FATIGUE FROM DEFECTS

摘要

Artificial defects of different geometry, size and shape are introduced at the surface of fatigue samples in order to evaluate the influence of defect on the fatigue limit (tension and torsion). Results show that for a given size, the geometry of the defect influences the fatigue limit. Fatigue mechanisms are observed at the tip of each defect and reveal the existence of the stage I which is very short due to the 3D stress distribution around the defect. On the basis of these results, a multiaxial fatigue criterion is proposed, including the defect by the mean of the stress gradient at the tip of the defect. Validation of the criterion is done for C36 steel and nodular cast iron : results are good.