Joshi Research Group

Materials and Mechanics Research

Size-effects in crystal plasticity Internal stresses in FCC metals

Slip and twinning in pure Mg and Mg-composites

Magnesium (Mg) and its composites are potential candidates for structural applications ranging from energy-savvy automotive and aerospace sectors to biomedical components, due to its low mass density (~35% lighter than aluminum) and excellent biocompatibility. There has been a renewed emphasis toward developing novel micro-architectures with impressive specific strengths (strength/ density) using pure Mg or its alloys by inducing barriers to plastic deformation through a variety of techniques including grain size refinement, nano-reinforcements, or combinations thereof. A cleaner understanding of the inelastic deformation mechanisms in Mg is also vital to successful applications. However, modeling such intricate holistic responses is a challenging task because of the myriad interactions between the different deformation mechanisms that prevail in this hexagonal close-packed (HCP) crystal structure. In this project, we developed a Single Crystal Plasticity (SCP) model for pure Mg that attempts to address the following objectives:

  1. To provide improved phenomenological descriptions of slip and twin (compression as well as tension twins) v.f. evolution including the slip-slip, twin-slip and twin-twin interactions while retaining the basic structure of the conventional self- and latent-hardening laws.
  2. To rigorously characterize the material parameters corresponding to these improved descriptions by simulating a range of experiments and critically corroborating the orientation-dependent macroscopic and microscopic responses through single crystal simulations.
  3. To probe the effect of the twinning-induced lattice reorientation on the strain hardening behavior vis-à-vis the twin v.f. evolution and the effect of initial defect population (e.g. initial twin v.f.) on the macroscopic response for twin-friendly orientations.
  4. To use the constitutive parameters of single crystal Mg in predicting the macroscopic responses of polycrystalline pure Mg with different textures.
  5. To apply the SCP model in predicting the orientation-dependent micro-macro characteristics of pure Mg single crystals with embedded inclusions in connection with its applicability to Mg composites.

The bottom-up approach from single to polycrystalline simulations provides several exciting prospects. It provides a way to explicitly investigate effects of grain orientation, size and shape distribution effects. The approach could be further enhanced by accounting for grain boundary effects such as grain boundary sliding, probabilistic descriptions of the twin nucleation. Another important direction that interests us is that of systematically incorporating the effects of alloying elements on the slip and twin system characteristics of single crystals. Also, the temperature dependence of the slip and twin modes of single crystals would be a vital extension to render its utility in addressing formability and texture evolution. Our on-going effort aims at incorporating size-effects in pure Mg.

Funding Agencies