Sirris Materials Workshop - 5 december 2013 - Monitoring composite structures with fibre optic sensors - Geert Luyckx, UGent and Damien Kinet, Multitel

1. Smart Composites
Monitoring composite structures with optical fibers
Geert Luyckx
Damien Kinet
© sirris | www.sirris.be | info@sirris.be |
5.12.13
1

2. Overview
Life1. Objective
cycle of a composite structure
Production and assembly monitoring
2. Rationale
A. Production and
Application monitoring assembly monitoring
B. Operation/Health monitoring
Opportunities
3. Sensor technologies
Novel Envisaged applications
4. technologies
5. Research consortium
6. Research
Applications approach
7. Industrial user consortium
Health monitoring in marine environment

3. MANUFACTURING
Life cycle of a composite structure
Use Phase
Assembly
Assembly
Assembly
Assembly
“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)

4. Life cycle monitoring: Wind turbine

5. Life cycle monitoring: Wind turbine
Production
Assembly
Design
Exploitation

6. Production monitoring & opportunities
Production
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

7. Technology: Fiber Bragg Gratings

8. Combination of Optical fibers and Ultrasound
Optical fiber

9. Combination of Optical fibers and Ultrasound
1
Gelation
2
Temperature
FBG strain
Residual strain magnitude
Ultrasound
2 regions:
1. Composite does not exist! Resin in a fluid state
2. Composite exist
strain transfer

10. 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

11. Follow-up of bonded structures
Initiated cracks reach sensor
Safety level

12. Application monitoring & opportunities
Design
Today
Visual inspection
Load monitoring (edge, flap, combined)
External strain gauges
No information from the inside
Exploitation
Opportunities
Pitch control (blade deformation)
predict life time blades
Use material as sensor (CNT, CB,…),
Digital Image Correlation?
Design support tool
Reduce costly inspection

13. Pitch control monitoring
MOOG inc: System to Adjust
Windmill Wing Pitch Angle
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 ↑↑
www.moog.com/markets/
energy/wind-turbines/

14. Composite life cycle monitoring: Opportunities
Difficulties
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 Eigenfrequencies
via online strain date
Relation of the sensor signal with the real situation

15. Novel sensor technologies
Micro-structured optical fibers
Polymer waveguides
Deformable electronics

16. Dr. ir. Geert Luyckx
Geert.Luyckx@UGent.be
+32 486 95 32 04
12/5/2013
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17. Structural Health Monitoring
applied to Marine Applications

18. Structural Health Monitoring
applied 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

19. Structural Health Monitoring
applied 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

20. Structural Health Monitoring
applied to Marine Applications
Sensor
Evolution
Simulation
Sensor
Interrogation
Sensor
Embedding
Sensor
Fabrication

21. 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
Shrouds
Fibre Bragg gratings
Location of the future
housing connectors
Spreader
1.10m
0.70m
0.70m
8.90m
9.25m
15.25m
17.75m
Front view: Schematic representation

22. Preliminary tests
Fibre n°1
Fibre n°3
Fibre n°2
Fibre n°4
Fibres n°2, 5
and 8
Fibre n°6
Fibre n°5
Fibres n°1,
4 and 7
Fibres n°3, 6
and 9
350 mm
190 mm
Shape of the mast base
Fibre n°7
Fibre n°9
Fibre n°8
Location of the future
housing connectors
Base of the mast

23. Preliminary tests
Naked mast

24. Preliminary tests
Fibre maintained on the
mast with tape

25. Preliminary tests
FBGs are glued on the mast
with epoxy resin

26. Preliminary tests
Mast with FBGs

27. Preliminary tests
Mast is let free and is only maintained at both extremities

28. Preliminary tests
Schematic representation of the mast during this test
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

29. Bragg wavelength shift
(pm)
Preliminary tests
0
y = -3E-10x4 + 1E-06x3 - 0.0012x2
- 0.078x - 19.343
R² = 0.92681
-100
-200
-300
-400
-500
0
500
1000
Position (cm)
1500
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

30. Preliminary tests
Mast is let free and is only maintained at both
extremities but turned on its side

31. 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.
Bragg wavelength shift
(pm)
Fibre n°4
Fibre n°6
600
400
200
0
-200
-400
-600
1
3
5
N° of the FBG
7

32. 2nd phase: Embedding
- Realisation of small
grooves
- Optical fibers embedding
- Filling of the grooves and
protection of the sensors
with epoxy glue

33. 2nd phase: Embedding
Splicing of the optical fibers
Ingress/egress
of the optical fibers

34. 2nd phase: Embedding
MPO (Multi-fiber Push-On) connector
between the mast and the interrogator
Rapid prototyping of a waterproof
housing for the connection.
This one will be attached to the mast

35. Interrogator set-up
FBG 1
FBG x
FBG 1
FBG x
FBG 1
FBG x
Optical circulator
…
e-LED
Photodiode &
Data processing
Tunable filter
Light, small size, low power consuming

36. Interrogator set-up
Light, small size, low power consuming

37. Damien KINET
Damien.KINET@umons.ac.be
+32 (0) 65 37 41 96
© sirris | www.sirris.be | info@sirris.be |
5.12.13

38. SBO Self sensing composites
Production
monitoring
Structural
health
monitoring

39. Case: control arm
2 optical fibers, 10 sensors
Designed and manufactured by
and
12/5/2013
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40. http://www.sirris.be
http://techniline.sirris.be
#sirris
http://www.linkedin.com/company/sirris
© sirris | www.sirris.be | info@sirris.be |
5.12.13