In-situ evaluation of structural changes of glass under a sharp indenter

Reference Presenter Authors
10-015 Satoshi Yoshida Yoshida, S.(The University of Shiga Prefecture); Nguyen, T.(The University of Shiga Prefecture); Yamada, A.(The University of Shiga Prefecture); Matsuoka, J.(The University of Shiga Prefecture); It is well known that the indentation test is used to model the contact damages of glass against foreign bodies. Using a Vickers indenter, for example, we can obtain a permanent imprint with various cracks. It is also known that the deformation mechanism is one key aspect of the cracking event during the indentation. A larger contribution of densification of glass under the indenter impedes the formation of the radial/median crack, because densification reduces a driving force for the cracking. However, it has been reported that this correlation cannot be observed for some borosilicate or aluminosilicate systems. This is probably because permanent deformation in glass is not as straight forward as implied by the contribution of densification, and because we lack information on structural changes of glass under complex stress states. Depending on the glass composition and/or on the loading condition, various veiled factors should affect the driving force for cracking during the contact. Since the cracking is a dynamic event, it is of primary importance to look at dynamic changes in the structure of glass under the indenter. In this study, we focus on in-situ structural changes of glass under a sharp diamond indenter using a micro-Raman spectrophotometer coupled with a self-made indentation equipment. Structural changes of glass under a Vickers indenter were successfully confirmed through in-situ Raman spectra. The structure of soda-lime glass under the indenter is similar to that of sodium silicate glass under hydrostatic pressure. However, in-situ Raman spectra of silica glass under the indenter are different from those of hydrostatically compressed silica glass. This suggests that indentation-induced shear stress causes the structure to be deformed into a different one with a wider bond angle distribution. Such a shear-induced structural change could play a key role on the contact damage, especially for a glass with a high degree of polymerization.
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