A probabilistic assessment is made of the design curves for 1Cr18Ni9Ti pipe-welded joint. The material exhibits a character of random cyclic stress-strain and fatigue life responses. Then, both the and in the virtual stress amplitude-fatigue crack initiation life () data are random variables. A general maximum likelihood method, which considers the randomness of the test data, is developed to model the probabilistic relations of material. The design N curves with reduction factors of 20 on cycles, 2 on stress and 2.5 on stress applied to the best-fit curve of test data as used in the ASME code and general practice, are assessed in a probabilistic sense. The results reveal that in the lower S regime the 20 and 2.5 reduction factor curves may be appropriate, while the reduction factor of 2 is slightly nonconservative. But in the higher S regime these curves are all much more conservative. The intrinsic cause is that the standard deviation of logN exhibits an increase with the decreasing, while the constant reduction factors do not consider this increase. It is shown that from the general statistical scatter of data the design curves should be appropriately determined by a probabilistic approach.
A Probabilistic Assessment of the Design S-N Curves for 1Cr18Ni9Ti Pipe-Welded Joint
Contributed by the Pressure Vessels and Piping Division for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received by the PVP Division August 3, 2001; revised manuscript received November 25, 2002. Associate Editor: S. Rahman.
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Zhao, Y. X. (May 5, 2003). "A Probabilistic Assessment of the Design S-N Curves for 1Cr18Ni9Ti Pipe-Welded Joint ." ASME. J. Pressure Vessel Technol. May 2003; 125(2): 195–200. https://doi.org/10.1115/1.1556857
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