Abstract
This research highlights the novel properties of pseudo-elastic Ni-Ti bar owing to their ability to reverse macroscopically inelastic deformation during earthquake known as recentering capability and large elastic strain capacity which originated from the reversible austenite to martensite phase transformation. Hence, this paper presents and evaluates the cyclic properties of pseudo elastic Ni–Ti shape memory alloys to assess their prospective use for seismic applications to be exploited as seismic resistant design and retrofit. In addition, the correlation of hysteretic behavior of Ni-Ti alloy in terms of cyclic loading number and history, mechanical properties at ambient temperature, equivalent damping, energy dissipation and recovery stress were evaluated. The NiTi bar used is with weight percentage of Ti-43.98 at. % Ni 56.02 and diameter of 12 mm. The tensile cyclic test obtained demonstrated a rounded loading curve based on a 0.2 % offset. The as received bar exhibited superior pseudo-elastic behaviour and recentering through repeated cycling without significant degradation or permanent deformation but low energy dissipation due to narrow hysteresis while the steel rebar showed vice versa. Experimental results show potential for the use of SMAs in seismic applications and provide areas for continued research. It was concluded that the as-received pseudo elastic Ni-Ti bar is suitable for use in seismic mitigation despite of their ability to undergo cyclical strains at 6 % which is greater than 5 %, with minimal residual strain of 0.15% which is less than 1%.   Â
Highlights
Shape Memory Alloy (SMA) is a relatively new class of functional material, exhibiting special thermomechanical behaviours, such as shape memory effect and super elasticity, is developed based on the demands of smart material systems that play an important role in structural application which provides the material that can act as control element or structural member
Pseudoelastic NiTi alloys have a NiTi ratio that are super elastic at room temperature when they are cold drawn and tempered while High Strength Superelastic Nickel alloys have higher NiTi ratio that are super elastic at room temperature with higher super elastic plateau stresses
The ultimate tensile strength (UTS), yield strength or yield point, elastic modulus (E) and percentage of elongation (ΔL%) that were attained during the tension test for all the 9 specimens are tabulated in Table 1 below
Summary
Shape Memory Alloy (SMA) is a relatively new class of functional material, exhibiting special thermomechanical behaviours, such as shape memory effect and super elasticity, is developed based on the demands of smart material systems that play an important role in structural application which provides the material that can act as control element or structural member. A number of experimental techniques have been developed by engineers for mechanical testing of engineering materials subjected to tension, compression, bending or torsion loading. The mechanical behaviour of cyclic properties of NiTi shape memory alloys for large coupon of 12.7, 19.1, and 31.8 mm bars were studied by [2] to investigate their potential for seismic application. The SMA specimens were different in shape (wires and bars with different diameter), have different physical characteristics (alloy composition, thermomechanical treatment and material phase) and subjected to different stress modes (tension, torsion, bending and shear). The cyclic properties of Super elastic Shape Memory Alloy Wires and
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