Due to numerous advantages, shape memory actuators offer the possibility of replacing conventional actuators. These include high energy density in addition to the small required space, low weight, and high biocompatibility. Apart from the few mass applications of pseudoplastic shape memory elements in medical technology and the even fewer mass applications of shape memory actuators, they are currently rarely used in large series, which is mainly due to the costly testing and associated development times. This is due to the fact that the cost of a service life test in the development process is very high because of the low switch-off dynamics and the associated cooling times. A complete fatigue testing cycle can take several months. However, a test of electromagnets of the same service life and performance class would only take three to five days, which is why shape memory technology is often not considered applicable in actuator development despite its advantages.A particular obstacle in the development process is structural fatigue, which cannot be reliably estimated today because there are no implemented prediction tools for smart memory actuators to date. The shape memory effect and its change over the lifetime depends significantly on the material composition, the heat treatment as well as the operating parameters, such as the applied load, the ambient temperature or the type of activation. There are still a few conclusions which need to be drawn on the extent to which these parameters influence the lifetime of the shape memory elements.The main objective of this study is to reduce development time by building an improved understanding of the relationships between the critical material-dependent parameters and the damage that occurs to the shape memory elements.For this purpose, a test rig was constructed which is capable to create reproducible and thus comparable tests in order to subsequently examine the resulting samples metallographically and assess the microstructure. The aim of the test environment was to create standardized, uniform test conditions by developing a standardized test method including measuring equipment adapted to the technical test conditions for smart memory actuator systems.On the basis of various test series, analyses were carried out using conventional light microscopy and REM methods in order to investigate the differences between various stress levels within a test series as well as differences between the various test series, i.e. the influences of the changes in various parameters on the microstructure of the shape memory elements.

Influences of Various Parameters on the Microstructure and Their Effects on the Structural Fatigue of Shape Memory Systems

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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