A micromechanically based model for strain rate effects in unidirectional composites
This article addresses dynamic behaviour of fibre reinforced polymer composites in terms of a transversely isotropic viscoelastic-viscoplastic constitutive model established at the unidirectional ply level. The model captures the prelocalized response of the ply in terms of rate dependent elasticity and strength without damage. A major novelty is that the model draws from computational homogenization, with matrix and fibre materials as subscale constituents for a representative volume element of the ply. The micromechanics of the strain rate dependent polymer matrix is represented by an isotropic pressure sensitive viscoelastic-viscoplastic prototype model. For the fibre material, transverse elasticity is assumed. The constituents are homogenized via the fluctuating strain of the subscale, where a simple ansatz is applied to allow for constant stress in the plane transverse to the fibre orientation. Despite the relatively simple modelling assumptions for the constituents, the homogenized model compares favourably to experimental data for an epoxy/carbon fibre based composite, subjected to a variety of challenging uniaxial off-axis tests. The model response clearly reflects observed strain rate dependencies under both tensile and compressive loadings.