Buckling of tubular superelastic shape memory alloy shafts

The torsional buckling of tubular superelastic shape memory alloy (SMA) shafts was demonstrated. A digital camera was used for showing the change in the shape of the deformed SMA shafts that take place when placed near buckling loads. Three different specimens with same slenderness ratio were observed for buckling. Two shafts with high slenderness and an unsupported length of 90 mm were used for presenting the results. The observations shows that stress distribution for a superelastic SMA tubular shaft is highly different from that of a solid shaft. This occurs because the torsional strength of superelastic SMA increases nonlinearly for increasing strain. At room temperature, it is shown that superelastic SMAs have low Young's modulus, which results in low torsional buckling load. As a result, under pure torsion, the slender tubular SMA shafts are found to buckle when the critical twisting moment is exceeded.