Length Effect

The fatigue characterization of structural members or mechanical components using the S-N field implies, unavoidably, limited information, due to testing difficulties. When real elements or components cannot be tested directly and have to be replaced by reduced size specimens, the experimental information obtained from the corresponding tests should be used with caution, because these results can be strongly dependent on the specimen size, material characteristics, and test conditions. An extrapolation of the test results to other conditions or sizes must be carefully done, and based on empirical relations.