The Damage Coupled Macro- And Micro-Constitutive Models For Ceramic Matrix Composites

The failure of Ceramic Matrix Composites (CMCs) is produced due to the pre-existence of various types of defects in microstructure. This increases the necessity of developing a Damage Coupled Macro/Micro Constitutive Model (DCMMCM) for the application of this material to the high thrust-to-weight aero engine. However, few research works about DCMMCM has been done in China. The purpose of the research undertaken during this doctoral program and which is detailed in this manuscript is to develop a new DCMMCM for predicting the evolution of the damage, as well as the resulting material behavior for CMCs.A new global strain is defined as the integration of displacements on the RVE's boundary for the first time. The close problem for this new global strain which is important for Micro/Macro Constitutive Model (MMCM) is proposed and proved. Then, the theoritical framework of MMCM is developed based on the new global strain and the multiscale theory.The High Fiedility Quadrangular Cell Method and Node Interpolation Cell Method are developed saparetly by applying the weight method and virtual work principle to solve the basic equations of the framework. The advantages of these new models are (1) the variables in the microscopic lever and the macroscopic lever are coupled, the formulations of the global elastic modulus and the micro-stress/strain field are derived from these models, (2) the non-regular subcells are employed into the new models to discretize the repeating unit cell, this manner of discretization increases the ability of the models for mimicking the microstructure of material, (3) it is convenient to imposed damage model of material into these models to develop corresponding DCMMCM, (4) it is possible to combined these models with a common Finite Element Analysis code to perform multi-scale analysis for structure. The accuracy and efficient of these models are demonstrated by some numerical examples.The monotonic tensile tests are performed to obtain the stress-strain responds of C/SiC composite. The non-destructive inspection is also performed to estimate the damage within the C/SiC composite. Through these experiments, the failure mechanism of C/SiC composite is understanded, and some failure models are developed to modeling the evolution of damage at micro lever. At last the DCMMCM for C/SiC composite are developed by combinding the damage model and the MMCM proposed in this paper.The stress-strain responses of several kinds of CMCs obtained from the present DCMMCM are compared with their experimental counterparts. In all cases, the predicted material behavior is consistent with the experimental data.