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Multiscale methods for the analysis of plastic deformation of amorphous materials
Silicate glasses are used for many technical purposes, especially where stiffness and transparency are required. These glasses are brittle on the macroscopic scale but ductile at the micron level. The study deals with the analysis of the elasto-plastic response of sodium silicate glasses. We propose a new method using atomistic simulations combined with coarse-grained analysis to calculate structural and mechanical properties at different scales.
The numerical simulations were performed on large samples, and the results were ompared to experiments (neutron scattering, NMR, Brillouin scattering). The systems were tested by deforming the periodic simulation box in a homogeneous way. During compression or tension the dimensions of the simulation box was reduced by a constant displacement step while the positions of the particles were rescaled in a homogeneous way. After the box displacement a new equilibrium position was searched using the Polak-Ribiere conjugate gradient algorithm. Combining quasi static shear and compressive mechanical deformation, we were able to reconstruct hardening yield surfaces in the 3D stress space, parameterized by the residual shear strain and densification.
After identifying the smallest scale where the material could be considered homogeneous and isotropic we were able to develop continuum based material models. The observed mechanical response was described using a pressure dependent, hydrostatic hardening yield surface. The functions were then implemented in a finite element code. The continuum models made possible to compare atomistic results to real life experiments. We have used the results of micropillar, microsphear and nanoindentation to fine-tuned and verify our model.