Variation of Amplitude-Dependent Internal Friction in Single Crystals of Copper with Frequency and Temperature

Abstract

The amplitude-dependent internal friction which originates in the motion of dislocations in single crystals of copper is studied as a function of frequency and temperature. Quantities are introduced which express the dependence of internal friction and of Young's modulus on strain amplitude and it is shown that these quantities are significant measures of the properties of a crystal. Measurements made between -60\ifmmode^\circ\else\textdegree\fi{}C and +33\ifmmode^\circ\else\textdegree\fi{}C show that the observed internal friction can be expressed as the product of a function of temperature and a function of amplitude alone. The data also indicate that the internal friction and elastic modulus are frequency independent when the structure sensitivity of the material is taken into account. The results are considered in terms of two viewpoints: a mechanism of relaxation by which dissipation is controlled through a rate process, and simple hysteresis, by which the stress-strain loop is independent of the rate of traversal. It is shown that the latter mechanism gives much better agreement with the experimental facts. Finally, simple hysteresis is interpreted in terms of the dislocation theory.