Imagination at work.
Dr. Tobias Bruch, Richard Freemantle
GE Sensing & Inspection Technologies, Wavelength NDT 05.10.2015,BINDT2015, Birmingham
Large area ultrasonic scanning of composites using phased arrays
Outline
• Ultrasound Principles
• Inspection of CFK materials
• Inspection of GFK materials
• Inspection of Honeycomb structures
• Summary
Ultrasound Principles
Conventional Ultrasound
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Signal from a single transducer
• Reflection amplitude as a function of material depth: A-Scan
• Information only from current position of the transducer
A-Scan
Linear Phased Array Ultrasound
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Signal from multiple transducers fired in sequence • Reflection amplitude as a
function of material depth combined from all
transducers: E-Scan
• Amplitude of the reflection signal is color coded
• Information from a slice in the material at the position of the transducer
E-Scan
Encoded Linear Phased Array Ultrasound
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E-Scan
C-Scan
Inspection using conventional technology
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A-Scan of a non damaged area • Backwall echo with good reflection
signal strength
• No significant reflection signals prior to backwall echo.
A-Scan of a damaged area • Defects are identified as reflection
signals prior to the backwall echo
• Defects can only be displayed at a single fixed position using the A-Scan
Inspection using conventional technology
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Determining the dimension of a defective area • Measuring the dimensions is done by
employing the „-6 dB drop“ Method
• Elaborate when a measuring a 2-dimensional defective area.
• Documentation hardly possible in
most Inspection environments
Advantages of inspections using phased-array technology
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Detection of defects using phased-array technology • Direct visualization in C- Scan and
E-Scan
• Inspection of large areas in a short
amount of time
• Direct localization and dimension of defects in the inspection volume
• Position encoded documentation of inspection data over the full inspection are directly in the
instrument
Advantages of inspections using phased-array technology
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• Direct visual representation of the condition of inspected part • Full information via A-Scan, E-Scan, C-Scan in real time available
Phased-Array roller-probe
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Features of the Phased-Array roller -probe • Coupling realized via flexible fluid
filled tire
• Compact and easy to handle design
• Integrated position encoder on the
probe axis
• Theoretical penetration range of up to 130 mm theoretical.
Penetration tested up to 80 mm GFK (depends on GFK quality)
Inspection of CFK materials
Inspection of CFK materials
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• CFK materials are widely used in the aerospace sector
• Volumetric inspection via ultrasound offers reliable inspections and
documentation • Reoccurring inspection of airplane
wings and hulls
• Detection of CFK-Layer delamination usually couple of mm thick
• Inspection also applicable to other CFK
materials used in other segments
(automotive for example)
Inspection of CFK materials
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• Thin materials demand high
resolution frequency ( 5MHz) • High resolution of good quality CFK,
down to approx. 1.5 mm near surface
• Example from an aircraft hull with stiffeners
• Stiffener structure can be imaged in
the C-Scan and B-Scan • Defective are identified by not
detecting the expected signal from
the cross running stiffener
Inspection of GFK materials
Inspection of GFK materials
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• GFK materials are widely used in the wind power sector
• Volumetric inspection via ultrasound offers reliable inspections and
documentation • Inspection of wind blades either after
production or in-service
• Detection of GFK-Layer delamination or dis-bonding of the shear-web
• Inspection applicable to other thick
GFK materials used in other segments
(depending on GFK quality)
Sensitivity
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S/N Measurement on 13 mm FBH in GFK
Signal of a 13 mm FBH in a depth of 30 mm at 80 % Screen height
Material microstructure or ring-down of the probe at 10 % screen-height in a
depth of 30 mm. S/N: 18 dB in in a depth of 30 mm
Sensitivity
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S/N Measurement on 13 mm FBH in GFK • Nearly constant sensitivity of the
phased array probe as a function of
material depth • Comparable to conventional probes at
large material depth
• Drop in sensitivity of the conventional probe caused by large ring-down
• Flexible water-delay of the phased
Array probe allows better coupling to
the surface compared to rexolite delay lines
Resolution
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Measurement performed on a GFK step-block
• Detection of defects starting at 8 mm below the surface • Defects closer to the surface can be compromised by the interface echo
Imaging Delaminations
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Measurement performed on a GFK test piece with artificial delamination • Direct imaging of delamination in C-Scan
• Detection of delamination with diameters down to 12 mm in depths up to 65mm
Inspection of shear web bonding
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Inspection of bonding by backwall echo drop • Shear web glued on a 400 mm x 250
mm large and 60mm thick GFK piece • Glued area on the test pieces shows
air channels. • Detection of glued areas via damping
of the backwall echo • Inspection via C-Scan with gated
acquisition of the backwall echo
• Air channels can be identified in the glued area
Image courtesy of Wavelenght NDT Ltd
Inspection of Honeycomb Structures
Title or Job Number | XX Month 201X 23
Inspection of honeycomb structures
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• Honeycomb structures are widely used in the aerospace and marine sector
• Basically air/alumina columns filled with air
• No clear understanding how the ultrasound propagates in these structures
• Whether an inspection is possible via
ultrasound is highly material dependent and needs to be checked
for each test piece
• For good quality material penetration depths of 100 mm have been achieved
Inspection of honeycomb structures
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Inspection of honeycomb by backwall echo drop • 40 mm thick honey-comb • Inspection by monitoring the
backwall echo. • Detection of defect areas by
vanishing of backwall echo • Inspection via C-Scan with gated
acquisition of the backwall echo
• Position of defective areas can be
identified but not the depth in the honeycomb
Summary
• Phased-Array roller probe allows volumetric inspection for defects in various composite materials
• Combination of low-frequency ultrasound with the advantages of phased array technology for inspecting highly attenuative materials
• Encoded recording of E-and C-Scans allow efficient inspection of large areas, and enables on-site interpretation and documentation of the data
• Compact and light weight design of the probe according to the requirements for a frequent usage in demanding environments
• Field proven technology in the aerospace and wind power sector
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