Predicting the effect of preforming on RTM mold filling

In resin transfer molding (RTM) the step of making the preform - shaping layers of woven or random-fiber materials into the geometry of the final part - introduces local variations in the resistance of the preform to resin flow. These permeability variations affect the mold filling pattern when the part is impregnated with resin. In this study a mathematical model for this effect is proposed. The model predicts the fiber orientation and porosity at each point in the preform from the stretch ratios obtained from an ideal forming theory. It then computes the local permeability using a new self-consistent theory. The permeabilities serve as input to a mold filling simulating for preforms of variable permeability. An example demonstrates the importance of preforming for mold filling.