Modeling Rate Dependent Response of Shape Memory Alloys Using a Thermo-Mechanical Continuum Phase Field Approach

Abstract

A recently developed thermomechanically coupled, thermodynamically consistent, constitutive model based on phase field theory is used to describe the rate dependent response of polycrystalline shape memory alloys (SMAs). The model, which constitutively accounts for transformation rate, is used to study the evolution of phase transformation coupled with different mechanical and thermal response of SMA. The goal is to model the rate dependent behavior of SMAs. Phase transformation is simulated for an SMA axisymmetric rod. Simulation conditions are varied between isothermal and adiabatic conditions under quasi-static pseudoelastic loading. The effect of kinetic coefficient, which relates to the phase transformation kinetics, is studied. Stress relaxation and creep behavior reported in experiments is described. Heterogeneous rise in temperature, which occurs at the material interface as well as its influence on thermal hardening for different loading rates are also described. Results suggest that the rate dependency in SMA is a result of the latent heat of transformation, heat conduction and convection, strain rates, transformation kinetics and their couplings. Therefore, this work demonstrates that the reported model is able to capture the rate dependent response of SMA constitutively. The simulation results affirm the need for application specific testing conditions in order to account for the complex thermomechanical interaction, rate dependency and length scale effects in the design of SMAs. Based on these simulation results, the model provides new insight into the design of SMAs for thermomechanical engineering applications