In this paper, a bio-inspired carbon-fibre/epoxy composite with nacre-like tiled microstructure is designed, synthesised and tested. Analytical models are developed to predict the energy dissipation and crack deflection properties of such composite, and the predictions for the stress-strain response during tile pull-out are validated against direct numerical simulation. Suitable configurations for tile geometry with interlocks are then identified (with dimensions of the order of 0.6 mm) and used for the subsequent prototyping. In-situ three-point bend tests are then carried out in a SEM environment, showing the capability of the interlocking micro-structure in deflecting the crack, avoiding sudden failure in the most highly loaded cross-section of the specimen. The results suggest that further damage diffusion could in principle be achieved by additionally modifying the interface between tiles

In this work, we developed a film-casting technique to deposit thin (⇠13 m) layers of poly(lactic acid) (PLA) on the interface of carbon/epoxy prepregs, with the aim of increasing the interlaminar toughness. PLA patches with fractal shape were explored, based on preliminary results showing that the toughening e↵ect increases when PLA is deposited at multiple scales simultaneously. Double Cantilever Beam (DCB) and 4-point End-Notched Flexure (4ENF) tests showed an increase in interlaminar toughness of, respectively, up to 80% for Mode I and 12% for Mode II. This is specially remarkable because the interface thickness is only 13 m. Moreover, it was demonstrated that this technique can promote interaction between neighbouring layers where PLA has been cast, thus triggering fibre bridging and leading to a further enhancement of toughness.

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In this work, a nacre-inspired Carbon Fibre Reinforced Polymer (CFRP) composite is designed, synthesised and tested. Analytical and numerical models are used to design a tiled micro-structure, mimicking the staggered arrangement of ceramic platelets in nacre and exploiting geometrical interlocks for crack deflection and damage diffusion. The designed pattern of tiles is then laser-engraved in the laminate plies. In order to increase the damage-spreading capability of the material, a thin layer of poly(lactic acid) (PLA) is film-cast on the interlaminar region, both as a continuous film and as a pattern of fractal-shaped patches. Three-point bending tests show how the nacre-like micro-structure succeeds in deflecting cracks, with damage diffusion being significantly improved by the addition of PLA at the interface between tiles. It is observed that a texture of discontinuous fractal-shaped PLA patches can increase damage diffusion, by promoting the unlocking of tiles whilst preserving the interface strength.

In this paper, a carbon-fibre/epoxy (CF) composite with nacre-inspired tiled micro-structure is designed and synthesised. The aim is to investigate the interaction between the CF discontinuous micro-structure and continuous glass-fibre/epoxy (GF) layers, which are intended to act as crack stoppers, similarly to the organic interlayers that separate layers of ceramic tiles in natural nacre. Firstly, we use a GF skin to trigger unstable failure in nacre-like mesolayers, and show how the damage mode in the latter changes from pull-out to brittle fibre fracture due to the interaction with the GF skin. Secondly, we demonstrate how continuous GF interlayers can succeed in arresting unstable crack propagation in the nacre mesolayers. Furthermore, we show that they can also change the morphology of damage in the nacre, promoting a transition from brittle tile fracture to more damagetolerant tile pull-out.