SEDL / STP / STP744-EB / STP29330S

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

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

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

Pages: 25    Published: Jan 1981

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Abstract

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.