Fatigue design methods

These results are based on some key features (based on the measurements) which imply that application of standard fatigue design methods give conservative results. These features are mainly ... 

Creep-fatigue design methods based on elastic analysis... 

A new cree-fatigue design method, which is based on the concept of a generalized elastic follow-up model, is being developed. The elastic followup equations to predict strain magnification and creep relaxation for structural discontinuities are established. 

T. Asayama, Update and improve subsection NH — alternative simplified creep-fatigue design methods, ASME ST-LLC, STP-NU-041 (2011). 

In the case of the ASME codes for nuclear pressurised components, the questions of fatigue design and of flaw evaluation are dealt with separately in ASME Section III and Section XI Appendix A, respectively. The design S-A curve for machined butt welds typical of thick section pressurised components is set at a factor of two on stress range or twenty on cyclic life, whichever is more conservative, below the mean of S-N data developed on smooth cylindrical specimens in air. (A somewhat similar design curve obtained by a different method from experimental S-A data for machined butt welds is given in British Standard 5500.) These safety factors are intended to encompass any adverse influence of minor weld defects, size effects, data scatter and environment. As far as environmental effects are... 

If a fatigue analysis is required, the code provides design methods (Article 5-1 for vessels... 

A comparison of the EEUA and FMP shaft design methods applied to the same problem. Worked examples are used to demonstrate the comparison. The FMP method yields a shaft size 20% smaller than the EEUA method. Fatigue life assessment is undertaken and this shows the FMP shaft is safe. 

Gonyea, D.C., Method for low-cycle fatigue design including biaxial stress and notch effects. Fatigue at Elevated Temperatures, ASTM STP 520, American Society for Testing and Materials, Philadelphia, 1973, pp. 673-687. 

Division 2. With the advent of higher design pressures the ASME recognized the need for alternative rules permitting thinner walls with adequate safety factors. Division 2 provides for these alternative rules it is more restrictive in both materials and methods of analysis, but it makes use of higher allowable stresses than does Division 1. The maximum allowable stresses were increased from one-fourth to one-third of the ultimate tensile stress or two-thkds of the yield stress, whichever is least for materials at any temperature. Division 2 requkes an analysis of combined stress, stress concentration factors, fatigue stresses, and thermal stress. The same type of materials are covered as in Division 1. 

Bloom, J. M. (ed.) 1983 Probabilistic Fracture Mechanics and Fatigue Methods Applications for Structural Design and Maintenance. American Society for Testing and Materials. 

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