Failure Mechanisms And Damage Model Of Fiber-reinforced Ceramic Matrix Composite

Ceramic matrix composites are potential candidate materials for future aero engine of a high thrust to weight ratio.Comprehensive research of failure mechanisms and failure models must be conducted to promote engineering application of ceramic matrix composites,and to develop performance prediction methods and damage research technology of ceramic matrix composites.An energy criterion based the energy release rates is used to study matrix crack deflection at interface in ceramic matrix composites.The energy release rates of possible crack paths are estimated by applying the virtual crack closure technique, and the effects of elastic mismatch parameters, the crack growth length, the relative crack growth length, and thermal expanding coefficient are analyzed on crack deflection of the matrix. The results show that double matrix crack are more likely to expand than single matrix crack if not consider the effects of temperature, thermal expansion match and interface performance.Failure models of matrix crack at the interface depends on closing forces caused by load and temperature at high temperature,and matrix cracks at the interface can be able to expand only the closing force caused by load is greater than that caused by temperature.Analyzed failure mechanism of ceramic matrix composites under uniaxial tensile loading and studied the mechanical relation between common characteristic of the stress-strain response and three dominant damage modes: matrix cracking, interface debonding and fiber breakage through analyzing the damage microstructure. Based on discrete regions method of stress-strain curve, discrete structure method is set up to divide laminated ceramic matrix composites into unidirectional ceramic matrix composites, and to divide stress-strain curve of unidirectional ceramic matrix composites into different regions which characterize three dominant damage modes.Unidirectional tension testing methods and testing systems for unidirectional C/SiC composite are studied. Specimen geometries and gripping fixture are designed, and the tensile test of unidirectional C/SiC is conducted successfully. Elastic modulus, strength and stress-strain curves of test are obtained. In-situ of damage evolution and fracture are researched by analyzing the fracture surfaces of damaged specimens.Assembled unified macro- and micro-mechanic constitutive model with failure criterias and damage evolutions of three dominant damage modes, a unified macro- and micro-mechanic constitutive model coupled with damage is improved to predict macro-mechanical properties of unidirectional and Laminates ceramic matrix composites.