PSI - Issue 18

Matthias Hell et al. / Procedia Structural Integrity 18 (2019) 823–836 Hell et al. / Structural Integrity Procedia 00 (2019) 000–000

833

11

5. Application of the transfer functions

Fig. 13 shows the fatigue life estimation for a round specimen made of 42CrMo4+QT quenched and tempered heat treatable steel. The results of the fatigue assessment underestimate the experimental fatigue life. This is mainly related to the fact, that only the notch support effect is implemented by the numerical modeling.

Fig. 13. Comparison between numerical and experimental fatigue for notched specimens made of 42CrMo4+QT

The related volume or area integrals over the stress function, which are required for the application of the Weakest Link approach acc. to Weibull can be calculated from the finite element results during the postprocessing. As Fig. 14 indicates, for the given fatigue life estimation of the notched specimen, the application of the Weakest Link Approach improves the numerical results in comparison with the experimental test results.

Fig. 14. Additional consideration of the statistical size effect improves fatigue assessment

The deviations in the slope of the S-N curve may be resulting from the cyclic softening of the material in the LCF Regime. In case of constant amplitude loading, a simplified approach in order to assign a cycle dependent material behaviour is shown in Fig. 15. For constant cycles, the points describing the stress-strain relation are extracted from the cyclic deformation curves under strain cycling with constant amplitude loading. With respect to the load magnitude, those curves are implemented in the numerical model.