Annealing in slip bands in copper fatigued at 90°K

Abstract

The number of slip bands formed during the fatigue of O.F.H.C. copper at 90°K and 293°K have been compared. For equivalent stresses to cause failure in 2 ×10⁶ cycles, more slip bands are formed at 90°K than at 293°K. The number of slip bands formed increases with the length of the test. When specimens are fatigued at 90°K, and heated to room temperature at intermediate stages, the rate of increase of slip bands is much smaller than for specimens kept entirely at 90°K. The intermediate heating effectively makes the slip bands softer than the surrounding regions so that on further fatiguing slip is localized near or within the slip band. The critical temperature for the intermediate heating, above which the annealing occurs, is approximately 180°K. The results are attributed to point defect hardening during the annealing treatment.