ELASTIC-PLASTIC FRACTURE MECHANICS APPROACH TO FATIGUE CRACK PROPAGATION.

The following conclusions were obtained as the result of the theoretical and experimental analysis of fatigue crack propagation from the point of view of elasto-plastic fracture mechanics approach: (1) The monotonic plastic zone length fairly well agrees with the curve calculated using a modified DM model. (2) The propagation rate of fatigue crack is proportional to the square of monotonic plastic zone length. The fatigue crack propagates in the plane strain condition in the case omega //B less than less than t, and in the plane stress condition in the base omega //B greater than greater than t. The transition phenomena exist between the plane strain propagation and plane stress propagation. (3) The plastic zone length at the tip of fatigue crack is nearly equal to the plastic zone width and omega //B saturates for a certain value of omega //L.