A new, indentation-scratch, technique was developed in order to generate high-quality cleavage-surface pre-cracks in brittle materials. A weighted indentation roller was rolled across the surface in order to generate pre-cracks in 4-point bending specimens. The residual stresses that were introduced during indentation were eliminated by grinding away the inelastically deformed surface layer. It was found that the intrinsic fracture toughness which was measured by using the present method was in good agreement with published data. The dislocation nucleation condition which was associated with the onset of an increase in subsequent room-temperature fracture toughness, following high-temperature pre-stressing at 500C, was determined.

Y.B.Xin, K.J.Hsia: Acta Materialia, 1996, 44[3], 845-53