Abstract
Fatigue crack growth tests were conducted to clarify the coalescence behavior of multiple cracks due to fatigue fracture. SUS304 was used as the material, the shape of the specimen was plate-shaped, and notches were introduced by electrical discharge machining (EDM) on both sides of the smooth part in the center. The crack position was expressed by the distance between the crack faces and the distance between the crack tips. Slit-type fatigue cracks were adopted assuming cracks initiated by thermal stress in structural materials in fast reactors. The crack tip distance, S, was set to approximately 4.5 mm in order to investigate the relationship between the crack coalescence behavior under fatigue conditions and the crack coalescence behavior with the crack face distance, H. Fatigue tests were performed on specimens with a fixed S and varying H between 1.69 and 6.48 to 6.71. As a result of the experiment, the following facts were found. A white streak thought to be caused by plastic collapse was observed. However, the two cracks did not eventually coalesce. On the other hand, in past creep tests, when H is small (1.78), the cracks coalesce, and the creep test results and fatigue test results differ from past creep test results.
