Tuesday, 12 October 2004 - 1:50 PM

This presentation is part of : Graduate Student Competition

Characterization and Modeling of the Plastic Deformation Behavior for Metals with Different Crystal Structures: Physically Based

Farid H. Abed and George Z, Voyiadjis. Louisiana State University, 275 W Roosevelt St. Apt.3255, Baton Rouge, LA 70802

Microstructural physical based constitutive models are developed in this work in order to simulate the adiabatic and isothermal plastic flow stresses for polycrystalline metals at low and high strain rates and temperatures. The thermomechanical response is characterized here for bcc, fcc, and hcp crystal structures of metals as well as different steel types. The present models are derived based on the concept of thermal activation energy, the additive decomposition of the flow stress, dislocations interaction mechanisms and the role of dislocations dynamic in crystals taking into consideration the effect of the total dislocation density evolution with the plastic strain accumulation. The material parameters of the proposed modeling are physically defined and related to the nano-/micro-structure quantities. Experimental data for Niobium, Tantalum, Vanadium, Oxygen Free High Conductivity Copper, Titanium, and AL6-XN Stainless Steel are used in evaluating the proposed models. Good correlations are observed over a wide range of strain rates (0.001-10000 s-1) and temperatures (77K-1000K). The predicted results show that the effect of dislocation densities evolution on the thermal stress of bcc metals is almost negligible and pertained totally to the athermal stress part whereas, the plastic strain evolution of these dislocation densities play crucial roles in determining the thermal component of the flow stress in most fcc and hcp metals. On the other hand, steels, depending on their microstructure composition, show a behavior that is a combination of that for both bcc and fcc plastic deformation models.

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