Unbuckling of superelastic shape memory alloy columns

Our recent buckling experiments on superelastic shape memory alloy columns (initially straight rods and tubes) discovered that during axial shortening, certain specimens bent (buckled) at a critical compressive load and then, surprisingly, straightened (unbuckled) at a larger compressive load. This “buckling–unbuckling” phenomenon, defined here as the deviation from and then return to a straight configuration during monotonic loading, is not only an intriguing phenomenon (contrary to the post-buckling behavior of conventional materials) but also presents the possibility for novel applications. This work aims to provide a clearer understanding of when and why unbuckling occurs, presenting the experimental observations of this phenomenon and the stability analysis of a modified Shanley column model that captures the unbuckling behavior.Unbuckling behavior is shown to be a consequence of a secondary branch that deviates from the principal path at a low-load level (critical buckling load), but reattaches to t...