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International Journal of Engineering & Technology, 7 (4.14) (2018) 482-487 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper Correlation of Pseudoelastic NiTi Egineering and True Stress- Strain Curves on the Effects of Nickel Titanium Composition Nubailah Abd Hamid 1 *, Azlan Adnan 2 , Muhammad Hussain Ismail 1 , Azmi Ibrahim 1 1,4 Faculty of Civil Engineering, Universiti Teknologi Mara,40450 Shah Alam, Selangor, Malaysia 2 Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia *Corresponding author E-mail: nubailah_hamid@yahoo.com 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 with- out 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%. Keywords: Shape memory alloy; Nickel Titanium ratio; Pseudoelastic; Phase Transformation; Engineering and True Stress-strain Relationship 1. Introduction Shape Memory Alloy (SMA) is a relatively new class of func- tional 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 im- portant role in structural application which provides the material that can act as control element or structural member. Different types of SMA are available in the market previously and have been used in the aerospace industry, medical equipment and struc- tural control. Nickel-Titanium (Ni-Ti) is one of the most com- monly used type because of its relatively functional properties compared to other smart materials. However, the development of new material must guarantee that the material possesses enough strength and rigidity to withstand the loads it will experience in its service life whenever it is being used in engineering structure [1]. Hence, a number of experimen- tal 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 appli- cation. While the testing(test) on the torsion were conducted by [3]. The influence of different heat treatments on the engineering stress – strain curve was investigated by [4]. 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 Bars were investigated by [5]. 2. Significance of Research The fundamental properties of engineering materials along with development of new materials and also quality control of materials for application in design and construction cannot be neglected where the tensile method is the accepted method commonly prac- ticed in order to evaluate the material properties in elastic design.[6] However, research on the engineering of true stress and true strain for NiTi is limited. Faridmehr et al., in 2014 conducted research on the true stress and true strain of low carbon steel with diameter 6 mm, 8 mm and 10 mm [1] . The aim of this paper is to investi- gate the engineering and true stress-strain relationships of nine specimens in conformance with ASTM F2516-07 and the (Stand- ard Test Method for Tension Testing of Nickel-Titanium Super elastic Materials 2007) and Standard Test Methods for Tension Testing of Metallic Materials. In this research, the true stress and strain of mild steel rebar and Ni-Ti are compared to determine the mechanical properties in terms of maximum tensile stress and strain, ultimate tensile strength, modulus of young, yield strength, percentage of elongation and percentage of reduction once the specimens were subjected to uniaxial tensile loading. In addition, NiTi are complex materials and their material behavior depends on a number of parameters. Depending upon the