Median Cracking of Brittle Solids Due to Scribing with Sharp Indenters

The process of moving a loaded hard indenter across the surface of a brittle solid to produce a median crack is referred to as "scribing." As a first step in predicting the depth of median cracking due to sharp indenters, an approximate plastic plane strain analysis is presented for the region under the indenter. This allows the horizontal force transverse to the scribing direction to be predicted. Taking this force and an approximate solution for the stress intensity factor for the crack geometry in scribing leads to a prediction for crack depth as a function of load. The residual stresses which arise on unloading are shown to be a strong function of indenter geometry and may act to extend or partially close the original median crack formed during loading. Reasonable agreement is found between prediction and experiment for six indenter configurations.