Xi. The origin of fatigue fracture in copper

Abstract The paper describes metallographic observations of the development of fatigue cracks in copper. The specimens (polycrystal and single crystals) were tested in push-pull at 1000 c.p.s. It was shown that the fatigue crack started in a slip band inside a single grain. An electropolishing technique showed changes in the character of the slip band after 5% of the life had expired. Cracks more than one grain long were present when half the life had expired. It was confirmed that the fatigue life could be increased by preventing access of oxygen to the surface. The bearing of these observations on the problem of the origin of a fatigue crack is discussed.