Numerical simulations of ductile crack initiation and growth in a textured magnesium alloy

In this work, the mechanics of ductile fracture near a notch tip in a basal textured Mg alloy is investigated through crystal plasticity based finite element analysis. An array of circular voids ahead of the tip subjected to mode I, plane strain, small scale yielding conditions is modelled. The effect of plastic anisotropy is examined by considering two notch orientations and contrasting the results against an isotropic plastic solid. The notch and the line perpendicular to it are chosen parallel to the transverse and rolling directions (TD and RD) in the first orientation, and along normal direction (ND) and TD in the second orientation. The TD-RD and isotropic cases show void-by-void growth for low initial porosity, fv0, and simultaneous multiple void growth for high fv0. By contrast, the ND-TD orientation displays the former even at high fv0. This is attributed to slower porosity evolution with J for this case due to high macroscopic hardening in the voided cells caused by pyramidal slip and tensile twinning. The predicted crack growth resistance curves are also strongly influenced by fv0 and notch orientation.