Delamination Failure Mechanism Of Carbon Fiber Reinforced Composite T-joints

With highly excellent mechanical properties of strength and modulus, Fiber reinforced composite have been widely applied in many engineering fields, such as aerospace, aviation, automobile, construction and bridges. In recent years, the development tendency of the composite is to achieve the integration of material structure, which is an important and efficient way widely recognized at home and abroad to get high-efficiency composite. The T joint is a typical representative of structure integration. However, under the action of load, laminated structure between the layers of composite are prone to delaminate. Layer delaminating is the main damage form of composite laminated structure, which can make serious degradation to the structure mechanical properties.In this thesis, research on the deformation and energy release rate between the composite laminated plate with defects and tee joint under the action of external load are presented.(1) The energy release rate of the double cantilever beam with delamination at any height under tensile load is calculated through calculating the difference between the external work and strain energy. The energy release rate of the DCB specimen with delamination at mid-plane is achieved using the ANSYS finite element software based on virtual crack closure method,which matches with theoretical predictions.(2) The 3D fracture problems of composite T-joint is studied by using SOLID46 three-dimensional entity unit. The distribution of energy release rate on the crack front of three kinds of fracture mode is calculated, depended on which stress field of the crack tip is achieved,and the dangerous position is known.(3) The composites T-joint geometry factors affecting the tensile properties of composites T-joint are studied in which skin length and chamfering radius are the main. The results prove that the longer the skin is, the smaller the energy release rate of T-joint of composite materials is, also is the less stress field. When the chamfering radius increases, the energy release rate of ModeⅠ increases but the one of Mode Ⅱ decreases. It proves that the ModeⅠ fracture is easier to happen when the chamfering radius increases. However, the possibility of Mode Ⅱ fracture is smaller.(4) Using the finite element analysis software ANSYS, based on the linear fracture criterion, the crack propagation of double cantilever beam and tee joint is simulated through the predefined crack propagation path, the critical reaction force of the loading point when the crack starts to propagate is obtained.