Simultaneous measurements of permeability and capillary pressure of thermosetting matrices in woven fabric reinforcements

TLDR

The woven fabric preform used in this study has a permeability comparable to a unidirectional fibrous preform in the transverse direction. A simple apparatus was designed and constructed to simultaneously measure unsteady‑state permeability and capillary pressure in a simulated composite impregnation experiment. The study confirmed that the Kozeny‑Carman equation accurately predicts permeability up to a porosity of 0.5, while higher porosities show interfacial deviations; a maximum capillary pressure of 3.7 × 10⁴ Pa was measured at low porosity, indicating that capillary forces can rival other pressures in low‑pressure processes, and the existing modeling approach remains valid for complex‑orientation preforms.

Abstract

Abstract A simple apparatus was designed and constructed capable of measuring the unsteady‐state permeability and the capillary pressure simultaneously in a simulated composite impregnation experiment. It was found that the Kozeny‐Carman equation used to describe the permeability of composites during impregnation adequately described experimental results for woven fabric preform up to porosity values of 0.5. Above this value, observed deviations were attributed to interfacial effects between adjacent woven fabric layers. For woven fabric preforms made of T‐300 carbon fibers, a maximum capillary pressure of 3.7 × 10 4 Pa (=5.4 psi) was observed at low porosity values. Thus, the capillary pressure may compete with other pressure sources in low pressure processes, such as the prepregging process. The woven fabric preform used in this study is observed to have a permeability similar to a unidirectional fibrous preform along the transverse direction. Furthermore, an existing modeling methodology capable of predicting permeability and capillary pressure through different preforms was found to be valid for fibrous preforms of complex orientation.