Spectroscopic Analysis of the Mechanical Properties of Silicates – MECASIL

MecaSil is a pluridisciplinar project, at the interface between optics and mechanics. The project MECASIL proposes to use combined high performance physical measurements and atomistic numerical simulations to identify the small scale response of model amorphous materials, and develop if possible in situ predictive tools for plastic deformation and crack initiation in these materials. The referee report given by ANR last year (2011) suggested us to resubmit the manuscript as it is. The MecaSil project benefits of the expertise and combined forces of five different well recognized partners (SVI-Saint-Gobain, PCML université Lyon 1, L2C-CVN université Montpellier 2 for the experimental part, and PMMH-ESPCI regrouped with LPMCN université Lyon 1 for the theoretical part). More precisely, the aim of the MecaSil project is to use highly sensitive spectroscopic methods (micro-Raman, micro-HyperRaman, micro-Brillouin) to study the small scale mechanical response of a wide class of amorphous solids: namely silicate glasses with different compositions, submitted in situ to high performance mechanical load (hydrostatic pressure in Diamond-Anvil cell, shear deformation, uniaxial compression on micro-pillars..). Amorphous silicates form an excellent playground to study the mechanisms of plastic deformation in amorphous solids because they exhibit a wide range of plastic behaviours as a function of composition, such as a densification or not upon high local pressure. Such a difference related to the composition of the glass is ideal to understand the role played by the microstructure on the mechanical response of disordered materials. This topic is however until now not very well understood, due to the lack of long-range order and the difficulty to identify experimentally a typical defect responsible for plastic deformation, unlike dislocations in crystals. The mechanical properties of silicate glasses are remarkable, with high hardness and fracturation at large scale, but plastic deformation at the micron-scale, as already measured recently through nanoindentation experiments for example. Depending on the composition, the plastic deformation can localize along shear bands, or display volumetric changes like a local densification as in pure silica.
The small scale mechanical response of these transparent materials can be explored experimentally by vibrational spectroscopy, such as Raman, Hyper-Raman and Brillouin scattering and their recent developments with a micron-scale resolution. It is now well known that the mechanical behaviour of such kind of strong glasses involves collective plastic rearrangements at the nanometer scale. However, the precise structure-dependence and the progressive organization of the plastic rearrangements giving rise to shear band and crack propagation at a larger scale is not well understood. A good theoretical description of the spectroscopic response needs thus to perform calculations on large systems of at least few ten thousands of atoms, at the nanometer scale and above. In this project, we propose to perform semi-classical calculations of the vibrational spectra, that could be compared to the experiments. Moreover, we propose to improve our understanding of the plastic behavior of silica based materials, by performing original in situ spectroscopic measurements of the local plastic rearrangements upon different mechanical loads (hydrostatic pressure, shear deformation, uniaxial compression of micro-pillars..) and with a sufficiently high strain sensitivity in order to predict local plastic damage and identify possible initiators of crack propagation. The experimental measurements will be closely combined to a theoretical atomistic study of the mechanical response and associated vibrational spectra.