Effect of Z-pin inclined angle on the impact damage suppression effectiveness for cross-ply composite laminates

Z-pins can enhance through-thickness direction of composite laminates effectively by reducing the delamination damage area. In this paper, the low velocity impact behaviors of [0₂/90₂]_4S cross-ply composite laminates by inserting Z-pins with two different angle 0° and ±45° along the thickness direction were compared. T300 carbon fiber Z-pins were used as the reinforcements for Z-pinned laminates impacted by 5 J, 10 J, 20 J and 30 J impact energies. The mechanical responses including the impact force-time/central displacement curves were recorded during the tests. Afterwards, ultrasonic C-scanner, scanning electron microscope (SEM) and X-ray micro-computed tomography (μCT) techniques were used to characterize the impact damage. Experimental results demonstrated that the Z-pins were unable to delay the delamination initiation, which led to basically consistent delamination initiation threshold regardless of Z-pin inclined angle. Based on the mechanical characteristics, 0° Z-pinning could improve the resistance to the onset of penetration by comparing to the ±45° Z-pinning. In addition, the effectiveness of 0° Z-pinning on suppression of delamination damage and internal defects was better than the ±45° Z-pinning at high impact energy.