Development of Contacting Solutions for Shape Memory Alloy Wires

Shape Memory Alloys (SMA) are thermosensitive materials that can change their geometry when a certain temperature is reached. Compared to conventional drives SMA based actuator systems provide many advantages and have already been successfully established on the market in various applications. Nevertheless, the manufacturing-related system integration of SMA actuators, especially for electrically activated wire actuators, is still a challenge. There are a variety of techniques to establish a connection between an SMA wire and its system environment. However, most of these solutions are not suitable for mass production. In any known industrialized application, only crimp or splice connectors are currently used. This paper provides an overview of the crimp connectors already on the market. These were discussed with regard to their suitability for possible applications. Since precise information on manufacturing parameters or performance characteristics is usually not available, various influences on the mechanical and electrical functionality of the connection and on the thermal and cyclic properties of the system were analyzed and discussed. Different approaches to create a reliable connection were investigated. This ranges from connectors based solely on frictional closure, to more complex approaches, that realize both frictional and form closure as well as material-fit connection. Pull-out tests were carried out to check the connection strength and thus to evaluate the concepts. The determined preferred variant was then tested for cyclic strength. In subsequent fatigue tests, the preferred variant was shown to have a cycle strength of over 2500 cycles at 400 MPa (50 N). The results provide a basis for future results to further increase the current level of technological maturity and enable broader application.