Simulation on rate-dependent transformation pattern evolution of super-elastic NiTi alloy

Based on thin plate tensile tests of super-elastic NiTi alloy at different temperatures, a trilinear elasto-plastic constitutive model was adopted and the effect of latent heat of phase transformation on the temperature rise was considered through an equivalent method of thermo-physical constants.The transformation pattern evolutions were simulated by finite element software ABAQUS, and the rate-dependent mechanisms were also revealed. The simulated results show that the stress-induced martensitic transformation occurs under tensile loading, which macroscopically exhibits as the initiation, propagation and merging of local transformation bands; due to the release of latent heat, the initiation of transformation bands is accompanied by local temperature rise, and peak temperature rise is closely related to the loading strain rate; the local transformation bands are at a certain angle to the loading direction, which is about 50°-65°; with the increase of loading rate, the sample is changed from the isothermal state to the adiabatic one, the transformation stress and local temperature rise increase then. Therefore, the transformation tends to occur in the low temperature region, which results in an increasing number of transformation bands. The simulated transformation patterns and temperature field evolutions of super-elastic NiTi alloy at different strain rates are in good agreement with the corresponding experimental results, which provide a reference for clarifying the evolution of transformation localization of the alloy.