The crack surface morphology investigation of S355J2 steel after bending-torsion fatigue

Abstract

The paper describes the analysis of crack surface morphology of S355J2 steel specimens after bending-torsion fatigue. These experimental investigations of the surface topography were carried out using the focus variation microscope, an optical 3D measurement device. Selected results of measured fracture surfaces for S355J2 steel were analysed according to the surface texture ISO 25178 standard. Differences in roughness values for different loadings were demonstrated. For profile Rx and areal Sx parameters, characteristic relationships of fracture zones have been demonstrated. It has been shown that roughness profile Ra for the rupture area is higher than for the propagation area, as well as increases after both the LCF and HCF tests and increases with the torsional loading level. However, Sa in the propagation area increases and the rupture area decreases.