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MECHANISMS UNDERLYING TWO KINDS OF SURFACE EFFECTS ON elastic CONSTANTS

Acta Mechanica Solida Sinica 2009年第6期22卷 605-622页

作者： Yizhe Tang Zhijun Zheng Mengfen Xia Yilong Bai State Key Laboratory of Nonlinear Mechanics （LNM） Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Department of Physics Peking University Beijing 100871 China

Recently, people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample： elastic modulus either decreases or increases with decreasing sample size. In this paper, based on intermolecular potentials and a one dimensional model, we provide a unified understanding of the two opposite size effects. Firstly, we analyzed the microstructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential. It is found that the atomic lattice near the surface becomes looser in comparison with the bulk, indicating that atoms in the bulk are located at the balance of repulsive forces, and the elastic moduli decrease with the decreasing thickness of the film accordingly. In addition, the decrease in moduli should be attributed to both the looser surface layer and smaller coordination number of surface atoms. Furthermore, it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair potential. Surprisingly, the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface respectively. To justify this concept, we examined ZnO in terms of Buckingham potential with long range Coulomb interactions. It is found that compared to its bulk lattice, the ZnO lattice near the surface becomes tighter, indicating the atoms in the bulk are located at the balance of attractive forces, owing to the long range Coulomb interaction. Correspondingly, the elastic modulus of one-dimensional ZnO chain increases with decreasing size. Finally, a kind of many-body potential for Cu was examined. In this case, the surface layer becomes tighter than the bulk and the modulus increases with deceasing size, owing to the long range repulsive pair interaction, as well a

关键词： size effect elastic modulus surface effect atomic/molecular potential surface layer

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Biocompatible Zr-Al-Fe bulk metallic glasses with large plasticity

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Science China(Physics,Mechanics & Astronomy) 2012年第9期55卷 1664-1669页

作者： HUA NengBin LI Ran WANG JianFeng ZHANG Tao Key Laboratory of Aerospace Materials and Performance (Ministry of Education) School of Materials Science and Engineering Beihang University Beijing 100191 China Department of Materials Science and Engineering Fujian University of Technology Fuzhou 350108 China

In the present study,high-zirconium ternary Zr-Al-Fe bulk metallic glasses(BMGs) with low Young's modulus and good plasticity were ***75 Al7.5 Fe17.5 BMG exhibits a low Young's modulus of 70 GPa and high Poisson's ratio of *** plasticity was demonstrated under both compression and bending conditions for the ***,the alloys show high corrosion resistance in phosphate buffered *** combination of desirable mechanical and chemical properties implies potential for biomedical applications.

关键词： bulk metallic glass mechanical properties elastic modulus corrosion behavior biomedical application

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MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINA COATINGS PLASMA-SPRAYED AT DIFFERENT SUBSTRATE TEMPERATURES

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Acta Mechanica Solida Sinica 2011年第5期24卷 461-466页

作者： Yazhe Xing Chaoping Jiang Hong Chen Jianmin Hao School of Materials Science and Engineering Chang＇an University Xi＇an 710064 China

Alumina coatings are prepared by atmospheric plasma spraying through controlling the substrate temperature during spraying. The changes in microstructure and mechanical properties of the coatings prepared at different substrate temperatures are examined. The hard-ness and the elastic modulus of the coatings are measured by indentation methods. The results show that interlamellar bonding in the coatings is significantly improved with increasing the substrate temperature. Moreover, long through-thickness columnar grains form in the coatings when the substrate temperature reaches above 430℃. As a result, the cross-sectional hardness and the elastic modulus perpendicular to the coating surface increase with increasing the substrate temperature.

关键词： plasma spraying alumina interlamellar bonding elastic modulus

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Stress-dependent shear wave splitting and permeability in fractured porous rock

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Journal of Rock Mechanics and Geotechnical Engineering 2019年第1期11卷 1-11页

作者： Daisuke Katsuki Marte Gutierrez Abdulhadi Almrabat Petroleum Engineering Department Colorado School of Mines Department of Civil and Environmental Engineering Colorado School of Mines

It is well known that shear wave propagates slower across than parallel to a fracture, and as a result, a travelling shear wave splits into two directions when it encounters a fracture. Shear wave splitting and permeability of porous rock core samples having single fracture were experimentally investigated using a high-pressure triaxial cell, which can measure seismic shear wave velocities in two directions mutually perpendicular to the sample axis in addition to the longitudinal compressive wave velocity. A single fracture was created in the samples using a modified Brazilian split test device, where the cylindrical sample edges were loaded on two diametrically opposite lines by sharp guillotines along the sample length. Based on tilt tests and fracture surface profilometry, the method of artificially induced tensile fracture in the sample was found to create repeatable fracture surfaces and morphologies. Seismic velocities of the fractured samples were determined under different levels of stress confinement and fracture shear displacement or mismatch. The effective confining stress was varied from 0.5 MPa to55 MPa, while the fractures were mismatched by 0 mm, 0.45 mm and 1 mm. The degree of matching of the fracture surfaces in the core samples was evaluated using the joint matching coefficient(JMC). Shear wave splitting, as measured by the difference in the magnitudes of shear wave velocities parallel(V_(S1))and perpendicular(V_(S2)) to the fracture, is found to be insensitive to the degree of mismatching of the fracture joint surfaces at 2 MPa, and decreased and approached zero as the effective stress was *** models for the stress-and JMC-dependent shear wave splitting and fractured rock permeability were developed based on the experimental observations. The effects of the joint wall compressive strength(JCS), JMC and stress on the stress dependency of joint aperture were discussed in terms of hydro-mechanical response. Finally, a useful relationship

关键词： Fractured rock Sandstone Stress dependency Shear wave splitting Wave velocity Permeability Fracture stiffness elastic modulus

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Mechanical and dielectric behaviors of perovskite(Ba,Sr)TiO_(3) borosilicate glass ceramics

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Journal of Advanced Ceramics 2014年第2期3卷 137-146页

作者： Avadhesh Kumar YADAV C.R.GAUTAM Abhinay MISHRA Department of Physics University of Lucknow Lucknow-226007India School of Materials Science and Technology Indian Institute of TechnologyBanaras Hindu UniversityVaranasi-221005India

Perovskite(Ba,Sr)TiO_(3)glass ceramics were crystallized in the presence of La_(2)O_(3)for glass ceramic system[(Ba_(1-x)Sr_(x))TiO_(3)]-[2SiO_(2)-B2O_(3)]-[K2O]-[La_(2)O_(3)](x=0.0 and 0.4).The formation of major crystalline phase of BaTiO_(3)along with secondary phase of Ba_(2)TiSi_(2)O_(8) was confirmed by X-ray diffraction(XRD)*** crystalline phase was clearly seen in the micrographs of(Ba,Sr)TiO_(3)borosilicate glass ceramic *** prepared glass ceramic samples showed very high values of toughness and elastic *** strontium titanate(BST)glass ceramics are used in barrier layer capacitors for storage of high energy due to their very high dielectric constant and low dielectric loss.

关键词： (Ba,Sr)TiO_(3) X-ray diffraction(XRD) scanning electron microscopy(SEM) elastic modulus dielectric constant

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A DAMAGE MECHANICS MODEL FOR TWISTED CARBON NANOTUBE FIBERS

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Acta Mechanica Solida Sinica 2012年第4期25卷 342-347页

作者： Qingqing Rong Jianshan Wang Yilan Kang Yali Li Qing-Hua Qin Tianjin Key Laboratory of Modern Engineering Mechanics Department of MechanicsSchool of Mechanical EngineeringTianjin UniversityTianjin 300072China Key Laboratory of Advanced Ceramics and Machining Technology Ministry capable of EducationSchool of Materials Science and EngineeringTianjin UniversityTianjin 300072China School of Engineering Australian National UniversityCanberraACT 0200Australia

Carbon nanotube fibers can be fabricated by the chemical vapor deposition spinning process. They are promising for a wide range of applications such as the building blocks of high-performance composite materials and micro-electrochemical sensors. Mechanical twisting is an effective means of enhancing the mechanical properties of carbon nanotube fibers during fabrication or by post processing. However, the effects of twisting on the mechanical properties remain an unsolved issue. In this paper, we present a two-scale damage mechanics model to quantitatively investigate the effects of twisting on the mechanical properties of carbon nanotube fibers. The numerical results demonstrate that the developed damage mechanics model can effectively describe the elastic and the plastic-like behaviors of carbon nanotube fibers during the tension process. A definite range of twisting which can effectively enhance the mechanical properties of carbon nanotube fiber is given. The results can be used to guide the mechanical twisting of carbon nanotube fibers to improve their properties and help optimize the mechanical performance of carbon nanotube-based materials.

关键词： carbon nanotube fibers damage twisting, multi-level structures elastic modulus

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In-plane isotropic separator-induced highly efficient sodium plating for unlocking the fast-charging capability of anode-free sodium battery at practical conditions

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Journal of Materiomics 2024年第3期10卷 643-651页

作者： Haocheng Yuan Kaihua Wen Shundong Guan Ying Liang Yu-Hsien Wu Sijie Liu Dengfeng Yu Liangliang Li Ce-Wen Nan State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing100084China

Ether-based electrolytes with excellent reductive stability are compatible with sodium(Na)metal an-odes,which enables stable cycling for Na metal batteries even in an anode-free ***,the practical applications of anode-free sodium batteries(AFSBs)with a high theoretical energy density are restricted by the low-rate capability and limited cycle *** we demonstrate that the mechanical properties of the separators,which have been overlooked in previous studies,can significantly affect the cycling stability of AFSBs due to the intrinsic softness of Na and the large volume variation of AFSBs during Na plating/*** using various separators including polypropylene(PP),polyethylene(PE),PP/PE/PP tri-layer,and aluminum oxide-coated separators,we find that the balanced elastic moduli of the separator along the machine direction and transverse direction are crucial for enabling highly effi-cient Na plating and unlocking the 4 C fast-charging capability of the AFSBs at practical conditions including a high cathode active mass loading(13.5 mg/cm^(2)),lean electrolyte addition(8.8 mL/cm^(2)),and no pre-sodiation *** study provides an important separator design principle for the develop-ment of high-rate and long-cycle-life AFSBs.

关键词： Sodium metal elastic modulus Ether electrolyte Sodium battery Short circuit

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Test and Analysis of the Sound Insulation Performance of Four Types of Timber Structure Floors under Jumping Excitation

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Journal of Renewable Materials 2021年第4期9卷 829-840页

作者： Yujie Huang Hao Zhu Dauletbek Assima Zheng Wang Minmin Li Xinyue Zhao College of Materials Science and Engineering Nanjing Forestry UniversityNanjing210037China College of Mechanical and Electronic Engineering Nanjing Forestry UniversityNanjing210037China College of Civil Engineering Tongji UniversityShanghai200092China College of Civil Engineering Nanjing Forestry UniversityNanjing210037China

To improve the impact sound insulation performance of building floors and meet the objective requirements for living comfort of residents,in this article,three kinds of elastic cushion materials,Portuguese cork board,BGL insulation sound insulation foam board,and EPP polypropylene plastic foam board,are applied to the sound insulation of a light frame wood floor structure of the same bedroom and compared to the ordinary *** study uses the transfer function method and transient excitation method to measure the sound insulation,damping ratio,and elastic modulus of materials,as well as the sound insulation of the floor under the jumping excitation method of daily *** comparative analysis,the results and factors of improving the sound insulation performance of the floor are obtained,according to which three types of elastic cushion materials and the floor covering composed of them have higher vibration and noise reduction *** them,the overall sound insulation performance of BGL board floor is the highest,followed by EPP board and cork board floor,and ordinary OSB floor is the *** the jumping excitation method,three floating floors can improve the impact sound insulation performance of the middle and low-frequency bands.

关键词： Timber floor structure elastic cushion material damping ratio elastic modulus jumping excitation method of daily behavior testing and comparative analysis

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Nanoindentation study of a Cu/Ta/SiO_2/Si multilayer system

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Journal of Semiconductors 2012年第4期33卷 17-22页

作者：张昕卢茜吴子景吴晓京 Shen Weidian 蒋宾 Department of Materials Science Fudan UniversityShanghai 200433China Micro-Nanoelectronics Platform Fudan UniversityShanghai 200433China Department of Physics and Astronomy Eastem Michigan UniversityYpsilantiMI 48197USA Shanghai Integrated Circuit R&D Center Shanghai 201203China

Tantalum and copper layers were deposited on a thermally oxidized Si substrate in a magnetron sputtering process. Nanoindentation was adopted to investigate the hardness and elastic modulus of the Cu/Ta/Si02/Si multilayer system. The hardness shows an apparent dependence on the film thickness, and decreases with the increase of film thickness, whereas the elastic modulus does not. To reveal the structural change, a trench through the center of a residual indent was cut by a focused ion beam, and then examined using an ionicroscope. TEM analysis showed that delamination occurs at the interface between the Ta and the Si02 layer of the residual indent, suggesting that the destruction under a relatively large load is due to weak bonding.

关键词： copper tantalum nanoindentation hardness elastic modulus

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Mechanical Behavior of Polyurethane Polymer Materials under Triaxial Cyclic Loading:A Particle Flow Code Approach

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Journal of Wuhan University of Technology(Materials Science) 2018年第4期33卷 980-986页

作者：刘恒 WANG Fuming 石明生 TIAN Wenling School of Water Conservancy and Environment Zhengzhou University School of Civil and Transportation Engineering Henan University of Urban Construction State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining & TechnologyXuzhou

Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.

关键词： polymer particle flow code cyclic loading elastic modulus micro-cracks axial strain

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