Abstract
Fracture toughness values of engineering ceramics are often obtained by conventional three point bending tests. In these tests, an initial crack usually extends unstably, and therefore it is quite difficult and also labourious to determine R-curves on ceramics. In order to perform stable crack extension tests, the stable condition for the crack extension was studied in three point bending tests. The stable condition was depicted on EBΛ*-x diagram (E; Youngs modulus of the specimen, B; the thickness of the specimen, Λ*; the compliance of the testing machine and x; the non-dimensional crack length). The diagram shows that the stable crack extension test can be performed when the value of EBΛ* is small.
On the basis of the study, a crack stabilizer was newly designed to achieve the small value of EBΛ*. By using the stabilizer, the stable crack extension tests were successfully performed in an alumina ceramic.
