NiTi Shape Memory Alloy Active Element Behavior in Long Time Solicitation Conditions

Abstract

Equi-qtomic NiTi (nitinol) shape memory alloy (SMA) is a good potential candidate material for use as thermo-mechanical actuator in a large variety of engineering like automotive and aerospace applications. Shape memory alloy in action are required to perform a large number of actuation cycles under cyclic thermo-mechanical loads and therefor are subject of fatigue. A shape memory alloy, supplied from Nimesis Technology, with martensite to austenite temperature transformation domain 76-80 °C. The material characteristics were investigated through differential calorimetry (DSC) before and after the thermo-mechanical solicitations. Under Joule effect and a timer, the active element goes up to 3000 cycles with a 500g weight on. The properties of thermo-elastic martensite transformation are the elastic accommodation of volume and shape change that takes place due to change in crystal structure upon phase transformation. A modification of the first coil of the intelligent arch-wire suffer a modification of the temperature transformation domain increasing the As and Af temperature values.