Fracture toughness characterization of nanoreinforced carbon-fiber composite materials for damage mitigation

Continuous polyacrylonitrile (PAN) nanofibers fabricated via the electrospinning process and commercially available silica nanoparticles were investigated and compared for their impact mitigating effects when incorporated into composite materials. The nanofibers were introduced at ply interfaces using two different approaches while the nanoparticles were mixed into the matrix material. Behavior was experimentally characterized by determining the fracture toughness of flat carbon-fiber composite coupons using the double cantilever beam (DCB) test according to ASTM D5528. The nanofibers were introduced to the composite coupons by directly electrospinning the fibers onto the ply surfaces or transferring the fibers from an interim substrate, or "nanomat", while the nanosilica particles were mixed into the resin system during vacuum bagging hand layup. Testing facilitated the calculation of Mode I strain energy release rates. Preliminary results show that when compared to a baseline coupon without nanoreinforcement, there is a 54.5%, 43.1%, and 26.9% reduction in G_avg for the nanomat, nanosilica, and directly deposited nanomaterial coupons, respectively. Directly deposited nanofibers outperformed the nanosilica reinforcement by 16.2% and the nanomat approach by 27.6%. Basic materials (carbon-fiber ply material and matrix system) and incomplete composite consolidation were cited as contributors to poor test coupon quality and detrimental to Mode I performance.