The results of experiments on the variation for aging of internal friction of metals which have been fatigued under repeated load, the effect of small reversed stress taking place on the heels of large one and relations between internal friction and slip bands through a microscope are described in this paper. Electrolytic iron, aluminium and 70-30 brass were used as testing metals and Shenck type torsional fatigue testing machines were used for giving repeated load. The internal friction was measured by the same a method as had been stated in the previous paper. The results of experiments are as follows: 1. The internal friction of metals subjected to reversal of stress increased more remarkably in the measuring range of small vibration amplitude than that of those subjected to statical cold working. 2. The internal friction of metals which had been increased by applying reversal of stress decreased by smaller succeeding stress. An effect of such mechanical aging was greater than that of the aging from leaving metals to take their course, which fact suggests that the fatigue strength is affected by redundant load. 3. The breaking out of slip bands and their increase in metal crystals subjected to repeated load were observed through a microscope and it was found that slip bands showed the change corresponding to the increase of internal friction.
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