A comparative fractographic analysis for the effect of polymeric nanofiber reinforcements on the tensile behavior of multi-layered epoxy nanocomposites

This study presents a comparative investigation into the effects of four different nanofibers—PA66, PStX, PAN, and PVB—on the mechanical performance and failure mechanisms of epoxy adhesive films. These nanofiber-reinforced adhesive layers were manufactured via a dry-reinforcement resin film infusion method and tested under uniaxial tensile loading. Mechanical results showed that PA66 and PStX nanofibers improved tensile strength by up to 25%, primarily by mitigating crack initiation at free edges and promoting effective fiber–matrix bonding. In contrast, PAN nanofibers induced micro-cracks at the fiber–resin interface, amplifying crack coalescence and reducing strength by 25%. PVB nanofibers, which lost their fibrous morphology due to a relatively low glass transition temperature, formed a separate polymeric phase with a negligible reinforcement effect. Detailed fractographic analyses identified key features—ratchet marks, ridges, interlayer failures, and river lines—that elucidate how nanofiber type, compatibility with the epoxy matrix, and cure conditions dictate the final failure modes. A “top-down” approach to fractography revealed that manufacturing-induced free-edge cracks and nanofiber-based interactions converge to influence the ultimate tensile performance of these adhesive films. Finally, a fishbone diagram synthesizes the findings, offering a practical reference for the effects of fiber selection, processing parameters, and testing protocols in developing high-performance, nanofiber-reinforced epoxy adhesive films. Highlights: Tensile failure mechanisms for novel laminated nanofiber/epoxy nanocomposites. Effect of nanofiber base polymer choice on mechanical response of epoxy adhesive films. Multi-scaled perspective for efficient fractographic analysis. A top to bottom approach on failure analysis of nanocomposites.