Bio-inspired designs for enhanced damage resistance of composite structures: Bouligand, Herringbone and multi-tailored bone-inspired strategies
File(s)
Author(s)
Mencattelli, Lorenzo
Type
Thesis or dissertation
Abstract
This thesis presents three novel bio-inspired microstructural concepts, for point-by-point tailorable composite solutions, that exploit the ability to diffuse damage in a sub-critical state; these aim at enhancing the damage resistance and the energy dissipation capability of conventional composite structures. To this end, we investigated three bio-inspired concepts: Bouligand, Herringbone-Bouligand and multi-tailored bone-inspired. The Bouligand concept, inspired by the impact-resistant periodic region of the mantis shrimp’s dactyl club and consisting of a helicoidal lay-up with very small inter-ply (pitch) angles, was used to address the inherent low performance to through-the-thickness loading (static and dynamic) of CFRPs. We designed, manufactured, tested and analysed several ultra-thin-ply CFRP Bouligand microstructures, with the smallest pitch angle (2:5°) ever reached in the literature. Experimental studies, as well as detailed analytical and numerical modelling showed that tailored Bouligand microstructures achieved enhanced damage resistance via: smooth double-helicoidal evolution of damage, reduced delamination areas and sub-critical Bouligand cracks. Quasi-static indentation test showed that, compared to conventional CFRPs, tailored Bouligand microstructures achieved a simultaneous 92% increase in load-bearing capability, 74% delay in catastrophic failure and 97% increase in total dissipated energy. The Herringbone-Bouligand concept, inspired by the high-damage-resistant features of the mantis shrimp’s dactyl club impact region and impact surface, was used to improve further the damage resistance of Bouligand-inspired CFRPs. We designed, prototyped, tested and analysed the first high-performance Herringbone-Bouligand microstructure in the literature. We also devised the first prototyping procedure to manufacture point-by-point tailorable Herringbone-Bouligand CFRPs. Quasi-static indentation tests showed that, compared to standard Bouligand solutions, the Herringbone-Bouligand microstructure delays onset of delaminations, reduces the in-plane spreading of damage (71%), increases the energy dissipation capability (13%) and contains damage within the tailored Herringbone-Bouligand region. The multi-tailored bone-inspired concept, based on the introduction of patterns of discontinuities in the form of laser-cuts across the load-carrying fibres of FRPs, was adopted to devise a versatile design strategy that can be used to locally-tailor different damage resistance requirements at different locations within the same structure. Specifically, for a SRPP/CFPP hybrid composite, we demonstrate that patterns of discontinuities can be successfully tailored to create high-energy dissipation paths through which damage is stabilised and diffused at sub-critical levels. This results in a great increase (90%) in energy dissipation with respect to a non-engineered structure, i.e. a similar SRPP/CFPP hybrid structure without discontinuities. We demonstrate that discontinuities can be successfully tailored to enhance impact damage resistance, achieved with increased energy dissipation at sub-critical levels and delayed catastrophic failure.
Version
Open Access
Date Issued
2019-11
Online Publication Date
2020-06-24T10:45:59Z
Date Awarded
2020-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Pinho, Silvestre
Sponsor
European Union
Grant Number
722626
Publisher Department
Aeronautics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)