Cycling-induced evolution of transformation strain bands in superelastic NiTi

Cyclic super elasticity in shape memory alloys (SMAs) is governed by complex transformation mechanisms that evolve under repeated loading, yet these stabilization effects remain insufficiently resolved at the full-field scale. This work presents an experimental investigation of the cyclic superelastic response of Nitinol subjected to 77 loading cycles, with particular emphasis on the progression of stress-induced martensitic transformation. High-resolution digital image correlation (DIC) was employed to capture in-situ strain localization and the corresponding evolution of transformation morphology. The full-field measurements reveal distinct changes in transformation band formation, propagation, and recovery as cyclic stabilization develops. Local strain evolution was further analyzed to elucidate micromechanical deformation pathways that influence functional fatigue behavior. The results provide new insight into the spatially heterogeneous deformation characteristics of Nitinol under cyclic superelastic loading, offering experimentally grounded evidence critical for advancing intelligent material systems and their reliability in repetitive actuation or structural applications.