Thermo-Mechanically Coupled Phase-field Fracture Model Considering Elastocaloric Effect of Shape Memory Alloy

Modeling the fracture behaviour of the shape memory alloy (SMA) that interacts with martensitic transformation and the associated elastocaloric effect (eCE) still remains challenging. Herein, a thermo-mechanically coupled phase-field fracture model considering the elastocaloric effect of SMA is proposed to simulate the cracking process coupled with non-isothermal martensitic transformation and the associated eCE. In the phase-field model, both the thermal strain induced by eCE and the eigen strain induced by the phase transition are considered. An empirical degradation function is adopted to describe the thermal conductivity decreasing with the fracture order parameter. The model is validated with the finite element method and tensile fracture properties of Mn-Cu SMA are simulated. It is found that the martensite variant nucleates at the stress concentration where the crack initiates, and commonly spreads at an angle of 45 degree. The thermal expansion strain caused by the eCE could strengthen the critical load capacity. A high phase transformation rate and a low temperature can increase the critical fracture strain and decrease the critical load. The rising effect of critical fracture strain exhibits significant anisotropy. The phase-field model demonstrates its ability in the thermal-mechanically coupled fracture simulations of SMA. It also provides a possible fracture-resistance strategy by the utilization of eCE for elastocaloric devices.