MSE Seminar: Harshad Paranjape, Modeling of Shape Memory Alloys: Phase Transformation/Plasticity Interaction at the Nano Scale and the Statistics of Variation in Pseudoelastic Performance

Abstract

Shape memory alloys (SMA) exhibit two interesting properties due to a reversible martensite phase transformation that they undergo. First, they “remember” their high temperature shape, irrespective of the deformation imposed at a lower temperature. Second, they produce large recoverable strain on isothermal stretching. Because of these, SMAs are commercially used in actuators and arterial stents. However there are two issues hindering their wider use. First, their performance degrades on stress or thermal cycling; due to defect generation and accumulation. Second, the performance of polycrystalline SMAs depends on a variety of factors; making alloy design a difficult process. These issues are addressed through a modeling based approach spanning nano and micro length scales.

A new modeling approach is developed that couples the deformation mechanisms of phase transformation and plasticity at nano-scale. It is implemented in a finite element framework, allowing modeling of complex boundary conditions. Two case studies are presented to investigate martensite induced plasticity. These modeling studies couple with the state-of-the-art micron-scale experiments on Ni-Ti SMA being carried out in our department. At the micro scale, factors influencing the granular performance in polycrystalline SMA are systematically studied. Key outcomes of this are- a predictive function of performance in terms of grain neighborhood and strategies to improve performance.

Bio

Harshad got interested in computational materials science while doing undergraduate research. He graduated with a Bachelor of Technology degree in Materials Science from the Indian Institute of Technology Bombay in India. Since fall 2009, he is part of the mechanical behavior computing lab, pursuing his Ph.D. under the guidance of Dr. Peter Anderson. During this time, he has mainly worked on modeling the mechanical response of shape memory alloys at the continuum scale and additionally modeled electrospun fiber scaffolds. Harshad enjoys running, photography and painting in his spare time.