ESTIMATION AND CORRELATION OF FATIGUE LIVES FOR RANDOM LOADING

Where the constant amplitude stress vs life curve of a test specimen or component is a straight line when plotted on log-log coordinates, the Palmgren-Miner rule predicts a parallel straight line for random loading. This paper suggests several other methods of correlating the data between random and constant amplitude loading so that the parallel stress-life lines coincide. As an example, the methods are applied to random loading data recently reported in this journal by Stanzl et al. It is significant that an endurance limit may not appear for random loading until very long lives have been reached, and then only when all stresses are below the endurance limit derived from constant amplitude data.