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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.
Can Wind Turbine Blade Designs Benefit from the Application of Aircraft Health Monitoring
and Advanced Materials Research?
Can Wind Turbine Blade Designs Benefit from the Application of Aircraft Health Monitoring
and Advanced Materials Research?
Dennis RoachSandia National Labs
Airworthiness Assurance Department(505) 844-6078
• Initiated in 1988 under the Aviation Safety Act
• Provides a mechanism to develop, evaluate, and bring new aircraft technologies to market
• Partnerships with industry, academia, and government
B737B737--200200Test BedTest Bed
Fairchild Metro IIFairchild Metro IITest Bed Test Bed
FAA Airworthiness Assurance CenterFAA Airworthiness Assurance Center
Typical Aircraft Flaw ScenariosTypical Aircraft Flaw Scenarios
Substructure – Longeron CrackComposite Skin Disbonded
from Honeycomb
Corrosion Around Riveted Joint
Prevent Catastrophic Failures, Implement Condition Based Maintenance, Extend Blade Lifetime
Composite Structures on Boeing 787 Aircraft
Aircraft and Wind Energy Common “Bond” -Use of Composites and Health Monitoring
Aircraft and Wind Energy Common “Bond” -Use of Composites and Health Monitoring
Focused Inspections with Hand-Held DevicesFocused Inspections with Hand-Held Devices
Windshield
3 ply lap joint
Windshield
3 ply lap joint
Thermography
MAUSSystem
SAM System
Shearography
Wide Area and C-Scan Inspection MethodsWide Area and C-Scan Inspection Methods
PE Phased Array UT UT Wheel Array
UltraImage Scanner
MAUS Image
Shearography (LTI) Image
Ultrasonic Wheel Array
SAM Image
Thermography (TWI) Image
Pulse-Echo Ultrasonic Method for Health Monitoring of Space Shuttle Thermal Protection System
Pulse-Echo Ultrasonic Method for Health Monitoring of Space Shuttle Thermal Protection System
Wing Leading Edge & Nose Cap RCC Panels
SiC
Carbon
SiC Coating Loss Mechanism via Convective Mass Loss
Photo of Impact -
RCC Front Surface
UT Image of
Flaw
MAUS MIA C-Scan of Airbus Rudder
Developed P-E UT inspection –added for carbon laminate lug
NTSB - AA587 Crash InvestigationNTSB - AA587 Crash Investigation
1 2
Inspection of Wind Turbine BladesInspection of Wind Turbine Blades
Depth of penetration in thick, attenuative laminates is key issue
Voids Resonance Scan 152 kHz
Pulse-echo energy & frequency
optimization needed
• Allows advanced rotorcraft design concepts to be safely integrated into routine use
• Produce regulatory measures to meet new NDI demands stemming from damage tolerance analysis approach
• Results integrated into maintenance depots (training, procedures)
Damage Tolerance & NDI Assessment of Composite Rotor Hubs
100 1000 104 105 106 1070
2
4
6
8
10
12
14
16
Cycles to Mid-Plane Failure
Ang
ular
Def
lect
ion
(deg
rees
)
Cycles to onset of delamination in high cycle fatigue environment
Rotorcraft Inspection &Damage Tolerance Program
Rotorcraft Inspection &Damage Tolerance Program
0
2000
4000
6000
8000
10000
12000
0 5000 10000 15000 20000 25000 30000 35000
Repaired Panel #9Ultimate Failure Test
Gage 19 AxialGage 22 AxialGage 17 AxialGage 24 Axial
Stra
in (M
icro
stra
in)
Load (lbs)
Uniform Axial Strain Outside of Repair
Strain at Center of Patch
Strain at Edge of Patch
Strain in Patch - Solid Geometric ShapesSrain in Parent Material - Open Geometric Shapes
Strain Next to Patch
Strain field & repair efficiency assessment
vs. NDI findings
Laminate Repair Systems – Compare Mechanical Performance with NDI Results
Laminate Repair Systems – Compare Mechanical Performance with NDI Results
Damaged and undamaged; pristine and defective repairsFAA REPAIR PANEL: PATCH LAY-UP
[EDGE VIEW]
Ply #1
Ply #7 (0°)
1234567
Stair Step Repair
Scarf
Adhesive Film
FAA REPAIR PANEL: PATCH LAY-UP[EDGE VIEW]
Ply #1
Ply #7 (0°)
1234567
Stair Step Repair
Scarf
Adhesive Film
Impact, Repair & Damage Tolerance of Airframe Composites
Impact, Repair & Damage Tolerance of Airframe Composites
Goals and Objectives:
• To understand critical impact threats, residual strength and reliable inspection methods for aircraft sandwich designs
• Damage tolerance guidelines for AC revisions and/or ongoing certification programs
• Correlation of field damage detection with residual strength
• Evaluation of repair strength and NDI sensitivity/flaw sizing
0 1 2 3 4TTU PLANAR DAMAGE RADIUS Rdamage [in]
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
NO
RM
ALI
ZED
RE
SID
UA
L S
TRE
NG
TH N
XX/N
XXV
IRG
IN
PANELS IMPACTED WITH 1” IMPACTOR
PANELS IMPACTED WITH 3”IMPACTOR
Relation Between NDI Flaw Detection/Sizing
And Residual Strength
Goals:100% recovery of mechanical integrityContinuous healing over lifetimeSeamless integration in structure
Self-Healing of Composite StructuresSelf-Healing of Composite Structures
30
35
40
45
50
0 1 105 2 105 3 105 4 105 5 105 6 105 7 105
Cra
ck le
ngth
(mm
)
Cycles, N
Localizedretardation
self-healing
control(no healing)
no rest period30
35
40
45
50
0 2 106 4 106 6 106 8 106
Cra
ck le
ngth
(mm
)
Cycles, N
Precrack tip location
control(no healing)
self-healing
with rest period
R = 0.1, ω = 5 Hz
Kmax = 0.38 MPa m1/2
Fatigue LifeFatigue LifeEnhancementEnhancement
Distributed Sensor Networks for Structural Health Monitoring
Distributed Sensor Networks for Structural Health Monitoring
• Remotely monitored sensors allow for condition-based maintenance
• Automatically process data, assess structural condition, & signal need for maintenance actions
Smart Structures: include in-situ distributed sensors for real- time health monitoring; ensure integrity with minimal need for human intervention
Some candidate sensors:Comparative Vacuum MonitoringMicro eddy current & flexible eddy current arrayCapacitive micromachined ultrasonic transducer (cMUT)RFEC Carpet ProbeMWM arraysPiezoelectric filmsAcoustic emission sensorsFiber opticsChemical & sacrificial sensors in concert with FONickel strip magnetostrictive sensorsStrain gages
• Overcome accessibility problems; sealed parts• Real-time information or more frequent, remote interrogation• Initial focus – identified problem areas• Long term possibilities – distributed systems
In-Situ Health Monitoring for Aircraft(and Civil Structures)
In-Situ Health Monitoring for Aircraft(and Civil Structures)
Upper Skin
Lower SkinSaddle
Longeron
Bulkhead
Installed CVM SensorsInstalled CVM Sensors
Sensor Applications for Hidden Flaws and Complex GeometrySensor Applications for Hidden Flaws and Complex Geometry
Flexible Eddy Current Array
Crack Detection & Growth Monitoringwith Piezoelectric Sensors
Crack Detection & Growth Monitoringwith Piezoelectric Sensors
0K Cycles PZT crack length estimates within 5% of measured
17K Cycles47K Cycles67K Cycles87K Cycles5.
00"
6.00
"
SEED
ED F
ATIG
UE C
RACK 3.
00"
Disbond Detection & Growth Monitoringwith Piezoelectric Sensors
Disbond Detection & Growth Monitoringwith Piezoelectric Sensors
-0.3
-0.2
-0.1
0.1
0.2
0.3
Volta
ge (V
)
1000 2000 3000 4000Time (S X 10-7)
Blue = Signal Through Good Bondline RegionRed = Signal Through Disbond Region
0
Piezoelectric Sensor Network
Sensor Data
Actuation Signal
Damage Detection
Damage Identification
Residual Strength Evaluation
Assessment for Continued Use
1 2 3 4
5 6 7 8
9 10 11 12
Sensor/Actuator
Structural Flaw
Disbond Detection & Growth Monitoringwith Piezoelectric Sensors
Disbond Detection & Growth Monitoringwith Piezoelectric Sensors
Pull tab flawAfter mold release flaw growth(50 KHz inspection)
1.00"5.00"
1.00"
1.00"
MO
LD RELEASE (CREATE
WEAK BO
ND AREA)
1.00"6.00"
PULL TAB(CREATE LAM
INATE-TO-
STEEL DISBOND)
3.00"
Embedded Piezoelectric Sensors on Filament Wound Vessels - Detection of Impact DamageEmbedded Piezoelectric Sensors on Filament Wound Vessels - Detection of Impact Damage
Visualization methods can locate and size flaws
Sens
or O
utpu
t
Before Damage
After Damage
Time
DamageDamage
Fiber Optic Bragg Sensor Systems Fiber Optic Bragg Sensor Systems
.625”
.625”
0.5”0.5”3.00”
5.00”
0.5” min.
Mold Release
.003”Thk.
Teflon Insert
0.5”
0.75”
B
AD
C
Health Monitoring with Fiber Optic Sensors Health Monitoring with Fiber Optic Sensors
Axial Strain Distribution Along
Sensor D as a Crack Tip Approaches
-1000
-500
0
500
1000
1500
2000
2500
3000
1460 1480 1500 1520 1540 1560 1580 1600
16382 Cycles34428 Cycles50428 Cycles66428 Cycles76428 Cycles
Stra
in (x
10e
6)
Position (mm)
-1000
-500
0
500
1000
1500
2000
2500
3000
1460 1480 1500 1520 1540 1560 1580 1600
16382 Cycles34428 Cycles50428 Cycles66428 Cycles76428 Cycles
Stra
in (x
10e
6)
Position (mm)
Disbond Detection - Grating A Shear Strain Evolution at 34 kips Load
Strain ReliefCaused by Disbond
(lack of load transfer)
Uniform strain regionof 1000µε confirmed
-2000-1000
0100020003000400050006000
1100 1150 1200 1250Position (mm)
Stra
in (x
10e6
)
17k cycles44k cycles67k cycles
Panel 2
Strain ReliefCaused by Disbond
(lack of load transfer)
Uniform strain regionof 1000µε confirmed
-2000-1000
0100020003000400050006000
1100 1150 1200 1250Position (mm)
Stra
in (x
10e6
)
17k cycles44k cycles67k cycles
17k cycles44k cycles67k cycles
Panel 2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass 3 Ply Carbon
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass
0
0.1
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0.5
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0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon
0
0.1
0.2
0.3
0.4
0.5
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0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2 2.5 3
Flaw Size (Dia. in Inches)
Prob
abili
ty o
f Det
ectio
n
3 Ply Fiberglass 3 Ply Carbon 6 Ply Fiberglass 6 Ply Carbon 9 Ply Fiberglass 9 Ply Carbon
Probability of Detection - Inspection Performance Over a Range of Test Specimen Types
Probability of Detection - Inspection Performance Over a Range of Test Specimen Types
Flaws in Composite Honeycomb Construction
Tailoring Aircraft Technology forWind Turbine Blades
Tailoring Aircraft Technology forWind Turbine Blades
• Aviation & wind energy needs could be addressed through jointefforts in composite manufacture, utilization, repair & inspection
Simultaneous study of damage tolerance and inspection sensitivityFirmly establish inspection needs to minimize maintenance costs (offshore applications)
• Recent advances in health monitoring methods have produced viable systems for on-board aircraft inspections; could be tailored for wind energy systems
Embedded sensors must be durable & reliableMinimize repair costs through early detection of structural damageSHM can decrease maintenance costs (NDI man-hours; disassembly) & allow for condition-based maintenanceSHM may be desirable to address unexpected phenomena
Can Wind Turbine Blade Designs Benefit from the Application ofAircraft Health Monitoring and Advanced Materials Research?
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) 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 specific research programs that may provide useful technology for the wind energy industry. Research areas will be described through references to the general programs described below.
Structural Health Monitoring
Improved Flaw Detection Through Increased NDI Sensitivity and Use of In-Situ Sensors - The number of commercial aircraft operating at or beyond their initial design lives continues to grow. Multi-site fatigue damage, hidden cracks in hard-to-reach locations, disbonded joints, erosion, impact, and corrosion are among the major flaws encountered in today’s extensive fleet of aging aircraft and space vehicles. Furthermore, the extreme damage tolerance and high strength-to-weight ratio of composites have motivated designers to expand the role of advanced materials in aircraft structures. These developments, coupled with new and unexpected phenomena, have placed greater demands on the application of advanced nondestructive inspection and health monitoring techniques. In addition, innovative deployment methods must be employed to overcome a myriad of inspection impediments stemming from accessibility limitations, complex geometries, and the location and depth of hidden damage. The use of in-situ sensors for real-time health monitoring of aircraft structures appears to be a viable option in the near future. Reliable, structural health monitoring systems can automatically process data, assess structural condition, and signal the need for human intervention. Prevention of unexpected flaw growth and structural failure could be improved if on-board health monitoring systems are used to continuously assess structural integrity. Such systems would be able to detect incipient damage before catastrophic failures occurs. Condition-based maintenance practices could be substituted for the current time-based maintenance approach. Other advantages of on-board distributed sensor systems are that they can eliminate costly, and potentially damaging, disassembly, improve sensitivity by producing optimum placement of sensors with minimized human factors concerns, and decrease maintenance costs by eliminating more time-consuming manual inspections.
This presentation compares and contrasts the capabilities of promising health monitoring methods. Wide area inspection techniques have recently been introduced in airline maintenance depots. Recent requests for real-time monitoring of structures have produced a niche for active sensor systems using remote field eddy currents, fiber optics, piezoelectric materials, and ultrasonic devices that lend themselves to direct damage detection. Successful field testing with the airlines is used to illustrate the performance of advanced methods that have recently been validated for the aviation industry while laboratory research results highlight the potential use of technology that has not yet been integrated into maintenance hangars.
Composite Structures
Validation of Advanced Nondestructive Inspection Methods - The aircraft industry continues to increase its use of composite materials, most 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 an 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. A Probability of Detection experiment was completed to assess the performance of both conventional and advanced NDI techniques. Industry-wide performance curves have been 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.
Structural Integrity - The AANC evaluated the use of scarfed patch repairs in solid laminate composites. The study employed both destructive and nondestructive tests on full-scale repaired panels to evaluate the performance of pristine and defective repairs in severe loading conditions. Impact damage was applied to the specimens and subsequently repaired in accordance with manufacturer Structural Repair Manual specifications. Both advanced, wide area inspection techniques and conventional, hand-held inspection methods were applied to a series of test specimens before, during, and after the application of static and fatigue loading conditions. Mechanical tests were conducted to establish the residual strength of the damaged, unrepaired panels as well as the residual strength of the repaired panels. A finite element model was developed to evaluate the stress field within and adjacent to the patch area. The model was capable of evaluating the stresses in each laminate by accounting for the differences in the patch and the parent material properties brought on by the repair installation process. The results of this study are being used to quantify the effectiveness of the scarfed repair process in laminate structures while simultaneously demonstrating the ability of nondestructive inspections to ensure the structural integrity of these repairs over time.
Rotor Hubs: Increasing niche applications, growing international markets, and the emergence of advanced rotorcraft technology are expected to greatly increase the population of helicopters over the next decade. As the helicopter industry adopts the damage tolerance philosophy, the appropriate application of nondestructive inspection (NDI) equipment will play a critical role in managing safety. One such program studied composite rotor hubs. The rotorcraft industry is constantly evaluating new types of lightweight composite materials that not only enhance the safety and reliability of rotor components, but also improve performance and extend operating life as well. Composite rotor hubs have led to the use of bearingless rotor systems that are less complex and require less maintenance than their predecessors. The AANC developed a test facility that allows the structural stability and damage tolerance of composite hubs to be evaluated using realistic flight load spectra of centrifugal force (CF) and bending loads. NDI was integrated into the life-cycle fatigue tests in order to evaluate flaw detection sensitivity simultaneously with residual strength and general rotor hub performance. This program studied the evolving use of damage tolerance analysis (DTA) to direct and improve rotorcraft maintenance along with the related use of nondestructive inspections to manage helicopter safety. Overall, the data from this project provided information to improve the manufacture, inspection, and cost effectiveness of rotorcraft components.
