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UBC Theses and Dissertations

Determination of the dynamic strength of iron at low temperature Lockhart, Gary T.


Measurements of the stress sensitivity of the strain rate and of the strain vs stress in a titanium-doped, "interstitial free" (IF) iron were done at three temperatures, -20, -50 and -75° C. By application of a deformation model, based on a new theory of mobile dislocation density, these measurements permit the determination of (1) the constants of the power law describing the dislocation velocity as a function of the effective stress, and (2) the mean free dislocation path, which is descriptive of parabolic strain hardening. The theory is then used to calculate the microstructural parameters which determine the inelastic strain rate and the deformation resistance as they evolve, over time, with stress, stress rate and temperature. These parameters include the mobile and network dislocation densities, dislocation velocity, and effective stress. Theoretical predictions of the dynamic properties show excellent agreement with experiment. These properties include: (1) the stress sensitivity of the strain rate, as influenced by stress, stress rate and the magnitude of the stress decrease; (2) the nature and recovery time of the strain rate following a stress decrease; (3) the relative level of hard machine stress vs strain curves as a function of crosshead speed; and (4) the temperature dependence of both the microyield and macroyield stresses.

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