Application of the generalized Kitagawa diagram on cast steel

This paper deals with the assessment of cast steel defects in terms of macroscopic shrinkage porosity. Thereby, a generalized Kitagawa diagram is developed by numerical analyses of V-notched specimens with varying opening angles, which is verified by the application of the NSIF concept on experimental fatigue tests under rotating bending and axial loading. At first, casting simulations are performed to establish representative specimen geometries. The design study focusses on macroscopic shrinkage pores with different spatial shapes. Thereby, several sample geometries are obtained and subsequently steel cast to obtain varying defect shapes and sizes. At second, fatigue tests under axial loading are conducted. Subsequent fracture surface analysis by light optical and scanning electron microscopy provide 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, a numerical analysis of a representative defect is performed to illustrate the crack growth behaviour of a steel cast defect and demonstrate crack coalescence path tendencies. Summing up, the application of the NSIF approach on cast steel containing macroscopic imperfections shows a sound accordance to experiments and provides an engineering-feasible fatigue assessment method of cast steel components.