2012 1 7 1 January 2012 Vol. 7 No. 1 1 1 2 1 1. 100095 2. 448035 V215. 5 O346. 2 1673-6214 2012 01-0050-07 A doi 10. 3969 /j. issn. 1673-6214. 2012. 01. 012 Advance in Fatigue Life Prediction Techniques for Pre- corroded Aluminium Alloy CHEN Bo 1 LIU Jian-zhong 1 WANG Hao-wei 2 MA Shao-jun 1 1. Beijing Institute of Aeronautical Materials Beijing 100095 China 2. China Special Vehicle Research Institute Hubei Jingmen 448035 China Abstract Corrosion especially pit corrosion is a key problem facing aluminium aircraft structures. Prediction of the fatigue life of pre-corroded aluminum alloy is critical to the safety of aged aircrafts. In this paper the fatigue life prediction techniques for pre-corroded aluminum alloy were discussed and summarized. And main analysis models for fatigue life prediction based on fracture mechanics and their critical techniques were introduced in detail. Key words pre-corrosion pit corrosion fatigue life prediction fracture mechanics 0 1 1 Goswami 3 7 1 2 85% 8% 2 4 2011 3 29 2011 8 6 1977 -
1 51 Pit nucleation Pit growth Short crack growth Long crack growth t t Transition t Transition t Fracture pn pg sc tc for pit to from short short crack to long growth crack t Fig. 1 1 7 Seven stages of pitting corrosion fatigue life Gruenberg 4 4 4a 4b 2024-T3 3 3 Leek Howard 3 4c 4a FASTRAN 2 2 4b 4c 5 Cycles to Failure 10 5 6.0 5.0 4.0 2.0 20 ksi LT(e) L(e) 26 ksi LT(s) LT(e) Experiment Prediction 32 ksi LT(e) Load Direction Fracture Surface Randomly Distributed Pits Single Semi elliptical Surface Crack Develops at a Pit Some 鄄 where on the Corroded Face K t Effect Negligible (K t<5) Crack 0 2 Hours of Corrosion Exposure Corroded Face Pit Fig. 2 Predicted fatigue life and experimental results Sankaran 2 Initial Crack Dimension= 7075 3 Average or Maximum Pit Size AFGROW Corroded Face Length DuQuesnay 5 Sankaran 3 Fig. 3 7075 Medved 6 Propagating Crack Ciack 7475 Walde 7 Depth Schematic illustration of the assumption used in the modeling of fatigue crack growth and life prediction 2
52 7 2. 1 a Growth of only the largest nucleating pit Sankaran 2 6 96 h b Growth of all nucleating pits without connection between each other Maximum Stress /MPa 500 450 400 350 300 250 200 10 3 10 4 10 5 10 6 Fatigue Life /cycles Average Fatigue Life 10 5 3.5 2.5 2.0 1.5 0.5 0 LT,138MPa, 6 h Fig. 5 Legeng: Measured life(specimens exposed for 96 h in prohesion spray) Predicted life (average pit size of specimens exposed for 96 h in prohesion spray) c Growth of all nucleating pits Predicted life (maximum pit size of specimens 4 exposed for 96 h in prohesion spray) Measured life (non-corroded specimens) Fig. 4 Three prediction models for LT30 5 LT,138MPa, 24 h LT 180 MPa 24 h Experimental Method 1:Single Largest Nucleating Pit Method 2:All Nucleating Pits and Nonnuc leating Pits Method 3:All Nucleating Pits 6 h 24 h 6 h 24 h LT,220MPa, LT,220MPa, 6 h 24 h Average experimental life and predicted life Gruenberg 4 8 2 Gruenberg 6 96 h Fig. 6 Predicted and measured fatigue life of 7075-T6 pre-corroded for 96 h DuQuesnay 5 7075 2 mm 1. 5 mm 2. 5 mm 7 Lankford 8 Newman 9
1 53 10 Crack Length of 1.27 mm Cumulative Distribution of Numer of Cycles to Reach a SFH,PFH 10 4 4.0 3.5 2.5 2.0 1.5 0.5 Experiment AFGROW(2c=2.0 mm) AFGROW(2c=1.5 mm) AFGROW(2c=2.5 mm) Empirical Trend 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Pit Depth, a /mm Cumulative Density Function F /N 0.8 0.6 0.4 0.2 0 0.5 1.5 2.0 2.5 10 5 cycles Weibull CDF(AFGROW Data) AFGROW TTCL 1.27mm-c Experimental TTCL 1.27mm-c 7 Fig. 7 (a) (b) (c) Fig. 8 AFGROW Comparison of AFGROW life prediction data and experimental data based on average surface width of corrosion pits 8 Observation Flaw area=a Transformation Semi-circular model Flaw area=a Equivalent processing method for the fatigue nucleation sites EIFSD K Dolley 11 a /t 0 EIFSD EIFSD Medved 6 EIFSD AF- AFGROW NASGROW FAS- GROW TRAN AFGROW EIFSD AFGROW 2 5-6 1. 27 mm TTCI 9 NASGROW NASA EIFSD 6 FASTRAN da /dn - K eff K max / K min 9 Fig. 9 1. 27 mm TTCI Cumulative distribution of number of cycles to achieve the crack length of 1. 27 mm based on AFGROW EIFSD EIFSD 2. 2 SIF SIF Newman - Raju 12 Newman - Raju 13 Newman - Raju 14 SIF -
54 7 4 10 3 5 2. 3 Sankaran 2 50 μm 16 K 14-15 4 6 FASTRAN 2 2. 5 5 7075 2 6 DKEFF da /dn - K eff da /dn - K 10 Walde 7 1.E-04 1.E-05 R=0.1 da/dn /(m/cycle) 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 Aloca Long CrackData Newman's Short and Long Crack Data Back-Calculated 1.E-11 1 10 100 ΔK applied /MPa m 1/2 Fig. 10 10 Back-calculated short crack and long crack growth data 3 19-20 C - T C - T 21 22 C - T C - T 22 C 2. 4 - T C - T 16 C - T 1 000 T 17 17-18 2024 7075
1 55 Sankaran 2 7075 K t = 1 2 2 K t = 2 11 Gruenberg 10 3 Rokhlin 23 24 Shi 1 National Research Council Committee on Aging of U. S. Air 24 Force Aircraft. Aging of U. S. air force aircraft final report MSD Publication NMAB - 488-2 M. Washington DC National A- 25 cademy Press 1997. Maximum Stress /MPa 500 450 400 350 300 250 200 10 3 10 4 10 5 Fatigue Life /cycles 10 6 Legend: 1 536 h 1 768 h 384 h 96 h No Exposure Mil-Hdbk-5 Data,K t=1(r=0.1) Mil-Hdbk-5 Data, K t=2(r=0.1) 11 7075 6 Medved J J Breton A M Irving P E. Corrosion pit size distributions Fig. 11 Fatigue property of pre-corroded 2 mm thick 7075-T6 compared to design data and fatigue lives a study of the EIFS technique for fatigue design in the presence of corrosion J. International Journal of Fatigue 2004 26 1 71-80. 4 8 Lankford J. The growth of small fatigue cracks in 7075-T6 alumi- num J Structures 1982 5 3 233-248. 2 Sankaran K K Perez R Jata K V. Effects of pitting corrosion on the fatigue behavior of aluminum alloy 7075-T6 modeling and experimental studies J. Materials Science and Engineering 2001 297 1-2 223-229. 3 Goswami T K Hoeppner D W. Pitting corrosion fatigue of structural materials J. Structural integrityin aging aircraft 1995 AD 42-47. 4 Gruenberg K M Craig B A Hillberry B M et al. Predicting fatigue life of pre-corroded 2024-T3 aluminum J. International Journal of Fatigue 2004 26 6 629-640. 5 DuQuesnay D L Underhill P R Britt H J. Fatigue crack growth from corrosion damage in 7075-T6511 aluminium alloy under aircraft loading J. International Journal of Fatigue 2003 25 5 371-377. 7 Walde K Brockenbrough J R Craig B A et al. Multiple fatigue crack growth in pre-corroded 2024-T3 aluminum J. International Journal of Fatigue 2005 27 10-12 1509-1518.. Fatigue and Fracture of Engineering Materials and 9 Newman J C Edwards P R. Short-crack growth behavior in an a- luminum alloy an AGARD cooperative test programme R. AGARD Report 1998 732. 10 Gruenberg K M Craig B A Hillberry B M et al. Predicting fatigue life of pre-corroded 2024-T3 aluminum from breaking load 1 tests J. International Journal of Fatigue 627. fatigue life J and Structures 2000 23 7 555-560. 2004 26 6 615-11 Dolley E J Lee B Wei R P. The effect of pitting corrosion on. Fatigue and Fracture of Engineering Materials
56 7 12 Newman J C Reuter W G Aveline J C. Stress and fracture analyses of semi-elliptical surface cracks C. St. Louis MO 1998. 13 Walde K. Corrosion-nucleated fatigue crack growth D. Purdue University 2005 5. 14 Newman J C Edwards P R. Short crack growth behaviour in an aluminum alloy - An AGARD cooperative test programme M. AGARDR - 732 Advisory Group for Aerospace Research and Development 1988. 15 Wu X R Newman J C Zhao W et al. Small crack growth and fatigue life predictions for high-strength aluminium alloys Part I Experimental and fracture mechanics analysis J. Fatigue and Fracture of Engineering Materials and Structures 1998 21 11 1289-1306. 17 Piascik R S. Willard S A. The Growth of small corrosion fatigue cracks in alloy 2024 J. Fatigue and Fracture of Engineering Materials and Structures 1994 17 11 1247-1259. 18 Piascik R S. The Growth of small corrosion fatigue cracks in alloy 7050 J. International Journal of Fatigue 2003 25 457-469. 19. C - T J. 2005 26 2 184-189. 20. M. 2004. 21. J. 2003 29 2 161-164. 22. J. 2006 18 4 265-267. 23 Rokhlin S I Kim J Y Nagy H et al. Effect of pitting corrosion on fatigue crack initiation and fatigue life J. Engineering Fracture Mechanics 1999 62 4-5 425-444. 16. 2024-T3 24 Shi P Mahadevan S. Damage tolerance approach for probabilistic pitting corrosion fatigue life prediction J. Engineering Frac- J. 2006 3 14-17. ture Mechanics 2001 68 13 1493-1507. 25 Shi P Mahadevan S. Corrosion fatigue and multiple site damage reliability analysis J. International Journal of Fatigue 2003 25 6 457-469. 櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬櫬 檿檿檿檿檿檿檿檿 檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿檿