Hierarchical enhancement of carbon fiber reinforced polymer laminate with randomly hybridized carbon nanotubes and aramid‐pulp micro/nano‐fibers

Abstract In this study, inspired by human teeth, random hybrid carbon nanotubes (CNTs) and aramid‐pulp micro/nano‐fibers (AP) with different mixing ratios were experimentally interleaved into carbon fiber reinforced polymer (CFRP) panels to form a gradient interface for hierarchical enhancement and synthetic effects. Due to different out‐of‐plane movability or penetrability of the CNTs, AP, and resin, 3rd and 4th order bio‐inspired gradient interfaces between the carbon‐fiber plies were formed in situ. According to flexural testing, hybrid CNT/AP‐interleaved CFRP with a CNT of 3.6 gsm and an AP of 2.4 gsm showed an improvement of 47.35% in flexural strength. Furthermore, the synthetic effects of hybrid CNT/AP‐interleaving were investigated by analyzing the mer3its and demerits of the CNT‐ or AP‐interleaving methods. It was identified that the hybridization of multiple length‐scale fibers as interleaves can be used to produce more hierarchical enhancements and synthetic effects. The new insights into multi‐scale strengthening mechanisms were systematically revealed from the models of hierarchical fiber‐bridging. And the graded penetration mechanisms of multi‐scale fiber‐reinforced CFRP laminates were analyzed. Highlights The in situ gradient interfaces form by Z‐direction penetration of CNT/AP. CNT/AP‐interleaving can form hierarchical enhancements and synthetic effects. Multi‐scale strengthening via fiber‐bridging and graded penetrations achieved. More fiber‐bridging occur at sub‐surface regions of the carbon‐fiber plies.