Fatigue strength characterization of high and ultra-high-strength steel cut edges

Abstract

This paper investigates the fatigue strength characteristics of CO2 laser, fiber laser and plasma cut edges of S690 and S1100 steel grades. The effect on fatigue performance of surface quality, which was examined by contact measurements and 3D scanning, residual stresses and microhardness profile, is studied and edge surface characteristics are compared for different cutting methods and 8 mm and 12 mm plate thicknesses. Four main experimental fatigue test series were performed and analyzed to estimate fatigue performance (defined as FAT classes) of the cut surface. Additional tests were conducted to study critical defects and residual stresses influence on fatigue properties. Scanning electron microscopy (SEM) revealed multiple critical locations in the specimens. Fatigue properties were characterized based on critical defects and crack initiation and propagation origins. Geometrical discontinuity points in the cut edges were found to have a significant influence on fatigue performance. It is concluded that classification of thermally cut edges by cut edge characteristics could be used in fatigue strength assessment as an alternative to standard FAT classes.