Interfacial design and flexural property of CFRP/aluminum-honeycomb sandwich with Aramid-pulp micro/nano-fiber interlays

This study proposes three interfacial designs for CFRP/aluminum-honeycomb sandwich to enhance interlayer of CFRP panels and adhesive interface between CFRP panel and honeycomb using sparsely distributed Aramid-pulp (AP) micro-/nano-fibers as interlayers. In laminar CFRP, AP-fiber free-ends protruded into adjacent carbon-fiber plies generate strong cross-ply fiber-bridging to prevent premature delamination. Adhesive joints with AP at the interfaces between CFRP and honeycomb form in-situ fillets and a randomly AP-reinforced composite layer. Meanwhile, Resin Pre-Coating (RPC) on the sanded CFRP and honeycomb core is used to improve the bonding capacity and create rounded fillet joints at the honeycomb edge. Three-point-bending tests show the sandwiches with toughened interfacial designs have higher peak load (+43.04%–57.60%), post-peak average load (+28.38%–163.25%) and energy-absorption (+15.52%–81.69%). The AP-toughened sandwich with 8-plies CFRP is stronger than the common sandwich with 10-plies even 12-plies CFRP. Failure and toughening mechanisms from both interfaces (e.g., delamination with fiber-bridging, matrix cracks in CFRP, debonding, cohesive failure with fiber-bridging, pulling-up of fiber, buckling of core, etc.) were explained by micrographs combined with schematic illustration.