A technique to generate straight through thickness surface cracks and its application to studying dislocation nucleation in Si

A new technique, indentation-scratch is developed to generate high quality, cleavage surface precracks in brittle materials. An indentation roller equipped with weight attachment rolls across the specimen surfaces to generate precracks in four-point bending specimens. The residual stresses induced during indentation are effectively eliminated by mechanically grinding away the inelastically deformed surface layer. The intrinsic fracture toughness measured by the present method is in good agreement with the data in the literature. The dislocation nucleation condition, associated with the onset of the increase of subsequent room temperature fracture toughness following high-temperature prestressing at 500 degrees C, is determined.