Task 5: Environment Effects in Component Cracking Prediction for

DoD Applications FATIGUE

James Burns (UVa) Scott Fawaz (SAFE)

University of Virginia TCC Semi-Annual Review

July 2012

Pre-existing Corrosion Degradation

High Altitude/Cold /Dry

Low Altitude/Warm/Moist/NaCl

Loading Environment Effects

Inhibitors

Pre-existing Corrosion Degradation

High Altitude/Cold /Dry

Low Altitude/Warm/Moist/NaCl

Loading Environment Effects

Inhibitors

Steps for Technical Transition of Lifing Methods: 1. Laboratory based technical understanding

2. Develop engineering methods - Rigorous, Simple to Implement, and Lab Validated

3. Inform ASIP community of benefits – Gather feedback on practical technical issues

4. Interface with ASIP community (directly or through DoD Lab/Small Business) to support field level validation/integrate methods in ASIP framework

Result: Engineering tool for TARGETED environment induced

issues – Increased Safety, Reduced Over-conservatism

Objectives (1) Integrate corrosion topography into DTA/AFGROW framework for fatigue (2) Account for loading environment in fatigue (low-temperature, inhibitors,

etc.)

Deliverables

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

(4) Environmental Fatigue and Fracture education Academic (USAFA) and SPO modules

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

- Hill AFB – Mark Thomsen - Strong interest in the influence of low temperature growth rate for 2024

- Testing matrix has been proposed and logistics are being arranged.

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

- Hill AFB – Mark Thomsen - Strong interest in the influence of low temperature growth rate for 2024

- Testing matrix has been proposed and logistics are being arranged. - Patuxent River Naval Air Station – Bill Nickerson, Craig Matzdorf, P. Rusk

- Strong overlap of interest with pit-to-crack modeling (Rusk) - No concrete action taken

- Strong interest in the Task 1 CF testing protocol - RFP issued by ONR (Nickerson) and will be submitted by Aug 2012

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

- Hill AFB – Mark Thomsen - Strong interest in the influence of low temperature growth rate for 2024

- Testing matrix has been proposed and logistics are being arranged. - Patuxent River Naval Air Station – Bill Nickerson, Craig Matzdorf, P. Rusk

- Strong overlap of interest with pit-to-crack modeling (Rusk) - No concrete action taken

- Strong interest in the Task 1 CF testing protocol - RFP issued by ONR (Nickerson) and will be submitted by Aug 2012

- Air Force Research Laboratory – K. Jata, J. Larsen - Discussions of joint AFRL/UVa collaborations for validation/transition

testing and serving as a conduit to SPO – interest but no concrete action - Collaboration regarding environmental fatigue mechanistic work

- UVa experimentation/AFRL characterization (FIB, TEM, etc) - Student internship – interest but no concrete action

- NASA-Langley Research Center – S. Smith, E. Glaessgan - Strong interest in a collaboration looking at low temperature fatigue and

coupling UVa environmental fatigue expertise with NASA-LaRC computation and characterization expertise. - Actively pursuing joint funding opportunities – ARO, ONR

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

- NASA-Langley Research Center – S. Smith, E. Glaessgan - Strong interest in a collaboration looking at low temperature fatigue and

coupling UVa environmental fatigue expertise with NASA-LaRC computation and characterization expertise. - Actively pursuing joint funding opportunities – ARO, ONR

- Monash University/DSTO – Rhys Jones, Loris Molent (no visit) - Small crack growth from corrosion at various loading levels - Technical collaboration topics and joint publication outlined

- Implementation into prognosis framework - MU work beginning, UVa/CAStLE participation level TBD based on funding

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

- NASA-Langley Research Center – S. Smith, E. Glaessgan - Strong interest in a collaboration looking at low temperature fatigue and

coupling UVa environmental fatigue expertise with NASA-LaRC computation and characterization expertise. - Actively pursuing joint funding opportunities – ARO, ONR

- Monash University/DSTO – Rhys Jones, Loris Molent (no visit) - Small crack growth from corrosion at various loading levels - Technical collaboration topics and joint publication outlined

- Implementation into prognosis framework - MU work beginning, UVa/CAStLE participation level TBD based on funding

- ALCOA – Gary Bray, Jen Warner - Low temperature fatigue behavior pertinent to alloy development and

airframe lifing - Continued collaboration; Student internship

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

- Application of pit-to-crack methodology to Abbott beach exposed specimens

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

- Application of pit-to-crack methodology to Abbott beach exposed specimens

- Loading conditions (3 specimens each) - 66.7 MPa (Kt = 3) - CA (R=0.5 w/MB) and VA (Mini-TWIST) - High Humidity

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

- Application of pit-to-crack methodology to Abbott beach exposed specimens

- Loading conditions (3 specimens each) - 66.7 MPa (Kt = 3) - CA (R=0.5 w/MB) and VA (Mini-TWIST) - High Humidity

- Characterization - Fractography

- Morphology/MB crack progression - Pit nucleation feature (XR Tomo, cross-section, fracture surface, etc)

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

- Application of pit-to-crack methodology to Abbott beach exposed specimens

- Loading conditions (3 specimens each) - 66.7 MPa (Kt = 3) - CA (R=0.5 w/MB) and VA (Mini-TWIST) - High Humidity

- Characterization - Fractography

- Morphology/MB crack progression - Pit nucleation feature (XR Tomo, cross-section, fracture surface, etc)

- Analysis/Validation - CM-EIFS comparison to previously established from no hole - Are initiating features aligned with previous broad surface work - Tracking crack growth initiated from multiple corrosion sites

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

- Application of pit-to-crack methodology to Abbott beach exposed specimens

- Loading conditions (3 specimens each) - 66.7 MPa (Kt = 3) - CA (R=0.5 w/MB) and VA (Mini-TWIST) - High Humidity

- Characterization - Fractography

- Morphology/MB crack progression - Pit nucleation feature (XR Tomo, cross-section, fracture surface, etc)

- Analysis/Validation - CM-EIFS comparison to previously established from no hole - Are initiating features aligned with previous broad surface work - Tracking crack growth initiated from multiple corrosion sites

Progress: - 3rd Year UG student training complete (D. Bae)

- Fracture mechanics testing, SEM validation

- Specimen environment cell complete

- Marker-band protocol validated (dummy sample/SEM)

- Corroded specimen testing to begin in Aug 2012

(4) Environmental Fatigue and Fracture education Academic (USAFA) and SPO modules

- Syllabus for a 9 topic sequence on “Environmental Effects on Structural Integrity” submitted and approved by USAFA

- Great Failures and Environmental Cracking - Electrochemical Basics - Fatigue and Fracture Mechanics Basics - Effect of Corrosion on Fatigue - Environmental Fatigue - Internal Hydrogen Embrittlement - Laboratory (as student team project) - Computer Simulation and Life Prediction (as student team project)

- Incremental progress toward completion - Logistical plan has been formed and is being implemented.

Future Work

- Engagement - Follow up with DoD agencies that have expressed interest

but have not produced actionable progress - Submit abstract to present ICAF Conference

- Engage additional agencies looking for targeted application

- Validation - Complete corroded testing, characterization and modeling

- Incorporation into LEFM codes - Use Task 2-4 results to work with AFGROW personnel to

incorporate environmental effects in software program

Questions??

Damage Tolerant Approach to Pre-existing Corrosion

Major Hurdles… 1. Crack Formation Life?

-Coffin/Manson (SWT) Approach

High Fidelity Validation of

Existing Engineering Techniques Applied

to Corrosion Damage

Major Hurdles… 1. Crack Formation Life? 2. Low ΔK da/dN?

Extrapolation??

Trend

Damage Tolerant Approach to Pre-existing Corrosion

Major Hurdles… 1. Crack Formation Life? 2. Low ΔK da/dN? ?

Trend

Marker-band Data

AFGROW Successful Paris Law

(Long Crack) Extrapolation to

Predict Small Crack Progression

Sophisticated Mechanics

Simple 2D Approach

Damage Tolerant Approach to Pre-existing Corrosion

CM-EIFS

Major Hurdles… 1. Crack Formation Life? 2. Low ΔK da/dN? 3. Initial Flaw Size?

• CM-EIFS Approach

Corroded “Material Property” • Back Calculation from Np

• Appropriate: a/c, σ, da/dN • Stress Independent CM-EIFS Distribution

• Then…Forward Predict Remaining Life • For other σ, da/dNenvironment – Successful!

Damage Tolerant Approach to Pre-existing Corrosion

– Validation on non-laboratory corrosion samples • Planned: Fatigue and modeling on Abbott-Daytona exposed 7075 specimens

(UVA Student - Douglas Bae – 2nd Year MSE) – Testing at CA and VA loading coupled with corrosion characterization

– Pursue ASIP community PARTNER; identify components suitable for validation/demonstration of these technologies

• Complete: Engage new AFRL initiative (Jata); ONR Structures (Vasudevan) • Planned: 13 Jan - Hill AFB (A-10, F-16, Landing Gear) • Future: Visit WR-ALC personnel (F-15, C-130, C-5), Present at ASIP

Conference – Perform component level validation and component demonstration

(non-funded) • Future : Obtain corroded stress critical component; apply methodology -

characterization, load specific prediction, lab testing, validation… • Future: Apply methods to TARGETED corroded area to increase MC

– Work with AFGROW personnel to enhance fatigue crack formation capabilities

• Planned: Funding included in proposal

Needs/Actions for Transition

Structural Life Predictions (DTA and Safe-Life)

use Ambient Air Material Properties,

HOWEVER…

Real World Loading Environments = Low T, Low PH2O, Salt Spray, Inhibitor-

Laden Coatings, etc.

Large Environment Dependence!!!

Mo Inhibitor

– Further develop maturity of technical understanding • Planned: Task 2-4 – Tech challenges/details discussed elsewhere

– Identify the true environment-load spectra experienced in airframe structures

• Planned: Analysis of USCG C-130 data; Solicit ASIP/SPO input • Planned: Task 2 – Specifics of inhibitor leaching from coatings

– Inform ASIP of tools to model the strong environmental effects • Complete: Engage new AFRL initiative (Jata); ONR (Vasudevan) • Planned: 13 Jan - Hill AFB (A-10, F-16, Landing Gear) • Future: Visit WR-ALC personnel (F-15, C-130, C-5), Present at ASIP

Conference

– Work with AFGROW personnel to incorporate stream-lined capabilities

• Planned: Funding included in proposal

Needs/Actions for Transition

NOTE: ALCOA Collab for complimentary aspects of Env-Fatigue (low T, CM-EIFS, etc)

Objectives (1) Incorporate corrosion into DTA/AFGROW framework for fatigue (2) Account for loading environment in fatigue (low-temperature, inhibitors,

etc.)

Deliverables

(1) Engage ASIP community to inform of the methods and benefits of incorporating corrosion and environment into structural life prediction

(2) Probe ASIP community on targeted application for infield demonstration and validation of these concepts

(3) Support development of environmental fatigue algorithms and their integration into software and prognosis tools by providing scientific basis to justify assumptions and methodologies.

(4) Environmental Fatigue and Fracture education USAFA - Eight 55 min PPT academic modules Program Office – Short course development

Aircraft Applicability? CM-EIFS from EITHER… • Service exposed coupon

• Fatigue-life PLATEAU: independent of corrosion morphology and severity

• Upper-bound CM-EIFS

OR

~300 x 900 µm b/c in all cases

fatigue life controlled by

severe pit clusters