Modeling of hardening and thermal recovery in metals is considered within the context of unified elastic-viscoplastic theories. Specifically, the choices of internal variables and hardening measures, and the resulting hardening response obtained by incorporating saturation-type evolution equations into two general forms of the flow law are examined. Based on the analytical considerations, a procedure for delineating directional and isotropic hardening from uniaxial hardening data has been developed for the Bodner-Partom model and applied to a nickel-base superalloy, B1900 + Hf. Predictions based on the directional hardening properties deduced from the monotonic loading data are shown to be a good agreement with results of cyclic tests.
The effects of weak clay particles on the creep response of argillaceous salt have been analyzed by considering the particles as damage initiation sites where local tensile stresses and microcracks are induced under triaxial compression. The thermodynamic driving force for the damage process is formulated in terms of an appropriate power-conjucate equivalent stress measure, and the damage kinetics are described in terms of an evolution equation formulated on the basis of the conjugate equivalent stress and the scalar damage variable from Kachanov (1958). This treatment of clay particle effects is then incorporated into the Multimechanism Deformation Coupled Fracture (MDCF) constitutive model. A summary of the constitutive model is presented with an evaluation of the model calculations against experimental data of clean and argillaceous salt. The results suggest that the higher creep rate observed in argillaceous salt compared to clean salt is the consequence of increased damage growth in argillaceous salt due to the presence of weak clay particles.
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