Consideration on Behavior of Fatigue Crack Propagation by Dislocation Dynamics Simulation
Tatsuro MORITA and Kenji SAITO
Abstract:The influence of the loading history and stress ratio on the behavior of fatigue crack propagation was investigated through the computer simulation based upon the emission and movement of dislocations from the crack-tip. The result of the simulation showed that there is a power relation between the stress intensity range in the preceding cycles and the threshold value where the crack stops propagating. It was also found that the threshold value obtained by the simulation is closely connected with the stress ratio through the Walker relation. The existence of those relations was explained from the viewpoint that the above two parameters control not only the maximum stress intensity but also the crack opening stress intensity level which is determined by the degree of the shielding effect due to the residual dislocations. This idea was supported by the simulation result that the crack propagation rate was clearly related to the effective stress intensity range which was defined as the difference between the maximum stress intensity and the above crack opening stress intensity. Key Words:Fatigue, Micromechanics, Dislocation dynamics, Crack propagation, Loading history, Stress ratio, Threshold stress intensity range