Smart CompositesMonitoring composite structures with optical fibers

Geert Luyckx

Damien Kinet

15.12.13© sirris | www.sirris.be | info@sirris.be |

1. Objective2. Rationale

A. Production and assembly monitoringB. Operation/Health monitoring

3. Sensor technologies4. Envisaged applications5. Research consortium6. Research approach7. Industrial user consortium

� Life cycle of a composite structure

� Production and assembly monitoring

� Application monitoring

� Opportunities

� Novel technologies

� Applications

� Health monitoring in marine environment

Overview

Life cycle of a composite structure

“Life cycle monitoring of large-scale CFRP VARTM structure by fiber-optic-based distributed sensing,”

S. Minakuchi, et. al., Composites Part A, 42(6),669-676 (2011)

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Life cycle monitoring: Wind turbine

Assembly

Exploitation

DesignProductionProductionProductionProduction

Life cycle monitoring: Wind turbine

Production monitoring & opportunities

ProductionProductionProductionProduction Today

� Thermocouples

� Pressure sensors

� Ultrasonic inspection

No sensor able to predict initial strain state!

Opportunities

� Initial strain state (residual strains)

e.g. with embedded sensors (Fiber optics, Polymer waveguides,…)

� In-situ Cure monitoring e.g. with ultrasonic transducers, Fresnel reflection, capacitive sensing,…

� NECESSITY FOR MULTI-INSTRUMENTATION

ProductionProductionProductionProduction

Technology: Fiber Bragg Gratings

Optical fiberOptical fiberOptical fiberOptical fiberOptical fiberOptical fiberOptical fiberOptical fiber

Combination of Optical fibers and Ultrasound

Combination of Optical fibers and Ultrasound

2 regions:1. Composite does not exist! Resin in a fluid state2. Composite exist � strain transfer

1111 2222Gelation

Ultrasound

Temperature

FBG�strain

Residual strain magnitude

Assembly monitoring & opportunities

Assembly+

Finishing

Today

� Visual inspection

Opportunities

� Embed sensors in adhesive zone

� Use finishing layer as sensor (coating)?

� Ageing sensors?

� Impact damage, tool drop

� Speed of monitoring

� event measurement or offline monitoring

Follow-up of bonded structures

Initiated cracks reach sensor

Safety level

Exploitation

Design

Application monitoring & opportunities

Today� Visual inspection

� Load monitoring (edge, flap, combined)

� External strain gauges

No information from the inside

Opportunities� Pitch control (blade deformation)

� predict life time blades

� Use material as sensor (CNT, CB,…), Digital Image Correlation?

� Design support tool

� Reduce costly inspection

Pitch control monitoring

� MOOG inc: System to Adjust Windmill Wing Pitch Angle

www.moog.com/markets/energy/wind-turbines/

� Provide edgewise and flap wise bending moment data to the individual pitch control system.

� 10-20% of load reduction in the blades

� 20-30% in the main shaft

� Life time ↑↑

� Read-out and integration

� Cost and size of interrogator system

� Go for less performing system?

� More dedicated?

� Cheaper?

� Number of sensors needed to monitor structure?

� The least possible (design or exploitation)

� Reparability: Sensor should survive the structure with 100% certainty or possibility for repair

� Prediction of Eigenfrequenciesvia online strain date

� Relation of the sensor signal with the real situation

Composite life cycle monitoring: DifficultiesOpportunities

� Micro-structured optical fibers

� Polymer waveguides

� Deformable electronics

Novel sensor technologies

+32 486 95 32 04

Geert.Luyckx@UGent.be

Dr. ir. Geert Luyckx

12/5/2013 16

Structural Health Monitoringapplied to Marine Applications

Structural Health Monitoringapplied to Marine Applications

� Development of FBG sensors based on silica & plastic optical fibres

� Investigating sensor embedding processes and positioning the optical fibres at different layers according to the strains to monitor

� Developing a complete catamaran in carbon fibre reinforced polymer which will be used for further investigation and embedding of smart components

Structural Health Monitoringapplied to Marine Applications

� Developing low cost optical interrogator

� Physical validation for finite element simulation

• Real-time strain monitoring• Composite material properties investigation• Broken down and failure detection

Simulation

SensorFabrication

SensorEmbedding

SensorInterrogation

SensorEvolution

Structural Health Monitoringapplied to Marine Applications

8.90m

9.25m

15.25m

17.75m

1.10m

0.70m

0.70m

Spreader

Fibre Bragg gratings

Location of the future housing connectors

Shrouds

Front view: Schematic representation

Preliminary tests

• More then 60 FBGs were glued on the catamaran mast

• FBGs realized by the phase mask technique.

• Chirped phase mask: 15nm/cm, length of each FBG: 1mm

Location of the future housing connectors

Fibre n°1

Fibre n°2Fibre n°3

Fibre n°4

Fibre n°5

Fibre n°7

Fibre n°6

Fibre n°8Fibre n°9

190 mm

35

0 m

m

Shape of the mast base

Base of the mast

Fibres n°1, 4 and 7

Fibres n°3, 6 and 9

Fibres n°2, 5 and 8

Preliminary tests

Naked mast

Preliminary tests

Fibre maintained on themast with tape

Preliminary tests

FBGs are glued on the mastwith epoxy resin

Preliminary tests

Mast with FBGs

Preliminary tests

Mast is let free and is only maintained at both extremities

Preliminary tests

Schematic representation of the mast during this test

Preliminary tests

� We follow the evolution of the Bragg wavelength of the FBGs. As expected:

� The Bragg wavelength shifts of the FBGs of the fibres n°1, 3, 4, 6, 7 and 9 are very small

� The FBGs of the fibres n° 2, 5 and 8 are under compression

y=-3E-10x4+1E-06x3-0.0012x2-0.078x-19.343

R²=0.92681

-500

-400

-300

-200

-100

0

0 500 1000 1500

Bra

ggw

avele

ngth

shif

t(p

m)

Position(cm)

Preliminary tests

This figure presents the shift of the Bragg wavelength of the FBGs of the fibres n° 2, 5, 8 with an attempt to adjust a curve of the 4th order

Mast is let free and is only maintained at both extremities but turned on its side

Preliminary tests

-600

-400

-200

0

200

400

600

1 3 5 7

Bra

ggw

avele

ngth

shif

t(p

m)

N°oftheFBG

Fibre n°4 Fibre n°6

Preliminary tests

� We follow the evolution of the Bragg wavelength of the FBGs. As expected:

� The Bragg wavelength shifts of the FBGs of the fibres n°1, 4 and 7 are under traction.

� The Bragg wavelength shifts of the FBGs of the fibres n°3, 6 and 9 are under compression.

2nd phase: Embedding

- Realisation of smallgrooves- Optical fibers embedding- Filling of the grooves and protection of the sensorswith epoxy glue

2nd phase: Embedding

Ingress/egressof the optical fibers

Splicing of the optical fibers

MPO (Multi-fiber Push-On) connectorbetween the mast and the interrogator

Rapid prototyping of a waterproof housing for the connection. This one will be attached to the mast

2nd phase: Embedding

Interrogator set-up

…

e-LED

Photodiode &

Data processing

Tunable filter

Optical circulator

FBG 1 FBG x

FBG 1 FBG x

FBG 1 FBG x

Light, small size, low power consuming

Interrogator set-up

Light, small size, low power consuming

+32 (0) 65 37 41 96

Damien.KINET@umons.ac.be

Damien KINET

5.12.13© sirris | www.sirris.be | info@sirris.be |

SBO Self sensing composites

Structural health

monitoring

Production monitoring

� 2 optical fibers, 10 sensors

� Designed and manufactured by

and

12/5/2013 39

Case: control arm

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