We present modeling and simulation of air void formation in composite materials manufactured by the Resin Transfer Molding (RTM) process. The prediction of air void formation has been an important topic because air voids in composite materials deteriorate the mechanical properties of the part.
It has been found by experimental observations that the void content, for a specific preform, can be correlated with capillary number which is the ratio of the viscous force and the surface tension. It is still difficult, however, to predict the void formation without experimental measurement. Moreover, the capillary number may not be the exclusive parameter in practical cases, because the modeling by the capillary number does not work well for large and complex parts.
In this context, we propose a mathematical model to predict the air void formation in the channel which is on open gap between fiber tows and inside the fiber tow. Moreover, the void formation in the warp and the weft are modeled separately by considering the tow orientation with respect to the flow direction. We also modeled two other important phenomena, namely air void compression or expansion, and void migration. To validate the model, void content was experimentally measured by injecting an electrically conductive liquid into a preform. The voltage drop was correlated with the air void content considering the air as a non-conducting material. For a unidirectional fabric, a good agreement was obtained between the model prediction and the experimental result.