Experimental study of thin-walled TiNi tubes under radial quasi-static compression

TiNi tubes with various sizes and boundary constraints subjected to radial quasi-static compression were systematically studied. The contour curves of the tubes were extracted from the real-time charge-coupled device (CCD) images, and the circumferential strain, bending moment, and phase composition distribution were calculated based on the contour curves and some assumptions. It was found that the load–displacement curves had hysteretic loops, and all specimens could recover to their initial shape after unloading, which was attributed to the effects of austenite–martensite phase transformation and phase transformation hinges (THs). For single-tube experiments, the numbers of TH were observed to be twice the numbers of constraints. For vertical double-tube experiments, the main deformation of each tube was concentrated on its upper half circle. The energy dissipation rate (EDR) and the dissipated specific energy (SE) in single-tube case increased with decrease of the diameter–wall thickness ratio (DTR; D/ t) or increase of the constraint number. With a four-directional constraint condition and same D/ t, the EDR and SE of vertical double tubes were greater than that of a single tube and close-packed seven tubes. The present results could give a reference for designing repeatedly used shock-resistant element with higher energy absorption capacity.