J積分을 이용한 CFRP積層板의 動的破壞靭性 評價

다국어 초록 (Multilingual Abstract)

Carbon Fiber Reinforced Plastics(CFRP), one of the advanced composite materials, is widely used today in various fields including space and aviation industries, sports and leisure industries and general structural members and parts. The material, however, is also susceptible to the damages from collision of the foreign objects.
Internal damages like the inter-layer delamination even under a relatively low speed impact have become an important factor in the safety design of CFRP composite plates. Besides, the fact that CFRP is a material composite of carbon fiber and plastic resin makes its characteristics inhomogenious and anisotropic. This makes it very difficult to predict analytically the mechanism and scope of damage generation unless depending on experimental method for evaluating their structural reliability. To predict any fracture mode in whatever methods, finding out the value of inter-layer fracture toughness under the load of both static and dynamic impacts is one of the most important works for a safety design.
This research work has been carried out for finding J-integral in mode Ⅱ of CFRP laminate plates based on the classical bar theory in dynamic conditions with consideration of the effect of inertia forces, eventually to lead to finding the dynamic inter-layer fracture toughness. Dynamic inter-layer fracture toughness was found by a self-made ENF experimental apparatus using SHPB, and also observed the variation of the fracture toughness having different resin contents and fiber arrangements of CFRP specimen. Work is summarized as follows:
1) Critical load f_(c) could be obtained by finding the time t_(c) when the load applied to the test specimen becomes maximum and the inter-layer delamination starts to develop. Using this critical load f_(c) it was found that the inter-layer fracture toughness could be obtained.
2) Inter-layer fracture toughness under a static load condition could be obtained through J-integral in the ENF experimental test specimen, and the same under a dynamic load condition with consideration of inertia forces could be obtained through J-integral.
3) Variation of inter-layer fracture toughness depending on the fiber strengths of CFRP laminate plates was very minute in case of quasi-static load condition and slightly varied in case of dynamic load condition. This is thought to be within an experimental error limit coming from application errors of loads In the dynamic experiment. Effect of fiber strengths on the inter-layer fracture toughness was found to be very minute compared to the effect of resin contents and fiber arrangements.
4) In either cases of quasi-static or dynamic load condition, the critical load and the inter-layer fracture toughness increased sharply depending on the increase of resin contents. It could, therefore, be concluded that the effect by resin contents is the major factor determining the inter-layer fracture toughness in the CFRP laminate plates.
5) Higher inter-layer fracture toughness was shown in specimen haying the fiber arrangements of [0_(3)°/90_(3)°/0_(6)°/90_(3)°/0_(3)°] than those of either. [0_(20)°] or [0_(5)°/90_(10)°/0_(5)°] Considering the fact the CFRP laminates are having various arrangements of fiber angles in actual application and no inter-layer fracture is seen in the layer of fiber having single direction, it may be said that fracture toughness becomes higher in the laminates having more layers. However, further study is required to find factors affecting the fracture toughness depending on the change of shears and radii of curvature at the position of initial delamination development.
6) Observation of the fracture surfaces through SEM revealed that hackle becomes finer at higher impact velocity and coarser at lower impact velocity. In case of higher resin contents, the hackle became coarser, and finer in lower resin contents. This tells that the resin contents give important effect in Mode Ⅱ CFRP laminated plates.

목차 (Table of Contents)

• 목차
• LIST OF FIGURES = Ⅲ
• LIST OF TARIES = Ⅶ
• LIST OF PHOTOGRAPHS = Ⅸ
• ABSTRACT = Ⅹ
• 第1章 緖論 = 1
• 1.1 硏究背景 = 1
• 1.2 硏究目的 = 3
• 1.3 硏究方法 = 5
• 第2章 試驗片 및 實驗裝置 = 8
• 2.1 試驗片 = 8
• 2.2 實驗裝置 = 18
• 2.2.1 準靜的 ENF 實驗裝置 = 18
• 2.2.2 動的 ENF 實驗裝置 = 19
• 第3章 CFRP積層板의 層間破壞에 對한 J積分의 解析 = 31
• 3.1 ENF試驗片의 動的變形 解析 = 31
• 3.2 ENF 試驗片에 對한 J積分의 解析 = 43
• 第4章 CFRP 積層板의 破壞靭性値 評價 = 50
• 4.1 準靜的 ENF實驗 = 50
• 4.1.1 收支含有量의 形響 = 53
• 4.1.2 纖維强度의 影響 = 58
• 4.1.3 積層構成의 影響 = 61
• 4.2 動的 ENF實驗 = 65
• 4.3 ENF試驗片의 層間剝離面 觀察 = 93
• 第5章 結論 = 105
• 參考丈獻 = 107