Bias stress detection of dislocation resonance in lead
Read, David Thomas
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Permalink
https://hdl.handle.net/2142/30670
Description
Title
Bias stress detection of dislocation resonance in lead
Author(s)
Read, David Thomas
Issue Date
1975
Director of Research (if dissertation) or Advisor (if thesis)
Granato, A.V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Ultrasonic Attenuation
Bias stress effects
String Theory
Lead
Language
en
Abstract
Measurements of the ultrasonic attenuation and velocity and their changes with bias stress are used to test theories of bias stress effects by Hikata, Johnson, and Elbaum (HJE). Hikata amd Elbaum (HE), Alefeld, and one presented here. The only theory which survives the test and is supported by measurements is the present string theory, according to which the principal effect of the bias stress is to change the average segment length of some of the dislocations from that determined by weak pinning points L to that determined by strong pinning
c points LN. The fact that the kink models of HE and Alefeld are found to be invalid means that there still exists no direct experimental evidence for kinks on dislocations in crystals. The bias stress technique was applied to a study of dislocation behavior in lead. The principal result found is that dislocations are underdamped in lead in the superconducting state, and also in the normal state. This provides experimental evidence for the inertial
model of strength changes in superconductors, which requires underdamped dislocations in both states to fit the observed data, and against the Natsik increased attack frequency model, which requires overdamped dislocations in the normal state. An electronic drag constant is derived of B = 2 x 10-6 cgs, which is lower than previous estimates, but in good agreement with a recent calculation by Brailsford. The measurements are also used to derive dislocation segment length distribution functions.
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