DYNAMIC PROPERTIES OF POST-BUCKLED SHAPE MEMORY ALLOY AND ITS APPLICATION TO A BASE ISOLATOR FOR VERTICAL VIBRATION

Abstract

In recent years, high performance and compact vibration isolators have been in demand to support the advancement of precision technology. Among various vibration isolators, a passive vibration isolator is the most commonly adopted form due to its simplicity, stability and low cost. Previously, the authors have proposed a simple and compact passive vibration isolator for the vertical direction using a post-buckled shape memory alloy (SMA) beam. This isolator achieved a low natural frequency assuring high static stiffness by utilizing the negative tangent stiffness of a post-buckled SMA beam. It is expected that the appearance of the negative stiffness is related to the phase transformation of a post-buckled SMA beam, however, the fundamental principle of the appearance and the response for a reciprocating motion (vibration) have not been clarified. In this study, to clarify these characteristics, the restoring force of an SMA beam subjected to reciprocating motion in its post-buckled state was measured experimentally and predicted by Finite Element Analysis in which the phase transformation of the post-buckled SMA was considered. As the result, it was found that the restoring force converged to a certain force when SMA was subjected to reciprocating motion. It was also found that the negative tangent stiffness arose when the phase of SMA transforms from Austenite phase to Martensite phase in compression process. Therefore, SMA with small hysteretic property in the stress-strain curve is appropriate for an effective isolation element. In future research, it will be necessary to validate the performance of the isolator considering the phase transformation.