Numerical stress intensity factor calculation in flawed round bars validated by crack propagation tests

• Analysis of the crack geometry of flawed round bars under cyclic tension and bending loading.
• Validation of the numerical stress intensity factor calculation by crack propagation tests.
• Numerical investigations of the three-dimensional stress and displacement fields and determination of the boundary layer.

In this paper the results of crack propagation tests on round bars under cyclic tension and bending loading are presented. The tests were performed to investigate the crack geometry and its dependencies e.g. on the stress ratio and overloads. Furthermore, the crack propagation tests were used to validate the numerical stress intensity factor (SIF) calculation. This validation is necessary, due to the uncertainties in the numerical calculation of three-dimensional crack problems. As shown in literature, the 1/r-singularity of the stress field is not fulfilled in general for surface cracks in the near surface domain. Due to this boundary layer effect, the classical SIF is not valid. In order to calculate SIFs at the surface point an extrapolation is used. The method’s parameters are validated by the crack propagation tests and ensured by numerical investigations concerning the singularity of the stress field and the boundary layer thickness. These investigations were performed on a CT-specimen with a straight crack front.