Cone cracks around Vickers indentations in fused silica glass

Abstract

Surface and subsurface deformation and cracking around Vickers identations in fused silica have been studied. The indentations were sectioned by making the Vickers indents on and near the tip of a pre-existing crack. The characteristic median and lateral cracks around the impression and shallow cracks within the surface of the indentation were observed on the specimen surface. The subsurface deformation showed compacted or densified zones, devoid of any flow line rosettes. The dominant cracks, similar to the Hertzian cone cracks observed around purely elastic spherical indentations, occurred outside the compacted zones. These cone cracks make angles of 30 to 40° with the specimen surface. Multiple cone cracks with shallower angles often formed outside the major cone cracks. It has been suggested that the expansion of the boundary of the compacted zone as the indenter load is increased can cause median cracks during loading while the mismatch of strain at this boundary may give rise to lateral cracks during unloading.