Cumulative Fatigue Damage due to Spectral Loading

The fatigue life of a metal part subjected to a spectrum of load intensities cannot be adequately evaluated from the results of a constant stress vs. cycles (S-N curve) experiment alone. A number of experiments have been conducted on this subject in the past, each for different materials and under different loading conditions. A review of this data reveals somewhat conflicting conclusions.

An attempt is made to resolve some of these differences and to suggest a consistent approach which would take into consideration the differences, and yield a solution which coincides with each of the individual results. In conclusion a spectral loading problem is worked out, demonstrating the application of this approach to reliability predictions.