Multi-scale Modeling And Mechanical Properities Analysis Of Continuous Carbon Fiber Toughened ZrB₂-SiC Matrix Composites

The continuous carbon fiber reinforced Zr B₂-SiC matrix composite?C_f/ZrB₂-SiC?has excellent anti-oxidation and ablation properties,high specific strength and high specific stiffness,which can significantly improve the shape maintenance in high temperature.It has great application potential in the hot end components of spacecraft.By depositing different thickness pyrolytic carbon coating on the surface of carbon fiber,the bonding form between the fiber and the matrix can be changed,and the thermal residual stress state in the composite can be controlled.The effect of pyrolytic carbon coating on the toughening and strengthening of ultra high temperature ceramic matrix was promoted.It is very important to study the strengthening and toughening mechanism of carbon fiber for the design,preparation and application of C_f/ZrB₂-SiC.The interface layer and the damage of interface layer by thermal residual stress are important factors affecting the mechanical properties of C_f/ZrB₂-SiC.In this paper,based on the in-situ tensile test and damage mode analysis under the electron microscope,from the microscopic point of view,the microscopic and mesoscopic cells are established in line with the actual situation according to the periodic characteristics of C f/Zr B₂-SiC structure at different scales,and the mechanical properties of C_f/ZrB₂-SiC are analyzed.First of all,the thermal residual stress and microstructure on mechanical properties of materials are reviewed in this paper,discusses the research status of continuous carbon fiber toughened ceramic matrix composites at home and abroad,and provides the basic idea to analyze the mechanical properties of C f/Zr B₂-SiC at different scales.The shortcomings of micro modeling of materials are mainly reflected in the lack of considering the finite thickness of the interface layer,the initial damage of the interface layer caused by the thermal residual stress when the material is cooled from the preparation temperature to room temperature.Then,in order to clearly observe the real-time deformation behavior and surface damage initiation and evolution of C_f/ZrB₂-SiC during the experiment,the in-situ tensile test under the electron microscope and digital image correlation technology are used to analyze the surface deformation and strain field of the sample by correlation analysis,and the micro morphology of the fracture is observed by micro scanning.The internal damage failure mode and toughening principle can be obtained,which provides guidance for the finite element numerical analysis.Secondly,a micro cell is established by random algorithm,which includes a finite thickness interface layer and randomly distributed fiber and periodic boundary.The initial thermal residual stress and the interface damage mode are studied by combining with the bilinear cohesive force model and the bat ch insertion cohesive force element technology.After considering the damage mode of the interface layer caused by the initial thermal residual stress,the equivalent properties of RVE at room temperature and high temperature are predicted,and the effects of different interface thickness on the equivalent properties are analyzed.Finally,the micro cell model of matrix with random crack distribution is established to predict the equivalent elastic properties of matrix with different crack density.Considering the real shape of the yarn,Micro-CT and Tex Gen are combined to establish the micro cell with enough accuracy,and three-dimensional periodic boundary conditions are applied to predict the equivalent stiffness at room temperature and high temperature.The three-point bending experiment is simulated from multi-scale,and the correctness of the calculation model is verified.