Stabilization of the Cyclic Response of the Ni49.9Ti50.1 Shape Memory Actuators under Thermomechanical Loads

This work is focused on the development of a novel strategy to achieve dimensional stability for 55NiTi actuators that operate at a relatively higher temperature; i.e., with an austenite finish temperature, A(f), greater than 90 degrees C. The key ingredient in this is to place the actuators in a state of significant deformations before the thermal cycling. Correspondingly, this will provide increased-stiffness regions purely due to kinematic/geometric nonlinearity effects. In turn, this effectively counteracts the tendency for cyclic evolutionary behavior inherent in the commercial NiTi material. To demonstrate the success of the new approach, modeling results are presented involving different actuators having various shapes, i.e., beams, disks, and rings, which are operating for many repeated thermal cycles under different bias load conditions, such as concentrated point force, ring line load, or distributed surface tractions. (C) 2020 American Society of Civil Engineers.