Abstract: 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 remains in its initial stage, characterized by a primarily qualitative understanding of their mechanical property failure mechanisms. In this study, an improved liquid-phase impregnation method, which integrates 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. The microstructure and composition of typical composites were comprehensively characterized using different techniques. The mechanical properties of composites with different densification degrees were tested and analyzed. By integrating porosity data obtained from CT testing with simulation calculation, a relationship model linking mechanical property failure of composites to porosity and pore size 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 the rationality of the simulation model. The laws that the n-th power of tensile strength shows a negative linear correlation with porosity, and the tensile strength exponent factor is negatively linearly correlated with the pore defect radius size. These findings provide a research basis for the performance optimization and practical application of continuous alumina fiber-reinforced silica composites.

Key words: alumina fiber, silica composite, mechanical property, porosity, pore defect size, failure