Prediction of fracture strength for ceramics containing a surface defect with arbitrary shape

Abstract

To investigate the influence of surface defect with arbitrary shape on fracture strength of ceramics, three-point bending tests on alumina-silicon carbide (Al₂O₃/SiC) ceramic composites were carried out. A standard pre-crack, a tilted pre-crack and multiple pre-cracks were introduced on the specimen surface using a Knoop indenter. The specimens without pre-cracks were also prepared to investigate the effects of natural defect. Test results showed that the fracture strength of each specimen depended on which is representative value of defect size. To evaluate the fracture strength of ceramics with arbitrary defect, a new evaluation equation was proposed based on the process zone size fracture criterion and the parameter model. The relationship between defect size and fracture strength can be predicted using this equation using the fracture toughness and the fracture strength of non-defect specimen. The predicted fracture strengths were in good agreement with the experimental fracture strengths. Thus, the usefulness of this equation was suggested.