Kitagawa-Takahashi diagram for real defects: the role of local matrix and secondary cracksWednesday (27.05.2020) 17:40 - 18:00
This work focuses on the applicability of the Kitagawa-Takahashi diagram on real defects' experimental data gained by crossing axial fatigue testing, computed tomography, 3D metrology and optical microscopy.
Solidification shrinkages and degenerated graphite clusters are detected using computed tomography on samples taken from core areas of heavy-walled spheroidal cast iron castings. Following Murakami's approach, each defect is described by its projected area and a different shape factor for surface and internal defects. A fatigue limit is associated with each of them, using an El-Haddad formulation, and the defects are then ranked. The samples are fatigue tested and the killer defect is identified among all others. Subsequently, optical microscopy analysis is performed on the killer and a selection of the most critical defects. Local matrix phases and short crack presence are assessed. Most critical defects show some degree of crack initiation and propagation. The results allow a better understanding of the real defects' behavior and the validity of the model.