Experimental investigation into NiTi shape memory alloy panels under cyclic shear loading

Abstract

Shape memory alloys (SMAs) are widely employed in buildings and bridges as energy dissipation devices because of their superelasticity, shape memory, fatigue resistance, and high damping performance. In this study, SMA plates were fabricated into a shear device as a seismic structure. To understand the seismic performance of the SMA plate, an experimental study was conducted on the tension and shear behaviours of SMA plates under cyclic loading. Monotonic and cyclic tensile tests were carried out on 12 SMA plate coupons, and the important influencing factors, including the annealing temperature, annealing duration, and loading protocol, were evaluated. Based on the principle of maximum elastic modulus of austenite, maximum energy dissipation, and minimum residual strain, an optimal heat treatment scheme for a Ti–55.8 wt%Ni SMA plate with a thickness of 1.6 mm was suggested: annealing at 500 °C for 5 min. Further, the optimised SMA plate was installed in a shear device to conduct cyclic shear loading tests. Three pure shear tests with the SMA plate, structural steel, and stainless steel were designed and performed. The test results showed that the elastic modulus of the SMA plate is the lowest, which facilitates elastic shear buckling, and the tension field effect could significantly enhance the ultimate bearing capacity after buckling. In particular, when the applied shear is unloaded to zero, the SMA plate does not produce any residual deformation. Compared with the structural and stainless steel, the SMA plate exhibits more ideal self-centring behaviours, perfect fatigue fracture resistance, slow stiffness degradation, and greater yield deformation capacity; however, the initial stiffness, displacement ductility ratio, and energy dissipation capacity are slightly lower than those of the other test specimens. Although the SMA plate develops a large deformation, it produces a fracture failure mode without any evident sign.