A viscoelastic damage model for nanoparticle/epoxy nanocomposites at finite strain: A multiscale approach

Experimental tests show that nonlinear viscoelasticity characterizes the mechanical behavior of boehmite nanoparticle (BNP)/epoxy nanocomposites. This paper presents the development and numerical implementation of a physically based constitutive model for BNP/epoxy nanocomposites undergoing finite strain. The proposed constitutive model allows capturing the main features of the stress-strain relationship of BNP/epoxy nanocomposites, including the nonlinear hyperelastic, time-dependent and softening behavior. The characterizing feature of this study is to propose a methodological framework based on molecular dynamics simulations and experimental tests to identify the material parameters for the model. Molecular simulations in conjunction with the Eyring viscosity theory are used to characterize the viscoelastic deformation of epoxy resins under loading. The concept of strain amplification is also adopted to account for the effect of nanoparticles on the stress-strain response of the nanocomposites. The stress softening behavior is captured by a monotonically increasing function of deformation, so-called damage variable. The results show that the model predictions of stress-strain relationships are in good agreement with experimental data at different BNP weight fractions. Finally, the constitutive model is implemented in the finite element analysis and examined by means of a benchmark example. Experimental-numerical validation confirms the predictive capability of the present modeling framework, which provides a suitable tool for analyzing BNP/epoxy nanocomposites. (C) 2019 Elsevier Ltd. All rights reserved.