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Copper-based shape memory alloys (Cu-SMA) are known for their high transition temperatures and therefore their potential for actuation applications in environments with higher temperatures than tolerable for binary NiTi. Due to the higher transition temperatures of Cu-SMA cooling rates are higher, so technical applications could work with higher dynamics. A huge disadvantage is the low durability in the lifecycle of actuation compared to NiTi-SMA. As already known, there are many factors influencing the lifetime of SMA-elements, such as applied load, stroke, and the element’s temperature during activation. Besides the SMA’s typical degradation of strain, the transition temperatures of CuAlNi are influenced under high actuation temperatures and stresses, so that they are constantly shifting over the lifetime. This behavior is not tolerable for industrial applications since it makes the designing of the actuators highly demanding and high ranges for the attainable stroke must be considered for the dimensioning process. To overcome these problems a deeper understanding of the dependencies of the values such as stroke and the activation temperature on the cycle number is necessary. In this study, the effects of electrical cyclic heating of single crystalline CuAlNi SMA wires were investigated to analyze influencing factors on the life cycle behavior. Therefore, samples were loaded with constant stresses varying from 80–200 MPa in four steps. Various actuation temperatures were applied to the specimen, from “overheated” to slightly above Af and temperatures relating to partly activated (about 50% austenite). |
