Enhancement mechanism for <scp>Z</scp>‐pin on carbon fiber composite

Abstract The effect of Z‐pin on the impact property of carbon fiber reinforced epoxy resin composite was investigated. Carbon fiber Z‐pin and aramid fiber Z‐pin were used to improve the impact property of composite laminate. The impact property and damage mode of the composite were studied under low‐velocity and high‐velocity impact. The low‐velocity impact was conducted by a drop hammer machine, and high‐velocity was carried out on a modified Hopkinson bar system. The maximum impact load, absorbed energy, impact damage area, and failure morphology of composites with and without Z‐pin were evaluated from impact experiments. It demonstrates that the damage modes of the composite under low‐velocity and high‐velocity are similar, while the matrix damage, fracture, and delamination damages are the dominant failure mode under high‐velocity and low‐velocity damage, respectively. The effects of Z‐pin on low‐velocity and high‐velocity impact depend on impact energy and the damage mode of Z‐pin. Carbon fiber Z‐pin shows better enhancement on impact property due to more energy absorption through its damage under the low impact energy range with both low and high velocity impact. Aramid fiber Z‐pin performs with higher efficiency when the impact energy reaches a high level, due to strong energy dissipation by its fracture and pull‐out failure. Especially, high impact energy from high‐velocity impact promotes aramid fiber Z‐pin to pull out, resulting in an excellent enhancement effect. It denotes that the type of fiber used in Z‐pin needs to be chosen based on the levels of impact velocity and energy, and a suitable failure mode of Z‐pin is the key for improvement of the impact property. Highlights The low‐velocity and high‐velocity impacts under the same boundary were conducted. Matrix damage, fracture, and delamination are dominant failure modes under impact. Carbon fiber Z‐pin shows better enhancement in impact property under low energy. Aramid fiber Z‐pin performs a higher effect on impact property under high energy.