On the relations between the threshold values of the fatigue crack growth and the cyclic deformation behavior of materials

In the present paper, the relation between fatigue crack growth threshold and material's cyclic saturation behavior is investigated. The dislocation-free zone (DFZ) model is used to determine the dislocation distribution ahead of the crack tip. A cohesive zone model is developed to determine the stress field of the DFZ under cyclic loading. The effect of cyclic loading makes the plastic zone hardening (or softening), which raises the stress level in DFZ, and may lead to fracture. It is found that the near threshold characteristics are mostly determined by the cyclic deformation behavior of the material, and might be theoretically determinable from the standard cyclic loading test.