Fibre kinematics in dilute non-Newtonian fibre suspensions during confined and lubricated squeeze flow: Direct numerical simulation and analytical modelling

Abstract

The properties of short fibre-reinforced polymer composites depend on the distribution and the orientation of fibres which drastically changes during the forming of composites. During this stage, these materials behave as fibre suspensions and usually flow in confined geometries. To analyse their flow-induced fibrous microstructures, we previously conducted 3D real-time in situ observations of the compression of non-Newtonian dilute fibre suspensions using fast X-ray microtomography [T. Laurencin et al., Compos Sci Technol134 (2016)]. Here, we successfully simulated these experiments with a multi-domain Finite Element code and compared them with the predictions of Jeffery's model. Often, the Jeffery's equations agree with the experimental and numerical data. However, for fibres closed to compression platens, important deviations were observed with faster simulated and experimental fibre rotation. Adopting the dumbbell approach and revisiting the recent work of Perez et al. [J non-Newtonian Fluid Mech233 (2016)], an extension of the Jeffery's model is proposed to account both for the non-Newtonian rheology of the suspending fluid and confinement effects. Despite its simplicity, the new model allows a good description of simulation and experimental results.