Variation of Poisson’s Ratio of NiTi During Pseudoelastic Deformation

NiTi alloy exhibits a stress-induced B2 ↔ B19' martensitic transformation. This transformation is practically isochoric, thus has a Poisson’s ratio of 0.5. This imposes a complex interaction with elastic deformation which has a lower Poisson’s ratio and with plastic deformation which is not recoverable when interacting with other materials in a composite or an assembly, thus a challenge for the design of such materials or devices using them. This study investigated the variation of the Poisson’s ratio of a NiTi alloy during pseudoelastic deformation by means of the digital image correlation technique. The Poisson’s ratio of the alloy was found to increase from 0.39 in the apparent elastic deformation stage to 0.44 prior to the onset of the Lüders-type deformation and then to 0.48 after the passing of the Lüders band.