PSI - Issue 57

Felix-Christian Reissner et al. / Procedia Structural Integrity 57 (2024) 411–419 F.-C. Reissner et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 4. Comparison between the simulated residual stresses and XRD measurement for (a) EN-GJS-700-2 and (b) 34CrN iMo6+QT with an assumed standard deviation of 50 MPa for the XRD measurement.

The change in the residual stresses is approximated by simulating two load cycles. After two load cycles there is already a significant change in the residual stresses for both materials, especially at high load levels, Figure 5. However, it cannot be assumed that the residual stresses have converged after two load cycles. To remove the influence of the last half cycle on the residual stresses, the difference of the residual stresses at the reversal point of the last cycle is taken as the final residual stress.

Fig. 5. Transformation of the residual stresses after two load cycles at different torque amplitudes for (a) EN-GJS-700-2 and (b) 34CrNiMo6+QT.

4. Lifetime Assessment 4.1. Estimation method for design S-N Curves

As shown in Section 2.2 and 3.2 the residual stresses and the change of residual stresses has an influence on the fatigue strength and should be considered when estimating the design S-N curve of a component. However, design guidelines such as the FKM-Guideline usually do not consider a change of residual stresses. Nevertheless, chapter 5.5 of the FKM-Guideline contains a method which can be augmented by the use of simulated residual stresses to overcome this problem. From the simulation, the residual stresses at the surface and the position of the transition point are needed. The transition point is defined as the point, where the residual stresses change from compressive to tensile stresses. In addition, the hardness at the surface is needed for cast iron. In the following, the application range of chapter 5.5 of the FKM-Guideline is extended to include cast iron and the results for both materials are shown.