Mechanical Property Failure of Alumina Fiber Reinforced Silica Composite

Continuous alumina fiber-reinforced silica ceramic matrix composites exhibit excellent properties, such as high-temperature oxidation resistance, high strength and high toughness. As a dual-use material for both military and civilian applications, they hold broad prospects in numerous fields, including aviation, aerospace and energy. However, domestic research currently still remains on its initial stage and is characterized by a primarily qualitative understanding of their mechanical property failure mechanisms. In this study, an improved liquid-phase impregnation method, which integrated the process characteristics of the Sol-Gel method and slurry impregnation method, was adopted to prepare continuous alumina fiber-reinforced silica composites with tunable porosity. Microstructure and composition of the typical composite were comprehensively characterized using different techniques. Mechanical properties of these composites with different densification degrees were tested and analyzed. By integrating porosity data obtained from computed tomography (CT) test with simulation calculation, a relationship model linking mechanical property failure of the composites to porosity and pore size parameters was established. The results indicated that composites prepared via the improved liquid-phase impregnation method had significantly enhanced mechanical properties due to the presence of pore defects and weak interfacial bonding. Notably, as the composite porosity increased from 2.2% to 15.2%, the tensile strength decreased from 24.5 MPa to 17.8 MPa. Further modeling and simulation analysis revealed that, at a pore defect radius of 250 μm, an increase in porosity from 4.5% to 13.5% led to a corresponding reduction in tensile strength from 27.2 MPa to 20.6 MPa, thereby validating rationality of the simulation model. The law that the n-th power of tensile strength shows a negative linear correlation with porosity, and the tensile strength exponent factor n is negatively linearly correlated with the pore defect radius r. These findings provide a research basis for the performance optimization and practical application of continuous alumina fiber-reinforced silica composites.