Variational Thermomechanically Coupled Shape Memory Alloy Material Model and Optimization of Shape Memory Alloy Based Out‐of‐Plane Bistable Microactuator

ABSTRACT This work presents a fully thermomechanically coupled material model for shape memory alloys (SMAs), capable of predicting shape memory effect, superelasticity, stress and strain recovery, and martensite reorientation. Formulated within the Generalized Standard Material (GSM) framework, the model employs a rate potential, whose variations yield the governing equations, including linear momentum balance, energy balance, and evolution of internal variables. A potential‐based line search method integrated with a Newton–Raphson scheme enhances the robustness and convergence of the solution algorithm. Extending the Sedlák [14] model's energy and dissipation formulations, we apply the proposed framework to an SMA‐based out‐of‐plane bistable microactuator design. The actuator features two antagonistically coupled SMA microbridges and exhibits bistable behavior, snapping between stable states under thermomechanical loading and using constrained recovery forces to perform work. Results demonstrate the model's efficiency and accuracy in capturing the complex thermomechanical response of SMA devices, highlighting its potential for advanced bistable actuator design.