Flexural Properties and Fracture Mechanism of Three-Dimensional and Four-Directional Braided (SiO2)f/SiO2 Composites

Abstract

Three-dimensional and four-directional braided (SiO₂)_f/SiO₂ composites were prepared by silicasol-infiltration-sintering method. The specimen density was determined to be 1.71 g/cm³ by using the Archimedes principle. The flexural properties were evaluated by three-point bending test. The flexural strength and flexural elastic modulus were found to be 62 MPa and 11 GPa, respectively. The stress vs. deflection curve showed a typical composite behaviour, initially a linear elastic response, followed a nonlinear region and finally failed gracefully. The SEM micrograph of the fracture sections showed extensive fibers pull-out, indicating the composites exhibited good toughness. A distinctly crevice was observed along the interfacial region, indicating the weak interfacial bonding between fiber and matrix, resulting in extensive fibers pull-out with a failure strain. The results of stress vs. deflection and SEM examination revealed that the fracture mechanism of the (SiO₂)_f/SiO₂ composite was a mixed mode of brittle and ductile.