Processing and flexural properties of 3D, seven-directional braided (SiO2)f/SiO2 composites prepared by silica sol-infiltration-sintering method

Three dimensional (3D), seven-directional braided (SiO2)f/SiO2 composites were prepared by silica sol-infiltration-sintering (SIS) method. The flexural properties were evaluated by three-point bending test. The flexural strength and flexural elastic modulus were found to be about 107 MPa and 17.5 GPa, respectively. The results of stress vs. deflection curve and SEM examination revealed that the fracture mechanism of the (SiO2)f/SiO2 composite was a mixed mode of brittle and ductile. The bond strength of fiber/matrix was weak at low temperature, causing the extensive fiber pull-out. On the other hand, the brittle fracture of some fibers maybe caused by the propagation of micro defect or crack, which existed in the as-prepared composites for the ten-cycle process.