Capillary Flow
Mathematical models describing the penetration of a liquid into a porous medium or narrow tube define the relationship between time and distance traveled. Within the context of resin impregnation of glass fabrics, lucas-washburn dynamics govern how the liquid resin wicks into the bundles. The model assumes that the driving force is capillary pressure balanced by viscous drag.
It provides a foundational understanding of how void free laminates are formed.
Penetration Kinetics
Liquid velocity decreases as the fluid moves deeper into the structure because the frictional resistance increases with the length of the wetted path. The application of lucas-washburn dynamics requires knowledge of the surface tension of the resin and the contact angle with the glass fibers. Smaller pore sizes in high density weaves create higher capillary pressures but also restrict the flow volume.
If the resin viscosity is too high, the wicking process slows down, potentially leaving dry spots in the center of the glass bundles. Precise control of the temperature during the initial stages of lamination ensures the resin is thin enough to penetrate the tightest spaces.
Saturation Boundary
The validity of the model depends on the existence of a stable pore geometry and a newtonian fluid behavior. In reality, the complex geometry of woven glass and the changing chemistry of the resin limit the accuracy of lucas-washburn dynamics over long periods. Once the resin begins to cross link, the viscosity increases nonlinearly and the capillary model no longer applies.
