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Abstract

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.

Grain-size dependent mechanical behavior of nanocrystalline metals

“…As computation power climbs and cost plummets, it is to be expected that fundamental insights into the structure and properties of crystalline defects, as well as physical mechanisms ranging from atomic diffusion to interface migration and grain rotation, will be made through atomic-scale simulation and modeling. Simulations deriving from atomic and quantum models extend their reach by providing valuable input criteria for multi-scale models, continuum models, and materials design [24][25][26][27][28][29][30][31][32] especially in iterative feedback loops [33].…”

Density functional theory and molecular dynamics studies of the energetics and kinetics of electroactive polymers: PVDF and P(VDF-TrFE)

“…(3)] is very general in nature and can describe various mechanisms such as free volume-based deformation in metallic glasses 24,25 and dislocation-based single crystal plasticity. 26,27 The resulting effective volume in the parallel case is V 0 = 281.4 Å 3 and in the perpendicular direction is 116.3 Å 3 ; the characteristic frequencies ␥ 0 are 1.33ϫ 10 10 1/s and 0.17ϫ 10 10 1 / s in the parallel and perpendicular directions, respectively. As expected, we find that the direction of easy slip has a larger characteristic frequency [␥ 0 is proportional to exp ͑⌬G / k b T͒ where ⌬G is an activation barrier [24][25][26] ] and a larger effective volume.…”

Hybrid atomistic-coarse-grained treatment of thin-film lubrication. II

“…Irregular large-amplitude atomic motions near the defect must be coupled to smooth, small displacements in regions remote from the defect. A number of techniques combining atomistic and continuum descriptions of the behavior of defects in solids have been put forth since the early 1990's [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and these have been exhaustively reviewed in the last couple of years. [15][16][17][18][19] Of particular relevance is the quasicontinuum ͑QC͒ method, 3,15,16,19 which we have adapted in formulating our new hybrid atomistic-coarsegrained description of the prototypal tribological system.…”