To determine the lifespan of a system, the lifespan of all parts as well as the interaction of the parts as a system must be known. Accordingly, in systems where shape memory alloy (SMA) wires are used as actuator elements, their lifespan must be determined as well. Therefore, a test bench to determine the lifespan of SMA wires is needed. Since the requirements of actuator systems differ for example in stroke, response time or force, the test bench will be designed in an as modular way as possible. This allows for testing different actuator configurations as for example single wires or wire bundles of different diameters. This work outlines the development of the test bench, discusses first measurements of a 3D printed validation setup and concludes with a summary and an outlook on the optimization steps as well as the tests to be performed.

Today, Nickel-Titanium (NiTi)-based shape memory alloy (SMA) wires are already used in a wide range of commercial actuator applications. The combination of their unique properties, such as their high energy density as well as their biocompatibility provides a broad range of applications. The former in particular allows for designing light-weight actuator systems with high forces using small installation spaces. In systems like emergency brakes or switch disconnectors, which require high forces as well as high actuation speed, the high-power capability of NiTi actuators is exploited. The presented work discusses the development of a giant power catapult demonstrator, that combines the high-speed and high-force capability of SMA wires. To illustrate the vast force, speed, and power potential of SMA wires, a bowling ball is launched from its resting position into the air using SMA wire bundles. For demonstration purposes a target altitude for the bowling ball of 500 mm is chosen, requiring a theoretical actuation force of F ≅ 920 N. To be able to launch the bowling ball to the desired height, an instantaneous energy release with an overall peak-power of P ≅ 0.5 MW is required.

For repeated actuation in shape memory alloy (SMA) actuators, a restoring force is needed to return to the initial starting position after activation. Therefore, SMA wires are often coupled with mechanical springs, which lengthen said wires again after activation through heating and resulting contraction. In more advanced SMA actuation systems a second SMA wire is used as an actively controllable restoring element instead of passively working spring forces. A disadvantage of these antagonistic SMA actuator systems is that after activation of the first SMA wire, the return movement cannot be carried out immediately by the antagonistic partner. This delay caused by the first SMA wire’s cooling time leads to longer cycle times. To compensate for this disadvantage, a decoupled antagonistic SMA actuator has been developed. This enables the actuator to move back to its initial position immediately, regardless of the state of the antagonistic SMA wire. This work deals with the construction as well as the control of two rotatory decoupled antagonistic SMA actuators. The first actuator enables a 90° rotational movement through 2 mm of SMA wire stroke via a gear drive. The second actuator contains a bistable element to enable two energy-free switching positions. This bistable element serves as output device of the actuator and an output stroke of 8 mm is realized by an SMA wire stroke of 1.9 mm.