Integrated product development with shape memory alloys: On the importance of the interface between alloy design and product development.

Shape memory alloys have found their way into medical technology with great success in recent decades. Constant conditions in the human body have certainly contributed to this. However, the situation is quite different when SMA are used for actuator applications. There, they often represent the key element of a complicated functional unit that is exposed to alternating conditions and must be well adapted to the other components to meet the product requirement. Therefore, the product designer of such actuator should ideally incorporate a SMA manufacturer who is able to design and provide a microstructure that fits the requirements of his actuator best.

In this study we consider both, wire actuators and compression spring actuators of the latest generations. In addition to the design and tailor-made alloy and component manufacturing, the selection of suitable preload elements and the real friction conditions in housings affects the resulting thermomechanical hysteresis in operation. For the chosen SMA element the installation in terms of the working principle as well as the mechanical guidance of the moving element is of key importance for functional properties, stability and durability.

Ambient air or fluid flows in the target application significantly influence the heating and cooling behavior of the actuator. This does not only reduce the system performance but might also negative impact on the fatigue behavior. To avoid failure or performance reduction for thin wires of 200µm or smaller these influences urgently need to be monitored and if needed eliminated by an appropriate electronic controller.