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. © 2004 Elsevier B.V. All rights reserved.