In situ study of fracture mechanisms in advanced ceramics using fluorescence and Raman microprobe spectroscopy

A procedure is described for the evaluation of the fracture behaviour of po lycrystalline ceramics using an in-situ stress analysis involving either fl uorescence or Raman microprobe spectroscopy. The full details of the experi mental set-up, calibration procedures and stress calculations are shown, an d their reliability discussed in some detail. Stress maps were obtained alo ng the wake of cracks stably propagated in six selected polycrystalline cer amics with representative microstructures. A conventional fracture mechanic s assessment was concurrently performed to relate microscopic stress data t o the macroscopic fracture resistance of the materials. It is demonstrated that the most effective toughening mechanism in polycrystalline ceramics ta kes place in the crack wake and arises from both elastic and frictional shi elding tractions operated by crystallites which are left unfractured behind the crack tip. Copyright (C) 1999 John Wiley & Sons, Ltd.