Corrosion Modeling Beyond Crevice Corrosion Presented by David W. - - PowerPoint PPT Presentation

D.W. Hoeppner FASIDE

Corrosion Modeling Beyond Crevice Corrosion

Presented by

David W. Hoeppner, P.E., Ph.D. FASIDE International Incorporated 1146 S. Oak Hills Way Salt Lake City, UT 84108-2026 May 1998

D.W. Hoeppner FASIDE

Outline of Presentation

I

• Introduction
• The Degradation Process
• Methods of Each Life Phase
• Brief Discussion about Review Report
• Report Conclusions and Recommendations

D.W. Hoeppner FASIDE

II

• Brief Discussion About My Visit to Boeing Seattle

III

• Experimental Details
• Observations from Experiments
• Video Clips

Outline of Presentation (Continued)

D.W. Hoeppner FASIDE

Next Three Slides

• - Phases of Life
• - The Degradation Process
• - Methods for Each Life Phase

D.W. Hoeppner FASIDE

Corrosion and Corrosion Fatigue Predictive Modeling - State of the Art Review Introduction-Review Report Section 1 - Corrosion in Aircraft Structural Aluminum Alloys Section 2 - Pitting Corrosion Section 3 - Microstructure and Environment Effects on “Short” Crack Behavior of Materials Section 4 - Conclusions and Recommendations

D.W. Hoeppner FASIDE

The review of the literature clearly shows that much progress has been made

• n modeling the effects of corrosion on material behavior and structural

integrity. It is clear that to date the models have centered around characterizing the corrosion and modeling the effects of the corrosion as

• ne or more of the following:
• section change that affects the area/volume that modifies the stress.
• nucleation of localized debris that may modify the stress (part of pillowing)

that modifies the stress or stress intensity.

Report Conclusions and recommendations

D.W. Hoeppner FASIDE

• nucleation of intergranular corrosion that is involved in pillowing that

modifies the stress or stress intensity.

• nucleation of localized corrosion (pitting, fretting, etc..) that modifies

the local stress and may ultimately nucleate cracks.

• production of products of corrosion that produce localized embrittlement

effects that may alter the material behavior and produce accelerated crack propagation.

Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• Even though fracture mechanics based modeling

has been extremely useful in modeling the effects

• f corrosion it has taken many simplifications and,

depending on the manner in which the fracture mechanics is used in the model, has resulted in downgrading the real characterization issue and understanding the 3-D nature of the corrosion degradation process. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• New tools and models will have to be brought to bear
• n the nucleation and growth of the corrosion with or

without load of either sustained (SCC) or cyclic nature (EANC/F)-(Environmentally-assisted nucleation and cracking with fatigue loading).

• Furthermore the transitions of corrosion to actual

cracks will have to be understood to improve the models that currently exist and any new ones that may be developed. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• In addition, the efforts currently underway in other

portions of the NCI Information systems, efforts at

• U. Of Virginia under the leadership of Dr. Kelly and

those at Vanderbilt University under the leadership of

• Dr. Wikswo and some of the internal NCI efforts may

provide additional insight into the characterization issue. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• From the work of L. Grimes at Utah and the effort

underway at U. Virginia, as well as additional efforts at the U. of Utah, the use of the confocal microscope will be of great assistance in characterizing the three-dimensional (3-D) surface “damage” that results from corrosion of various forms. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• Some recent work at Lehigh University on the

characterization of pits also will be useful. These efforts must be developed further to enhance the models and their development. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

• The characterization of chemically dependent short

crack propagation and modeling of it will have to be much better understood.

• The efforts of Dr. Piascik and Dr. Newman and those

at Utah will have to be expanded to enhance this area as well as the transition to cracking. Report Conclusions and recommendations (Continued)

D.W. Hoeppner FASIDE

My Visit to Boeing, Seattle (3/27/98)

Attendees:

• Michael Hyatt, Associate Technical Fellow, Materials Technology
• Girindra K. Das, Ph.D., Principal Engineer, Structures Technology Support
• Roy T. Watanabe, Supervisor, Structures Technology Support
• Ulf Goranson, Ph.D., Chief Engineer, Structures Laboratories &

Technology Standards

• David W. Hoeppner, P.E., Ph.D., University of Utah.

D.W. Hoeppner FASIDE

My Visit to Boeing, Seattle (3/27/98) - Continued Purpose: Determine the method that Boeing Commercial Airplane Group uses for dealing with corrosion; current work underway; and plans for future work.

D.W. Hoeppner FASIDE

My Visit to Boeing, Seattle (3/27/98) - Continued Discussion:

• Depend on Timely Detection
• Have A Model of Fleet Experience
• Do Not Do Allowables in Environment Except Crack

Growth

• Don’t Know How to Handle Corrosion Fatigue
• Have No Work Underway
• No Work Is Planned
• They Are Doing Limited Work On CPCP

D.W. Hoeppner FASIDE

My Visit to Boeing, Seattle (3/27/98) - Continued Conclusion:

• Reliance On Experience
• Depend On Inspectors/NDI
• Have No Models
• Depend On Finding All Level II & Level III Corrosion

D.W. Hoeppner FASIDE

Model Extensions And Revision

• Currently Underway

D.W. Hoeppner FASIDE

EXPERIMENTAL DETAILS

Objective To correlate the fatigue life of specimens with respect to the loss of material resulting from corrosion damage Material Used -- 2024-T3 Aluminum Alloy

D.W. Hoeppner FASIDE

• Prior crevice corrosion damage was produced using

technique as per ASTM G 48-92.

• EXCO solution was used as per ASTM G34-97.
• Exposure time of specimens in EXCO solution was

varied to attain different degree of corrosion.

• Specimen weight was measured before and after

exposure to EXCO Solution to characterize loss of material.

• Fatigue tests were performed at max. stress levels

ranging from 6 ksi to 24 ksi.

EXPERIMENTAL DETAILS (Continued)

D.W. Hoeppner FASIDE

EXPERIMENTAL DETAILS (Continued)

Specimen # Material Loss (g) Material Loss %

• Max. Stress (Ksi)

Cycles to Failure (N)

1 0.005 0.17 24 1500 2 0.019 0.64 12 3500 3 0.0003 0.009 6 750000* 4 0.034 1.1 10 178360 5 0.0004 0.01 20 51600 6 0.0007 0.02 10 469800* 7 0.003 0.1 12 38400 8 0.0007 0.02 20 50900** 9 0.0001 0.003 20 138500***

* Did not fracture. Test stopped. ** Max. Stress level reduced to 10 ksi after 40,000 cycles. ***Max. Stress level was reduced to 10 ksi after 120000 cycles. Note: Test frequency was 10 Hz except when crack propagation was recorded in higher magnification the frequency was reduced to 1 Hz.

D.W. Hoeppner FASIDE

OBSERVATION FROM EXPERIMENTS

• The More the loss of material the lower is the fatigue life of specimens.
• Multiple cracks were observed to form from corrosion damages.
• Although several cracks were observed to form, the lead crack that

caused failure was the one that formed from the edge (of the specimen) corrosion damage.

D.W. Hoeppner FASIDE

VIDEO CLIP 1* (Macro View)

• Material - 2024-T3 Aluminum Alloy-Specimen was prior corroded.
• Max. Stress Level 20 ksi.
• Frequency 10 Hz.
• Material Loss - 0.0004g; %Loss by weight 0.01
• Crack was observed to form from corrosion damage at the bottom edge
• f the specimen after 49800 cycles.
• In about 1800 cycles the crack propagated resulting in fracture of the
• specimen. Fractured in 51600 cycles.

* Reference to specimen# 5

D.W. Hoeppner FASIDE

VIDEO CLIP 2*

* Reference to specimen# 8

• Material - 2024-T3 Aluminum Alloy-Specimen was prior corroded.
• Max. Stress Level 20 ksi.
• Frequency 10 Hz.
• Material Loss - 0.0007g; %Loss by weight 0.02
• Crack was observed to form from corrosion damage at the bottom edge
• f the specimen after 40000 cycles. Frequency and the max. stress level were

decreased to 1Hz and 10 ksi respectively.

• Multiple cracks from corrosion damages were noted. Fractured in

50900 cycles

D.W. Hoeppner FASIDE

VIDEO CLIP 3*

* Reference to specimen# 9

• Material - 2024-T3 Aluminum Alloy-Specimen was prior corroded.
• Max. Stress Level 20 ksi.
• Frequency 10 Hz.
• Material Loss - 0.0001g; %Loss by weight 0.003
• “Small” cracks in the order of 0.1mm were observed to form from corrosion

damages at the top as well as from bottom edges and other places of the specimen after 20000 cycles. Test continued. After 120000 cycles, propagation

• f crack from bottom edge corrosion damage was noted.
• Then, Frequency and the max. stress level were decreased to 1Hz and

10 ksi respectively.

• Three “Large” cracks that were parallel to each other were observed but the
• ne that formed from the bottom edge of the damage was found to be the

lead crack that caused fracture of the specimen.

• Multiple cracks from corrosion damages were noted. Fractured in

138500 cycles.

D.W. Hoeppner FASIDE

Current And Future Work

• Effort on Model Revisions Is Underway
• Energy And Damage Mechanics Approaches Are To Be

Pursued.

• Additional Contacts Are Planned Regarding Current

Models And Modeling Efforts