153 research outputs found
A Multiscale Approach for Modeling Crystalline Solids
In this paper we present a modeling approach to bridge the atomistic with
macroscopic scales in crystalline materials. The methodology combines
identification and modeling of the controlling unit processes at microscopic
level with the direct atomistic determination of fundamental material
properties. These properties are computed using a many body Force Field derived
from ab initio quantum-mechanical calculations. This approach is exercised to
describe the mechanical response of high-purity Tantalum single crystals,
including the effect of temperature and strain-rate on the hardening rate. The
resulting atomistically informed model is found to capture salient features of
the behavior of these crystals such as: the dependence of the initial yield
point on temperature and strain rate; the presence of a marked stage I of easy
glide, specially at low temperatures and high strain rates; the sharp onset of
stage II hardening and its tendency to shift towards lower strains, and
eventually disappear, as the temperature increases or the strain rate
decreases; the parabolic stage II hardening at low strain rates or high
temperatures; the stage II softening at high strain rates or low temperatures;
the trend towards saturation at high strains; the temperature and strain-rate
dependence of the saturation stress; and the orientation dependence of the
hardening rate.Comment: 25 pages, 15 figures, LaTe
The analysis of the stress corrosion effects for H atom in the symmetrical tilt Ni Σ 5 (012) grain boundary structure
We employ a first-principles total energy method based on density functional theory as implemented in the Vienna ab-initio simulation package (VASP) for a detailed analysis of the symmetrical tilt Ni Σ 5 (012) GB with H impurity atoms in the structure of Σ 5 (012) GB. The effects of H segregation at the Ni Σ 5 (012) GB are investigated in details. The main goal of this study is to perform the ab initio simulations for the Ni Σ 5 (012) GB including the various impurity atoms at GB level as well as pure grain boundary models of Ni Σ 5 (012) GB. The grains can either be pushed apart or pulled together depending on the size of the impurity and nature of the local relaxations. Fundamental understanding of stress-corrosion cracking in metals and alloys including various impurity atoms is important to develop a new-structural material. Our calculations are compatible with the other first principle calculations. © 2017 Elsevier Ltd. All rights reserved
Melting of tantalum at high pressure determined by angle dispersive x-ray diffraction in a double-sided laser-heated diamond-anvil cell
The high pressure and high temperature phase diagram of Ta has been studied
in a laser-heated diamond-anvil cell (DAC) using x-ray diffraction measurements
up to 52 GPa and 3800 K. The melting was observed at nine different pressures,
being the melting temperature in good agreement with previous laser-heated DAC
experiments, but in contradiction with several theoretical calculations and
previous piston-cylinder apparatus experiments. A small slope for the melting
curve of Ta is estimated (dTm/dP = 24 K/GPa at 1 bar) and a possible
explanation for this behaviour is given. Finally, a P-V-T equation of states is
obtained, being the temperature dependence of the thermal expansion coefficient
and the bulk modulus estimated.Comment: 31 pages, 8 figures, to appear in J.Phys.:Cond.Matte
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