Ultrasonic Imaging and NonDestructive Evaluation of
Composite Components
Paul Wilcox
on behalf of Ultrasonics and Non-Destructive Testing Group
www.bris.ac.uk/composites
Ultrasonics and NDT Group
Prof. Bruce Drinkwater (Head of Group)
Prof. Paul Wilcox, Prof. Robert Smith (EPSRC Fellow)
Dr. Anthony Croxford, Dr. Alexander Velichko
5 PDRAs, 6 PhDs, 7 EngDs
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Challenges of NDT for composites
Ray curvature and
refraction
Velocity anisotropy
Material back-scatter
• Challenges of composite material
– Multiple length scales of heterogeneity
1. Fibre-level (~0.01 mm fibre diameter)
2. Ply-level (~0.1 mm ply thickness)
Typical ultrasonic wavelength ~1 mm
Micrograph by S Clifford, Department of
Materials Science and Metallurgy,
University of Cambridge
3. Component-level (~10 mm)
100mm
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Array imaging of composites
Image
1-1
1-2
2-1
Physical
measurement
n
f11(t)
f12(t)
...
f1n(t)
2
f21(t)
f22(t)
...
f2n(t)
n
fn1(t)
fn2(t)
...
fnn(t)
...
1
...
• Research
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...
Transmit element
Receive element
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Integrity assessment
Part sentencing
Rawdata
data
Raw
– Small/subtle defects
– Thick-section components
– Characterising ply waviness and elastic properties
Interpretation
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Array imaging of composites
Ultrasonic velocity (m/s)
• Effect of angle-dependent
velocity on imaging
Angle dependent velocity
Angle to ply-normal (°)
Constant velocity
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Array imaging of composites
• 3D imaging with 2D array
– Image of 3 mm diameter “delamination” (teflon insert)
(Note: array is at bottom of picture)
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-20 dB isosurface
Section (60 dB scale)
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Array imaging of composites
• Immersion inspection of curved components
Array
Water
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Array imaging of composites
• Immersion inspection of curved
components
– Planar plies = straight ray paths
– Curved plies = curved ray paths
Local velocity
profile
Array imaging of composites
1.
Image in water to obtain
component surface profile
(−)
2.
Compute refracted raypaths and image
component interior
Array
Water
16 mm
• Two-stage postprocessing imaging
operation
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40 mm
Array imaging of composites
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• Example results
Away
from
holes
Array
Over
holes
24 dB colour scale (normalised to back wall)
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Other activities
• Prof. Robert Smith – EPSRC Manufacturing Fellow
• Aim: to demonstrate that NDT can provide a route to
‘leaner’ composite structures
– WP1: 3D characterisation for manufacturing
Porosity
Ply waviness
– WP2: Rapid large-area impact detection
– WP3: In-process NDT
FE model of asmanufactured component
Other activities
• Embedded ultrasonic sensors
– Inductively-coupled sensor embedded between plies
– Measurements made using external “wand”
• No couplant
• Sensor always in
exactly same position
• RFID or QR identifiers
• De-skilled inspection
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Conclusions
• Advances in instrumentation and processing power →
array imaging for NDT is growing
• Challenges for composite imaging → anisotropy and
multiple levels of heterogeneity
• Greater integration of NDT into design and manufacture
• Embedded sensors for rapid, de-skilled NDT
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Spare slides
Homogenisation to obtain 𝑐𝑐(𝜃𝜃)
1. Fibres in epoxy matrix → homogenous anisotropic ply
– Hashin’s quasi-static method used (fibre diameter ≪ wavelength)
2. Laminate of plies → homogenous anisotropic solid
– Backus method to obtain equivalent stiffness matrix then solve
Christoffel equation to obtain group velocity vs. angle
Hashin. J. Appl. Mech. 46, 546, 1979
Backus, J. Geophys. Res., 67, 4427, 1962
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Planar components
2. Effect of frequency
𝑐𝑐 𝜃𝜃
𝑐𝑐𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓
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Planar components
3. Effect of aperture angle limit
𝑐𝑐𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓
𝑐𝑐 𝜃𝜃
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Planar components
• Tailoring of classical imaging for composites
– Example results (all from same raw array data)
Standard swept aperture B-scan
Optimised TFM
Li, Pain, Wilcox, Drinkwater,
NDT&E Int.. 53, 8, 2013
Uncorrected TFM
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Material characterisation
• Imaging fibre waviness
In-plane
Out-of-plane
Image courtesy
of Qinetiq
• Goal: 3D mapping of as-manufactured elastic properties
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