Mixed-mode fracture in an R-curve material

Mixed-mode fracture of a mica glass ceramic, an R-curve material, was analyzed. Vickers indentation cracks of varying sizes were introduced on the tensile surface of glass ceramic bars fractured in three point flexure. Mixed-mode fracture from indentation cracks was governed by a rising crack growth resistance behavior. Minimum Strain Energy Density theory based on the singular stress terms was effective in describing mixed-mode fracture in the glass ceramic and in previously studied non R-curve ceramics in flexure. This agreement implies that the effect of non singular stress terms in mixed-mode fracture from relatively small surface cracks in flexure is negligible.