• Langelaar, Matthijs
• Van Keulen, Fred

Abstract

Shape memory alloys (SMAs) are active materials with a high power density, capable of producing comparatively large actuation strains and stresses. However, designing effective multi-dimensional SMA actuators is a challenging task, due to the complex behavior of the material and the fact that often electrical, thermal and mechanical aspects have to be considered simultaneously. For this reason, interest in the application of systematic computational design approaches, such as design optimization techniques, to the design of SMA structures is increasing. To enable efficient SMA design optimization procedures, the availability of sensitivity information is crucial. This paper presents the formulation and computation of design sensitivities of SMA shell structues using the direct differentiation method, in a steady state electro-thermo-mechanical finite element context. The SMA constitutive model used in this study is specifically aimed at the description of the superelastic behavior of NiTi alloys, based on the R-phase transformation. This behavior is characterized by its negligible hysteresis, which is attractive for actuator applications. The history-independent nature of the material model makes it well suited for design optimization of SMA structures and actuators, as this property simplifies the sensitivity analysis considerably. Finite difference, semi-analytical and refined semi-analytical sensitivity analysis approaches are considered, and a comparison is given in terms of efficiency, accuracy and implementation effort, based on a representative finite element model of a miniature gripper.

Topics

• density
• impedance spectroscopy
• phase