Soda–borosilicate glass: normal or anomalous behavior under Vickers indentation?

Borosilicate glasses, together with silica glass, are commonly considered as ‘anomalous’ glasses. This definition regards the occurrence of Hertzian-like cone cracks during Vickers indentation. Such a particular behavior can be related to anelastic densification processes occurring in the highly stressed region beneath the indenter. Conversely, glasses defined as ‘normal’ show mainly a median/radial crack system and plastic deformation is accounted for shear faulting. Quite surprisingly, in this work both median and conical crack systems were observed in soda–borosilicate glasses under Vickers indentation. Three glasses, with different composition mainly related to the network-modifier content, were considered. The surface and in-depth crack morphology was analyzed as a function of chemical composition, test environment and indenter geometry and the influence of the experimental conditions on the actual glass behavior was discussed.