Fatigue crack propagation limit curves for high strength steels based on two-stage relationship

Nowadays, the environmental impact reduction and the reliability enhancement of operating structures are basic trends in the heavy industry, which can be achieved using advanced materials and technologies. Metal structures are often operated with microstructural failures (e.g. cracks), and under cyclic loading conditions. The research work has focused on the high strength steels from the world of materials, on the welding technologies from the manufacturing processes, and on the fatigue cracks from the material failures. In order to determine and compare the fatigue resistance of different high strength steels grades and their gas metal arc welded joints, fatigue crack growth tests were performed on S690QL, S960QL and S960M steel grades. Statistical aspects were applied both for the presenting of the possible locations of cracks in base materials and welded joints and for the processing of the measured data. Fatigue crack propagation limit curves were derived based on two-stage crack growth relationship, using probability methods. The determined limit curves can be applied for engineering critical assessment and structural integrity calculations.