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2. Improving Fibre Reinforced Plastics’ Through Thickness Propertiesfor Aerospace Applications:Modelling and Testing of DesignedFibre Shapes in Polymer Composites JM Harris, IP Bond, PM Weaver, MR Wisnom University of Bristol, UK

3. In This Presentation • Problem - Through thickness reinforcement • Proposal - Novel shaped fibres • Possibilities - Qualitative guidelines • Production - Shaped fibre composites • Partnership • Stress concentration modelling • Mechanical testing • Questions

4. Z Y X Problem • Continuous fibre reinforced plastics • Excellent in plane properties • BUT poor out of plane properties • A design driver

5. 3D fibre architectures • weaving, braiding or knitting • Translaminar Reinforcement • stitching or Z-pinning Dickinson et al ’99, Freitas et al, Mouritz et al ‘97 • Matrix Modification • the use of thermoplastics or bulk toughening • Boundary Modification • fibre interface control or interleaving The Current Remedies Bannister et al ‘00 , Brandt et al ’96, Mouritz et al ’99 Garg & Mai ‘88 Marston et al ‘74

6. Desired Attributes • The solution should not start out as an inherent trade-off, seeking an improvement in through-thickness properties at the expense of other properties. 3D fibre networks (Brandt ’96) • The solution should be an evolution and not a revolution of existing technology. Z-pinning (Miller et al ’94) • The solution should not demand additional processing steps. Cost reductions (Bannister ’00) • The solution should be contained within the reinforcement or matrix materials so that it can be applied across a range of manufacturing techniques. Interleaved layers and RTM/RFI

7. Proposal Desired Attributes? • Through-thickness properties at the expense of other properties? Shouldn’t, Halpin-Tsai • An evolution and not a revolution? Yes, controlled shape only • No additional processing steps? Partially, but offline • Solution within the reinforcement or matrix? Yes, AND can be combined

8. 14 Guidelines covering: Chand ‘00, Hughes ‘91, Drzal et al ‘93, Hucker ‘01 Deng et al ‘99 Beyerlein et al ‘01 Atkins ‘73 Tsai et al ‘66, Deng et al ‘99 “Provisional Modelling” • Surface area to volume ratio • Orientation & symmetry • Mechanical interlocking • Predictable relative weakness • Features on the fibre perimeter • Packing

9. Lobe Aspect Ratio Undercut Matrix Layer Thickness Precise Possibilities

10. 50 micron borosilicate glass fibres Early Composite A localised example of interlocking Production – Composites

11. Stress Concentrations 2D Airy Stress Function 2D Slow Steady Flow Tools Analytic Formulation Elliptic Functions Matrix Inversion Conformal Mapping PARAMETRIC STUDY & DESIGN REFINEMENT Circular v’s Shaped Initial Tests 3-point Bending DCB Curved beam bending Flexural Test PROOF OF CONCEPT Partnership = Test + Model

12. y n x m Modelling Overview

13. Summary • Identified four desirable attributes for through thickness reinforcement • Proposed shaped fibres as an approach • Identified a range of shapes to investigate • Developed a composite of shaped fibres • Developing Model & Beginning Testing • MUCH PROMISE, MANY QUESTIONS

14. … and please do approach me later too with further questions. Questions