Interlaminar and translaminar fracture toughness of Automated Manufactured Bio-inspired CFRP laminates

Natural structures such as nacre show an outstanding balance of strength and toughness, despite comprising mainly brittle constituents; this is a highly desirable combination of properties scarcely seen in synthetic composites. In this study, carbon fibre-reinforced polymer (CFRP) laminates mimicking the structure of nacre ('brick and-mortar') were manufactured using the automated tape laying (ATL) technique, as a means of enhancing their interlaminar properties and fracture toughness. The interlaminar fracture toughness of the bio-inspired CFRP laminates was measured via double cantilever beam (DCB) and three-point bending end-notched flexure (3ENF) tests. The results indicated increments of up to 32% and 92%, respectively, in the interlaminar fracture toughness when compared with that of conventional continuous CFRP samples. In addition, the translaminar fracture toughness of the developed nacre-inspired CFRPs was measured through a compact tension (CT) test, which revealed increments of up to 30%. Finally, different reinforcement mechanisms were analysed to understand the effect of the 'brick-and-mortar' structure.