Internal Friction of LiF and NaCl

ABSTRACTS A modification of the Koehler-Granato-Liicke dislocation dampiog theory* The

dislocation damping theory of Koehler, Granato and Lticke is modified for metals with high stacking fault energy. It is assumed that the most abundant impurity atom species interacts only with the edge component of each dislocation. For this model the hysteretic, or frequency independent, damping initially increases linearly with stress amplitude and approaches the Granato-Liicke amplitude dependence at higher stresses. The influence of a second, fess abundant, impurity atom species which can interact with both screw and edge components also is considered. When the glide distance of a dislocation after breakaway becomes comparable with the mean spacing of the second type of impurity, the hysteretic damping becomes amplitude independent. This modification is best suited for application to the damping of b.c.c. metals containing a higher concentration of substitutional impurities than interstitial impurities.

of a pinned dislocation line as a function of external stress is required. This is done here for the two simple specific examples of a dislocation with a single pinning point and a dislocation with a continuous pinning agent. Also, it is shown in a general way how the damping and modulus change can be computed from these results. The qualitative behavior expected is discussed, although the detailed calculations of these quantities together with a comparison with measurements is given in other papers. For high concentrations of pinning points, the theory is of interest in the field of yield point phenomena, and the results found here are compared with previous calculations. Institute fiir Allgemeine L. J. TEUTONICO Metallkunde u. Metail’hysik, A. V. GRANATO Technische Hochschule, K. LfJCKE Aachen, Germany Internal Friction of LiF and NaClS

The amplitude dependence of dislocation damping J. C. SWARTZ and Young’s modulus of LiF and NaCl has been Edgar C. Bain Laboratory, investigated. The damping behavior of the two crysU.S. Steel Corporation Research Center, tals is essentially the same. The log. dec. is small Monroeville Pa. (<10V4) at low strain amplitudes and raises steeply Materials Science Department, J. WEERTMAN at higher strain amplitudes. Periodic dislocation The Technological Institute, motion of IOOObis seen at stress levels an order of ~orth~lestern ~n~versit~~, magnitude below the macro~opic yield stress. At Evanston, Illinois the higher strain amplitudes the vibrations themselves cause changes in damping, both at the high Theory of the thermal breakaway of a pinned strain amplitudes and at subsequent low strain dislocation line with application to damping amplitudes. The time dependence of these changes phenomena t in damping has been measured and will be discussed in terms of Granato-Liicke theory and various types Although the mechanical theory of Granato of pinnings. The decrease in damping upon high and Lticke for the internal friction and modulus changes of solids containing dislocations gives a strain amplitude damping in NaCl reported by Whitworth was observed. This decrease in damping fair account of many of the observed effects, simple was accompanied by a decrease in modulus and an theoretical considerations show that the effect of increase in low strain amplitude damping. thermal fluctuations should be very important. To University of Utah, G.S. BAKER extend the theory to finite temperatures, a detailed study of the possible static equilibrium positions Salt Lake City, Utah U.S.A. * Abstract of Paper 15 presented

at the Conference on 11 July 1961 at Cornell

Internal Friction held on 10 and University. t Abstract of Paper 16 presented at the Conference on Internal Friction held on IO and 11 July, 1961, at Cornell University. ACTA METALLURGIC&

VOL. 10, APRIL

1962

REFERENCES 1.

WHI~W~RTH

P&if. &Zag. 5, 425 (1960).

$ Abstract of Paper 22 presented at the Conference on Internal Friction held on 10 and 11 July, 1961, at Cornell University.