Buckling behaviour of laminated viscoelastic composites under axial loads

Abstract

This study investigates the buckling response of viscoelastic composite laminates under compression with the objective of better understanding the ply wrinkling behaviour at the early stage of thermoset composite manufacturing. The composite laminate is modelled as a 3-D viscoelastic solid using two different approaches in Abaqus©. As the application of the built-in viscoelastic model of Abaqus© is limited to isotropic materials, a more versatile orthotropic viscoelastic constitutive model based on differential form (DF) of viscoelasticity implemented as a user material subroutine (UMAT) is employed to elucidate the effect of ply anisotropy on the buckling response of uncured/partially cured unidirectional laminates. Numerical results are compared with the experimental data available in the literature to evaluate the accuracy of the proposed approach. Using the numerical model, the influence of various parameters including loading rates, the instantaneous elastic modulus, and in particular the effects of the ply anisotropy on the buckling behaviour of composite laminates are analysed. It has been found that unlike cured composites, the compressive stiffness of uncured prepregs is mainly dominated by the resin modulus rather than the fibre modulus. Additionally, it is shown that the waviness of fibres (fibre-bed effect) which stiffens the prepreg's transverse and shear properties increases its compressive stiffness slightly while the waviness effect on the post buckling stiffness is relatively significant. Hence, conducting compressive tests on uncured and partially cured prepregs as well as partially cured resin films with different thicknesses is suggested to validate the proposed modelling approach more rigorously.