Formation of microvoids during resin-transfer molding process

Voids in a composite part are deleterious because they degrade its strength and modulus. In resin-transfer molding (RTM), voids result mainly from inhomogeneous fiber architecture. Such inhomogeneity leads to non-uniform permeability of the fiber preform, which in turn causes the resin velocity to vary from point to point at a micro scale. The capillary pressure, which also prevails at this length scale, exacerbates the spatial variation of the resin velocity. The combined effect of pressure gradient and capillary pressure can be described by the capillary number. The resulting microscopic perturbations in the resin-flow front allow voids to form. The present paper proposes a mathematical model to describe the mechanisms of void formation. The existing data are used to validate the assumptions introduced. The model is then used to analyze new data from one-dimensional RTM experiments.