Experimental study of crack diversion, bridging mechanisms and enhanced delamination strength by dispersed carbon nanotubes in glass fibers composite laminates

• Carbon nanotubes and glass fibers produce a synergetic effect in promoting mechanical properties of composites. • Glass fibers serve as primary reinforcement, while carbon nanotube stick–slip mechanisms bridge and deflect micro-cracks. • SEM showed carbon nanotube dispersion and pullout; DMA tests revealed better damping, less chain mobility, and higher energy absorption. Due to low toughness and strain-to-fracture, glass fibers (GFs) based composites suffer greatly from edge delamination and are therefore barely applied in automotive and aerospace technology. The self-similar crack propagation (SSCP), which occurs in metals and alloys, also plays a crucial role in controlling delamination strength and toughness of GFs composites. Carbon nanotubes (CNTs) are one-dimensional conductors made of rounded graphite sheets and can be incorporated into polymers to create a new type of composites with electrical conductivity and mechanical stiffness much greater at a similar filling fraction compared with carbon black and graphene systems. In this work, multi-walled CNTs are used as secondary reinforcements and are dispersed at inter-regions of GFs/epoxy composite laminates. Microscopic analyses indicate that aligned GFs provide the primary reinforcement and micro-cracks around fibers are bridged and diverted by CNT stick–slip mechanism, namely, the SSCP retardation by CNTs. Mechanical measurements reveal improvements by 75% in bending stress, 46% in bending modulus, 75.24% fracture strain and 186.36% in toughness (delamination strength).