Mode II interlaminar fracture toughness enhancement of fine z-pin reinforced carbon fiber composite with low fraction of pins

This article aims to improve the shear delamination resistance of composite laminate and minimize implantation damage on fiber orientation by using fine z-pins. The z-pins with the diameters as small as 0.1 and 0.2 mm were prepared by using different carbon fibers. The results show that z-pinning method significantly improves the mode II interlaminar fracture toughness, and the G_IIC value becomes larger with the decrease in z-pin diameter. Compared with the control sample, the precracked G_IIC values of (carbon fiber-reinforced polymer composite) CFRP_{(0.5CF4X−pin)}, CFRP_{(0.2CF4X−pin)}, and CFRP_{(0.1CF4X−pin)} increase by 67%, 142%, and 176%, respectively. As z-pin diameter decreases from 0.5 to 0.1 mm, the failure mode changes from z-pin pullout to shear fracture. The evolution of failure mode greatly enhances the resistance to crack propagation and the final G_IIC value. The carbon fiber type of pin_(0.5mm) has no obvious influence on the delamination sliding resistance. For pin_(0.1mm) and pin_(0.2mm), the strong deformation resistance of z-pin is the dominant factor driving the improvement of the G_IIC values though providing high-shear traction load. In addition, the z-pins with large shear deformation capacity can also enhance the crack sliding resistance.