Three dimensional effects on mode I notch tip fields in a textured Magnesium alloy

Abstract

The objective of this work is to investigate the three-dimensional nature of stationary mode I notch tip fields in a basal-textured magnesium alloy. To this end, crystal plasticity based finite element analyses are performed pertaining to a four-point bend fracture specimen for two notch orientations. In the first orientation, the notch and line perpendicular to it are taken parallel to transverse and rolling directions, respectively, while in the second, they are chosen along normal and transverse directions. An additional simulation is performed corresponding to an isotropic plastic solid obeying the von Mises yield condition. The macroscopic results from the simulations agree well with an experimental study conducted pertaining to the first orientation. A pronounced thickness variation in stresses is perceived up to a radial distance of about 0.4 times specimen thickness from the tip. The stresses and plastic strains near the tip on the specimen mid-plane are higher for the ND-TD orientation, whereas on the surface they are more for the TD-RD case. In the former, multiple slip systems along with profuse tensile twinning is observed near the tip, whereas prismatic slip is preponderant for the latter. The strong anisotropy of this alloy manifests in terms of plastic zone shape and size, near-tip plastic strain/slip distributions and plane strain constraint ratio.