Abstract: ased on load cycle fatigue life interference model,the character as well as the calculating method of fatigue reliability under program loading is analyzed。Contrary to the traditional method using a recurrence formula according to “equivalent failure probability” to transform fatigue damage under different load levels and calculate reliability, according to the analysis on fatigue process and its physical nature,a “damage equivalent” recurrence method is proposed. Experiment under multi level load condition shows that the error of the “damage equivalent” recurrence formula is equal to 32.8%,while that of the “equivalent failure probability” recurrence formula is as high as 96.8%.

Key words: fatgue ( forces), reliability, damage