Fatigue damage accumulation modelling in the range of complex low-cycle loadings – The strain approach and its experimental verification on the basis of EN AW-2007 aluminum alloy

The paper presents the fatigue damage accumulation model created to analyse fatigue life of structure elements operating in conditions of multiaxial, non-proportional low-cycle loadings. The authors used the approach connected with the critical plane in the presented model. In the discussed approach the damage variable depends on the stress damage accumulation function and the increments of plastic non-dilatational strain. The components of the stress and strain tensor in the conditions of complex low-cycle loadings were determined using constitutive relations and the law of kinematic hardening. It was assumed that cracks occur when either the normal stress or damage variable on any physical plane reaches critical values. The presented model was verified experimentally on the base of EN AW-2007 aluminum alloy. The main body of tests were performed in the conditions of biaxial loadings (tension–compression and torsion), proportional and non-proportional, according to the assumed research program, on research stands which allow performing complex loading histories. These were preceded by uniaxial loading state tests (cyclic tension–compression or torsion) on the basis of which parameters of the calculation model should be calculated.