evaluation of ndi methods
TRANSCRIPT
Nationaal Lucht- en Ruimtevaartlaboratorium – National Aerospace Laboratory NLR
Evaluation of In-service NDI Methods for Composite Aerospace Structures
Jaap H. Heida and Derk J. Platenkamp
Aerospace Vehicles Division
6th Int. Workshop NDT in Progress, Prague, 10-12 October 2011
6th International Workshop NDT in Progress, Prague, 10-12 October 2011 2
National Aerospace Laboratory NLR
Staff of 700
Turnover ~ 80 MEuro/yr
Amsterdam Flevoland
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Contents
National Technology Project in NL on NDI/repair for composite aerospace structures
� Composite benchmark
� Base-line ultrasonic C-scan inspection
� Selection of NDI methods
� Evaluation of NDI methods
� Conclusions
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Composite benchmark- structural details -
Damage type/size
• Range of impact damage relative to BVID (initial dent depth of 1.0 mm)
• Interply delaminations in skin, diameter range 0.25 – 1.0 inch
• Skin-to-stiffener disbonds, diameter range 0.25 – 2.0 inch
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Composite benchmark- structural details -
Damage type/size• Range of impact damage relative to BVID (initial dent depth of 1.0 mm)
• Interply delaminations in outer skin, diameter range 0.25 – 1.0 inch
• Outer skin-to-honeycomb core disbonds, diameter range 0.25 – 2.0 inch
• Skin-to-rib/frame disbonds, diameter range 0.25 – 2.0 inch
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Composite benchmark- specimen manufacture -
Panel NTP-D
Material based on carbon fabric- HTA carbon fibres- HexPly M18-1 resin- HRH-10 Nomex honeycomb
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Composite benchmark- application of paint system -
Paint system� Aerodur 37047 CF primer� PUR-Declack topcoat (PU Finish 03-66207 RAL 6031 F9), colour bronze green
� Standard paint system used on military weapon systems such as Cougar, Chinook and Apache helicopters
� Two cross layers with total paint thickness of ~30 micron
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Composite benchmark- infliction of low-velocity impact damage -
Instrumented impact tester
• Guided drop weight device
• Impactor with hemispherical steel tupwith diameter 0.5 or 1.0 inch
• Specimens clamped in frame
• Strain gauge bridge mounted near top of impactor to provide a force-time plot
• Range of impact damage varying from non-visible to clearly visible damage
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Base-line ultrasonic C-scan inspection
Scan window 4.0 x 2.5 x 2.5 mImmersion and squirter inspectionPulse-echo and through-transmission Complex scan profilesTurntable for circular components
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Base-line ultrasonic C-scan inspection
Immersion inspection, pulse-echo backwall skin reflection
NTP-B
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Selection of in-service NDI methods
Selection criteria for NDI methods
� Practical in use:
- portable
- one-sided accessibility
- limited safety precautions
� Proven applicability for the in-service detection of the following defect types in composite structures:
- impact damage
- interply delaminations
- disbonds (skin-honeycomb, skin-stiffener)
� Cost-effective
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Selection of in-service NDI methods
Down-selection of:� Laser-ultrasonics (costs)� Local UT with conventional handheld transducers (no 2-dimensional plan view of defects)
� Portable UT C-scan system (no specific advantage over phased array UT)
� Single element dry-coupling UT roller probes (multiple element roller probes will be included)
� Air coupled UT (through-transmission mode)� Low kV radiography (two-sided access, safety precautions)� Edge of Light and D-Sight optical techniques (no through-the-thickness damage information)
� Some speckle techniques (sensitive to vibration, no through-the-thickness damage information)
� Eddy current (only applicable to conducting materials)
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Selection of inspection methods- visual inspection and NDI -
Tap hammer AcoustoCam UT cameraBondmaster 1000e+
RapidScan roller probe Thermography
Phased array UT Shearography
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Evaluation of NDI methods- visual inspection -
•General visual� Close-proximity, intense visual examination of relatively
localised areas of internal and/or external structure for
indications of impact damage or other structural anomaly
•Results of general visual inspection� Primary technique for in-service inspection of composites
� Low-cost, relatively fast with a large field of view
� Detectable: all impacts with initial dent depth > 0.5 mm
(½ BVID-size)
� Delaminations and disbonds not detectable
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Evaluation of NDI methods- automated tap test -
Mitsui Woodpecker WP-632• Light-weight device (~ 0.5 kg): battery-driven solenoid hammer with force sensor built in the hammer tip
• Measurement of the contact time (increases in areas with defects that lower the local contact stiffness of the part)
• Instrument settings� Four Average modes (1/2/4/8)
� Four frequencies for the tapping speed (2/4/8/16 Hz)
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Evaluation of NDI methods- BondMaster inspection -
BondMaster 1000e+ (Olympus NDT)• Light-weight device (2 kg) for mechanical impedance and sonic testing
• Three inspection modes: MIA, pitch-catch and resonance• NTP: pitch-catch mode
� Dual-element, point-contact UT probe (transmitter-receiver) that measures amplitude and phase changes
� Three inspection methods: RF, impulse and swept frequency
Pitch-catch technique
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Evaluation of NDI methods- handheld UT camera -
AcoustoCam i500 (Imperium, Inc.)• Handheld camera for fast and real-time UT inspection• C-scan image by array transducer (120x120 elements)• Field of view 1 inch2, frequency range 1 – 7.5 MHz• Couplant necessary
i600 i500
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Evaluation of NDI methods- handheld UT camera -
Presentation of C-scan image and A-scan
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Evaluation of NDI methods- handheld UT camera -
Examples of AcoustoCam images on panel NTP-A1
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Evaluation of NDI methods- handheld UT camera -
Examples of AcoustoCam images panel NTP-A1
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Evaluation of NDI methods- phased array UT -
Omniscan (Olympus NDT)with a 128-element PA transducer
Multiple element transducer for electronic scanning, steering and focusing of the UT beam
Real-time imaging of defects during scanning
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Evaluation of NDI methods- phased array UT -
Omniscan (Olympus NDT)- 5 MHz, 128-element PA transducer- wedge + encoder- UT coupling by application of water film
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Evaluation of NDI methods- phased array UT -
NTP-B
BW skin BW stiffener Time-of-flight
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Evaluation of NDI methods- UT dry coupling roller probe -
RapidScan (Sonatest Ltd.)• UT phased array probe housed within in a rubber coupled and water-filled wheel probe (50 or 100 mm active array)
• Almost couplant-free (fine water spray on test part provides adequate coupling)
• Manual scan or 3D scan with 7-axis Faro scanning arm
50 mm probe, 64 PA elements
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Evaluation of NDI methods- UT dry coupling roller probe -
NTP-B
Ampl. wide gate BW skin Time-of-flight
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Evaluation of NDI methods- shearography inspection -
ISISmobile 3100mobile equipment(Steinbichler)
- Thermal loading (3 kW heating lamps)- Vacuum loading- FOV 220x160 mm
Optical method based on speckle interferometry for measurement of out-of-plane deformations
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Evaluation of NDI methods- shearography inspection -
Mobile systemthermal load technique
impact locations
NTP-B
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Evaluation of NDI methods- shearography inspection -
Stationary systemvacuum load technique
NTP-C
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Evaluation of NDI methods- thermography inspection -
External heat source- Lockin (low-freq. modulated heating)- Transient (pulse of long t: > 10 s)- Flash (pulse of short t: << 1 s)
Theolt, NL
FLIR Systems IR camera ThermoCAM SC6000
Measurement of infrared radiation after thermal stimulation of an object with a heat source
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Evaluation of NDI methods- thermography inspection -
NTP-D
Lockin technique Transient technique
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Summary of evaluation of NDI methods
Defect detection/sizing/depth estimation and portability0 not, - with limitation, + yes, ++ very well (primary technique)
Yellow – positive, white – with limitation, grey - negative
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Conclusions
•Visual inspection� Primary method for in-service inspection of composites� Low-cost, relatively fast and capable of detecting relevant impact damages (initial dent depth > 0.5 mm)
•Automated tap tester Woodpecker� Low-cost, couplant-free inspection unit for smaller areas where damage is suspected
� Impact damages generally well detectable� Detectability for delaminations and disbonds is varying and not always consistent
•BondMaster 1000e+� Relatively low-cost, couplant-free instrument for local inspection of structures with the pitch-catch technique
� Limited detection performance for in-service defects
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Conclusions (continued)
•Ultrasonic inspection� Primary method for in-service inspection of composites, regarding its capability for defect characterization
� Limitation can be the requirement to use couplant
AcoustoCam� Handheld ultrasonic imaging camera that produces a C-scan image real-time
� Limited field of view (~1 inch2)
Ultrasonic phased-array inspection� Best capabilities for in-service inspection of composites� Position encoder is required to produce a C-scan image
RapidScan� Phased array, handheld roller probe, almost couplant-free� With a multi-axis scanning arm: fast and real-time UT inspection of relatively large areas
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Conclusions (continued)
•Shearography and thermography� Relatively fast, non-contact methods that require no coupling
or complex scanning equipment
� Impact damages are readily detectable but detectability for
delaminations and disbonds is poor/moderate when
compared to UT
� Detectable defect size decreases with increasing defect depth
� Both techniques not suited for defect depth estimation
Options
� Shearography may be promising for inspection of honeycomb
sandwich structures
� Thermography may be promising for fast inspections and
inspection of water ingress in composite structures
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Recommendations
• Evaluate other inspection configurations
� Curved panels (curvature can limit the application of e.g.
large phased array probes)
� Panels with other defect types (e.g. water ingress in
honeycomb structures)
• Investigate the NDI of repaired composite structure
� Delaminations within a repair patch
� Disbond (or poor bonding) between patch and sub-structure
� Delaminations in the sub-structure underneath the repair
� Impact damage at/near the repair location
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Questions?