Characterization of elastic and transformation behavior of NiTiNOL tube under radial loading.

The stress-induced transformation from austenite (B2) to martensite (B19’) in NiTiNOL is highly sensitive to crystallographic texture and the nature of the applied mechanical load, regardless of processing parameters such as transformation temperature, extend of cold work, and thermal treatment history. Notable differences in transformation (plateau loads) onset and hysteresis have been observed between tensile and compressive loading modes. Similar deviations have been observed under torsional loading in tubular specimens, challenging the applicability of Von Mises' equivalency in describing transformation behavior. Texture-dependent transformation responses have also been documented in uniaxial tests on dog-bone specimens extracted at varying orientations from rolled plates. These findings underscores the importance of accurately predicting strain behavior under various loading conditions is essential for reliable modeling of mechanical durability and, consequently, the long-term performance of NiTiNOL-base implants.

Conventionally, longitudinal testing of NiTiNOL tubes has been employed to characterize elastic compliance and transformation behavior. However, observed deviations (reference?) from Von Mises behavior suggest the need to independently investigate radial mechanical responses. In this study,:

• We will present the case study regarding optimization of specimen geometry for radial loading.
• A comparative analysis of elastic modulus and transformation characteristics in the circumferential (hoop) direction versus the longitudinal direction.

These insights aim to enhance the predictive modeling of NiTiNOL components under complex loading scenarios, particularly in biomedical applications.