Papers by Author: Rui Zhang

Abstract: 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.

Abstract: The relation between material’s cyclic plastic behavior and fatigue crack growth is investigated. The present model is proposed on the dislocation-free zone (DFZ) theory. A cohesive zone theory is developed to determine the stress field of the DFZ and the value of J-integer under cyclic loading. The crack growth criterion is proposed based on J-integral. The calculated curve of fatigue crack growth rate da/dN is agreement with the general propagation pattern and the predicted threshold accords with the experiment threshold well. It is found that the near threshold characteristics are most determined by the cyclic deformation behavior of the material. The relation between fatigue crack growth threshold and material’s cyclic hardening behavior is discussed.