Experimental investigation of Z-pin insertion angles on the mechanical behavior and failure mechanism of compression after impact for CFRP laminates

This paper studied the effects of Z-pin insertion angles (60 degrees, 75 degrees and 90 degrees) on the behavior and failure modes of compression after impact (CAI) for composite laminates. Unpinned and different angle Z-pinned [0/90]4s and [45/0/-45/90]2s laminates were impacted at 25-60 J to introduce damage ranging from barely visible impact damage (BVID) up to penetration, then subjected to compression load until failure. The damage induced by low -velocity impact (LVI) was introduced, and the damage status after compression was inspected and evaluated by micro-CT, scanning electron microscope (SEM) techniques and visual observation of surfaces. Experimental re-sults demonstrate that the effects of Z-pin insertion angles on CAI behavior and failure modes are related to layups and impact energies. 90 degrees Z-pin is the most effective in improving CAI strength for both [0/90]4s and [45/ 0/-45/90]2s laminates by stitching delaminated sub-laminates together. Decreasing Z-pin insertion angles will reduce the enhancement of CAI strength, which is more evident for [0/90]4s laminates at relatively high impact energies. This study provides new insight into the effect of Z-pin insertion angles on the CAI failure mechanism and performance of composite laminates.

Automated summary

This study investigated the influence of Z-pin insertion angles (60 degrees, 75 degrees and 90 degrees) on the behavior and failure modes of compression after impact (CAI) for composite laminates. Different laminates with Z-pins at various angles were impacted and then tested under compression load until failure. The results showed that the effects of Z-pin insertion angles on CAI behavior and failure modes depended on the layups and impact energies. The 90 degrees Z-pin was found to be the most effective in improving CAI strength for both [0/90]4s and [45/ 0/-45/90]2s laminates. Decreasing Z-pin insertion angles reduced the enhancement of CAI strength, particularly for [0/90]4s laminates at higher impact energies. This study provides new insights into the effect of Z-pin insertion angles on the CAI failure mechanism and performance of composite laminates.