Investigation of Different Activation Profiles During Electrical Activation of Shape-Memory Wires Regarding the Lifetime and Wire Temperature

Abstract For a progressive and economically viable use of Shape-Memory Alloys (SMA), it is necessary to further investigate the fatigue behavior and its influence on the lifetime of SMA. In addition to material-scientific research findings, an understanding of the influences in the field of application of SMA is necessary to increase its reliability. Especially when used as an actuator with electrical activation, high numbers of cycles are often required. One of the numerous influences on the lifetime is the type of activation of the wire, which can be carried out electrically or thermally. In the case of electrical activation, the shape of the activation profile can be varied. In addition to the step response, other profiles such as triangular profiles can be run, although in this work the focus is only on linear profiles. This varies the speed of the energy input and thus the activation behavior, which may influence the lifetime. In this publication, different activation profiles are examined regarding the thermal influence on the wire. For this purpose, these profiles are tested one after the other while the wire is monitored with a thermal imaging camera, and the respective wire temperature is recorded. The maximum temperatures reached for each activation profile are then correlated with the lifetime achieved and the stroke generated. To ensure comparability of the activation profiles, the electrical energy input is kept constant across the different activation profiles. To achieve this, the integrals of the electrical energy for the profiles are determined and calculated in advance. This results in two adaptable factors for keeping the applied energy constant for the different profiles. These factors are the maximum current and the duration of activation, whereby only one factor can be kept constant at a time. The test series are therefore carried out twice, whereby the applied energy is kept constant in both series, once with a constant activation duration of the profiles and once with a constant maximum current. Together with the reached lifetime data of the individual activation profiles, conclusions are to be drawn regarding the suitability of a respective profile for use in the field of actuators and a basic understanding of the relationship between activation profile, wire temperature, and lifetime of the wire is to be achieved.