Modeling of Transient Flow inside a Fiber Tow During Liquid Composite Molding Available to Purchase

In liquid composite molding processes, the macroscopic flow in fiber preforms is simultaneously accompanied by the micro-scale impregnation of fiber tows. Because the interstitial space within an individual fiber tow is much smaller than the space between tows themselves, the macroscopic flow front is able to reach the downstream side of the tow before gas entrapped inside the tow can be forced out by the resin impregnation process. In this work, a quasi-2-D model for the dynamic flow behavior inside a fiber tow completely surrounded by a macroscopic resin flow is developed. In contrast to the existing models, the new model accounts for not only the surface tension effects that could influence the flow behavior at this length scale, but also the multidimensional effects and the vapor-liquid phase transition of the entrapped gas, which occurs in resin systems used in liquid composite molding. This model simulates the transient dynamics of the multi-component gas mixture entrapped inside the tow on the time scale associated with infiltrating the intra-tow region. One of the advantages of the new model is its ability to account for the delayed impregnation inside fiber tows, which eliminates the ambiguity in determining the intra-tow infiltration time of the “sink” volume, which is a required parameter for some previously developed models. The model also quantitatively predicts the time-dependent behavior of the sink term, which is needed to accurately simulate the macroscopic resin flow in the preform. The model development and analysis of the transient intra-tow flow behavior under various thermodynamic conditions are presented, and the relevance of the numerical results to the micro-void formation in liquid composite molding processes is discussed.