1. 1 HCAT LANDING GEAR JTP FATIGUE PROGRAM P. E. Bretz J. Schell Metcut GEAE 12-14 December 2000

2. 2 OBJECTIVES l Follow-on work to previous HCAT Fatigue Test Program l Establish fatigue test protocol for evaluating coatings in landing gear applications l Develop statistical comparison of coating performance

3. 3 MATERIALS

4. 4 FATIGUE SPECIMEN PREPARATION l Blank to length, face & center l Vacuum heat treat to target TYS, as follows: [Vac Aero] –4340 & 300M: per MIL-H-6875 –A100: per P.S. 15169 –Specimen blanks + excess in 1 HT load –Verify HT with tensile test l Rough machine + low stress grind gages per MIL-STD-866 l Nital etch all specimens per MIL-STD-867, followed by H 2 bakeout l Shot peen gages per AMS-2432: 8-10A, S230, wrought steel shot, 100% coverage, computer control [Metal Improvement]

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19. 19 4340/WCCo, 165 ksi, R = 0.10 O1-31, Unpeened 13,768,157 O1-63, Peened 10,000,180

20. 20 Air, 180 ksi, R = -1, 300M Peened M1-41, WCCo 16,675 cycles M1-109, EHC 18,510 cycles Spalling at fracture plane No spalling

21. 21 Air, 300M/WCCo Peened, R = -1 M1-53, 180 ksi 11,928 cycles M1-50, 140 ksi 532,624 cycles Spalling at fracture plane Complete spalling of coating patch

22. 22 NaCl, 300M/WCCo Peened, R = -1 M1-69, 180 ksi 10,580 cycles M1-76, 125 ksi 1,323,924 cycles Spalling at fracture plane

23. 23 NaCl, 300M Peened, 125 ksi, R = -1 M1-140, EHC 967,816 cycles M1-76, WCCo 1,323,924 cycles Spalling at fracture plane

24. 24 NaCl, A100, 150 ksi, R = -1 Smooth Specimen A2-10, WCCo 51,967 cycles A2-18, WCCo 119,473 cycles A2-34, EHC 65,673 cycles Spalling at fracture plane Complete spalling Little/no spalling

25. 25 Large Hourglass Specimen, R = - 1 O4-25, 4340/EHC 175 ksi in air 4,510 cycles M4-37, 300M/EHC 180 ksi in NaCl 6,957 cycles M4-9, 300M/WCCo 180 ksi in NaCl 5,880 cycles Little/no spalling Spalling at fracture plane Complete spalling

26. 26 Specimen O1-31: 4340/WCCo, Unpeened Tested in Air at Pmax = 165 ksi, R = 0.10, Runout x10 Transverse coating cracks

27. 27 Coating Appearance @ Fracture Smooth Specimen (0.25” dia x 0.75” L)

28. 28 Coating Appearance @ Fracture Large HG Specimen (0.5” dia)

29. 29 Coating Appearance @ Fracture Small HG Specimen (0.25” dia)

30. 30 Distribution of Totally Spalled Specimens

31. 31 Distribution of Totally Spalled Specimens

32. 32 Distribution of Totally Spalled Specimens

33. 33 Summary of Total Spalling Counts

34. 34 Additional Coating Behavior Testing l Objective: Observe coating behavior during cycling for specific 1-to-1 comparisons l 0.25” dia x 0.75” L smooth gage bar (C-HCAT buttonhead version), 300M l Coating Matrix: –WC-Co vs. WC-Co-Cr –0.5” coating patch vs. fully coated gage/radius –0.003” +/- 0.0005” ground thickness, all bars l Test Matrix

35. 35 Summary of Coating Behavior Observations @ Fracture l EFFECT OF SUBSTRATE –Some evidence that total spalling is more prevalent for A100, although no obvious cause/effect relationship exists. l EFFECT OF PEENING –No consistent difference. There is a higher percentage completely spalled for peened A100. l EFFECT OF ENVIRONMENT –Pre-exposure and testing in NaCl did not increase either the amount of spalling or the number of completely spalled specimens, as compared to those tested in air. l EFFECT OF SPECIMEN TYPE (Small HG vs. Smooth) –No obvious difference. Spalling near fracture plane common to all specimens. Total spalling inconsistent for both types of bars. (All observations @ R=-1 unless noted)

36. 36 Summary of Coating Behavior Observations @ Fracture (cont’d) l EFFECT OF COATING THICKNESS/SPECIMEN SIZE (HG only) –Complete spalling occurred for all 0.5” dia/0.010” coated WC-Co specimens, regardless of stress level. For 0.25” dia/0.003” specimens, only 20 of 180 (11%) were completely spalled. l EFFECT OF R RATIO (Small HG, 4340 only) –No difference. Spalling near fracture plane for all bars; no completely spalled bars. Some cracking/spalling in RO’s. l EFFECT OF COATING TYPE –EHC: generally no evidence of test-induced cracking or spalling, except for large HG bars. –WC-Co: Cracking, spalling, and complete coating loss at fracture, as described above. (All observations @ R=-1 unless noted)

37. 37 PROGRAM SUMMARY Despite the unexpected and as yet poorly understood differences in coating behavior, the fact remains that for all test conditions the fatigue performance of WC-Co coated bars matches or exceeds that of EHC coated bars.