP disc alloy, and the predicted fatigue life is within the two-time scatter band of the experimental results. The established fatigue life prediction method is expected to provide a more accurate tool for the fatigue life design and durability assessment of LSP turbine discs.

1College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

*Corresponding author: rjiang@nuaa.edu.cn

ADVANTAGES OF LASER SHOCK PEENING OVER THE CONVENTIONAL SHOT PEENING OF THE FATIGUE LIFETIME

OF ALUMINIUM 2024

ALLOY

H. Y. Ahmad1* & M. Craig1

Aluminium alloys are ideal for aerospace, automotive and power generation industries because of their weight to strength ratio. They also offer the safest, most environmentally friendly and cost-effective way to increase performance, boost fuel economy and reduce emissions while maintaining or improving safety and durability. Furthermore, aluminium alloys provide high resistance to corrosion and excellent fatigue resistance. However, in some application where an alternating load is applied over many cycles the use of an aluminium alloy may be limited due to its fatigue strength. Therefore, in order to improve its fatigue lifetime, aluminium alloy component can be treated either by Laser Shock Peening (LSP) or by Conventional Shot Peening (CSP).

This research will validate the advantages of Laser Shock Peening (LSP) over the Conventional Shot Peening (CSP) in an industrial context. The advantages of LSP over CSP will be verified by measuring the fatigue properties of 2024 aluminium round bar test specimens. The specimens will be tested and compared using rotating bending fatigue loading at different load ratios. This investigation focused on the role that the peening induced microstructure, surface morphology and hardness have on the fatigue life of the test specimens.

1Safran Electrical & Power, Pitstone, Buckinghamshire, UK

*Corresponding author: hayder.ahmad@safrangroup.com

9. HIGH TEMPERATURE

THE EFFECTS OF H+ FUSION PLASMA LOADING ON THE LOW-CYCLE THERMAL FATIGUE

BEHAVIOUR OF TUNGSTEN

J. Hargreaves1,2, J. Scholten1 & T. Morgan1

The extreme environmental conditions within a prototype fusion reactor will pose many complex materials science and structural integrity challenges. These challenges are most severe at the divertor, a mission-critical tungsten component responsible for plasma exhaust. During service, this hightemperature component will be repeatedly exposed to cyclic thermal loading by a plethora of plasma transients, giving rise to low cycle thermal fatigue [1]. Furthermore, fatigue crack growth and nucleation may be accelerated by a range of synergistic degradation phenomena arising from exposure to the highly energetic plasma, including He/H void and W fuzz formation, neutron damage and transformation, and recrystallisation of the W surface [2], [3], [4].

To-date, few experimental studies have investigated the effects of plasmamaterial interactions on tungsten’s fatigue behaviour [5]. This data is considered to be critically important to both the EU and UK fusion energy programmes [6], [7]. To address this, a novel campaign of thermal fatigue experiments have been conducted using the Magnum-PSI linear plasma device to emulate fusion plasma-loading conditions. Representative 40×40×3 mm samples of ITER-grade tungsten were exposed to H+ plasma for up to 5000 cycles of 0-50 MW m-2, at a base temperature of 1230°C. Fatigue-affected samples were characterised via scanning electron microscopy and electron backscatter diffraction (EBSD), and correlated with the results of time-dependent thermo-mechanical finite element analysis (FEA). Comparisons between these experimental results and published W fatigue data without plasma-loading are drawn, and the synergistic effects of plasma-loading on W’s fatigue behaviour are quantitatively discussed.

References:

[1] F. Maviglia et al., ‘Impact of plasma-wall interaction and exhaust on the EU-DEMO design’, Nuclear Materials and Energy, vol. 26, p. 100897, Mar. 2021, doi: 10.1016/j.nme.2020.100897.

[2] S. Kajita, W. Sakaguchi, N. Ohno, N. Yoshida, and T. Saeki, ‘Formation process of tungsten nanostructure by the exposure to helium plasma under fusion relevant plasma conditions’, Nucl. Fusion, vol. 49, no. 9, p. 095005, Aug. 2009, doi: 10.1088/0029-5515/49/9/095005.

[3] Y. Li et al., ‘Recrystallization-mediated crack initiation in tungsten under simultaneous high-flux hydrogen plasma loads and high-cycle transient heating’, Nucl. Fusion, vol. 61, no. 4, p. 046018, Mar. 2021, doi: 10.1088/1741-4326/abe312.

[4] Y. Li, T. Vermeij, J. P. M. Hoefnagels, Q. Zhu, and T. W. Morgan, ‘Influence of porosity and blistering on the thermal fatigue behavior of tungsten’, Nucl. Fusion, vol. 62, no. 7, p. 076039, May 2022, doi: 10.1088/1741-4326/ac6a65.

[5] R. E. Schmunk, G. E. Korth, and M. Ulrickson, ‘Tensile and lowcycle fatigue measurements on cross-rolled tungsten at 1505 K’, Journal of Nuclear Materials, vol. 122, no. 1, pp. 850–854, May 1984, doi: 10.1016/0022-3115(84)90711-6.

[6] UK Atomic Energy Agency, ‘UK Fusion Materials Roadmap: 20212040’, Royce Institute, 2021.

[7] M. Gorley, E. Diegele, S. Dudarev, and G. Pintsuk, ‘Materials engineering and design for fusion—Towards DEMO design criteria’, Fusion Engineering and Design, vol. 136, pp. 298–303, Nov. 2018, doi: 10.1016/j.fusengdes.2018.02.012.

1Dutch Institute for Fundamental Energy Research (DIFFER), TU/e Science Park, De Zaale 20, 5612 AJ Eindhoven, Netherlands

2University of Bristol, School of Physics, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom

EFFECTS OF TEMPERATURE MEASUREMENT AND ADIABATIC HEATING DURING STRAIN CONTROLLED FATIGUE

TESTS

P. B. S. Bailey1

Low cycle fatigue, particularly at elevated temperature, is an established characterisation requirement for materials in both aerospace turbines and land-based thermal power plant. There has been growing commercial demand for tighter control of specimen temperature, with the aspiration to improve repeatability and confidence, but better control also needs to be underpinned by reliable measurement. First, this paper will present a case study based on the ISO 21913 technical specification, for applying a verification process, to compare an “ideal” specimen temperature measurement with methods in common practice. Secondly, evidence with be presented to show that some commonly used practices can generate significant cyclic temperature variation in the specimen. The conflict between need for comparability with legacy design data and demand for higher test fidelity will be discussed.

1Instron Dynamic Systems, Coronation Road, High Wycombe, UK

REAL TIME STRUCTURAL HEALTH PREDICTION FOR CRITICAL INDUSTRIAL APPLICATION

C. J. Hyde1, B. Engel2 & A. Morris3

Monitoring and evaluating components and systems that are subject to thermomechanical fatigue due to variable temperatures and mechanical stress proves to be a complex task.Current monitoring software, used among other things in energy generation and plant engineering, is based on the monitoring of sensor data, such as temperature and pressure, on critical components. Current measured values are compared with data patterns or design limits to obtain a qualitative assessment of the component status. However, no detailed quantitaive statements can be made about the resulting material damage and the associated reduction in service life due to operating behaviour. This usually requires complex numerical simulations, which are rarely carried out due to high time and cost requirements.

CITRUS (Component Integrity Readiness Utilisation System) combines complex numerical simulations with continuous component monitoring to predict material damage or service life reduction in real time, using machine learning methods.

The use of the CITRUS tool is demonstrated here via a power plant industrial case study.

1Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK

2MatAlytics Ltd, Sir Colin Campbell Building, University of Nottingham Innovation Park, Nottingham, NG7 2TU, UK

3EDF Energy, Central Technical Organisation, Generation Coal and Gas Operations, West Burton Power Station, Retford, Nottinghamshire, DN22 9BL, UK

CONSIDERATION OF ELASTOPLASTICITY AND VISCOPLASTICITY DURING THERMOMECHANICAL FATIGUE

SIMULATIONS OF A PIPE BEND USING THE FEM-IMPLEMENTED PRANDTL OPERATOR APPROACH

D. Šeruga1*, M. Nagode1, J. Klemenc1 & S. Oman1

In this paper, the results of a metallic pipe bend are presented which is subjected to a variable thermomechanical load history and then its stressstrain response is simulated using the FEM-implemented Prandtl operator approach. This method has recently been extended to consider the division of the total strain into elastoplastic and viscoplastic parts using the non-unified theory. This consideration is especially important at higher temperatures where viscoplastic properties of the material become more significant. A critical location on the pipe bend was chosen and examined from the simulated stress-strain point of view. Six different operating conditions were simulated. It has been shown that a far more critical stress-strain response can be expected if the temperature-dependent viscoplastic material properties are considered during the exposure to variable thermomechanical loads. Moreover, the complexity of the stress-strain response considerably increased with increased load temperatures.

1University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva 6, SI-1000 Ljubljana, Slovenia

*Corresponding author: domen.seruga@fs.uni-lj.si

EFFECTS OF FREQUENCY AND DWELL ON THE FATIGUE CRACK PROPAGATION IN SINGLE

CRYSTAL Ni-BASED SUPERALLOY CMSX-4 AT INTERMEDIATE SERVICE TEMPERATURE

J. C. Doyle1, A. Evangelou1,2, E. A. Saunders3, J. M. Woolrich4, N. Gao1 & P. A. S. Reed1

Ni-based single crystal superalloys are used in turbine blades due to their excellent combination of high temperature mechanical properties and corrosion resistance. Although service temperatures in the turbine gas stream of a jet engine can exceed 1000°C, a large temperature gradient is experienced across the blade with the cooler regions towards the blade root where intermediate service temperatures (450-650°C) are observed. Often, blade aerofoils are coated to help protect from high temperature oxidation. However, where the blade is exposed to intermediate temperatures towards the root, the blade is commonly left uncoated so is directly exposed to oxidation damage and oxidation-fatigue mechanisms. The effects of oxidation and dwell will influence fatigue crack propagation rates and damage mechanisms at elevated temperatures. In this work the effects of frequency on the fatigue crack growth rate have been studied on CMSX-4 at an intermediate service temperature 550°C through a series of frequency scan tests to obtain the transition from cycle to time dependent crack growth. Tests were conducted on single edge notched bend bar specimens in air at a load ratio 0.1 at constant ΔK. Frequencies tested range from high frequency 5Hz to low frequency long dwell waveforms. The effects of frequency on crack growth rate are shown in Figure 1. Fatigue crack propagation mechanisms have been compared between each frequency using a combination of optical microscopy, scanning electron microscopy and Alicona IFM (Infinite Focus Microscope) to characterise the fracture surfaces and assess fatigue and time dependent failure mechanisms.

University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva 6,

*Corresponding author: domen.seruga@fs.uni-lj.si

Figure 1 – Effect of frequency on the crack growth rate of CMSX-4 at 550°C (at constant ΔK=25MPa√m and 35MPa√m) with respect to a) time and b) cycles

1Engineering Materials Research Group, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

2Engineering Powder Technology Laboratory, Department of Mechanical and Manufacturing, University of Cyprus

3Rolls-Royce plc., Materials — Failure Investigation, Bristol BS34 7QE, UK

4Rolls-Royce plc., Materials — Failure Investigation, Derby DE24 8BJ, UK

THERMOMECHANICAL FATIGUE PROPERTIES

OF ADDITIVELY MANUFACTURED NICKEL-BASED SUPERALLOY IN939

M. Gálíková1*, I. Šulák1 & I. Kuběna1

Nickel-based superalloys are highly suitable for applications that involve high-temperature exposure and loading. Since they exhibit exceptional resistance to oxidation and creep, and possess remarkable mechanical strength, these alloys find extensive use in various fields, particularly in engines, hot section of turbines, nuclear reactors, and aerospace components. A typical degradation mechanism observed in these critical components is caused by low cycle fatigue. Frequently, high stresses exceeding the material yield strength are developed due to mechanical loading or thermal gradients, resulting in large plastic deformation.

The present contribution refers to the thermomechanical fatigue (TMF) behaviour in polycrystalline nickel-based superalloy IN939 manufactured by means of laser powder bed fusion (L-PBF) technique. The microstructure consists of elongated grains with a preferential orientation (001) parallel to building direction (Fig. 1a). To achieve the desired microstructure and optimal mechanical properties for this alloy, the material underwent a three-step heat treatment that triggered the precipitation of the gamma prime (γ’) strengthening phase with bimodal size distribution (Fig. 1a). The smooth cylindrical specimens were subjected to TMF loading under inphase (maximum tension coincides with maximum temperature) and outof-phase (maximum compression coincides with maximum temperature) conditions in temperature range from 400 °C to 800 °C with constant heating and cooling rate of 10 °C/s. Furthermore, isothermal fatigue tests at peak temperature of 800 °C were conducted.

The results show that TMF loading is more detrimental than isothermal loading performed at 800 °C (Fig. 1b). In-Phase loading with dominant fatigue-creep interaction appears to be the most damaging for loading with high mechanical strain amplitudes. However, at higher lifetimes (lower

mechanical strain amplitudes), a crossover occurs, indicating a gradual predominance of fatigue-oxidation interaction typical for out-of-phase loading. The obtained results of the TMF tests will be discussed concerning the manufacturing specifics and microstructural features revealed by SEM and TEM analyses.

Figure 1 (a) Microstructure of IN 939 manufactured by L-PBF, (b) Fatigue life curves.

Acknowledgement:

This work was supported by the project “Mechanical Engineering of Biological and Bio-inspired Systems”, funded as project No. CZ.02.01.01/00/22_008/0004634 by Programme Johannes Amos Commenius, call Excellent Research.

1Institute of Physics of Materials, Czech Academy of Sciences, 61600 Brno, Czech Republic

*Corresponding author: galikova@ipm.cz

HIGH-TEMPERATURE VISCOELASTICVISCOPLASTIC DEFORMATION OF 316 STAINLESS STEEL

K. Sithole1, W. Lavie1, B. Engel1, J. P. Rouse1 & C. J. Hyde1

In contemporary engineering material modelling methodologies, irreversible, viscous behaviour is typically confined to post-yield (plastic) deformation. However, experimental evidence readily demonstrates irreversibility within the purportedly elastic domain of deformation. Comprehending “elastic” viscous effects is critical as component deformation during operation will frequently induce sub-yield stress states. For instance, consider components in sectors such as the power generation industry that are subjected to “two-shifting” operating strategies involving frequent start-up and shutdown cycles, which impose significant stresses on the components. Ratedependent viscous behaviour at stress states below yield is encountered in such components and is more pronounced due to elevated operating temperatures. Understanding the behaviour of such components is essential for developing predictive material models that can inform their design and safe operation.

In the present work, viscoelastic irreversibilities (i.e., stress relaxation below yield) are demonstrated in a 316 stainless steel material at elevated temperatures of 400°C, 600°C, and 700°C. Through experimental observation of stress relaxation, cyclic hardening, and rate-dependency associated with viscoplasticity, a thermodynamically-based constitutive model is calibrated using various novel waveforms at a strain rate of 0.03%s⁻¹ and at various strain holds (0.1%, 0.15%, 0.3%, 0.35%, and 0.5%). The model is validated against experimental results of a realistic waveform experienced by an in-service steam header. The calibrated material model can be utilised to rectify otherwise static stress distributions for in-service components at elevated temperatures. By incorporating a viscoelastic term, damage can be characterised for this region of deformation.

1Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK

10. DESIGN

SCALE-BRIDGING FATIGUE ASSESSMENT OF STEELS – FROM PRODUCTION TO PERFORMANCE

N. Baak1, K. Donnerbauer1, A. Kalenborn1, H. Kanagarajah1, L. Lücker1, L. Lingnau1, J. L. Otto1, J. Rozo Vasquez1, S. Strodick1 & F. Walther1,*

In times of increasing energy and material costs, the precise monitoring of machined parts is crucial for reliably achieving the maximum service life under fatigue loading. The conditions and states of components need to be accurately observed starting from the manufacturing process over the service time to maintenance and end-of-life.

This paper gives an overview of fatigue research on steels, focusing on the improvement of production processes and non-destructive evaluation of deformation/damage states with respect to increasing fatigue requirements. The research work links production engineering and materials science and engineering. The development of approaches for robust online evaluation for damage-controlled forming processes [1] and the adjustment of desirable surface integrity in forming and machining procedures, considering the production-induced formation of white etching layers (WEL) [2], will be presented. Moreover, the development and validation of concepts for evaluating damage evolution under relevant service conditions are discussed, focusing on machined parts [3], brazed joints [4] and nuclear power plant [5] steels. The mechanisms considered include e.g. the fatigue-induced relaxation of residual stresses and the microstructural evolution of the component’s surface edge zone under fatigue loading. The mechanism-oriented consideration of the influencing variables and cause-effect relationships is of decisive importance, since distinguishing between superimposing effects that occur presents a central challenge in the identification of robust correlations.

References [1] Lücker, L.; Lingnau, L. A.; Walther, F.: Non-destructive direct current potential drop assessment of forming-induced pre-damage in AISI 5115

steel. Procedia Structural Integrity 42 (2022) 368-373.

[2] Baak, N.; Hajavifard, R.; Lücker, L.; Rozo Vasquez, J.; Strodick, S.; Teschke, M.; Walther, F.: Micromagnetic approaches for microstructure analysis and capability assessment. Materials Characterization 178, 111189 (2021) 1-14.

[3] Baak, N.; Schaldach, F.; Nickel, J.; Biermann, D.; Walther, F.: Barkhausen noise assessment of the surface conditions due to deep hole drilling and their influence on the fatigue behaviour of AISI 4140. Metals 8 (9), 720 (2018) 1-12.

[4] Otto, J. L.; Fedotov, I.; Penyaz, M.; Schaum, T.; Kalenborn, A.; Kalin, B.; Sevryukov, O.; Walther, F.: Microstructure and defect-based fatigue mechanism evaluation of brazed coaxial Ti/Al2O3 joints for enhanced endoprosthesis design.Materials 14 (24), 7895 (2021) 1-15.

[5] Donnerbauer, K.; Acosta, R.; Boller, C.; Bill, T.; Starke, P.; Heckmann, K.; Sievers, J.; Schopf, T.; Walther, F.: Fatigue damage evaluation of stainless AISI 347 steel by advanced microstructure-sensitive NDT analysis. Procedia Structural Integrity 42 (2022) 738-744.

1Chair of Materials Test Engineering (WPT), TU Dortmund University, D-44227 Dortmund, Germany

*Corresponding author: frank.walther@tu-dortmund.de

FATIGUE DESIGN OF CAST ALUMINIUM PASSENGER CAR WHEELS WITH RESPECT TO THE TRANSFER OF CYCLIC MATERIAL PROPERTIES

M. Hell1

Wheels of passenger cars combine aesthetic and aerodynamic aspects and are crucial for vehicle dynamics and safety. Driven by the vehicle design and the vehicle dynamics, especially the huge weight of electric vehicles, tire widths and wheel sizes increase steadily while weight targets are lowered at the same time. Looking at the sheer numbers of produced wheels around the globe, the impact of weight reductions on energy consumption and emissions for production and vehicle usage are obvious. A weight optimised design requires the full exploitation of the material potential using an approach for the consideration of specific influences on the mechanical performance and the structural durability already during the early product development phases. The paper presents an approach, which combines material testing with a knowledge base from prior testing and production by a modified Weibull approach. The implementation of already existing information allows a lean fatigue evaluation with a considerable increase of material utilisation without compromising safety margins.

1RONAL GmbH, Forst, Germany

PREDICTING THE FATIGUE LIFE OF STEEL CABLES

L. Larippe3*, A. Lecercle3, A. Jamoneau3, C. Gandiolle1, J-Y. Buffière2 & V. Aubin1*

A tyre is a complex object composed of a stack of steel cables in an elastomer matrix composite plies.One cable is an assembly of drawn pearlitic steel wires. The cable in service is subjected to mechanical (tension and bending) and chemical (diffusion of species) cyclic loading leading to fatigue damage. Responding to environmental issues requires reducing the weight of tires without reducing their performance, especially their fatigue life.

A fatigue model of the steel wire has been developed, based on the assumption of existing defects at the surface of the steel wires, from which crack initiate. A crack propagation law was determined from tensile cyclic tests on single wire, under synchrotron beam to measure crack shape and length. The distribution of defect sizes has been measured from fracture surface analysis, whereas other model parameters have been obtained by inverse method from Wöhler curves.

The model is able to simulate accurately the number of cycles to failure of wires submitted to a constant loading (fig. 1a) but also to variable loading (fig. 1b).

Fig. 1. Comparison between experimental fatigue lifes and model predictions a) under constant loading, b) after a pre-cycling.

1Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, CNRS, LMPSLaboratoire de Mécanique Paris-Saclay, 91190, Gif-sur-Yvette, France

2Laboratoire Mateis, INSA Lyon, CNRS, Villeurbanne, France

3Michelin, Clermont-Ferrand, France

*Corresponding authors: veronique.aubin@centralesupelec.fr & laure.larippe@michelin.com

IMPLEMENTATION OF FATIGUE CRACK GROWTH LAWS IN ABAQUS

H. Farid1

For many engineering structures, fatigue is the most dominant failure mode. Understanding the fatigue crack growth can be a critical aspect in many structural designs, as it helps limiting and mitigating failure risks due to fatigue loading.

Classically, Paris law had been widely used to model/predict the fatigue crack growth, however it is incapable of capturing the crack growth nonlinear behaviour at the initiation phase thresholds, or near the critical value of the stress intensity factor where the crack propagation is more unstable. Furthermore, Paris Law cannot model the fatigue stress ratio dependency.

Several models in literature, such as Walker, Forman, or NASGRO equations, have addressed the limitations of the Paris law.

In this work, we will present a methodology to implement some of these fatigue crack growth equations into the finite element code Abaqus. This enables the analysis of more realistic engineering structures under realistic cyclic fatigue loading scenarios. Furthermore, we will include the mixed mode behaviour to show the influence of difference cracking modes and their interaction on the fatigue behaviour and life.

1Dassault Systèmes Canada Inc., 110 Yonge Street, Suite 514, Toronto, ON M5C 1T6, Canada

FINITE ELEMENT ANALYSIS OF THE MAGEC

SPINAL ROD UNDER COMPRESSIVE AND SHEAR LOADING CONDITIONS

T. S. Mosley1, M. Birkett1, T. J. Joyce2 & F. Farhad1*

Advancements in spinal surgery have led to the development of innovative implant systems, such as the MAGEC (Magnetic Expansion Control) spinal rod, which offers dynamic deformity correction in patients of EOS (Earlyonset scoliosis). To assess the mechanical behaviour of this groundbreaking technology, finite element analysis (FEA) is employed to simulate the response of the MAGEC spinal rod when subjected to compressive and shear loading conditions. This study unveils insights into structural integrity, stress distribution, and deformation patterns, aiding in optimising design and informing clinical decisions for improved patient outcomes in spinal deformity correction.

1Department of Mechanical and Construction Engineering, Northumbria University, Newcastle Upon Tyne, NE1 8ST, UK

2School of Engineering, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.

*Corresponding author: farnoosh.farhad@northumbria.ac.uk

11. KEYNOTE

DESIGN & MANUFACTURING CHALLENGES FOR HIGH PRESSURE DISC ROTORS IN AIRCRAFT ENGINES

M. Hardy1*, C. Argyrakis1, P. Bowen2, R. Buckingham1, H. Cockings3, B. Grant1, S. Gray4, T. Jackson1, H. Kitaguchi2, H. Li2, D. MacLachlan1, H. Tai1 & M. Taylor2

High bypass ratio turbofan aircraft engines and cycles are continuously evolving to provide improved efficiencies for reducing fuel consumption and emissions. However, whilst propulsive and aerodynamic optimisations of aircraft engines are possible, the increased demands upon nickel based superalloys, which are used in the hot section parts, limit the thermal efficiency improvements that can be achieved. The requirements for reduced engine core sizes and increased temperatures and stresses pose a complex set of seemingly conflicting property requirements for the materials considered for safety-critical disc rotor applications. The apparent conflict is in the design priority between strength and damage tolerance or crack growth resistance. Alloys with higher strength levels have often been preferred to reduce the size and weight of components, with disc forgings showing a fine grain microstructure, from billet produced by ingot metallurgy. Yet such grain structures have (i) less appealing time dependent crack growth behaviour and (ii) an increased sensitivity to fatigue crack nucleation from features that originate from material or component manufacture and handling. These attributes are likely to limit the fatigue life of the component or the interval between inspections for operating temperatures above 600°C and from long periods of sustained peak load. This is particularly relevant in today’s aircraft engines as high climb rates are increasingly required by commercial airlines to move aircraft more quickly to altitude to reduce fuel consumption.

For nickel disc alloys with increased amounts of the gamma prime (γ´) phase (> circa 40 %), acceptable strength can be achieved from coarse grain microstructures, by means of effective γ´ precipitation strengthening and control of grain size. This is possible using powder metallurgy and

isothermal forging by producing a uniform average grain size of 20-40 µm from super-solvus solution heat treatment. Such a microstructure enables an ideal balance in material properties between tensile strength and resistance to time dependent crack growth.

This paper examines the effects of microstructure, service temperature and manufacturing artefacts on the low cycle fatigue properties of nickel disc alloys that are made using ingot and powder metallurgy. Attention is given to the consequences of changing slip behaviour, the role of oxide and carbide/carbonitride particles and surface modification (shot peening & environmental damage) on fatigue crack nucleation behaviour. Crack growth mechanisms will also be discussed, notably the effect of microstructure on time dependent crack growth. This understanding of material deformation and damage has been developed from the extensive use of advanced electron microscopy, finite element simulations and micromechanics, in addition to fatigue testing of laboratory test pieces and cyclic spin tests on components.

1Rolls-Royce plc, PO Box 31, Moor Lane, Derby, DE24 8BJ, UK

2School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2SE, UK

3Institute of Structural Materials, Swansea University, Swansea SA1 8EN, UK

4Surface Engineering Science, Cranfield University, MK43 0AL, UK

*Corresponding author: mark.hardy@rolls-royce.com

12. SUPERALLOYS I

PHASE ANGLE EFFECTS ON THERMOMECHANICAL FATIGUE (TMF) IN A SINGLE CRYSTAL

A. Gonzalez

Garcia1,

NICKEL SUPERALLOY

J. Jones1, R. Lancaster1, M. Whittaker1, S. John1 & J. Mason-Flucke2

In hot-section components of jet engines, the overlay of cyclic mechanical and thermal loads can result in a complex failure mechanism known as Thermo-Mechanical Fatigue (TMF), where the combination of fatigue, creep, and oxidation damage can lead to the nucleation and propagation of cracks, and ultimately catastrophic failure. In this research, a series of TMF tests were undertaken on a single crystal nickel-based superalloy, CMSX-4, under a variety of phase angles (-180°, -135°, -90°, 90°, 45° & 0°) to understand the evolving damage mechanisms that can occur under the various loading conditions. The generated data has shown that for the strain ranges tested, fatigue life is significantly affected by the employed phase angle. Furthermore, the length of time that the material is exposed to elevated temperature also has a substantial influence on the material’s microstructure, and thus, the dominant mode of damage that occurs.

1Institute of Structural Materials, Swansea University, Bay Campus, Swansea, SA1 8E

2Rolls-Royce plc, Bristol, BS11JQ, UK

COUPLING EFFECTS OF TEMPERATURE AND FATIGUE, CREEP-FATIGUE INTERACTION AND THERMO-MECHANICAL LOADING CONDITIONS ON CRACK GROWTH AND DOMINANT FAILURE MECHANISMS OF A NICKEL-BASED ALLOY

V. Shlyannikov1, A. Shanyavskiy2, A. Sulamanidze1 & D. Kosov1

This study presents analysis and evaluation of a range of isothermal and non-isothermal experimental crack growth data generated by four type tests carrying out under stress-controlled pure fatigue, creep-fatigue interaction, in-phase (IP) and out-of-phase (OOP) thermo-mechanical fatigue (TMF) conditions. The tests have been carried out using stress cycles with a trapezoidal or triangular waveform and a temperature range of 400–650°C for XH73M nickel-based alloy. As a result of the tests performed, it was found that from the crack growth acceleration point of view, the levels of influence on the alloy’s final fracture mechanisms are in the following order: isothermal creep-fatigue interaction, non-isothermal in-phase thermo-mechanical fatigue, isothermal pure fatigue and non-isothermal out-of-phase thermo-mechanical fatigue. The ordering of the crack growth rate curves is supported by detailed fractographic analysis.

1Institute of Power Engineering and Advanced Technologies, FRC Kazan Scientific Center of Russian Academy of Sciences, Russia

2Aviation Register for the Russian Federation, Airport Sheremetievo-1, PO Box 54, Moscow region, 4 Chimkinskiy State, 141426, Russia

STUDY ON THERMO-MECHANICAL FATIGUE

CRACK PROPAGATION BEHAVIOUR OF POWDER METALLURGY SUPERALLOY

L. Zhang1*, Y. Z. Wang1, Z. W. Yu1, R. Jiang1, L. G. Zhao1 & Y. D. Song1

Aero-engines are subjected to complex force/heat multi-field coupled alternating loads during takeoff, landing, etc., which lead to thermomechanical fatigue (TMF) failure. To investigate the TMF mechanisms, fatigue crack propagation tests were carried out under in-phase (IP) / outof-phase (OP) TMF (350°C~650°C) and isothermal fatigue (IF) (650°C) conditions for nickel-based powder metallurgy (PM) superalloy coarse- and fine- grain. The fatigue crack growth rates were measured using combined methods of direct current potential drop (DCPD) and long focal-length telemicroscope.

The results show that the crack growth rate of IP is the fastest, while OP the slowest and IF intermediate. The mechanisms of TMF crack propagation were studied using SEM and TEM characterization. It is observed from fracture surface that cracks propagate intergranularly in IP, with grain boundary oxidized; while transgranular cracks grow in OP with fatigue strips. In IP condition, the dislocations nucleate at and weaken the grain boundary, and the interaction by mechanical stress and thermal stress accelerates the intergranular crack propagation. While in OP condition, the stacking layers evolve into the deformation twins, thereby hindering the crack transgranular propagation in the stress field at crack tip. A proper TMF crack propagation prediction model is established, which can simulate the TMF crack propagation life well, and support the design of damage tolerance for aero-engine superalloy.

1College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China

*Corresponding author: luzhang@nuaa.edu.cn

EVALUATION OF FATIGUE STRIATIONS IN A NICKEL-BASED SUPERALLOY

Y. Alyousif1, E. A. Saunders2, S. Taylor2, J. C. Walker1 & P. A. S. Reed1

Fatigue is the most common mode of failure in aerospace components, placing a great demand on the quality and reliability of analytical failure investigations. Fractography continues to be the most effective method of mapping and understanding the propagation history of a fatigue crack, thus motivating the need to further develop the mechanistic understanding of fatigue crack growth at the various stages of fatigue life.

One of the main fractographic markings used to characterise fatigue crack growth (FCG) are striations, where each marking can represent a single loading cycle, with their individual spacing’s believed to indicate the local crack growth rate (da/dN). While fatigue striations have been known to be most prominent during stage II of fatigue crack propagation, they can also be observed at the early stages of crack growth, but the validity of assuming their spacing always directly represents da/dN has been questioned when used in failure investigations.

Inconel 718 (IN718) is a cast and wrought Ni-based superalloy commonly used in the manufacturing of high-pressure turbine discs in gas turbine engines due to their strong high temperature performance and excellent corrosion resistance. The temperature of these components can reach 600°C while having to withstand extended service times and high mechanical loads.

The microstructure of IN718 was characterised using optical and scanning electron microscopy (SEM) prior to mechanical testing. A carefully designed testing matrix, exploring different load ratios, loading frequencies and temperatures was employed to provide a variety of fracture surfaces to compare striation morphology and investigate their mechanistic origin. Striations have been measured and assessed using surface tilt reconstructions and sectioning studies.

The results of this work have shown that fatigue striation spacings are indicative of FCG rates in the stable Stage II region of fatigue at relatively high stress-intensity ranges (∆K) (Figure 1), however at near threshold and low ∆K, the striation-like markings observed (Figure 2) bear little relation to loading cycles or FCG rate. These markings can therefore be considered a product of slip processes and be linked to the crystallographic mode of FCG seen at low stress intensity ranges, where the plastic zone size at the crack tip is small in comparison to the grain size of the material.

1Engineering Materials Research Group, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

2Rolls-Royce plc., Materials — Failure Investigation, Bristol BS34 7QE, UK

Figure 1: Striations at high ΔK

Figure 2: Slip bands at low ΔK

13. NON-METALLIC MATERIALS

CRACK GROWTH IN A PIEZOELECTRIC CERAMIC

INDUCED BY A CYCLIC ELECTRIC FIELD

K. Hockauf1, F. Poschmann1 & R. Pleul2

In piezoelectric materials, an electric charge is generated in response to an applied mechanical stress (piezoelectric effect). Vice versa, given an applied electric field, these materials will show elastic deformation (inverse piezoelectric effect). In the case of high electric driving fields, cyclic electrical loading can cause electrical and mechanical degradation, such as the initiation and growth of cracks. In this study, commercial hard-PZT (lead zirconate titanate) discs are pre-damaged by a Vickers indent and subjected to cyclic electrical loading with a high electric field. Fatigue crack growth is monitored until fracture occurs. Fatigue life until fracture is displayed in a Weibull plot, showing three classes of failure (early, intermediate and late). Fracture surfaces are observed postmortem through scanning electron microscopy.

1Chair of Smart Materials, University of Applied Sciences Mittweida, Faculty of Engineering Sciences, 09648 Mittweida, Germany

2Chair of Electrical Engineering/ Measurement Technology, University of Applied Sciences Mittweida, Faculty of Engineering Sciences, 09648 Mittweida, Germany

HIGH- AND LOW-CYCLE TENSILE FATIGUE OF

ALL-CARBON HYBRID QUASI-ISOTROPIC LAMINATE

V. Carvelli1, S. B. Sapozhnikov2, S. V. Lomov3 & Y. Swolfs3

Is the pseudo-ductile quasi-static tensile behaviour of all-carbon hybrid composites retained under fatigue loading? This paper addresses this question by examining the low-cycle tensile-tensile fatigue behaviour of a unidirectional carbon laminate and the high-cycle fatigue behaviour of an all-carbon fibre hybrid quasi-isotropic laminate. The low-cycle fatigue, monitored with the acoustic emission recordings, indicates that the damage pattern observed during the first cycle is maintained in subsequent cycles, albeit with reduced intensity than the initial damage. The high-cycle tensile-tensile fatigue performance of an all-carbon fibre hybrid quasiisotropic laminate revealed that its load-carrying ability is retained for load levels below the pseudo-ductile regime, while it is not beyond the limit of elastic response. Conversely, the all-carbon hybrid composite maintains its load-carrying ability during strain-controlled fatigue in the pseudo-ductile regime, albeit with a lower stiffness.

1Department A.B.C., Politecnico di Milano, Milan, Italy

2Aerospace Department, South Ural State University, Chelyabinsk, Russia

3Department of Materials Engineering, KU Leuven, Leuven, Belgium

MEAN STRESS CORRECTION FOR CARBON FIBRE REINFORCED POLYMER COMPOSITES UNDER FATIGUE LOADING

Z. Lu1

Carbon Fibre Reinforced Polymer (CFRP) composites were widely used in different engineering applications for their light weight and high strength characteristics. The fatigue behaviour of CFRP composites is significantly affected by the mean stress. The existing mean stress correction equations failed to correlate the mean stress effect for CFRP composites especially under compressive loadings. A new mean stress correction equation was created to account for the mean stress effect for the CFRP composites under fatigue loadings.

1Department of Materials Engineering, Jaguar Land Rover Ltd., Abbey Road, Coventry CV3 4LF, UK

FRACTURE AND FATIGUE CHARACTERISATION OF THE SHOT-EARTH 772

A. Zanichelli1, A. Carpinteri1, C. Ronchei1, D. Scorza1 & S. Vantadori1

Among the earthen construction techniques, the innovative shot-earth technique employs a material, named shot-earth, which is a dry mixture composed of excavated soil, aggregates and water, where the soil may be either unstabilised or stabilised by a chemical binder. More precisely, the mixture here examined is the shot-earth 772, consisting of 7 parts of soil, 7 parts of aggregates, 2 parts of cement (by volume) and about 3% of water (by volume). The fracture toughness of such a material is herein evaluated by applying a method recently proposed by the authors, named the Modified Two-Parameter Model. Then, both compressive and flexural fatigue tests are performed under different levels of maximum stress, being the fatigue ratio equal to zero, and the corresponding S-N curves are determined. Finally, the above experimental campaigns are numerically simulated by employing a micromechanical model, implemented in a nonlinear 2D finite element homemade code.

1Department of Engineering & Architecture, University of Parma, Parco Area delle Scienze 181/A, 43124 Parma, Italy

INVESTIGATIONS ON EXPERIMENTAL FATIGUE

LIFE AND DAMAGE OF DESIGNED HYBRID COMPOSITE LAMINATES WITH NEGATIVE AND POSITIVE POISSON’S RATIO

H. Hosseini-Toudeshky1*, M. Tashayyoee1, A. Navaei1, J. Nafar Dastgerdi1,2 & S. Esmaeili1

Composite material design with negative Poisson’s ratio may be employed in many specific industrial applications to increase the fatigue strength and improve resistance to failure. For this purpose, the authors designed an 8-layer hybrid laminate of carbon/glass/epoxy with negative Poisson’s ratio of -0.161 and elastic modulus of 27.50 GPa. For comparison another laminate was made with only different angle of layers, but with positive Poisson’s ratio of 0.156 and similar elastic modulus of about 27.78 GPa. The obtained mechanical properties from classical laminate theory and experiments are in excellent agreement. The fatigue strength of the laminate with negative Poisson’s ratio is about 60% larger than that obtained for positive Poisson’s ratio. The failure type of the laminate with negative Poisson’s ratio is not catastrophic and behaves similar to pseudo-ductile fracture. More details of the experiments and results are discussed in this paper.

1Fatigue and Fracture Lab., Department of Aerospace Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave, Tehran, Iran

2Mechanical Engineering Group, School of Engineering, University of Kent, Canterbury CT2 7NT, United Kingdom

*Corresponding Author, hosseini@aut.ac.ir

14. VARIABLE AMPLITUDE

FATIGUE CRACK GROWTH BEHAVIOUR OF 9310

STEEL UNDER CONSTANT AND VARIABLE-AMPLITUDE LOADING

T. M. Senhaji1 & J. C. Newman Jr.2

Fatigue-crack-growth-rate tests were conducted on compact, C(T), specimens made of 9310 steel (B = 6.35 mm) under constant- and variableamplitude loading. The specimens were tested over a wide range in load ratios (0.1 ≤ R ≤ 0.9) to generate crack growth rate data from threshold to near fracture. Several loading sequences were used to generate near threshold data: (1) ASTM Standard E647 load reduction (LR), (2) compression precracking constant amplitude (CPCA), and (3) compression pre-cracking load reduction (CPLR). Results were compared with either existing loadreduction data from the literature or with data that were generated using the various procedures. In the 9310 steel, very little difference was observed between the ASTM load reduction and CPCA/CPLR test methods, although compression pre-cracking allowed lower initial ΔK values to start the loadreduction procedure.

The back-face strain (BFS) gauge method was used to monitor crack lengths and to measure crack-opening loads from remote strain records during all tests. A crack-compliance method using the BFS gauge was used to determine that the crack-starter notch tensile residual-stress effects from compression pre-cracking dissipated in about two compressive plasticzone sizes, to stabilise crack-closure behaviour, and to achieve steadystate constant-amplitude data. A crack-closure analysis was performed to calculate the effective stress-intensity factor (ΔKeff) against rate using measured values of crack-opening loads for low R (0.1 and 0.4). The zero percent offset value (OP0) crack-opening load, similar to Elber’s crack-opening load, was extrapolated using the one-percent (OP1) and two-percent (OP2) offset compliance values recorded from the BFS and crack-monitoring software using Elber’s load-reduced-strain approach. The remote BFS method was also able to detect crack closure at R = 0.7 conditions during the load-reduction tests in the low-rate (threshold) region.

At low R, all three major shielding mechanisms (plasticity, roughness and fretting debris) are suspected to cause crack closure. But for high R, plasticity effects cause crack closure near the minimum load, but roughness and fretting debris are suspected to cause crack closure above the minimum load. The fatigue-crack-growth-rate data also correlated very well onto a unique curve in the near-threshold regime using the strip-yield model in FASTRAN, a life prediction code, where a plane-strain constraint factor of α = 2.5 was required. Under variable-amplitude loading, a constraint-loss (plane strain to plane stress) behaviour was required to match the test data.

1Aerospace Engineering and Mechanics, University of Alabama, Tuscaloosa, AL USA

2Department of Aerospace Engineering, Mississippi State University, Mississippi State, MS USA

PLASTIC CTOD AS FATIGUE CRACK GROWTH

CHARACTERISING PARAMETER UNDER VARIABLE AMPLITUDE LOADING BY USING DIC

G. L. Gómez-Gonzales1, A. Camacho-Reyes1, J. M. Vasco-Olmo1, F. A. Díaz1, D. Neto2 & F. V. Antunes2

Although Paris’ ΔK approach has been a useful tool for characterising fatigue crack growth, it has not been without controversy due to its linear and elastic nature and therefore, its limitations in modelling some scenarios such as those involving large plasticity levels, among others. Thus, a potential way forward consists of developing new approaches based on parameters able to account for plasticity effects. Recent published works show promising results in terms of a more effective characterisation of fatigue crack growth by the plastic component of the crack tip opening displacement range. This work shows how the plastic component of the crack tip opening displacement range is a suitable parameter to characterise fatigue crack growth rates under variable amplitude situations such as an overload. In this work, fatigue crack growth testing was performed in pure grade 2 Titanium Compact-Tension-specimens at low stress ratios for constant amplitude and variable amplitude loading scenarios. Plastic components of the crack tip opening displacement range for different crack lengths were measured using a high-resolution digital image correlation system. The obtained results show how the plastic component of the crack tip opening displacement range can perfectly model fatigue crack growth rates even for a phenomenon involving nonlinearity and plasticity such as the application of an overload on a specimen growing at constant amplitude loading.

1Departamento de Ingeniería Mecánica y Minera, Universidad de Jaén. Campus las Lagunillas, 23071, Jaén, Spain.

2Univ Coimbra, Centre for Mechanical Engineering, Materials and Processes (CEMMPRE), Department of Mechanical Engineering, Portugal

MACHINE LEARNING BASED FATIGUE LIFE

PREDICTION OF METAL COMPONENTS SUBJECTED TO BLOCK LOADING

K. Hectors1, Q. Bouckaert1, J. Plets1 & W. De Waele1

Accurate lifetime prediction of metal components subjected to cyclic loading remains challenging. Many analytical, (non)linear fatigue damage accumulation models have been developed since the Palmgren-Miner rule was first presented. Analytical models are often strongly biased towards particular datasets and limited by simplifications and assumptions. Machine learning, however, offers a promising solution by learning relationships directly from the data without human bias. In this work, 13 different machine learning models are trained for fatigue life prediction of metal components subjected to block loading. The number of high-quality datasets in literature was rather limited, hence nearly 160 fatigue experiments were performed to improve the training set. A comparison study is performed to determine the best performing machine learning model. Finally, the best performing models are compared to Miner’s rule. The results show that the machine learning models consistently outperform Miner’s rule.

1Department of EMSME, Laboratory Soete, Faculty of Engineering and Architecture, Ghent University, Technologiepark 46, BE-9052, Zwijnaarde, Belgium

15. WELDS

INDUSTRY-ORIENTED ASSESSMENT OF THE FATIGUE LIFE OF THIN-WALLED PROFILE WELDMENTS USED

IN THE CONSTRUCTION OF BUS BODIES

M. Kepka1, R. Minich1, M. Krizek1 & M. Kepka Jr.1

The paper presents findings from the intensive cooperation of the university research center with manufacturers of buses, trolleybuses, and electric buses in solving commercial projects, which are aimed, among other things, at solving the strength and fatigue life of their bodywork. The successive steps of the methodology are the creation of the MBS model of the vehicle and the simulation of its driving over an artificial standardised obstacle. The FEM model of the body is loaded with the calculated forces acting in the suspension elements (shock absorbers and air springs) and the stress responses on the critical structural nodes are calculated. Then, the S-N curves of these structural nodes are estimated or, even better, determined experimentally, and the future service stress spectra for the vehicle’s design life are estimated. Using the fatigue damage accumulation hypothesis, the permissible maximum stress amplitude in the design spectrum can be determined and compared with the calculated or measured value. A case study from practice concretely documents the procedure.

1University of West Bohemia, Regional Technological Institute – research center of the Faculty of Mechanical Engineering, Univerzitni 2732/8, 301 00 Pilsen, Czech Republic

INFLUENCE FACTORS ON FATIGUE STRENGTH

OF ARC-WELDED JOINTS USING ULTRA-HIGH STRENGTH STEEL SHEETS AND ITS IMPROVING METHODS

N. Yamaguchi1,2,*, T. Shiozaki1, Y.

Tamai1,

Y. Ichikawa2 & K. Ogawa2

The fatigue strength of arc welded joints with ultra-high strength steel (UHSS) is known to be low, yet the underlying cause remains elusive. This study aims to elucidate the effect of base metal strength and stress concentration on the fatigue strength of these joints, employing a fracture mechanics approach. Experimentally, we examined arc welded joints with mechanically ground toe radii ranging from 0.5 mm to 1.5 mm, using two types of steel with tensile strengths of 440 MPa and 980 MPa. Our findings indicate that the fatigue strength of mechanically ground joints improved drastically when UHSS was used, and this improvement was accurately predicted. However, this was not the case for as-welded joints. The study suggests that this discrepancy may be attributed to the microstructural effect. Lastly, we compared several methods for enhancing fatigue strength, finding that significant improvements were achieved by altering the residual stress and microstructure, without the need to reduce stress concentration.

1Steel Research Laboratory, JFE Steel Corporation, 1 Kawasaki-cho, Chiba, Japan

2Fracture and Reliability Research Institute, Tohoku University, 6-6-11, Aoba, Aramaki, Aoba-ku, Sendai, Japan

*Corresponding author: n-yamaguchi@jfe-steel.co.jp

FATIGUE OF ULTRASONIC SPOT WELDED JOINTS OF LIGHTWEIGHT MATERIALS

D. Chen1*

Lightweight materials, including aluminium and magnesium alloys, are increasingly used in automotive and other transportation industries for weight reduction, fuel efficiency improvement and sustainable development goals. The lightweighting strategies can be further enhanced via a multi-material design concept, where the characteristics of different materials are optimised for the desired application for lightweighting, cost effectiveness and value addition. The structural applications of multi-materials unavoidably involve welding and joining, particularly dissimilar welding. This presents significant challenges due to different physical, mechanical and thermal properties and the related safety, reliability, and durability of welded joints. There are many knowledge gaps concerning the resulting changes in the composition and microstructure, and fatigue and fracture resistance of welded joints. Dissimilar welding between magnesium alloys and other alloys (e.g., aluminium alloys, and steels) represents a huge challenge, since intermetallic compounds may be present to potentially cause premature failure especially under cyclic loading. Several emerging and promising solid-state welding techniques, such as ultrasonic spot welding, friction stir (spot) welding, have been developed to join the lightweight alloys in both similar and dissimilar material combinations. In this talk, some examples on the welding of similar magnesium-to-magnesium and aluminium-toaluminium and dissimilar magnesium-to-aluminium, magnesium-to-steel and aluminium-to-steel using ultrasonic spot welding will be presented, focusing on the fatigue resistance of welded joints in relation to the welding parameters and interfacial structures. The weld interface was observed to undergo dynamic recrystallisation during similar welding, while an intermetallic compound layer or a eutectic layer was formed during dissimilar welding, depending on the material combinations and welding parameters. To inhibit the occurrence of intermetallic compounds, an interlayer of tin or zinc was used during dissimilar welding. Subsequently, the tensile lap shear strength and fatigue strength of the dissimilar welded

joints were effectively enhanced. The evolution in the microstructure and texture and fatigue failure mechanisms of the welded joints will also be presented.

1Department of Mechanical, Industrial and Mechatronics Engineering Toronto Metropolitan University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada

*Corresponding author: dchen@torontomu.ca

16. CONTACT

EVALUATION OF NON-PROPORTIONAL MULTIAXIAL STRESS STATES IN DRIVE-TRAIN COMPONENTS RELATED TO CONTACTS

J. Schanner1*, A. Hasse1 & L. Suchý1

Estimating the fatigue strength of multiaxially loaded components using current standards has shortcomings for certain stress conditions. Therefore, different methods to estimate the severity of non-proportionality of load cases are investigated. First, four integral-based calculation methods are analysed on a simple plane stress load case. Their spatial capabilities are then tested for contact on an example of a shaft-hub shrink fit model. Qualitative two of the four selected methods perform well for this type of loading. Consequently, the basis for subsequent quantitative fatigue analyses with experimental validation has been prepared.

1Institute for Engineering Design and Drive Technology, Chemnitz University of Technology, 09126 Chemnitz, Germany

*Corresponding author: jonathan.schanner@mb.tu-chemnitz.de

FRETTING FATIGUE OF SHAFTS UNDER VARYING CONTACT PRESSURE

AND CREEP SLIP CONDITIONS IN BEARING-SHAFT CONTACTS

D. Knabner1, L. Suchý1, S. Busch1 & A. Hasse1

The shafts, used to transmit rotary motion in drive trains, often receive the dynamic load of rotating bending. The support of the shaft is normally realised with press fitted roller bearings. The elastic deflection during operation of the shaft leads to microslip movements in contact with the bearing inner ring, resulting in the phenomenon of fretting fatigue and thus failure of the shaft. The special characteristic of this connection is found on the one hand in the kinematics of the slip – besides a clearly reversing slip in axial direction when changing from bending tension to bending pressure, a creeping slip in circumferential direction occurs – and on the other hand in the cyclical change of the contact pressure– up to a gaping of the contact. For the determination of the fatigue limits of the connection, experimental investigations were first carried out in the high cycle fatigue domain. The material used for the shaft was C45+N. The material of the bearing inner ring was 100Cr6. At run-out specimen as well as at broken specimen the slip zones in axial direction resulting from the bending and in circumferential direction resulting from the creeping slipping of the bearing inner ring are visible. Numerical investigations were then carried out to determine the local stresses at the interface. Subsequently, a comparative strength study of integral and critical-plane approaches was carried out. The fretting fatigue strength was defined as a nonuniform function of pressure and slip at the interface.

1Institute for Engineering Design and Drive Technology, Chemnitz University of Technology, 09126 Chemnitz, Germany

INFLUENCE OF MICROSTRUCTURE, STRESS GRADIENT AND DEFECT SIZE ON THE STABILITY OF THE CRITICAL DISTANCE

METHOD FOR FRETTING CRACK NUCLEATION

H. Lannay1, S. Fouvry1, B. Berthel1 & C. Gandiolle2

To prevent failure due to fretting and fretting-fatigue loading, it is important to understand the crack nucleation process and the influence of the microstructure and the geometries. This study aims to discuss the stability of the critical distance method with the grain size, the stress gradient and the crack nucleation length, in order to understand their impact on fretting crack nucleation. Cylinder/plane fretting tests were performed to determine experimental crack nucleation thresholds and use them in an elastic FEM simulation of the contact. Using an inverse method, a link has been established between the critical distance, the microstructure and the stress gradient. This study suggests that this link is very dependent on the considered crack nucleation length.

1LTDS – Laboratoire de Tribologie et Dynamique des Systèmes, Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France

2Université Paris-Saclay, CentraleSupélec, ENS Paris-Saclay, LMPS –Laboratoire de Mécanique Paris-Saclay, 91190 Gif-sur-Yvette, France

17. MULTI AXIAL

CRACKING BEHAVIOUR AND LIFETIME

PREDICTABILITY OF P558 STEEL IN ANNEALED AND COLD DEFORMED STATES UNDER MIXED COMPLEX LOADING

T. Ngeru1* & S. Hanke1

Samples were cold deformed at 5% and 10% strains before being subjected to simultaneous loading of static compressive stress (250 MPa) and different shear stress amplitudes, Δγyx (in terms of 5°, 10°, 15° and 20° angles of twist). Pure torsion cyclic fatigue was also carried out as a reference, with the same Δγyx but without the static compressive stress. Furthermore, samples with 250 and 350 MPa static compressive stress and the same Δγyx listed above were also tested without cold deformation.

The low shear stress amplitude samples fail in mode I, the high amplitude samples fail in mode II while the mid-range (10° and 15° angles of twist) fail in mixed mode. The static compressive stress seems beneficial for the low Δγyx since their application results in a 2-fold and a 4-fold increase in fatigue life for the non-cold-worked and cold-worked samples respectively. In the high Δγyx experiments, the static compressive stress results in a reduction of fatigue life, we also see a stress effect here where 350 MPa results in a much more reduction than the 250 MPa. The cold deformation helps herein to offset the negative effect of the static compressive stress.

Critical plane predictions using Smith-Watson-Topper and Fatemi-Socie models gave mixed results signifying that a single model is not sufficient to predict which planes the cracks will be initiated and/or will propagate. This is especially difficult for the mid-range Δγyx where crack branching occurs, both models seem unsuited in these situations.

1Materials Science and Engineering, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany,

*Corresponding author: timothy.ngeru@uni-due.de

FATIGUE CRACK GROWTH

IN AIR OR IN OIL, UNDER CYCLIC MODE II + STATIC BIAXIAL COMPRESSION

M. Zaid1,2,3, V. Bonnand1, D. Pacou1, V. Chiaruttini1, V. Doquet3* & P. Depouhon2

Mode II fatigue crack growth under reversed shear and static biaxial compression was investigated in two bearing steels representative of the base metal, and case-hardened surface layer of gears used in helicopters power transmission systems. Since these systems are lubricated, crack growth tests were run on cruciform-shaped specimens in air, but also in oil, using Digital Image Correlation (DIC) to track the crack tips positions [1], and to measure the displacement field. Many aborted branches, quasiorthogonal to the main crack, were observed along the crack face. EBSD analyses showed that a majority of these branches formed along slip planes. The compressive stress parallel to the main crack hindered the growth of these branches and favoured coplanar mode II crack growth. The crack face sliding displacement profiles measured by DIC were used to derive ΔKII,eff, at the main crack tip, using elastic-plastic FE simulations with crack face friction, by an inverse method [2, 3]. While the apparent friction coefficient was found to increase during mode II crack growth in air, due to a progressive decrease in the degree of crack face oxidation, and a transition from abrasive to adhesive wear, it was found to decrease with the crack length in oil. Friction-corrected kinetics were obtained for mode II crack growth in air, for both steels [3], and, for one of the steels, both in air and in oil. The similarity of the latter two suggests that the main influence of oil resides in the lubrication of the crack faces.

References

[1] S. Feld-Payet, G. Le Besnerais, V. Bonnand, D. Pacou, L. Thiercelin. Crack path tracking from full field measurements: A novel empirical methodology, Strain, 56 (2020).https://doi.org/10.1111/str.12333

[2] T. Bonniot, V. Doquet, S.H. Mai. Determination of effective stress intensity factors under mixed-mode from digital image correlation fields in

presence of contact stresses and plasticity, Strain, 56 (2020).

https://doi.org/10.1111/str.12332

[3] M. Zaid, V. Bonnand, V. Doquet, V. Chiaruttini, D. Pacou, P. Depouhon, Fatigue crack growth in bearing steel under cyclic mode II + static biaxial compression, Int. J. Fatigue, 163, 2022, 107074, https://doi.org/10.1016/j.ijfatigue.2022.107074

1Université Paris-Saclay, ONERA, Matériaux et Structures, 92322, Châtillon, France

2Airbus Helicopters, Aéroport International Marseille Provence, 13700 Marignane

3Laboratoire de Mécanique des Solides, CNRS, UMR 7649, Ecole Polytechnique, Institut Polytechnique de Paris, France

*Corresponding author: veronique.doquet@polytechnique.edu

THE CRITICAL DISTANCE CONCEPT TO DESIGN

NOTCHED 3D-PRINTED METALS AGAINST UNIAXIAL/MULTIAXIAL FATIGUE

L. Susmel1

As far as notched components are concerned, the term “Theory of Critical Distances” (TCD) encompasses a set of design methodologies that employ a material length scale parameter to post-process the local linear-elastic stress fields damaging the material in the vicinity of the crack initiation points. This paper aims to review the ways the linear-elastic TCD is recommended to be applied to predict the fatigue strength of notched components fabricated from 3D-printed metals. To this end, the accuracy and reliability of the TCD in estimating fatigue strength of additively manufactured (AM) materials are assessed against a large dataset of experimental results. This dataset was generated by testing under both uniaxial and bi-axial cyclic loading AM specimens containing geometrical features of different sharpness. Through a systematic reanalysis, it becomes evident that TCD demonstrates high accuracy, with estimates predominantly falling within the calibration scatter bands of the parent material. This outcome holds significant relevance as it underscores the effectiveness of the linear-elastic TCD in successfully designing against fatigue loading notched components of AM metals, with this being achieved by directly processing the results from standard linearelastic Finite Element (FE) models.

1Department of Civil and Structural Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK

EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF MIXED

MODE FATIGUE

CRACK PROPAGATION

B. Sheen1, C. M. Davies1 & D. Nowell1

Bladed disks (or ‘blisks’) are often subjected to foreign object damage which may result in the initiation of cracks. Cracks in aero-engine blisks are affected by a combination of loads which propagate a crack in a multiaxial stress field. Depending on the local stress field, a crack may propagate through the blade, or more undesirably grow towards the bore of the disc due to hoop stress. A test rig and Ti-6Al-4V cruciform test sample have been designed and built to capture the key features of crack propagation in a blisk. The results of the experiments will enable modification and validation of a crack growth model. Experimental results correlate reasonably well with predictions from the maximum tensile stress criterion, in both trajectory and crack growth rate, and demonstrate the influence of hoop stress on the crack trajectory in a blisk.

1Department of Mechanical Engineering, Imperial College London, SW7 2AZ, London, UK

18. TITANIUM ALLOYS II

HIGH-CYCLE AND VERY-HIGH-CYCLE FATIGUE BEHAVIOUR AND LIFE PREDICTION OF Ti-6Al-4V FABRICATED BY LASER POWDER BED FUSION

C. Ling1 & L. Zheng1*

Microstructural defects in titanium alloys fabricated by laser powder bed fusion (L-PBF) make their fatigue behaviours much more complicated than conventionally made ones, especially in the very-high-cycle fatigue (VHCF) regime. In this paper, the fatigue behaviour of L-PBF Ti-6Al4V were investigated up to the VHCF regime incorporating the effect of stress ratio. Then a deep belief neural network-back propagation (DBNBP) model was proposed to predict the fatigue life of L-PBF Ti-6Al-4V up to the VHCF regime. Investigation indicates that the stress amplitude decreases with the increase of stress ratio with the order of: σ a (R = -1) > σa (R = -0.5) > σa (R= 0.1) > σa (R = 0.5). The DBN-BP model exhibits high precision in predicting the fatigue life of L-PBF Ti-6Al-4V in both HCF and VHCF regimes. Finally, this innovative DBN-BP model was applied to predict the relation between mean stress and stress amplitude, and the effect of energy density on the fatigue behaviour of L-PBF Ti-6Al-4V up to the VHCF regime.

1School of Science, Harbin Institute of Technology (Shenzhen).

*Corresponding author: icon_lzheng@hit.edu.cn

EFFECT OF DISCONTINUOUS PRINTING ON THE FATIGUE LIMIT OF SELECTIVE LASER MELTED Ti6Al4V SPECIMENS

A. H. Jabbari Mostahsan1,2,*, F. Farahmand1 & J. Domitner2

Discontinuous printing caused by the interruption of additive manufacturing processes may affect the microstructure and the mechanical properties of metallic components. This work investigates the influence of a deliberate stop of printing on the fatigue limit and the fracture surface of additively manufactured Ti6Al4V specimens. The specimens were vertically printed using the selective laser melting (SLM) method. Under rotating-bending load by using the Locati step-loading method, discontinuously printed specimens exhibited a fatigue limit of 311 MPa, which was about 34 % less than the fatigue limit of the continuously printed specimens. Although the microstructure at the position of interruption did not notably differ, a small offset was observed along the main axis of each specimen. This offset could either be attributed to the thermal expansion/contraction of the specimen and of the printing bed during interruption, or to the limited ability of the SLM machine to resume printing from the exact position. This lack of exact alignment caused an undesirable stress distribution inside the specimen during fatigue testing, which reduced the fatigue limit. Only in one out of five discontinuously printed samples fracture occurred at the position of interruption. The fracture surface of this particular specimen showed less lack of fusion than the fracture surface of continuously printed parts, which could be attributed to applying remelting steps before resuming the process. Hence, applying a machining process in the critical position may increase the fatigue limit, reduce the stress concentration and improve the alignment of discontinuously printed specimens.

1Sharif University of Technology, Department of Mechanical Engineering, Azadi Avenue, Tehran, Iran

2Graz University of Technology, Research Group of Lightweight and Forming Technologies, Institute of Materials Science, Joining and Forming, Inffeldgasse, Graz, Austria

*Corresponding author: jabbarimostahsan@tugraz.at

INFLUENCE OF DEFECT SHAPE

AND

POSITION

ON THE HIGH CYCLE FATIGUE BEHAVIOUR OF ADDITIVELY MANUFACTURED TA6V ALLOY

M. Bonneric1, N. Saintier1, D. El-Khoukhi2 & J. Bega1

The presence of process induced defects in parts produced by Laser Powder Bed Fusion (L-PBF) is today a well-known issue. It is therefore crucial to account for the defects when designing additively manufactured components against fatigue. To address this question TA6V samples with different defect populations have been produced by varying the process parameters. These defect populations have been characterised using X-ray tomography, while the samples have been subjected to uniaxial fatigue testing (R=-1). The results have demonstrated the detrimental impact of lack-of-fusion defects as compared to the gas pores for the case of surface crack initiation. In addition, the control of the distance between the defective areas and the surface of the samples allowed for the investigation of the criticality of internal defects. The establishment of a Kitagawa diagram for internal defects highlighted that the criticality of internal defects does not depend on the defect type, as opposed to surface defects.

1Arts et Métiers Institute of Technology, University of Bordeaux, CNRS, Bordeaux INP, INRAE, HESAM Université, I2M Bordeaux, F-33400 Talence, France

2Centre Technique des Industries Mécaniques (CETIM), Senlis, France,

19. ENVIRONMENT I

IN VITRO SHORT-TIME TESTING METHOD FOR EVALUATING THE LONG-TIME CORROSION

FATIGUE STRENGTH OF BIOMEDICAL MAGNESIUM ALLOYS

N. Wegner1*, K. Donnerbauer1, L. Hempel1 & F. Walther1

Research on biodegradable metals for surgical disciplines has been increasing for decades, with magnesium (Mg) alloys considered promising candidates. The corrosion properties, being inadequate for technical applications, prove to be an advantage as the implant corrodes in the presence of aqueous body fluids, supporting the body functions for a defined time (functional phase) and then degrading completely, eliminating the need for a second surgery to remove the implant [1]. While numerous alloy systems, additional process steps, and surface modifications to control the corrosion properties are currently investigated, the number of approved Mg-based products is severely limited. However, this is due to the inadequate interaction of the corrosion rate with excessive hydrogen gas evolution, the corrosion morphology, and the corrosion fatigue strength [2]. In vitro investigations for characterising these three factors for a corresponding functional phase of several weeks are time-consuming and costintensive. To address this issue, an electrochemical in vitro short-time testing method is developed to accelerate the corrosion process. The method is based on the already known relationship between galvanostatic anodic polarisation, accompanied by an increase in hydrogen evolution rate with increasing current densities, which in turn allows the corrosion rate to be determined and the mass loss.

Three-week immersion tests with the detection of the hydrogen gas generated during corrosion were carried out on the established Mg alloys WE43 (yttrium, rare earth) [3] and ZX10 (zinc, calcium). The data are used to calculate the time-dependent corrosion rates and serve as a starting point for the study. In addition, an experimentally determined relationship between the anodic current density and the corrosion rate (calculated via hydrogen evolution rate) is used [4]. The aim is to reproduce the corrosion process within three days by applying anodic polarisation. For this purpose,

the hydrogen evolution under anodic polarisation with varying current densities is investigated in the first step. The resulting corrosion morphology is evaluated using μCT, the remaining fatigue strength is estimated through instrumented load increase tests, and each are compared with the immersion tests without polarisation. To evaluate the influence of a superimposed fatigue loading, corrosion fatigue tests with and without polarisation are carried out for selected test periods allowing the validity of the in vitro short-time testing method to be assessed.

The methodology allows a simulation of the hydrogen evolution rates and, thus, the time-dependent corrosion rates with deviations of less than 15%. Whereas the corrosion fatigue strengths between the tests with and without polarisation differ significantly, resulting from increased pitting, especially for the rare earth alloying elements. Thus, the method has to be considered as a worst-case estimation, excluding unsuitable Mg-based biomaterials before further preclinical studies.

References

[1] Chen, Y.; Xu, Z.; Smith, C.; Sankar, J.: Recent advances on the development of magnesium alloys for biodegradable implants. Acta Biomaterialia 10 (2014) 4561-4573.

[2] Raman, R.K.S.; Jafari, S.; Harandi, S.E.: Corrosion fatigue fracture of magnesium alloys in bioimplant applications: A review. Engineering Fracture Mechanics 137 (2015) 97-108.

[3] Hartjen, P.; Wegner, N.; Ahmadi, P.; Matthies, L.; Nada, O.; Fuest, S.; Yan, M.; Knipfer, C.; Gosau, M.; Walther, F.; Smeets, R.: Toward tailoring the degradation rate of magnesium-based biomaterials for various medical applications: Assessing corrosion, cytocompatibility and immunological effects. International Journal of Molecular Sciences 22(2) (2021) 971.

[4] Wegner, N.; Walther, F.: Assessment of galvanostatic anodic polarization to accelerate the corrosion of the bioresorbable magnesium alloy WE43. Applied Sciences 11 (2021) 2128.

1Chair of Materials Test Engineering (WPT), TU Dortmund University, D-44227 Dortmund, Germany

*Corresponding author: nils.wegner@tu-dortmund.de

EFFECT OF ARTIFICIAL CORROSION ON RETARDATION OF FATIGUE CRACK GROWTH

– ASSESSMENT BY LOCAL CYCLIC PLASTICITY

H. Shibata1, K. Satoh1, R. Fincato2 & S. Tsutsumi2

In recent years, several numerical research projects have focused on fatigue crack closure. This study presents numerical investigations concerning the retardation of fatigue crack growth induced by artificial corrosion products on crack surfaces. To conduct these analyses, the authors employed an unconventional elasto-plasticity material model they developed. Consequently, the evaluation of fatigue crack growth life was predicated on the cyclic elasto-plastic response at the crack tip. The simulation of the volume expansion caused by corrosion was accomplished by applying heat input to the crack surface elements. The results indicate the occurrence of fatigue crack closure, leading to a subsequent reduction in stress and strain ranges at the crack tip. Furthermore, the obtained a-N results exhibit good accuracy, not only in predicting significant crack extension but also in modelling the subsequent recovery behaviour, aligning closely with experimental findings.

1Sumitomo Heavy Industries, Ltd., Japan

2Department of Civil Engineering, Osaka University, Japan

EXPERIMENTAL VALIDATION OF A MODEL FOR PREDICTING THE BENDING FATIGUE

STRENGTH OF CORRODED GREY CAST IRON WATER PIPES

E. John1, J. Boxall1, R. Collins1, E. Bowman1 & L. Susmel1

Leakage of drinking water caused by mechanical failures of old, buried, Grey Cast Iron (GCI) water pipes is a serious issue for water utilities in the UK and around the world. To enable better-informed pipe health assessments to be made, this work aimed to experimentally validate a method that could be used to assess the damaging effect of corrosion pitting on GCI pipes subject to bending fatigue loading. Fatigue testing of GCI pipes revealed pitting had a small detrimental effect on the pipes’ bending fatigue strength, characterised by Kt = 1.38 for the sharp pit specimens. An effective volume approach coupled with the SWT multiaxial fatigue criterion was found to provide reasonable fatigue life predictions, at the expense of requiring the 3D geometry of the pit to be known. Making predictions simply using the net stresses provided conservative predictions, but only required the pit’s depth.

1Department of Civil and Structural Engineering, The University of Sheffield, Sheffield, UK

20. SIMULATION

PREDICTIONS OF CRACK GROWTH RATES,

R-RATIO EFFECTS AND OVERLOAD BEHAVIOUR

BASED ON SMOOTH SPECIMEN LCF TEST DATA AND USING A STRIP YIELD-TYPE MODEL

S. J. Williams1, M. T. Whittaker1 & M. C. Hardy2

Plastic 2D plane stress analyses have been run on a finite element (FE) model containing a sharp semi-circular notch representing an edge crack. Stress-distance profiles ahead of the crack tip (notch root) were extracted at the maximum and minimum points of a range of fatigue cycles with different loading amplitudes. These were used with data from smooth specimen Low Cycle Fatigue (LCF) tests to predict the build-up of fatigue damage at regularly-spaced locations ahead of the crack tip as it moves towards them. Knowledge of the number of fatigue cycles required to fail the material at successive calculation locations then allows crack growth rates to be calculated at the corresponding crack lengths. FE analyses were performed for a wide range of Kmax values at loading R-ratios of 0, -1 and 0.5, and the growth rate predictions were compared with test data. The method was then extended to predict how the crack growth rates recover after a change in the applied load. The material studied was the nickelbased superalloy fine grain (FG) RR1000 at 20°C.

1Institute of Structural Materials, Swansea University, Fabian Way, Swansea SA1 8EN, United Kingdom

2Rolls-Royce plc, PO Box 31, Moor Lane, Derby DE22 8BJ, United Kingdom

AN INVESTIGATION OF THE RSE-M CRACK

CLOSURE PARAMETER F(R) ON A LARGE FERRITIC PWR COMPONENT WITH NEGATIVE R-RATIO INCLUDING WELDING RESIDUAL

STRESS

M. P. Nielsen1

Operation of a civil nuclear PWR facility results in a complex variable loading sequence arising from combined mechanical and thermal loadings, which must be evaluated in conjunction with welding residual stresses. This presents a challenge for FCG assessments at the design stage, with no load history, in support of a safety case for components where gross failure must be shown to be incredible within the design life. Assessment methods for FCG are generally contained within in-service inspection codes e.g. RSE-M, ASME XI. The codified methods were not developed for use at the design stage and can be overly conservative as a result. This study considers the treatment of crack closure in the RSE-M code in the case of a low alloy steel component. The aim is to understand the reasonableness of the approach and if this assessment parameter is a potential source of significant conservatism. The primary focus is the treatment of the startup/shutdown transients, with a negative R-ratio modified via the inclusion of welding residual stress. The study has been carried out using elasticplastic cracked-body finite element models with a constant defect size i.e., propagation is not explicitly modelled. Crack growth is inferred by examination of behaviour ahead of the crack-tip and CTOD to determine an effective load range on an un-cracked elastic model to subsequently derive an effective ΔK.

1EASL (A Division of Kinectrics) on behalf of EdF Energy UK, Gloucester, GL3 4AE

FATIGUE CRACK GROWTH AND CRACK

CLOSURE IN 304L LARGE COMPACT TENSION SPECIMENS WITH CYCLIC CRACK TIP PLASTICITY

M. M. J. Gillet1* & C. M. Davies1

Nuclear reactors in the UK such as Sizewell B are in need of life extensions. The primary cooling circuits of such reactors are often made of 304L stainless steel, and the fatigue of these components is a limiting factor on lifetime. It is necessary to understand the fatigue crack growth of 304L in plant conditions to safely assess life extensions. The models that are currently used rely on the empirical Paris Law and stress intensity factor range ΔK which requires small scale yielding. However, the components in plant conditions tend to be geometrically large and to undergo high stresses in thermal fatigue. Hence the crack tip constraint and applied ΔK will be relatively high, which implies significant crack tip plasticity. As there is no universal way of interpreting crack growth rate in these conditions, further investigation was warranted.

The Paris-type relationship used to describe the crack growth rate of 304L in valid small scale yielding conditions (ASTM E647 Standard), appears to be applicable in the high ΔK regime with significant plasticity. This is the case in specimen geometries and loads that do not adhere to the standard requirements. It is suspected that a possible explanation to this could be found by investigating the cyclic hardening at the crack tip during crack growth, and the proximity to elastic shakedown of the material ahead of the crack tip.

In this work, cyclic plasticity at the crack tip was investigated both experimentally and in simulation. Initial experiments were performed to measure the monotonic and cyclic mechanical properties of the material. Large Compact Tension specimens (LC(T)) were used to measure crack growth rates that are more representative of plant conditions. Digital image correlation was used to monitor macro-strain at the crack tip, to observe the

cyclic plastic zone, and to monitor its proximity to elastic shakedown. The experimental data was input to simulations to offer insight past the surface of the specimen.

FIGURE 1. Mises stress contour at the crack tip in a half-Large Compact Tension Specimen (LC(T) 187.5 × 90 × 25 mm) showing the reverse yielded cyclic plastic zone from crack closure in a ductile stainless steel. The size of the reverse-yielded plastic zone (≈ 4 mm) is highlighted relative to crack length.

REFERENCES

(1) H. Gao, Z. Lin, X. Huang, H. Shang, J. Zhan. In Situ Measurement of Cyclic Plastic Zone and Internal Strain Response of Q&P Steel near Fatigue Crack Tip Region Based on Micro-DIC Materials 2022; 15, 6114.

(2) Q. Wang, R. Bao, B. Liu, S. Lu, H. Peng, B. Chen. Comparison of fatigue crack growth behaviour in electron-beam and laser powder-bed-fusion Inconel 718. Materials Science and Engineering: A, 2024. 0921-5093

1Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ. UK.

*Corresponding author: m.gillet22@imperial.ac.uk

NUMERICAL APPROACHES IN THE FATIGUE DAMAGE SIMULATION IN QUASI-BRITTLE MATERIALS

L.

Ferreira Friedrich1, A. Bordin Colpo2, S. Vantadori3, F. Soares2 & I.

Iturrioz

2*

Simulating fatigue damage processes has been a challenging task for researchers in various engineering fields. Continuum Damage Mechanics (CDM) has been extensively used with success in ductile materials, taking into account their plasticity. However, quasi-brittle materials exhibit characteristic phenomena which are difficult to simulate using CDM. An alternative approach is to use Discrete Element Methods (DEM), which involves building a spatial discretisation using nodes with masses and mechanical interaction functions represented by elements such as bars or beams. The mechanical behaviour of the solid up to the point of collapse can be represented using simple constitutive laws associated with these bonds. This work explores the possibilities of representing the evolution of damage using models based on DEM in the context of fatigue. Two examples are presented to demonstrate the capabilities of these approaches in representing the main features of fatigue methodologies.

1Federal University of Pampa - Campus Alegrete, RS, Brazil.

2PROMEC, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil.

3Universita degli Studi di Parma, Italia

*Corresponding author:ignacio@mecanica.ufrgs.br

PROPOSAL OF A FATIGUE CRACK EXTENSION

MODE AND ITS PREDICTION METHOD

— DAMAGE ACCUMULATION MODE FATIGUE CRACK PROPAGATION

S. Hamada1*, Y. Okawa1 & Y. Araki1

A novel fatigue crack extension mode, not deformation mode, and methods for predicting fatigue properties in high-strength steels are proposed as the reason why high-strength steels exhibit different fatigue properties from those of conventional steels. An example of a different fatigue property is that the threshold stress intensity factor range of a long crack in highstrength steel is still not as high as expected from the hardness. At present, there is no clear explanation for this reason. Therefore, the material cannot be used with confidence. The authors propose that this is due to a different crack extension mechanism. In other words, the authors propose the existence of a mechanism of fatigue crack extension other than the generally accepted mechanism of fatigue crack extension. Fatigue crack is generally considered to grow due to plastic deformation by alternating slip. Based on the proposed novel mechanism, the mode of fatigue crack extension is called damage accumulation mode fatigue crack propagation. This name differs from the conventional name. The names focus on the loading mode, i.e., Modes I, II, and III. The proposed name focuses on the extension mechanism. The presentation reviews examples of damage accumulation mode fatigue crack propagation in various high-strength steels and presents a method for predicting the propagation behaviour.

1Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka-shi, Fukuoka 819-0395, Japan

*Corresponding author: hamada@mech.kyushu-u.ac.jp

21. ADDITIVE MANUFACTURING II

THE TRANSITION OF GRAIN BOUNDARY IN AN ADDITIVELY MANUFACTURED ALUMINIUM

ALLOY UNDER VERY-HIGH-CYCLE FATIGUE

X.

Pan1 & Y. Hong1*

Additive manufacturing (AM), also known as 3D printing, is an innovative and promising technique that can easily prepare parts and structures with complex configurations. For metals and alloys, selected laser melting (SLM) or called laser powder bed fusion (L-PBF) is one of the most popular AM technologies. In this paper, we designed and additively manufactured (AMed) an aluminium alloy (AlSi10Mg) via SLM process to investigate their unique microstructures before and after fatigue loading by using electron backscatter diffraction (EBSD), focused ion beam (FIB), transmission Kikuchi diffraction (TKD), scanning and transmission electron microscopy (SEM and TEM).

High-cycle and very-high-cycle fatigue (HCF and VHCF, below and beyond 107 loading cycles) tests were conducted via ultrasonic axial cycling (20 kHz) superimposed by an amount of tensile load in the range of 105 ~ 2 × 109 cycles under stress ratios R from –1 to 0.86. The S-N (stress amplitude – number of failure cycles Nf) data show duplex shape at negative stress ratios, and in the second slope, a fine granular area (FGA) in SEM or an optical dark area (ODA) in light microscopy appears at Nf > 4 × 108 cycles encircling the AMed pores on the fracture surface as the characteristic region of crack initiation and early growth.

The original AMed alloy exhibits hierarchic microstructures of melt pool, Al solid solution and Si distribution. The boundary of melt pool is composed of fine equiaxed Al grains, while the interior of melt pool consists of many coarse columnar or lamellar crystals oriented to the scanning track. The morphologies of Si distributed in Al matrix are from solute atoms at 10-10 m, nano particles at 10-9 m, other precipitates at 10-9 ~ 10-7 m to interconnected networks. The Si networks divide Al matrix into many cells that are of finer

sizes in the interior of melt pool than those in the boundary region. These Al cells make up the grains of Al solid solution whose grain boundaries are with interfacial Si walls, named as GB-0. For VHCF failed specimens, the profile microstructure of FGA is determined as a surface layer of nanograins and refined grains with thickness about 2~3 μm top on the survival AMed microstructure. The FGA morphology and its microstructure are the products of surface nano crystallisation during numerous cyclic pressing (NCP). Here, we first reported that: in the surface layer of FGA, the Si networks, nanoparticles and other precipitates are broken, dissolved, and rearranged; the GB-0 with interfacial Si walls is annihilated; and the coarse grains of Al solid solution are refined and formed to nanograins separated by a new type of grain boundary without Si-rich interface, i.e. GB-1.

1LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China

*Corresponding author: hongys@imech.ac.cn

ROLE OF COLUMNAR β GRAINS ON FATIGUE

CRACK GROWTH BEHAVIOUR IN ADDITIVE

MANUFACTURED TITANIUM ALLOY Ti64V

A. Khadar Syed1*, A. E. Davis2 & X. Zhang1

Additive manufacturing (AM) of titanium alloy Ti6Al4V is rapidly maturing to produce load bearing parts for aerospace applications where design for durability and damage tolerance is paramount. AM built Ti6Al4V is characterised by epitaxially grown columnar β grains aligned along the material build direction. Depending on the AM process, the average columnar grain width varies between 50-100 microns (powder bed processes) [1, 2] and 200-500 (wire-arc process) [3] and the length varies from mm to cm scale [1, 2, 3]. These columnar grains consist of strong crystallographic texture clustering of small α colonies and basketweave microstructure along the grain boundary. Consequently, considerable anisotropy in fatigue property was observed in Ti6Al4V built by major AM processes i.e., Laser Powder Bed Fusion (L-PBF), Electron Beam Powder Bed Fusion (EB-PBF) and Wire and Arc Additive Manufacturing (WAAM) [4]. For damage tolerance design, fatigue crack growth rate is a key property which is directly linked to material’s microstructure and texture. Therefore, it is important to understand the influence of columnar grain width and associated texture on fatigue crack growth (FCG) behaviour of AM built Ti6Al4V.

Compact tension (CT) samples were produced by L-PBF, EB-PBF and WAAM providing samples with columnar grain width ranging between 50 and 500 microns. All samples are post process by β annealing which is a standard heat treatment process practiced by aerospace industries. The β annealing results in similar transformation microstructure consisting of fully transformed α+β colonies in all the samples across three AM processes. It has also eliminated process induced residual stresses, if any present. A detailed microstructure and texture analysis has revealed that the size and texture of colonies is influenced by the orientation and width of the columnar β grains. Samples were tested with crack propagation either

across or along the columnar β grains. The crack length was measured visually, and the fatigue crack growth rate was obtained in the threshold region and the stable crack growth stage. The influence of columnar grain width, α+β colony size and associated texture on the crack growth rate was clearly evident where microscopic torturous crack path and crack path deviation was observed. Test results will be further analysed in the light of detailed microstructure and crack path analysis using high resolution images from optical and scanning electron microscopes to elucidate the effect of columnar grain width on the crack growth behavior and the interaction between the crack front and microstructure.

References

[1] AK Syed et. al., Materials Science and Engineering: A (2019) 755, 246257.

[2] H Sharma et. al., Materials Science and Engineering: A (2019) 744, 182-194.

[3] AK Syed et. al., Materials Science and Engineering: A (2021) 814, 141194.

[4] T DebRoy et.al., Progress in Materials Science (2018) 92, 112-224.

1Centre for Manufacturing and Materials, Coventry University, CV1 5FB, Coventry, United Kingdom

2Department of Materials, University of Manchester, M13 9PL, Manchester, United Kingdom

*Corresponding author: abdul.syed@coventry.ac.uk

USING FATIGUE CRACK GROWTH TESTS FOR QUALITY ASSESSMENT IN ADDITIVE MANUFACTURE

P. B. S. Bailey1

Additive manufacturing is now a highly commercial group of process technologies (for both metal and polymer based materials) and there is a clear industrial movement to adopt it for complex and high performance components. Increasing ease of achieving comparable quasi-static mechanical properties with conventional manufacture has led to a perceived level of maturity, but there is now also a good awareness of just how critical processing parameters are to resulting properties. Fatigue, crack growth, and crack extension characteristics are well known to be much more probing of multiple aspects of material quality than quasistatic property measurements, so these types of test could offer effective quality metrics, even if the specific material performance metrics are not deemed relevant by the end user.

This paper presents a short case study of applying conventional fatigue crack growth tests to additively manufactured material, with a view to assessing relative homogeneity within individual builds. Standard specimens were tested under a constant stress intensity range, to evaluate Mode I crack growth characteristics in the build direction and allow comparison between results from “good” processing and those for deliberately non-optimised builds.

1Instron Dynamic Systems, Coronation Road, High Wycombe, UK

INVESTIGATION ON THE FATIGUE BEHAVIOUR OF STAINLESS STEEL 316L PRODUCED BY LASER POWDER BED FUSION PROCESS

M. Shahriarifar1*, M. Doré1, M. Dodge1, K. Khan2 & X. Zhang2

Additive manufacturing (AM) is an emerging technology that has recently gained large interest due to its potential to produce customised components with complex geometries. The laser powder bed fusion (L-PBF) process is one of the most widely employed AM processes for fabricating 3D metallic parts where the powder bed is melted selectively by a high energy density fibre laser, which enables material-efficient production of components with complex geometries. However, L-PBF components generally suffer from the presence of process-induced imperfection, such as porosity and lack-offusion. These imperfections can act as stress raisers and lead to the initiation of cracks under fatigue loading. Therefore, it is crucial to investigate the fatigue behaviour of L-PBF materials, and if possible, employ suitable solutions, for example post-processing, to improve material behaviour. The effect of defects, anisotropy, and post-processing on fatigue strength and cracking mechanism requires further insight to provide an understanding of the structural integrity performance of the material under cyclic loading. This study investigated the effect of build orientation and post-processing on the fatigue behaviour of stainless steel 316L produced by L-PBF process. Hot isostatic pressing (HIP) was conducted on L-PBF samples that were built in vertical and horizontal orientations, and comparisons were made with the as-built condition in terms of microstructure, defect distribution, hardness, tensile, and fatigue strength properties. Correlations were made between microstructure, defect, and build orientation with static and fatigue properties. HIP was found to improve static and fatigue properties. The as-built samples had large porosity and lack-of-fusion defects resulting in defect-driven crack initiation, which decreased the fatigue life. HIP resulted in shrinking the defects and increasing the fatigue strength. In addition, the horizontally built samples were found to have higher strength compared to the vertically built samples, which was correlated to the defect alignment with respect to the loading direction.

1TWI Ltd, Granta Park, Great Abington, Cambridge, United Kingdom, CB21 6AL

2Faculty of Engineering, Environment and Computing, Coventry University, Priory Street, Coventry, United Kingdom, CV1 5FB

*Corresponding author: m.shahriarifar@twi.co.uk

22. ENVIRONMENT II

DEFECT-BASED ASSESSMENT OF MECHANICAL AND CORROSIVE LOADS ON THE CAPABILITY OF LIGHT METAL STRUCTURES

N. Wegner,1* A. Koch1 & F. Walther1

Light metals are widely used in various applications due to their excellent properties. For instance, aluminium alloys are commonly used in lightweight industries such as automotive and aerospace due to their high specific strength. Solid-state recycling of aluminium chips has emerged as a promising alternative to energy-intensive re-melting. In this process, aluminium chips are pre-compacted and then further processed into profiles using hot extrusion [1]. The quality of the resulting profiles depends on the bonding quality between the individual chips, which is achieved through microstructural welding. Insufficient welding can result in inner defects such as delaminations. Biodegradable implants, e.g., made of magnesium, are designed for temporary support of the human body, and take advantage of the inherent biodegradability of these materials in aqueous environments. However, the low corrosion resistance of these materials, which may be disadvantageous in technical applications, must be precisely understood in terms of long-time degradation behaviour, degradation morphology, the effect of corrosion pits as surface defects, and the associated reduction in mechanical stability [2]. In the case of light metal structures, such as detachable joints, the presence of defects can significantly impact their performance due to complex geometries that result in stress concentrations. Axial thread forming is a newly developed high-performance process that has gained interest from various producers due to its combined drilling and thread forming capabilities, leading to reduced process times, and increased technological potential [3]. In addition to stress concentration, the thermal influence resulting from application-specific conditions must be considered in the assessment of these structures.

To responsibly design components for applications involving light metal structures, it is essential to reliably assess their capability under mechanical,

thermal, and corrosive loading conditions. Novel testing methods and advanced modelling strategies have been employed and validated for various light metal structures. Fracture mechanics approaches aided by measurement techniques have been developed to determine the influence of microstructure and defect structure. To characterise the long-time corrosion effects, a new short-time testing method based on galvanostatic polarisation has been devised. Simulation approaches have been utilised to extrapolate the findings to complex components with and without thermal loading. By employing a combination of testing strategies, innovative measurement techniques, modelling and simulation approaches, a comprehensive characterisation of light metal structures subjected to complex mechanical, thermal, and corrosive loading conditions has been achieved. Effective damage mechanisms have been identified and separated, leading to reproducible and reliable component design that considers process- and application-induced defects in these structures.

References

[1] Koch, A.; Bonhage, M.; Teschke, M.; Luecker, L.; Behrens, B.A.; Walther, F.: Electrical resistance-based fatigue assessment and capability prediction of extrudates from recycled field-assisted sintered EN AW-6082 aluminium chips. Materials Characterization 169 (2020) 110644.

[2] Clausius, B.; Wegner, N.; Jeyavalan, S.; Hartweg, H.; Walther, F.; Maier, P.: Influence of corrosion extent on residual tensile strength and corrosion fatigue properties of an Mg-Y-Nd alloy characterized by μCT. Magnesium Technology - The Minerals, Metals & Materials Series (2023) 95-98.

[3] Sarafraz, Y.; Koch, A.; Felinks, N.; Biermann, D.; Walther, F.: Influence of pre-drilling on hardness and tensile failure of formed internal threads in thin-walled AZ91 cast alloys. Engineering Failure Analysis 130 (2021) 105783.

1Chair of Materials Test Engineering (WPT), TU Dortmund University, D-44227 Dortmund, Germany

*Corresponding author: nils.wegner@tu-dortmund.de

EFFECTS

OF

PITTING

CORROSION ON FATIGUE PERFORMANCE OF LEGACY CAST IRON PIPE MATERIALS

L. Ronayne1, J. A. Wharton2 & P.A.S. Reed1

Grey cast irons were the preferred material for water pipe networks worldwide for over a century, due to their low-cost nature and ease of manufacture. Since the advent of ductile iron and PVC pipes, the installation of cast iron water pipes has largely come to a stop. This has led of a lack of research on these materials using modern techniques, and with an increasing amount of the pipe network reaching the end of its lifetime and beginning to fail, it is necessary to understand the fatigue behaviour of these materials and the influence of aggressive soil environments on their performance. Previous work has established the ‘leak before burst’ concept, however, how these leaks occur and the key factors aggravating the formation of a pinhole leak has yet to be thoroughly investigated. The focus of this work has been to characterise the microstructure of grey cast iron materials representative of what is typically used in the water network, and to investigate the effect of this microstructure on the fatigue and corrosion performance of the materials. In addition to this, the aggressive soil conditions have been characterised into key parameters that govern the corrosion reaction on the surface of the material; from this, a study of pit geometries in varying soil conditions was conducted, and the effect of the interplay between the three distinct phases of the material on the nucleation and morphology of corrosion pits.

Fatigue tests were carried out to study the initiation and propagation of fatigue cracks through grey cast iron specimens. These tests were conducted on both polished specimens, to establish a baseline performance, as well as corroded specimens that have been subjected to a corrosive environment to force the nucleation of corrosion pits on the specimen surface. The effect of the surface corrosion pits on the initiation of fatigue cracks was determined, as well as the mechanisms that drive the propagation of cracks through the microstructure. Furthermore, the fatigue performance of grey cast iron samples while undergoing an active corrosion process was explored, and

the effect the active process has on the crack morphology.

1Engineering Materials Group, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

2nCATS, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

INVESTIGATING THE ROLE OF LOW TEMPERATURE HOT CORROSION ON CRACK

INITIATION AND PROPAGATION IN SINGLECRYSTAL NICKEL ALLOYS UNDER FATIGUE CONDITIONS

M. Elsherkisi1*, L. Brooking1, J. Mason-Flucke2 & S. Gray3

Single-crystal nickel superalloys are often used for components exposed to high-temperature environments, such as turbine blades, due to their high-temperature creep and thermal fatigue resistance. However, environmental factors such as the presence of corrosive contaminants, gaseous environments, and humidity, all have an effect on reducing the lifespan of such components. Microstructural effects also play a role, with a recent drive to develop alloys with higher gamma prime volume fractions to combat continuously increasing operational temperatures, in turn makes materials more susceptible to low-temperature corrosion mechanisms, such as sub-Type II hot corrosion (450 - 650°C).

This presentation will outline modelling and predictive lifing techniques developed to better understand the effect of hot corrosion mechanisms on the three stages of fatigue crack growth (crack initiation, linear timedependent propagation, and final fracture). Emphasis is placed on how experimental data can be used to validate and calibrate both predictive and finite element models, before using findings to characterise any correlation between fatigue crack growth and hot corrosion mechanisms. Finally, the presentation will highlight how such techniques can be used with realtime data, to make more informed decisions on the lifing of in-service components.

1Frazer-Nash Consultancy, Bristol, UK

2Rolls-Royce Plc, Bristol, UK

3School of Aerospace, Transport, and Manufacturing. Cranfield University, Bedfordshire, UK

23. KEYNOTE

CHARACTERISING FATIGUE CRACK TIP

DEFORMATION STATES IN NICKEL BASE

SUPERALLOYS: SLIP CHARACTER, STRAIN ACCUMULATION AND OXIDATION EFFECTS

P.

A. S. Reed1

More and more techniques exist which now allow us to characterise the crack path and crack tip geometry during fatigue in great detail. 3D evaluations via X-ray CT techniques can be linked to full field surface evaluations such as SEM DIC and EBSD to understand the development of fatigue, from initiation, through the early stages of crack growth and finally into “stable” long crack growth. The crack path and crack tip geometry are strongly linked to the locally developing stress and strain states at the crack tip which control the evolution of the fatigue process. Combining these techniques and comparing the information that is revealed gives us a much clearer insight into how deformation processes and strain accumulation interact with other processes (e.g. oxidation) and allows better prediction of fatigue behaviour (over a range of temperatures) in these materials in both turbine disc and blade applications, allowing a more focussed alloy development pathway for improved service performance.

1Engineering Materials Research Group, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

24. SUPERALLOYS II

FATIGUE CRACK PROPAGATION BEHAVIOUR OF THE GRAIN SIZE TRANSITION ZONE IN A DUAL

MICROSTRUCTURE TURBINE DISC

Y. C. Wang, R. Jiang*, L. C. Zhang & Y. D. Song

For dual microstructure powder metallurgy (PM) Ni based superalloy turbine discs, fatigue crack propagation (FCP) behaviour in the grain size transition zone with gradient structure (GS) between the disc rim (with coarse grained (CG) structure) and bore (with fine grained (FG) structure has a direct impact on the reliability and durability of the turbine disc for engineering applications. In this study, constant load amplitude and constant ΔK FCP tests havebeen carried out to investigate the FCP behaviour of grain size transition zone in a trial dual microstructure turbine disc followed by detailed microscopic characterisation of fracture surfaces and crack paths. The results show that the FCP rate of GS structure at 650C is somewhere between the CG and FG structure, but is closer to that of the FG structure at 750C . The FCP tests under constant ΔK show grain size exerts more significant influence in the time dependent FCP regime, but the effects of grain size is relatively limited in the cycle dependent FCP regime. Larger local plastic deformation zone indicated by the high KAM value is found in the FG region in the GS specimen at the crack tip with the same Δ K level. Introduction of dwell time at the peak load can promote the development of the local plastic deformation. This local plastic deformation is believed to be the reason that causes more significant grain boundary oxidation in the FG region along with the contribution from more grain boundaries acting as short circuit diffusion paths of oxide-forming elements, resulting in accelerated FCP.

1College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China

*Corresponding author: rjiang@nuaa.edu.cn

EFFECTS OF MICROSTRUCTURE AND OXIDATION ON FATIGUE CRACK INITIATION BEHAVIOUR IN A TITANIUM ALUMINIDE ALLOY

Y. Yamazaki1, K. Okada2 & K. Yoshida2

Titanium aluminide alloys have attracted attention because of their excellent specific strength. The mechanical properties, such as fatigue strength, are sensitive to their microstructure in titanium aluminide alloys. In addition, their fatigue strength is affected by oxidation; in most cases, it degrades. This study conducted small punch fatigue (SPF) tests to investigate the effects of microstructure and oxidising atmosphere on fatigue crack initiation behaviour in a forged titanium aluminide alloy. First, the fatigue lives obtained by the SPF test were compared with the conventional uniaxial test data by means of Ni-base alloy IN718 alloy. As a result, it was confirmed that the SPF test can be applied to the fatigue test. The experimental results revealed that the microstructure significantly affected the fatigue crack initiation behaviour, and the fatigue life was shorter when fatigue cracks were initiated at the lamellar phase. The thermal exposure at elevated temperatures reduced the fatigue life considerably. Such life reduction by oxidation was due to cracking the brittle oxide layer formed on the alloy surface. The fatigue strength was unaffected by the differences in thickness and kinds of oxide films formed on the specimen surface.

1Graduate School of Engineering, Chiba University, 1-33, Yayoicho, Inage-ku, Chiba-shi, Chiba, 263-8522 Japan, Y.yamazaki@chiba-u.jp, 2Graduate School of Science and Engineering, Chiba University, 1-33, Yayoicho, Inage-ku, Chiba-shi, Chiba, 263-8522 Japan

STUDY ON FATIGUE CRACK PROPAGATION

MECHANISM AND MODEL OF A POWDER

METALLURGY SUPERALLOY UNDER GASMARINE ENVIRONMENT

L. C. Zhang1, R. Jiang1, J. T. Liu2, Y. W. Zhang2 & Y.D. Song1

Environmental degradation of the hot end components of aeroengines in marine environment is more serious compared with that in continental environment. In this study, the fatigue crack growth test under the gasmarine environment has been realised through a self-built fatigue test system. The fatigue crack growth tests of an advanced powder metallurgy Ni-based superalloy which is widely used for turbine disc were carried out under cyclic trapezoidal loading waveforms at elevated temperatures (i.e. 650℃, 700℃ and 750℃) in marine environment. The corrosion fatigue crack growth mechanism of this disc alloy under the gas-marine environment was analysed by nanoindentation, EBSD, TEM and EDX.

The results show that the hot corrosion caused by the high temperature and marine environment accelerates the fatigue crack growth rate by 2-4 times. The coupling effect of the strain field and the chemical field at the crack tip causes the oxidation/sulphidation of the plastic zone at the crack tip, which is intensified with the increase of temperature and dwell time. This stressassisted oxidation/sulfidation damage lowers the fatigue crack growth resistance of the investigated alloy. As the number of defects (e.g. pores) of sulfide is higher than that of oxide, the presence of sulfide in the stress field often leads to the rapid destruction of the alloy matrix. Combined with the experimental data and corrosion fatigue crack propagation mechanism, a modified corrosion fatigue crack growth model is established by considering the hot corrosion influence, which improves the prediction accuracy of fatigue crack growth in the gas-marine environment. The established model is expected to provide a theoretical tool for the environmental adaptability assessment and damage tolerance design of the turbine disc as well as aeroengines.

1College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China; 2Central Iron and Steel Research Institute, Beijing 100081, P.R. China

*Corresponding author: rjiang@nuaa.edu.cn

25. LIFING

INTEGRATION OF PHYSICAL AND VIRTUAL TESTS FOR ACHIEVING HIGH CONFIDENCE IN FATIGUE RELIABILITY OF AUTOMOTIVE BATTERY SYSTEMS

A. Halfpenny1, K. Tahera2, B. Thumati3 & C. Wynn-Jones1

In a concerted effort to minimise humanity’s adverse impact on our environment, the automotive industry is keen to develop new and innovative solutions for a carbon-neutral future. They therefore face a critical requirement to offer extended warranties on new and relatively unfamiliar technologies such as advanced battery systems. This paper considers how the existing simulation, verification, and validation design process, may be enhanced to offer significant improvements in predicted confidence. Particular attention is paid to simulating the physical fatigue qualification test using a process called ‘virtual testing’. This allows simulation to be better verified using evidence from fewer physical tests. The paper highlights the need for additional low-cost measurements during testing and a need to test to failure. It considers how virtual and physical tests may be integrated into a typical automotive design management process. It demonstrates how these tests mutually benefit one another.

1Hottinger Bruel & Kjaer UK Ltd.

2The Open University Business School.

3Hottinger Bruel & Kjaer USA

MECHANISTICALLY BASED FATIGUE LIFETIME

PREDICTIVE MODEL

FOR LEGACY STEAM TURBINE BLADES

A. Masis Khodavirdi1*, A. Hamilton1 & P. A. S. Reed1*

The transition to renewable energy sources has made the energy output demand from traditional power plants more inhomogeneous. As a consequence, the steam turbine blades in traditional power plants are reaching the end of fatigue life quicker than that for which they were originally designed. The refurbishing of the blades as an alternative to substituting/ replacing them has been evaluated as a solution to extend their fatigue lifetime. The process of grinding out the existing cracks and shot peening the surface as a maintenance process and its effectiveness has been studied. The challenge of creating a prediction model for the refurbished blades’ lifetime lies in the variation of mechanical properties between blades and how this interplays with the mechanisms of crack initiation and growth in the re-polished and shot peened layers. Hence, a mechanistic understanding needs to be developed to account for mechanical property variations, how this affects the evolving notch strain fields under fatigue, and the actual mechanisms of crack initiation and growth. Low cycle fatigue testing of shot peened notched samples extracted from legacy FV520B martensitic stainless steel blade materials has been conducted. Detailed microstructural analysis was performed on to understand the influence of the underlying microstructure and its response to peening stress states under fatigue loading in a notch field. Additionally, tensile and hardness testing was performed to assess the variability between blades’ mechanical properties to allow the use of in-service hardness testing to estimate mechanical properties to use in a predictive lifetime model. Finally, a mechanistic model is proposed to predict the lifetime of refurbished blades by measuring the individual blade hardness and accounting for the peening process.

1Engineering Materials, Engineering and Physical Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

*Corresponding authors: amk1g15@soton.ac.uk & p.a.reed@soton.ac.uk

FREQUENCY DOMAIN FATIGUE APPROACH FOR SINE SWEPT LOADINGS

G. De Morais1

Many automotive manufacturers do not have accurate fatigue loading data for the mechanical components they build. In such cases the solution is to design in compliance with particular guidelines or rely on simplified tests that are able to cover the worst case scenarios. The Sine Sweep Vibration Test is one of those simplified tests that can be used to obtain relevant modal parameters and/or evaluate structural integrity. The design of reliable sine sweep tests depends on the accuracy of the finite element analysis and the fatigue approach used in the design process. The time domain approach is the most commonly used for fatigue analysis (partially due to its simplicity) but it is computationally expensive. This paper brings the frequency domain approach as the most viable alternative to evaluating a sine sweep fatigue analysis from finite element results. It will be shown that sweep type, duration and damping are the most important parameters to be observed in order to keep the error (difference between time and frequency domain) under 10%. It was found that the error decreases the larger the damping and sweep duration. 1Dassault Systèmes, UK

KEY ISSUES WITH RESIDUAL FATIGUE LIFE

ESTIMATION IN STEELS, HIGHLY SCATTERED AND NON-CONSERVATIVE THRESHOLDS, CRACK

CLOSURE MECHANISMS, INFLUENCING FACTORS, RELEVANT MATERIAL PROPERTIES

T. Vojtek1*, R. Kubíček1, P. Pokorný1, M. Jambor1, L. Náhlík1 & P. Hutař1

The damage tolerance design is required for applications where safety is the most critical factor, such as railway vehicles or nuclear power plants. The commonly used concepts for fatigue crack propagation modelling have several issues leading to a critical dependence of the estimated residual fatigue lives on the solution to these problems, especially regarding the transferability of laboratory results to real components. Extensive experimental data were obtained for various steels at room temperature for different load ratios. The work includes separation of loading components and mechanisms (effective ΔK, plasticity-, roughness- and oxide-induced crack closure) and analysis of their dependency on influencing factors such as air humidity, specimen geometry, threshold measurement procedure, loading frequency and crack length beyond the short crack regime. Variation of thresholds due to these effects can be as serious as a two-fold increase in the value, which has an immense effect on the residual fatigue life. In general, the threshold value is affected by loading history. In relation to this, the oxide-induced crack closure was identified to be responsible for the largest part of the scatter obtained under different conditions and by different laboratories. The lack of consideration of oxide-induced crack closure can lead to several non-conservative and misleading scenarios. Threshold measurement techniques developed to minimise plasticity-induced crack closure lead to maximisation of oxide-induced crack closure. A combined experimental-numerical strategy is proposed to reach a less scattered, more universal and conservative threshold as a material parameter. The available plasticity-induced crack closure models are too weakly dependent on material properties. The FASTRAN software was used for simulation of loading history effects and for a proposal of a new parameter enabling

a broader range of modelled crack closure values depending on material cyclic plasticity behaviour and microstructure, which was necessary to match the experimental crack growth data. From the remaining issues, a variation of stress intensity factor along the real curved crack fronts can be named. Another one is that the 2D plane stress solutions describing stress and strain fields at free surfaces of cracked bodies are invalid. They should not be used for comparison with the results of full field surface measurement techniques such as DIC or for modelling of plastic zones and CTOD, which is often done to analyse crack closure and overload problems.

1Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 616 00 Brno, Czech Republic

*Corresponding author: vojtek@ipm.cz

26. HYDROGEN

DESIGN, USAGE AND SAFETY ASPECTS FOR TUBULAR SPECIMENS FOR

MATERIALS

QUALIFICATION WITH PRESSURISED HYDROGEN

K. Wackermann1, F. Ebling1, T. Michler1, F. Schweizer1 & H. Oesterlin1

Typically, autoclaves are used to characterise materials under a hydrogen atmosphere. Those systems are expensive in installation and usage due to the high safety requirements. A cost efficient and reliable alternative without the need of explosive protection might be the tubular specimen technique. In this technique a small diameter axial hole is machined in the centre of the specimen, which is pressurised with gas. Comparing the results of specimens filled with pressurised hydrogen and, for reference with ambient air or pressurised nitrogen allows to conclude for the effect of hydrogen on material properties. The advantage of the tubular specimen technique is the very low volume of the explosive gas, compared to conventional autoclaves. This reduces safety risks and allows the implementation in existing testing machines with low efforts. This paper describes in detail the setup of a tubular specimen test system for tensile tests, addresses safety aspects and shows exemplary results.

1Fraunhofer Institute of Mechanics of Materials, Freiburg, Germany

PHASE FIELD MODELLING OF

HYDROGEN-ASSISTED FATIGUE

E. Martínez-Pañeda1*, A. Golahmar2 & C. F. Niordson3

There is a growing interest in understanding and optimising the fatigue behaviour of metallic materials in the presence of hydrogen (see, e.g. [1] and Refs. therein). Two aspects have mainly motivated this interest: (i) the pervasive observation of hydrogen-assisted failures across the construction, transport, defence and energy sectors, partly due to the higher susceptibility of modern, high-strength alloys; and (ii) the role that hydrogen is deemed to play in our road towards net-zero, which has fostered a notable interest in the design and prognosis of infrastructure for hydrogen transportation and storage.

In this work, we present a computational phase field-based framework for predicting hydrogen-assisted fatigue. The coupled deformation-diffusiondamage finite element model presented enables predicting fatigue crack nucleation and growth for arbitrary loading patterns and specimen geometries [2]. The role of hydrogen in increasing fatigue crack growth rates and decreasing the number of cycles to failure is investigated. Our numerical experiments enable mapping the three loading frequency regimes and naturally recover Paris law behaviour for various hydrogen concentrations. The role of hydrogen in elevating – by orders of magnitude – fatigue crack growth rates is captured, without any ‘ad hoc’ criterion. In addition, Virtual S–N curves are obtained for both notched and smooth samples, exhibiting a good agreement with experiments. Moreover, the model captures, for the first time, the intrinsic relation between S-N and Paris law behaviour, the fatigue endurance limit, and the mean stress effect The computational framework development can be used to efficiently assess the behaviour of structures and components exposed to hydrogen-containing environments, preventing catastrophic failures and mapping safe regimes of operation.

References

[1] S. del Busto, C. Betegón, E. Martínez-Pañeda. A cohesive zone framework for environmentally assisted fatigue. Engineering Fracture Mechanics 185, pp. 210-226 (2017).

[2] A. Golahmar, P.K. Kristensen, C.F. Niordson, E. Martínez-Pañeda. A phase field model for hydrogen-assisted fatigue. International Journal of Fatigue 154, 106521 (2022).

1Department of Civil & Environmental Engineering. Imperial College London

2Vattenfall Vindkraft A/S

3Department of Mechanical Engineering, Technical University of Denmark (DTU)

*Corresponding author: e.martinez-paneda@imperial.ac.uk

CORRELATION OF FATIGUE BEHAVIOUR

IN PRESSURISED HYDROGEN AND ELECTROLYTICALLY SUPPLIED HYDROGEN

S. Schönborn1 & A. Kansy1

In order to achieve the goal of carbon neutrality in 2050 by the development of a hydrogen-based infrastructure, it is necessary to address the safety and reliability of systems and materials in contact with hydrogen. For this purpose, fatigue tests in high-pressure autoclaves are required, which are limited in number and are very complex in terms of testing. Therefore, another possibility was researched in which the hydrogen was generated by electrolysis on the surface of the material. This study investigated the possibility of adjusting the process parameters of the electrolytic charging in such a way that the specimens of the investigated steel 1.5132 achieve a comparable lifetime in the fatigue tests as in a pressurised hydrogen environment. Following the tests, selected specimens were analysed by thermal desorption analysis to determine the hydrogen uptake. In addition, the fracture surfaces were documented and comparisons made with tests in pressurised hydrogen.

1Fraunhofer Institute for Structural Durability and System Reliability LBF, Research Division: Structural Durability, Department: Material and Components, Bartningstr. 47, 64289 Darmstadt, Germany

EFFECT OF PRESSURISED HYDROGEN ON LOW CYCLE FATIGUE OF INCONEL 718: MODELLING AND TESTING

F. Ebling1, H. Oesterlin1 & K. Wackermann1

Inconel 718 is used for many technical applications. However, it is known that it is prone to hydrogen embrittlement. The tubular specimen technique is used for strain controlled low cycle fatigue (LCF) tests at 0.1 Hz with internal pressurised hydrogen at 10 bar and 100 bar. The comparison to reference tests in air shows the effect of the different hydrogen pressures on the fatigue lifetime. For a better understanding of a possible influence of the tubular specimen geometry, reference tests on conventional specimens were completed. The results are used to propose a model based on a damaging parameter to have a better prediction of the fatigue life.

The experiments on tubular specimens with internal hydrogen gas pressure showed a significant reduction of ductility in the tensile tests and of fatigue life in the LCF experiments compared to tests in air. A Manson-Coffin strainlife curve was fitted to the data obtained in air and modified to conclude from the ductility loss in the tensile test under hydrogen to the fatigue life under hydrogen. Thereby, a good agreement with the experiments could be achieved.

1Fraunhofer Institute for Mechanics of Materials IWM

27. MICROSTRUCTURAL INFLUENCES

FATIGUE DAMAGE ASSESSMENT OF C45 SAMPLES

VIA DIFFERENT EXPERIMENTAL TECHNIQUES AND MICROSTRUCTURAL INVESTIGATIONS

A. Saponaro1, R. De Finis1, G. Renna1, P. Leo1 & R. Nobile1

The complete understanding of microstructural changes caused by fatigue loadings is fundamental for studying the basic damage mechanisms and for an optimised fatigue life calculation of metallic materials. Beside conventional strain measurements, which lead to obtain the energy dissipated per cycle, in recent years experimental techniques such as the electrical resistance measurements were additionally used for the determination of fatigue relevant data during constant and variable amplitude loading.

By using the definition of the damage variable ‘D’, that it can be assumed as related to the effective density of microdefects on a representative volume element, the present work is focused on finding an effective damage parameter based on electrical measurements by exploring the crossproperty connections between changes in elastic and conductive properties of metals induced by damage. In effect, the resistivity of metals increases during cyclic loading as a function of the increasing defect density. In this way, the electrical resistance measurements offer additional information about the cyclic deformation behaviour also in the range of very low plastic deformations and in the case of materials with a very low ductility.

In present research, the fatigue behaviour of a carbon steel is studied by using different techniques: the one based on electrical response changes leading to the use of resistance variations as damage parameter and the one using the mechanical energy input related to energy dissipated during fatigue processes.

In view of this, the aim of present research is to investigate the relationship between material electrical response and mechanical energy input for a C45 steel undergoing constant amplitude tests. The analysis allows assessing

a possible relationship between electrical and mechanical response under different loading conditions (two stress ratios) and in the low deformations regime. Moreover, present research also focuses on quantitative evaluation of the microstructural changes - growth of the dislocation density - in the material undergoing a fatigue loading. In particular, quantitative microscopy will be adopted to correlate the specific damage mechanism to electrical resistance changes.

It will be also investigated the possibility to use a unique relationship to model mechanical data, in terms of mechanical supplied energy, and electrical data independently by loading conditions, the damage level and cycles run.

The approach leads to a volumetric damage analysis and to the assessment of the beginning of the damage (useful information to carry out structural health monitoring) and does not require specific loading conditions because no hypothesis are made on it.

1University of Salento, Department of Engineering for Innovation Campus Ecotekne, via per Monteroni di Lecce-73100, Lecce, Italy

CYCLIC LOADING INDUCED DYNAMIC

REFINEMENTS OF LOCAL MICROSTRUCTURES IN HIGH-STRENGTH MARTENSITIC STEELS

S-S. Rui1, S. Wei2 & C. Sun1,3

High-strength martensitic steels are widely employed at some key metallic components of industrial equipment subjected to cyclic loading. Cyclic loading induced dynamic refinements of local microstructures featured by Fine Granular Area (FGA) in high-strength martensitic steels have close ties to the fatigue crack initiation and early growth, which are worthy of being investigated. On this issue, we conducted Very High Cycle Fatigue (VHCF), High Cycle Fatigue (HCF) and Low Cycle Fatigue (LCF) tests on different types of specimens. By post-mortem/quasi in-situ Scanning Electron Microscope (SEM) and Electron Back-Scattered Diffraction (EBSD) observations, as well as further Transmission Kikuchi Diffraction (TKD) and Transmission Electron Microscope (TEM) analyses, we captured two types of local microstructure refinement behaviours during the cyclic loading. One is the “dynamic precipitation”, a kind of phase transformation from martensitic matrix (BCC) to Nb- and Mo-rich small carbides (MC, M7C3) accelerated by repeated slight plastic deformation, whose formation does not rely on the stress concentration effect but also has no ties to the plastic strain localisation and fatigue crack initiation. Another is the “local grain refinement” around stress singularities (crack tip, or interior inclusion) generating substantial amounts of fine sub-grains in all VHCF, HCF and LCF regimes, which promotes fatigue crack initiation and early growth along sub-grain boundaries, fine/coarse grain boundaries and martensitic block boundaries.

FIGURE 1 Schematic of local microstructure evolution and crack initiation during cyclic loading.

1State Key Laboratory of Nonlinear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China

2Max-Planck-Institut für Eisenforschung, Max-Planck-Straße 1, Düsseldorf 40237, Germany

3School of Engineering Science, University of Chinese Academy of Sciences, Beijing 100049, China

A CORROBORATIVE STUDY ON THE FATIGUE

MECHANISMS AT ROOM AND ELEVATED TEMPERATURES OF A DUAL-PHASE HIGH ENTROPY ALLOY

Q. Han1,2,*, Y. T. Tang1* & R. C. Reed1,3

High entropy alloys (HEAs) consist of a variety of elements of similar atomic fractions and they show many promising properties, for example, excellent strength, ductility, resistance to corrosion, fatigue and high temperatures. Among them, eutectic high entropy alloy (EHEA) AlCoCrFeNi2.1, a promising candidate with a large range of properties, subject to processing route, has been studied in this work. It has a dual-phase structure and is composed of the disordered FCC phase and an ordered B2 phase. This research aims to study the fatigue mechanism of AlCoCrFeNi2.1 by observing fatigue crack growth using an in-situ scanning electron microscope (SEM) at room temperature and 600 °C. The as-cast AlCoCrFeNi2.1 EHEA was examined using electron backscattered diffraction (EBSD) before and after fatigue crack growth. Numerous damage mechanisms were captured in real-time, with evidence showing slip traces, short crack initiation and propagation. The results were then rationalised using a crystal plasticity finite element (CPFE) simulation where dual-phase real grain reconstruction was imported from EBSD data. The corroborative approach combining in-situ SEM, EBSD and CPFE was able to provide new insights into competitive transgranular and intergranular crack growth with strain partitioning within each phase.

1School of Metallurgy and Materials, University of Birmingham, Elms Road, Birmingham, B15 2TT, UK

2College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

3Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK

*Corresponding authors. q.han.1@bham.ac.uk, y.t.tang@bham.ac.uk

SHORT FATIGUE CRACK BEHAVIOUR IN A NEW ALUMINIUM ALLOY AlMgSc FABRICATED BY WIRE

BASED DIRECTED ENERGY DEPOSITION

J. Ye1*, A. Khadar Syed1 & X. Zhang1

Aluminium alloys have received substantial interest for the fabrication of complex geometry and large size components for the aerospace industry via additive manufacturing (AM) processes. The 5xxx series aluminium alloys, Al-Mg, are suitable to the AM processes as they are weldable. Their low density is particularly appealing to the space industry. This work explores the fatigue performance of a new Al-Mg alloy with added Scandium (Sc) fabricated by wire-based Directed Energy Deposition (w-DED), also referred as the wire arc additive manufacturing (WAAM) technology.

Recent literature has shown that addition of scandium (Sc) into Al alloy can develop finely dispersed primary Al3Sc precipitates during the solidification resulting in grain refinement [1, 2]. Secondary precipitates formed during post process heat treatment further strengthen the α-Al matrix (e.g., 70% increase in tensile strengths compared to similar materials without Sc) [1, 3]. However, only a few studies are found in the open literature on the fatigue durability and fatigue crack growth behaviour of AM Al-Mg-Sc alloys. For example, a similar alloy Al-Mg-Sc-Zr made by laser powder bed fusion (L-PBF) showed little evidence of roughness-induced crack closure owing to the small grain sizes, which reduced the threshold stress intensity factor range (∆Kth) [4]. Crack growth rate in the Paris law region was in agreement with similar aluminium alloys [4].

This work has been focused on the fatigue crack growth behaviour especially at the short crack regime which can be exploited for design for longer life. This part of work is completed by testing standard specimens in two material directions. Test result has shown slower crack growth rate than conventional materials. A strong direction dependence in the threshold stress intensity factor range (∆Kth) as well as the crack growth rate at lower values of stress intensity factor (SIF) range are also found.

Values of the ∆Kth between two major material orientations differ by 50%. Since a significant amount of fatigue life is spent in the near-threshold and short crack growth regions, fatigue life can be significantly increased if the material build direction can be adjusted so that higher resistance to crack growth is aligned to the potential crack trajectory.

To investigate the observed crack growth behaviour from experiment, part of our current work is focused on the crack closure effect which has been extensively studied for long cracks since Elber’s work [5]. Crack closure in the ∆Kth and short crack growth regime is not well understood, e.g., whether the mechanism being cyclic plasticity and/or crack surface roughness. In AM materials, inhomogeneous and directional microstructure can also play a role and interact with the mechanics. These results can promote the development and application of AM Al-Mg alloys.

References

[1] S. Lathabai, P.G. Lloyd, The effect of scandium on the microstructure, mechanical properties and weldability of a cast Al–Mg alloy, Acta Materialia. 50 (2002) 4275-4292.

[2] Y.A. Filatov, V.I. Yelagin, V.V. Zakharov, New Al–Mg–Sc alloys, Materials Science and Engineering: A. 280 (2000) 97-101.

[3] J. Taendl, A. Orthacker, H. Amenitsch, G. Kothleitner, C. Poletti, Influence of the degree of scandium supersaturation on the precipitation kinetics of rapidly solidified Al-Mg-Sc-Zr alloys, Acta Materialia. 117 (2016) 43-50.

[4] P. Chernyshova, T. Guraya, S. Singamneni, T. Zhu, Z.W. Chen, Fatigue crack growth behaviour of Al-4.5Mg-0.6Sc-0.3Zr alloy processed by laser powder bed fusion, Journal of materials engineering and performance (2021).

[5] W. Elber, The significance of fatigue crack closure (1971).

1Centre for Manufacturing and Materials, Coventry University, CV1 5FB, Coventry, United Kingdom

*Corresponding author: yej22@uni.coventry.ac.uk

ON THE ROLE OF THE INTERNAL AND SURFACE DEFECTS IN THE FATIGUE AND STRUCTURAL INTEGRITY OF ADDITIVELY MANUFACTURED 316L STAINLESS STEEL

J. Nafar Dastgerdi1,2*, O. Jaberi2 & H. Remes3

This study aims to clarify the effect of process-related defects on the fatigue integrity of additive manufacturing (AM) stainless steel 316 L. X-ray computed tomography (XCT) is used to characterise process-related defects’ features and their synergistic interaction to define the effective defect size parameter leading to identifying potential sites for fatigue crack initiation before testing. The introduced equivalent defect size critical value is considered an initial semi-elliptic surface short crack in the critical defect-based fatigue crack growth model for the fatigue life prediction of AM components. The proposed single crack growth model demonstrates promise to be suited as an engineering approach for fatigue life prediction of AM components. This model shows a good correlation between XCT imaging in a temporal domain during fatigue testing and the predicted crack initiation and propagation phases for the tested AM 316L stainless steel samples.

1Mechanical Engineering Group, School of Engineering, University of Kent, Canterbury CT2 7NT, United Kingdom

2Department of Aerospace Engineering, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, Tehran, Iran

3Department of Mechanical Engineering, School of Engineering, Aalto University, P.O. Box 14300, FIN-00076 Aalto, Finland

*Corresponding author: j.nafar-dastgerdi@kent.ac.uk

CONTINUUM DAMAGE MECHANICS APPROACH FOR SLM-MANUFACTURED NICKEL-BASED SUPERALLOY

UNDER MULTIAXIAL FATIGUE

LOADING CONDITIONS

H. Yuan1, J. Xu1 & J. Lu1

In the present work, Inconel 718 manufactured by selective laser melting (SLM) was investigated with a focus on the microstructure, the orientation-dependent mechanical properties and the fatigue performance. Fatigue performance under multiaxial loading conditions was studied experimentally and computationally. Comparative material testing and characterisation of the SLM and the forged Inconel 718 revealed significant differences in both microstructure and mechanical properties. The columnar grain structure of the SLM alloy leads to orientation-dependent mechanical properties, which match the Hall-Petch relation. The inhomogeneous microstructures and slit-shaped lack-of-fusion (LoF) defects from the SLM process result in significantly lower fatigue properties and poorer fatigue crack growth behaviour. An accumulated plastic strain-based damage model was proposed in the present work to predict the damage evolution in SLM Inconel 718 under both monotonic and cyclic loading with varying amplitudes. The damage mechanism related to detrimental second-phase particles and lack-of-fusion defects in the SLM material is discussed and considered in the present model, which could predict both monotonic and cyclic material degradation processes with good agreement.

1Tsinghua University, School of Aerospace Engineering, Beijing 100084, China

29. WELD II

IMPROVED FATIGUE CALCULATION OF ATTACHMENT WELDS IN OFFSHORE WIND STRUCTURES USING ADDITIVE MK FACTOR

J. Taylor1*

Secondary attachments are an essential part of any offshore structure. Typically these attachments are welded on to the primary structure, and therefore their fatigue performance impacts the integrity of the structure. While design of these details follows normal practice utilising S-N fatigue design approach, in many cases integrity management requires assessment of fatigue crack growth at these details, to quantify risk or develop inspection requirements etc. Fatigue crack growth of these welds typically follows the BS7910 or similar industry accepted standards. These represent the effect of the welded joints using an Mk multiplication factor. Small initial flaws tend to dominate the life of a welded joint, but this is where the Mk-factor is not well suited. The current project proposes an alternative approach which improves the calculation of this effect by considering an additive “Mk” effect rather than a multiplicative factor. This initial study gives a new method for determining the weld magnification effect which is a much simpler approach than the current method in BS7910. This has the potential to simplify the assessment of small flaws at an attachment weld toe.

1Kent, Office 3.12, Thomas House, 84 Eccleston Square, London, SW1V 1PX

*Corresponding author: jessica.taylor@kentplc.com

FATIGUE PERFORMANCE OF MODERN SUBMERGED ARC WELDS IN 85MM GRADE S355 STEEL

C. Johnston1

The fatigue design documents BS 7608 and DNV RP C203, include a ‘thickness correction’ which reduces the design S-N curve for components thicker than the reference value. Wind turbine structures use very large plate thicknesses (>>50mm) with fatigue-critical circumferential welds made with submerged arc welding (SAW). There is concern in the industry that the thickness correction included in the fatigue design standards are overly conservative. This paper presents results of recent fatigue tests on SAW welds in 85mm thick grade S355 steel, allowing the suitability of the thickness correction to be investigated. The results suggest that a thickness exponent of 0.125 may be more suitable for modern SAW welds in thick S355 steel.

1TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL

IMPACT OF SHOT PEENING ON THE FATIGUE

STRENGTH OF ARC-WELDED ADVANCED HIGH STRENGTH STEEL ASSEMBLIES

A. Nabara1,2, C. Mareau1, F. Morel1, M-R. Chini2, R. Munier3, P. Kusakin3 & M.

L. Facchinetti4

The present work aims at investigating the effect of shot peening on the fatigue behaviour of welded joints made of advanced high strength steel with a tensile strength of 600 MPa. Uniaxial fatigue tests were conducted on double lap joint specimens with both as-welded and shot-peened conditions at two loading ratios of 0.1 and -1. These tests were completed by X-ray diffraction analyses and roughness measurements. The fatigue test results indicate that shot peening improves the fatigue strength of welded specimens, especially at R = -1. The beneficial effect at R = 0.1 is reduced because of the redistribution of the residual stresses induced by cyclic plasticity. The effects of residual stresses, work hardening and surface roughness on the fatigue strength were estimated separately by comparing the results obtained for heat-treated and preloaded specimens. According to the results, the generation of compressive residual stress by shot peening is the major factor controlling the fatigue strength of lap joints. The effects of work hardening and surface roughness are negligible.

1LAMPA, Arts et Métiers, Sciences et Technologies, 49035 Angers, Cedex, France

2IRT M2P, 57070 Metz, France

3ArcelorMittal Maizières Research SAS, 57283 Maizières-lès-Metz Cedex, France

4Stellantis (ex-Groupe PSA), Chassis System Engineering, 25420 Voujeaucourt, France

POSTERS

EFFECT OF ENVIRONMENT ON FATIGUE CRACK

GROWTH OF POLYCRYSTALLINE NICKEL-BASED SUPERALLOYS AT HIGH TEMPERATURES

J. Buckley1, H. L. Cockings1, Y. Li1 & M. Hardy2

Over the past fifty years, the aerospace industry has made significant strides in improving the efficiency of aircraft engines. One key approach to boosting efficiency has been to increase the maximum operating temperature of the engine, which has resulted in higher compressor exit temperatures and hotter turbine discs. Modern turbine discs are manufactured from polycrystalline nickel superalloys, which are renowned for their excellent mechanical properties at high temperatures, however, whilst operating under extreme conditions, they become susceptible to environmental degradation. Environmental degradation in polycrystalline Ni based superalloys can take multiple forms, including oxidation and hot corrosion, and understanding these phenomena are key to their mitigation. While oxidation and the role of hot corrosion in fatigue crack initiation has been well explored, further understanding is required on the effect of the environment on the growth of fatigue cracks. Since crack growth rate measurements and damage tolerances are used extensively in the lifing of critical aerospace components such as the turbine disc, it is essential to capture and understand the effects that the operating environment can have on the data. This work provides a comprehensive overview of the current state of knowledge on the effect of environmental factors on fatigue crack growth in polycrystalline Ni- based superalloys. Recent findings on the effect of a representative, hot corrosion environment on coarse grain RR1000 will also be presented.

1Institute of Structural Materials, Swansea University, SA1 8EN, United Kingdom

2Rolls–Royce plc, P.O. Box 31, Derby, DE24 8BJ, United Kingdom

INVESTIGATIONS OF THE GRP BEAMS FOR DYNAMIC LOADED STRUCTURES BEHAVIOUR

DURING THREE-POINT BENDING TEST

M. Fikrle1 & J. Chvojan1*

Paper includes research on the strength characteristics of composite GRP beams of different composition of glass fibers and matrix by three-point bending with the aim of describing their properties, especially interlamellar shear stress and other important quantities. For this research, samples of different sizes (100 mm, 400 mm) with different glass fiber orientations (UD, EBX) are used.

Tapped GRP beams with 35 layers of glass fibers and the length of 1000 mm were instrumented with a dense network of strain gauges in order to verify the distribution of stress responses in different parts of the tested specimen.

Tested beams subjected to mechanical properties research form the basis for the construction of the GRP bogie frame of the half scale freight wagon.

The paper further describes procedures how to investigate the static and fatigue properties of this GRP bogie for half scale freight wagon.

Figure 1 – Set-up of the 3-point bending tests

1Research and Testing Institute Plzen, Dynamic Testing Laboratory, Tylova 1581/46, 30100 Plzen, Czech Republic

*Corresponding author: chvojan@vzuplzen.cz

EFFECTS OF BUILD ORIENTATION ON HIGHTEMPERATURE FATIGUE BEHAVIOUR OF LASER POWDER BED FUSION INCONEL 718

M. Hulbert1, P. A. S. Reed1 & A. Hamilton1

Inconel 718 is a nickel-based superalloy commonly used in aerospace engine technology due to the stability of its mechanical performance up to temperatures of ~650°C. The weldability of this material, along with the increasing complexity of aerospace engines, makes it a good choice for Laser Powder Bed Fusion (LPBF) manufacturing. However, when understanding the fatigue performance, significant complications arise due to the unique microstructure formed as a result of the thermal conditions during the manufacturing process. In particular, a predominantly columnar microstructure, aligned parallel with the build direction, is characteristic of parts manufactured in this way. This gives rise to anisotropic properties within the material. Therefore, this study considers the effect of build direction on the fatigue response at high temperatures.

At these high temperatures, the anisotropic effects of the microstructure are amplified due to the grain boundaries providing preferential crack paths through the component. This results in significantly different crack behaviour between build orientations. Within this study, Single Edge Notch Bend (SENB) specimens, built in vertical and horizontal orientations, were tested at elevated temperatures of 650°C. Tests were conducted at constant load and a frequency of 0.25Hz, with data recorded using a Direct Current Potential Drop (DCPD) approach. The resultant data was calibrated and compared between the two build orientations, and various techniques were employed to gather further information from the fracture surfaces. These techniques included optical microscopy and macroscopy of the fracture surface, crack path, and crack tip (where applicable). In addition, Alicona Infinite Focus Microscope (IFM) scans and Scanning Electron Microscope (SEM) imaging of the samples were also used.

Further investigation at room temperature, including a comparison of crack

propagation behaviour in equivalent samples, may aid in developing the understanding of the complex and unique crack paths observed as a part of this study.

1Engineering Materials Research Group, School of Engineering, University of Southampton, Highfield, Southampton, SO17 1BJ, UK

PREDICTING THE FATIGUE LIMIT OF LATH MARTENSITIC STEEL MICROSTRUCTURES

S. Kino1, D. Itoh1,2, S. Ueki1 & S. Hamada1*

In recent years, high-strength steels have been attracting attention to reduce the weight of machines. Lath martensite is one of the microstructures for high-strength steels. Lath martensite is a hierarchical microstructure with a nested packet, block, and lath microstructure with prior austenite grains as the parent grain. This complex microstructure in the lath martensite makes the steel high strength. However, the fatigue limit ratios for the lath martensitic steels are lower than the traditional empirical estimated values. Therefore, predicting the fatigue limit for lath martensitic steels is difficult.

Murakami et al. proposed a fatigue limit prediction method for specimens with small defects, such as non-metallic inclusions. In Murakami’s theory, the fatigue limit is predicted by two parameters: the first one is √area, and the second is Vickers hardness. Here, √area is the square root of the area of the defect projected onto a plane perpendicular to the direction of the maximum principal stress. Hamada et al. proposed a fatigue limit prediction method for plain specimens by treating the grain diameter as the √area. We have focused on the fatigue prediction method proposed by Hamada et al. Some papers have reported that the grain boundary is the dominant barrier for crack growth and the non-propagating crack length is the grain size, approximately. Therefore, we propose to predict the fatigue limit for plane lath martensitic steels by using Murakami’s fatigue limit prediction method and treating the grain size as √area.

However, as explained above, lath martensite is a hierarchical microstructure with many kinds of boundary. Therefore, we need to discover the effective microstructural size for predicting the fatigue limit. In this poster, we will explain our findings about the relationship between the non-propagating crack size and the lath martensite microstructure. Furthermore, we will propose an effective microstructural size for predicting the fatigue limit of lath martensitic steels.

1Kyushu University, 744, Motooka, Nishi-ku, Fukuoka-shi, Fukuoka, 819-0385, Japan

2Nippon Steel Co., 1-1, Tobihata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka, 8040001, Japan

*Corresponding author: hamada@mech.kyushu-u.ac.jp

MECHANISTIC UNDERSTANDING OF LIFE EXTENSITION OF AGEING OFFSHORE STRUCTURES

S. Manzoor1,2*, K. Khan1, X. Sun1,3 & N. Larrosa4

Pitting corrosion poses a significant threat to offshore structures, leading to stress concentration and crack initiation. The synergetic effect of corrosion and fatigue is well recognized, yet the pit-to-crack transition remains poorly understood, representing a significant knowledge gap. Existing integrity assessment codes provide limited guidance on safety assessment of corrosion pits and treat them as cracks of equivalent size neglecting the crack initiation life which is 70% of the total life [1]-[3]. It has been found in recent studies that once surface strain around mouth of the pit reaches a critical value, the crack initiates [4]-[6] but the cycles to reach this critical strain is still unknown.

This project aims to conduct fatigue testing of samples containing electrochemically generated single corrosion pit and similar blunt notches of different aspect ratio charged with hydrogen using cathodic charging in simulated seawater. DIC (Digital Image Correlation) will be carried out on notched fatigue samples both in air and simulated seawater to find the strain threshold for crack initiation. Synchrotron studies will also be carried out to track strain evolution around the pit on the surface as well as further ahead of the pit into the material and image the crack initiation. A criterion can then be established based on critical strain for crack initiation from corrosion pits. This criterion will be validated against fatigue testing of corroded samples from a decommissioned offshore jacket structure with real corrosion pit morphology. The jacket structure along with pit morphology and the chamber for sea water DIC are shown in Figure 1.

FEM analysis will also be carried out to model pit to crack transition. Once the criterion based on critical strain is validated through experiment it will be used as input to FEM to study crack initiation from a real tubular structure with real pit morphology obtained through 3D scanning. Different variables

based on loading, frequency and the crack shapes can then be tested in FEM to gain an understanding of pit to crack transition under different scenarios. This ongoing research, funded by the Lloyd’s Register Foundation and supported by TWI Ltd and the National Structural Integrity Research Centre, addresses critical knowledge gaps and promises vital insights into the treatment of corrosion pits in offshore structures with less conservative approaches.

Figure1. (a) Decommissioned tubular structure and associated corrosion morphology. (b) Chamber for sea water DIC

References

(1) N. O. Larrosa et al., (2018). Corrosion-fatigue: a review of damage tolerance models. Inter. Mater. Rev., 63, 283-308.

(2) R. M. Katona et al., (2023). A review of the governing factors in pit-tocrack transitions of metallic structures. Corrosion, 79, 72-96.

(3) R. Akid et al., (2006). Fatigue damage accumulation: the role of corrosion on the early stages of crack development. Corros. Eng., Sci. Technol., 41, 328-335.

(4) C. Evans et al., (2018). Strain evolution around corrosion pits under fatigue loading. Theor. Appl. Fract. Mech., 95, 253-260.

(5) F. Farhad et al., (2019). Fatigue behaviour of corrosion pits in X65 steel pipelines. Proc. Inst. Mech. Eng. Pt. C J. Mechan. Eng. Sci., 233, 17711782.

(6) M. Hashim, (2020). Influence of Pit Morphology on Crack Propagation. U. of Man. (UK).

1Faculty of Engineering and Computing, Coventry University, Coventry, CV15FB, UK

2NSIRC, TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK

3TWI Ltd., Cambridge CB21 6AL, UK

4School of Electrical, Electronic and Mechanical Engineering, University of Bristol, Bristol, BS8 1TH, UK

INVESTIGATION INTO THE FATIGUE

PERFORMANCE OF ALUMINIUM COLD SPRAY SUBSTRATE ALLOYS

R. Reed1, P. A. S. Reed1, A. A. Bakir2,3, A. W-Y. Tan4 & A. G. S. Araujo1

Aluminium alloys are commonly used in aerospace structures due to their high specific strength, durability, and machinability. However, these components can experience damage due to wear, corrosion, and cyclic loading. Cold spray (CS) technology presents an effective approach for repairing such components, utilising high-temperature compressed gases to accelerate powders onto damaged substrates at critical velocities (2001500m/s). This process induces substantial plastic deformation in the impacting powder, facilitating deposition through metallurgical bonding and/or mechanical interlocking. However, attainable coating adhesion is contingent upon the material property combinations of both the feedstock powder and substrate, subsequently influencing the mechanical properties of the repaired material, thus their fatigue performance.

Fatigue is the most common mode of failure in aerospace components. Many studies have shown that cold spray coatings maintain or improve the fatigue life of the substrate material however the new generation aluminium alloy, AA7037, remains unexplored. The effect of CS on substrate microstructure and mechanical behaviour has provided a strong motivation for this research.

This work will focus on two AA-7xxx alloys – AA-7075, commonly used in aerospace structures and AA-7037, a recently developed alloy with minimal fatigue research to date. The microstructures of the two alloys were characterised using optical and scanning electron microscopy (SEM), with both alloys found to contain complex intermetallic systems. Electron backscatter diffraction (EBSD) was also used to evaluate grain structure and the mechanical variations within grains. Following characterisation, the short crack fatigue performance of the alloys was investigated using crack replication techniques. A fractographic study was carried out using

advanced microscopy methods and 3D reconstruction techniques. The results of this work have shown the variations in microstructure between AA-7075 and AA-7037 and the relationship these variations have to the fatigue behaviour of the respective alloys, such as the microstructural impacts on fatigue crack initiation and propagation.

This study lays the foundations for future investigations utilising Digital Image Correlation (DIC) as a tool to determine the load transfer from substrate to CS and the formation of potential delamination.

1Materials Research Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK

2Faculty of Engineering and Computing, Coventry University, Coventry, CV15FB, UK

3NSIRC, TWI Ltd, Granta Park, Great Abington, Cambridge, CB21 6AL, UK

4Materials Research Group, School of Engineering Sciences, University of Southampton, 79200 Nusajaya, Johor, Malaysia

NOTCH-STRESS APPROACH FOR THE FATIGUE

LIFE EVALUATION OF ROUGH WIRE ARC

ADDITIVELY MANUFACTURED PLATES

X. Ruan1*, B. Karabulut1, J. Dobric2 & B. Rossi1,3

The fatigue behaviour of steel plates is very sensitive to roughness, as the concentration of stress arising from surface roughness leads to fatigue cracks. This research investigates the influence of roughness on the fatigue strength of wire arc additively manufactured (WAAM) carbon steel plates made of unalloyed S355 grade (3Dprint AM35). As part of this study, as-deposited specimens with two different roughnesses were additively manufactured by cold metal transfer welding. 3D scans of the sample geometries were obtained using a three-dimensional laser scanner (3D Design FARO Scan Arm) to precisely characterise the surface roughness. Finite element (FE) models of the rough samples were then used to identify the location and magnitude of the concentration of stresses. In parallel, nominal fatigue strengths versus maximum roughness amplitudes (r) were collected from the existing literature. Additionally, previously obtained milled surface (r = 0) fatigue lives for the same steel grade were compared with these reference results. Based on these preliminary data, we concluded that there is a linear relationship between fatigue strength and roughness, which partly conflicts with other authors’ recent findings. Future steps will involve determining the fatigue lives of rough coupons experimentally. Based on which, a parametric assessment will be carried out to further validate these early conclusions.

1KU Leuven, Faculty of Engineering Technology, Sint-Katelijne-Waver, Belgium

2University of Belgrade, Department of Civil Engineering, Belgrade, Serbia

3University of Oxford, Department of Engineering Science, Oxford, UK

*Corresponding author: xiongfeng.ruan@kuleuven.be