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Granato, A.V. Read, David Thomas 2012-04-19T17:44:22Z 2012-04-19T17:44:22Z 10000-01-01 1975 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. Submitted by Megan O'Donnell (mnodonn2@illinois.edu) on 2012-04-19T17:44:22Z No. of bitstreams: 1 1975_read.pdf: 4441457 bytes, checksum: 07057f88c6ac69b45c9b16cf706d54e3 (MD5) Made available in DSpace on 2012-04-19T17:44:22Z (GMT). No. of bitstreams: 1 1975_read.pdf: 4441457 bytes, checksum: 07057f88c6ac69b45c9b16cf706d54e3 (MD5) Previous issue date: 1975 Restriction data tranferred 2014-07-01T11:33:24-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: thesis/dissertation Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Megan O'Donnell (mnodonn2@illinois.edu) on 2012-04-19T17:44:22Z Item is restricted indefinitely. thesis/dissertation U of I Only 3035035 http://hdl.handle.net/2142/30670 en Copyright 1975 David Thomas Read Ultrasonic Attenuation Bias stress effects String Theory Lead Bias stress detection of dislocation resonance in lead Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.