Internal Friction and Plastic Extension of Zinc Single Crystals

Abstract

This paper presents data on the internal friction of four single crystals of zinc while oscillating longitudinally, and a description of various slow speed tension tests on a fifth crystal within and beyond the elastic limit. In the first named measurements the behavior of the crystals bears little resemblance to that of crystals of zinc of greater purity prepared by another method, which has previously been reported (see reference 1). The most outstanding feature is that the decrement, although higher at the lowest stress amplitude than for the previous ones, shows very little rise with increasing stress amplitude, even up to stresses far beyond the statically‐determined elastic limit. The difference in behavior seems to be caused by the difference in purity of the zincs. An optically mosaic structure, such as that described by Schilling (see reference 4), does not appear to be responsible. In the slow speed tension tests the zinc crystal, after a period of self‐annealing at room temperature, has a Hooke's law region up to about 70 g/mm² (R.S.S.=28 g/mm²) and at greater stress shows transient and steady creep. Under some circumstances the transient creep is in two parts, a slow starting creep followed by much more rapid creep. The crystal, when measured following a permanent strain, shows creep at loads well below the previous elastic limit and has a large amount of hysteresis. Self‐annealing occurs during rest periods and the initial elastic limit is gradually regained while the hysteresis disappears.