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 inh omogeneous fiber architecture. Such inhomogeneity leads to non-uniform perm eability of the fiber preform, which in turn causes the resin velocity to v ary from point to point at a micro scale. The capillary pressure, which als o prevails at this length scale, exacerbates the spatial variation of the r esin velocity. The combined effect of pressure gradient and capillary press ure can be described by the capillary number. The resulting microscopic per turbations in the resin-flow front allow voids to form. The present paper p roposes a mathematical model to describe the mechanisms of void formation. The existing data are used to validate the assumptions introduced. The mode l is then used to analyze new data from one-dimensional RTM experiments. (C ) 2000 Elsevier Science Ltd. All rights reserved.