Cyclic deformation and the interplay between phase transformation and plasticity in shape-memory alloys.
Kaushik Bhattacharya (California Institute of Technology)
Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials
Mon 9:00 - 10:30
MacMillan 117
This work seeks to understand the the cyclic behavior of shape-memory alloys. The shape-memory effect as well as super-elastic properties evolve with cycling as a result of interplay between phase transformation and plasticity. The interplay between these two modes of deformation becomes especially intricate in polycrystalline materials due to crystalline anisotropy and inter-granular constraints. For example, plastic slip enables the progression of transformation that is inhibited by intergranular constraints; it may also retard the reverse transformation due to the creation of microscopic stress. The interplay can also have important technological implications like the loss of memory during cycling in shape-memory alloys and unusual strain-rate effects in steel. Unfortunately, this is a difficult multi-scale problem with the formation of intricate transformation and dislocation structures at the sub-granular level and the complex interactions across multiple grains. Consequently, the interplay between these two mechanisms and their combined effects on the macroscopic response of polycrystalline materials remains poorly understood. This talk will describe a computational study of this interplay. We start with a coarse-grained model at the single crystal that implicitly accounts for the transformation and dislocation microstructures. This makes the model quite efficient and allows us to study polycrystalline specimens. The results provide interesting insights into the phenomenon, and provides hint for the development of a detailed macroscopic model.