Strength of Brillouin spectroscopy to identify spatial densification model in indented silica

The aim of this work is to analyse and understand the densification process of silica glasses at the micrometer scale under micro-indentation. At the mesoscopic scale, silica glass, with a very low Poisson's ratio, exhibits a high maximum density change, up to 21% and a very low shear flow under shear stress, in contrast to normal glasses such as float glass, which have a low densification change and a high shear flow under non-isotropic compression. In the case of silica glass, it is observed that the evolution of the densification in the lateral dimension is gradual, as for high Poisson's ratio glasses. However, we find that along the central axis, the evolution with depth is quite different : it presents two regions. In the area immediately below the indenter, the densification is high and almost constant. Just under this imprint, there is a relatively sharp transition to the purely elastic region. Our present study, based on Brillouin diffusion measurements, allows us to improve the description of the imprint for normal/anomalous glass and to explain the localisation of cracks in the silica imprint : in this strained transition zone between these two densified and undensified regions.