THEORY OF THE THERMAL BREAKAWAY OF A PINNED DISLOCATION LINE WITH APPLICATION TO DAMPING PHENOMENA

Technical Report · Thu May 01 04:00:00 EDT 1958

OSTI ID:4303633

Teutonico, L J; Granato, A; Lucke, K

An investigation is made of the model of a pinned dislocation line under stress. The model used is that originaily given by Koehler and later employed by Granato and Lucke in their theory of mechanical damping due to dislocations. By taking into account thermal fluctuations, the probability of the thermal unpinning (breakaway) of such a dislocation Iine is calulated. The effect of this breakaway on the decrement and apparent modulus change felt by a stress wave traveling through a solid is also considered. The decrement is found to be both hysteretic and relaxational in nature: hysteretic, since the dislocation is irreversibly broken away from the pinning agents; relaxational, since the dislocation passes with a temperature-dependent mean frequency from one configuration of minimum energy through a saddle point configuration to another minimum configuration. A comparison of this theory with the GranatoLucke theory of mechanical damping (of which the present work is both an extension and a modification) reveals the following: (1) This theory contains the effect of temperature which the Granato-Lucke theory does not. The results of this theory reduce to those of Granato and Lucke when the temperature approaches zero. (2) This theory appears to have the proper frequency dependence while the results of the Granato-Lucke theory are frequency independent. (3) The dependence of the decrement on stress is slightly different in this theory from that in the Granato- Lucke theory, but thus far experimental results do not determine which is more appropriate since both seem to fit the available data rather well. (auth)

• Research Organization: Brown Univ., Providence. Metals Research Lab.
• NSA Number: NSA-12-011404
• OSTI ID: 4303633
• Report Number(s): AECU-3708
• Country of Publication: United States
• Language: English

Related Subjects

DEFECTS
DISLOCATIONS
ENGINEERING
FREQUENCY
FRICTION
MATERIALS TESTING
MECHANICAL PROPERTIES
SOLIDS
STRESSES
TEMPERATURE
VARIATIONS