Hierarchical mode I interlaminar toughening of unidirectional CFRP laminates by the synergistic effects of CNT powders and veils

While carbon fiber reinforced polymer (CFRP) composites are widely used in structural components because of their excellent mechanical properties, delamination between reinforcing plies remains a well-known Achilles heel, weakening the composite structure and limiting their more widespread applications. This work tried to improve the interlaminar properties of unidirectional CFRP laminates by the synergistic effects of CNT powders and veils. The short CNT powders (average length <1 mu m) were adopted for toughening the matrix, which effectively avoids the self-filtration effect commonly found in the VARTM process and allows the CNTs to penetrate between the tiny gap of the carbon fibers and be uniformly dispersed in the composites. In addition, an ultrathin CNT fiber veil (similar to 100 nm in thickness) was used as the interleaf material, offering the opportunity to reinforce the interlaminar bonding with minimal weight penalty and effectively avoid reductions in in-plane properties. The results showed that 0.5 wt% is the optimum loading level of CNT powders for matrix toughening. The Mode I interlaminar fracture toughness (propagation value, G(IC,prop)) of the unidirectional CFRP composites increased as much as 32 %, 62 % and 123 % when integrating CNT veil, CNT powder and CNT veil + powder, respectively. The figure of merit for interlaminar reinforcement, consisting of the change in interlaminar properties normalized by interleaf thickness and ply thickness, comes out as high as 2460, which far outweighs the state of the art.

Automated summary

This study aimed to enhance the interlaminar properties of unidirectional CFRP laminates by using the synergistic effects of CNT powders and veils. By adopting short CNT powders and ultrathin CNT fiber veils, the mechanical properties and interlaminar bonding strength of the composites were effectively improved, expanding their potential applications.