Sliding of a diamond sphere on fused silica under ramping load

Abstract

A diamond sphere of radius 105 μm was used to slide on fused silica under ramping load from 5 mN to 5 N in order to investigate scratch-induced deformation and micro-cracking of brittle solids. Complete circular cracks were observed with elastic deformation playing the predominant role. Results show: initial cracking can be detected by acoustic emission; the valleys of horizontal mean contact pressure and the apparent friction coefficient together with the sudden rise of the ratio of vertical work over horizontal work indicate the beginning stage of circular cracks; micro-comminution is signified by the decrease in residual depth. Values of fracture toughness obtained by Vickers hardness techniques are larger than reasonable ones. Scratch-based approaches by linear elastic fracture mechanics and microscopic energetic size effect laws are found to be applicable to assess fracture toughness of brittle glass by scratch test with a spherical indenter under an appropriate range for curve fitting. Fracture toughness of fused silica measured by scratch test is 0.7 MPa• m1/2, which is compared favorably with the values obtained by conventional methods.