Inorganic glasses are brittle materials and fail macroscopically in a purely elastic way at room temperature. Yet, under constrained deformation loadings, glasses experience permanent deformation, without damage nor fracture. As an example, this is the case for the hydrostatic compression test, where, for pressures around 25 GPa, permanent volume changes up to 16 % for silica glass are developed. This is also the case underneath an indenter during nano-indentation tests. There has been a long lasting controversy about the nature of the permanent indentation deformation mechanisms. Densification (permanent volume changes) underneath the imprint was deduced from changes in the refractive index, while observations of shear lines and pile-up around imprints suggested the occurrence of shear flow at room temperature.

Understanding and modelling the permanent deformation of glasses are necessary not only from a fundamental point of view but also from an engineering one. For the former, the relationships between the short-to-medium range order and the deformation mechanisms are required to understand the physics of amorphous materials and the possibility to design glasses with tailored properties. For the latter, glasses often fail from the surface flaws generated during processing or during service. Preventing failures in glass products requires to establish a link between the mechanical fields, the residual stresses, the occurrence of cracking systems and the propagation of cracks.

The aim of this presentation is to present recent advances of our group in these areas. The case of very different families of inorganic glasses (chalcogenide, metallic, oxide) will be presented to broaden the example of silica glass. Micro or nano-indentation experiments are conducted on different glasses. The mechanical response of the tests (load-displacement curves), as well as the residual imprints, are studied in detail. Densification or dilation as well shear plasticity underneath the indenter are investigated via complementary and dedicated procedures. Constitutive modelling is employed to discuss these experimental results via finite element analyses. In particular, the densification process is properly modelled thanks to recent in situ and ex situ experiments of hydrostatic compression. The roles of shear and shear flow will then be discussed with respect to nano- indentation results.

Different aspects of the mechanical behaviour will be addressed, including permanent deformation, viscoplasticity, viscoelasticity, fracture toughness, shear localisation...

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