Hierarchical strengthening of carbon fibre composite T-joints using nanoparticles and Z-pins

This paper presents an experimental investigation of the hierarchical strengthening of composite T-shaped bonded joints using dual-length-scale reinforcements: carbon nanomaterials and carbon z-pins. The nanomaterials were carbon nanotubes (CNTs), carbon nanofibres (CNFs) and graphene nanoplatelets (GNPs), which were ∼ 10 nm – 200 μm in length whereas the z-pins were 510 μm (diameter) and 5 mm (length). T-joints were made by dispersing the nanomaterials in the polymer matrix phase and reinforcing with z-pins. The results of the stiffener pull-off tests revealed that all three nanomaterials are effective in increasing the onset failure strength, ultimate strength and energy absorption, with CNFs yielding the highest improvements in these joint properties. Among the three nanofillers, GNPs were found to be less effective at increasing the joint properties compared to CNTs and CNFs due to their shape, aspect ratio and size. Key strengthening mechanisms induced by combining nanoparticles with z-pins are identified which stem from greater energy absorption due to the interaction between the nanoparticles and z-pins.