Strain mapping at propagating interfaces in pseudoelastic NiTi

Abstract
Pseudoelastic NiTi often exhibits an inhomogeneous martensitic phase transformation: Martensite bands propagate through the specimen, distinct phase interfaces separate transformed from untransformed regions, and local strains increase step-like but smoothly by ~5 % across these interfaces. In the present study, we use an advanced strain mapping method (digital image correlation) to characterize local strain states and strain rates at propagating phase interfaces in a thin NiTi ribbon. The resulting strain data allows a detailed analysis of the interface geometry. The narrow transition regions are characterized by a finite width of 4-5 mm which generally increases near the outer edges of the specimen. Furthermore, the maximum local strain rates at the interfaces are one order of magnitude higher than the macroscopic strain rate that is usually used to characterize thermo-mechanical loading conditions.