Shape Recovery Effects of Solid, Forged Nitinol Products In Orthopedics

As Nitinol emerges to find more applications in engineered medical device products, understanding the effects of material processing becomes increasingly important. Its mechanical behavior is highly non-linear and is strongly dependent on alloy composition, heat treatment history and mechanical work. Published Nitinol literature is almost exclusively related to processing and testing of thin wall tubing and wire devices, usually exhibiting superelastic characteristics. There is a dearth of information in the public domain regarding the compressive deformation mode of solid blocks of Nitinol and whether or not “bulk” Nitinol products can exhibit shape recovery effects and superelastic characteristics. The potential for strain recovery of compressed solid Nitinol products, combined with the material's low modulus and biocompatibility can enable the design of improved medical devices, specifically in the orthopedic realm. The motivation for this research is to provide the first characterization of the shape recovery effects of “bulk" size, solid Nitinol material under compressive deformation versus the often practiced and well understood tensile loading of wire and thin wall tubing.