CRACK-STABILITY ANALYSIS AND FRACTURE-TOUGHNESS OF CERAMIC BEND BARS WITH A MODIFIED CIRCULAR CROSS-SECTION

Previous analysis has shown that the round bend bar is more stable tha n the rectangular bend beam. The geometry of the round bend bar was sl ightly modified to permit precracking of ceramic bars for subsequent f racture-toughness testing. Stability solutions of this new modified ro und bend bar were found as a function of precrack length for several m achine-compliance values. A threshold crack length was determined whic h predicted the transition from unstable to stable fracture behavior. Experiments with silicon nitride and alumina specimens verified the re sults of the analysis.