Grain-Size Dependence of Fracture Energy in Ceramics: I, Experiment

Evaluation of literature data combined with new experimental measurements shows that crystal structure is a basic factor in the grain-size dependence of the critical fracture energy of ceramics. Notch beam (NB), double cantilever beam (DCB), and work-of-fracture (WOF) tests of materials having a cubic crystal structure generally agree and show, at most, a limited variation of fracture energy with grain size. However, maxima of the order of 25% in γ at intermediate grain size and 25% decreases in γ at larger grain size may occur. Materials of noncubic crystal structure show broader variations in γ with G . Both DCB and WOF tests show γ passing through maxima that are typically 100 to >400% of values at fine or large grain size. Limited DT data are consistent with this trend but various results of NB tests are mixed. Some NB test data agree with the DCB and WOF trends, whereas others taken from the same materials show no change or only a limited continuous decrease of γ as G increases.