DC Field | Value | Language |
---|---|---|
dc.contributor.advisor | 윤정환 | - |
dc.contributor.author | Kang, Chun Gu | - |
dc.contributor.author | 강춘구 | - |
dc.date.accessioned | 2024-08-08T19:30:51Z | - |
dc.date.available | 2024-08-08T19:30:51Z | - |
dc.date.issued | 2024 | - |
dc.identifier.uri | http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=1097781&flag=dissertation | en_US |
dc.identifier.uri | http://hdl.handle.net/10203/321946 | - |
dc.description | 학위논문(박사) - 한국과학기술원 : 기계공학과, 2024.2,[xvii, 131 p. :] | - |
dc.description.abstract | however, certain grains may grow larger because of factors such as chemical composition, manufacturing processes, and heat treatment conditions, thereby resulting in a bimodal distribution of grain sizes. Previous studies on the bimodal distribution of grain sizes primarily focused on nanocrystalline, ultrafine-grained, or multi-phase materials, wherein the presence of coarse grains enhanced strain hardening ability, uniform elongation, and drawing formability. In contrast, our observations in practical industrial materials, which contain a mixture of fine and coarse grains, revealed a decrease in the strain hardening exponent and uniform elongation. In addition, unlike in previous research, coarse grains were found to be incapable of accommodating deformations. Therefore, the microstructural non-uniformity of grain size leads to localised deformation and a decline in stretch formability. In this study, we developed a chemical composition model for ultra-low carbon steel containing a small amount of niobium precipitates using Thermo-Calc software and determined appropriate heat treatment temperatures. Materials with a bimodal distribution of grain sizes were artificially obtained by dissolving precipitates after hot and cold rolling. The mechanical properties of these manufactured materials were evaluated using uniaxial tensile tests, limit dome height, and limit drawing ratio. We analysed microstructural changes before and after plastic deformation using scanning electron microscopy equipped with electron backscatter diffraction to gain insights into the microstructure, texture, and deformation distribution of these materials. We conducted tensile tests at various strain rates (0.002, 0.02, 0.2, and 2.0$^{-1}$) and derived the material constants for the crystal plasticity finite element method (CPFEM) analysis from these results. Subsequently, we created a virtual microstructure with varying sizes, fractions, and orientations of coarse grains and performed CPFEM analysis to evaluate the mechanical properties such as strain hardening exponent and uniform elongation. Our study confirms microstructures with grain sizes ranging from a few to tens of micrometres experience localised deformation influenced by the crystallographic characteristics of non-uniform microstructures and the presence of coarse grains. | - |
dc.description.abstract | The accumulation of dislocations in a cold-rolled sheet acts as the primary driving force for recovery and recrystallization during heat treatment. During continued heat treatment, grains tend to grow uniformly and continuously | - |
dc.language | eng | - |
dc.publisher | 한국과학기술원 | - |
dc.subject | Inhomogeneous microstructure▼aUltra-low carbon steel▼aGrain size▼aBimodal distribution▼aCrystal plasticity finite element method▼aStrain localization | - |
dc.subject | 불균일 미세조직▼a극저탄소강▼a결정립도▼a이산분포▼a결정소성유한요소해석▼a변형 집중 | - |
dc.title | Influence of non-uniform grain size distribution on mechanical properties of metal sheet | - |
dc.title.alternative | 불균일 결정립 크기 분포가 금속 판재의 기계적 물성에 미치는 영향 | - |
dc.type | Thesis(Ph.D) | - |
dc.identifier.CNRN | 325007 | - |
dc.description.department | 한국과학기술원 :기계공학과, | - |
dc.contributor.alternativeauthor | Yoon, Jeong Whan | - |
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