β Scribed by G. Saada; T. Kruml
No coin nor oath required. For personal study only.
This paper is an attempt to discuss the relevance of the physical concepts used to describe the plastic flow behaviour of a wide class of nanograined metallic polycrystals, by critically analyzing recent experimental observations on nanograined Ni and Cu. The paper focuses on the description of the elastic-plastic transition, and of the strain rate sensitivity. Using the generally accepted assumption that plastic flow results from dislocation nucleation at grain boundaries, it is shown that two deformation regimes must be distinguished: a nucleation-controlled mechanism at low strain rates, and a combined nucleation and propagation mechanism at high strain rates. At low deformation rates, the average nucleation rate is determined either from knowledge of the stress-strain curve, or from analysis of creep or relaxation kinetics. The strain rate sensitivity is shown to be related to the effect of stress on the nucleation rate.
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A method for the determination of the components of the Frank vector of disclinations in triple junctions (TJ) of real polycrystalline aggregates has been proposed. Using this method we found that real polycrystals contain junction disclinations (JD), the nature of which is related to their thermo-m
The upgraded Estrin-TΓ³th dislocation model has been suggested to describe deformation behavior of materials, subjected to severe plastic deformation, which in its turn is realized under high imposed pressure of several GPa. The model was applied to study high pressure torsion of Cu samples. The disl
We analyze the macroscopic deformation of a polycrystalline solid due to local deformation events in the core of grain boundaries. The central result is an equation that decomposes the effective macroscopic strain into contributions from three deformation modes, namely: (i) the elastic strain in the