Abstract
This study is aimed to investigate the properties of Ni-rich Ni-Ti shape memory alloy sheet parts during and after deep drawing process at room temperature, in which the metal is under plane tension-compression stress state. After annealing at different elevated temperature, shape memory alloy sheet is formed at room temperature by a circular cylindrical punch in different forming depths. Thereafter the deep drawn sheet part is subjected to aging for shape memory treatment. A free shape recovery test is further conducted onto the deep drawn shape memory alloy sheet part. As a result, the sheet metal has austenitic phase at room temperature, which shows superelasticity. Too small forming amount causes severe springback and the form of the deep drawn sheet part is very hard to detect with the naked eye. Only if a forming amount greater than or equal to 4 mm is applied, a form can be achieved on to the sheet part. The subsequent aging shape memory treatment can induce further springback of the deep drawn sheet part. The higher the temperature of the previous annealing, the less the springback by aging. The free shape recovery test shows that the deep drawn sheet part only undergoing annealing without shape memory treatment still possesses shape memory effect. Nevertheless, the deep drawn sheet part aged for shape memory can show a better shape recovery.
Highlights
SetupsNi-rich Ni-Ti shape memory alloy sheets having a thickness of 0.8mm were commercially acquired from a local manufacturer (Zhongrui Material Technology Corp., Taiwan)
A simulation of deep drawing Ni-Ti shape memory alloy sheets had been conducted with the commercial finite element software DEFORM 2D [11] under elastic-plastic deformation, because the formulation for an elasticsuperelastic constitution is similar to elastic-plastic one [12]
As the deep drawing process was performed by a forming depth of 4 mm, the punch was at the stroke of 2.69 mm from its starting position at the time that the punch load disappeared
Summary
Ni-rich Ni-Ti shape memory alloy sheets having a thickness of 0.8mm were commercially acquired from a local manufacturer (Zhongrui Material Technology Corp., Taiwan). The metal sheet blank was put onto the bottom die without further surface treatment and any lubrication. The metal sheet blank was clamped by the blankholder with four bolts. The bottom die had a corner radius of 2.5 mm and the four bolts could provide a 680 N blankholder force on to the sheet blank, which was determined according the handbook [10]. The whole die set was mounted on the test bench, which was a universal material test machine driven by a servo motor. The cylindrical punch in a diameter of 20 mm having a corner radius of 4 mm was installed on to the cross head of the test machine. The approaching speed of the punch to the blank was set as 6 mm/min
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