Enhancing structural integrity of the continuous fiber-reinforced 3D printed composites by self-reinforcing nanofiber interleaves

In this study, we demonstrated a straightforward method to improve the structural integrity of the fused filament fabricated (FFF) continuous carbon fiber-reinforced (CCFR) composites using self-reinforcing nanofiber interleaves. A dual-head printer that deposits polyamide 12 (PA12) filaments and polyamide 12 towpreg filament with 60 v/v% continuous carbon fibers (CF/PA12/tw) was utilized to fabricate composites. Such 3D printed structure suffers weak interlaminar properties if it is not subsequently consolidated via hot pressing. Instead of consolidation, we introduce polyamide 6 (PA6) nanofiber mat interleaving, which is applied between CF/PA12/tw and PA12 printed struts. The self-reinforcing nanofibers improved the laminate's tensile strength, flexural strength, and flexural modulus by 15, 22, and 26 %, respectively, compared to the non-interleaved one. Furthermore, the nanofiber interleaves maintained FFF laminate stiffness under fatigue loading, for which nearly a 50 % improvement was recorded at the end of one million cycles compared to the non-interleaved ones. These findings can help further utilization of the CCFR FFF composites and improve the structural integrity using straightforward and cost-efficient nanofiber interleaves.