a b s t r a c tVarious self-consistent polycrystal plasticity models for hexagonal close packed (HCP) polycrystals are evaluated by studying the deformation behavior of magnesium alloy AZ31B sheet under different uniaxial strain paths. In all employed polycrystal plasticity models both slip and twinning contribute to plastic deformation. The material parameters for the various models are fitted to experimental uniaxial tension and compression along the rolling direction (RD) and then used to predict uniaxial tension and compression along the traverse direction (TD) and uniaxial compression in the normal direction (ND). An assessment of the predictive capability of the polycrystal plasticity models is made based on comparisons of the predicted and experimental stress responses and R values. It is found that, among the models examined, the self-consistent models with grain interaction stiffness halfway between those of the limiting Secant (stiff) and Tangent (compliant) approximations give the best results. Among the available options, the Affine self-consistent scheme results in the best overall performance. Furthermore, it is demonstrated that the R values under uniaxial tension and compression within the sheet plane show a strong dependence on imposed strain. This suggests that developing anisotropic yield functions using measured R values must account for the strain dependence.

Recent experimental studies have reported improved combinations of strength and uniform elongation in ultrafine-grained polycrystals with bi-modal grain size distributions. Despite these results, the extent to which the grain size distribution affects macroscopic tensile response, particularly at large strains, is unclear. This issue is examined here for polycrystals with varying grain sizes and grain size distributions using a grain size dependent constitutive model within the viscoplastic self-consistent formalism. The evolution of the macroscopic and grain-level stresses and strains has been monitored as a function of the width and mean of the grain size distribution. As an example of highly heterogeneous structures, the stress–strain response of a number of bi-modal microstructures have been examined and compared with their uni-modal counterparts.

No abstract

No abstract

No abstract