Investigation of the Lifetime of Antagonistic Shape Memory Wires With Focus on Accelerated Resetting

Abstract

The antagonistic setup of shape memory actuators enables a multitude of further applications than designs with only one shape memory element. In these actuators, two opposed shape memory elements work against each other and also ensure mutual resetting. This setup allows easily controlled and powersaving actuators for applications with two end positions such as locks or latches. It not only eliminates mechanical resetting, for example by a spring, but also offers a simple realization of holding the end positions energy-free and thereby conserving the shape memory effect. In order to maximize the potential of this actuator design, the authors investigate the interdependencies between antagonistic wires. This paper focuses on the effect of resetting a previously activated NiTi wire by another, similar antagonistic wire before it cooled down completely. On the one hand, very early resetting can have a negative effect on both the cooling and especially the activated wire. This is mainly noticeable in a shortened lifetime of the actuator elements. On the other hand, applying mechanical strain by activating the opposed wire can accelerate phase transformation within the cooling wire. The authors performed corresponding fatigue tests with different cooling times in the antagonistic setup, in order to narrow down a timeframe for the optimized usability of an antagonistic wire actuator.