Thermo-mechanically coupled superelastic response of initially-textured Ti-Ni sheet

摘要

A three-dimensional crystal-mechanics based model for the thermo-mechanically coupled superelastic response of initially-textured polycrystalline shape-memory materials is used to simulate the response of Ti-Ni shape-memory alloy in sheet form. Both manifestations of superelasticity: stress-strain response at a fixed temperature, and strain-temperature response at a fixed stress have been experimentally studied. The model, when suitably numerically implemented and calibrated, is shown to accurately predict the anisotropic superelastic response of tension specimens which were cut along different directions to the rolling direction of the sheet. Also, the strain-temperature cycling experiments under different constant axial stresses are predicted with reasonable accuracy. The effects of self-heating and cooling due to the exothermic and endothermic nature of the austenite-to-martensite and martensite-to-austenite transformations were investigated by performing superelastic tension experiments at strain rates which are high enough to result in non-isothermal testing conditions. The thermo-mechanically coupled theory is able to capture the resulting inhomogenous deformation associated with the nucleation and propagation of transformation fronts, and also the 'apparent hardening' of the nominal stress-strain curves observed in the experiments.