Computational framework for fatigue analysis of metals with nonconstant cyclic stress-strain curve

The cyclic stress-strain behavior is often modelled using the Ramberg-Osgood equation assuming that the material-related parameters are constant. However, nonconstant cyclic deformation curves are observed due to hardening or softening of the material. Fatigue tests of an experimental X2CrNiCuN17-6-4 steel were analyzed to determine the parameters in several intervals with the result that they were nonconstant. The parameters were fitted by a polynomial function to calculate the increase of damage for each cycle individually. Repeating this procedure up to the damage sum of one delivers the lifetime. The study shows the increase of computation accuracy from the approach of constant parameters to the approach of calculating the damage per cycle with transient material parameters.