Statistical analysis of ductile fracture properties of an aluminum casting

This paper presents a statistical study on plasticity and fracture properties of a ductile aluminum casting. Thirty conventional tensile tests on round bars and 30 shear fracture tests on butterfly-like flat specimens are conducted. The load–displacement curves obtained vary within 5% of the average response and thus plasticity behaviors can be represented by one single true stress–strain curve. However, the distribution of fracture strain has to be described in a probabilistic way. The test data are fitted well with the normal and the Weibull probability function and no major differences can be discerned between them. The shear fracture strains spread in a narrower range than the tensile ones, which is consistent with the fact that the casting is of much higher ductility under shear than under tension. The fractographic study reveals that the present round bar specimens can be generally categorized into two groups in terms of the size of pores. This requires two separate probability functions to describe their respective distributions. By treating all of the tensile fracture strains as one single population, the normal probability distribution predicts an unrealistic, negative value at the probability of 0.01%.