INVESTIGATE THE IN-PLANE SHEAR PROPERTIES IMPROVEMENT OF CARBON FIBER REINFORCED POLYMER LAMINATE ENHANCED WITH CARBON NANOFIBER Z-THREADS BY USING DIGITAL IMAGE CORRELATION SYSTEM

In-plane shear strength is an important issue for the structural integrity of carbon fiber reinforced polymers (CFRP). In this study [± 45°]4s in-plane shear test was performed for both Z-threaded CFRP (ZT-CFRP) and traditional CFRP. A newly developed proprietary Bisphenol-F based epoxy blend was used in this study. A significant improvement of +24% in the in-plane shear strength for ZT-CFRP was observed. There was a notable difference found in the failure modes between control CFRP and ZT-CFRP samples. Intralaminar and interlaminar delamination modes were noticed in control CFRP samples spreading to all plies whereas the ZT-CFRP samples experienced a confined failure in the interlaminar region. Digital image correlation (DIC) showed more uniform stress distribution and higher strain in ZT-CFRP, which suggested ZT-CFRP was stronger and tougher under the in-plane shear testing. Microscopic analysis of failure mode indicated that the z-threaded CNFs act as effective nano-structural reinforcement between and inside the laminas to keep the interlaminar/intralaminar bonding stronger.