Electro-thermo-mechanical finite element modeling of shape memory composite structures: material model, training, and actuation

Structurally integrated composite actuators offer great potential for compact, lightweight actuation systems. Embedding shape memory alloy (SMA) wires into an elastomeric matrix enables an intrinsic two-way effect, eliminating the need for external reset forces. Simulation-based design has so far been limited by the lack of a closed electro-thermo-mechanical modeling environment. This work presents such an environment, implementing a three-dimensional finite-strain material model for coupled multiphysics simulations in COMSOL Multiphysics and capturing both the thermo-mechanical training of the SMA wire and the subsequent electro-thermal composite actuation. The environment is validated on an additively manufactured NiTi-TPU composite actuator, where the simulated maximum tip deflection after heating deviates by 5.3% from experimental data. On this basis, the spatio-temporal phase transformation within the embedded wire is analyzed. With material parameters adopted from literature rather than identified on the wire used, the simulation predicts that the compliant matrix loads the eccentric wire mainly in axial tension. As the backstress aligns with the current stress in the model, it stays axial, and the wire transforms almost simultaneously. Extending the simulation to the cooling phase, the environment predicts a complete two-way stroke recovery, which was not measured experimentally. The gap of the printed groove governs the activation time. The proposed environment provides a foundation, validated for the actuation stroke during heating, for designing structurally integrated SMA composite actuators and can be extended to other geometries.