Radial fracture during indentation by acute probes: II, Experimental observations of cube-corner and Vickers indentation

The companion article proposed a model for radial crack development at sharp contacts. The major extension of this model from previous works is the inclusion of a 'wedging' mechanism, to form a three-stress-field description of indentation crack evolution. Here, the amplitude terms of the three stress-intensity factors comprising the model are calibrated from experimental in situ and post situ inert-environment radial crack measurements on soda-lime glass. These values are scaled to predict radial crack evolution during cube corner and Vickers indentation of fused silica and soda lime glass in inert and ambient air environments. Both the conventional two-field and the proposed three-field model predictions are compared with radial crack lengths measured during indentation load-unload cycles (through the transparent materials with an in-situ apparatus). The three-field model is shown to be a great improvement over the two-field model in the description of crack evolution at cube-corner indentations, particularly with respect to the significant crack extension during loading and the attainment of a maximum crack length during unloading. The three-field model is consistent with observations of Vickers fracture in soda-lime glass and is able to reproduce the features of radial fracture evolution on the 'anomalous' glass, fused silica.