Abstract
Presented is a simulation of microcrack growth under alternating stresses. Microstructural barriers and the state of stress play a dominant role in the early stages of crack growth of metals. The polycristalline metal was modeled as an aggregat of hexagonal grains with a different crystallographic orientation of each grain. The effect of grain bounderies on stage I crack growth is considered in the model. The mode of sear crack growth is analyzed on the basis of microstructural crack growth within the first few grains, where the crack growth decelerates as the crack tip gets closer to the grain boundery. Normal stress crack growth has been considered for those cracks which are longer than microstructurelly short cracks, socalled physically small cracks. Furthermore the transition from stage I to stage II growth is considered. The model is applied for thinwalled tubular specimens of the ferritic steel AlSI 1015 and the aluminium alloy Al Mg Si 1 subjected to tension and torsion as well as combined tension-torsion loading. Also different load sequences are investigated. The microstructural crack pattern and crack distribution can sucessfully simulated with the model. The crack growth behaviour and the effect of lifetime until a crack length of 500 μm ist presented for numerous parameters.
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