K Variations and Anisotropy: Microstructure Effect and Numerical Predictions

K Variations and Anisotropy: Microstructure Effect and Numerical Predictions

Computer experiments were performed on simulated polycrystalline material samples that possess locally anisotropic microstructures to investigate stress intensity factor ( K ) variations and anisotropy along fronts of microcracks of different sizes. The anisotropic K , arising from inhomogeneous stresses in broken grains, was determined for planar microcracks by using a weight function-based numerical technique. It has been found that the grain-orientation-geometry-induced local anisotropy produces large variations in K along front of microcracks, when the crack size is of the order of few grain diameters. Synergetic effect of grain orientation and geometry of broken grains control K variations and evolution along the microcrack front. The K variations may diminish at large crack sizes, signifying a shift of K calculation to bulk stress dependence from local stress dependence. Local grain geometry and texture may lead to K anisotropy, producing unusually higher/lower K at a segment of the crack front. Either K variation or anisotropy cannot be ignored when assessing a microcrack.