Simulation Study of Multiple Loading Conditions for Shape Memory Alloy films

This study investigates the damping behaviour of a miniature NiTiFe shape memory alloy (SMA) thin film device under various loads. SMAs are known for their shape memory effect and pseudoelasticity, making them ideal candidates for energy dissipation in dynamic systems. To model the thermomechanical behaviour of SMA films under rapid loading conditions, the Müller-Achenbach-Seelecke model is combined with a phase-field approach and implemented in the FEM package COMSOL Multiphysics. The simulation setup represents a 2D film rectangular geometry fixed at one end, with a weight attached to the other end to allow free vibration.
Various loading conditions are examined: In harmonic excitation the frequency dependence of the system is examined. In ramp loading a strong temperature dependence for the Austenite-to-Martensite transformation is shown. Two simulation studies are conducted for the situation of shock loading: one to determine the maximum possible prestrain without transformation and the other to find the minimal excitation force required for transformation. These values are 275 MPa and 4 N, respectively. Two simulation series are carried out with different prestrain and excitation force pairings. As results, z direction displacement, logarithmic decrement, temperature evolution, and martensite fraction are analyzed in detail. Additionally, the evolution of martensite and temperature during the first cycle is visually represented.
The study reveals that as the excitation force increases, the frequency, speed, and work done also increase. The damping capacity is higher at lower excitation force values. Prestrain has a significant impact on the logarithmic decrement, with higher prestrain leading to a more constant damping over longer periods. A higher prestrain value negatively affects the work done and damping capacity. The maximum damping values are achieved at 50 MPa prestress, after which the values decrease.