Effect of Impact-Induced Strain on the Stress-Induced Martensitic Transformation of Superelastic NiTi Shape-Memory Alloy Wires

The stress-induced martensitic (SIM) transformation of NiTi shape-memory alloy wires has been studied as a function of the maximum strain induced during tensile deformation at impact and quasi-static strain rates. The SIM transformation stresses are higher at impact than at quasi-static strain rates. Only the lower plateau strength is sensitive to the maximum strain achieved during transformation when this is higher than necessary to complete the SIM transformation. For the same maximum strain achieved, the deformation energy (E d) and recoverable strain energy (E r) are greater at impact than at quasi-static strain rates, and the dissipated energy (W d) is slightly lower at impact, reaching values close to those obtained at quasi-static strain rates.