Experimental study on the low-velocity impact and post-impact flexural properties of curved CFRP laminates reinforced by pre-hole Z-pinning (PHZ) technique

This paper presents an experimental investigation into the effect of Z-pin on the low-velocity impact response and flexural properties after impact of the curved CFRP laminates. The Z-pinned specimens are produced using a low-damage pre-hole Z-pinning (PHZ) technique. Unpinned and Z-pinned [0/45/-45/90](4S) specimens are both subjected to low-velocity impacts. Nondestructive inspection technique is used to evaluate the internal damage after impact. Subsequently, three-point bending tests are performed to characterize the flexural properties of the impacted specimens. Experimental results indicate that Z-pinned laminate, due to the bridging traction across the delamination cracks provided by pins, can provide an efficient crack arrest mechanism both in impact and bending after impact tests. Compared with the unpinned specimens, the delamination damage projection area (DDPA) is reduced by 28.5-63.5%, depending on the diameter and volume fraction of Z-pin. In addition, Z-pin could improve the residual flexural strength significantly. The specimens with a high Z-pin volume fraction have excellent damage tolerance, leading to an 18.1-76.1% improvement in the residual flexural strength compared with unpinned specimens.