Effects of perturbations on a trained shape memory micro-actuator

Abstract
The so-called Two-Way-Shape-Memory Effect (TWSME) introduced using a training process has been used to produce a reversible motion in a small actuator. It is usually noted that the TWSME induces a preferred oriented martensite which results, during the reverse transformation, in a spontaneous shape change on cooling. While heating up, the material transforms to austenite and recovers its original shape. However, if the material is mechanically deformed in martensite, in order to modify the martensite variants distribution induced by the TWSME, a two-step transformation occurs : when heating up, the material first transforms into the low-temperature shape, -i.e. the "memorized" shape induced by the training process"- and then to the high-temperature shape. This two-step transformation has been observed in a SMA micro-device. These experiments are presented in details and possible interpretations will be discussed.