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Research and Development on Advanced Graphite Materials: Volume II - Applications of Anisotropic Elastic Continuum Theory to Dislocations in Graphite

Report Number: WADD TR 61-72 Volume II
Author: Spence, G. B.
Corporate Author: National Carbon Company
Laboratory: Directorate of Materials and Processes
Date of Publication: 1962-07
Pages: 54
Contract: AF 33(616)-6915
Project: 7350
Task: 735002
AD Number: AD0286090

Eshelby, Read, and Shockley's theory of dislocations in an anisotropic elastic continuum has been used to derive formulas not involving complex numbers for the stress components of straight dislocations in certain symmetry directions. From these the dependence of stacking fault energy γF on the orientation of the Burgers vector and on the width of extended dislocations and triple partial ribbons and the dependence of γF on the radius of curvature of extended nodes were calculated. The results are rigorous for hexagonal crystals and approximate for general directions in (111) planes of FCC crystals. The theory is applied to graphite and lose-packed metals. All three methods of determining γF for graphite yield results which are compatible with the value 0.6 ± 0.2 erg/cm2. The rough estimate of error is based on uncertainties in the elastic constants and differences in experimental results. The dependence of width on depth from the stress-free surface has been calculated for an arbitrarily oriented dislocation lying parallel to the surface of a semi-infinite isotropic body and 30° extended dislocation and a symmetrical, screw triple partial ribbon in certain symmetry directions in an anisotropic plate. A procedure for correcting the widths observed in electron microscopy of thin films is given.

Lockheed Martin Missiles & Fire Control
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