Viscoelastic damage behavior of fiber reinforced nanoparticle-filled epoxy nanocomposites: Multiscale modeling and experimental validation

The development of a physically based constitutive model for glass fiber reinforced boehmite nanoparticle-filled epoxy nanocomposites undergoing finite strain is investigated. The constitutive model allows capturing the main features of the stress-strain relationship of the nanocomposites, including the nonlinear hyperelastic, time-dependent and softening behavior. A methodological framework based on molecular dynamics simulations and experimental tests is proposed to identify the material parameters required for the model. The fiber-matrix interaction is characterized by a composite model, which multiplicatively decomposes the deformation gradient into a uniaxial deformation along the fiber direction and a subsequent shear deformation. The effect of the nanoparticles on the stress-strain response is taken into account through the adoption of a modulus enhancement model. The Eyring model parametrized using molecular simulations is used to describe the rate-dependent viscoelastic deformation under loading. The stress softening behavior is captured by a monotonically increasing function of deformation, so-called softening variable. The results show that the model predictions of stress-strain relationships are in good agreement with experimental data at different fiber and nanoparticle 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 fiber reinforced nanoparticle/epoxy nanocomposites.