A Probabilistic Model of Fatigue Strength Controlled by Porosity Population in a 319-Type Cast Aluminum Alloy: Part II. Monte-Carlo Simulation

摘要

In Part I, the fatigue strength of a cast 319-type aluminum alloy at 108 cycles was evaluated using an ultrasonic testing system, and a simple probabilistic model was developed to establish the relationship between the porosity population and the resultant fatigue strength of the alloy. In Part II, a detailed analysis and comprehensive simulation based on this model were performed to examine the effects of casting porosity characteristics on fatigue strength in cast aluminum alloys. The results predict that, when fatigue life is controlled by porosity population, the mean and standard deviation of the fatigue strength decrease with increasing mean pore size, pore size standard deviation, and porosity number density in the castings. In addition, the specimen size and shape are predicted to influence the fatigue strength by affecting the number of pores and the probability of intersection of pores with the specimen surface within the stressed volume. In general, a large specimen volume containing a large number of pores (>1000) or surface over volume ratio in the range of 5.0 to 6.0 can lead to a decrease in fatigue strength up to 10 pct, as compared with the counterparts. The applicability of the model to a cast W319-T7 aluminum alloy is demonstrated.