| Project/Area Number |
20K04165
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 18010:Mechanics of materials and materials-related
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| Research Institution | Keio University |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Project Status |
Completed (Fiscal Year 2022)
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| Budget Amount *help |
¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000)
Fiscal Year 2022: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000)
Fiscal Year 2021: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Fiscal Year 2020: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
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| Keywords | LPSO型Mg二相合金 / 有限変形理論 / 結晶塑性Cosseratモデル / キンク帯 / 回位密度 / 転位密度 / 強度発現機構 / 寸法効果 / Mg基LPSO二相合金 / メッシュフリー法 / LPSO相 / キンク / 結晶塑性 |
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| Outline of Research at the Start |
長周期積層構造(LPSO)を有するマグネシウム(Mg)合金は，微視的な塑性座屈であるキンク帯形成に端を発する材料強化によって飛躍的に性能を向上させ得る．しかしながら，キンク帯の形成機構および形成条件は十分に解明されておらず，従来のせん断モード(転位の移動，蓄積)に加えて回転性の塑性変形機構(回位の移動，蓄積)を考慮したモデルの構築が期待されている．本研究では，転位に加えて回転性の結晶欠陥である回位を考慮した大変形結晶塑性モデルを構築し，高次ひずみこう配の解析に適するメッシュフリー法を用いてLPSO型Mg二相合金におけるキンク帯形成およびその後の強化の再現を可能とする数値解析手法を確立する．
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| Outline of Final Research Achievements |
The mechanical properties of Mg dual-phase alloys with long-period stacking ordered (LPSO) phase are significantly enhanced by the formation of fine kink bands. In this study, to clarify the strengthening mechanism owing to the kink bands, the Cosserat model was formulated in the framework of crystal plasticity based on finite deformation theory and a new material model was developed, in which the accumulation of dislocations and the generation of disclinations were simultaneously considered. Using the obtained model, a mesh-free analysis was performed for a strip-shaped tri-crystal. As a result, it was showed that when a kink band is formed by compressive loading and then reverse loading is applied, if ridge-shaped kinks tend to occur, local orientation differences and accumulated dislocations remain more, and the terminal strength is higher. In addition, the smaller the average grain size of the α-Mg phase becomes, the higher the terminal strength after reverse loading reaches.
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| Academic Significance and Societal Importance of the Research Achievements |
構造材料の軽量化と強化の立場から脱炭素社会実現に寄与する以下のような知見を得た．有限変形理論の範疇では，GN転位密度はすべりこう配のみならず回位密度にも依存する．また，試験片端部の回転を拘束できる本モデルでは，試験片寸法によらずキンク帯を再現できる．さらに，微視回転と巨視回転を独立変数としつつペナルティ法で一致させれば，C0級要素を用いたFEM解析によってメッシュフリー法と同程度の精度で計算コストを低減させ得る．加えて，底面系を荷重軸にほぼ平行に配置するとともに初期方位の不均一性を増大させ，α-Mg相を微細化すれば，圧縮後に逆負荷を加えた際，終端強度を1～3割程度増加させ得る．
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