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atomistic simulation of dynamical and defect properties of multiferroic hexagonal YMnO_3

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Science China(Physics,Mechanics & Astronomy) 2011年第5期54卷 836-840页

作者： ZHANG ChengGuo ZHANG XiaoZhong SUN YongHao LIU ShuYi Key Laboratory of Advanced Materials Department of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Beijing National Center of Electron Microscopy Beijing 100084China

atomistic simulation has been performed to investigate the dynamical and defect properties of multiferroic hexagonal YMnO3 with newly developed interaction potentials. Dynamical calculation reveals that phonon vibrations of hexagonal YMnO3 are quite different from those of orthorhombic YMnO3. Defect calculation finds that O Frenkel is the most probable intrinsic disorder, and Mn antisite defect is favorable to exist, especially for Mn ions entering the Y2 sites. It is also found that holes prefer to localize at O2sites rather than at Mn3+ sites, while the electron can be localized at the Mn3+ site. The disproportionation of Mn3+ ions is unlikely to occur in hexagonal YMnO3.

关键词： atomistic simulation YMnO3 lattice dynamics defect

atomistic/CONTINUUM simulation OF INTERFACIAL FRACTURE——PART Ⅰ: atomistic simulation

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Acta Mechanica Sinica 1994年第3期10卷 150-161页

作者：谭鸿来杨卫 Department of Engineering Mechanics Tsinghua University Beijing China 100084

The phenomenon of interfacial fracture, as manifested by atom- istic cleavage, debonding and dislocation emission, provides a challenge for combined atomistic-continuum analysis. As a precursor for fully coupled atomistic-continuum simulation of interfacial fracture, we focus here on the atomistic behavior within a nanoscopic core surrounding the crack tip. The inter-atomic potential under Em- bedded Atom Method is recapitulated to form an essential framework of atomistic simulation. The calculations are performed for a side-cracked disc configuration un- der a remote K field loading. It is revealed that a critical loading rate defines the brittle-to-ductile transition of homogeneous materials. We further observe that the near tip mode mixity dictates the nanoscopic profile near an interfacial crack tip. A zigzag interface structure is simulated which plays a significant role in the dislocation emission from an interfacial crack tip, as will be explored in the second part of this investigation.

关键词： interfacial fracture atomistic simulation mode mixity loading rate zigzag interface

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atomistic simulation of Interaction between Grain Boundary and Dislocations in Ni_3Al

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Journal of Materials Science & Technology 1993年第5期9卷 327-337页

作者： Dongliang LIN(T.L.Lin) Da CHEN Min LU Department of Materials Science,Shanghai Jiaotong University,Shanghai,200030,China

The embedded atom type potentials and static relaxation method combined with a steepest decent computational technique have been used to simulate the interaction between the grain boundary (GB) and dislocations in Ni_3Al *** focus has been placed on the energy feature of the interaction,the distortion of GB structural units,and the dislocation core structure near the ***- plication has also been made on the results for the understanding of the mechanism responsible for B-enhanced ductility.

关键词： atomistic simulation grain boundary dislocation Ni_3Al

atomistic simulation of thermal effects and defect structures during nanomachining of copper

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Transactions of Nonferrous Metals Society of China 2012年第11期22卷 2762-2770页

作者：郭永博梁迎春哈尔滨工业大学机电工程学院哈尔滨150001

Molecular dynamics （MD） simulations of monocrystalline copper （100） surface during nanomachining process were performed based on a new 3D simulation model. The material removal mechanism and system temperature distribution were discussed. The simulation results indicate that the system temperature distribution presents a roughly concentric shape, a steep temperature gradient is observed in diamond cutting tool, and the highest temperature is located in chip. Centrosymmetry parameter method was used to monitor defect structures. Dislocations and vacancies are the two principal types of defect structures. Residual defect structures impose a major change on the workpiece physical properties and machined surface quality. The defect structures in workpiece are temperature dependent. As the temperature increases, the dislocations are mainly mediated from the workpiece surface, while the others are dissociated into point defects. The relatively high cutting speed used in nanomachining results in less defect structures, beneficial to obtain highly machined surface quality.

关键词： monocrystalline copper atomistic simulation thermal effects molecular dynamics simulation nanomachining temperature distribution defect structures dislocations vacancies

INVESTIGATION ON APPLICABILITY OF VARIOUS STRESS DEFINITIONS IN atomistic simulation

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Acta Mechanica Solida Sinica 2009年第6期22卷 644-649页

作者： Ran Xu Bin Liu AML Department of Engineering Mechanics Tsinghua University Beijing 100084 China

How to correctly extract Cauchy stress from the atomistic simulations is a crucial issue in studying the mechanical behaviours of atomic systems, but is still in controversy. In this paper, three typical atomistic simulation examples are used to validate various existing stress definitions. It is found that the classical virial stress fails in predicting the stresses in these examples, because the velocity depends on the choice of the local average volume or the reference frame velocity and other factors. In contrast, the Lagrangian cross-section stress and Lagrangian virial stress are validated by these examples, and the instantaneous Lagrangian atomic stress definition is also proposed for dynamical problems.

关键词： atomic stress virial stress atomistic simulation

atomistic simulation OF SEGREGATION IN Cu-Bi SYSTEM Ⅰ.SATURATED SEGREGATION

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Acta Metallurgica Sinica(English Letters) 1988年 1-6页

作者： V.VITEK University of Pennsylvania USA

Atomic structure of the Σ=5 B(210)/[001]symmetrical tilt boundary in Cu con-taining different amount of segregated Bi has been *** most importantstructural effects found in this stucly are strong anisotropy of the segregation energy fordifferent sites and formation of an ordered alloy structure in the region of the grainboundaries.A saturation level of 1.25 monolayers beyond which no further segregationcan occur,was found.

关键词： segregation atomistic simulation grain boundary Cu-Bi alloy

atomistic simulation OF SEGREGATION IN Cu-Bi SYSTEM Ⅱ.SEGREGATION INDUCED STRUCTURAL TRANSFORMATIONS AT GRAIN BOUNDARIES

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Acta Metallurgica Sinica(English Letters) 1988年 7-12页

作者： V.VITEK University of Pennsylvania USA

Atomic structures *** Σ=17(530)/[001]symmetrical boundaries in Cu con-taining segregated Bi atoms at different sites have been *** segregation inducedstructural transformations frorn one structure to another accompanied by the displace-ment of the upper grain in respect to the lower grain and the migration of the grainboundary plane have been observed.A shear mechanism has been proposed in order toexplain such findings on the basis of the grain boundary,structural unit model and thestructural multiplicity.

关键词： transformation atomistic simulation grain boundary Cu-Bi alloy

atomistic simulations on adhesive contact of single crystal Cu and wear behavior of Cu-Zn alloy

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Chinese Physics B 2021年第2期30卷 442-448页

作者： You-Jun Ye Le Qin Jing Li Lin Liu Ling-Kang Wu National Quality Supervision and Inspection Center of Pressure Pipe Components Special Equipment Safety Supervision Inspection Institute of Jiangsu ProvinceNanjing 210036China School of Mechanical Engineering Changzhou UniversityChangzhou 213164China Jiangsu Power Equipment Co. LtdChangzhou 213000China School of Material Science and Engineering Georgia Institute of TechnologyAtlantaGeorgia 30332-0245USA

atomistic simulations are carried out to investigate the nano-indentation of single crystal Cu and the sliding of the Cu-Zn *** the contact zone is extended due to adhesive interaction between the contact atoms,the contact area on a nanoscale is redefined.A comparison of contact area and contact force between molecular dynamics(MD)and contact theory based on Greenwood-Williamson(GW)model is *** roughness causes the adhesive interaction to weaken,showing the better consistency between the calculated results by MD and those from the theoretical *** simulations of the sliding show that the substrate wear decreases with the mol%of Zn increasing,due to the fact that the diffusion movements of Zn atoms in substrate are blocked during the sliding because of the hexagonal close packed(hcp)structure of Zn.

关键词： atomistic simulation nano-indentation wear behavior

Propagation Properties of Shock Waves in Polyurethane Foam based on atomistic simulations

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Defence Technology（防务技术） 2024年第1期31卷 117-129页

作者： Zhiqiang Hu Jianli Shao Shiyu Jia Weidong Song Cheng Wang State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China

Porous materials are widely used in the field of protection because of their excellent energy absorption *** this work,a series of polyurethane microscopic models are established and the effect of porosity on the shock waves is studied with classical molecular dynamics ***,shock Hugoniot relations for different porosities are obtained,which compare well with the experimental *** pores collapse and form local stress wave,which results in the complex multi-wave structure of the shock *** microstructure analysis shows that the local stress increases and the local velocity decreases gradually during the process of pore collapse to complete ***,it leads to stress relaxation and velocity *** shock stress peaks can be fitted with two exponential functions,and the amplitude of attenuation coefficient decreases with the increase of ***,the pore collapse under shock or non-shock are discussed by the entropy increase rate of the *** energy is dissipated mainly through the multiple interactions of the waves under *** energy is dissipated mainly by the friction between atoms under non-shock.

关键词： Polyurethane foam Shock wave Attenuation atomistic simulation