Mixed‐Mode Fracture from Controlled Surface Flaws in Hot‐Pressed Si ₃ N ₄

Abstract

The room‐temperature mixed‐mode fracture of commercial hot‐pressed Si 3 N 4 was examined using controlled surface flaws in 4‐point bending, oriented at various angles 6 with respect to the outer fiber tensile stress direction. Catastrophic fracture paths were non‐coplanar with the initial flaw plane, and the stress intensity factor ratio K I /K IC was < 1 for fracture in modes II and III. A non‐coplanar maximum strain‐energy release rate fracture criterion best described mixed‐mode fracture.