A probabilistic method for predicting fatigue life controlled by defects

The probability with which defects become fatigue crack origins is determined, during fatigue tests at a specified stress range. On this basis a probabilistic method is proposed to predict the fatigue life when it is strongly dependent on the fatigue crack initiating defects. In this case the scatter in the fatigue life is due to variations of the size of the initiating defects and the probability with which they initiate fatigue cracks, rather than on variations in fatigue crack initiation or propagation life. A Monte-Carlo simulation was applied to predict the fatigue life of cast aluminium alloys. The model handles fatigue crack initiation from discontinuities and other defects. A method to find the group of defects most detrimental to the fatigue life is also proposed.