ABSTRACT
Externally applied pressure gradient during the filling phase in LCM processes is responsible for the macroscopic resin flow. Comparison of experimental and numerical simulation* results for fibrous media consisting of random preforms show excellent agreement implying that capillary forces can be neglected. For woven or stitched preforms with dual-length scales, macroscopic flow fronts do reasonably match when visually observed. However, as evident from Fig. 5, the saturation near the flow front is not instantaneous and partially saturated region of finite depth near the flow front is visible. This occurs because the permeability of the fiber tows is usually couple of magnitudes lower than the permeability of the region in between the tows. Secondly, the capillary forces at the microscale become at least as significant as the external pressure gradient in deciding the movement of the resin. Generally, filling of the fiber tows is delayed because the flow must overcome very low permeability of the tows as shown in Fig. 6. On the other hand, the capillary effects that are stronger inside the fiber bundle than in between the fiber bundles facilitate flow. To accurately understand capillary contribution, we will address the simplest case first.
