Behaviour of Young’s Modulus in Shape Memory Alloys upon Mechanical Loading

Abstract

The behavior of the Young’s modulus vs. strain relationship of shape memory alloys was investigated in uniaxial tension on NiTi polycrystalline wires of different phases and in an austenite CuAlNi single crystal under uniaxial compression. In all tests, there is an apparent V-shape in the Young’s modulus vs. strain relationship, where the bottom is at round the point where hardening starts. Optical observation of the CuAlNi sample surface reveals that the occurrence of V-shape is accompanied by the abrupt reorientation of martensite variant(s). It is concluded that the same mechanism should be re-sponsible for the similar phenomenon in polycrystals. Reorientation of martensite variant(s), which was clearly observed in CuAlNi single crystal by surface study, is suggested as the mechanism behind this phenomenon