2021 Volume 46 Issue 1 Pages 3-8
A straight-shaped Ti-Ni shape memory alloy (SMA) element shows negative stiffness during post-buckling deformation, and the buckling deformation is recovered with unloading due to the shape memory properties (superelastic behavior). This negative stiffness and shape recovery properties are applied to a passive vibration isolator using a zero-stiffness structure. We devised and fabricated the passive vibration isolator using the negative stiffness of tape-shaped SMA element, and this isolator shows the excellent vibration characteristic. However, control of the magnitude of the negative stiffness of the SMA element during post-buckling deformation is necessary for this isolator. In previous our studies, the variation of tangential stiffness of SMA element during post-buckling deformation is thought to be due to the variation of the volume fraction of martensitic-phase during post-buckling deformation by Three-dimensional finite element method (3D-FEM) analyses. In this study, effects of the volume fraction of martensitic-phase during buckling deformation on post-buckling behavior of tape-shaped SMA element are investigated by actual buckling tests for tape-shaped SMA elements with various length and 3D-FEM analyses. The results of buckling tests and 3D-FEM analyses suggest that the increase of the negative tangential stiffness during post-buckling deformation is due to the increase in the rate of increase of the volume fraction of the martensitic-phase during buckling deformation.