Abstract: In order to overcome the disadvantages of the complexity and slow response time of the traditional shape memory alloy (SMA) actuators, a two-way shape memory alloy (SMA) linear actuator without any bias mechanism is designed and fabricated by using pre-strained one-way shape memory effect wires. The actuator consists of two SMA wires, a pulley, a component, a track and some bolts used to fix SMA wires. Based on Brinson’s one dimensional constitutive equation and transformation equations, strain expressions of the two SMA wires are deduced under different conditions. Then, on the assumption that stresses during martensite transformation are regarded as volume forces in SMA wires, displacements of the actuator at different temperatures and its maximum displacements under different loading weights is analyzed. For verifying the predicated values, some experiments are implemented. The results indicate that the proposed method can be used to develop two-way SMA actuators. With the temperatures of SMA wire rising, the displacements of actuator are nonlinearly increasing. When the temperature of SMA wire is above Af, the displacement reach the maximum value. However, the maximum displacement of initial process is half of that of the whole process. For the effect of load on displacements, on the other hand, maximum displacements of the actuator are gradually decreasing with the increasing of loading. When the weight of load reaches 51.0 N, the motion of actuator ceases, that is, the maximum displacement become zero.

Key words: Actuators, Characterization, Constitutive equations, Shape memory alloys