Crack nucleation and growth modeling in biaxial fatigue

Abstract Differences in stress state, strain level and material type are known to significantly influence the fatigue cracking behavior of metals. Two modes of shear crack growth have been considered. Cracks may nucleate within individual grains and grow by coalescence mechanisms. In the analysis of this mode, a polycrystalline material was modeled as an aggregate of square grains with a double primary-conjugate slip system. A dislocation model is used to compute the nucleation of cracks within individual grains. In the second mode, cracks become large enough to generate their own stress fields and grow as a single dominant crack. This mode is analysed using fracture mechanics concepts with an equivalent strain intensity factor. The cracking behavior of a material is determined by a competition between the two modes of cracking. The model was employed to simulate cracking behavior in SAE 1045 steel. Both crack distribution and fatigue life estimates were obtained from the model. Good correlation between experimental and analytical results was found.