3D simulation of a shape memory microactuator

A three-dimensional (3D) model has been developed for simulation of the physical properties of an electrically driven shape memory alloy (SMA) microactuator used for control of a microvalve. The mechanical behavior is decribed by a two phase macromodel taking into account material and geometrical nonlinearity including history effects. The simulation makes use of mechanical, electrical and thermal finite element programs, which are coupled by a control program. Mechanical tests confirm the simulated forces and displacements. By using the flow-dependent heat transfer coefficient as a fit parameter, a quantitative agreement is obtained with experimentally determined time constants of the microvalve. For a heating power of 85 mW, the closing and opening times are about 30 ms and 100 ms, respectively.