MultiSil

The remarkable plastic deformation properties of amorphous silicates have numerous technological implications. In glass technology they control the occurrence of surface damage on glass and in this way strongly impact he practical strength of glass, while they may also be connected to the intrinsic strength of the material. In terms of scientific comprehension, the plastic behaviour of amorphous silicates is still largely ill-understood. There are three reasons: 1) the amorphous structure is difficult to analyse and to describe, and in fact there is a continuous range of possible amorphous structures; 2) the mechanical response of amorphous silicates at larger scales is dominated by fracture so that the plastic response must be measured at the micron length-scales: the range of devices available to date to perform such experiments has been very limited. 3) due to the absence of long-range order, modelling is more difficult since the tools adequate for crystalline materials break down. Such major questions as : how can we describe the plastic response of amorphous silicates at the continuum lengthscale ? how does this response depend on the structure of the amorphous material ? what are the relevent atomistic mechanisms ? remain very open However recent evolutions make it now possible to provide answers. Several relevent micromechanics experiments can now be designed to probe the plastic response of silicates at the micron scale, while Molecular Dynamics has reached a point of development where it can connect to continuum lengthscale description of plastic response. Starting from these ideas, the aim of the MultiSil project is to bring together four research groups to produce a significant increase in our knowledge of the plastic deformation of amorphous silicates and its relation to the amorphous structure. Relying on our current projects, selected ranges of silicates with smoothly varying structure parameters will be generated: increasingly densified silica and binary sodo-silicates at Na contents lower than 15%. These two series of samples span the interesting ranges of plastic properties. Adequate micromechanics esperiments will be designed to carry out stress strain experiments at the micron scale in various loading conditions. In particular Raman micro-spectroscopy will be used as a micron scale deformation gauge. These experiments will provide the basis for Finite Element Analysis, bringing to light the most adequate forms of the constitutive equations for amorphous silicates and their dependence upon amorphous structure. The results in turn will be used as benchmarks for the developments of reliable Molecular Dynamics simulations to provide direct insight into the local rearrangement mechanisms involved at the atomic scale and the connection between plastic response and amorphous structure. This direct connection between MD and constitutive equation is expected to hold true because of the small representative volume for amorphous systems, which are devoid of long-range order. We also propose to demonstrate the impact of the range of expected plastic behaviour by monitoring its impact on indentation induced fracture. The results will be quantitatively connected to the constitutive behaviours evidenced earlier by Extended Finite Element Analysis. Upon completion of the project, a considerably refined picture of the plastic behaviour of amorphous silicates both at the atomic and the continuum lengthscale will emerge. A range of plastic response will have been quantified as a function of amorphous material. Direct consequences of plastic deformation on macroscopic response will have been demonstrated and quantified. Atomistic mechanisms will have been identified and their connexion to the type of amorphous structure demonstrated.