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

Abstract

This paper studied the effects of Z-pin insertion angles (60°, 75° and 90°) 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 results demonstrate that the effects of Z-pin insertion angles on CAI behavior and failure modes are related to layups and impact energies. 90° 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.