Interlaminar fracture toughness and impact resistance of carbon fiber reinforced composite with magnetic aligned CNTs

Abstract

This study draws inspiration from Z-pins employed in fiber composites. Carbon fiber reinforced polymer (CFRP) laminates modified with Z-oriented carbon nanotubes (Z-CNTs) were fabricated utilizing a magnetic field orientation technique. The interlaminar fracture toughness, impact resistance and damage tolerance of CFRP modified with Z-CNTs were evaluated through end-notched flexure (ENF), low-velocity impact (LVI) tests, and compression after impact (CAI) testing. The enhancement mechanisms were investigated using multiscale techniques, including digital image correlation (DIC), scanning electron microscopy (SEM), molecular dynamics (MD), and finite element (FE) simulations. CFRP modified with 0.3 wt% CNTs showed optimum interlaminar fracture toughness, which improved by 62.9 % in CNT-random samples compared to non-modified samples and further enhanced by 95.2 % in CNT-oriented samples. The DIC and SEM analysis revealed the enhancement mechanism of Z-CNTs in fracture toughness, including (1) enlarging the toughness deformation of resin; (2) broadening the fracture process zone to dissipate the energy; and (3) shifting the failure mode of CNTs from pull-out dominance to fracture dominance. Furthermore, MD simulations showed that the crack propagation location significantly influences the different enhancement mechanisms exhibited by CNTs, which was accord with SEM observations. LVI and CAI tests indicated that specimens modified with Z-CNTs exhibit greater impact resistance and damage tolerance. FE simulation revealed that the mode II interlaminar fracture toughness plays a dominant role in the impact resistance of the laminate. These findings provide an effective strategy and theoretical supports for the design of impact resistance of composite laminates.