Abstract: To predict the probabilistic fatigue life of long life, high reliability components, the three parameter Weibull distribution is used to describe the probability distribution of fatigue life. A two-stage stress cycle equivalence method is proposed, fatigue damage equivalent basted and failure probability equivalent based cycle number models are established. For the stress cycles less than the location parameter of the fatigue life under the associated stress level, the equivalent number of stress cycles under different stress levels is converted according to location parameter–fatigue life equation; For the stress cycles greater than the location parameter of life distribution, the number of stress cycles at different cyclic stress levels is converted according to equivalent fatigue failure probability. To calculate fatigue failure probability or predict probabilistic fatigue life under variable amplitude stress history by means of this method and related models, the zero-failure probability stage, i.e., the stage that the stress cycle number is less than the location parameter of the associated fatigue life, can be well managed, meanwhile the equivalent failure probability criterion is applied for equivalent cyclic number calculation at different stress levels.

Key words: probabilistic fatigue life, fatigue failure probability, equivalent damage, equivalent cycle number, critical damage