Meaning
Fluid dynamics processes where liquid resin flows through and fills the interstitial spaces of a porous fiber reinforcement govern the quality of composite manufacturing. Achieving complete fiber bed impregnation requires the resin to wet the individual fiber filaments and expel all trapped air. This process is highly dependent on both the viscosity of the resin and the structural alignment of the fibers.
Incomplete impregnation results in dry patches, which degrade the strength and load-carrying capacity of the completed laminate.
Permeability Control
Resistance to fluid flow through the dense fiber architecture is determined by the arrangement and density of the reinforcement. For successful fiber bed impregnation, the flow path must remain open long enough for the resin to reach the furthest edges of the mold. Tight weaves or high fiber densities reduce the effective permeability, requiring higher injection pressures or lower resin viscosities to achieve uniform coverage.
Structural designers must therefore balance the mechanical need for high fiber volume fractions with the process limits of the injection equipment.
Capillary Pressure
Surface energy differences between the liquid polymer and the solid fiber surface generate local forces that either draw the resin in or resist its flow. In fine micro-channels, this pressure drives the resin into the tiny gaps between filaments. If the surface chemistry is poorly matched, the resin will bypass the dense fiber bundles, leaving dry spots within the core of the composite.
Wetting Optimization
Thermal management is used to control the resin viscosity during the injection phase. Keeping the resin hot lowers its viscosity, speeding up the flow and improving the saturation rate. However, if the temperature is too high, the resin will begin to cure prematurely, blocking the flow channels and causing incomplete saturation of the fiber bed.
