Studies on Dislocation Dynamical Model having an Emitting Source at a Crack Tip on Supposition of Crack Propagation

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The present research deals with the analysis of the interaction between a crack and an inclusion from the standpoint of the dynamics of dislocations which are emitted from the crack tip and pile up against an inclusion. The criteria for emission of dislocations are assumed to be governed by the local stress intensity factor at the crack tip. The equations of motions for dislocations can be obtained by considering the swelling of the applied stress due to the inclusion, image dislocations in it, and the interactions between a crack and dislocations. The effects of the rigidity and the radius of the inclusion, etc., on the shear strain near the inclusion can be evaluated.In addition to this, in order to determine the effect of the orientation of crystal grains on the fatigue crack growth, the analysis of the model that edge dislocations emitted from a crack tip and located on an inclined slip plane pile up against a grain boundary is performed and both the angular dependence of crack tip opening displacement and the change of CTOD during the crack growth through a crystal grain are examined. It is suggested from the results that the fatigue crack most easily propagates through a crystal grain and its boundary when an angle between the crack front and the slip plane is between 70 and 80 degress.Furthermore, the analysis of the screw dislocations piled up against a thin-surface-layr is performed as one of the application of the dislocation dynamics and calculated the stress field generated in the layr by both the pile-up of dislocations and applied stress. The effects of the thickness of the layr, misfit of shear moduli, grain size and friction stress on the magnitude of the stress field in the thin-layr can be evaluated.