From Dilute to Entangled Fiber Suspensions Involved in Reinforced Polymers and Composites

In SMC processes, a charge of a composite material - which typically consists of a matrix reinforced with chopped glass fibres or carbon fibre bundles and fillers - is placed on the bottom half of a preheated mould. The upper half of the mould is then closed rapidly at a high speed, causing the charge to flow inside the cavity, the reinforcing fibres are carried by the resin and experience a change of configuration, which strongly influences the mechanical properties of the final part. Then, the process simulation must track the entire fluid flow history in order to be able to predict the final reinforcement structure, and predict the defects that compression moulding can generate. All along the process, the fiber concentration increases leading to a change in the flow regimes: (i) at very low concentrations, the fiber and the fluid are moving with the same velocity, (ii) when the concentration is extremely high, fibers cannot move anymore and the fluid flows throughout the quasi-rigid entangled fibers skeleton, (iii) in between these two cases, fibers move with a velocity lower than the one of the suspending fluid. The process simulations must then be able to take into account all these regimes and go from one to the other. Even if the two first regimes (dilute and highly concentrated) are well known and described using Jeffery's [4] and Darcy's equations, the transition between the two is still badly modeled. In this work a general model able to adapt continuously to all these scenarios is elaborated.