TOW IMPREGNATION DURING RESIN TRANSFER MOLDING OF BIDIRECTIONAL NONWOVEN FABRICS

A model has been developed for analyzing resin impregnation of fiber tows during resin transfer molding of bi-directional nonwoven flber preforms. The model is based on the existence of two main regions of resin flow: the macropore space formed among flber tows and the micropore space formed among individual fiber filaments within a tow. The large difference in permeability between these two regions of flow leads to the potential for void formation during resin transfer molding. The model was formulated for both constant flow rate and constant pressure mold filling. For ambient pressure mold filling, the model predicts a difference in the size of the voids and distribution between axial tows (oriented along the flow direction) and transverse tows (oriented in the transverse direction). When vacuum is imposed on the mold, the model predicts the same resin impregnation behavior for both axial and transverse tows. Furthermore, given sufficient time, voids generated under vacuum mold filling will eventually collapse because of the absence of an opposing internal void pressure. In addition to insights on void formation, the model also provides a basis for the study of the relationship between resin transfer molding parameters and the resin impregnation process.