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Title: Damage mechanisms of biological crossed-lamellar microstructures applied to high-performance carbon-fibre and hybrid composites
Author: Häsä, Riikka
ISNI:       0000 0004 7963 8241
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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The ability of components to preserve their structural integrity and diffuse damage under stable conditions is paramount for various applications in the automotive and aerospace industries. At the same time, requirements for weight savings have driven these industries towards extensive use of Carbon Fibre Reinforced Polymers (CFRPs) that have high specific strength and stiffness. However, CFRPs are inherently brittle and suffer from low damage tolerance, which has been identified as the main limitation for their use. Recent research has shown that these seemingly contradictory design requirements can be met through careful microstructural design. Natural composites have proven an excellent source of inspiration for new microstructures, as they typically retain their structural integrity under the attacks of predators despite their weak and brittle main constituents. In particular, the crossed-lamellar microstructure, found in many mollusc shells, exhibits remarkable damage behaviour due to its complex microstructure, leading to torturous cracks paths through various damage diffusion mechanisms. In this work, we design, prototype and test CFRPs with a crossed-lamellar microstructure. First, the feasibility of such microstructure in CFRP is studied using a parametric unit cell Finite Element (FE) model, and prototyping procedures for such microstructure are subsequently developed. Experimental characterisation of the failure mechanisms of the microstructures shows that the toughening mechanisms of the natural crossed-lamellar microstructure can be reproduced in CFRP. To further improve damage diffusion in the microstructure, hybrid metal/crossed lamellar composites are conceived and tested. The results show that such composites diffuse damage under stable conditions up to record large curvatures, while also retaining their structural integrity. Finally, we investigate metal/crossed-lamellar composites with in-plane fibres to improve the stiffness and strength of the microstructures. These composites are able to resist separation into several pieces upon bending, thus providing an attractive alternative for applications that need to retain their structural integrity against penetration damage.
Supervisor: Pinho, Silvestre Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral