Densification of fused silica: Effects on nanoindentation

As compared to other optical glasses, when fused silica (SiO2) is ground or polished, it has some unique features, such as low surface microroughness and subsurface damage, low grinding-induced residual stresses, and low removal rates. It also has higher hardness. On the other hand, fused silica's Young's modulus and fracture toughness are in the middle range of the optical glasses. So, compared to other optical glasses, fused silica behaves differently under compressive loads. When subjected to sufficiently large compressive stresses, fused silica glass will densify permanently. It is also noticed that shear will facilitate densification. We model this behavior by a simple constitutive law including both shear flow and densification. The constitutive model was used to interpret nanoindentation tests on fused silica via 3D finite element simulations of indentations of Berkovich indenter. This work extends our previous work on axisymmetric (2D) indentation.