Design approach of shape memory alloy actuators with applications in structural vibration control

Shape memory alloys (SMAs) have several unique characteristics, including their Young's modulus-temperature relations, shape memory effects, and damping characteristics. The Young's modulus of the high-temperature austenite of SMAs is about three to four times as large as that of low-temperature martensite. Therefore, a spring made of shape memory alloy can change its spring constant by a factor of three to four. Since a shape memory alloy spring can vary its spring constant, provide recovery stress (shape memory effects), or be designed with a high damping capacity, it may be useful in adaptive vibration control. Some vibration control concepts utilizing the unique characteristics of SMAs will be presented in this paper. Shape memory alloy springs have been used as actuators in many applications although their use in vibration control area is very recent. Since a shape memory alloys differ from conventional alloy material in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some design approaches based on linear theory have been proposed for shape memory alloy springs. A more accurate design approach for SMA springs based upon a new nonlinear thermo-mechanical constitutive relation of SMA is also presented in this paper.