Research On Mechanical Properties Of 2D Woven Ceramic Matrix Composites Based On Multi-scale Method

Woven ceramic matrix composites not only have good properties at room temperature and high temperature,but also have better toughness than the traditional single-phase ceramic materials.Therefore,they have become a new type of composite material that has been vigorously developed in the field of aerospace and nuclear energy.However,due to the complex material properties and braided structure of woven ceramic matrix composites,the mechanical properties and damage process of them are often not accurately obtained in the test process,which further affects the design and engineering application of woven ceramic matrix composites.The study of microstructure,mechanical properties and damage process of ceramic matrix composites will provide important reference for actual engineering design.In this dissertation,two-dimensional woven SiC_f/SiC ceramic matrix composite is taken as the research object,and the multi-scale finite element method is adopted to obtain the equivalent mechanical properties,strength and damage process of this material at micro and meso-scale.In the micro-scale research,representative unit cell models for studying micro-scale fiber bundles are established by using random packing method algorithm based on molecular dynamics.By using periodic boundary conditions,homogenization theory and Weibull random strength distribution,the equivalent elastic properties and strength of micro-scale fiber bundles are obtained,and the causes and processes of damage and failure in all directions are discussed.The finite element simulation results are similar to the actual damage and failure tests.In the meso-scale research,based on the actual composite optical microscope images,a meso-scale woven unit cell model is established and 3D Hashin strength criterion is used to judge the damage of fiber bundles,so as to obtain the equivalent elastic properties and strength of two-dimensional woven SiC_f/SiC ceramic matrix composites.Then,the equivalent stress-strain curve and damage cloud map of in-plane tension finite element simulation are compared with the experimental results.The results show that the finite element results are in good agreement with the experiment results.Therefore,this method can accurately predict the mechanical properties and damage behavior of this type of composite.Pores are often generated during the production of two-dimensional woven SiC_f/SiC ceramic matrix composites.The meso-scale finite element models with random pore elements distribution are established,and the effects of porosity on equivalent elastic property,strength and fracture strain of the composite are discussed.The results show that the equivalent elastic parameters and strength of the material decrease with the increase of porosity,and the fracture strain trend is different from elastic property and strength.The fracture strain of in-plane tension climbs up and then declines,while the out-of-plane tension and in-plane shear shows a trend of increasing.This phenomenon indicates that porosity has a certain degree of toughening effect on two-dimensional braided SiC_f/SiC ceramic matrix composites.