Abstract
Abstract Strain amplitude dependent internal friction in zone-refined aluminum, containing silver and copper as impurities, was measured as a function of hydrostatic pressure with cold-work as an additional parameter. Using a modification of the torsional pendulum apparatus, the measurements were conducted at room temperature under forced vibrations with a frequency of 8.3 × 10−3Hz. For a given strain amplitude the damping was found to decrease as pressure increased, the magnitude of the drop being dependent on the strain amplitude. At a strain of approximately 10−5 damping changes of the order of −10−4 kbar−1 were observed. The dislocation damping theory by Granato and Lucke, well suited to describe the strain amplitude dependence at constant pressure, is used to predict the pressure dependence of the damping. The theory predicts the observed trends of the damping changes due to pressure, if it is assumed that the pressure response of the impurity atoms is governed by the bulk modulus of the impurity material. The measured changes, however, were two to three times larger than the predicted ones. It is suggested that the lack of treatment of thermally activated depinning in the theory is a possible reason for these discrepancies. The cold-work condition of the specimens also appears to have affected the magnitudes of the changes in internal friction, but the data is not conclusive in this regard.
Published Version
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