Electro–Thermo–Mechanical Characterization of Shape Memory Alloy Wires for Actuator and Sensor Applications, Part 2: High‐Ambient‐Temperature Behavior

The typical phase transformation temperatures of commercially available shape memory alloys (SMA) for actuator applications are in the region of 80–90 °C for austenite finish and around 60 °C for martensite start. That limits the areas of application for SMA actuators, as increased ambient temperatures restrict their functionality. Especially in the industrial and automotive sectors, operational temperatures of 80 °C and higher are commonly required. This article discusses the limits of operation temperatures for commercially available SMA actuator wires. Also, methods to increase this critical temperature limit, at which the SMA actuation strain falls below a certain threshold, are proposed. By means of electrothermal actuation experiments, the influence of the variation of bias loads and an additional training method are investigated. Supported by these results, an exemplary valve actuator system is designed, which exhibits consistent stroke in a wide range of ambient temperatures. All experiments and measurements are conducted on a custom designed test bench with the same commercially available SMA wire. The test bench is in the following used again to evaluate the designed SMA valve actuator.