Abstract
The object of this series of studies is to find the mechanism and the characteristics of internal friction of metals due to plastic strains, and in this report, the method of experiments and the characteristics of internal friction vs. stress curves are described. Low speed torsional damping vibration was used for the measurement of internal friction, as it is believed to be better for minimizing the effect of thermo-elastic internal friction than any other methods and accordingly the most effective for observing the effect only of the internal friction due to plasticity.
According to the results of the measurements of various metals, the plastic internal friction is closely related to the plasticity obtained statically; in other words, both of them have structure sensitivity and show changes corresponding to each other by heat treating, cold working, etc. The causality of them is confirmed by considerable coincidence between experimental values of internal friction and calculated ones induced from plastic strains which were measured statically.In all metals used for the measurements. except aluminium, existence of shoulders on the internal friction vs. stress function curves and specially distinct ones for gray cast iron were recognized. This is considered to be due to existence of exceedingly plastic components (such as free carbons), and these shoulders can be made to reappear by combining models of two specimens having remarkably different plastic strengths. As the plastic internal friction, varies with stress amplitudes, it is desirable that the friction should not be dealt with as having a single numerical value, as to any materials, but attention should be paid to the function curve of stress, because it is useful for ascertaining the internal state of materials.
