Is the Bouligand architecture tougher than regular cross-ply laminates? A discrete element method study

The Bouligand structure, prominent in arthropod cuticles and fish scales, is a fibrous laminate where the orientation of the fibers increases incrementally across the thickness. Complex three-dimensional fracture mechanisms (crack twisting) have recently been intriguing researchers as a potential source of toughness. Capturing the interaction of propagating cracks with this complex architecture, however, remains a challenge and usually requires computationally expensive models. We ask the question: Given identical fibers and interfaces, is the Bouligand architecture tougher than other types of cross-plies? Here we use the discrete element method (DEM) to capture the main fracture mechanisms in fibrous laminates: crack deflection, crack twisting, delamination, process zone and fiber fracture, and to capture how various contrasts of properties between fibers and matrix affect these mechanisms. Our main conclusion is that in terms of fracture toughness (initiation and propagation), the Bouligand is outperformed by the (00/900) cross-ply for any crack orientation. The Bouligand structure is however more isotropic in-plane in terms of both stiffness and toughness, which may confer some advantage for multiaxial loading and could explain why this architecture is often found in nature. (C) 2020 Published by Elsevier Ltd.