Transient viscosity of fibre-filled composites incorporating evolution of fibre orientation and concentration

The combined influence of fibre orientation evolution and fibre concentration migration on rheological properties was considered in this study. Simple shear flow was imposed on centre-gated injection moulded PA6-33GF samples in a cone-plate geometry with a cone angle of 0.105 rad and a truncation height of 0.8 mm. Evolution of fibre orientation and fibre concentration distributions were imaged from sheared samples using X-ray computed tomography (X-CT). It was determined experimentally that the shell-core fibre orientation and fibre concentration distributions evolved towards a steady-state distribution. The orientation and concentration evolution was modelled using the Reduced Strain Closure (RSC) and Suspension Balance Model (SBM), respectively, and showed a reasonable fit. Numerical predictions for transient viscosity were obtained using constitutive equations for fibre-composite suspensions by including predicted results from the RSC and SBM models. Viscosity predictions from four different empirical models were compared with experimental data. The predictions from the Evans Model showed the best fit when comparing absolute viscosity values. Examination of the transient rheological response predicted by the empirical models revealed that they all had a lower overshoot magnitude and displayed a quicker decay of the overshoot when compared with the experimental results.