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2. Improving Fibre Reinforced Plastics’ Through Thickness Properties for Aerospace Applications: Modelling and Testing of Designed Fibre 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. Problem Continuous fibre reinforced plastics Excellent in plane properties A design driver BUT poor out of plane properties X Y Z

5. 3D fibre architectures –weaving, braiding or knitting The Current Remedies Translaminar Reinforcement –stitching or Z-pinning Matrix Modification –the use of thermoplastics or bulk toughening Boundary Modification –fibre interface control or interleaving Dickinson et al ’99, Freitas et al, Mouritz et al ‘97 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. “Provisional Modelling” Surface area to volume ratio Orientation & symmetry Mechanical interlocking Predictable relative weakness Features on the fibre perimeter Packing 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

9. Precise Possibilities Matrix Layer Thickness Lobe Aspect Ratio Undercut

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

11. Partnership = Test + Model 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

12. y x n 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. Questions … and please do approach me later too with further questions.