January 7th 2015

NCC Workshop

Project Background

Research on the application of magnetostrictive materials for,

(1) the control of induction heating for curing composite repairs;

(2) the structural health monitoring of composite structures.

Part-funded by InnovateUK in collaboration with Stirling Dynamics, TheWelding Institute, Argon Design, Hitex and McWade Monitoring(www.inheatpro.eu).

A 3-year project from 2014 to 2017.

2014-15 discussions with the UK composites community to direct the research for the greatest overall benefit

2015-16 technology research at The Welding Institute

2016-17 prototype development & test

2017 demonstration and dissemination

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Objectives for Today

• Introduce the research project to a wider audience.

• Discuss the research concepts.

• Discuss potential applications.

• To inform the direction for the TWI research during 2015.

• To inform the nature of the prototype demonstrator for 2016/7.

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Magnetostriction

Magnetostriction is the property of ferromagnetic materials that change in shape when subject to a magnetic field.

It is called the Joule effect, after James Joule who discovered it in 1842.

The reciprocal Villari effect is the change of magnetic susceptibility when subjected to a mechanical stress.

It causes the low-pitched buzzing sound that can be heard near transformers.

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Induction Curing (1)

• the repair patch has a magnetostrictive layer (a mesh and/or particulates)

• curing through induction heating

• tuned to heat this layer rather than the surrounding carbon structure

• directed heating

• much lower power than heating blankets – approx. 40W for 60cm2 patch

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Induction Curing (1)

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The Cure Monitoring and Control Concept (1)

• magnetostrictive layer is deformed during cure and develops residual stress

• the residual stress changes the magnetic susceptibility of the layer

• this can be sensed (Villari) to provide non-contact cure monitoring

• can be used as feedback to control the curing process

• “kissing” bonds will create regions of low residual stress

���� a potential means of detection both during the repair and in-service

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The Structural Health Monitoring Concept (2)

• a layer of filaments is embedded within the composite structure

• structural damage will act to deform or break the filaments

• each filament is coated with a thin magnetostrictive film

• Guided Lamb Waves used to sense the condition of the filaments

High. freq. magnetic field ���� ultrasonic excitation (Joule effect)

sensed response ultrasonic reflections (Villari effect)

• analysis of sensed response used to characterise damage

• excitation & sensing performed using a low-power portable unit

• a non-contact means of structural health monitoring

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A System View

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Patch Repair – A Starting Point for the Research

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Patch Repair – A Starting Point for the Research

Applicability of patches?

• Surface repairs only - “Non-structural”

Patch type?

• Repairs with pre-preg. patches much faster than using a wet lay-up

• however, pre-preg. material must be stored at low temperatures

• so use pre-cured patches

• only curing the adhesive layer between patch and repair surface

• monitoring the patch deformation during the cure near this layer

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Patch Repair – A Starting Point for the Research

Pre-Cured Patches

• Quick curing – only curing the adhesive layer

• Much faster than curing the whole patch

• however the patches must be pre-shaped.

• Maybe have a family of standard patches

• The repair surface would be prepared to accept one of these standard patches

• Only for patches with a flat or cylindrical external surface

• more complex shapes are hard to produce

• may only be suitable for common fleet repairs

• where “standard” repair patches might be produced in volume

• e.g. for cargo door damage

• may also facilitate repair automation

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Some Comments Received So Far

1. Surface preparation inhibits repairs for “more complex surfaces”.

2. The capability to identify “kissing” bonds is beyond current ultrasonic NDE.

3. Any new patch technology will need to be certified,

so will require engagement with composites manufacturers

e.g. Hexcel or Cytec.

4. A thin metallic gauze is fitted under the paint layer for electrical bonding,

i.e. on top of the repair patch,

an obstacle to the magnetic coupling measurement for in-service SHM?

5. The authorities need to be convinced that bonded repairs have sufficient integrity for large commercial aircraft. Enhanced SHM may facilitate acceptance.

6. This SHM methodology may have application beyond patch repair e.g.

Wind-turbine blades Fan blades In-service fatigue monitoring.

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Current Activity

Work to specify

• suitable composite materials

• typical damage

• inspection protocols

• industry applications

So that the TWI research during 2015 and the subsequent demonstrator reflect current practice and address current problems.

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Specification Headings

• Structure

– Primary

– Secondary

• Materials

– Reinforcement- Fibre type, layup

– Matrix- Polymer, cure conditions, service conditions

• Damage

– Type of damage- dent, chipping, delamination, cracking, etc…

– Dimensions

• Design of the patch

– Reinforcement

– Matrix

– Dimensions & lay-up

• Bonding material

– Adhesive type

• Patch repair assessment

– Type of test- G1c, G2c, etc…

– Standards

• Requirement of the accuracy of the measurement of the cure conditions

• Requirement of the resolution of the damage detection

– After/during curing- kissing bond etc.

– In operation

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Contact

Stirling Dynamics

Adrian Harrison aharrison@stirling-dynamics.com

Justin Simmons jsimmons@stirling-dynamics.com

Ian Gambon igambon@stirling-dynamics.com

TWI

Jasmin Stein jasmin.stein@twi.co.uk

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Supporting Slide - related research on monitoring

INDUCER - Composite repair patches with magnetostrictive mesh*

http://www.cleansky.eu/sites/default/files/documents/Activities/GRA1/INDUCER.pdf

http://aviationweek.com/awin/embedded-sensing-can-monitor-composite-repairs-service

Non-contact structural health monitoring at Bristol University

http://www.bristol.ac.uk/composites/research/intelligent-structures/#tab7

Optical cables within carbon fibre plies to allow measurement of strainshttp://www.gkn.com/aerospace/media/GKN%20Aerospace%20in%20the%20media/Challenges-in-composites.pdf

Self-monitoring composite patches for the repair of aircraft

(using Fibre-Bragg Grating technology)

http://www.aost.co.uk/pdf/smart_patch.pdf

* Note that InHeatPro has a wider scope than INDUCER

- particulates as well as mesh

- cure monitoring and control

- structural health monitoring using lamb waves & magnetostrictive thin film

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Supporting Slide - research on repair automation

Aiming to automate and standardize bonded composite repairs to help tackle certification and quality assurance issues

http://aviationweek.com/mro/composite-repair-research-gathers-momentum

Research on automated composites repair

http://www.compositesworld.com/articles/primary-structure-repair-the-quest-for-quality

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Copyright

Presentation prepared for the

National Composites Centre Workshop January 7th 2015

TWI and Stirling Dynamics hold copyright on this presentation.

All rights reserved. No part of this presentation may bereproduced or transmitted in any form or by any means,electronic or mechanical, including photocopy, recording,or any information storage and retrieval system, without

the express permission of the above.

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