A TECHNIQUE TO GENERATE STRAIGHT THROUGH-THICKNESS SURFACE CRACKS ANDITS APPLICATION TO STUDYING DISLOCATION NUCLEATION IN SI

A new technique, indentation-scratch is developed to generate high qua lity, cleavage surface precracks in brittle materials. An indentation roller equipped with weight attachment rolls across the specimen surfa ces to generate precracks in four-point bending specimens. The residua l stresses induced during indentation are effectively eliminated by me chanically grinding away the inelastically deformed surface layer. The intrinsic fracture toughness measured by the present method is in goo d agreement with the data in the literature. The dislocation nucleatio n condition, associated with the onset of the increase of subsequent r oom temperature fracture toughness following high-temperature prestres sing at 500 degrees C, is determined.