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A SYSTEMATIC STUDY OF FATIGUE MECHANISMS IN IRON.
Interim technical rept.,
COLUMBIA UNIV NEW YORK HENRY KRUMB SCHOOL OF MINES
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Monocrystals and polycrystals of Ferrovac E iron were subjected to pull-release fatigue cycles of constant load amplitudes. Luders band velocity was measured under cyclic stress conditions. Cyclic creep measurements were done at low temperatures. At low stress amplitudes, the cyclic creep rate could be made to vanish by stress cycling. At this stage the applied stress amplitude equals the internal stress, so the effective stress could be determined. It has been shown that the mobile dislocation density remains constant throughout the fatigue life of a specimen. On the basis of dislocation dynamics, a cyclic strain rate equation has been derived and experimentally verified. The characteristic rapid and saturation hardening stages have been shown to be a result of the dislocation multiplication rate obeying a first order kinetics in multiplication and a second order kinetics in dynamic recovery. Author
APPROVED FOR PUBLIC RELEASE