Presentation on theme: "1 HCAT LANDING GEAR JTP FATIGUE PROGRAM P. E. Bretz J. Schell Metcut GEAE 12-14 December 2000."— Presentation transcript:
1 HCAT LANDING GEAR JTP FATIGUE PROGRAM P. E. Bretz J. Schell Metcut GEAE 12-14 December 2000
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
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]
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 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 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 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.