Title：A Large Strain Elastic-Viscoplastic Self-Consistent Model for HCP Polycrystals

Speakers：Dr. P.D. Wu

　　　　　　Department of Mechanical Engineering,

　　　　　　McMaster University

Time：09:00-11:00, 05,July (Tues.) 2011

Venue：Room 468, Lee Hsun building

Welcome to attend! 

Abstract

A large strain elastic-viscoplastic self-consistent (EVPSC) model for HCP polycrystals is developed. At single crystal level, both the rate sensitive slip and twinning are included as the plastic deformation mechanisms, while elastic anisotropy is accounted in the elastic moduli. The transition from the single crystal plasticity to polycrystal plasticity is based on a completely self-consistent approach. It is demonstrated that the EVPSC model is a completely general elastic-viscoplastic, fully anisotropic, self-consistent polycrystal model, applicable at large strains and to any crystal symmetry.

The EVPSC model with various self-consistent schemes is evaluated by studying the deformation behavior of magnesium alloy AZ31B sheet under different uniaxial strain paths. 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 available options, the Affine self-consistent scheme results in the best overall performance.

Finally, the effect of the basal texture on the mechanical behaviour of AZ31B magnesium alloy sheet is studied numerically using the　EVPSC model. We simulate uniaxial tension within the sheet plane using starting textures having the basal poles tilted at varying degrees from the normal direction. It is found that increasing the tilt angle increases the uniform strain, but decreases the 0.2% proof strength and the R-value. The numerical results are found to be in good qualitative agreement with experimental observations.