Analysis of Bias-Type Actuator Using Shape Memory Alloy Based on Its Thermomechanical Constitutive Description

Dynamic behaviour of a bias type actuator using Ti-Ni shape memory alloy is examined theoretically as well as experimentally. The constitutive and the heat equations for the shape memory alloy, derived in the framework of continuum thermomechanics with phase transformation taken into account, are employed to describe the response of the considered actuator to applied electric input varying in time. Material parameters in the constitutive model adopted are determined from uniaxial loading unloading tests at different temperatures. An experimental setup of the actuator, consisting of a shape memory alloy wire and a bias spring connected serially, is also manufactured, and the response of the actuator to cyclic electric input is measured. The experimental results obtained are compared with the predictions of the analytical model, which proves promising to describe the behaviour of the actuator very well in terms of its dependence on various factors such as the rigidity of the bias spring, as well as the magnitude and the period of cyclic input.