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    Some Considerations in the Statistical Determination of the Shape of S-N Curves

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    This paper discusses the need for defining the shape of S-N curves, the various kinds of test data available for this purpose, and the problems in their statistical evaluation, including the assumptions that must be made.

    A method is proposed for finding the “cutoff” point, that is the endurance at which conventionally shaped S-N curves change slope to the horizontal. It is based on maximum likelihood principles and deals with runouts in a statistically acceptable way. A sharp or a continuous transition from the horizontal to the sloped straight line log S/log N curve may be considered.

    The method can be used for analysis and comparison of fatigue test results with a computer program, described and listed elsewhere by the authors, but it is subject to certain amendments, which are described in the paper.


    S-N, curve, log , S, /log , N, curve slope, endurance limit, statistical analysis, maximum likelihood method, computer program, fatigue

    Author Information:

    Spindel, JE
    Bridge development engineer, British Railways Board, London,

    Haibach, E
    Director, Fraunhofer-Institut für Betriebsfestigkeit (LBF), Darmstadt,

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP29330S