Influence of Fixation Structures on the In-Plane Permeability of Unidirectional Glass Fiber Tapes

Abstract

In this study the influence of a fixation grid on the permeability of a uni-directional glass fiber tape has been experimentally investigated with respect to processing of the material applying Liquid Composites Molding technology. Two-dimensional flow experiments show that for the given material and configuration the fixation structure has a strong influence on the permeability. The ratio of the permeability principal values is found to depend on the porosity. For a critical porosity even isotropic behavior can be expected. This result is verified by additional one-dimensional flow experiments with variation of the fiber angle of the lay-ups, showing that for the critical porosity the fiber angle has no significant influence on the permeability. The ratio of the permeability principal values does not significantly differ from 1. For the glass fiber tape without fixation structure the permeability principal values have been found to differ by one order of magnitude. Comparison of the absolute permeability values for the tape with and without fixation structure suggests that (for a total of 12 material layers) each layer of the fixation grid reduces the permeability of the lay-up by 8% (parallel) and 6% (transversal) for completely parallel oriented material and by 8% for a 0°/90° alternating lay-up. For a given fiber material, the influence of the fixation structure on the permeability is predicted to increase with decreasing porosity and to decrease with increasing area related mass, i.e. overall thickness, of the tape.