Measurement of two-dimensional residual stress in nanocrystalline superelastic NiTi fabricated with pre-strain laser shock peening

The measurement of residual stress is a challenging issue in industrial fields. In this work, focused ion beam (FIB) and digital image correlation (DIC) are combined together to measure the two-dimensional residual stress in nanocrystalline NiTi plates processed with pre-strain laser shock peening (LSP). A four-point bending experiment verifies the accuracy of this measurement method. The pre-strain LSP-treated surfaces are found to have significant compressive residual stress along the pre-strain direction and tensile residual stress along the vertical to pre-strain direction, which verifies pre-strain LSP as an efficient approach to create gradient residual stress layers in nanocrystalline NiTi plates. The FIB-DIC method has also proven to be an attractive tool to measure the two-dimensional residual stress in phase transition nanocrystalline materials.