Energy Dissipation and Strain Recovery of Pseudo-Elastic Shape Memory Alloy Ni-Ti Wire

Abstract

Shape Memory Alloy (SMA) is classified as a novel functional material characterized by pseudo elastic and shape memory effect and has caught the interest across many research disciplines recently. Owing to its wide properties, originated from reversible austenite to martensite phase transformation, this alloy has been used widely in many applications from medical, aerospace and civil applications. The discoveries of SMAs to be exploited as intelligent materials have become the sparked research to be addressed for their prospective use as seismic resistant design and retrofit. Highlighting the unique properties of pseudo-elastic wire, it is not only have the ability to reverse macroscopically inelastic deformation during earthquake by stress removal to recover their original shape but also have significant promises to dissipate energy, large elastic strain capacity, hysteretic damping, excellent high, low-cycle fatigue resistance, re-centering capabilities and excellent corrosion resistance. Hence, this study evaluates the cyclic properties of pseudo elastic Ni–Ti shape memory alloys to assess their potential for seismic applications. An attempt is devoted to correlate the influence of annealing temperatures to the hysteretic behavior of Ni-Ti alloys in terms of fatigue resistant in cyclic loading, mechanical properties at ambient temperature, loading history, equivalent damping, energy dissipation and recovery stress were investigated experimentally. The sample of Ni-Ti wire of 0.127 mm diameter of as received wire had a nickel to titanium ratio of 0.49:0.51 and were heat treated to produce pseudo-elastic response at room temperature. Based on the experimental findings, the pseudo-elastic properties of as received wires have found to be in a good agreement in terms of their ability to dissipate energy through repeated cycling without significant degradation or permanent deformation and better response for seismic application to be optimized. The tensile cyclic test obtained demonstrated a rounded loading curve based on a 0.2 % offset. The as-treated has improved the energy dissipation, but has reduced in pseudo-elasticity. This is due to the formation of martensitic phase upon heating. It is evident from the XRD results, the presence of both austenite and martensite at room temperature. The improvement in energy absorption could be resulted from the greater enthalphy for the phase transition. This is due to pseudo elastic is highly sensitive to the temperature. Extreme temperature can completely eliminate the superelastic effect due to the formation of martensite and unwanted secondary phases such as Ni4Ti3 and and Ti2Ni. The experimental results show potential for the use of SMAs in seismic applications and provide areas for continued research.