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| dc.contributor.author | Biniam, Tamrea | |
| dc.date.accessioned | 2022-12-31T10:31:57Z | |
| dc.date.available | 2022-12-31T10:31:57Z | |
| dc.date.issued | 2022-11-10 | |
| dc.identifier.uri | http://ir.bdu.edu.et/handle/123456789/14858 | |
| dc.description.abstract | A nitinol (NiTi) is a shape memory alloy that can be characterized by its shape memory effect and super elasticity behavior. The super elastic properties of SMA lead the material to be used as energy storage. Due to its unique shape memory effect (SME) and super elasticity (SE) properties, it is commonly subjected to different fatigue loadings. The aim of this research is to develop a technique which can improve the NiTi shape memory alloy fatigue resistance through microstructural evolution. In this work, a cantilever beam under bending fatigue loading has been considered to investigate the full-scale fatigue behavior of NiTi after carried out the plastic deformation process to examine the effect of microstructure evolution of NiTi from the previous undeformed NiTi. First, to increase resilience to fatigue of NiTi, a stress relief grooves geometry has been developed by using Deform 3D software. The impact of deforming temperature, groove depth, and groove radius was investigated during microstructure analysis and the optimum deforming temperature, groove radius, and groove diameter was selected for further analysis. The grain size of NiTi drops and the material's fatigue resistance rises as the groove depth and groove radius increase. After the deformation processes, the deformed NiTi shape memory alloy microstructural analysis was applied to investigate the dynamic recrystallization processes. Due to the severe plastic deformation induced by the constrained groove pressing, the grain refinement of the NiTi alloy was observed at the surface of the groove from initial grain size of 49 𝜈𝑛 to 2.5277𝜈𝑛 − 15.8𝑜𝑛. By using the Hall-Petch method, the grain refinement induced in NiTi yield strength improvement was functionally graded and the ultimate improvement of yield strength was determined by 239% in the groove region. In comparison to undeformed NiTi, the fatigue strength increased by 54.6% as a result of microstructural evolution. Therefore, the ideal way to accelerate NiTi microstructural evolution and enhance its mechanical properties is to use the plastic deformation technique with constrained groove pressing. Keywords: NiTi shape memory alloy; Fatigue strength; Microstructure evolution; Constrained groove pressing; Recrystallization; Deform 3D | en_US |
| dc.language.iso | en_US | en_US |
| dc.subject | MECHANICAL AND INDUSTRIAL ENGINEERING | en_US |
| dc.title | Investigation on microstructure evolution for the enhancement of NiTi fatigue strength using constrained grooves pressing modeling | en_US |
| dc.type | Thesis | en_US |
