Elasticity and strength of silica aerogels: A molecular dynamics study on large volumes

W Goncalves and J Morthomas and P Chantrenne and M Perez and G Foray and CL Martin, ACTA MATERIALIA, 145, 165-174 (2018).

DOI: 10.1016/j.actamat.2017.12.005

The nanoporous structure and the mechanical properties of silica aerogels are studied by molecular dynamics simulations on large samples. For the first time, atomistic simulations are able to reproduce a pore size distribution, centered on 10 nm, comparable to experimental values. Using an unprecedented combination for silica aerogels of large volumes, large strains, and relatively small strain-rates, direct evidence of their peculiar mechanical behavior at the nanoscale is provided, from elasticity to fracture. The surface stress that silica ligaments experience produces a significant tension-compression asymmetry and an unusual discontinuity in the Poisson effect. The ductility of highly porous silica aerogels arises from an interplay between surface stress and a significant amount of reorganization in ligaments. Taking advantage of the large volumes accessible here, the very heterogeneous nature of low-density silica aerogels is reproduced, with an impact both on their elasticity and on their strength. In particular, a clear dependence between tensile strength and sample volume is uncovered, which opens perspectives for the elaboration of multi-scale models. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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