Probabilistic modeling of fatigue life distribution and size effect of components with random defects

Engineering components made of ductile cast irons and aluminum alloys, show fatigue lives which are normally dominated by crack initiation from defects raised by manufacturing processes. This study presents a probabilistic model to account for the influence of manufacturing defects on fatigue life, based on size and position of those defects. Specifically, a correction factor considering the influence of defect surface position is developed by modeling the damage mechanism of surface initial cracks with Weibull distribution. Experimental data of three cast irons and aluminum alloys are used for model validation and comparison. Moreover, the statistical size effect influence on fatigue life distribution under constant amplitude loading is explored. Fatigue lives of three materials with different sizes are evaluated respectively, and P-S-N diagrams show that proposed model predictions agree well with the probabilistic scatter bands.