Effect of resin infusion on fibre orientation level of aligned discontinuous fibre composites

Aligned discontinuous fibre reinforced composites offer an attractive balance between manufacturability and mechanical performance, provided that fibre orientation is maintained throughout processing. However, manufacturing processes including Vacuum Assisted Resin Transfer Moulding (VARTM) and High Pressure Resin Transfer Moulding (HP-RTM) are known to introduce fibre deviations through mechanisms such as resin flow, non-uniform impregnation, and consolidation effects . Most studies to date have focused on continuous fibre systems, while the extent of fibre misorientation in aligned discontinuous fibre composites remains insufficiently investigated. This study therefore provides a preliminary investigation into the effect of resin infusion on fibre alignment in aligned discontinuous fibre composites.
Highly aligned discontinuous fibre preforms, and composite samples manufactured from these preforms were prepared to analyse the fibre orientation level before and after resin infusion. Two different epoxy resin systems were used to experimentally investigate the effect of resin viscosity and associated flow velocity on fibre rearrangement during infusion. Cross-sectional images of cured composite samples were obtained using optical microscopy, and fibre orientation was quantified using image analysis based on the Yurgartis elliptical method [6]. Initial results indicate that the higher-viscosity resin system may induce greater disturbance within the aligned discontinuous fibre structure during infusion. Under constant vacuum pressure in VARTM, however, increases in resin viscosity are accompanied by reductions in resin flow velocity, leading to hydrodynamic compensation. Consequently, the increased fibre disturbance observed with higher-viscosity resin cannot be explained solely by the hydrodynamic drag associated with fibre rotation. Instead, local pressure concentration is considered a more plausible contributing mechanism, with weak fibre–fibre contact networks likely being more susceptible to viscous drag effects.