臺灣博碩士論文加值系統

本研究以數值模擬方式，探討混凝土靶體受高速彈體撞擊下，所呈現的大應變、高應變率及高壓下之材料動態行為。數值模擬採用LS-DYNA有限元素分析軟體，並採用內建的兩種不同混凝土材料模型：Mat_Johnson_Holmquist_Concrete與Mat_Soil_Concrete來做數值模擬分析的比較。
首先建立合理的數值模型檢討三種參數：元素尺寸之收斂性分析，歸納出一個適合的λ(projectile radius/mesh size)值範圍，並討論時間步幅(t)與罰函數因子等參數對數值結果影響之比較，再與Hanchak實驗結果進行比較，以驗證數值分析模式之可靠性。此數值模型，再與撞擊深度經驗公式之結果比較，確認數值模擬能完整呈現混凝土之結構抗衝擊特性。最後針對混凝土的破壞模式來做一個分析與說明，探討不同網格尺寸對彈體撞擊混凝土之破壞模式之影響，並歸納出彈體貫穿混凝土靶體不同歷程下所呈現的破壞情形。
根據前述建立的數值模型，探討穿透彈體貫穿單層混凝土靶體與等厚度多層混凝土靶體情況下，其抗侵徹性能之差異性。研究結果顯示，本研究所建立之數值分析模型能有效預測混凝土大應變、高應變率及高壓情況下之動態反應與破壞型態。

In this study, numerical simulation methods to analysis the dynamic response of concrete subjected to penetration of high speed projectile. The effects of large strain, high strain rate and high pressure on the dynamic behavior have been investigated. The LS-DYNA finite element analysis software was used for numerical simulation, and the characteristic of two different models of concrete materials: Mat_Johnson_Holmquist_Concrete and Mat_Soil_Concrete were compared.
First, a reasonable numerical model was examined through three parameters: the effects of element size on the convergence of analysis result, a reasonable size parameter λ(projectile radius/mesh size) was summarized. The effect of time step size(t) and penalty stiffness factor(f_s) on the differences of numerical results have been discussed. Numerical analysis for Hanchak’s experiments was carried out, the results were compared with experiment results to verify the reliability of numerical models. The numerical model was above compared to empricial formula to predict the penetration depth to display the characteristic of concrete structure. Finally, we summarized the concrete’s failure model during the process of projectile penetration concrete target.
Finally, the difference of anti-penetration properties between the single concrete target and multiple concrete targets were investigated. The results show that the proposed numerical model can predict effectively the dynamic response and failure conditions under consideration of large strain, high strain rate and high pressure situations

口試委員會審定書 #
誌謝 i
摘要 iii
Abstract iv
目錄 v
圖目錄 viii
表目錄 xi
第一章 序論 1
1.1 研究動機與目的 1
1.2 文獻回顧 1
1.2.1 實驗及經驗估算法 2
1.2.2 數值模擬法 4
1.3 本文內容 5
第二章 LS-DYNA理論介紹 7
2.1 Lagrangian及Eulerian描述法 7
2.2 時間積分法之選取 8
2.2.1 中央差分法 9
2.3 時間步幅之控制 10
2.4 元素型態 11
2.5 沙漏效應(Hourglass Effect) 12
2.6 接觸演算法與接觸類型 13
2.6.1 接觸演算法 13
2.6.2 接觸類型 15
第三章 材料侵蝕破壞準則與材料模型說明 17
3.1 材料結構受衝擊損傷基本理論 17
3.1.1 高速衝擊現象與影響 20
3.1.2 高速衝擊對介質之作用 20
3.2 材料失效與侵蝕效應 21
3.2.1 材料失效準則 21
3.2.2 侵蝕效應 25
3.4 混凝土材料模型介紹 26
3.4.1 Soil_Concrete_Model 27
3.4.2 Johnson_Holmquist_Concrete Model 29
第四章 模擬流程與模型建立 33
4.1 分析流程 33
4.2 模型建立 34
4.2.1 實驗模型概述 34
4.2.2 彈體及靶體有限元素模型建立 36
4.3 材料模型參數設定 37
4.3.1 Soil_Concrete材料參數設定 37
4.3.2 Johnson_Holmquist_Concrete材料參數設定 38
4.3.2 彈體材料參數設定 39
4.3.4 接觸模式與邊界條件設定 40
4.3.5 沙漏效應控制設定 42
4.4 混凝土之衝擊深度經驗公式介紹 42
第五章 數值模擬結果分析與討論 47
5.1 合理數值模型驗證 47
5.1.1 網格尺寸之收斂性 47
5.1.2 時間步幅之收斂性 50
5.1.3 罰函數因子探討 52
5.2 混凝土衝擊深度經驗公式驗證 56
5.3 混凝土靶體之破壞型態驗證 62
5.3.1 不同網格尺寸對混凝土靶體破壞型態之影響 62
5.3.2 混凝土破壞模式探討 65
第六章 彈體撞擊多層間隔混凝土靶體之抗撞性能分析 71
6.1 模型建立 71
6.2 彈體與靶體材料模型 72
6.3 接觸定義與邊界條件設定 72
6.4 彈體撞擊多層且有間隔靶體之數值模擬結果 73
第七章 結論與展望 79
7.1 結果與討論 79
7.2 未來展望 80
參考文獻 81

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