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Carbon-fiber reinforced polymer (CFRP) composites offer benefits of reduced weight and increased specific strength; however, these materials can have relatively weak interlaminar toughness. The first modes of composite material failure often remain undetected, since failure is not always visually apparent on the surface of composite materials. In this study, several nano-sized materials and integration approaches are investigated as nanoreinforcement for composite materials. Performance is characterized by the ability of each nanoreinforced composite type to improve Mode I interlaminar toughness. The nanomaterials include 1) commercially available surface-modified silica nanoparticles and 2) continuous polyacrylonitrile (PAN) nanofibers. Test articles are manufactured using hand-layup vacuum bagging and feature either reinforced unidirectional carbon fiber or woven carbon fiber material and one of two investigated epoxy-based resin systems. The nanosilica particles were integrated into the fiber composite structure by mixing with the resin system prior to layup. The PAN nanofibers were produced by an electrospinning process; these fibers were integrated by either collecting the fibers of various areal densities as respective “nanomats” on an interim substrate for subsequent transfer during layup, or directly electrospun onto dry carbon fiber ply surfaces. Test articles were characterized according to ASTM D5528 for finding Mode I strain energy release rates. Results were compared to baseline coupons to determine fracture toughness performance. Results showed that the nanosilica-reinforced coupons increased an average of 35% and 25% in strain energy release rates for the coupons featuring unidirectional fibers and woven fibers, respectively, as compared to the corresponding baseline, whereas the nanomat-reinforced and directly deposited nanofiber-reinforced composites decreased. Low strain energy release rates for the PAN nanofiber-reinforced coupons is attributed to voids in the test coupons as a result of unconventional composite coupon manufacturing.
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