An Examination of the Mechanical Behavior of Shape Memory Nitinol Wires at Various Temperatures

Shape memory Nitinol alloys are commonly used in a myriad of strain recovery applications. Understanding the behavior of the material at different temperatures influences the choices of the application designer when selecting different grades of Nitinol. This study focuses on six Nitinol ingot austenitic start (A _s) temperatures (Ingot A _s = 95.0, 84.0, 62.3, 41.6, 29.3, and 13.4 °C). Each sample was drawn to wire diameters ranging from 0.076 to 1 mm, two sizes per ingot A _s, with varying heat treatments to achieve various active austenite transformation temperatures ranges (TTR). TTR behavior was measured utilizing a linear variable displacement transducer (LVDT) bend and free recovery (BFR) method, per ASTM F2082. Mechanical characterization was determined by a series of uniaxial tensile tests performed at 5, 10, 15, 20, 30, 50, 75, and 100 °C above respective active A _f transformation temperatures. This study will detail the methods utilized in determining the results and potential impact on current industry test modalities and standards.