A comprehensive framework for modeling volatile transport and bubble dynamics in liquid composite molding processes

In Liquid Composite Molding (LCM), the complete impregnation of fibrous preforms is essential to minimize porosity and achieve the desired mechanical performance. Voids may form when entrapped air, moisture, or resin-induced volatiles are not effectively removed prior to gelation. This work focuses on the transport and transformation of volatiles, either dissolved in the resin or present as nucleated bubbles, during the mold filling process. To accomplish this, it is necessary to predict the phenomena of nucleation, dissolution, and transport of both nucleated and dissolved volatiles. This paper presents a framework to model the dissolution, nucleation and tracking of nucleated bubbles during resin impregnation. The framework is integrated with the simulation of the resin impregnation process which provides the resin velocity and pressures during the filling. This integration enables the prediction of void locations and sizes at the end of the impregnation process as a function of the material properties, process parameters and part geometry.

The model is exercised to verify the patterns of volatile nucleation and dissolution and examine the effect of bubble mobility on bubble dynamics. The impact of bubble mobility, particularly its size dependence, is evaluated. Larger bubbles exhibit sufficient mobility to escape through the vents, facilitating passive degassing, while smaller bubbles tend to remain and may re-dissolve with pressure recovery. Finally, bubble entrapment near the location of merging flow fronts in the absence of a vent is demonstrated, highlighting the tendency for porosity accumulation around weld-lines as observed experimentally.