Damage Tolerance Testing and Analysis Protocols for Full-Scale ...
Transcript of Damage Tolerance Testing and Analysis Protocols for Full-Scale ...
The Joint Advanced Materials and Structures Center of Excellence
Damage Tolerance Testing and Analysis Protocols for Damage Tolerance Testing and Analysis Protocols for FullFull--Scale Composite Airframe Structures Under Scale Composite Airframe Structures Under
Repeated LoadingRepeated LoadingJohn Tomblin, John Tomblin, PhDPhD
Executive Director, NIAR andExecutive Director, NIAR andSam Bloomfield Distinguished Professor of Aerospace EngineeringSam Bloomfield Distinguished Professor of Aerospace Engineering
Waruna SeneviratneWaruna SeneviratneSr. Research Engineer, NIARSr. Research Engineer, NIAR
2The Joint Advanced Materials and Structures Center of Excellence
Motivation & Key Issues
• Produce a guideline FAA document, which demonstrates a “best practice” procedure for full-scale testing protocols for composite airframe structures with examples
• Although the materials, processes, layup, loading modes, failure modes, etc. are significantly different, most of current certification programs use the load-life factors generated for NAVY F/A-18 program.
– Guidance to ensure safe reliable approach– Correlate certified “life” to improved LEF (load-life shift)
• With increased use of composite materials in primary structures, there is growing need to investigate extremely improbable high energy impact threats that reduce the residual strength of a composite structure to limit load.
– Synthesize damage philosophy into the scatter analysis– Multiple LEF for different stage of test substantiation
3The Joint Advanced Materials and Structures Center of Excellence
Primary Objective• Develop a probabilistic approach to synthesize life factor, load factor
and damage in composite structure to determine fatigue life of a damage tolerant aircraft
– Demonstrate acceptable means of compliance for fatigue, damage tolerance and static strength substantiation of composite airframe structures
– Evaluate existing analysis methods and building-block database needs as applied to practical problems crucial to composite airframe structural substantiation
– Investigate realistic service damage scenarios and the inspection & repair procedures suitable for field practice
Secondary Objectives• Extend the current certification approach to explore extremely improbable
high energy impact threats, i.e. damages that reduce residual strength of aircraft to limit load capability
– Investigate realistic service damage scenarios – Inspection & repair procedures suitable for field practice
• Incorporating certain design changes into full-scale substantiation without the burden of additional time-consuming and costly tests
Objectives
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Approach
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FAA Sponsored Project Information
• Principal Investigators– Dr. John Tomblin and Waruna Seneviratne
• FAA Technical Monitor– Curt Davis
• Other FAA Personnel Involved– Dr. Larry Ilcewicz– Peter Shyprykevich (consultant ret. FAA)
• Industry Participation
.
Workshops for Composite Damage Tolerance & Maintenance2008 CMH-17: PMC Forum & DTTG Meeting
2007 FAA/CACRC/EASA - Amsterdam, Netherlands
2006 FAA Workshop - Chicago, IL
6The Joint Advanced Materials and Structures Center of Excellence
We all think about these
applications …but …
Transport Aircraft Applications
7The Joint Advanced Materials and Structures Center of Excellence
Adam Aircraft
CirrusLancair
Citation X
Premier I
Bell Helicopter
Horizon
Liberty
Javelin
Honda
Toyota AircraftSpaceshipOne
Epic
Global Hawk
Predator
Spectrum
Other Applications of Advanced Materials
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Scatter Analysis
• Background – most test programs reference the Navy/FAA reports by Whitehead, et. al., (1986) and follow that approach– Most test programs have
used the conclusions developed in this report regardless of design features, failure modes and/or materials
• EADS-CASA study used the same approach (2001) but redefined the shape factors
Integrates well into building-block approach based upon design-specific information gained from various coupon and element
9The Joint Advanced Materials and Structures Center of Excellence
Flaw Growth
• Complex failure modes• Require extensive NDI• Variable B-basis (scatter) at
different stress levels
• Compliance change is a function of material, layup, test environment, loading mode, stress level, etc.
10The Joint Advanced Materials and Structures Center of Excellence
Load-Life Combined Approach
Increase applied loads in fatigue tests so that the
same level of reliabilitycan be achieved with a
shorter test duration
Structure is tested for additional fatigue life to achieve the desired level of reliability
N
LEF
11The Joint Advanced Materials and Structures Center of Excellence
Material Databases
– FAA-LEF» AS4/E7K8 PW» T700/#2510 PW» 7781/#2510 8HS
– FAA-Laminate» T700/#2510 UNI» T700/#2510 PW» T700/E765 UNI» T300/E765 PW» AS4C/MTM45 UNI» AS4C/MTM45 8HS
– FAA-Adhesive Fatigue» Loctite Paste» PTM&W paste (two bondline thicknesses) » EA 9696 film
– FAA-Adhesive Effects of Defects» T700/#2510 PW & EA9394
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0
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0 70.0014.00 28.00 42.00 56.00
ReliaSoft's Weibull++ 6.0 - www.Weibull.com
Reliability vs Time
Time, (t)
Rel
iabi
lity,
R(t)
=1-F
(t)
2/6/2007 22:52NIARWaruna Seneviratne
WeibullStatic
W2 RRX - SRM MEDF=48 / S=0
β=2.9412, η=39.8364, ρ=0.9955
40/20/40 Single Shear Bearing-Tension -- (RTD) 45.4085Double Shear Bearing-Tension -- (RTD) 49.696Bearing-Bypass 50%-Tension 43.4258Bearing-Bypass 50%-Compression 42.102Bearing-Bypass 50%-Tension [t/D=0.475] 40.0401Bearing-Bypass 50%-Tension [t/D=0.570] 42.5935Bearing-Bypass 50%-Tension [t/D=0.949] 38.1976Open Hole-Tension [w/D=6] 27.2021Filled Hole-Tension 20.2959No Hole-Tension 29.8203No Hole-Compression 20.5843Open Hole-Compression 30.4534Critical Hole-Tension -- (CTD) 29.9075Critical Hole-Tension -- (ETD) 25.1923V-Notched Rail Shear 59.2079Open Hole-Tension [w/D=3] 20.594Open Hole-Tension [w/D=4] 27.0538Open Hole-Tension [w/D=8] 25.4413
25/50/25 Double Shear Bearing-Tension -- (CTD) 25.7206Double Shear Bearing-Tension -- (RTD) 43.8267Double Shear Bearing-Tension -- (ETW) 34.7752Single Shear Bearing-Tension -- (CTD) 28.956Single Shear Bearing-Tension -- (RTD) 18.1315Single Shear Bearing-Tension -- (ETW) 33.8501Bearing-Bypass 50%-Tension 44.2636Bearing-Bypass 50%-Compression 48.0284Open Hole-Tension [w/D=6] -- (CTD) 35.8156Open Hole-Tension [w/D=6] -- (RTD) 34.0488Open Hole-Tension [w/D=6] -- (ETW) 25.2227No Hole-Tension -- (CTD) 51.1531No Hole-Tension -- (RTD) 40.1864No Hole-Tension -- (ETW) 38.383No Hole-Compression -- (CTD) 31.498No Hole-Compression -- (RTD) 27.0743No Hole-Compression -- (ETW) 23.6762Open Hole-Compression -- (CTD) 34.4747Open Hole-Compression -- (RTD) 46.9989Open Hole-Compression -- (ETW) 33.3186V-Notched Rail Shear 16.4582
10/80/10 Bearing-Bypass 50%-Tension 65.4454Bearing-Bypass 50%-Compression 74.3601Open Hole-Tension [w/D=6] 51.7133No Hole-Tension 58.0843No Hole-Compression 36.0558Open Hole-Compression 50.909V-Notched Rail Shear -- (CTD) 9.9634V-Notched Rail Shear -- (RTD) 17.2784V-Notched Rail Shear -- (ETW) 13.1027
0 40.00 80.00
α 2.941β 39.836
MODAL (EXTREAM) αR 34.587
Laminate Statistical Allowable Generation for Fiber-Reinforced Composite Materials: Lamina Variability Method
[DOT/FAA/AR-06/53]
T700SC-12K-50C/#2510 -Plain Weave Fabric863 specimens
Shared Databases
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• Individual Weibull• Joint Weibull• Sedeckyj Equivalent Strength Model
Fatigue Scatter Analysis Techniques
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CA
I- B
VID
[20-
ply]
(R =
5)
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I - V
ID [4
0-pl
y] (R
= 5
)
DN
C (R
= -1
)
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C (R
= -0
.2)
OH
(R =
-1)
TAI -
BVI
D (R
= 0
)
TAI -
VID
(R =
0)
OH
T (R
= 0
)
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010
(R =
0.1
)
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060
(R =
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)
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(R =
-1)
CA
I - B
VID
(R =
5)
CA
I - V
ID (R
= 5
)
CA
I - V
ID (R
= 5
)
10/80/10 0/100/0 Sandwich BondedJoints
25/50/25 40/20/40
Life
Par
amet
er,
αF
Sendeckyj (w / static)
Sendeckyj (w /o static)
Individual Weibull (w /o static)
NADC Fatigue Scatter Analysis
αI > αJ > αS
Data Pooling Techniques
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(R=5
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(R=0
)
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(R=-
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CAI-
BVID
(R=5
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VID
(R=5
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DNC
(R=-
1)
DNC
(R=-
0.2)
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(R=-
1)
TAI -
BV
ID(R
=0)
TAI -
VID
(R=0
)
Flex
(R=0
)
OH
(R=-
1)
CAI -
BV
ID(R
=5)
CAI -
VID
(R=5
)
CAI -
VID
(R=5
)
10/80/10 0/100/0 HRH 10Sandwich
25/50/25 40/20/40
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ngth
(psi
)
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ff. V
aria
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(%)
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Sendeckyj
Kassapoglou
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si)
Experiment
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Equivalent Static Sterngth
Sendeckyj
Kassapoglou
Adhesive Scatter Analysis
Shape Parameters for Fatigue Data [2, 5, and 10 -Hz combined]w/ Static Data
CTD RTD RTW # of Specs.Loctite 0.805 0.662 0.682 95EA9696 0.847 0.403 0.379 103PTM&W (0.06") 0.870 1.051 0.681 101PTM&W (0.16") 0.363 0.856 0.671 91
Total 390α 3.8538β 0.7641
Modal Value 0.707
w/o Static Data (Sendeckyj)CTD RTD RTW # of Specs.
Loctite 0.821 1.624 0.644 86EA9696 4.119 1.389 2.189 88PTM&W (0.06") 1.376 1.483 1.169 92PTM&W (0.16") 0.669 4.296 1.618 82
Total 348α 1.6789β 2.016
Modal Value 1.176
w/o Static Data (Individual Weibull)CTD RTD RTW
Loctite 1.069 1.226 1.109EA9696 2.372 2.077 1.110PTM&W (0.06") 1.541 1.179 1.417PTM&W (0.16") 1.165 2.170 1.061
α 3.3394β 1.6255
Modal Value 1.461
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Life Scatter Summary
0.0
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/ sta
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adhe
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w/ s
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/o a
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ve
w/o
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w/o
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adhe
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w/ s
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&ad
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/o a
dhei
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w/o
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w/o
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adhe
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FAA-LEF & FAA-Adhesive FAA-LEF & FAA-Adhesive FAA-LEF & FAA-Adhesive
Fatig
ue S
catte
r Fa
ctor
AS4/E7K8 PW T700/#2510 PW 7781/#2510 8HS
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Methodology Automation
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Equivalent Static Strength Data
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1.00
1.10
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1.30
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Test Duration, N
LEF
NAVYCASAAS4/E7K8 - CAS4/E7K8 - C+AT700/#2510 - CT700/#2510 - C+A7781/#2510 - C7781/#2510 - C+A
Scatter Analysis Guidelines
0 R 0 L NF 0.5 1.0 1.5 3.0AS4 ~ Individual (C) 32.193 4.057 2.070 1.196 1.096 1.041 0.954
AS4 ~ Individual (C+A) 32.193 2.083 4.418 1.151 1.101 1.072 1.025AS4 ~ Sendeckyj (C) 32.193 1.438 9.312 1.140 1.105 1.085 1.052
AS4 ~ Sendeckyj (C+A) 32.193 0.772 88.705 1.132 1.114 1.103 1.085AS4 ~ Sendeckyj (C) +Individual (A) 32.193 1.421 9.589 1.139 1.105 1.085 1.053
T700 ~ Sendeckyj (C) +Individual (A) 32.845 1.576 7.516 1.139 1.102 1.080 1.0457781 ~ Sendeckyj (C) +Individual (A) 36.416 1.660 6.715 1.126 1.091 1.071 1.037
NAVY 20.000 1.250 13.558 1.229 1.177 1.148 1.099CASA 19.630 2.740 3.019 1.285 1.167 1.103 1.001
N
Reduced test matrixFactors affecting LEF
Shared database
Choice of analysis techniques
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1.00
1.10
1.20
1.30
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Test Duration, N
LEF
NAVYCASAScenario 1Scenario 2Scenario 3Scenario 4
Further improvements to MSSP
NF
Case Studies
• Improved LEF• Improved NF• Improved “life”
– Load-life shift
• Shared database• Multiple scatter analysis
techniques
1.00
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1.30
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Test Duration, N
LEF
NAVYCASAScenario 1Scenario 2Scenario 3Scenario 4
Improvements to MFSP
NF
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Beechcraft Starship Forward Wings (BSFW)Approx. average of 1000 flight hours (assume
minimal aging effect), NDE examination
Full-Scale Specimens
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1AMTAS Spring 2006 Meeting
April 11, 2006Federal AviationAdministration 1
Categories of Damage & Defect Considerations for Primary Composite Aircraft Structures
Requires new substantiation Requires operations awareness for safety (immediate reporting)
Damage occurring due to rare service events or to an extent beyond that considered in design
Category 5: Severe damage created by anomalous ground or flight events (repair scenario)
Defined discrete-source eventsRetain “Get Home” capabilityDesign, operations, maintenance
Damage in flight from events that are obvious to pilot (rotor burst, bird-strike, lightning)
Category 4: Discrete source damage known by pilot to limit flight maneuvers (repair scenario)
Demonstrate quick detectionRetain Limit Load capabilityDesign, maintenance, operations
Damage obvious to operations in a “walk-around” inspection or due to loss of form/fit/function
Category 3: Obvious damage detected within a few flights by operations focal (repair scenario)
Demonstrate reliable inspectionRetain Limit Load capabilityDesign, maintenance, mfg.
VID (ranging small to large), mfg. defects/mistakes, major environmental degradation
Category 2: Damage detected by field inspection methods @ specified intervals (repair scenario)
Demonstrate reliable service lifeRetain Ultimate Load capabilityDesign-driven safety
BVID, minor environmental degradation, scratches, gouges, allowable mfg. defects
Category 1: Damage that may go undetected by field inspection methods (or allowable defects)
Safety Considerations(Substantiation, Management)
ExamplesCategory
REFERRENCE: Ilcewicz, L., “Composite Damage Tolerance and Maintenance Safety Issues,”
FAA Damage Tolerance and Maintenance Workshop, Rosemont, IL, July, 2006.
Damage Scenarios
CAT2
Allowable Damage Limit
(ADL)Increasing Damage Severity
Ultimate
~ Maximum load per lifetime
Design Load Level
Continued safe flight
Critical Damage Threshold
(CDT)
1.5 Factor of Safety
Allowable Damage Limit
(ADL)Increasing Damage Severity
~ Maximum load per lifetime
Design Load Level
Continued safe flight
Limit
Critical Damage Threshold
(CDT)
1.5 Factor of Safety CAT3
CAT1
Ultimate CAT2
Allowable Damage Limit
(ADL)Increasing Damage Severity
Ultimate
~ Maximum load per lifetime
Design Load Level
Continued safe flight
Critical Damage Threshold
(CDT)
1.5 Factor of Safety
Allowable Damage Limit
(ADL)Increasing Damage Severity
~ Maximum load per lifetime
Design Load Level
Continued safe flight
Limit
Critical Damage Threshold
(CDT)
1.5 Factor of Safety CAT3
CAT1
Ultimate
21The Joint Advanced Materials and Structures Center of Excellence
Load-Life-Damage (LLD)Hybrid Approach
• Incorporate the effects of damage to scatter analysis• Minimum risk of premature failure of full-scale article• Application to hybrid structure• post certification
– Additional load cases that were not included in the original certification, but found to be significant or worth investigating can be studied
• Provide an opportunity to further investigate large VID without additional test articles
DAMAGE
LIFE FACTOR
LOAD FACTOR
CAT1
CAT2
CAT3
22The Joint Advanced Materials and Structures Center of Excellence
Damage Tolerance Investigation
NF with no LEF (Typically LEF is applied to reduce
test duration)
Loa
d
LL
Damage Category
2 1 3
UL
1 with LEF
No-growth Threshold and load requirements up to
large VID
Help define inspection intervals Help define CDT
Help define ADL Durability Damage Tolerance
CAT1Defect
IntroduceVID
Limit Load in critical condition
LimitLoad in critical
condition
DLT & LEF DLT & LEF
Limit Load in critical condition
23The Joint Advanced Materials and Structures Center of Excellence
1.00
1.10
1.20
1.0 10.0
Test Duration, N
LEF
Tested LEFNEW LEF
NTNR NF
LEFT
LEFR%∆Load
NRT
Design Change Substantiation
24The Joint Advanced Materials and Structures Center of Excellence
Impactor Setup
• 1-inch Wedge (pry bar) • 3-inch Wedge (wood-splitter)
25The Joint Advanced Materials and Structures Center of Excellence
Damage Infliction- BSFW Front Spar -
• Primary load path• Scaling CAT3 damages
into full-scale article• Thick part - unitape• Wound - no layers
Energy
Energy
BVID
Large VID
Limit Load
Ultimate Load
Window for damage infliction for CAT3
Thin Parts
Thick Parts
Starship Forward Wing
Front Spar
Extremely Improbably
Energy
Realistic Energy
After 1000 ft-lb damage at FWS 66.5 (top skin – front spar)
26The Joint Advanced Materials and Structures Center of Excellence
ST001, ST002, ST003Static Tests (CAT1)
BDLL NRLL
ST001(R)Static Test (CAT2)
CAT2 &
CAT3
Full-scale Impact Tests
ST005Static Test (CAT3)
ST004Fatigue Test (CAT2)
ST006Fatigue Test (CAT3)
ST004(R)Fatigue Test (CAT3 1)
Damage Tolerance
NDI
NLFEM
Element
Static
DurabilityRepair
LLD Hybrid Approach
Load-Life Shift
Full-Scale Validation
27The Joint Advanced Materials and Structures Center of Excellence
Full-Scale Substantiation- LLD Hybrid Approach -
• Demonstrate LLD hybrid approach
• Application of load-life shift
• Determine fail safety• Fatigue capability of CAT3
Damage Tolerance
CAT3 Defect
DLT (until failure) LEF = 1
Min/Max spectrum
load
Fail
Safety
Damage Tolerance Repair Durability
CAT2 Defect
Repair
VID
Limit Load in critical condition
Ultimate Load in critical
condition
DLT & LEF (TBD)
DLT & LEF (TBD)
Limit Load in critical condition
28The Joint Advanced Materials and Structures Center of Excellence
1.00
1.10
1.20
1.30
0.0 2.0 4.0 6.0 8.0 10.0
Test Duration, N
LEF
NAVYCASAScenario 1Scenario 2Scenario 3Scenario 4
Improvements to MFSP
NF
Benefits to Aviation
• FAA guideline document, which demonstrates a “best practice” procedure for full-scale testing protocols for composite airframe structures with examples– Cost effective and reliable certification approach(s)– Integrate design specific details gained from coupon and
subelement tests into the LEF approach• Layup, loading modes/R ratios, Environments, ..• Bonded joints, interlaminar shear, sandwich, ..
– Address evolution/maturity of material systems, manufacturing processes, test techniques, etc.
• Reduced test matrix• Shared database concept
– Realistic analysis approach for scatter• Appropriate analysis techniques for diverse design details• User-friendly automated procedures and analysis guidelines• Notch effects on scatter for damage tolerance testing
29The Joint Advanced Materials and Structures Center of Excellence
Benefits to Aviation
DAMAGELIFE FACTOR
LOAD FACTOR
Category 1 Damage
Category 2 Damage
Category 3 Damage
• Incorporation of damage into scatter analysis: Load-Life-Damage– Investigate large VID damage– Further studies
• Load-Life Shift– Investigate different categories of damages/repairs in the
same full-scale test article damage– Design changes, i.e. gross weight increase– LEF during certification vs. improved LEF
• Reliability of designed life
30The Joint Advanced Materials and Structures Center of Excellence
-600
-400
-200
0
200
Axi
al
Stra
in (
mic
rost
rain
) 0.00 Life
0.25 Life
0.50 Life
0.75 Life
1.00 Life
1.25 Life
1 50 Life50% +NRLL
50% -NRLL• Training
• Reliable NDI and health monitoring techniques for damage characterization during full-scale testing and service ~ & Training
• Further studies on extremely improbable high energy impact threats and their impact on the residual strength of the composite structure and inspection intervals
Future Needs
31The Joint Advanced Materials and Structures Center of Excellence
Questions