Case Study: Failure Modes and Effects Analysis of Rigid Flange Coupling Through a Simulation-Based A

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Case Study: Failure Modes and Effects Analysis of Rigid Flange Coupling Through a Simulation-Based Approach Tejas Satpute1, Sattyaksh Mangsulikar2, Aditya Shetty3, Aditya Rasal4 1Student, Mechanical Engineering, SPPU

2Student, Mechanical Engineering, SPPU 3Student, Mechanical Engineering, SPPU 4Student, Mechanical Engineering, SPPU

---------------------------------------------------------------------***--------------------------------------------------------------------During operation, rigid flange couplings experience a Abstract

combination of torsional loading, cyclic stress, and potential geometric discontinuities, all of which contribute to structural fatigue or sudden mechanical failure. In highperformance or mission-critical systems, early identification of failure-prone regions is essential to maintain safety, reliability, and operational efficiency.

Rigid flange couplings are widely used mechanical components in rotating machinery, designed to transmit torque between aligned shafts. Their performance is often influenced by factors such as load variations, material properties, and geometric discontinuities, which may lead to structural failures during service. This study investigates potential failure modes in a rigid flange coupling through a simulation-based analysis. The geometric model of the coupling was developed using computer-aided design (CAD) tools, and finite element analysis was conducted to evaluate structural behavior under operational conditions. Static structural analysis was used to identify regions of stress concentration and deformation, while modal analysis was performed to determine the natural frequencies of the assembly and assess susceptibility to vibration-induced failures. Based on these simulations, a systematic Failure Modes and Effects Analysis (FMEA) was developed to qualitatively evaluate the significance and impact of possible failure mechanisms. The study emphasizes predictive failure identification rather than structural validation, offering a methodological framework for integrating simulation data into failure analysis and component reliability assessment.

The present study aims to analyse potential failure mechanisms in a rigid flange coupling through a simulation-based approach. The coupling geometry was modelled based on standard machine design principles, and finite element analysis was conducted to evaluate stress distributions and deformation patterns under applied torque. Modal analysis was also performed to determine the natural frequencies of the assembly and assess susceptibility to vibration-induced failures.

Informed by the simulation results as well as established failure scenarios in mechanical design practice, a structured Failure Modes and Effects Analysis (FMEA) was developed to identify, classify, and evaluate potential failure modes affecting the coupling system.

The integration of classical design methodology, simulation tools, and engineering judgment provides a comprehensive framework for predictive failure analysis.

The outcomes of this study are intended to support informed decision-making during the design, assessment, and optimization of rigid flange coupling systems in engineering applications.

Key Words: Rigid Flange Coupling, Failure Modes and Effects Analysis, Finite Element Analysis, Design of Machine Elements, Computer-Aided Engineering

1.INTRODUCTION

2.1 Design calculations

Rigid flange couplings are mechanical devices used to connect two rotating shafts in order to transmit torque while maintaining alignment and mechanical continuity.

Commonly employed in industrial machinery, automotive drivetrains, and power transmission systems, they are favoured for their ability to ensure firm, backlash-free connections in high-load applications. Owing to their rigid construction, such couplings do not accommodate misalignment or flexibility, and are therefore subject to concentrated stress under torsional loads and assembly constraints.

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The preliminary geometric parameters of the rigid flange coupling were established using standard analytical methods provided in Design of Machine Elements by V. B. Bhandari [1]. The design was based on a power transmission requirement of 40 kW at a rotational speed of 200 revolutions per minute (rpm). To incorporate allowances for service irregularities and overload conditions, a service factor of 1.5 was applied.

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The design torque TTT was calculated using the following relation:

The design was finalized after confirming dimensional consistency and proper assembly alignment. The model was then exported in STEP format for compatibility with the finite element simulation environment used in the subsequent phase of the study.

2.3 Simulation Setup

Where:  T = Design torque (N·mm)  P = Power (kW)  Cs = Service factor  n = Rotational speed (rpm)

Finite element analysis of the rigid flange coupling assembly was carried out using ANSYS Workbench to evaluate its structural response under applied torque and to determine its natural frequencies. Two types of analyses were performed: static structural analysis to assess stress distribution and deformation, and modal analysis to study the system's dynamic behaviour.

Substituting P=40 kW, Cs=1.5 and n=200 rpm yields a design torque of approximately 2,864,788 N·mm.

The shaft diameter corresponding to this torque was computed using torsional strength criteria, resulting in an initial value of 57 mm. This was rounded to 60 mm to conform with standard shaft sizes used in mechanical design.

The coupling model consisted of three primary materials selected to represent typical mechanical design configurations. The shafts were assigned 40C8 steel, the keys were modelled using 30C8 steel, and the flanges were assigned gray cast iron. All materials were treated as linearly elastic, homogeneous, and isotropic, with material properties obtained from standard engineering references [3].

Using the finalized shaft diameter as a reference, the remaining dimensional parameters of the coupling assembly—such as hub length, flange diameter, key size, and bolt circle diameter—were determined according to empirical proportions and standard guidelines. These dimensions served as the geometric basis for the CAD model and subsequent simulation analyses. The focus of the study remains on the behaviour of the coupling under load rather than on design optimization; hence, the specific dimensions are treated as representative inputs rather than variables of interest.

In the static structural analysis, the shaft at one end was constrained using fixed support conditions to replicate real-world restraint. A torsional load was applied at the opposite end, corresponding to the design torque derived from power transmission calculations, multiplied by a service factor of 1.5 to account for operational variability.

All contact interfaces within the assembly—including those between shafts, keys, hubs, and flanges—were modelled as bonded to simulate ideal load transfer without relative motion.

2.2 Designing the CAD model

The assembly was meshed using unstructured tetrahedral elements with a uniform global element size of 10 mm.

Mesh quality was verified prior to solving to ensure convergence stability and acceptable element behaviour under both structural and modal conditions.

A three-dimensional computer-aided design (CAD) model of the rigid flange coupling was developed to support simulation-based structural and modal analysis.

The modelling was performed using Autodesk Fusion 360, a parametric design platform widely used for mechanical component development. All geometric parameters were defined according to the design calculations previously outlined, and proportions were selected based on standard machine design practices.

3.1 Results

The model consists of two co-axial shafts, each connected to a flange, which are joined together using multiple bolts distributed along a circular bolt pattern. A flat key was incorporated into the shaft-hub interface to facilitate torque transmission and prevent relative rotation. Geometric features such as the hub, flanges, bolt holes, and keyways were modelled in accordance with accepted engineering conventions to ensure representative mechanical behaviour under loading.

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Figure -3.1.1: Total deformation Contour

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Figure -3.1.2: Equivalent (von-mises) stress distribution

Fig -3.1.5: Total deformation at Mode 10 (1447.2 Hz) A modal analysis was conducted to evaluate the natural frequencies and associated mode shapes of the rigid flange coupling assembly. This analysis assists in identifying possible resonance conditions that could lead to vibrationinduced failures over time.

The simulation yielded ten mode shapes. The first three modes presented zero frequencies, corresponding to rigid body motion. Modes four to six displayed extremely low frequencies, which are considered negligible and typically associated with numerical artifacts or near-rigid motions due to boundary conditions. These modes were therefore excluded from practical interpretation.

Figure 3.1.3:Shear stress distribution under static loading The static structural analysis was conducted to assess the deformation and stress response of the rigid flange coupling under design torque. The simulation showed a maximum total deformation of 0.27238 mm, occurring on the flanges as shown in Figure 3.1.1. The deformation followed a torsional profile consistent with the loading conditions, with minimal displacement observed along the fixed shaft.

The first meaningful natural frequency was observed at 230.95 Hz, followed closely by 231.06 Hz, 330.81 Hz, and 1447.2 Hz. These represent structural resonances involving torsional and bending behaviour of the coupled shafts and flanges. Since the operating speed of the system (200 rpm) is well below these natural frequencies, the likelihood of resonance during normal operation is minimal. However, the identified modes are relevant in assessing potential dynamic failure scenarios considered in the FMEA.

The von Mises stress distribution is shown in Figure 3.1.2, with a maximum stress of 355.93 MPa located near the shaft–key interface. This region experiences high torsional load transfer, making it a critical stress zone within the assembly.

3.2 Failure modes and effects analysis (FMEA)

The maximum shear stress obtained was 170.53 MPa, concentrated in the same region as the peak von Mises stress (Figure 3.1.3). This is consistent with expected shear behaviour in keyed connections under torque. The results of the static analysis serve as the basis for identifying potential failure modes addressed in the subsequent FMEA.

Failure Modes and Effects Analysis (FMEA) is a systematic approach used to identify potential failure modes within a system, assess their causes and effects, and prioritize them based on risk. In this study, FMEA is employed to evaluate the rigid flange coupling assembly based on structural and modal simulation results, material properties, and mechanical design considerations [2].

The analysis incorporates observed stress concentrations, deformation patterns, and dynamic behaviour obtained through finite element simulations. In addition, failure modes related to fatigue, wear, loosening, and misalignment are considered based on engineering judgment and common industrial failure scenarios. Each failure mode is assessed using the standard Risk Priority Number (RPN) method, based on severity (S), occurrence (O), and detection (D) ratings. This process facilitates early

Fig -3.1.4: Total deformation at Mode 7 (230.95 Hz)

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identification of critical failure points and supports preventive design or maintenance actions.

The application of finite element simulation provided detailed insight into stress and deformation patterns across the coupling assembly, enabling a data-driven approach to failure mode identification. Static structural analysis revealed critical stress zones, particularly at the shaft–key interface, indicating susceptibility to shear and yielding in those regions. Modal analysis further contributed by identifying natural frequencies that, if matched with operational harmonics, could lead to vibration-related fatigue. These simulation results served as the foundation for defining failure modes associated with structural overstress, wear, and dynamic instability.

Fig -3.2.1: Cut section showing the location of max stress Part

Failure Mode

Potential Cause(s)

Effects (Consequence)

S

O D RPN

Shaft (40C8 steel)

Bending/torsiona l fatigue fracture

Repeated cyclic torque and bending; stress concentrations

Shaft crack, shaft fracture, immediate drive failure, possible secondary equipment damage

9

4

6

216

Key (30C8 steel)

Shear or fatigue failure

High torque/shear load or shock; movement in keyway; material fatigue

Key shears, loss of torque transmission, shaft-hub slippage, coupling lockup

8

6

4

192

Keyway (shaft or hub)

Wear or fatigue cracking

Fretting; stress concentration at sharp corners

Loosening fit, increased vibration/backlash, key drop-out or shaft fracture

6

4

6

144

Flange (Gray cast iron)

Brittle fracture or fatigue crack

Overload or bending; casting defects or uneven loads

Flange crack/break, complete failure, possible equipment damage

9

3

7

189

Fatigue fracture or loosening

Cyclic bending; improper tightening; corrosion

Bolt breaks or loosens, flange separation or slip, loss of clamp preload

8

6

3

144

Misalignment/vib ration; torque loss

Shaft misalignment; thermal expansion; loose guards

Vibration/noise, accelerated wear, eventual failure

7

5

4

140

Bolts

Assembly

Table 1: Failure modes and effects analysis (FMEA) table

3.3 Interpretation of results

Deformation analysis revealed the highest displacement (0.27238 mm) occurring in the flanges, consistent with expectations for components made from gray cast iron, a material known for its brittleness and lower ductility.

However, the overall stress distribution within the flanges remained within the material’s permissible limits, suggesting a low probability of fracture under static loading. The bolts, although critical to assembly integrity, did not exhibit significant stress concentrations in the simulation, justifying their comparatively lower severity and occurrence ratings in the FMEA table [4].

The simulation-driven analysis of the rigid flange coupling provided critical insights into its structural integrity and potential failure mechanisms. The static structural results indicated a maximum von Mises stress of 355.93 MPa, concentrated at the shaft–key interface, which closely approaches the yield strength of the 30C8 steel used for the key. Additionally, the maximum shear stress— recorded at 170.53 MPa—further substantiates the key's susceptibility to shear-induced failure. These observations strongly support the FMEA outcome, wherein the key was assigned a higher Risk Priority Number (RPN) than the surrounding keyway, reflecting its greater vulnerability under applied torque.

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Importantly, the modal analysis provided valuable information regarding the system’s dynamic behaviour.

The first significant natural frequency, 230.95 Hz, was

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found to be substantially higher than the coupling’s operational excitation frequency (3.33 Hz at 200 rpm).

This wide separation effectively eliminates the possibility of resonance under normal service conditions, and as such, resonance-induced failure modes were deliberately excluded from the FMEA. The inclusion of modal characteristics in the failure analysis thus enhanced the robustness of the study by eliminating a common but potentially misattributed source of dynamic failure.

to be evaluated under realistic mechanical conditions rather than solely theoretical assumptions.

This approach allowed for data-driven assignment of RPN values and provided insight into the vulnerability of specific components, notably the key and shaft.

Additionally, the inclusion of modal analysis allowed resonance-related failures to be excluded with confidence, streamlining the focus toward more probable mechanical issues such as fatigue, shear, and friction.

Overall, the integration of simulation results into the FMEA framework allowed for an evidence-based assessment of failure risks. By correlating areas of high stress and deformation with material properties and loading conditions, the study provides a rational basis for prioritizing inspection, design modification, or preventive strategies.

The methodology demonstrates the effectiveness of combining structural simulation with engineering judgment in the context of early-stage failure assessment for mechanical assemblies.

The outcome is a structured and replicable methodology that strengthens early-stage design validation and failure prediction. It contributes both as a practical assessment of a commonly used mechanical joint and as a methodological reference for integrating simulation with failure analysis in mechanical engineering applications.

REFERENCES [1] Bhandari, V. B. Design of Machine Elements, 4th Edition, McGraw Hill Education.

4 Future Scope While this study provides a comprehensive failure mode analysis of a rigid flange coupling through structural simulation and FMEA, certain limitations open avenues for further work. For instance, dynamic loading conditions such as shock and vibration during start–stop operations were not simulated, and thermal effects were excluded.

Future studies may incorporate transient dynamic analysis, fatigue life prediction, and thermal-mechanical coupling to obtain more holistic insights.

[2] Stamatis, D. H. Failure Mode and Effect Analysis: FMEA from Theory to Execution, 2nd Edition, ASQ Quality Press, 2003.

[3] Khurmi, R. S., and Gupta, J. K. A Textbook of Machine Design, Revised 2022 Edition, S. Chand Publishing.

[4] Callister, W. D. Materials Science and Engineering: An Introduction, 10th Edition, Wiley.

The structured FMEA approach developed here lays a foundation for predictive maintenance frameworks in industrial environments. By identifying high-risk components such as keys and flanges, this methodology can support condition monitoring systems in anticipating failures before they occur. Furthermore, this analysis may aid design engineers in optimizing geometry, materials, or tolerances during early development, and assist maintenance planners in prioritizing inspections and preventive actions based on risk-priority values.

There is also scope to extend this work to different coupling types, compare alternative materials, and integrate machine learning-based health monitoring using historical failure data and simulation parameters.

5 Conclusion The simulation-assisted FMEA of the rigid flange coupling enabled the identification and prioritization of critical failure modes through a combination of structural analysis, modal analysis, and engineering judgment. By leveraging simulation results, the study enhanced the objectivity of risk assessment and enabled failure modes

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