Development of Fatigue Design Curves for Pressure Vessel Alloys Using a Modified Langer Equation

[+] Author and Article Information
D. R. Diercks

Department of Materials Sciences, Southwest Research Institute, San Antonio, Tex. 78284

J. Pressure Vessel Technol 101(4), 292-297 (Nov 01, 1979) (6 pages) doi:10.1115/1.3454636 History: Received March 20, 1979; Online October 25, 2010


The Jaske and O’Donnell [1 ] curve-fitting procedure for analyzing fatigue data generated between room temperature and 427° C (800° F) for several pressure vessel alloys is reexamined in the present paper. Substantial improvements over their best-fit curves to the data are found to result from two proposed modifications to their procedure, namely 1 ) the use of a variable exponent in the Langer equation, and 2 ) minimization of the sum of the squares of the errors in the logarithms of the cyclic-stress amplitudes rather than in the stress amplitudes directly. Likewise, important differences are observed for the resultant allowable stress-amplitude values for design purposes. In particular, the present analysis permits higher allowable stress amplitudes in the critical low-cycle fatigue-life region for the austenitic stainless steels, alloy 800, and alloy 600. Two best-fit curves and the associated sets of allowable stress amplitudes, corresponding to the inclusion or deletion of load-controlled data, are obtained for alloy 718.

Copyright © 1979 by ASME
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