Numerical crack growth study on porosity afflicted cast steel specimens

Abstract

This paper deals with the fatigue assessment of cast steel defects in terms of macroscopic shrinkage porosity. Within preliminary studies, a generalized Kitagawa diagram GKD was established by numerical analyses of V-notched specimens with varying opening angles. It was experimentally verified by the application of the notch stress intensity factor (NSIF) concept on fatigue tests under rotating bending and axial loading. This paper continuous the work by an application of the GKD to real cast steel pores. At first, casting simulations are performed to design representative cast specimen geometries. The study focusses on macroscopic shrinkage pores with different spatial shapes. 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 GKD. In order to define an equivalent defect size of the complexly shaped defects, numerical crack growth analyses are performed demonstrating crack coalescence path tendencies. Summing up, the application of the NSIF approach based on a GKD shows a sound accordance to the experimental results and thus provides an engineering-feasible fatigue assessment method of cast steel components with macroscopic imperfections.