Crustacean-inspired helicoidal laminates

Comprising layers of aligned chitin filaments stacked together, the exoskeletons of many crustaceans are analogous to fibre reinforced composites. A unique feature of crustacean laminates is their helicoidal lay-up. Each ply is rotated a slight angle from the ply like the steps of a spiral staircase – an unusual configuration for structural composites. Carbon fibre reinforced epoxy with helicoidal lay-ups were fabricated and tested to determine if they offered any advantage. Under transverse loads, these bio-inspired plates displayed a monotonically increasing load-displacement response followed by abrupt failure without the intermittent load drops seen in cross-plys. When the interply angle in the helicoidal laminates is small, they can sustain higher loads than the crossplys. A 34% increase in peak load was obtained for 19-ply helicoidal laminates over crossplys. Micro-CT scans reveal obvious transverse cracks and delamination at all interply interfaces around the point of loading in crossplys whereas delamination in helicoidal specimens climbs from one interface to the next forming a spiral pattern which extends to the edge of the specimens. Load-displacement predictions from finite element simulations showed quantitative agreement with experiments and key damage features were also replicated.