Effects of residual stress on the isothermal tensile behavior of nanocrystalline superelastic NiTi shape memory alloy

The residual stress greatly affects the mechanical behavior of a material. In this work, the effect of residual stress on the isothermal tensile behavior of NiTi shape memory alloy is studied. The focused ion beam (FIB) and digital image correlation (DIC) are combined to measure the two-dimensional residual stress in nanocrystalline NiTi plates processed with prestrain laser shock peening. A four-point bending experiment is used to verify the accuracy of this measurement method. The results show that FIB-DIC method is an attractive tool for measuring the two-dimensional residual stress in nanocrystalline materials. It is shown that the internal residual stress can significantly reduce the phase transition stress, and the mechanism is studied via finite element and theoretical analyses. This work demonstrates that the mechanical behavior of NiTi shape memory alloys can be tailored via residual stress engineering.