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.