Abstract
Mechanical properties are very important when choosing a material for a specific application. They help to determine the range of usefulness of a material, establish the service life, and classify and identify materials. The size effect on mechanical properties has been well established numerically and experimentally. However, the role of the size effect combined with boundary and loading conditions on mechanical properties remains unknown. In this paper, by using molecular dynamics (MD) simulations with the state-of-the-art ReaxFF force field, we study mechanical properties of amorphous silica (e.g., Young’s modulus, Poisson’s ratio) as a function of domain size, full-/semi-periodic boundary condition, and tensile/compressive loading. We found that the domain-size effect on Young’s modulus and Poisson’s ratio is much more significant in semi-periodic domains compared to full-periodic domains. The results, for the first time, revealed the bimodular and anisotropic nature of amorphous silica at the atomic level. We also defined a “safe zone” regarding the domain size, where the bulk properties of amorphous silica can be reproducible, while the computational cost and accuracy are in balance.
Highlights
Mechanical properties are a subset of physical properties that are based on the laws of mechanics dealing with energy and forces, as well as their effects on bodies
We investigate the effect of domain-size, boundary and loading conditions on mechanical properties of amorphous silica (a-SiO2) by using molecular dynamics (MD) simulations and the state-of-the-art ReaxFF force field [18]
One of the critical challenges in modeling silicates is the availability of an MD force field that is able to reproduce the mechanical properties under different compositions and chemical environments [28]
Summary
Mechanical properties are a subset of physical properties that are based on the laws of mechanics dealing with energy and forces, as well as their effects on bodies. Numerous experimental and numerical studies have indicated the size effects on mechanical properties at the sub-micron scale as presented in review articles [1,2] These articles summarize two major mechanisms of the size effect as follows: (i) Plastic deformation, which in macroscopic samples is essentially size independent, it becomes strongly size dependent and intermittent at microscale and below; (ii) The surface-to-volume ratio starts to increase dramatically when the sample is reduced down to nanoscale. We investigate the effect of domain-size, boundary and loading conditions on mechanical properties of amorphous silica (a-SiO2) by using MD simulations and the state-of-the-art ReaxFF force field [18].
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