Tuning interlaminar fracture toughness of fine z-pin reinforced polymer composite

This paper aims to improve the interlaminar fracture toughness of carbon fiber reinforced polymer (CFRP) composites by implanting fine z-pins with the minimum damage on in-plane fibers. Z-pins with diameters as small as 0.1 mm and 0.2 mm were prepared by using carbon fiber tows with different mechanical properties. The effect of the mechanical property of carbon fiber pin on the interlaminar fracture toughness of composite laminate was investigated to reveal the enhancement mechanism. The results show that fine z-pins significantly improve the interlaminar fracture toughness and simultaneously are favorable for maintaining high retentions of in-plane mechanical properties of composite laminate. Compared with control sample, the propagation G_IC values of CFRPs implanted with 0.2 mm and 0.1 mm CCF800 z-pins increase by 276 % and 541 % respectively at a low pin volume fraction of 0.16 vol%. Both z-pin pull-out and z-pin fracture failure behaviors can be observed for these fine z-pin reinforced composites. The higher tensile properties of z-pins and better transverse shear resistance tend to result in the failure of z-pin pull-out. With the decrease of z-pin diameter, the probability of z-pin fracture failure becomes greater, and correspondingly stronger pinning effect and larger failure load are achieved.