Densification dependent yield criteria for sodium silicate glasses – An atomistic simulation approach

Gergely Molnár,Patrick Ganster,Anne Tanguy,Etienne Barthel,Guillaume Kermouche

doi:10.1016/j.actamat.2016.03.053

Abstract

Silicate glasses are macroscopically brittle but ductile at the micron scale. This plastic response is complex: in open structure materials, such as amorphous silica, plastic yield results in significant densification. While, more compact structures (e.g. soda-silicate glasses) are known to suppress densification and promote shear flow. We have carried out atomic scale simulations to analyze the plastic response of a series of silicates with increasing sodium content. Quasi-static, multi-axial deformation tests were performed on large samples (≈103 nm3). Their yield behavior was quantified at different stress states, by measuring permanent volume changes. Qualitative agreement was found between the response of modeled systems and experimental results. Strong coupling between plastic yield and densification was observed. Our results also suggest that sodium silicates may densify not only under hydrostatic compression but also upon shear at large strains. Based on these numerical results, we propose a general yield criterion for soda-silicate glasses in which density is an internal variable. As density increases, the elliptic yield surface (characterizing amorphous silicates with open structures) gradually evolves into a Drucker-Prager-like model for fully densified samples.

Highlights

Silicate glasses are used for many technical purposes, especially where stiffness and transparency are required
It was soon found that there is an unusual feature in the plastic response of amorphous silicates
Our aim is to simulate the mechanical response of amorphous silicate materials with open structures with increasing depolymerization

Summary

Introduction

Silicate glasses are used for many technical purposes, especially where stiffness and transparency are required. Silicate glasses are brittle on the macroscopic scale but ductile at the micron scale [1]. This plastic response is expected to be key to understand brittleness. Open structure glasses exhibit irreversible volumetric strain upon compression: for amorphous silica this densification saturates at ca. For technical silicate glasses, sodium oxide (Na2O) is usually added to silica, along with other compounds. Upon hydrostatic compression soda-lime-silicates show less densification [6], and at reduced pressures values [7]. This behavior results from the phenomena that sodium gradually fills up the open structures

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