This paper describes a new simplified elastic-plastic analysis method, which utilizes a plastic strain multiplication factor factor) obtained from elastic-plastic finite element analysis (FEA) results for the same structural model in the design stress calculation. ASME Code, Sec. III specifies a simplified elastic-plastic analysis method which can be used when intensity exceeds the limit, provided that the rules to prevent thermal stress ratchet are satisfied. The conventional method requires using factors given by a closed-form equation having a value of intensity as a variable. The elastically calculated peak stresses need be multiplied by the factors, before performing the fatigue analysis. The factors in the Code were derived from strain multiplication factors calculated for rather simple structural elements, which are assumed to cover a wide range of structural components. Consequently, although the rule can be applied safely to most of the cases, the results are usually too conservative. On the other hand, when intensities are near level, it has been pointed out based on experiments and analyses that the current has a lack of margin. We propose to use the factors obtained by FEA of the real structural model, in order to avoid the foregoing overconservatism and the lack of margin. The procedure also makes it unnecessary to extract category, which is necessary in the conventional evaluation method. Elastic and elastic-plastic FEAs were performed for the axisymmetric nozzle in a vessel, and the effectiveness of the proposed procedure was shown in a practical case. Generalization of the procedure is also discussed.
Simplified Elastic-Plastic Analysis Method Using Factors Obtained for the Real Structural Model
Contributed by the Pressure Vessels and Piping Division and presented at the Pressure Vessels and Piping Conference, Seattle, Washington, July 23–27, 2000, of THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. Manuscript received by the PVP Division, September 27, 2000; revised manuscript received August 19, 2002. Associate Editor: S. Rahman.
Okamoto, A., and Ohtake, Y. (January 31, 2003). "Simplified Elastic-Plastic Analysis Method Using Factors Obtained for the Real Structural Model ." ASME. J. Pressure Vessel Technol. February 2003; 125(1): 59–64. https://doi.org/10.1115/1.1522416
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