Experimental and compactional studies of interface toughening on GFRP by hierarchical distribution of halloysite nanotubes

The incorporation of nano-inclusions into the fiber-matrix interfacial regions to create hierarchical structured fiber reinforced polymers (FRPs) is a novel approach aimed at enhancing mechanical properties. However, the specific toughening mechanism facilitated by the hierarchical structure has not been extensively explored or discussed in detail. This study investigates the mechanical properties of glass fiber reinforced polymers (GFRPs) that have been hierarchically incorporated with natural halloysite nanotubes (HNTs) using experimental, computational, and numerical approaches. The hierarchical distribution of HNTs is achieved through electrophoretic deposition (EPD). The stiffening effect of HNTs incorporation is computed using the random-averaged micromechanical Mori-Tanaka model. Subsequently, stiffness and stress concentration analyses are carried out on mesoscale representative volume elements (RVEs) of GFRPs with periodic boundary condition (PBC) assignments in ABAQUS. Overall, the experimental results are consistent with the numerical and computational results in terms of trend and magnitude. The amorphous HNTs (AHNTs) with larger cross-sectional aspect ratios demonstrate significant enhancement of 45 % in transverse modulus. The in-plane stiffness and strength of GFRPs with hierarchical distribution are slightly inferior to those of GFRPs with random distribution. Nevertheless, the hierarchical distribution of nano-inclusions leads to a substantial improvement in interlaminar strength and toughness, with enhancements exceeding 70 % and 100 % respectively. This can be attributed to the reinforcement and toughening effects on the fiber-matrix interface brought about by the hierarchical distribution.