UBC Theses and Dissertations
Directionality of the strain aging effect in ultra low carbon steel Melo, Wendel
This thesis contributes to the understanding of strain aging in ultra-low carbon (ULC) steels. Three studies (chapters 5, 6 and 7) were performed to achieve the end results. First, the kinetics of strain aging following monotonic tensile tests were measured and compared to an analytical model that can be used to predict the upper and lower yield strength for different aging temperatures and times. Next, the stress-strain behavior was evaluated. Lüders band formation was investigated using a model coupled to simulations using the finite element method (FEM). Digital image correlation (DIC) experiments were performed for comparison with the FEM simulations. Results showed many similarities between both methods, which increases the credibility of the FEM application. Good agreement between experiments and simulations was found. Finally, the directionality of strain aging was studied. Samples were taken from rolled sheet at 0˚, 45˚ and 90˚ to the rolling direction (RD). These were reloaded in tension following aging, the results being very different to those obtained from monotonic tensile tests. In particular, the strain path change was found to result in a large change in work hardening rate and a small effect on the yield strength. This was discussed in terms of a physically based model for strain aging.
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