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Center for Aircraft Structural Life Extension
Providing Structural Integrity Technology to the Aerospace Community
DISTRIBUTION STATEMENT A: Approved for public release: distribution is unlimited
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Compilation of Damage Findings from Multiple Recent Teardown - - PowerPoint PPT Presentation
Compilation of Damage Findings from Multiple Recent Teardown - - PowerPoint PPT Presentation
Center for Aircraft Structural Life Extension Providing Structural Integrity Technology to the Aerospace Community Compilation of Damage Findings from Multiple Recent Teardown Analysis Programs 25 th International Conference on Aeronautical
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Purpose
To present an overview of failure analysis (FA)
findings from a variety of teardown analysis programs
Conducted 2005-2007 Three aircraft categories Eight total aircraft Aircraft production years between 1957 and 1968
All findings presented are from CAStLE analysis
711 total failure analysis
395 from light trainer/attack aircraft (1957-1968) 282 from medium transport aircraft (1968) 34 from heavy transport aircraft (1963)
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Teardown Program Goals
Assess damage state after a period of known usage Evaluate and/or revise damage prediction models Assist in the validation of inspection methods Other
Input to help determine inspection intervals (an output
- f damage prediction models)
Prepare for future repair action or redesign
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Teardown Program Tasks
Identify Purpose and Requirements Identify Subjects and Extract Disassemble Extracted Components Clean Parts and Remove Coatings Nondestructive Inspection of Parts Perform Failure Analysis Prioritize NDI Indications Analyze and Report Findings Select Vendors
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Subject Aircraft
Light trainer/attack class aircraft
All wing structure in four aircraft Wing to fuselage attach structure in four aircraft All fatigue critical structure throughout two aircraft Flight hours (FH) ranging between 16K and 23K
Medium transport aircraft
Center wing from a single aircraft 22K FH, 46K equivalent hours
Heavy transport aircraft
Fatigue critical structure throughout a single aircraft 18K FH, 12K landings, 3.5K pressure cycles
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Findings
Finding type NDI implications Operational usage damage scale Corrosion damage Damage location Initiation site size distribution
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1 10 100 1000 Bore Corrosion Corrosion IGC Exfoiliation SCC In-plane Cracks Fatigue Overstress Unknown Material Defect Mechanical Damage No Damage Non-operational Damage
Finding Type Number of Findings _
Finding Type
Damage findings resulting from operational usage Damage findings resulting from operational usage Environmental damage Environmental damage
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0% 5% 10% 15% 20% 25% 30% 35% 40% 45%
Environmental Environment & Stress Stress Non-
- perational
No Damage Unknown Primary Damage Source Percentage for Each Category __
Light Trainer/attack Medium Transport Heavy Transport
Finding Type by Aircraft Category
Newest aircraft, least corrosion
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0% 5% 10% 15% 20% 25% 30% 35% 40% 45%
Environmental Environment & Stress Stress Non-
- perational
No Damage Unknown Primary Damage Source Percentage for Each Category __
Light Trainer/attack Medium Transport Heavy Transport
Finding Type by Aircraft Category
Production and maintenance quality indicator and programmatic decisions
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0% 5% 10% 15% 20% 25% 30% 35% 40% 45%
Environmental Environment & Stress Stress Non-
- perational
No Damage Unknown Primary Damage Source Percentage for Each Category __
Light Trainer/attack Medium Transport Heavy Transport
Finding Type by Aircraft Category
Multiple vendors, less
- versight, varied NDI
expertise One highly skilled/experienced inspector, high degree of oversight
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0% 5% 10% 15% 20% 25% 30% 35% 40% 45%
Environmental Environment & Stress Stress Non-
- perational
No Damage Unknown Primary Damage Source Percentage for Each Category __
Light Trainer/attack Medium Transport Heavy Transport
Finding Type by Aircraft Category
We usually find the root cause
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0.01 0.1 1 10 100 20 40 60 80 100 Relative BHEC Indication Strength (%FSH) Fatigue Crack Size (mm) _ Light Trainer/attack Medium Transport Heavy Transport
NDI Implications
fatigue crack size vs. indication strength All damage found at sites below 70% FSH are smaller than 1.27 mm
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Component Type Corrosion SCC In-Plane Cracks Fatigue Overstress Unknown Skin 20 8 50 4 Skin Stiffenner 16 3 Rib Cap 11 14 1 Spar Cap 140 1 36 27 2 1 Fitting 4 2 2 13 1 1
357 total findings Most corrosion and most fatigue cracks are in hidden,
2nd layer, unreliable operational NDI available, if any
SCC cracks in skin; 4 in each of the transport aircraft In-plane cracks; no available inspection
NDI implications
damaged component type
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Operational Usage Damage Scale
crack damage only
205 crack findings attributed to operational usage 42% are smaller than 1.27 mm 4 findings are smaller than 0.127 mm
20 40 60 80 < 0.6 < 1.27 to 0.6 < 3 to 1.27 > 3 Maximum Damage Dimension (mm) Number of Findings _
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Operational Usage Damage Scale
crack damage by source
Majority of damage is due to stress “Unknown” only exists in the very small scale damage
5 10 15 20 25 30 35 < 0.6 < 1.27 to 0.6 < 3 to 1.27 > 3 Maximum Damage Dimension (mm) Number of Findings_
Environment Env & Stress Stress Unknown
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Operational Usage Damage Scale
by aircraft category
Lower two bins represent part through cracks for all
three aircraft categories
Lower three bins are part through cracks for medium
transport
5 10 15 20 25 30 35 40 < 0.6 < 1.27 to 0.6 < 3 to 1.27 > 3 Maximum Damage Dimension (mm) Number of Findings _ Light Trainer/attack Medium Transport Heavy Transport
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Light Trainer/attack category only No corrosion damage evaluated in medium transport
Severe corrosion in one region attributed to retirement decision No additional corrosion found during teardown program
Corrosion damage ignored in heavy transport Most damage broad but not deep Only 10 of 138 require maintenance action
Corrosion Damage
0.1 1 10 100 1000 10000 10 20 30 40 50 60 % Thickness Loss Surface Area (mm2)
require maintenance action
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Damage Location
light trainer/attack aircraft wing
Damage is concentrated on front and aft spar and
along two ribs near main gear attachment fitting
No significant difference right to left Data permits analysis for MSD, MED, WFD Wing Station Fuselage Station
Left Side Right Side
- utboard
- utboard
aft aft
- utboard
- utboard
aft aft
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Damage Location
medium transport aircraft wing
Damage concentrated near two critical wing details;
aft wing to body attach point and outboard wing fitting
No significant difference left to right Data permits analysis for MSD, MED, WFD
Wing Station Fuselage Station _
Left Side Right Side
- utboard
aft
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Fatigue, SCC & Corrosion-Fatigue Initiating Site Size Distribution
What is “initiation feature size”? Even with conservative approach, the largest site is 0.624 mm 90% are less than 0.254 mm 48% are less than 0.127 mm
Minimum Maximum Average Corrosion Pit 80% 0.022 0.624 0.135 Mechanical Damage 20% 0.040 0.326 0.156 31% Percentage of Initiation Sites on Faying Surface Dimensions (mm) Initiation Feature %
Feature identifiable as mechanical damage, pit or pit cluster Last resolvable striation Initiation site size
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Initiation Site Size Distribution
literature compared to the present work
As-Built As-Is To-Be Too Late!
Bulk Material Quality Corrosion and/or Fatigue Corrosion and Fatigue Manufacturing Defects Predicted range of flaws at future depot intervals
Flaw Size Probability of Occurrence
Similar distributions of corrosion (pits) and manufacturing defects (mechanical damage) Distribution of initiation site sizes from the present work
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Maximum Dimnesion (mm) Number of Occurances Corrosion Pits Mechanical Damage
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There is a notion in the literature that EIFS distributions track well with continuing damage distributions and are independent of structural detail
2 4 6 8 10 12 14 16 0.2 0.6 1 1.4 1.8 2.2 2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8 Damage Size (mm) Occurances From Corrosion Pits From Mechanical Damage
Initiation Site Size Distribution
compared to damage finding scale
2 4 6 8 10 12 14 16 0.05 0.15 0.25 0.35 0.45 0.55 0.65 Initiation Site Size (mm) Occurances Corrosion Pits Mechanical Damage
46 mm 27 mm Distribution of damage size does not track with distribution of corresponding initiation site size
EIFS is dependent upon the specific structural detail
What does the data show?
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