Investigation of the energy conversion efficiency of shape memory alloys

• Main Author: Lewis, Kingsley Earle
• Other Authors: Liu Yong
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/61441
• Institution: Nanyang Technological University

This project investigated the energy conversion efficiency of one way shape memory alloys (SMA). Energy conversion works by converting low grade thermal energy to mechanical energy, hence providing alternative sources of energy, useful to mankind. SMA energy conversion is however limited by its efficiency, hence prompting the need for accurate determination of the efficiency. The effects of pre-strain, constrained stress and heating rate on experimental efficiency were examined while the effects of constrained stress and recovery strain on theoretical efficiency were examined. The SMA wires underwent annealing followed by calorimetry to determine the transformation temperatures. Two types of deformation procedures were then used, namely fixed pre-strain with different constrained stresses and fixed constrained stress with changing pre-strains. Upon being loaded with the pre-strain, they were unloaded and reloaded with the constrained stress. Once the constrained stress was reached, the SMA wire was heated and the recovery strain was evaluated for efficiency calculations. Experimental efficiencies of 0.017- 0.102% were obtained compared to that of 1.11- 4.41% obtained theoretically. Experimental results suggested that efficiency increased with increasing pre-strain, constrained stress and the heating rate. However, at 13% pre-strain, the experimental efficiency reduced across all constrained stresses. Theoretical efficiencies showed increasing trend with increasing constrained stress and recovery strain. The following experimental and theoretical results will provide deep understanding of the energy conversion efficiency of NiTi SMA wire.