Realising bio-inspired impact damage-tolerant thin-ply CFRP Bouligand structures via promoting diffused sub-critical helicoidal damage

Abstract

In this work, we manufactured bio-inspired thin-ply Carbon Fibre Reinforced Plastic (CFRP) laminates, mimicking the helicoidal architecture of the mantis shrimp's dactyl club periodic region, with the smallest inter-ply (pitch) angle in the literature (2.5∘), thus better mimicking the actual micro-structure of the dactyl club. We conducted Low Velocity Impact (LVI) tests on a wide range of pitch angles (2.5∘, 5∘, 10∘, 20∘, 45∘), thus demonstrating that decreasing the pitch angle leads to a progressively smoother double helicoidal evolution of damage, reduces delamination areas, diffuses sub-critical damage, and enhances damage tolerance. We then conducted Compression After Impact (CAI) tests, thereby demonstrating that the residual strength and failure strain are preserved as the pitch angle is reduced, even though there is a steep decrease in the proportion of 0∘-plies (plies aligned with the loading direction) as the pitch angle decreases. Via detailed modelling, we then developed and proposed an explanation for why very small pitch angles are required to achieve the beneficial damage mechanisms exhibited by biological Bouligand structures.