Compaction and Transverse Permeability of Glass Rovings

Continuous reinforcements such as glass rovings are used in a variety of polymer processes such as filament winding and compression molding. In all these processes, impregnation of the roving fiber bundle by the liquid polymer is essential. Modeling polymer impregnation requires an estimate of the void fraction-compressive stress relationship and the transverse Darcy permeability. The void fraction of 2400 tex glass rovings of different glass fiber diameters and roving thicknesses was assessed as a function of the applied compressive stress. The results indicate that existing void fraction-compressive stress models can be used to adequately fit the experimental data. The transverse permeability of these rovings was also measured as a function of applied compressive stress, fiber diameter, roving thickness, fluid velocity and viscosity using two different permeameters developed for this research. The permeability was observed to depend strongly on the compressive stress, and hence void fraction. As expected, the permeability was independent of the roving thickness, fluid velocity and viscosity. A Kozeny constant value of 7 was found to reasonably fit the data from both permeameters. Scatter of the experimental data was observed. It is hypothesized that this may be due to variations in the roving void fraction resulting from twists, cross-overs and waviness among the fibers.