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Transcript of Research Motivation: Effect of Loading Environment on ... · PDF fileMulti‐SiteCrack Growth...
8/29/2014
1
The Effect of Loading Environment on Cracking in Structural Metals
James T. BurnsResearch Assistant Professor
Department of Materials Science and EngineeringUniversity of Virginia
MSE SeminarUniversity of Virginia
Department of Materials Science and Engineering
Aug 2014
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
Research Motivation:
Airframe‐ Cyclic Loading(Fatigue)‐ Ground Based Corrosion‐ Benign Env
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
Nuclear‐Monotonic and Cyclic Loading‐ PWR Reactor Environment
Staehle, 2013
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
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Pipeline ‐ Carbon Steel 5LX – Anhydrous Ammonia (NTSB‐DCA05‐MP001)
‐Monotonic Loading ‐ Aggressive Environment
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
Ships‐Monotonic Loading ‐ Aggressive Environment
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
Bridges‐Monotonic Loading ‐ Pre‐charged H
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
Bridges‐Monotonic Loading ‐ Pre‐charged H
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
8/29/2014
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Bridges‐Monotonic Loading ‐ Pre‐charged H
In each case material‐environment‐mechanics interactions play a critical role in determining the
cracking behavior that leads to failure
Understand and predict the influence of environment on subcritical cracking (ie, fatigue, SCC, HEE) to enhance the design and
safe management engineering components
How are engineering components managed to ensure safe operation?
To what extend are (or should!!) environmental effects be considered?
1. Safe Life: Stress/Strain Life Empirical Relationships
How is FATIGUE cracking managed to ensure safe operation?
Empirical S‐N Data
Test Specimen
1. Safe Life: Stress/Strain Life Empirical Relationships
How is FATIGUE cracking managed to ensure safe operation?
Empirical S‐N Data Establish Empirical Constants (b c σf’ ε f’ )
Test Specimen
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1. Safe Life: Stress/Strain Life Empirical Relationships
How is FATIGUE cracking managed to ensure safe operation?
Empirical S‐N Data Establish Empirical Constants (b c σf’ ε f’ )
Coffin‐Manson/Basquin (SWT)
Engineering Component
1. Safe Life: Stress/Strain Life Empirical Relationships
How is FATIGUE cracking managed to ensure safe operation?
Empirical S‐N Data Establish Empirical Constants (b c σf’ ε f’ )
Coffin‐Manson/Basquin (SWT)
Solve for life (Nf) = End of Component Life: For high performance “low‐cycle fatigue” application;
propagation is often considered negligible and Nf ≈ Initiation Life
1. Safe Life: Stress/Strain Life Empirical Relationships
How is FATIGUE cracking managed to ensure safe operation?
High Strength Stainless Steel
Zhou/Turnbull, 1999Total Cycles to Failure
104 105 106 107
Max
imum
Stre
ss (M
Pa)
50
100
150
200
250
300
350
400
Pristine (600 Grit)EXCO 6h LTEXCO 6h LSANCIT 24h LT
H2O/N2 (RH > 95%)R = 0.1 f = 10 Hz
7075-T6511
- Data offset about 150 and 240 MPa for clarity
Pristine
Corroded
Burns, Kim, 2009
Pristine
Corroded
Corrosion damage will drastically alter the empirical
S‐N relationship
Empirical S‐N Data
Airframe Aluminum Alloy
2. Damage Tolerance: Assume an existing flaw, model crack growth via Fracture Mechanics to set inspection protocol
How is FATIGUE cracking managed to ensure safe operation?
From KIC
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2. Damage Tolerance: Assume an existing flaw, model crack growth via Fracture Mechanics to set inspection protocol
Krishnamurthy, 1990
Speidel, 1990
Steel
Titanium
Burns
Aluminum
How is FATIGUE cracking managed to ensure safe operation?
Gangloff, 1990
Steel
This material property is critically dependent on
loading/crack tip environment
How is SCC/HE cracking managed to ensure safe operation?
“Go or No‐Go” Criteria: Material either considered immune or susceptible in a given environment
How is SCC/HE cracking managed to ensure safe operation?
Historical Approaches:“Go or No‐Go” Criteria: Material either considered immune or susceptible in a given
environment
How is SCC/HE cracking managed to ensure safe operation?
1. Non‐Fracture Mechanics ASTM Standardized Testing: ‐ SSRT, U‐bend, Cantilever, Breaking Load, C‐ring, Bolt, etc
Historical Approaches:
Bovard
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“Go or No‐Go” Criteria: Material either considered immune or susceptible in a given environment
How is SCC/HE cracking managed to ensure safe operation?
1. Non‐Fracture Mechanics ASTM Standardized Testing: ‐ SSRT, U‐bend, Cantilever, Breaking Load, C‐ring, Bolt, etc
2. Fracture Mechanics Based Approach: ‐ Continued Focus on Initiation (ie KTH or KISCC)
Historical Approaches:
How is SCC/HE cracking managed to ensure safe operation?
State of the Art Approach:Enhanced damage tolerant materials (0.5h → 10,000h lives) and characterization
capabilities (<1μm crack advance detection) enable:
How is SCC/HE cracking managed to ensure safe operation?
1. Quantification of crack growth kinetics as a function of K
State of the Art Approach:
UVa (Gangloff/Burns), GE (Andresen), VEXTEC (LEFM Software)
Enhanced damage tolerant materials (0.5h → 10,000h lives) and characterization capabilities (<1μm crack advance detection) enable:
‐ Participation in efforts to move technique towards ASTM Standardization
How is SCC/HE cracking managed to ensure safe operation?
1. Quantification of crack growth kinetics as a function of K
2. LEFM Modeling of crack progression
UVa (Gangloff/Burns), GE (Andresen), VEXTEC (LEFM Software)
State of the Art Approach:Enhanced damage tolerant materials (0.5h → 10,000h lives) and characterization
capabilities (<1μm crack advance detection) enable:
‐ For a specified loading condition, environment, and initial flaw size
‐ Directly analogous to fatigue modeling
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Response Surface to Select Particles Most Likely to Crack
Fatigue Incubation
Critical Plane Criterion, Coffin‐Manson (MSF)Select Particles Most Likely to Nucleate
Fatigue Nucleation
MSC FASTRAN AFGROWMicrostructurally Small Crack Growth
Transition Rules
Multi‐Site Crack Growth (FASTRAN, AFGROW)Crack Link-up to Dominant Crack
Large Crack Growth
Geometry, Material & Fatigue Loading
SelectMaterial
Calculate Notch & Grain Scale ResponseStresses & Strains
OUTPUT
Crack Size, a
P(a)
Crack Size, a
P(a)
INPUT
Next Load Cycle
Microstructure Statistics Grain SizeGrain OrientationParticle Aspect RatioParticle Size & SpacingConstitutive Rules
Processed DataParticle Filters (I&II)Material Samples
a
b
c
10 μm
(μStructure Builder)
DARPA‐SIPSRollet, Ingraffea, Horstmeyer
Newman, Tryon
Next Generation Life Management: Microstructure‐Based Multi‐scale Models
Response Surface to Select Particles Most Likely to Crack
Fatigue Incubation
Critical Plane Criterion, Coffin‐Manson (MSF)Select Particles Most Likely to Nucleate
Fatigue Nucleation
MSC FASTRAN AFGROWMicrostructurally Small Crack Growth
Transition Rules
Multi‐Site Crack Growth (FASTRAN, AFGROW)Crack Link-up to Dominant Crack
Large Crack Growth
Geometry, Material & Fatigue Loading
SelectMaterial
Calculate Notch & Grain Scale ResponseStresses & Strains
OUTPUT
Crack Size, a
P(a)
Crack Size, a
P(a)
INPUT
Next Load Cycle
Microstructure Statistics Grain SizeGrain OrientationParticle Aspect RatioParticle Size & SpacingConstitutive Rules
Processed DataParticle Filters (I&II)Material Samples
a
b
c
10 μm
(μStructure Builder)
DARPA‐SIPSRollet, Ingraffea, Horstmeyer,
Newman, Tryon
Computational muscle available, but needs:‐ A detailed understanding of the crack tip environment and material
interaction
‐ Understanding of the relationship between the governing failure mechanism and the microstructure
‐ High fidelity experimental data on crack formation, MSC cracking, and long crack kinetics to validate modeling efforts
‐ A realistic and validated Failure Criteria!!!
Next Generation Life Management: Microstructure‐Based Multi‐scale Models
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Environmental Cracking Research Focus:
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Governing factors for crack formation and microstructure scale cracking (MSC) growth about corrosion damage
Environmental Cracking Research Focus:
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Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Governing factors for crack formation and microstructure scale cracking (MSC) growth about corrosion damage
Environmental Cracking Research Focus:
Current Research Efforts:1. The effect of [Cl‐] concentration on pitting, crack formation and MSC in UHSSS
‐ ONR (Vasudevan): Burns2. Modeling crack formation life in air, chloride solutions and high temperatures in UHSSS and Ni‐alloys
‐ Rolls Royce (Mills): Burns3. Investigating the role of galvanic coupling parameters and inhibitors on the factors that govern crack formation from corrosion damage in aerospace Al
‐ ONR (Nickerson): Burns, Scully, Kelly4. LEFM modeling of remaining fatigue life of field exposed corroded components
‐ SAFE Inc.(Fawaz): Burns
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Governing factors for crack formation and microstructure scale cracking (MSC) growth about corrosion damage
Advised Effort: 1 PDRA 2 GRA 0 (1) Undergrad
Environmental Cracking Research Focus:
Current Research Efforts:1. The effect of [Cl‐] concentration on pitting, crack formation and MSC in UHSSS
‐ ONR (Vasudevan): Burns2. Modeling crack formation life in air, chloride solutions and high temperatures in UHSSS and Ni‐alloys
‐ Rolls Royce (Mills): Burns3. Investigating the role of galvanic coupling parameters and inhibitors on the factors that govern crack formation from corrosion damage in aerospace Al
‐ ONR (Nickerson): Burns, Scully, Kelly4. LEFM modeling of remaining fatigue life of field exposed corroded components
‐ SAFE Inc.(Fawaz): Burns
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Environmental Cracking Research Focus:
The effect of bulk and crack tip environments on crack growth kinetics
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
The effect of bulk and crack tip environments on crack growth kinetics
Current Research Efforts:5. The effect of low temperature on the crack growth behavior of 7075/2199 Al alloys
‐ALCOA (Warner), SAFE Inc.(Fawaz): Burns6. The effect of lot‐to‐lot variation on the HEAC behavior of Monel K‐500 and its impact on LEFM modeling
‐ ONR (Perez): Scully, Burns7. The effect of grain orientation and composition the HEAC of Al‐Mg alloys
‐ ONR (Perez): Burns, Kelly8. The effect of loading rate on the HEAC behavior of two Ni‐based super‐alloys
‐ USAFA (Shoales): Scully, Burns9. Mechanistic studies of IG corrosion and stress corrosion cracking under atmospheric exposure conditions
‐ ONR (Perez): Kelly, Burns, Scully10. Mechanism‐based approach to development of corrosion and hydrogen resistant aircraft alloys
‐ NAVMAR (Waldman): Burns, Gangloff11. The effect of plate thickness on the environmental fatigue behavior of 7085 aluminum
‐ ALCOA (Boselli): Burns12. The effect of precipitate character on the crack tip damage character during HEAC of Monel K‐500
‐ ALCOA Fellowship: Burns
Environmental Cracking Research Focus:
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Current Research Efforts:5. The effect of low temperature on the crack growth behavior of 7075/2199 Al alloys
‐ALCOA (Warner), SAFE Inc.(Fawaz): Burns6. The effect of lot‐to‐lot variation on the HEAC behavior of Monel K‐500 and its impact on LEFM modeling
‐ ONR (Perez): Scully, Burns7. The effect of grain orientation and composition the HEAC of Al‐Mg alloys
‐ ONR (Perez): Burns, Kelly8. The effect of loading rate on the HEAC behavior of two Ni‐based super‐alloys
‐ USAFA (Shoales): Scully, Burns9. Mechanistic studies of IG corrosion and stress corrosion cracking under atmospheric exposure conditions
‐ ONR (Perez): Kelly, Burns, Scully10. Mechanism‐based approach to development of corrosion and hydrogen resistant aircraft alloys
‐ NAVMAR (Waldman): Burns, Gangloff11. The effect of plate thickness on the environmental fatigue behavior of 7085 aluminum
‐ ALCOA (Boselli): Burns12. The effect of precipitate character on the crack tip damage character during HEAC of Monel K‐500
‐ ALCOA Fellowship: Burns
Use high fidelity experimental characterization to inform mechanism level understanding that feeds engineering level modeling: Two Foci
Environmental Cracking Research Focus:
Advised Effort: 1 PDRA 5 GRA 2 (1) Undergrad
The effect of bulk and crack tip environments on crack growth kinetics
Environmental Cracking Interests
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure
Environmental Cracking
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure
Environmental Cracking
Environmental Cracking Interests
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure
Environmental Cracking
Environmental Cracking Interests in the Context of: CESE Expertise
8/29/2014
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Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: CESE Expertise
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: CESE Expertise
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: CESE Expertise
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: CESE Expertise
8/29/2014
11
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: MSE Expertise
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: MSE Expertise
New ALCOA Research Scientist
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: MSE Expertise
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: MSE Expertise
8/29/2014
12
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: Current External Collaborators
Characterization:Robertson (UW), Goswami (NRL), Sofronis (UI), Burnett (Manchester)
Modeling:Microstructure: QuesTek (Olson),
VEXTEC (Tryon), GaTech(McDowell/Castelluccio)
Engineering: LUNA (Friedersdorf), SAFE (Fawaz)
ExperimentationWMTL (Plotner), NSWC (Gaies), NRL (Matzdorf), NRL (Bayles,
Knudsen), USNA (Schubbe), Sandia (Somerday), ALCOA (Bray, Warner)
Metallurgy
Chemistry/ElectrochemistryMechanics
‐ Strength ‐ Strengthening mechanism‐ GB character (PPC, orientation, segregation)
‐ Slip character ‐ Grain size‐ Composition ‐ PPC ‐ Crack tip dislocations‐ H‐trapping behavior ‐Surface modification
‐ Additive manufacturing properties
‐ Echem Potential ‐ Electrolyte ‐ Halides ‐ pH ‐Moist Gas‐ H‐pressure ‐ Solution flow
‐ Corrosion damage morphology ‐ Coatings
‐ Crack tip occlusion ‐ Temp‐ Irradiated Materials
‐ Bio‐medical conditions
‐ ΔK/K ‐Mean Stress‐ Crack tip stress/strain/plasticity
‐ Frequency ‐Wave‐form‐ Grain specific constitutive laws
‐ Corrosion concentrated stress/strains
‐ Crack closure ‐ Crack tip strain rate
Environmental Cracking
Environmental Cracking Interests in the Context of: Potential External Collaborators
Nuclear:Was (UM), Staehle, QuesTek/Bettis APL
Crystal Plasticity Modeling:McDowell/Neu (GT), Anderson (OSU), Solanki (ASU), Hochhalter
(NASA)
Bio‐Medical Materials/Environments:
Gilbert (SU)
Infrastructure:UVA‐CE, VDOT (Sharp),
Riddell (Rowan)
Characterization:Robertson (UW), Goswami (NRL), Sofronis (UI), Burnett (Manchester)
Modeling:Microstructure: QuesTek (Olson),
VEXTEC (Tryon), GaTech(McDowell/Castelluccio)
Engineering: LUNA (Friedersdorf), SAFE (Fawaz)
ExperimentationWMTL (Plotner), NSWC (Gaies), NRL (Matzdorf), NRL (Bayles,
Knudsen), USNA (Schubbe), Sandia (Somerday), ALCOA (Bray, Warner)
‐ High fidelity experimental capabilities (Cracking‐Burns; Echem‐Kelly/Scully)
‐ State of the art characterization techniques (Burns/UW/UI/NRL/UVa?)…
Field is poised for unprecedented advances in identifying the damage mechanism and failure criteria by coupling:
‐ High fidelity experimental capabilities (Cracking‐Burns; Echem‐Kelly/Scully)
‐ State of the art characterization techniques (Burns/UW/UI/NRL/UVa?)…
This mechanistic understanding will:
1. Inform next generation mechanism‐based multi‐scale computa on modeling (atoms → components)
(GaTech/QuesTek)
Field is poised for unprecedented advances in identifying the damage mechanism and failure criteria by coupling:
8/29/2014
13
‐ High fidelity experimental capabilities (Cracking‐Burns; Echem‐Kelly/Scully)
‐ State of the art characterization techniques (Burns/UW/UI/NRL/UVa?)…
This mechanistic understanding will:
1. Inform next generation mechanism‐based multi‐scale computa on modeling (atoms → components)
(GaTech/QuesTek)
2. Enable near‐term incorporation of environment into engineering‐scale structural management/alloy selection
(Burns/LUNA/Fawaz/VEXTEC)
Field is poised for unprecedented advances in identifying the damage mechanism and failure criteria by coupling:
‐ High fidelity experimental capabilities (Cracking‐Burns; Echem‐Kelly/Scully)
‐ State of the art characterization techniques (Burns/UW/UI/NRL/UVa?)…
This mechanistic understanding will:
1. Inform next generation mechanism‐based multi‐scale computa on modeling (atoms → components)
(GaTech/QuesTek)
2. Enable near‐term incorporation of environment into engineering‐scale structural management/alloy selection
(Burns/LUNA/Fawaz/VEXTEC)
3. Inform traditional and ICME‐based alloy development aimed at enhanced environmental cracking performance
Field is poised for unprecedented advances in identifying the damage mechanism and failure criteria by coupling:
The Effect of Water Vapor Pressure on the Threshold Behavior of Aerospace
Aluminum AlloysJames T. Burns
Research Assistant ProfessorDepartment of Materials Science and Engineering
University of Virginia
MSE SeminarUniversity of Virginia
Department of Materials Science and Engineering
Aug 2014
Fighter
Flight Environment…
Primary Loading• Aggressive Maneuvers• ≈30,000 ft = ‐44°C• f = 0.005‐0.2 Hz• Aicher, 1976; Aronstein, 1997
Jonge, 1979
40%
Transport
Wing Loads• Taxi/Take‐off/Landing• Wind Gusts• 40% >10,000 ft; Thus < ‐5°C• f = 0.1‐10 Hz• Jorge, 1979
Fuselage Loads• Pressurization• 8,000‐50,000 ft ‐5 to ‐57°C• f = 0.00003‐0.001 Hz• Hunt; Wanhill, 2001
Aerodynamic Loads• Fuselage/Control Surfaces• 0‐50,000ft; Thus 0‐60°C• f = 0.0003‐30 Hz• Fawaz
8/29/2014
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Flight Environment…
Active loading at Low Temperature
and Low Water Vapor Pressure
Fatigue Resistance is Drastically Increased at Low T and PH2O
Fatigue Resistance is Drastically Increased at Low T and PH2O1. Can be accurately modeled using LEFM and env‐specific rates
2. Potential to significantly reduce the inspection burden
Temperature/PH2O Specific Growth Rate Data
LEFM Code (AFGROW)
23C
‐50C
‐90C
Temperature/PH2O Specific Growth Rate Data
Fatigue Resistance is Drastically Increased at Low T and PH2O1. Can be accurately modeled using LEFM and env‐specific rates
2. Potential to significantly reduce the inspection burden
LEFM Code (AFGROW)
23C
‐50C
‐90C
TAKE AWAY: Significant fatigue loading likely takes place at low T and PH2O
Airframe Prognosis (Safe‐Life and DTA) = Laboratory Room Temp Material Properties for Life Prediction
Motivates investigation of low T/PH2Ocracking behavior
8/29/2014
15
7075 ‐ Complete23C; Low PH2O
7075 ‐ OngoingLow T
2199 ‐ Complete23C; Low PH2O
2199 ‐ OngoingLow T
Extensive and unprecedented data‐base for 7075 and 2199 at pertinent T/PH2OGrowth rates systematically decrease with decreasing exposure
In collaboration with ALCOA
2199 is more fatigue resistant at both High RH and UHVWhy?
2199 is more fatigue resistant at both High RH and UHV
2199‐T86 – Al‐Cu‐Li‐ Shearable δ’‐phase (Al3Li); strong texture‐ Heterogeneous planar slip ‐ reversibility‐ Extrinsic toughening mechanisms
‐ Roughness induced closure‐ Crack deflection/branching‐ Mode II displacement
7075‐T651 – Al‐Zn‐Mg‐Cu‐ Non‐shearable ƞ (or ƞ’)‐phase‐ Dislocation looping – Homogenous slip‐ Limits slip reversibility and crack
roughness‐ *However, SBC at UHV and low ΔK
2 3 4 5 6 7 8 9 10 11121314
10-7
10-6
10-5
10-4
10-3
AA 7075-T651--L-T
f = 20 Hz, C = -0.07 mm-1
Kmax = 16.5 MPa√m
T=16oC, Vacuum:0.25~0.50 μPa
T= 26oC, Water Vapor: 0.006 Pa
T= 26oC, Water Vapor: 0.053 Pa
T= 26oC, Water Vapor: 0.13 Pa
T= 26oC, Water Vapor: 0.26 Pa
T= 26oC, Water Vapor: 2.6 Pa
T= 23oC, Water Vapor: 2.4 kPa
T= 23oC, Water Vapor: 2.4 kPa
da/d
N, m
m/c
ycle
Applied ΔK, MPa√m
Constant Kmax of 16.5 MPa√mIncreasing R with decreasing ΔK
Constant R =0.5
Decreasing ΔK tests at various PH2O show a novel “apparent threshold” behavior At intermediate exposures a minima is followed by increasing da/dN for
both…
8/29/2014
16
Apparent Threshold behavior correlates with changes in fracture surface morphology
Transgranular features observed prior to the apparent threshold…
(1)
(1)
(1) ΔK=7 MPa√m
(1)
(1) ΔK=7 MPa√m
(2)
(1)(2)
(2) ΔK=6 MPa√m
Transgranular features observed prior to the apparent threshold…
(1)(2)
(1)(2)
(3)
(3)
(3) ΔK=5 MPa√m
A SBC morphology is observed in the “dip” region…
8/29/2014
17
(1)(2)
(1)(2)
(3)
(3)
(4)
(4)
(3) ΔK=5 MPa√m
(4) ΔK=3 MPa√m
Transitions back to transgranular as da/dN increases…
This behavior begs two questions:1. Why does the apparent threshold behavior initiate?
2. What causes the subsequent rise?
Understood via the Hydrogen Environment Embrittlement Process
23C HUMID
HighMouth PH2O
σ High: Plasticity, ┴
Hydrostatic stress
RAPID
Uptake:Interstitial H
Surface Reaction
Al
Atomic H
H2O
Process Zone
CrackPit
Mouth PH2O > Crack tip PH2O
Molecular Flow
23C HUMID
HighMouth PH2O
σ Molecular Flow High: Plasticity, ┴
Hydrostatic stress
RAPID
Uptake:Interstitial H
Surface Reaction
Al
Atomic H
H2O
Process Zone
CrackPit
Mouth PH2O > Crack tip PH2O
Literature models exist based on rate limitation by:Molecular flowSurface reaction
Diffusion
Understood via the Hydrogen Environment Embrittlement Process
8/29/2014
18
All “apparent threshold” behavior occurs in the regime where molecular flow governs the environmental cracking
1
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
Wei, et al.
Molecular transport can occur via either:
Advection (Turnbull)• Bulk fluid flow induced by
the cyclic displacement of the crack walls
Diffusion Based Flow (Wei)• Pressure gradient results from
flow impedance of water molecules interacting with crack walls
• Free molecular (Knudsen) flow for our test conditions
Molecular transport can occur via either:
Advection (Turnbull)• Bulk fluid flow induced by
the cyclic displacement of the crack walls
Diffusion Based Flow (Wei)• Pressure gradient results from
flow impedance of water molecules interacting with crack walls
• Free molecular (Knudsen) flow for our test conditions
A simple 1‐D flow criteria:
suggests that molecular transport will be dominated by:Diffusion Based Flow
How does this influence the da/dN?
lcrit ≈ (DH2O/f )1/2 / (1 – R1/2)Turnbull et al.
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
Wei, Ruiz
Solving coupled differential equations that account for tip surface reaction and impeded molecular (Knudsen) flow yielded a model for da/dNcf
8/29/2014
19
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
β is an empirical constant related to crack wake flow geometry
Wei, Ruiz
Solving coupled differential equations that account for tip surface reaction and impeded molecular (Knudsen) flow yielded a model for da/dNcf
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
Increased roughness causes flow geometry to change…
β decreases
Thus da/dN to fall!!!
Solving coupled differential equations that account for tip surface reaction and impeded molecular (Knudsen) flow yielded a model for da/dNcf
Wei, Ruiz
Decreasing β
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
Increased roughness causes flow geometry to change…
β decreases
Thus da/dN to fall!!!
Wei, Ruiz
Decreasing βWhy does roughness develop??
Solving coupled differential equations that account for tip surface reaction and impeded molecular (Knudsen) flow yielded a model for da/dNcf
7075-T651C(T) - L-T Orientation
R=0.5; f =20 Hz
ΔK (MPa m1/2)
1 10
da/d
N (m
m/c
ycle
)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
7075 - RH>95%7075 - UHV
Fracture surface morphology is strongly dependent on the environment and ΔK
TransgranularCleavage and
High Index Planes
TransgranularCleavage
Micro‐voidingSub‐boundary
TransgranularSome SBC
High ΔK enables cross‐slip
SBCShears ƞ (ƞ’)High Level ofRoughness
8/29/2014
20
7075-T651C(T) - L-T Orientation
R=0.5; f =20 Hz
ΔK (MPa m1/2)
1 10
da/d
N (m
m/c
ycle
)
10-8
10-7
10-6
10-5
10-4
10-3
10-2
7075 - RH>95%7075 - UHV
Fracture surface morphology is strongly dependent on the environment and ΔK
TransgranularCleavage and
High Index Planes
TransgranularCleavage
Micro‐voidingSub‐boundary
TransgranularSome SBC
High ΔK enables cross‐slip
SBCShears ƞ (ƞ’)High Level ofRoughness
Critically, the level of roughness increases with decreasing ΔK and exposure!!!!
What governs the morphology change?
Method: EBSD + Stereology
Identify the Crystallographic Character of the Crack Path Based on Fracture Surface Analysis
‐Classic Slip‐Band Cracking along {111}
‐ Observed for a wide range of planar slip Al‐alloys
‐ Also observed at low‐ΔK for wavy slip (7075‐T651)
Method: EBSD + Stereology
Gangloff, Ro, Gupta, Agnew
Ultra High Vacuum
High Purity 2024‐T351
‐{001}, {011}, high index; Never {111}
‐ H‐Enhanced Decohesionthrough:
‐ Planes with lowest cohesive strength {001}, {011}
‐ Dynamically recovered sub‐grain structures/LEDS
Method: EBSD + Stereology
Gangloff, Ro, Gupta, Agnew
High Humidity
High Purity 2024‐T351
8/29/2014
21
At low/intermediate exposures, as ∆K decreases the proportion of SBC features increases
1. Why does the apparent threshold behavior initiate?HYPOTHESIS:
At low/intermediate exposures, as ∆K decreases the proportion of SBC features increases
This increases roughness associated with these SBC
1. Why does the apparent threshold behavior initiate?HYPOTHESIS:
At low/intermediate exposures, as ∆K decreases the proportion of SBC features increases
This increases roughness associated with these SBC
This increased roughness leads to impeded flow (decreased β)
1. Why does the apparent threshold behavior initiate?HYPOTHESIS:
SAT2
2YSH2O
dNda
kEσf(R)
αNβ436
T1
fP
dNda
⎟⎠⎞
⎜⎝⎛
⎥⎦
⎤⎢⎣
⎡=
M
At low/intermediate exposures, as ∆K decreases the proportion of SBC features increases
This increases roughness associated with these SBC
This increased roughness leads to impeded flow (decreased β)
As predicted via Knudsen Flow models, this exacerbates the crack tip PH2O reduction
1. Why does the apparent threshold behavior initiate?HYPOTHESIS:
8/29/2014
22
At low/intermediate exposures, as ∆K decreases the proportion of SBC features increases
This increases roughness associated with these SBC
This increased roughness leads to impeded flow (decreased β)
As predicted via Knudsen Flow models, this exacerbates the crack tip PH2O reduction
Decreased crack tip PH2O results in less HEE and slower da/dN
1. Why does the apparent threshold behavior initiate?HYPOTHESIS:
Consistent with experimental findings:As PH2O Decreases
Consistent with experimental findings:As PH2O Decreases→ rougher crack wake
1.8 Pa
0.2 Pa
Consistent with experimental findings:As PH2O Decreases→ rougher crack wake → lower β
1.8 PaHigher β
0.2 PaLower β
8/29/2014
23
Consistent with experimental findings:As PH2O Decreases→ rougher crack wake → lower β→ lower minima
SAT2
2YSH2O
dNda
kEσf(R)
αNβ436
T1
fP
dNda
⎟⎠⎞
⎜⎝⎛
⎥⎦
⎤⎢⎣
⎡=
M
1.8 PaHigher β
0.2 PaLower β
2 3 4 5 6 7 8 9 10 11121314
10-7
10-6
10-5
10-4
10-3
AA 7075-T651--L-T
f = 20 Hz, C = -0.07 mm-1
Kmax = 16.5 MPa√m
T=16oC, Vacuum:0.25~0.50 μPa
T= 26oC, Water Vapor: 0.006 Pa
T= 26oC, Water Vapor: 0.053 Pa
T= 26oC, Water Vapor: 0.13 Pa
T= 26oC, Water Vapor: 0.26 Pa
T= 26oC, Water Vapor: 2.6 Pa
T= 23oC, Water Vapor: 2.4 kPa
T= 23oC, Water Vapor: 2.4 kPa
da/d
N, m
m/c
ycle
Applied ΔK, MPa√m
Constant Kmax of 16.5 MPa√mR ≈ 0.75 at dip
Constant R =0.5
≈5
≈4
P
1.8 Pa
0.13 Pa
Consistent with experimental findings:Minima occurs at lower ΔK and lower exposures for Constant Kmax
More open crack associated with higher R…
A more open crack requires more roughness to achieve the same level of flow impedance…
Consistent with experimental findings:Different loading histories results in changes in da/dN behavior in
molecular transport controlled regime.
( )Satcf
ysOH
cf dNda
MT
kTEd
RfNf
P
dNda
−
⎟⎠⎞
⎜⎝⎛
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛ 2
1
2
2
4362σ
αβ
Consistent with experimental findings:Thinner specimens → Decreased molecular flow distance
Original Flow Distance
New Flow Distance
8/29/2014
24
Consistent with experimental findings:Thinner specimens → Decreased molecular flow distance
→ faster da/dN
Original Flow Distance
New Flow Distance
As expected, thickness dependence only observed in molecular flow controlled regimeNot observed for High RH and UHV
2. What causes the subsequent rise?
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
This roughness leads to surface asperity contact during cycling
At constant CMOD
8/29/2014
25
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
This roughness leads to surface asperity contact during cycling
Transition from diffusion (Knudsen) controlled molecular flow to TURBULENT – GAS MIXING (Turnbull, Hartt)
Via Knudsen Flow Via Turbulent
Mixing
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
This roughness leads to surface asperity contact during cycling
Transition from diffusion (Knudsen) controlled molecular flow to TURBULENT – GAS MIXING (Turnbull, Haartt)
Turbulent mixing may increase the crack tip PH2O to near‐bulk levels
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
This roughness leads to surface asperity contact during cycling
Transition from diffusion (Knudsen) controlled molecular flow to TURBULENT – GAS MIXING (Turnbull, Haartt)
Turbulent mixing may increase the crack tip PH2O to near‐bulk levels
Increased tip PH2O leads to increased HEE;consistent with morphology change from SBC to flat TG
2. What causes the subsequent rise?
As ∆K continues to decrease, the area and proportion of SBC features in the crack wake increases
This roughness leads to surface asperity contact during cycling
Transition from diffusion (Knudsen) controlled molecular flow to TURBULENT – GAS MIXING (Turnbull, Haartt)
Turbulent mixing may increase the crack tip PH2O to near‐bulk levels
Increased tip PH2O leads to increased HEE;consistent with morphology change from SBC to flat TG
Thus an increase in da/dN!!!
8/29/2014
26
Is asperity contact in the crack wake feasible? Analysis Ongoing Yes!! Asperity contact in the crack wake is reasonable1. Comparing 3D fracture surface roughness to crack wake opening calcs
• 3D Crack wake roughness profiling • Fracture mechanics based crack wake opening displacement calculations
00.020.040.060.080.1
0.120.14
0 5 10 15 20
total displacem
ent (mm)
x (mm)
Crack Wake Profile with a crack length a=20 mm
Crack wake asperity ≈ 5‐20 μmCrack opening (at ‐500 μm) ≈ 5 μm
Yes!! Asperity contact in the crack wake is reasonable2. Use far‐field compliance‐based closure metrics to estimate the degree
of crack wake contact
2199-T860.2 Pa-sR=0.5
10
da/d
N (m
m/c
ycle
)
10-7
10-6
10-5
10-4
ACR
Rat
io
0.8
1.0
1.2
1.4
1.6
Kshed - 1
ACR Ratio = ΔKeffective / ΔKnominal
ΔK (MPa√m)
Yes!! Asperity contact in the crack wake is reasonable2. Use far‐field compliance‐based closure metrics to estimate the degree
of crack wake contact
2199-T860.2 Pa-sR=0.5
10
da/d
N (m
m/c
ycle
)
10-7
10-6
10-5
10-4
ACR
Rat
io
0.8
1.0
1.2
1.4
1.6
Kshed - 1
ACR Ratio = ΔKeffective / ΔKnominal
ΔK (MPa√m)
So What?How does this data and mechanistic understanding impact
fracture mechanics modeling?
8/29/2014
27
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
(a) Environmentally Induced False Threshold!!!
Common experimental stopping point
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
(a) Environmentally Induced False Threshold!!!
Failure to recognize the “apparent threshold” behavior
could lead to highly non‐conservative LEFM predictions
Common experimental stopping point
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
(a) Environmentally Induced False Threshold!!!
Failure to recognize the “apparent threshold” behavior
could lead to highly non‐conservative LEFM predictions
Options for mitigation:‐ K‐rise confirmation‐ Fractography‐ Testing to low da/dN
Common experimental stopping point
8/29/2014
28
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
(b) Component Geometry Influences Molecular Flow Path!!!
Similitude is compromised; Despite same ΔK
≠
Mechanistic understanding provides critical insights into the necessary loading protocol to characterize environmental fatigue
(b) Component Geometry Influences Molecular Flow Path!!!
Options for mitigation:Test specimens should be representative (similar flow path) of the component to
be modeled
Similitude is compromised; Despite same ΔK
≠
Significant increases (5‐10X) in LEFM predicted fatigue performance at exposures relevant to cruise altitude
Significant increases (5‐10X) in LEFM predicted fatigue performance at exposures relevant to cruise altitude
Format for LEFM Input
Mechanistic understanding of the dip informs the conservative assumption that the “dip” behavior
should be excluded from modeling
8/29/2014
29
Significant increases (5‐10X) in LEFM predicted fatigue performance at exposures relevant to cruise altitude
50
100
150
200
250
300
350
400
450
500
100 1000 10000 100000 1000000 10000000
Max Stress (MPa
)
Cycles to 1.5mm
AFGROW PredictionsSingle Corner Crack at HoleR=0.5; a=250µm, c=250µm
1334 Pa‐s0.2 Pa‐s0.027 Pa‐sUHV
LEFM Code (AFGROW)
Cruise Altitude(40,000 –60,000 ft)
Format for LEFM Input
Next Steps: Research
Next Steps: Research
Temp (oC) 23 ‐4 ‐15 ‐30 ‐37 ‐50 ‐57 ‐65 ‐73 ‐90Vacuum
PH2O/f (Pa‐s)133 17 8.25 1.9 0.9 0.2 0.09 0.027 0.009 UHV
Compare 23C‐Vacuum results with Low Temperature behavior at the same PH2O‐ICE (Burns/ALCOA)
1.9 Pa‐s23C, Vacuum
1.9 Pa‐s‐30C
Next Steps: Research
Temp (oC) 23 ‐4 ‐15 ‐30 ‐37 ‐50 ‐57 ‐65 ‐73 ‐90Vacuum
PH2O/f (Pa‐s)133 17 8.25 1.9 0.9 0.2 0.09 0.027 0.009 UHV
Compare 23C‐Vacuum results with Low Temperature behavior at the same PH2O‐ICE (Burns/ALCOA)
1.9 Pa‐s23C, Vacuum
1.9 Pa‐s‐30C
Temperature effect on either:Surface Reaction, Diffusion,
Dislocation Dynamics
8/29/2014
30
Next Steps: Research
Temp (oC) 23 ‐4 ‐15 ‐30 ‐37 ‐50 ‐57 ‐65 ‐73 ‐90Vacuum
PH2O/f (Pa‐s)133 17 8.25 1.9 0.9 0.2 0.09 0.027 0.009 UHV
Compare 23C‐Vacuum results with Low Temperature behavior at the same PH2O‐ICE (Burns/ALCOA)
FIB then TEM deformed structure, 20 to 200 nm under facet surface…Collaboration with I. Robertson
Al‐Cu‐Mg‐Mn(T351)
Moist Air
Gangloff, Ro
Dislocation Dynamics Behavior Studied via:
Next Steps: Application
Next Steps: Application
Supporting transition efforts with the listed collaborators:‐ Develop coupled load‐environment spectra (USAFA)
US Coast Guard; C‐130H
temperature
pressure
humidity
Mechanical Loading Spectrum Environmental Loading Spectrum
Time (s)
Next Steps: Application
Supporting transition efforts with the listed collaborators:‐ Develop coupled load‐environment spectra (USAFA)‐ Enhance LEFM software for Environmental‐Fatigue predictions
(SAFE/AFGROW)
+ Environmental Condition
8/29/2014
31
Next Steps: Application
Supporting transition efforts with the listed collaborators:‐ Develop coupled load‐environment spectra (USAFA)‐ Enhance LEFM software for Environmental‐Fatigue predictions
(SAFE/AFGROW)
‐ Investigate the effect of environmental and loading transients on the growth rate response (ALCOA/Airbus)
temperature
pressure
humidityTime (s)
Next Steps: Application
Supporting transition efforts with the listed collaborators:‐ Develop coupled load‐environment spectra (USAFA)‐ Enhance LEFM software for Environmental‐Fatigue predictions
(SAFE/AFGROW)
‐ Investigate the effect of environmental and loading transients on the growth rate response (ALCOA/Airbus)
‐ Support data generation for different alloys and flight conditions (ALCOA, Airbus, SAFE, A‐10 SPO)
Conclusions
1. Unprecedented data base developed for 7075 and 2199 showing increased fatigue resistance with decreasing exposure
Conclusions
1. Unprecedented data base developed for 7075 and 2199 showing increased fatigue resistance with decreasing exposure
2. At intermediate exposures and ΔK, a novel dip in fatigue crack growth rates was observed and understood via a molecular flow argument
8/29/2014
32
Conclusions
1. Unprecedented data base developed for 7075 and 2199 showing increased fatigue resistance with decreasing exposure
2. At intermediate exposures and ΔK, a novel dip in fatigue crack growth rates was observed and understood via a molecular flow argument
3. This work has outlined the considerations necessary to develop a testing protocol for environment assisted cracking (full ΔK ranges)• Test to below this threshold so predictions are conservative• The thickness is important due to it being the dominant flow distance
Conclusions
1. Unprecedented data base developed for 7075 and 2199 showing increased fatigue resistance with decreasing exposure
2. At intermediate exposures and ΔK, a novel dip in fatigue crack growth rates was observed and understood via a molecular flow argument
3. This work has outlined the considerations necessary to develop a testing protocol for environment assisted cracking (full ΔK ranges)• Test to below this threshold so predictions are conservative• The thickness is important due to it being the dominant flow distance
4. Incorporating the generated data into simple constant amplitude fracture mechanics modeling show a 5‐10x increase in lifetime
Collaborators –Students/PDRA: J. Jones, S. Winston, A. Lass, J. Ai
Colleagues: R. Bush, R. Gangloff, S. Agnew, A. Turnbull, S. Fawaz
Funding –USAFA‐TCC (Hayes/Dunmire); ALCOA (Warner/Bray)
Acknowledgments
Questions??
Collaborators –Students/PDRA: J. Jones, S. Winston, A. Lass, J. Ai
Colleagues: R. Bush, R. Gangloff, S. Agnew, A. Turnbull, S. Fawaz
Funding –USAFA‐TCC (Hayes/Dunmire); ALCOA (Warner/Bray)
Acknowledgments
8/29/2014
33
The Effect of Microstructure on the HEAC of Monel K‐500
James T. Burns (J. Dolph)John R. Scully (B. Rincon‐Troconis, H. Ha)
Department of Materials Science and EngineeringUniversity of Virginia
UVa‐MSE SeminarAug 2014
EXAMPLE
Monel K‐500 Long Life (10yr) Service Failures in Marine Cathodic
Polarization Conditions
State of the Art/High Fidelity Experimental Characterization
Cracking(Burns)
E‐chem (Scully)State of the Art/High Fidelity Experimental Characterization
Cracking(Burns)
E‐chem (Scully)
Generates Novel and Critical Data
Gangloff, Burns, Scully; 2014
8/29/2014
34
UVa:SEM, EBSD, EDS
UVa‐NMCF Characterization and Collaborations Provide Insights into How Metallurgy/Electrochemisty Influences Cracking Behavior
Burns, Scully
0 300 600 900 1200 1500
Arb
itrar
y un
it
Energy (eV)
Al
SCl
C
O
Ni
NiCu
Cu
Al
CuNi
CuNi
UVa‐NMCF Characterization and Collaborations Provide Insights into How Metallurgy/Electrochemisty Influences Cracking Behavior
0 2 4 6 8 10 12 14 16 18 200
2
4
6
8
Nor
mal
ized
%
Depth (nm)
S Ni Cu C
UVa:SEM, EBSD, EDS
Collaborators:FIB, TEM, STEM, Auger
Case Western
U Wisconsin (Robertson), U Manchester (Burnett)
Burns, Scully
Data are coupled to 1. Inform/evaluate micro‐mechanical models
0 200 400 600 800 1000 1200 1400
0
20
40
60
80
100
120
140
160
0
20
40
60
80
100
120
140
160
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
Stress Enhanced Crack Tip Diffusible H Concentration, CHσ (wppm)
Threshold Stress In
tensity
(M
Pa√m
)
Threshold Stress In
tensity
(MPa
√m)
Crack Tip Diffusible H Concentration, CH‐DFF (wppm)
ATI Allvac
Special Metals
Model Predicted
Low alpha (6.0)
High alpha (12.0)
Monel K‐5003.5% NaClTDS H Uptake (ATI Allvac)α = 7.3 MPa√m (at frac H)‐1
kIG = 0.65 MPa√m
⎥⎦
⎤⎢⎣
⎡ ⋅−=
YS
2HσIG
TH σα")Cα(kexp
β'1K
Gangloff, Burns, Scully; 2014
Data are coupled to 1. Inform/evaluate micro‐mechanical models
2. Provide insights into the controlling failure mechanisms0 200 400 600 800 1000 1200 1400
0
20
40
60
80
100
120
140
160
0
20
40
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140
160
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0
Stress Enhanced Crack Tip Diffusible H Concentration, CHσ (wppm)
Threshold Stress In
tensity
(M
Pa√m
)
Threshold Stress In
tensity
(MPa
√m)
Crack Tip Diffusible H Concentration, CH‐DFF (wppm)
ATI Allvac
Special Metals
Model Predicted
Low alpha (6.0)
High alpha (12.0)
Monel K‐5003.5% NaClTDS H Uptake (ATI Allvac)α = 7.3 MPa√m (at frac H)‐1
kIG = 0.65 MPa√m
⎥⎦
⎤⎢⎣
⎡ ⋅−=
YS
2HσIG
TH σα")Cα(kexp
β'1K
Robertson, et al (2012)
FIBSEM
TEM
Combined HELP/HEDE Mechanism
• Crack tip dislocation cell structure favors H trapping proximate to grain surface
• Cell structure promotes locally high work hardening to support high normal stress
• H decohesion is enabled
8/29/2014
35
‐850 mVSCE versus ‐1000 mVSCE
Mechanistic understanding is then used to inform engineering level alloy selection and structural management decisions…
SCCrack (LEFM Code)
0
10
20
30
40
50
60
1.E+00 1.E+02 1.E+04 1.E+06 1.E+08
Inial K (M
Pa√m
)
Time to Failure (h)
Monel K‐500 (DCT); Initial K vs. TTF
‐850 mVsce
‐1000 mVsce
Gangloff/VEXTEC
‐850 mVSCE versus ‐1000 mVSCE
Mechanistic understanding is then used to inform engineering level alloy selection and structural management decisions…
SCCrack (LEFM Code)
0
10
20
30
40
50
60
1.E+00 1.E+02 1.E+04 1.E+06 1.E+08
Inial K (M
Pa√m
)
Time to Failure (h)
Monel K‐500 (DCT); Initial K vs. TTF
‐850 mVsce
‐1000 mVsce
Has this concept worked??‐ LEFM‐based simulation used to help justify modification of the USN cathodicprotection system protocol
‐Burns, Bayles (NRL), Knudsen (NRL)
‐ Evaluation of next generation replacement alloy MP‐98T ‐Burns, Scully, Horton (NRL)
‐ Transition testing and modeling techniques to industry and DoD labs ‐Burns, Gangloff ‐ DoD ‐Waldman (NAVMAR), Knudsen/Lee (NRL), Frazier (NAVAIR), Graham (USN)‐ Industry/Academia ‐ Plotner (WMTL), Webler (CMU)