多層複合板之高速衝擊模擬

Abstract

在工業問題中，大變形造成材料破壞是常常遭遇到的問題。現今最常見之破壞計算問題，不外乎物件墜落、汽車碰撞及彈體衝擊等問題。本論文主要利用LS-DYNA有限元素數值模擬計算軟體探討彈體高速衝擊不同靶板的破壞問題，並以LS-DYNA中不同材料破壞模型應用至適當材料上，包括Elastic Plastic Hydro Spall彈塑性模型、Johnson Cook金屬材料破壞模型、Johnson Holmquist Concrete混凝土材料模型及Johnson Holmquist Ceramics陶瓷材料模型，比較應用之差異與適當性，有效應用至計算彈體高速衝擊複合靶體的計算。本文計算結果中不僅表現出混凝土材料破壞時脆性崩落的特性，亦成功描述陶瓷材料高硬度的特性造成彈體發生Dwell現象。 混凝土為一種複雜且多相之材料，在計算上面易造成許多不可預測的誤差，故本文在混凝土計算上的驗證，不僅應該用Johnson Holmquist Ceramics原文的計算結果比對，更利用WES公式、美國陸軍公式及Forrestal三種不同之混凝土靶板衝擊深度經驗公式，驗證Johnson Holmquist Concrete材料模型在高速衝擊問題中之計算結果。本文驗證結果與Johnson Holmquist Ceramics原文誤差在工程上可接受的範圍內，且與WES公式深度計算結果甚為吻合。 針對改善鋼混凝土複合板的抗衝擊之能力，本文利用添加B4C、SiC、AlN及Al2O3四種不同陶瓷材料於鋼混凝土複合板夾層中，經由計算結果預測不同陶瓷材料對於消耗彈體動能的能力，改善複合板抵禦衝擊的能力，並探討不同衝擊條件下之力學行為，以彈體不同入射角度的計算結果，求得影響9mm Luger彈體的衝擊能力之關鍵入射角度。此外，亦進一步探討B4C陶瓷材料厚度對於抵禦高速衝擊能力之影響，利用結果成功改善原複合靶體之設計。

Large strains often cause material destructions in industry and applications. In numerical simulations, we have to set up material models suitable for computation problems. This thesis simulated bullet penetration problems by LS-DYNA software with Elastic Plastic Hydro Spall Material Model, Johnson Cook Material Model for metals, Johnson Holmquist Concrete Material Model for concrete, and Johnson Holmquist Ceramics Material Model for ceramic. Concrete is more complicated than the other materials in penetration simulations due to its inhomogeneous composition, which results in errors and inconsistencies. This thesis validated penetration problems employing four concrete models, namely, Johnson Holmquist Concrete in their original document, WES, Forrestal, and U.S. Army empirical formulae. After verifications, we adapted the modeling parameters to calculate bullet impacts on sandwich composite panels. For 9mm Luger bullets with incident angles, the computing results evidence a pertinent angle about 20within which the bullet could penetrate the panel with larger residual kinetic energy than the normal impact. To improve the sandwich panel strength, we proposed to add a ceramic layer beneath the front steel. B4C, SiC, AlN, and Al2O3 were tested in this investigation. We found that B4C ceramic is the best among the four ceramics. Subsequently, we studied the effects of thickness of B4C ceramic layer on the impact resistance. Numerical results showed that adding 6mm B4C ceramic layer in between the front steal and inner concrete would efficiently enhance the capability of bullet impacting.