Testing the damping capacity of shape memory alloys

• Main Author: Foo, Raymond Mao Yann
• Other Authors: Liu Yong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials::Metallic materials::Alloys; DRNTU::Engineering::Materials::Testing of materials
• Online Access: http://hdl.handle.net/10356/53578
• Institution: Nanyang Technological University

In recent years, there has been an increasing interest in the study of shape memory alloys (SMAs) by many. This is because shape memory has two distinctive features and they are namely the shape memory effect and pseudoelasticity effect. The material also exhibits high damping capacity, biocompatibility and high kinetic output. An extensive study on the factors that will affect the damping capacity of the NiTi wire at different phases during the heating process, namely martensitic phase, austenitic phase and at transformation was carried out in this project. The phase transformation temperatures were measured using the differential scanning calorimeter (DSC) and the damping capacity of the NiTi wire was measured using a dynamic mechanical analyzer (DMA). Results from the DSC shows that there is a presence of R-phase in the as-received wire. Heat treatment was carried out to eliminate R-phase as the study of R-phase is not under the scope of this project. From the experiments, it is observed that the damping capacity of martensitic NiTi is significantly higher as compared to the austenitic NiTi. This is believed to be due to the twinning and detwinning effect of the martensitic variants. An increase in frequency at the low frequency range will result in a decrease in damping capacity while an increase in frequency at the high frequency range will lead to an increase in the damping capacity. This result was attributed to the inability of the NiTi wire to dissipate energy quickly and the resonant frequency respectively. An increase in the strain amplitude was found to result in a decrease in the damping capacity when the material is in the martensitic phase. On the other hand, when the material is in the austenitic phase, the strain amplitude does not have any significant effect on the damping capacity.