Cumulative damage in fatigue

The phenomenon of cumulative damage under repeated loads was assumed to be related to the net work absorbed by a specimen. The number of loading cycles applied expressed as a percentage of the number to failure at a given stress level would be the proportion of useful life expended. When the total damage, as defined by this concept, reached 100 per cent, the fatigue specimen should fail. Experimental verification of this concept for an aluminum alloy, using different types of specimens, various stress ratios, and various combinations of loading cycles is presented. These data are also analyzed to provide information on different stress ratios when an S-N curve for any one ratio is known. Results of a sample analysis based on experiments are given. It is concluded that a simple and conservative analysis is possible using the concept of cumulative fatigue damage.