Simulation of microcrack growth for different load sequences and comparison with experimental results

Generally, most machine parts are loaded with a combination of different variable forces and moments which often causes a state of multiaxial stress in the fatigue critical areas of the parts. In this paper, a model designed to simulate the damage process based on the growth of microcracks under the influence of cyclic loading is presented. The crack growth is initially dominated by shear stresses leading to microstructurally short cracks (stage I) and continues to grow under the influence of normal stresses (physically short cracks). The model is applied to tubular specimens of the aluminum alloy AlMgSi1, steel SAE 1015 and notched specimens of 42CrMo4V which are subjected to multiaxial random loading and loading sequences of high-low/low-high stress or a consecutive loading of torsion-tension/compression and tension/compression-torsion for various loading sequences. In terms of the microcrack distribution as a function of their orientation, the simulated crack growth behaviour reveals a close match with the experimental results. The results of the lifetime estimation generated by means of the new concept on the basis of microcrack growth are compared and verified with those experiences obtained from multiaxial fatigue testing.