A time-dependent damage operator approach to thermo-mechanical fatigue of Ni-resist D-5S

The damage operator approach is extended to time dependent viscoplasticity and creep. The oxidation is taken into account indirectly. Time efficient viscoplastic approximation based on the nonlinear Maxwell model and the corresponding lifetime prediction is presented. Both thermo-mechanical fatigue tests on the specimens and the thermal shock tests on turbine housings of a turbocharger subject to a complex change of temperature and strain are conducted for identification and verification purposes. The material is casting material Ni-resist D-5S. The research points out that the mean stress correction and the multiaxial criterion affect the predictive lifetimes significantly. For the turbine housing of a turbocharger the Smith–Watson–Topper mean stress correction, tensile-compressive creep and the critical plane mode I approach is the most suitable parameter combination. The lifetime predictions are convenient. The time consuming elastoviscoplastic finite element analyses can thus often be replaced by the elastoplastic FEA with kinematic hardening even at extreme conditions.