Phase-field models (PFMs) have established in the last 20 years in materials science, offering a thermodynamically consistent approach to describe microstructure evolution with solid and liquid phase transitions under various physical fields. In this talk, the focus is set on shape memory alloys as a class of functional materials with applications in actuation, sensing and solid state cooling.
Ferromagnetic shape memory alloys (FSMAs) exhibit a magneto-mechanic coupling under an external magnetic field. A micromechanic approach is chosen, where each twin variant is represented by a different phase field and the magnetization is computed on a finite difference grid using a spectral method. For polycrystalline NiTi thin films used in microcooling, the PFM is used to track the local deformation patterns on a coarse grained scale, capable to calculate the full device in standard FEM frameworks. The thermomechanical coupling in the simulations leads to sharply defined strain bands with accompanying thermal effects that well match the experimental data based on IR thermography and digital image correlation.
