Effect of Z-pin insertion angles on low-velocity impact mechanical response and damage mechanism of CFRP laminates with different layups

This paper investigates the effect of Z-pin insertion angles (60 degrees, 75 degrees and 90 degrees) on low-velocity impact mechanical response and damage mechanism for cross-ply and quasi-isotropic layups. The laminates were impacted with 25 J, 40 J and 60 J to obtain different mechanical response and damage status (permanent dent, delamination and backside damage). Experimental results demonstrate that the impact resistance is reduced with the decreasing Zpin insertion angles, which is accompanied by more severe backside cracking, larger impact dent and delamination area. This phenomenon is more significant in cross-ply laminates compared with quasi-isotropic layups. Additionally, 60 degrees pinned cross-ply laminates show asymmetry delamination because the damage modes of Z-pins on both sides of the impact center are different, which results in the different delamination resistance of the two sides. These findings can give some guidance for choosing Z-pin insertion angles when Z-pinning in different layups.