EXPERIMENTAL FATIGUE INVESTIGATION OF DEFLECTED SHAPE MEMORY ALLOY WIRES

In times of increasingly complex overall technical systems and the associated component integration, there is a need to downsize existing components. Due to their high energy density, shape memory alloy (SMA) actuators offer the possibility of developing lightweight and compact systems. These actuators are available in a variety of shapes, e.g., wires. A challenge for shape memory alloy wire actuators arises in the design. SMA actuator wires can typically generate strokes of 2-4 %. One possibility to integrate a certain wire length for a required actuator stroke without additional elements (e.g., levers) is the deflection of the wire. It can be observed, however, that the lifetime of the deflected wires is significantly shorter than in the non-deflected state, despite the same external mechanical stress and actuator stroke. It is also expected that cracks occur at the deflected points where the mechanical stress is high. Therefore, investigations on the influence of the deflections on the lifetime of SMA wires are necessary.

In this presentation, a test set-up for deflected SMA wires is developed, which is a modular extension of an existing lifetime test rig for SMA actuator wires. Fatigue tests are carried out on this set-up by varying parameters such as wire diameter, deflection radius, actuator elongation and deflection angle. In the results, the influence of these parameters is discussed and design guidelines for actuator components can be derived.