Durability and Damage Tolerance Certification for Additive ...
Transcript of Durability and Damage Tolerance Certification for Additive ...
Durability and Damage
Tolerance Certification for
Additive Manufacturing (AM)
of Aircraft Structural Parts
19 March 2019
Chuck Babish
U.S. Air Force
2019 Aircraft Structural Integrity Symposium
Melbourne, Australia; 18 – 20 March 2019
2
Outline
• Overview
• Aircraft Structural Integrity Program (ASIP)
Material & Process (M&P) requirements
• Challenge for Additive Manufacturing (AM) –
accurate prediction of Durability and Damage
Tolerance (DADT)– DADT Analysis (DADTA) foundation
– Surrogate damage
– DADT control
– Parts selection
• Probabilistic risk analysis for AM parts
• Summary
3
Overview
• Aircraft Structural Integrity Program (ASIP) MIL-STD-1530
establishes the framework for DADT CertificationTask I Task II Task III Task IV Task V
Design InformationDesign Analyses &
Development TestingFull-Scale Testing
Certification & Force
Management DevelopmentForce Management Execution
1. ASIP Master Plan 1. Materials and Structural
Allowables1. Static Tests 1. Structural Certification 1.L/ESS Execution
2. Design Service Life & Design
Usage 2. Loads Analysis
2. First Flight Verification Ground
Tests
2. Strength Summary & Operating
Restrictions (SSOR)2. IAT Execution
3. Structural Design Criteria 3. Design Loads/Environment
Spectra 3. Flight Tests
3. Force Structural Maintenance
Plan (FSMP)3. DADTA Updates
4. Durability & Damage Tolerance
Control4. Stress and Strength Analysis 4. Durability Tests
4. Loads/ Environment Spectra
Survey (L/ESS) System
Development
4. L/ESS and IAT System Updates
5. Corrosion Prevention & Control 5. Durability Analysis 5. Damage Tolerance Tests 5. Individual Aircraft Tracking (IAT)
System Development 5. NDI Updates
6. Nondestructive Inspection 6. Damage Tolerance Analysis 6. Climatic Tests 6. Force Management Database
Development
6. Structural Risk Analysis
Updates
7. Selection of Materials,
Processes, Joining Methods &
Structural Concepts
7. Corrosion Assessment 7. Interpretation & Evaluation of
Test Findings7. Technical Orders
7. CPC Plan & Corrosion
Assessment Updates
8. Sonic Fatigue Analysis 8. Resolution of Test Findings 8. Analytical Condition Inspection
9. Vibration Analysis 9. FSMP Updates
10. Aeroelastic and
Aeroservoelastic Analysis10. Technical Orders Updates
11. Mass Properties Analysis 11. Repairs
12. Survivability Analysis 12. Structural Maintenance
Database Execution
13. Design Development Tests 13. Structural Certification
Updates
14. Structural Risk Analysis14. Economic Service Life
Analysis Updates
15. Economic Service Life
Analysis15. Others as Required
4
Overview
• ASIP MIL-STD-1530 includes
key requirements for
selection of M&P
– Contained in Task I Design
Information section
– Applicable throughout life
cycle whenever new M&P are
considered
• Intent of Task V Force
Management Execution
(sustainment phase) is to revisit
any prior Task as required
– Applicable to AM pursuits!
Task I
Design Information
1. ASIP Master Plan
2. Design Service Life & Design
Usage
3. Structural Design Criteria
4. Durability & Damage Tolerance
Control
5. Corrosion Prevention & Control
6. Nondestructive Inspection
7. Selection of Materials,
Processes, Joining Methods &
Structural Concepts
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Outline
• Overview
• Aircraft Structural Integrity Program (ASIP)
Material & Process (M&P) requirements
• Challenge for Additive Manufacturing (AM) –
accurate prediction of Durability and Damage
Tolerance (DADT)– DADT Analysis (DADTA) foundation
– Surrogate damage
– DADT control
– Parts selection
• Probabilistic risk analysis for AM parts
• Summary
6
ASIP Selection of M&P
(MIL-STD-1530D Paragraph 5.1.7)
• …“materials, processes, joining methods, and structural
concepts shall be selected to result in a structurally
efficient, cost-effective aircraft structure that meets the
strength, rigidity, durability, damage tolerance, and other
requirements...”
• “Prior to a commitment to new materials…an evaluation
of their stability, producibility, characterization of
mechanical and physical properties, predictability of
structural performance, and supportability shall be
performed...” (aka “Lincoln’s 5 Factors”)
• “The risk associated with the selection of the new
materials, processes…shall be estimated and risk
mitigation actions defined”
“Satisfy Lincoln’s 5 Factors”
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ASIP M&P Requirements
Lincoln’s 5 Factors (1 of 3)
1. Stability - “Maturity of material, process, and joining
method selections shall be evaluated to determine if
consistent and repeatable quality and if predictable
costs can be achieved to meet system performance and
production requirements. Process parameters and
methods shall be established and controlled via
specifications, standards, and manufacturing
instructions”
2. Producibility - “Material, process, and joining method
selections shall be evaluated to determine if scale-up to
production sizes and rates can be achieved without
adversely affecting performance, costs, and quality. The
material, process, and joining method selections shall
consider inspectability during the manufacturing
process”
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ASIP M&P Requirements
Lincoln’s 5 Factors (2 of 3)
3. Characterization of mechanical and physical properties -
“Material, process, and joining method selections shall
be characterized to determine mechanical and physical
properties for the appropriate environments in the as-
fabricated condition using the manufacturing processes
and joining methods. Key mechanical properties include
but are not limited to: strength, elongation, fracture
toughness, damage growth rates, fatigue, stress
corrosion and damage growth rate thresholds. Key
physical properties include but are not limited to:
density, corrosion resistance, damage population,
surface reflectivity, thermal stability, coefficient of
thermal expansion, fire resistance, fluid resistance, and
surface roughness.”
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ASIP M&P Requirements
Lincoln’s 5 Factors (3 of 3)
4. Predictability of structural performance - “Material,
process, and joining method selections shall be
evaluated to determine if validated analysis methods
and/or empirical methods are established to enable
accurate prediction of structural performance (for
example, strength, rigidity, durability, damage
tolerance). If validated methods don’t exist at the time of
selection, risk mitigation actions shall be established.”
5. Supportability - “Material, process, and joining method
selections shall be evaluated to determine if cost-
effective inspection and repair methods are either
available or can be developed in a timely manner
considering the sustainment environment throughout
the entire life cycle…”
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Outline
• Overview
• Aircraft Structural Integrity Program (ASIP)
Material & Process (M&P) requirements
• Challenge for Additive Manufacturing (AM) –
accurate prediction of Durability and Damage
Tolerance (DADT)– DADT Analysis (DADTA) foundation
– Surrogate damage
– DADT control
– Parts selection
• Probabilistic risk analysis for AM parts
• Summary
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Most Difficult Challenge for AM of
Aircraft Structural Parts
• Validated analysis method for accurate
prediction of durability and damage tolerance
(ASIP M&P selection factor 4) which requires:
1. Established DADTA foundation
2. Established surrogate damage
3. Established DADT control
4. Methodical parts selection
“Work the Hardest Problem Up Front”
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1. DADTA Foundation
Introduction
• How many locations are potentially critical and
therefore require DADTA?
Subtractive Manufacturing Additive Manufacturing
2 to 3 Locations? 5 to 7 Locations?
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1. DADTA Foundation
Requirements (1 of 2)
1.1 Develop validated DADTA method
– Results in reasonable correlation with test data
– Accounts for complex geometries, load interaction,
residual stresses, etc. as needed
1.2 Generate material data
– Material data (fatigue crack growth rates, fracture
toughness) developed using the same processes,
machines, build orientation, etc. for the production parts
– Sufficient replicates to demonstrate material
consistency recognizing AM technology is particularly
susceptible to producing parts with discontinuities that
can serve as sites for crack nucleation reinforcing the
need for statistical characterization
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1. DADTA Foundation
Requirements (2 of 2)
1.3 Establish DADT criteria– Specific to the AM application for use in the DADTA
and to establish part-specific inspections
– For reference, current DADT criteria includes: • Average usage for damage tolerance stress spectra
• 90th percentile usage for durability stress spectra
• Nominal part dimensions
• Average crack growth rate
• Lower bound fracture toughness
• Typically no explicit residual stresses
• Specified initial crack sizes
• Factor of 2 on DADTA predictions to establish the initial
inspection requirement
• Note: If material data scatter is judged to be too high,
adjustments to 1 or more criteria are made
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2. Surrogate Damage
Introduction (1 of 5)
• MIL-STD-1530 defines damage as “any flaw, defect,
crack, corrosion, disbond, delamination, discontinuity,
or other type that degrades, or has the potential to
degrade, the performance of the affected component”
• MIL-STD-1530 states that “damage tolerance criteria
shall be applied to all safety-of-flight structure” and
“include establishment of surrogate damage types,
sizes, orientations, locations, with consideration of all
phases of the life cycle to include: material processing,
shipping, handling, manufacturing, flight operations, and
maintenance”
Surrogate Damage has 4 Attributes
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2. Surrogate Damage
Introduction (2 of 5)
• For DADT of structural parts made from wrought metallic
materials, surrogate damage type is a fatigue crack, in
the most critical orientation, in all critical locations (this
covers 3 of the 4 damage attributes)
• USAF developed Equivalent Initial Damage Size (EIDS)
distribution data to establish surrogate damage sizes for
use in the DADTA in the 1970s– MIL-STD-1530 states that the EIDS “is an analytical
characterization of the initial quality of the aircraft structure at
the time of manufacture, modification, or repair. The EIDS
distribution is derived by analytically determining the initial
damage size distribution that characterizes the measured
damage size distribution observed during test or in service”
• EIDS data used in structural risk analysis during past 20
years indicate this early work is still representative
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2. Surrogate Damage
Introduction (3 of 5)
0.000 0.005 0.010 0.015 0.020 0.025 0.030
Pro
ba
bilit
y D
en
sit
y F
un
cti
on
Equivalent Initial Damage Size (inches)
Wrought Aluminum, Individual & Combined Data
All 1.1
2.1 3.1
4.1 4.2
4.3 4.4
4.5 5.1
6.1 7.1
Initial Crack Size Assumption for
Durability
("Upper Bound of Normal Manufacturing
Quality")518 Total Cracks:
7 Aircraft
11 Materials
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2. Surrogate Damage
Introduction (4 of 5)
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045 0.050 0.055 0.060
Pro
ba
bilit
y D
en
sit
y F
un
cti
on
Equivalent Initial Damage Size (inches)
Wrought Aluminum, Combined Data
Initial Crack Size
Assumption for Damage Tolerance
("Rogue Damage Size")
Initial Crack Size
Assumption for Durability
("Upper Bound of Normal
Manufacturing Quality")
~Best NDI Capability
Combined
518 Cracks
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2. Surrogate Damage
Introduction (5 of 5)
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.090 0.100
Exceed
an
ce P
rob
ab
ilit
y
Equivalent Initial Damage Size (inches)
Wrought Aluminum, Individual & Combined Data
All 1.1
2.1 3.1
4.1 4.2
4.3 4.4
4.5 5.1
6.1 7.1
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2. Surrogate Damage
Requirements (1 of 3)
2.1 Establish surrogate damage type(s)– Generate data that demonstrates the surrogate
damage type(s) covers the full range of potential
damage such as lack of fusion, porosity, cracking,
and lack of penetration in AM parts
2.2 Establish surrogate damage locations– Most critical location(s) for the part
2.3 Establish surrogate damage orientation(s)– Most critical orientation(s) for the part
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2. Surrogate Damage
Requirements (2 of 3)
2.4 Establish surrogate damage sizes– Damage size for Normal Control (NC) parts based on a
probability of exceeding the EIDS of 1x10-1; but not
less than 0.01 inches
– Damage size for Durability Critical (DC) parts based on
a probability of exceeding the EIDS of 1x10-3; but not
less than 0.01 inches
– Damage size for Fracture Critical (FC) parts based on
a probability of exceeding the EIDS of 1x10-7; but not
less than 0.05 inches
Note: NC, DC, and FC Defined in Section 4
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 0.090 0.100
Ex
ce
ed
an
ce
Pro
ba
bilit
y
Equivalent Initial Damage Size (inches)
Wrought Aluminum, Individual & Combined Data
All 1.1
2.1 3.1
4.1 4.2
4.3 4.4
4.5 5.1
6.1 7.1
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2. Surrogate Damage
Requirements (3 of 3)
NC
DC
FC
2 of 11 > 0.01”
Combined < 0.01”
6 of 11 > 0.01”
Combined ~0.02”
2 of 11 > 0.05”
Combined ~0.05”
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3. DADT Control
Requirements (1 of 5)
3.1 Demonstrate process control– Address the stability and producibility factors
– Include residual stress management efforts such as
stress relief and additional manufacturing steps such
as heat-treating, Hot Isostatic Pressing (HIPing), and
machining to achieve surface finish requirements
3.2 Generate mechanical property data– Statistically-based design data from specimens using
the “production” processes and include worst-case
orientations and regions of the part
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3. DADT Control
Requirements (2 of 5)
3.3 Develop, validate, verify, and implement Non
Destructive Investigation (NDI)– Enable effective Quality Assurance (QA)
– If an NDI-based initial damage size assumption is
used (not preferred), verify the NDI capability for all
damage types, damage orientations, and damage
locations within specific regions of each part
considering access, part thickness, and other
important factors (this is not a trivial task!!!)
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3. DADT Control
Requirements (3 of 5)
3.4 Establish dimensional control and verification– After the AM process is completed and after all post-
processing is completed
3.5 Dissect “Production” parts and characterize
material– Perform mechanical testing of specimens made from
excised material to verify properties to include worst-
case orientations and regions of the part
– Perform metallographic and micrographic
examinations to determine if defects/damage are
within expectations and to evaluate/demonstrate NDI
performance
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3. DADT Control
Requirements (4 of 5)
3.6 Conduct mechanical property testing of
production parts– Fabricate and test “Witness” coupons from each
production part to verify properties, and to provide
data and experience to support the use of the AM
process to more critical/complex parts
– Fabricate the coupons using the same AM parameters
as production parts to include: scan schedule,
interpass time, and orientation on build plate
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3. DADT Control
Requirements (5 of 5)
3.7 Establish accept/reject criteria– Considering all of the DADT control results
– This includes establishing criteria to reject an AM part
based on the frequency of defects/damage, even if
none of the defects/damage exceed the initial damage
size assumption
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4. Methodical Parts Selection
Introduction (1 of 2)
• MIL-STD-1530 establishes part classification & definitions
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4. Methodical Parts Selection
Introduction (2 of 2)
• Safety-of-flight– Fracture-Critical (FC) traceable part
• Either single load path or judged to require serialization and
traceability
– Fracture-Critical (FC) part• Not single load path nor judged to require serialization and
traceability
• Not safety-of-flight– Durability-Critical (DC) part
• Judged to require additional controls beyond those for normal-
controls parts
– Normal Controls (NC) part• Standard aerospace practices are sufficient in the design,
manufacturing, and maintenance of the part to ensure
structural integrity
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4. Methodical Parts Selection
Requirements
4.1 Start with NC parts only– Lowest risk if unanticipated issues occur
– Still requires durability crack growth analysis, all
supporting material data, surrogate damage, etc.
– Expectation: an aggregate of NC parts will provide data
and experience necessary to evaluate risk of
proceeding with DC aircraft structural parts due to:• Varying geometries & complexities
• Multiple lots of materials
• Multiple AM machines & operators
• Characterized material property variability
• Additional data for EIDS characterization
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4. Methodical Parts Selection
Requirements
4.2 Then move to DC parts– Next level of risk
– Use NC & DC parts experience to provide confidence
for pursuing FC parts
4.3 Then pursue FC parts– Requires damage tolerance analysis and different
surrogate damage sizes (as a minimum)
– Requires improved understanding of variability
– Requires improved understanding of supportability
– Requires additional NDI development & validation
– Requires robust accept/reject criteria
32
DADT Certification of AM Parts
Summary (1 of 2)
1. Established DADTA foundationa. Method
b. Data
c. Criteria
2. Established surrogate damagea. Type
b. Orientation
c. Location
d. Size
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DADT Certification of AM Parts
Summary (2 of 2)
3. Established DADT controla. Process control
b. Mechanical property testing for design data
c. NDI
d. Dimensional control
e. Dissection of production parts
f. Mechanical property testing of production parts
g. Accept/reject criteria
4. Methodical parts selectiona. Normal control parts, then
b. Durability critical parts, then
c. Fracture critical parts
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Outline
• Overview
• Aircraft Structural Integrity Program (ASIP)
Material & Process (M&P) requirements
• Challenge for Additive Manufacturing (AM) –
accurate prediction of Durability and Damage
Tolerance (DADT)– DADT Analysis (DADTA) foundation
– Surrogate damage
– DADT control
– Parts selection
• Probabilistic risk analysis for AM parts
• Summary
35
Probabilistic Risk Analysis
Introduction
• Modified Lincoln method, see references:– Lincoln, J.W., ASD-TR-80-5035, “Method for Computation of
Structural Failure Probability for an Aircraft,” July 1980
– UDR-TR-2005-00240, “PRoF v3 PRobability Of Fracture Aging
Aircraft Risk Analysis Update,” December 2005
• Freudenthal method, see references:– Domyancic, L.; McFarland, J.; Cardinal, J.; and Burnside, H.,
“Review of Methods for Single Flight Probability of Failure
(SFPOF),” Southwest Research Institute, March 2011
– Brussat, T. R., “Recommended Methodology Updates to Improve
Single Flight Probability of Failure Estimation,” 2012 ASIP
Conference, San Antonio TX
– UDR-TR-2015-15, “PROF v3.2 Probability Of Failure – A-10 Fleet
Management Analysis Update,” July 2015
36
Probabilistic Risk Analysis
Inputs & Output
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
0 2000 4000 6000 8000 10000 12000
Sin
gle
Flig
ht P
robabili
ty o
f F
ailu
re
Flight Hours
SFPoF
Similar Details
Hours per Flight0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0 1 2 3 4 5 6
K/s
igm
a
Crack Size (in.)
Alpha Plot
BaselineK/σ vs
Crack
Size
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Exce
ed
an
ce
Pro
ba
bili
ty
Stress
Max Stress per Flight
BaselineMax
Stress
per Flight
Initial
Crack
Size 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.000 0.005 0.010 0.015 0.020
Cum
ula
tive
Pro
ba
bility
Crack Size (in.)
Initial Crack Size Distribution
Baseline
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.00 0.20 0.40 0.60 0.80 1.00
Cu
mu
lative
Pro
ba
bili
ty
Crack Size (Inches)
Probability of Detection
Baseline
Probability
of
Detection
Inspection
Intervals
0
0.5
1
1.5
2
2.5
3
3.5
4
0 5000 10000 15000 20000 25000
Cra
ck S
ize
(in
.)
Flight Hours
Crack Growth Curve
Baseline
Crack
Growth
Curve
Fracture
Toughness0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
20 25 30 35 40 45 50
Cu
mu
lative
Pro
ba
bili
ty
Fracture Toughness (Ksi * Inch ^ 0.5)
Fracture Toughness
Baseline
Repair
Crack
Size 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.000 0.005 0.010 0.015 0.020 0.025 0.030
Cum
ula
tive P
rob
ab
ility
Crack Size (in.)
Repair Crack Size Distribution
Baseline
ඵ
37
Risk Analysis Inputs & Output
Related to DADT for AM Challenges
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
0 2000 4000 6000 8000 10000 12000
Sin
gle
Flig
ht P
robabili
ty o
f F
ailu
re
Flight Hours
SFPoF
Similar Details
Hours per Flight0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0 1 2 3 4 5 6
K/s
igm
a
Crack Size (in.)
Alpha Plot
BaselineK/σ vs
Crack
Size
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Exce
ed
an
ce
Pro
ba
bili
ty
Stress
Max Stress per Flight
BaselineMax
Stress
per Flight
Initial
Crack
Size 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.000 0.005 0.010 0.015 0.020
Cum
ula
tive
Pro
ba
bility
Crack Size (in.)
Initial Crack Size Distribution
Baseline
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.00 0.20 0.40 0.60 0.80 1.00
Cu
mu
lative
Pro
ba
bili
ty
Crack Size (Inches)
Probability of Detection
Baseline
Probability
of
Detection
Inspection
Intervals
0
0.5
1
1.5
2
2.5
3
3.5
4
0 5000 10000 15000 20000 25000
Cra
ck S
ize
(in
.)
Flight Hours
Crack Growth Curve
Baseline
Crack
Growth
Curve
Fracture
Toughness0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
20 25 30 35 40 45 50
Cu
mu
lative
Pro
ba
bili
ty
Fracture Toughness (Ksi * Inch ^ 0.5)
Fracture Toughness
Baseline
Repair
Crack
Size 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.000 0.005 0.010 0.015 0.020 0.025 0.030
Cum
ula
tive P
rob
ab
ility
Crack Size (in.)
Repair Crack Size Distribution
Baseline
ඵ
DADTA
Found.
DADTA
Found.
DADTA
Found.
Surrogate
Damage
DADT
Control
38
Probabilistic Risk Analysis
Priorities• #1: Get the loads/environment and usage severity right
for each aircraft– Used in crack growth analysis
– Used in equivalent flight hours (EFH) calculations
– Used to generate max stress per flight distribution
• #2: Get the crack growth model right– Used to convert actual flight hours into EFH so that fleet and test
results can be combined
– Used to convert crack sizes at EFH into EIDS values to generate
flaw size distribution
– Used to project flaw size distribution in time
– Used to determine when failure criterion is reached
• #3: Get the EIDS distribution right and update it as
additional inspection results are obtained– Must consider that NDI is used to find/miss cracks and therefore
directly influences result
• #4: Get the NDI PoD function right
39
Outline
• Overview
• Aircraft Structural Integrity Program (ASIP)
Material & Process (M&P) requirements
• Challenge for Additive Manufacturing (AM) –
accurate prediction of Durability and Damage
Tolerance (DADT)– DADT Analysis (DADTA) foundation
– Surrogate damage
– DADT control
– Parts selection
• Probabilistic risk analysis for AM parts
• Summary
40
Summary
• DADT certification of structural parts requires significant
test data to characterize the variability in DADT properties
and to establish the initial damage type and size
assumptions used in the DADTA
• The pursuit of AM for structural parts should begin with
NC parts only
• If the test data and experience from building hundreds of
various NC parts supports it, the pursuit of DC parts can
begin
• Only when the test data and experience from building
many hundreds of various NC and DC parts exists and is
favorable, should the pursuit of FC parts begin
• This approach is expected to be more efficient in the long
run than performing significant testing for part-specific
AM applications only
41