臺灣博碩士論文加值系統

本論文使用分子動力學(Molecular Dynamics,MD)模擬奈米鐵線包含析出物之機械行為。模擬結果顯示， <110>與<100>單晶奈米鐵線與雙晶粒奈米鐵線在拉伸過程中，因較高之應變速率拉伸，導致奈米鐵線以雙晶變形為主。單晶奈米鐵線內部含析出物時，會破壞其完美晶體結構，造成降伏應力值降低;雙晶粒奈米鐵線若含析出物在晶界上，析出物會阻礙晶界上之雙晶變形啟動，使其降伏應變與應力值提高。析出物與基材界面鍵結較強者，因析出物與基材有較強之鍵結力，在雙晶變形擴展的過程中會有較大之剪應力，雙晶越過析出物時，會先形成差排環，隨後差排環會將析出物剪切變形;析出物與基材界面鍵結較弱者，析出物所受之應力值相對較低，使其無法被剪切變形，會在析出物周圍會形成差排環與微孔隙。微孔隙在頸縮後受到軸向應力之拉伸而被拉長並誘發應力集中，試片會在析出物周圍斷裂，並在破裂面形成dimple之延性破斷特徵。

The main purpose of this paper is using the molecular dynamics to investigate mechanical behavior of iron nanowire contains precipitate. Simulation results show, iron nanowires of <110>/<100> structure and Bi-Crystal will dominate by twin deformation in uniaxial tensile process. If iron nanowire of single crystalline contains precipitate, it will destroy perfect crystal structure of iron nanowire, resulting in reduced yield stress. When iron nanowire of Bi-Crystal contains precipitate on grain boundary, precipitate will obstruct twinning, resulting in strain and stress of yield are raised.If the interfacial bonding strength between precipitate and matrix is strong, due to precipitate and matrix have strong bonding force, in process of dislocations slip will be accompanied by high shearing stress. When dislocation bypass precipitate, it will form a dislocation loop, follow by dislocation loop will accompanied by a high shear force and shear of precipitate. If the interfacial bonding strength between precipitate and matrix is weak, due to shearing force of dislocation slipping cannot shear precipitate, the precipitate will prevent the dislocation slipping and form a dislocation loop and microvoid around the precipitate. The microvoid are stretched by stress after necking, and the microvoid will be elongate. Finally, the model break around the precipitate and form a ductile fracture feature “dimple” on the rupture surface.

目錄
摘要 I
ABSTRACT II
誌謝 III
目錄 IV
表索引 VI
圖索引 VII
第一章 緒論 1
1.1 研究動機及目的 1
1.2 文獻回顧 4
第二章 分子動力學基礎理論 8
2.1 分子動力學之基本假設 8
2.2 分子間作用力與勢能函數 8
2.3 運動方程式及演算法 14
2.4 VERLET 表列法 19
2.5 無因次化 22
2.6 原子級應力計算方法 24
2.7 CENTROSYMMETRY參數(CSP) 29
第三章 模擬步驟與模型建立 32
3.1 程式模擬步驟 32
3.1.1 初始設定(Initialization) 32
3.1.2 系統平衡(Equilibration) 43
3.1.3 動態模擬(Production) 44
3.2 模型建立 45
第四章 結果與討論 51
4.1 <110>奈米鐵線的拉伸變形機構分析 54
4.1.1 [101]奈米鐵線不含析出物之拉伸行為 57
4.1.2 [101]奈米鐵線含界面弱鍵結析出物之拉伸行為 69
4.1.3 [101]奈米鐵線含界面強鍵結析出物之拉伸行為 80
4.1.4 [101]奈米鐵線有/無內含析出物之機械性質比較 91
4.2 <100>奈米鐵線的拉伸變形機構分析 94
4.2.1 [001]奈米鐵線不含析出物的拉伸行為 96
4.2.2 [001]奈米鐵線含界面弱鍵結析出物之拉伸行為 107
4.2.3 [001]奈米鐵線含界面弱鍵結析出物於 應變率拉伸之行為 116
4.2.4 [001]奈米鐵線含界面強鍵結析出物之拉伸行為 123
4.2.5 [001]奈米鐵線含界面強鍵結析出物於 應變率拉伸之行為 134
4.2.6 [001]奈米鐵線有/無內含析出物之機械性質比較 141
4.3 雙晶粒奈米鐵線包含析出物之拉伸行為分析 145
4.3.1 雙晶粒奈米鐵線不包含析出物之拉伸行為 149
4.3.2 雙晶粒奈米鐵線含單一界面弱鍵結析出物之拉伸行為 159
4.3.3 雙晶粒奈米鐵線含單一界面強鍵結析出物之拉伸行為 170
4.3.4 雙晶粒奈米鐵線含兩顆界面弱鍵結析出物之拉伸行為 180
4.3.5 雙晶粒奈米鐵線含兩顆界面強鍵結析出物之拉伸行為 191
4.3.6 雙晶粒奈米鐵線有/無內含析出物之機械性質比較 201
4.3.7 單/雙晶粒奈米鐵線之機械性質比較 205
第五章 結論與建議 207
5.1 結論 207
5.2 未來研究方向與建議 209
參考文獻 210

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