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
Outline of Presentation (Continued) II • Brief Discussion About My Visit to Boeing Seattle III • Experimental Details • Observations from Experiments • Video Clips D.W. Hoeppner FASIDE
Next Three Slides -- Phases of Life -- The Degradation Process -- Methods for Each Life Phase D.W. Hoeppner FASIDE
Introduction-Review Report Corrosion and Corrosion Fatigue Predictive Modeling - State of the Art Review 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
Report Conclusions and recommendations The review of the literature clearly shows that much progress has been made on 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 one 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • Even though fracture mechanics based modeling has been extremely useful in modeling the effects of 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • New tools and models will have to be brought to bear on 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • 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. D.W. Hoeppner FASIDE
Report Conclusions and recommendations (Continued) • 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. 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
EXPERIMENTAL DETAILS (Continued) • 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. 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*** Note: Test frequency was 10 Hz except when crack propagation was recorded in higher magnification the frequency was reduced to 1 Hz. * Did not fracture. Test stopped. ** Max. Stress level reduced to 10 ksi after 40,000 cycles. D.W. Hoeppner ***Max. Stress level was reduced to 10 ksi after 120000 cycles. 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 of 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* • 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 of 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 * Reference to specimen# 8 D.W. Hoeppner FASIDE
VIDEO CLIP 3* • 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 of 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 one 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. * Reference to specimen# 9 D.W. Hoeppner FASIDE
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