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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