SMA semi-finished product conditioning

SMA are thermosensitive materials that change their geometry depending on the temperatures and further show elastic properties in certain temperature ranges. This effect, known as pseudoplasticity, is based on a reversible phase transformation and can be used as an actuator. A high-temperature and a low-temperature phase are distinguished. The development of such actuator systems is a particular challenge due to the complex properties of SMA.

The functional fatigue especially must be considered in the design to ensure the desired system properties are maintained over the entire service life. As this behavior is particularly significant in the first load cycles, actuator wires and spring actuators are usually conditioned or pre-cycled to compensate for these effects and ensure constant material behavior. For this purpose, it is necessary to cycle both material phases through repeated heating and cooling under mechanical load. In series production in particular, the time-consuming cooling process is an issue for efficient production.

In addition to pseudoplasticity, actuator wires also exhibit the effect of pseudoelasticity at higher temperatures, a material characteristic that is normally only used in passive systems. This enables a phase transformation through mechanical driving forces. When the load is removed, the phase is transformed back. This effect can be used to make the conditioning of semi-finished products more energy and time efficient, as both phases can be passed through at constant temperatures and a time-consuming cooling process is no longer necessary.