Effects of Repeated Polishing and Annealing on Fatigue Process of Copper : Experimental Studies on Fatigue Mechanism, 2nd Report

概要

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Following the 1st report, the mechanism of crack propagation in the initial stage of fatigue process was studied on copper by two kinds of test; (1) Repetition of stressing (for the equal number of cycles) and polishing, (2) that of stressing, polishing and annealing. The former test showed that the depth of cracks formed during one stress period decreased more or less in the earlier stages of the test as the sequence of operations was repeated, but increased gradually in the later stages. On perfect removals of such cracks, however, the test-pieces did not fatigue-fractured, even though cycled more than 10 times the expected life. And in these specimens, markedly developed fine cells were observed, in which dislocations were relatively diluted. The depth of cracks formed during one stress period increased when the specimen had been annealed in the preceding stage. Dislocation patches formed disappeared in the annealing at a relatively low temperature, but the cell structure did not, and most of cell boundaries composed of tangled dislocations transformed to twist ones. An inference can be drawn from these experiments that dislocations such as dipoles of vacancy type responsible for crack growth become less movable in the structure like patches, but relatively free to move through the cell structure.
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