Intra-bundle microvoid

Intra-bundle microvoid is the most common microvoid type which occurs due to the lower permeability of the fiber bundles than the permeability of the empty spaces between the bundles. The resin flow is faster between the fiber bundles than inside the bundles, and the resin encircles itself when it reaches a stitch or another bundle perpendicular to the flow direction, and entraps a microvoid inside the bundle as shown in Fig. 9.21. To avoid this type of microvoid, the common practice is to slow the resin flow down by decreasing the injection pressure/flow rate boundary condition. This allows sufficient time for the encircled microvoids to shrink and collapse due to the higher resin pressure around the microvoids than inside the voids. 

Figure 9.22 illustrates how intra-bundle microvoids are formed when the resin is injected into a fiber preform. Delayed impregnation of the fiber bundles is clearly observed when one examines the dark (completely saturated) and light (partially saturated) regions in the preform, and compares them with the actual flow front position. 

Microvoids trapped in the composite part [reference 1]. (Top) Inter-bundle voids are trapped when the resin races along the fiber bundles and encircles itself when it reaches a stitch. (Bottom) Intra-bundle voids are trapped in the fiber bundles when the resin races in between the bundles due to the high permeability, and the impregnation of the bundles is delayed due to the low permeability of bundles. (Source Reprinted with permission from reference 1, copyright 2010 CRC Press, Taylor Francis Group.)... 

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See also in sourсe #XX -- [ ]

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