In liquid composite molding processes (LCM) the capillary driven flow is, next to the permeability, determining the filling behavior of the composite. To optimize flow speed and thus efficiency, these parameters have to be determined for the given textile and a good balance between the flow forms needs to be found. Considering capillarity, the Lucas-Washburn equation is the basis for the description of capillary flow in tubes. It can be observed that for polymer composites this equation has its limitations. Consequently, it was modified by a regression-based porous tube model considering the peripheral fluid through the tube walls as well as the gravitational force. Compared to other extensions of the Lucas-Washburn equation, this approach is designed to be simple considering testing and calculation effort while still being accurate and close to the process.
In this work, capillary rise experiments were performed to evaluate the proposed model. Textiles immerge in a test fluid, here n-decane. The capillary flow is then determined based on the weight loss of the fluid container as well as by visual evaluation of the flow front progression. Glass and carbon reinforcements, each in four different forms, were tested repeatedly to establish a broad database. Comparison with the modeled results show good conformity. A high number of intersections, high fiber volume content, and a regular shape of the textile improve the accuracy of the model predictions. The estimation of the capillary radius and the term describing the peripheral fluid flow are identified to be the most important factors.