Session: 03-06: Design and Optimization of Intelligent Structures

Paper Number: 111107

111107 - Determination of Material Parameters and FEM Simulation for the Development of a Design System for Shape Memory Springs 

Shape Memory based actuator systems offer numerous advantages over conventional drives and have therefore already been successfully established on the market in many applications. The main reasons for this success are the extraordinarily high working density and the resulting lightweight design potential, the simple structure, the noiseless operation, and the possibilities for structural integration. Actuator springs made of SMA (Shape Memory Alloy), which are usually activated by the surrounding medium and can thus operate completely energy-autonomously as actuator and sensor at the same time, are of particular importance here. Compared to competing thermal actuators such as strain elements or bimetals, SMA springs can realize large strokes at precise switching temperatures and higher dynamics.

However, the design of these actuators represents a major challenge in industrial production. Discrete substitute models used today for manufacturing are not able to represent the specific properties such as pseudoplasticity and pseudoelasticity, nor do standardized measurement methods exist for characterizing the necessary material parameters. Complex actuator geometries usually require knowledge in the field of thermomechanical FEM (Finite Element Method) simulation, which makes it difficult for SMEs (Small Medium Enterprise) to access the technology.

This paper presents the development of a characteristic value-based system design method that enables SMEs to design shape memory springs as easily as conventional steel springs. The system design method is based on cause-effect relationships between the parameters of the material, the spring geometry, and the resulting actuator parameters, such as stroke and positioning force. To identify the relationships, FEM models of various spring geometries, such as helical, shaft and torsion springs, were implemented in the ANSYS Mechanical simulation software and the pseudoplastic behaviour was simulated using the Auricchio material model. The material parameters of the model are obtained from experimental analyses of SMA wire samples by standardized test methods such as tensile-compression tests and DSC (Differential Scanning Calorimetry) measurements. After comparing the simulation with the experimental results of the manufactured spring geometries, metrologically validated FEM models of various SMA spring geometries are available to determine the cause effect-relationships using the Design of Experiment method. From this, discrete mathematical descriptions of the relationships are derived, which can be used for the design of the SMA springs.

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.