Mesoscale investigation of constitutive behaviour of HCP metals based on full-field in situ strain measurement
Loading...
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022.
Abstract
Hexagonal close-packed (HCP) metals have received extensive attention from research and industrial communities for their exceptional properties. Among these HCP metals, Magnesium is the lightest and the most intriguing one. Its deformation incorporates significant twinning that depends heavily on microstructure and loading conditions. For this study, a common Mg alloy (AZ31) is considered with multiple crystallographic textures to aid the fundamental understanding of its deformation. This is predominantly an experimental effort with a novel in-situ digital image correlation (DIC) technique that provides deformation quantification with granular resolution over macroscopic fields. Further, samples are subjected to cyclic to study spatial aspects of strain accommodation via twinning, detwinning and slip plasticity. Shear band formation and progression due to the bursts of twins is quantitatively detailed and it is demonstrated that unlike twinning, detwinning is a nearly homogeneous phenomenon. Further tension after detwinning forces the material to plasticity. Another load reversal to compression pushes the material back into twinning regime but with reduced shear band compactness. It is also shown that the Lüders-like bands form with lower strain content in extruded samples compared to rolled samples that also show extreme plastic anisotropy. An open source spatially- resolved crystal plasticity solver (DAMASK) is used to test the fidelity level of basic constitutive models when confronted with twin coordination and detwinning. Two sets of representative volume elements (RVEs) are produced for both textures. In both cases, the simulated plastic deformation occurs earlier with considerable hardening at the twin plateau deviating from the near perfectly-plastic experimental results. The model is found to be incapable of predicting the strain compactness and intense anisotropy of the rolled sample shear bands. It is also not geared to model detwinning, highlighting the need for more advanced models if the goal is to attain high fidelity in micro-scale fields.