The Indentation Densification and Cracking Behavior of Fused Silica

The damage resistance of glass is of great scientific and economic interest. In oxide glasses crack formation is closely related to the plastic deformation processes that occur under contact stress, i.e. shear flow or structural compression. In this context an increased crack resistance is often attributed to an increased compaction capacity. However, the influence of densification on crack initiation and expansion remains unclear. In the present work the influence of densification on cracking is investigated using both cohesive zone finite element modelling and nanoindentation testing with fused silica serving as model system for densifying oxide glass. The densification information from hydrostatic compaction experiments was implemented into the FEA using modified Drucker-Prager cap plasticity. Nanoindentation experiments with various tip geometries and Raman spectroscopy were used to quantify densification and cracking experimentally. The fracture toughness of fused silica was assessed by indentation cracking and micro pillar splitting techniques, finding values in good accordance with literature