Linking MD and FEM to predict the mechanical behaviour of fullerene reinforced nylon-12

Abstract

In the present study an effort is made to numerically characterize the elastic mechanical behaviour of a polymer-based nanocomposite made of nylon-12, also known as polyamide-12 (PA-12), which is uniformly reinforced with C60 or C70 fullerenes. For this purpose, a numerical study is conducted in two stages.In the first one, a molecular dynamics (MD) approach is formulated to provide numerical solutions regarding the elastic properties of the nanocomposites under investigation, for a wide range of concentrations of the C60 or C70 reinforcing agents up to 8% by weight. During the analysis, appropriate cubic representative volume elements (RVEs) are developed which contain at its centers single fullerene nanocrystals surrounded by PA-12 polymer chains, in accordance with the assumed uniform nanoparticle distribution.In the second stage, the reinforcing ability of the most spherical fullerene C60 in nylon-12 matrix is only tested. Given the high computational cost of the MD-only simulations for small C60 mass fractions, a classical continuum mechanics (CM) method, grounded on the finite element method (FEM), is developed. The proposed method pre-requires the utilization of some MD data regarding the RVE of a nanocomposite of a rather high C60 mass fraction, in order to develop a same sized, continuum, equivalent volume unit. Then, nanocomposite RVEs of higher filler concentrations are treated in a continuum manner, by placing centrally the developed volume unit in perfect contact with the surrounded PA-12 matrix. Both components are discretized with appropriate solid finite elements to realize the simulations.The performance of the MD-only as well as the FEM-MD combined method is investigated through comparisons with relevant experimental measurements.