Deformations and damage to metallic materials under multiaxial non-proportional loading

The responsibility for the safe operation of engineering structures calls for trustworthy data and models to assess fatigue life. Material science develops models on the microscopic scale whereas engineering science has to consider length and time scales which can give accurate quantitative answers. In multiaxial non-proportional fatigue the applied plasticity models should be capable of capturing the non-proportional hardening and ratcheting with adequate accuracy. The capabilities of a previously introduced model are featured with respect to out-of-phase loading of stainless steel. In engineering the meso scale of about 10 μm turns out to be the smallest accessible scale of observation of fatigue damage. At this scale fatigue of metals is seen as growth of short surface cracks. A phenomenological model is proposed for describing the short crack growth taking into account non-proportional straining. Calculated and experimentally determined crack growth curves and lives to technical crack initiation have been found to be in reasonable accordance. Future research activities are indicated.