Abstract :
THE FAILURE of a metal part in service by “fatigue” may be expected if: 1. The stress is not constant, but repeatedly varies in a “cycle” between a lower (minimum) and a greater (maximum) stress; the most severe cycle being that in which minimum and maximum are equal and opposite (full reversal). 2. The greater stress, maximum, is of a sufficient intensity. 3. The cycle is repeated a sufficient number of times, meaning hundreds or thousands or millions according to the severity of items 1 and 2. (For a more complete introduction to the subject see reference 1, which also contains an extended bibliography.)
