Fracture analysis of porous Si–SiC ceramics with anisotropic three-dimensional network structure

The fracture mechanism and reliability of typical dense ceramics can be statistically analyzed using a Weibull distribution as a basis for device design. However, it is not understood if the Weibull distribution can even be applied to highly porous ceramics. In this study, porous Siliconized Silicon Carbide (Si–SiC) ceramics with anisotropic three-dimensional network structures in a porosity range of 71–92% were fabricated and subjected to a fracture analysis using the results of three-point bending tests. Observations of fracture behavior during the bending tests were conducted using a high-speed camera, image analysis of stress distribution, and observation of crack distribution inside the partially damaged specimens using X-ray computed tomography. The results indicate non-linear behavior with multiple peaks in the load–displacement curves. In this regard, the fracture mechanism of the porous Si–SiC ceramics was intrinsically different from the brittle fracture of dense ceramics and did not appear to be based on the weakest-link model. However, the Weibull distribution was found to be applicable to the bending strength of the porous ceramics with a confidence coefficient of 0.90. This was because although strain and cracks were generated sporadically during loading, the catastrophic fracture of the porous Si–SiC ceramic specimens occurred with a macroscopic crack opening at the bottom of the test specimens, almost the same as a Mode I crack opening in dense ceramics. Furthermore, graded three-layer structures can be formed integrally using the proposed novel replication method with uniaxial pressing, taking the plateau of the stress–strain curve of the template polyurethane foam into account, providing a kind of damage tolerance owing to the sporadic generation and sequential propagation of cracks, manifested as the multiple peaks shown in the load–displacement curves.