Resin-rich regions

Deleterious effects are introduced during the stitching process, which include the breakage and misalignment of the in-plane reinforcing fibers and the formation of resin rich regions at the stitch holes. 

The ratio of the toughness for ALF/epoxy to that for CF/epoxy was about two, and this ratio remained constant without respect to the fracture mode and test environment. This ratio was correlated to geometrical factors such as the thickness of the resin rich region at the prepreg interface. 

The evaluation of degradation in material properties is focused on the foam, the facings, and the foam/facing interface. That interface consists of a resin-rich region that bonds foam and facings together. 

Figure 9.9 shows the internal state and the magnified pictures of some PLA/BF/MFC specimens. It was observed that the BFs were well dispersed in the matrix and the resin-rich regions remarkably decreased for the specimen having an elevated content of the MFC. 

To decrease the thickness of a laminate, some of the laminae must be selectively stopped, dropped, or terminated. Moreover, the stopped laminae are covered with at least one continuous lamina as in Figure 7-31. There, resin-rich zones occur naturally in the vicinity of the ply drop. Such regions are also local stress-concentration sites. However, the tapered laminate creates a globally lessened stress concentration. 

Another chemical species which can be added to the interphase region in composites or in adhesive joints is the finish or primer . The finish is usually applied to the fiber before composite fabrication or as a primer to the adherend before joint formation. Both finish and primer are quite similar in that they consist of a resin rich... 

Defects such as voids, dry spots, resin-rich areas, premature failures, localized failure regions and non-uniform or incomplete cures can occur. Most aerospace components are held to within 2% weight tolerance and for strength, an excessive variation can result in uneven stress distribution, resulting in component failure. 

Resin-rich area n. A region in a reinforced-plastic article in which there is an objectionable excess of resin. 

A detailed numerical study (Bond 2005) has shown that for the same overall fiber volume fraction, the diffusion coefficient D is rather insensitive to the spacing or distribution of circular fibers, although, in the case of composite laminates, the presence of a resin-rich interlaminar region would affect the overall value of the transverse component of D. 

Figure 6.19. (A) Transmission electron microscopy image of onion PS/PMMA particles stained with RUO4 (B) STXM image at 285.1 eV (only PS is strongly absorbing) of a group of particles embedded in epoxy resin (C) STXM image of a cryomicrotomed sample at 285.1 eV. Note that the two STXM images are as-recorded transmission data in which the PS-rich regions appear dark. (From Takekoh et al. [348] reproduced with permission.)...

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