Geometry Modeling And Interface Damage Mechanics Research Of 3-D Braided Composites

3-D braided composites is widely used in aerospace, defense, medical, civilian facilities and other high-tech areas by its excellent performance and outstanding designability. The research of 3-D braided composites mechanical property and damage is a very important problem. At present, though the research of mechanics behavior of 3-D braided composites has some progress, there are many problems need to be further investigated. This paper studies 3-D braided composites by predicting elastic constants, analysing stress and damage of fiber and fiber matrix interface using theory and numerical analysis.In the first chapter, the development of 3-D braided composites is introduced, the recent research progress of 3-D braided composites on geometry modeling, process, numerical simulation of mechanical property, analysis of interfacial mechanics are reviewed, and the writer expounds the purpose of this topic and significance of research.In the second chapter, effective modulus of the 3-D braided composites is predicted by using internal cell curved fiber model, surface cell and angle cell polyline flber model. First, according to the geometric distribution of fiber in model, periodic three cell models is established, and fiber and matrix volume percentage of each model is separately calculated. Then, the stiffness matrix of each single cell model is get through averaging stiffness. Finally, the effective elastic modulus of 3D braided composites preform are obtained by the method of averaging volume.In the third chapter, the writer researches a single straight fiber and analyses stress of interface. First, curved fibre can be expressed as a combination of a series of infinitesimal straight fiber through coordinate transformation, fiber axial stress and the shear stress are get by the theoretical analysis of fiber drawing model. Then, the stress nephogram and data of fiber and matrix are obtained through simulating fiber drawing model using the finite element software. Finally, the numerical results are analysed.In the fourth chapter, the writer discusses the stress distribution of defective braided composites. First, through using the eigenvalue method of axisymmetric interface singular stress field, interface mechanics and fracture mechanics theory, the stress distribution and fracture criterion of defective 3-D braided composites are analysed. Then, through the numerical simulation for two defect of 3-D braided composites by the finite element software, the singular point of the stress distribution and the stress intensity factor are obtained. Finally, the crack scale effect for material stress distribution is simulated and analysed.