Evaluation of fracture toughness for ceramics by chevron-notched specimen.

Abstract

Chevron-notched specimens are being used recently to determine KIc. In this study, the stress intensity factors were calculated for chevron-notched three point bend and compact specimens. Three configurations of chevron-notched specimens were then subjected to fracture toughness tests to determine KIc of hot-pressed silicon nitride, Si3N4, with special attention paied to the fracture resistance curve (R-curve). Using this result, the optimum shape of the specimen was determined.The results obtained are summarized as follows.(1) By using the deeply chevron-notched specimen, KIc can be determined in a simple way with little scatter.(2) The KIc values determined by using the straight-notched specimens show a considerable scatter due to the effect of finite notch root radius and they overestimate the actual KIc value.(3) From the change in specimen compliance, the R-curve can be evaluated. The resistance to stable crack growth increases slightly as the crack grows.