The present study represents a first step towards an understanding of what we refer to as the functional fatigue behaviour of shape-memory polymers. These materials have a processing shape B and a programmed shape A . And when the material is exposed to an appropriate stimulus (in our case: heating above a critical temperature), a one way effect is observed: A → B (one way effect: 1WE). The objectives of the present study were to find out whether and how often programming can be repeated, whether repeated programming affects the 1WE and how much irreversible strain the material accumulates. We study the effect in dependence of different stress levels, and consider the effect of recovery temperature and recovery time. As a model material we examine the commercial amorphous shape-memory polymer Tecoflex® and subject it to 50 programming/1WE cycles. It turns out that programming, cooling, unloading and heating to trigger the 1WE causes an increase of irreversible strain and is associated with a corresponding decrease of the intensity of the 1WE in particular during the first thermomechanical cycles.
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The authors acknowledge funding through project B3 of the collaborative research centre SFB459 (shape-memory technology) funded by the Deutsche Forschungsgemeinschaft (DFG) and the State North Rhine Westphalia (NRW).
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Schmidt, C., Neuking, K. & Eggeler, G. Functional Fatigue of Shape-Memory Polymers. MRS Online Proceedings Library 1190, 0302 (2009). https://doi.org/10.1557/PROC-1190-NN03-02