The Analysis Of The Progressive Failure Mechanisms In Tubular Braided Carbon/carbon Composites

The excellent mechanical property of composites made them been widespread concerned at home and abroad since they are been found. In recent years, the composites are widely applied in the field of aviation, aerospace, transportation, construction and so on. Therefore, studying the failure mechanisms of composites has practical significance in service. Studying the damage and failure process is very complicate. When the local-damage is being emerge, the whole can continue to bear the loadings with increasing the load. A few filaments develop to carbon fiber bundle, then the carbon fibers bundle intertwining into the fabric, finally the fabric and carbon matrix composite components interact under certain conditions. Therefore, it is the multi-scale problems. In this paper, the progressive damage analysis is used from the micro and macro scales to study C/C composite’s failure mechanisms respectively.In the first chapter, the progressive damage failure of composites studied by experiment, simulating and theory are summarized separately in this part. At the same time, the current problems are also proposes of the composite in the damage failure analysis. In the end, the writer explains the purpose of this topic and significance of the research.In the second chapter, the circular tubular braided C/C composite are taken as the research object, the microscopic repeated unit cell (RUC) model for yarn and the macro-RUC model for three-braided composite, are presented. The micro-RUC model is used to describe the interaction between the fiber and the matrix and the macro-RUC model is used to describe the macroscopic properties. Used the periodic boundary conditions and the node methods, the RUC’s mean stress and mean strain are calculated. The average elastic constants in carbon fiber bundle are calculated through the parameter of micro-RUC, and then obtained the elastic constants of C/C composite.In the third chapter, the progressive failure analysis is introduced in theoretical. The stress analysis, failure criteria, the stiffness properties of the degradation are being the three main parts. The writer establishes the micro-RUC and uses the finite element method to simulate the micro-RUC failure and getting the global as well as local mechanical properties.In the fourth chapter, the writer analyzes 3-D braided composite’s progressive damage based on the rocket nozzle for the macro-scale model, simulating the rocket nozzle failure and damage propagation in the thermo-mechanical coupling by using ANSYS, obtaining the stress-strain curve, and compared with the experimental results. The nozzle stress concentration occurs in the contact portion firstly, because the contact portion has the irregular shape. Therefore the failure mechanisms occurred in the stress concentration and circumferential expansion.