Effect of carbon nanofiber z-threads on mode-I delamination toughness of carbon fiber reinforced plastic laminates

Delamination is a major drawback of carbon fiber reinforced plastics (CFRPs). Studies have reported that carbon nanofibers (CNFs) can improve the delamination toughness of various FRPs. However, lack of CNF alignment control caused substantial uncertainty in the improvements. In this study, a novel CNFs z-threaded CFRP (ZT-CFRP), which utilized z-aligned CNFs as long-range reinforcement threading through the packed carbon fiber bed, was manufactured. The mode-I delamination toughness (GIC) of the ZT-CFRPs was tested against both control CFRPs and unaligned CNF-modified CFRPs (UA-CFRPs). Through statistical comparison against control CFRPs, UA-CFRPs exhibited a relative change in mean GIC and coefficient of variation of +13.99% and +116.35%, respectively, whereas the ZT-CFRPs of equivalent CNF concentration exhibited a relative change in mean GIC and coefficient of variation of +28.93% and −12.33%, respectively. Accordingly, the CNF z-threads were found to play a positive role in toughening CFRPs, as supported by delamination experiments and microscopy analysis.