Numerical crack growth study on porosity afflicted cast steel specimens

This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Thereby, a generalized Kitagawa diagram GKD is established by numerical analyses of V-notched specimens with varying opening angles. It is experimentally verified by the application of the notch stress intensity factor (NSIF) concept on fatigue tests under rotating bending and axial loading. At first, casting simulations are performed to design representative cast specimen geometries. The study focusses on macroscopic shrinkage pores with different spatial shapes. Thereby, several sample geometries are cast exhibiting a variation in defect shapes and sizes. At second, fatigue tests under axial loading are conducted. Subsequent fracture surface analysis by light optical and scanning electron microscopy provides fracture mechanical based geometry parameters. Finally, the results of the experiments related to the failure relevant defect sizes are assessed by the generalized Kitagawa diagram. In addition, numerical fracture mechanical analysis of representative defects is performed to illustrate the crack growth behaviour of steel cast defects and demonstrate crack coalescence path tendencies. Summing up, the application of the NSIF approach shows a sound accordance to the experimental results and thus provides an engineering-feasible fatigue assessment method of cast steel components with macroscopic imperfections.