Session: 02-01: Shape Memory Alloy Actuators

Paper Number: 110991

110991 - High Load NiTi Shape Memory Alloy Actuators: A Study of Cyclic Behavior 

This paper advances the knowledge of the cyclic thermo-mechanical behavior and fatigue of high load SMA-Actuators. Since these particular actuators impress with their small volume and weight, they provide an attractive alternative to conventional actuators. Especially in production plants and machines, where the requirements for installation space and weight are becoming increasingly crucial for a successful manufacturing process, they find a wide field of application. However, mechanical and functional cycle fatigue are issues well known from wire based small force SMA-Actuators (N-range). Quite in contrast to small force applications, more massive geometries and new integration concepts of the shape memory components are thus substantial for high load SMA-Actuators (kN-range). Comprehending how these changes significantly alter the SMA behavior will eventually enable novel designing and optimizing.

In this paper, a practical approach is used to obtain data relevant to industrial applications. The approach is employing a high load SMA-Actuator that has been designed for its integration in machines tools. Therefore, the actuator and its design are introduced first. Actuator cycling is thermally obtained exploiting a heating wire and forced convection. For the cyclic testing, SMA-elements have been fabricated with different methods. Here, the classical method using casting, round forging and drawing combined with wire-EDM (electro-discharge-machining) for the final geometry are compared to a method using selective laser melting (SLM). In both cases, the utilized alloy is Ni42.5Ti50.0Cu7.5. In general, the measurements indicate a functional fatigue similar to wire based SMA-Actuators. In contrast, the mechanical cyclic behavior differs. The compression mode causes buckling of the cylindrical specimen but not breaking and complete failure as occurs with wires. Interestingly, despite the microcracks exhibited by the SLM specimens, the cyclic behavior and fatigue is comparable to the crack free classically produced specimen. Furthermore, shortening of the SMA-element was observed. Which is an effect that interacts strongly with the applied and appliable force and often requires compensation.

Presenting Author: Kenny Pagel Fraunhofer Institute for Machine Tools and Forming Technology IWU

Presenting Author Biography: K. Pagel received his Dipl.-Ing. degree by the Technical University Chemnitz in 2006. In 2007 he joined the Smart Materials Department at Fraunhofer IWU as a researcher and project manager. He received his doctoral degree in 2018 with a thesis about the development of shape memory actuators with inherent guidance function. Since 2022 he is head of the Shape-Memory-Alloy Department. His work is focused on the design of shape-memory-alloy applications and especially SMA micro actuators.