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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 WisnomUniversity of Bristol, UK

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

Problem

• Continuous fibre reinforced plastics

• Excellent in plane properties

• A design driver

• BUT poor out of plane properties

X

Y

Z

• 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

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

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

“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

Precise Possibilities

Matrix Layer

Thickness

Lobe

Aspect R

atio

Und

ercu

t

Production – Composites

50 micron borosilicate glass fibres

A localised example of interlocking

Early Composite

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

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Modelling Overview

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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

Questions

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