Experimental and analytical investigation on the interlaminar shear strength of carbon fiber composites reinforced with carbon nanofiber z-threads

This paper combines an experimental study of the interlaminar shear strength (ILSS) and fracture behavior of CFRPs reinforced with carbon nanofiber (CNF) z-threads (i.e., ZT-CFRPs) together with an analytical model to explain and predict the shear behaviors improved by the CNF z-threads. The ZT-CFRP prepreg was manufactured from resin film containing electrical-field-aligned CNFs by using a modified hot-melt flow-transfer process. The short-beam shear (SBS) test was conducted on the ILSS of ZT-CFRP laminates together with a microscopic morphology study to understand the roles of the CNF z-threads during the shear fracture process. The study revealed the significance of the alignment of the CNFs to increase the ILSS of CFRP laminates. It was shown that CNF z-threads statistically significantly increased the ILSS and the required shear fracture work of CFRPs when compared to the unmodified CFRP and the CFRPs reinforced with randomly dispersed CNFs due to energy transfer and mechanical interlocking from the CNF z-threads. Furthermore, calculations showed that CNF z-threads reduce unwanted stress concentrations, k(IC) during the double-notch shear (DNS) test. The analytical model helps to understand the interlaminar shear behavior of ZT-CFRPs further and is useful to predict additional experimental data and guide material design in the future.