Analysis of tensile strength and fracture toughness of ZrB₂–SiC ceramic from three-point bending samples with edge cracks

ZrB₂–SiC ceramic is one of most promising high temperature resistant materials in the field of thermal protection, and its strength and toughness are two key mechanical indicators which determine its application prospects. How to conveniently and accurately obtain its strength and toughness is of great value for engineering applications. In this paper, the tensile strength and fracture toughness of the ZrB₂–SiC ceramic were obtained according to the boundary effect model (BEM) from a series of three-point bending tests of ZrB₂–SiC ceramic samples. Then, the BEM method and normal distribution methodology were employed for analysis of strength and toughness of ZrB₂–SiC ceramic. Results show that there exists a linear relationship between maximum loads P_max and effective area A_e, and the slope of the straight line passing through the coordinate origin is the tensile strength f_t. The tensile strength f_t and fracture toughness K_IC of ZrB₂–SiC ceramic can be predicted simply from a set of three-point bending tests according to the BEM method. Similarly, the maximum loads P_max for three-point bending samples can also be predicted and determined when the f_t, K_IC and average grain size are available. Results indicate that the grain sizes, f_t and K_IC of the ZrB₂–SiC ceramic follow the law of normal distribution. Satisfactory results of the predicted f_t and K_IC between the upper and lower bounds with 95% reliability can be achieved based on BEM method.