Abstract
An automatic in-situ observation system was constructed for the evaluation of fatigue damage process. This system was composed of a torsional fatigue tester equipped with a microscope and a test specimen with stress concentration spots on the surface. Using this system, polycrystalline pure iron during fatigue crack initiation process was observed. In addition, the characterization of the crack initiation location was explained by the finite element method (FEM) assuming crystal anisotropic elasticity. Relationships between the crystal textures and the fatigue crack initiation location were discussed from these experimental and analytical results. As the results, the fatigue damage can occur more easily at the grains with the orientation [111] in the direction close to the thickness direction. Moreover, FEM results showed that grain boundary adjacent to the grain with higher value of the slip stress multiplied the thickness direction component |n∙ (ταsα)| became the crack initiation location. These results indicate that the slip activities in the out of plane direction cause the fatigue crack initiation.
