Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Nuclear Engineering

First Advisor

M. S. Wechsler

Abstract

A computer-based model is developed for the localized plastic deformation in irradiated metals by dislocation channeling, and it is applied to irradiated single crystals of niobium. In the model, the concentrated plastic deformation in the dislocation channels is postulated to occur by virtue of the motion of dislocations in a series of pile-tips on closely spaced parallel slip planes. The dynamics of this dislocation motion is governed by an experimentally determined dependence of dislocation velocity on shear stress. This leads to a set of coupled differential equations for the positions of the individual dislocations in the pile-up as a function of time. Shear displacement in the channel region is calculated from the total distance traveled by the dislocations. The macroscopic shape change in single crystal metal sheet samples is determined by the axial displacement produced by the shear displacements in the dislocation channels. Computer simulations are performed for the plastic deformation up to 20% engineering strain at a constant strain rate. Results of the computer calculations are compared with experimental observations of the shear stress-engineering strain curve obtained in tensile tests described in the literature. Agreement between the calculated and experimental stress-strain curves is obtained for shear displacement of 1.20-1.25 [mu]m and 1000 active slip planes per channel, which is reasonable in the view of experimental observations.

DOI

https://doi.org/10.31274/rtd-180813-12914

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Üner Çolak

Language

en

Proquest ID

AAI8920118

File Format

application/pdf

File Size

142 pages

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