Compression-after-impact properties of carbon fiber composites with interlays of Aramid pulp micro-/nanofibers

The inherent resin-rich ply interfaces in laminar carbon fiber reinforced polymer (CFRP) composites are toughened by ultrathin interlays formed by Aramid pulp (AP) micro-/nanofibers, to show that stronger and more impact-resistant CFRP can be manufactured with minimum disruption to the current composite forming process. Flexible nonwoven AP micro-/nano-fibers, less than 1 mm in length, can conveniently fit in the uneven surface profiles or microresin-rich areas between carbon fiber plies and form in situ quasi-Z-directional fiber-bridging across the ply interfaces. CFRPs with multiple interfacial AP interlays estimated to be around 3 and 6 g/m(2) were tested before and after low energy impact. Ultrathin resin-rich ply-interface layers in plain CFRP were transformed into ultrathin "Short Aramid Fiber Epoxy" layers by the AP interlays (20-50 mu m in thickness), leading to enhanced compressive energy absorption and up to 86.7% increase in Compression-After-Impact Strength. Keeping the interlay thin (around 30 mu m or thinner if possible), even the compressive strength (without impact) is not compromised, and the energy absorption under compressive loading (without impact) is 130% higher. The distinctly different compressive failure mechanisms, delamination failure of the plain CFRP was transformed into matrix shear failure in AP-toughened CFRP, as identified by nondestructive X-ray microcomputed tomography scans. Scanning electron microscopy was performed on the failure surface to inspect the microscopic toughening mechanisms.