Local fatigue strength assessment of induction hardened components based on numerical manufacturing process simulation

Induction hardening as common heat treatment process for highly-stressed automotive components significantly affects the surface layer properties leading to a compressive residual stress condition and a local hardening of the material. The beneficial effect of the post-treatment is generally well investigated and already implemented in industrial applicable guidelines by considering nominal fatigue strength enhancement factors. However, as the fatigue strength improvement essentially depends on the applied manufacturing process parameters, the resulting local material properties and the local load stress distribution, an elaborated numerical fatigue assessment procedure based on a manufacturing process simulation of a notched round specimen is presented in this paper. Thereby, a two-dimensional axi-symmetric model is set-up, whereby the inductive heating process is performed in COMSOL® and the subsequent quenching process in SYSWELD®. The resulting axial residual stress condition at the notch area of the specimen reveals a sound accordance to X-ray measurements. Finally, a local fatigue strength assessment based on the local strain approach is shown. Herein, manufacturing dependent residual stress states are considered as mean stresses on the basis of the damage parameter by Smith, Watson, and Topper. The estimated fatigue data points agree well to results of four-point bending fatigue tests, which basically prove the applicability of the presented fatigue design methodology.