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Yielding behavior of copper nanowire in the presence of vacancies

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 1010-1017页

作者： LIU XiaoMing YANG XiaoBin WEI YueGuang The State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Resources and Safety Engineering China University of Mining&TechnologyBeijing 100083China

In the present research,the measurement fluctuations of mechanical properties in nanowires (NWs) are investigated by using the molecular dynamics *** large numbers of simulations are performed to study the yield behaviors of the *** results have shown that the yield behavior of the smaller diameter NW is more sensitive to the presence of vacancies,and the dispersion of the measured mechanical properties for the small scale NW is larger than that for the large scale *** results have also shown that vacancies escape from the bulk to the free surfaces as a result of high stress applied at the small scale systems similar to the dislocation starvation phenomenon observed in the compression test of nano-pillars,and dislocation nucleation induced by surface defect occurs after the vacancy reaches free surface leading to lower yield ***,the strong surface vacancy interactions at the nanoscale level are also investigated.

关键词： nanowire yield strength vacancies size effect

The influence of agglomerates on the densification and microstructural evolution in sintering of a multi-particle system

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 1051-1058页

作者： WANG Chao CHEN ShaoHua The State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

Effects of agglomerates on the densification behavior and microstructural evolution during solid-state sintering of a cube of copper particles have been studied with discrete element method (DEM).It is found that the densification of the sintering system decreases as the volume fraction of agglomerates *** a given volume fraction of agglomerates,the smaller the size of agglomerates,the poorer the densification and more inhomogeneous the compact *** morphology and distribution of agglomerates have negligible effects on the densification,especially for the case with a low volume fraction of *** with a smaller average coordination number would have more restriction on the densification of sintering *** our best knowledge,it is the first time to study the effect of agglomerates on sintering behavior using *** study should be useful for further investigations of the effect of various inhomogeneities of microstructure on the complex sintering process by DEM.

关键词： solid-state sintering discrete element method agglomerate microstructure evolution

Stochastically driven vibrations of single-layered graphene sheets

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 1103-1110页

作者： LIU RuMeng WANG LiFeng State Key Laboratory.of mechanics and Control of Mechanical Structures Nanjing University Aeronautics and AstronauticsNanfing 210016China

Thermal vibration of single-layered graphene sheets (SLGSs) is investigated using plate model together with the law of equi-partition of energy and the molecular dynamics (MD) method based on the condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force *** in-plane stiffness and Poisson ratio of SLGSs are calculated by stretching *** effective thickness of SLGSs is obtained by the MD simulations for the thermal vibration of SLGSs through the natural *** root-mean-squared (RMS) amplitudes for SLGSs of differing temperatures and boundary conditions are calculated by the MD,and are compared with the results calculated by the thin plate model together with the law of equi-partition of *** the center of SLGSs,the thin plate theory can predict the MD results reasonably *** the difference of bonding structure of the edge atoms,the deviation between the MD results and plate theory becomes more readily apparent near the edges of SLGSs.

关键词： single-layered graphene sheets thermal vibration molecular dynamics simulation RMS amplitude thin plate theory equi-partition of energy

Effects of functionally graded materials on dynamics of molecular bond clusters

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 980-988页

作者： ZHANG WenLiang QIAN Jin YAO HaiMin CHEN WeiQiu GAO HuaJian Department of Engineering mechanics Zhejiang UniversityHangzhou 310027China Soft Matter Research Center Zhejiang UniversityHangzhou 310027China Department of Mechanical Engineering Hong Kong Polytechnic UniversityHong KongChina School of Engineering Brown UniversityProvidenceRI 02912USA

Unlike nonspecific adhesion of conventional hard materials in engineering commonly described by JKR and DMT type models,the molecular adhesion via specific receptor-ligand bonds is stochastic by nature and has the feature that its strength strongly depends on the medium stiffness surrounding the *** this paper,we demonstrate in a stochastic-elasticity framework that a type of materials with linearly graded elastic modulus can be designed to achieve "equal load sharing" and enhanced cooperative rebinding among interfacial molecular *** modulus gradation,multiple molecular bonds can be elastically decoupled but statistically *** general,uniform molecular adhesion can be accomplished by two strategies:homogeneous materials with sufficient stiffness higher than a threshold or heterogeneous materials satisfying the criterion on modulus *** results not only provide a theoretical principle for possible applications of functionally graded materials in quantitatively controlling cell-matrix adhesion,but also have general implications on adhesion between soft materials mediated by specific molecular binding.

关键词： graded material adhesion molecular bond stiffness gradation

Radial breathing modes of multi-walled carbon nanotubes by an atomic beam-spring model

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 940-946页

作者： MIAO ChunYang LI HaiJun GUO WanLin State Key Laboratory of mechanics and Control of Mechanical Structures and the Key Laboratory of Intelligent Nano Materials and Devices of MOE and Institute of Nano Science Nanjing University of Aeronautics and AstronauticsNanjing 210016China Maintenance Engineering Division Center of Aviation Safety and TechnologyCivil Aviation Administration of ChinaBeijing 100028China

Based on molecular force fields,a new finite element model is constructed for multi-walled carbon nanotubes where the interlayer interactions and C--C bonds are simulated by the elements of piece-wise linear spring and rectangular cross section beam,*** high computation efficiency and atomic reification,the radial breathing modes of multi-walled carbon nanotubes are studied systemically using this *** results show the correspondence between carbon nanotube structures and vibrational modes,which provide unequivocal data for the experimental characterization of carbon *** empirical relationship of radial breathing modes frequencies with the nanotube radius are also obtained for two-layer carbon nanotubes.

关键词： radial breathing modes multi-walled carbon nanotube atomic beam-spring model

Understanding formation mechanism of ZnO diatomic chain and multi-shell structure using physical mechanics:Molecular dynamics and first-principle simulations

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 1138-1146页

作者： WANG BinBin WANG FengChao ZHAO YaPu State Key Laboratory of Nonlinear mechanics(LNM) Institute of MechanicsChinese Academy of SciencesBeijing 100190China

In this paper,the possibility of the monatomic chain (MC) formation for ZnO material was studied by molecular dynamics (MD) *** process of MC formation and the effects of temperature,strain rate and size were studied *** tensile process can be divided to be five stages and the ZnO diatomic chain (DC) can be *** MD results show that most atoms in MC came from the original surface of ZnO nanowires (NWs).Temperature and strain rate are two important factors affecting the process,and both high temperature and low strain rate in a certain range would be beneficial to the formation of ***,the effects of strain rate and temperature could attribute to the Arrhenius model and the energy release ***,multi-shell structure was found for the samples under tensile strain and the layer-layer distance was about *** studies based on density functional theory showed that the most stable structure of ZnO DC was confirmed to be linear,and the I-V curve was also got using ATK.

关键词： diatomic chain multi-shell structure ZnO size effect temperature and strain rate effects

Shock tube study of kerosene ignition delay at high pressures

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 947-954页

作者： LIANG JinHu WANG Su HU HongHao ZHANG ShengTao FAN BingCheng CUI JiPing College of Chemistry and Chemical Engineering Chongqing UniversityChongqing 400044China State Key Laboratory of High Temperature Gas Dynamics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

Ignition delay times of China No.3 aviation kerosene were measured behind reflected shock waves using a heated high-pressure shock *** conditions covered a wider temperature range of 820-1500 K,at pressures of 5.5,11 and 22 atm,equivalence ratios of 0.5,1.0 and 1.5,and oxygen concentration of 20%.Adsorption of kerosene on the shock tube wall was taken into *** delay times were determined from the onset of the excited radical OH emission in conjunction with the pressure *** experimental results of ignition delay time were correlated with the equations:11 0.22 1.09 2 3.2 10 [Keros ene ] [O2] exp(69941 RT) and 7 0.88 0.23 4.72 10 P exp(62092 RT).The current measurements provide the ignition delay behavior of China No.3 aviation kerosene at high pressures and air-like O2 concentration.

关键词： ignition delay time kerosene shock tube high pressure

Fabrication technique of micro/nano-scale speckle patterns with focused ion beam

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Science China(Physics,mechanics & Astronomy) 2012年第6期55卷 1037-1044页

作者： LI YanJie XIE HuiMin LUO Qiang GU ChangZhi HU ZhenXing CHEN PengWan ZHANG QingMing AML Department of Engineering MechanicsTsinghua UniversityBeijing 100084China Institute of Physics Chinese Academy of SciencesBeijing 100190China State Key Laboratory of Explosion Science and Technology Beijing Institute of TechnologyBeijing 100081China

The fabrication technique of micro/nano-scale speckle patterns with focused ion beam (FIB) system is studied for digital image correlation (DIC) measurement under a scanning electron microscope (SEM).The speckle patterns are fabricated by directly etching the counterpart of the specimen to the black part of a *** intensity gradient is used to evaluate the quality of these SEM images of speckle patterns fabricated based on different templates to select an optimum *** pattern size depending on the displacement measurement sensitivity is adjusted by altering the magnification of FIB according to the relation curve of the etching size versus *** influencing factors including etching time and ion beam current are *** body translation tests and rotation tests are carried out under SEM to verify the reliability of the fabricated speckle *** calculated values are in good agreement with the imposed ones.

关键词： speckle pattern digital image correlation (DIC) micro/nano-scale focused ion beam (FIB) scanning electron microscope (SEM)

"Olympics of mechanics" Held in Beijng

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Bulletin of the Chinese Academy of Sciences 2012年第4期26卷 290-290页

From August 20 to 24,2012,more than 1,500 mechanical scientists and students from over 60 countries gathered in Beijing to attend the 23^(rd) international congress of theoretical and applied mechanics(ICTAM).The cong... 详细信息

关键词：应用力学北京市奥运专题讨论会科学家机械齐聚