Micromechanical investigation and numerical simulation of fatigue crack formation in welded joints

The present study is directed to the nucleation of micro cracks in polycrystalline metals due to fatigue. For this purpose, a micromechanics based numerical procedure is established. This procedure is based on the assumption that in the initial phase, the fatigue crack propagation follows the slip planes of the individual grains. The crack propagation is modelled in terms of a damage mechanics concept, assuming that fatigue damage is driven by the dissipated microplastic work. Using a generalized homogenization approach, the results of the micromechanical simulation are transferred to the macroscopic level. Using a stochastic finite element analysis, the corresponding uncertainty and scatter are assessed. The numerical scheme is validated against micromechanical experimental investigations of the crack formation using micro scale specimens with gauge sections in the range of 200 µm × 450 µm.