Modelling stress response of glass-fibre composites during shear flow using 3-dimensional fibre orientation evolution and fibre migration data

Constitutive models for stress predictions in fibre filled composites have considered the effects of evolving fibre orientation distribution. However, studies incorporating effects of fibre concentration migration have been limited. This work is aimed at evaluating the combined effects of fibre orientation evolution and fibre concentration migration on shear stress predictions. Steady shear rheology was performed on Nylon-6 containing 33% weight short glass fibres (PA6-33GF) which displayed a stress overshoot before reaching steady state values. This has been attributed to fibre orientation evolution and fibre migration taking place during shear. Samples subjected to different strain units were obtained from the rheometer and X-ray Computed Tomography (X-CT) was employed to obtain 3-dimensional fibre orientation tensors and fibre concentration distribution. With higher applied strains, the orientation of fibres in the shearing direction was observed to increase. The occurrence of fibre migration was also observed. The Reduced Strain Closure (RSC) model and Suspension Balance Model (SBM) were used for fibre orientation and fibre concentration modelling respectively. Empirical parameters for these models were fitted using experimental data. The fibre orientation and concentration values obtained from these models were incorporated into the Lipscomb stress equation to obtain stress predictions for simple shear flow. These predictions were compared with results obtained from a parallel plate rheometer. This constitutive model can be used for predicting stress responses more accurately in complex flow processes such as injection moulding.