Flow-Induced Fibre Compaction in Resin-Injection Pultrusion

Resin-injection pultrusion (RIP) processes utilise a high resin pressure to ensure fast resin impregnation. When the resin is injected, the fibre material may compress and deform, and since the material flow is closely related to the fibre volume fraction, it is important to understand and predict the effects of flow-induced fibre compaction. In this paper, we derive the governing equations and present a novel numerical framework for analyses of flow-induced fibre compaction in RIP. Based on temperature measurements and material characterisation of the fibre reinforcement (compaction behaviour and permeability), we analyse the effects of flow-induced fibre compaction on non-isothermal material flow in an industrial RIP process. For the case study, we found that fibre compaction reduced flow resistance and facilitated resin impregnation as the fibre volume fraction was locally reduced near the inlet. This meant that the flow front was moved upstream (asymptotic to 3 cm) and the exit pressure was increased from 4.8 to 6.2 bar. Also, the fibre volume fraction was increased in the centre of the profile, whereby impregnation took place over a longer distance as the flow front had a deeper apex. Finally, we showed that the compaction response of the fibre material remained largely unaffected by the magnitude of the injection pressure, which was not the case for the fibre volume fraction, pulling speed, and resin viscosity. This work and the presented methodology are important contributions towards improving the understanding of the material flow in RIP, in particular, for larger profiles with a lower fibre volume fraction.