The double slip plane model for the study of short cracks

Discrete dislocation plasticity modeling of short cracks in single crystals

“…Hence, at the crack tip, the "local K" regarded as a measure of the driving force for crack growth cannot be (and is not) less than K 0 . On the other hand, K max is a measure of the applied stress σ max via (10) and there is no requirement that K max reach K 0 ; the driving force for crack growth can substantially exceed K max . Indeed, the occurrence of fatigue crack growth below the "Griffith limit" was noted in Ref.…”

“…To inhibit crack growth, the cohesive properties in the stationary crack calculations are specified as σ cοh ϭ 3GPa and δ n ϭ 10b. The dislocation distributions at K I / (G√b) ϭ 0.65, where K I is calculated from (10), are shown in Fig. 3a and b for specimens with crack sizes a ϭ 10 µm and a ϭ 100 µm, respectively.…”

“…As long as the solid remains linearly elastic, (10) predicts that the initiation of crack growth, K Ic ϭ K 0 scales with √a. This scaling remains valid for sufficiently large specimens for which plastic deformation is confined to the near crack tip region.…”

“…However, the authors provided no physical basis for their hypothesis. Caracostas et al [10] analyzed the behavior of mode-III edge cracks via a double slip plane crack model. They calculated the dislocation density distribution on the two slip planes parallel to the crack and inferred crack growth rates from the slip rates.…”

“…The models in Refs. [9,10] predict a deviation from K-governed behavior only when the applied stress is approximately equal to the yield strength of the material; experiments suggest that fatigue crack growth is enhanced for short cracks in edge-cracked specimens even when the maximum applied stress is as low as a third of the yield strength [11].…”