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Methodology for Assessing theReliability of Nondestructive Inspections on
Wind Turbine Blades
Dennis RoachSandia National Labs
Infrastructure Assurance & NDI DepartmentFAA Airworthiness Assurance Center
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration
under contract DE-AC04-94AL85000.
FAA Airworthiness Assurance [email protected]
Aircraft and Wind Energy Common “Bond” -Use of Composites and Health Monitoring
Composite Structures on Boeing 787 Aircraft
A380 Pressure Bulkhead
Common Goals: Improve Flaw Detection Performance inDetection Performance in Composite Structure in Order to Prevent Failures, Extend Blade Lifetime, Implement Condition-Based MaintenanceBased Maintenance
Composite Flaw Scenarios- Ply waviness - Lightning Strike- Ply waviness - Lightning Strike- Erosion - Impact Damage- Disbonds, Delamination - Voids
Composite Skin Disbondedf H b
Voids
Foreign Object DamageGround Handling Damage
from Honeycomb
Damage
Lightning Damage
Focused Inspections with Hand-Held Devices
WindshieldWindshield
3 ply lap joint3 ply lap joint
Wide Area and C-Scan Inspection Methods
Shearography
UltraImage Scanner
SAM System
PE Phased Array UT
Thermography
MAUS
UT Wheel Array
MAUSSystem
Shearography
Ultrasonic Wheel Array
Shearography (LTI) Image
Thermography (TWI) Image
SAM Image
MAUS Imageg
B737 Composite Horizontal Stabilizer
Objective: Assess rapid (wide area) NDI methods that could have applications to B787 production and/or in-service inspection.
Ultrasonic Scan
Thermography Scan
Determining Performance ofComposite Inspections
Composite Flaw Detection Experiment
Participation from over 25 airlines and maintenance depotsmaintenance depots
Industry-wide performance curves generated to quantify:• how well current inspection• how well current inspection
techniques are able to reliably find flaws in composite honeycomb structure
Experiment to Assess Flaw
Detection
• the degree of improvements possible through integrating more advanced NDI techniques and procedures.
Detection Performance• Statistically relevant and realistic
flaw profiles• Blind application of techniques
to study hits, misses, false calls, and flaw sizing
Experiment DesignSpecimen Types - modeled after range of construction found on
i ft S lid l i t b (12 20 24 32 li ) C t d daircraft; Solid laminate carbon (12, 20, 24, 32 plies); Contoured and tapered surfaces, Substructures – (stringers, ribs, spars); Bonded & sealed joints
Fl T t ti ti ll l t fl di t ib ti ith i iFlaw Types - statistically relevant flaw distribution with sizes ranging from 0.2 in.2 to 3 in.21) interply delaminations; disbonds2) substructure damage3) ki t tiff di b d
Low Energy Impact
00
45+ 45
3) skin-to-stiffener disbonds4) impact damage
0
0
0
-45
-45
0
9090
+ 45
Pyramid Pattern Matrix Crack from impact
P id P tt M t i C k f i t
Application of NDI - blind tests implemented in aircraft maintenance depots; guideline procedures provided; use of ref standards to set up equipmentof ref. standards to set up equipment
Expected Results - evaluate performance attributes1) accuracy & sensitivity (hits, misses, false calls, sizing)2) versatility, portability, complexity, inspection time (human factors)2) versatility, portability, complexity, inspection time (human factors)3) produce guideline documents to improve inspections4) introduce advanced NDI where warranted
Thick Laminate With Complex Taper
RINGER 2.00" X 2.00" X .125" THK
20 PLIES
12 PLIES
.50" STEPPER PLY Type I Specimen
30 PLIES
20 PLIES
.25" STEP PER PLY
4.75"
7.25"
12 PLIES3.50"
4.75"
14.00".25" STEP PER PLY
38.00"8.25"
.50" STEPPER PLY
19 00"
8.00"
2.00"
1.00"
7.25"19.007.25" P-1
E-1
I-1
W-2
BB-3
HH-3
X-2
T-2
PP-2
TT-2
F-2
M-2
R-2B-3
L-2
O 3
FF-3
W-2
Y-2
BB 2
U-3
Z-3
GG-2
L-1
LL-3
19.00"
O-3 BB-2L 1
38.00"
Thick Laminate With Complex Taper - Fabrication
Flaw templates - ensure proper location of flaws
Flawsinserted
Specimen Set - Flaw Detection in Solid Laminate Composites
Thickness Range:12 – 64 plies
Specimen Set - Flaw Detection in Solid Laminate Composites
Thickness Range:12 – 64 plies
Simple Tapers
Complex tapers
Substructure FlawsSubstructure Flaws
Curved Surfaces
Array of flaw types
NDI Ref. Stds.
Experiment Implementation at Airlines, 3rd Party Maintenance and Adv. NDI Organizations
Application of Advanced NDI Methods
Laser Ultrasonics
Phased Array UTPhased Array UT
Probability of Detection - Inspection Performance Over a Range of Test Specimen TypesOver a Range of Test Specimen Types
Flaws in Composite Honeycomb Construction
1
3 Ply Fiberglass
1
3 Ply Fiberglass 3 Ply Carbon
1
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass
1
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon
1
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass
1
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass 9 Ply Carbon
0 6
0.7
0.8
0.9
tect
ion
0 6
0.7
0.8
0.9
tect
ion
0 6
0.7
0.8
0.9
tect
ion
0 6
0.7
0.8
0.9
tect
ion
0 6
0.7
0.8
0.9
tect
ion
0 6
0.7
0.8
0.9
tect
ion
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0.3
0.4
0.5
0.6
roba
bilit
y of
Det
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0
0.1
0.2
0 0 5 1 1 5 2 2 5 3
Pr
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Inspection Improvements Via Advanced NDI Techniques
Comparison of Advanced Inspection Techniques withBest Conventional NDI Result on 9 Ply Carbon
Thermography MAUS IV Shearography CATT S.A.M. Wichitech DTH
0 8
0.9
1False Calls 744000 4.4
0.6
0.7
0.8
Det
ectio
n
0.3
0.4
0.5
Prob
abili
ty o
f
0
0.1
0.2
00 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Variation in Performance of a Device O th S t f I t
PoD Curve Comparisons - LFBT on 6 Ply FiberglassPoD Curve Comparisons - LFBT on 6 Ply Fiberglass with Cumulative Average
Over the Set of Inspectors
PoD Curve Comparisons - MIA on 6 Ply CarbonPoD Curve Comparisons - MIA on 6 Ply CarbonPoD Curve Comparisons - LFBT on 6 Ply Fiberglass
0 7
0.8
0.9
1
PoD Curve Comparisons - LFBT on 6 Ply Fiberglass with Cumulative Average
0 7
0.8
0.9
1
PoD Curve Comparisons - MIA on 6 Ply Carbon
0 7
0.8
0.9
1
MIA 1
PoD Curve Comparisons - MIA on 6 Ply Carbon with Cumulative Average
0 7
0.8
0.9
1
MIA-1MIA-2
0.3
0.4
0.5
0.6
0.7
Prob
abili
ty o
f Det
ectio
n
LFBT-1LFBT-2LFBT-3LFBT-4LFBT-5LFBT-6LFBT 70.3
0.4
0.5
0.6
0.7
Prob
abili
ty o
f Det
ectio
n
LFBT-1
LFBT-2
LFBT-3
LFBT-4
LFBT-5
LFBT-6
LFBT-7 0.3
0.4
0.5
0.6
0.7
Prob
abili
ty o
f Det
ectio
n MIA-1MIA-2MIA-3MIA-4MIA-5MIA-6MIA-7MIA-8MIA 90.3
0.4
0.5
0.6
0.7
Prob
abili
ty o
f Det
ectio
n MIA-3MIA-4MIA-5MIA-6MIA-7MIA-8MIA-9MIA-10
0
0.1
0.2
0 3
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
LFBT-7LFBT-8LFBT-9LFBT-10LFBT-11
0
0.1
0.2
0.3
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
LFBT-8
LFBT-9
LFBT-10
LFBT-11
Cum. Ave.0
0.1
0.2
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
MIA-9MIA-10
0
0.1
0.2
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Cum. Ave.
( )( ) ( )( )
Large Variation in Device Performance Small Variation in Device Performance
Conclusions from CompositeNDI Performance Studies
90% POD is not achieved for 1” dia Flaws
• How are we doing? – Flaw Detection with Conventional NDI
90% POD is not achieved for 1 dia. FlawsPOD can improve as inspection time per area increases (up to a limit)Human factors issues (time, attention to detail, proper deployment)Coverage of large areas was randomg gComplex equipment produced large data spreadTop performing NDI methods were identified (reliability, repeatability, ease of use)
I t i fl d t ti d f 66% t 72%• How can advanced NDI help? – Flaw Detection with More Sophisticated NDI
Improvement in flaw detection ranged from 66% to 72%Automated deployment & data presentation/analysis reduces many human factors concerns (100% coverage; flaw recognition on images)Allow for more rapid inspectionsAllow for more rapid inspections
Math, glorious Math!Math, Glorious Math or…..How do we calculate Damage Tolerance ??How do we calculate Damage Tolerance ??
• Fatigue guy: Fantastic! I’ve calculated K to within 0.5%!
• Stress guy: Great! I’ve calculated stress to within 10%!
Loads guy: WOOHOO! I think I got the sign right!• Loads guy: WOOHOO! I think I got the sign right!
• NDI guy: You want me to find a crack how small??
You as the Inspector –pPerformance Assessment
You will be given three seconds to study a piece of artwork. Then one box will highlight.
You must decide if the box has changed color.
Did the selected square change color?
NOOCHANGE
Did the selected square change color?
YESSCHANGE
Did the selected square change color?
NOOCHANGE
Did the selected square change color?
YESSCHANGE
How did you do?How did you do?
• Did you try to game the system?– FACT: inspectors do better where they expect to find flaws
• Did you have the same level of concentration from the beginning to the end?
– There is significant research on how fatigue and difficulty of tasks affect performance.
Methodology for Assessing the Reliability ofMethodology for Assessing the Reliability ofNondestructive Inspections on Wind Turbine Blades
Dennis RoachSandia National Laboratories
FAA Airworthiness Assurance Center
As aircraft operators respond to calls for the ensured airworthiness of global airline fleets, the implementation of advanced airworthiness assurance technology is of growing importance. The development and application of new Nondestructive Inspection (NDI) techniques, the use of advanced materials, and general improvements in maintenance and repair practices need to keep pace with the growing understanding of aircraft structural aging phenomena. In 1991 the Federal Aviation Administration (FAA) established the Airworthiness Assurance Center (AANC) t S di N ti l L b t i Th AANC k ith i ft f t ilit d t d i li(AANC) at Sandia National Laboratories. The AANC works with aircraft manufacturers, military depots, and airlines to foster new technologies associated with nondestructive inspection (NDI), structural mechanics, repair methods, flight controls, fire safety, and crashworthiness. This presentation describes the structured methodology that the AANC has developed to quantify the performance of NDI techniques. This methodology may be useful to the wind energy industry since many of the inspection challenges, requirements and materials are similar to those encountered in the aviation industry. The aircraft industry continues to increase its use of composite materials,
t t th i th f i i l t t l l t Th t d t l d hi h t th tmost noteworthy in the arena of principle structural elements. The extreme damage tolerance and high strength-to-weight ratio of composites have motivated designers to expand the role of fiberglass and carbon graphite in aircraft structures. This has placed greater emphasis on the development of improved NDI methods that are more reliable and sensitive than conventional NDI. The AANC has been pursuing this goal via a host of studies on inspection of composite structures. Tap testing, which uses a human-detected change in acoustic response to locate flaws, and more sophisticated nondestructive inspection methods such as ultrasonics or thermography, have been applied to
i i b f li ti t d t t id di b d d d l i ti i dh i l b d d itan increasing number of applications to detect voids, disbonds, and delaminations in adhesively bonded composite aircraft parts. Low frequency bond testing and mechanical impedance analysis tests are often used to inspect thicker laminates. Probability of Detection experiments are underway to assess the performance of both conventional and advanced NDI techniques. Industry-wide performance curves are being produced to establish: 1) how well current inspection techniques are able to reliably find flaws in composite honeycomb structure, and 2) the degree of improvements possible through the integration of more advanced NDI techniques and procedures.
