Deformation behaviour and numerical fatigue lifetime prediction of metallic materials under multiaxial nonproportional loading

The development and evaluation of a model for lifetime prediction under multiaxial nonproportional loading is the aim of the current research project. It is assumed that the technical crack initiation life is consumed by short crack growth. This phenomenon is described using a fracture mechanics based approach. Herein, the effective cyclic J-integral is used as crack tip parameter. Crack opening levels and J-integral values are calculated applying approximation formulas. A plasticity model that is based on the Jiang model [Jia93] and extended to describe nonproportional hardening is used to predict the deformation behaviour. Experimental investigations on tubular and notched specimens with a wide range of different loading spectra serve for the verification of the model and for the identification of damage mechanisms.