Prediction of fatigue performance in aluminum shape castings containing defects

Fatigue properties of cast aluminum components are controlled by maximum defect size in the material. The larger the maximum defect size, the lower the fatigue strength and life. In the presence of casting defects, crack initiation can be ignored and fatigue life is mainly spent in crack propagation. Therefore, fatigue life of aluminum castings can be predicted by long or short crack growth models. The main problem is defining a starting defect size from readily available data, such as two-dimensional (2-D) pore size measurements on metallographic sections. In this article, an extreme-value statistics (EVS) method was used to estimate the maximum defect size in 319 castings from conventional metallographic data. The maximum defect size predicted by EVS agrees quite well with the initiation defect sizes measured from fracture surfaces, and the predicted fatigue life is in reasonable agreement with the experimental data.