P 927 - Investigation of initial defects and irregularities and their damage relevance in cyclically stressed welded joints (Subproject 1 - Cluster IBESS)

The irregularities were determined by metallographic microsections. Initial defects were to be detected by means of fracture surface analyses. From this, initial crack configurations were to be derived as input variables for a fracture mechanics concept. Furthermore, material parameters were determined and vibration tests were carried out. Sensitivity analyses were carried out with the determined material parameters, the defined initial defects and the analytical model developed in subproject A3 for the fracture mechanics estimation of the fatigue strength in order to determine the sensitivity of input variables. During the fractographic investigations, no inclusions could be detected as initial defects for most of the weld samples, despite the investigations in the scanning electron microscope (SEM). For this reason, a model was developed with which a lower limit of the initial crack size can be determined using a cyclic R-curve. From the sensitivity analyses with the IBESS model, it was determined that secondary notches (roughness, penetration notches), large seam transition radii and seam opening angles have a particularly large influence on the service life. The results from this sub-project and the research cluster in particular are intended to increase material utilisation, conserve resources and thus reduce costs and CO2 emissions