The study on the properties of Ni-Ti shape memory alloy by molecular dynamics simulation
| Autor: | Wei-JhihHong, 洪暐智 |
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| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 We employed molecular dynamics simulation to investigate the shape memory properties of Ni-Ti alloy bulks. The effects of Ni composition ratio and the simulated crystal orientation on phase transformation were studied. At low temperature, different loading conditions were applied to the alloy bulk till plasticity took place. Then the deformed models went through the temperature cycle without loadings to examine whether it would restore to its original shape or not. Form the simulation, we found the Ni-Ti alloy is body-centered cubic structure (austenite phase) at high temperature and transforms to monoclinic structure (martensite phase) at certain temperature, except for the 50% Ni composition ratio. The phase transformation temperature was affected by the Ni composition ratio. It was observed that the simulated models with different Ni atomic distribution and crystal orientations would have the same phase transformation temperature. For different loading simulations, it was found that not every plastic deformed model would restore to its original shape after the thermal cycle. Combined with common neighbor parameter observation, it was noticed that only those were able to force the twinning variants to move on the specific plane would exhibit shape memory behavior. For those loadings which would restore to its original shape, the corresponding maximum shear stress was clearly smaller than those that did not restore. With the assist of slip vector, it was known that the model which had dislocation would not have shape memory properties. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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