TTCI R&D
Determining Residual Stresses in Rails using Contour Method Research on residual stress estimation Ananyo Banerjee, Ph.D., Principal Investigator Transportation Technology Center, Inc.
technique involves cutting a specimen into two pieces and measuring the resulting deformation. The measured displacement data results are used to compute residual stresses through an analysis that involves FEA models of the specimen as deformed and as reconstrained.5
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The output is a two-dimensional map of residual stress normal to the measurement plane. Four rail samples were tested in two phases for this residual stress analysis. The first set of specimens sent for analysis comprised a new rail that was received from a manufacturer and had never been laid on
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ransportation Technology Center, Inc. (TTCI) recently generated estimates of residual stresses in railroad rail using the relatively new Contour Method. Modern cutting tools such as wire electric discharge machining (EDM), as well as advanced finite element analysis (FEA) and precision mapping of displacements at the micrometer scale, have led to the development of the Contour Method. Results provided maps of residual stress distributions of a new rail and three rails of differently worn head profiles. Analyses of the compressive and tensile residual stresses of the cross-section of the rails are being used to predict likely areas of highest tensile stresses in the rails.
Background Residual stress estimation has been a challenging area of research over the last few decades. X-ray and neutron diffraction measurements of atomic lattice spacings, interpreted as residual strains,1 have been used on rails as seen in Figure 1a, and other methods have used direct measurement of residual strains by instrumenting the rail cross-section with strain gages as seen in Figure 1b.2 TTCI has done previous research on residual stress estimation on a variety of metal components such as wheels, joint bars, and welds. The results gave some good indications of compressive and tensile stress distributions on the external surfaces, but no stresses within the cross-sections were determined from this approach.3,4 In all cases, the strain gage method was used as indicated with small rectangles in Figures 1c and 1d. Contour Method The Contour Method is a fairly new method of estimating residual stresses. The 4 Railway Track & Structures // May 2020
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Figure 1. (a) X-ray measurement of residual stresses in transverse direction of a worn rail; strain-gage rosettes installed on (b) cross-section of a rail head; (c) outer circumference of wheels; and (d) outer surface of a weld.
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