part 25 (appendix K) for airplane ETOPS type design approval. This section also requires the
1/21/10 AC 33.201-1 c. Section 21.4(b)(2) defines the 12 month rolling average total IFSD rates required for each level of ETOPS airplane type design approval. These IFSD rates are the same as required under part 25 (appendix K) for airplane ETOPS type design approval. This section also requires the type certificate holder to publish service information that will enable operators to maintain the required airplane/engine combination world fleet IFSD rates. Service information can take the form of Service Bulletins, Service Letters, All Ops Wires, etc., published as necessary.
Francis A. Favara, Manager, Engine and Propeller Directorate Aircraft Certification Service
Appendix A
1/21/10 AC 33.201-1 Appendix A APPENDIX A. Equivalent Amplitude Fatigue Exponent Determination a. Discussion. The Equivalent Amplitude Fatigue Exponent has its origin in the S.S. Manson (1) Method for Universal Slopes . Manson demonstrated that the fatigue exponents for many metals could be averaged and used to develop a universal fatigue exponent approximating either the low or high cycle capability of metallic materials. Although Manson used the approach to develop generic fatigue exponents representing a broad range of metals, the approach has been demonstrated to be applicable to characterizing the fatigue exponent for individual materials too (2)(3) . When the fatigue exponent is combined with cumulative damage calculations, it can be (4) used to assess accelerated fatigue tests . These various authors suggest the fatigue exponent may range from 4 to 20 depending on material and whether high cycle or low cycle fatigue is being evaluated. These authors also indicate that metallic materials typically exhibit high cycle fatigue exponents in the range of 4-8. The FAA determined that 5.68 is an overall acceptable value covering a variety of currently used turbine engine metals over a range of R-ratios for high cycle fatigue. If an engine design departs significantly from the use of conventional metals, then a reevaluation of the exponent in accordance with the references below may be required.
1. Manson, S.S., “Interfaces Between Fatigue, Creep, and Fracture”, NASA Technical Memorandum, NASA TM X-52189, 1966.
2. Lampman, S.R, et.al, “Fatigue and Fracture” ASM Handbook, Volume 19, 1996.
3. Delgado, I.R., G.R. Halford, B.M. Steinet & C.M. Rimnac, “Strain-Life Assessment of Grainex Mar-M 247 for NASA’s Turbine Seal Test Facility”.
4. Fackler, W.C., “Equivalence Techniques for Vibration Testing”, SMV-9, Shock and Vibration Information Center, US DoD, 1972.
A-1