Calculation of the fatigue limit of pulsed laser hardened specimen based on an engineering interpretation of the weakest-link concept

Specimen made of two steels, a 42CrMo4 (SAE 4140) and a 100Cr6 (SAE 52100), are hardened with a pulsed Nd:YAG-laser and tested under cyclic bending. A method based on Weibull’s weakest-link concept is developed to calculate the fatigue limit. The probability of endurance is calculated at each material point in order to take into account the local differences of quantities influencing failure like, e.g., the applied and residual stresses, the roughness and the hardness. Multiaxial stress states are considered by an equivalent stress criterion based on the approach of Dang Van. The model allows for two material-dependent fit parameters to adjust experimental results and theoretical predictions. The fatigue limit is determined by varying the applied load until the total endurance probability equals 0.5.