Multi-scale modeling of deformation of a magnesium alloy

摘要

At present a lack of suitable computer aided engineering tools to simulate multimaterial vehicle structures involving magnesium components is an impediment in incorporating magnesium alloys into automotive structures.;This dissertation is devoted to the development of predictive capabilities for modeling the deformation of Mg alloys for three dimensional loadings. Using two modeling approaches it is demonstrated that only by accounting for the combined effects of anisotropy and tension-compression asymmetry both at single crystal and polycrystal level, it is possible to explain and accurately predict the peculiarities of the behavior of magnesium and its alloys.;Two modeling frameworks, namely a self-consistent polycrystal model that accounts for tension-compression asymmetry introduced by twinning, and a macroscopic anisotropic plasticity model based on an orthotropic yield criterion that accounts for tension-compression asymmetry in plastic flow at polycrystal level were used. It was shown that unlike Hill's (1948) criterion, the latter macroscopic criterion quantitatively predicts the experimental results in torsion and axial crushing.Specifically, for the first time axial effects in torsion were predicted with accuracy using a polycrystalline framework. Moreover, it was shown that the observed experimental axial effects in torsion can be quantitatively predicted only if both slip and twinning are considered active, the level of accuracy being similar to that of the macroscopic model. However, if it is assumed that the plastic deformation is fully accommodated by crystallographic slip, the predicted axial strains are very close to that obtained with Hill (1948) criterion, which largely underestimates the measured axial strains in one orientation (along rolling direction) and cannot capture at all the development of axial strains in torsion along the normal direction.;For the first time, the unusual features of the buckling behavior of Mg AZ31 were explained. Furthermore, it was clearly demonstrated that the critical stress, the level of axial strain at buckling, and the deformed profiles can be predicted with accuracy.