Direct observation of indentation deformation and cracking of silicate glasses

Indentation deformation of glass under a sharp diamond indenter causes cracking during and after a loading–unloading cycle. To get a deeper insight into the indentation cracking in glass, it is critical to understand the elastic and inelastic deformation behavior of glass under the indenter. In this study, in situ observations during Vickers indentations are carried out for silica, soda-lime, and lead–silicate glasses. It is found that the true contact area during indentation is different from the area estimated from the contact depth and the indenter geometry, and that the ridges of a Vickers indenter affect the contact shape during indentation. The contact region of silicate glasses under a Vickers indenter is not a regular square but a concave square. This results in edge cracking during indentation. It is concluded that the contact shape and the deformation mechanism of glass under the indenter are closely related to its cracking behaviors.