Investigation on thermo-mechanical behavior of shape memory alloy spring using hot water and laser assisted actuation

Abstract

Shape memory alloys are relatively a new band of material which have not been utilized to their fullest potential. These materials are alloys composed essentially of Nickel, and Titanium, with possible addition of Copper, Zinc and Aluminum and recover pre-set shapes even after deformation, by heat activation. When deformed in the low temperature, these shape memory alloys rearrange themselves into ‗monoclinic‘ lattice structures, which will give them the shape of a parallelogram. This parallelogram shape converts into more ‗cubic‘ structure upon heating. The heat is supplied by any hot source which mainly is through DC power supply.In my research, the thermo-mechanical properties of shape memory alloy are studied when the actuation media is changed. Actuation with a laser beam and hot water is focused in this work. Certain key relationships between various physical changes like displacement, load, temperature and time are determined through experiments. These experiments lead to determine the effects of heat over the shape memory alloy spring. . Line laser at a wavelength of 532nm is made to fall over the NiTi Shape memory alloy (SMA) spring and a significant actuation (compression) of 7-8mm is visible. With hot water actuation as the temperature reaches 70-80 ºC, spring gets fully compressed for the first few cycles followed by loss in actuation. The actuation loss is then studied with different characterization methods such as Thermo Gravimetric Analysis (TGA) and Scanning Electron microscopy (SEM). With SEM results, it can be inferred that spring when actuated with hot water possesses more life as compared to the one actuated with Laser. Furthermore the rapid actuation shows no sign of fatigue with hot water but with laser, small ablation can be seen after some cycles.In my research, the thermo-mechanical properties of shape memory alloy are studied when the actuation media is changed. Actuation with a laser beam and hot water is focused in this work. Certain key relationships between various physical changes like displacement, load, temperature and time are determined through experiments. These experiments lead to determine the effects of heat over the shape memory alloy spring. . Line laser at a wavelength of 532nm is made to fall over the NiTi Shape memory alloy (SMA) spring and a significant actuation (compression) of 7-8mm is visible. With hot water actuation as the temperature reaches 70-80 ºC, spring gets fully compressed for the first few cycles followed by loss in actuation. The actuation loss is then studied with different characterization methods such as Thermo Gravimetric Analysis (TGA) and Scanning Electron microscopy (SEM). With SEM results, it can be inferred that spring when actuated with hot water possesses more life as compared to the one actuated with Laser. Furthermore the rapid actuation shows no sign of fatigue with hot water but with laser, small ablation can be seen after some cycles.Results observed from TGA shows high oxygen content at lower temperature limits with both laser and hot water actuation which suggest the need of conducting experiments in inert atmosphere. As a possible mechanism, actuation medium is changed and various results can be seen in the paper discussed below