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Journal of Materials Science & Technology 2019年第6期35卷 1147-1152页

作者： c.c.Roach y.c.Lu Department of Mechanical Engineering University of Kentucky

Understanding the roles of interlayers in reinforcement efficiencies by layered graphene is very important in order to produce strong and light graphene based nanocomposites. The present paper uses the finite element method to evaluate the interfacial strain transfers and reinforcement efficiencies in layered graphene-polymer composites. Results indicate that the presence of compliant interlayers in layered graphene plays significant roles in the transfers of strain/stress from matrix to graphene and subsequently the reinforcement effectiveness of layered graphene. In general, the magnitude of shear strain transferred onto the rigid graphene decreases as the thickness of the interlayer increases. This trend becomes insignificant as the graphene becomes sufficiently large(s>25,000). The shear strain at the interface of graphene-matrix is also greatly influenced by the interlayer modulus. A stiffer interlayer would result in a higher shear strain transferred on the graphene. The performance of the interlayers is further affected by the property of the composite and the architecture of the layered graphene stack. If a composite contains more graphene phase, the efficiency of reinforcement by a layered graphene becomes improved. If a graphene stack contains more interlayers, the effectiveness of reinforcement at the edges of the graphene becomes negatively affected.

关键词： Interlayer Layered graphene Nanocomposites Interfacial stress transfer Finite element method

Two sides of the heliopause

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Science china Earth Sciences 2011年第12期54卷 1830-1844页

作者： WHANG y. c catholic University of America

Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and termination shock. This article addresses three aspects of the plasma and magnetic field on two sides of the heliopause：（1） The interstellar magnetic field surrounding the heliopause. In the limit of very low plasma β-ratio an analytical solution is obtained for the 3D interstellar magnetic field by means of a line dipole method. The undisturbed magnetic field in the upstream is allowed to have an arbitrary inclination angle. The solution describes the heliosphere as having a blunt-nosed geometry on the upwind side and approaching a cylindrical geometry on the downwind side. The distortion of the magnetic field can penetrate very deep into the interstellar space. （2） Interaction of the interstellar neutral hydrogen with the global solar wind. The ionization process leads to removal of interstellar neutral hydrogen in the heliosphere： on the upwind side, 90% of hydrogen depletion occurs inside 60 AU, the hydrogen density changes rapidly inside 10 AU. A hydrogen cavity forms inside -4 AU; the cavity extends on the downwind side to form a long cavity wake. Outside the cavity and cavity wake, pickup protons are produced, they cause deceleration and heating of the solar wind. The wind speed and temperature also increase steadily with heliolatitude caused by the latitudinal increase in wind speed at the inner boundary. （3） The global geometry of the termination shock. The termination shock has been treated as having a closed geometry in previous heliosphere models. This study presents a new perspective that the global termination shock may have a bow-shaped open geometry. The termination shock forms on the upwind side because the forward motion of the supersonic solar wind is blocked at the blunt-nosed heliopause. However, the heliopause likely to be open on the downwind side; the motion of the supersonic solar wind is unobstructed for shock formation. Thus, the globa

关键词： solar wind interstellar medium magnetic fields plasmas magnetohydrodynamics (MHD)

Study on the wind field and pollutant dispersion in street canyons using a stable numerical method

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Journal of Environmental Sciences 2005年第3期17卷 488-490页

作者： Dennis y.c. LEUNG Department of Mechanical Engineering the University of Hong Kong Hong Kong China

A stable finite element method for the time dependent Navier-Stokes equations was used for studying the wind flow and pollutant dispersion within street canyons. A three-step fractional method was used to solve the velocity field and the pressure field separately from the governing equations. The Streamline Upwind Petrov-Galerkin(SUPG) method was used to get stable numerical results. Numerical oscillation was minimized and satisfactory results can be obtained for flows at high Reynolds numbers. Simulating the flow over a square cylinder within a wide range of Reynolds numbers validates the wind field model. The Strouhal numbers obtained from the numerical simulation had a good agreement with those obtained from experiment. The wind field model developed in the present study is applied to simulate more complex flow phenomena in street canyons with two different building configurations. The results indicated that the flow at rooftop of buildings might not be assumed parallel to the ground as some numerical modelers did. A counter-clockwise rotating vortex may be found in street canyons with an inflow from the left to right. In addition, increasing building height can increase velocity fluctuations in the street canyon under certain circumstances, which facilitate pollutant dispersion. At high Reynolds numbers, the flow regimes in street canyons do not change with inflow velocity.

关键词： finite element method Streamline Upwind Petrov-Galerkin method three-step fractional method

Effects of building aspect ratio,diurnal heating scenario,and wind speed on reactive pollutant dispersion in urban street canyons

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Journal of Environmental Sciences 2012年第12期24卷 2091-2103页

作者： Nelson y.O.Tong Dennis y.c.Leung Department of Mechanical Engineering The University of Hong Kong

A photochemistry coupled computational fluid dynamics （cFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario （solar radiation affections in nighttime, daytime, and sun-rise/set）, wind speed, building aspect ratio （building-height-to-street-width）, and dispersion of reactive gases, specifically nitric oxide （NO）, nitrogen dioxide （NO2） and ozone （O3） such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and 03. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of 03 concentrations into the street canyons along windward walls under all diurnal heating scenarios. comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios.

关键词： photochemistry reactive pollutant dispersion building aspect ratio diurnal heating scenario wind speed urban streetcanyon

MEcHANIcAL PROPERTIES OF Ti_3Sic_2 AT HIGH TEMPERATURE

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Acta Metallurgica Sinica(English Letters) 2004年第4期17卷 465-470页

作者： y.W.Bao y.c.Zhou Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 ChinaShenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

creep and stress relaxation behavior, the elastic modulus and fracture toughness of machinable Ti3Sic2 at various temperatures from 20 to 1250℃ were investigated by means of three-point bending tests. The experiments were performed respectively at: (i) fixed stress and changed temperatures, and (ii) fixed temperature and changed stresses. A creep resistance parameter that represents the probability of creep deformation in a given condition was defined as a function of both applied stress and the threshold stress, varying in a range from 0 to 1. Elastic modulus at high temperatures was measured through comparing relative slopes of loading curves in cyclic loading curve. The fracture toughness measured by SENB method showed a stable value in the range of 25-1000℃, but over 1000℃, it declined abruptly from -6.7MPa·m1/2 to -2.0MPa·m1/2 at 1200℃.

关键词： high-temperature Ti3Sic2 creep stress relaxation fracture toughness

cyclic stress-controlled tests on offshore clay

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Journal of Rock Mechanics and Geotechnical Engineering 2017年第2期9卷 376-381页

作者： S.y. Thian c.y. Lee Department of civil Engineering Jalan Ikram-UnitenUniversiti Tenaga NasionalKajang43000Malaysia

One of the main concerns in cyclic behavior of soft clay is gradual degradation with the progression of loading cycle.A series of cyclic constant-volume direct simple shear(cDSS) loading tests was performed on Malaysia offshore clay to study its undrained *** testing program consists of stresscontrolled tests with cyclic shear ratio ranging from 0.34 to 0.83 at different overconsolidation ratios(OcRs).For a given cyclic stress ratio in stress-controlled tests,the accumulated cyclic strain and pore water pressure increase with elevated number of *** heavily overconsolidated clay specimens,the negative cyclic pore water pressure is generated followed by positive cyclic pore water pressure as cyclic tests *** post-cyclic strength of offshore clay specimens is reduced by undrained cyclic stresscontrolled loading.

关键词： Offshore clay cyclic degradation Undrained cyclic loading Shear strength Pore pressure Overconsolidation ratio(OcR)

AN AccURATE TWO-DIMENSIONAL THEORy OF VIBRATIONS OF ISOTROPIc,ELASTIc PLATES

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Acta Mechanica Solida Sinica 2011年第2期24卷 125-134页

作者： Peter c.y.Lee Department of civil and Environmental Engineering Princeton University

An infinite system of two-dimensional equations of motion of isotropic elastic plates with edge and corner conditions are deduced from the three-dimensional equations of elasticity by expansion of displacements in a series of trigonometrical functions and a linear function of the thickness coordinate of the plate. The linear term in the expansion is to accommodate the in-plane displacements induced by the rotation of the plate normal in low-frequency flexural motions. A system of first-order equations of flexural motions and accompanying boundary conditions are extracted from the infinite system. It is shown that the present system of equations is equivalent to the Mindlin＇s first-order equations, and the dispersion relation of straight-crested waves of the present theory is identical to that of the Mindlin＇s without introducing any corrections. Reduction of present equations and boundary conditions to those of classical plate theories of flexural motions is also presented.

关键词： isotropic elastic plates first-order equations boundary conditions flexural andthickness-shear vibrations

Asymptotic Properties of a Modified Semi-Parametric MLE in Linear Regression with Right-censored Data

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Acta Mathematica Sinica,English Series 2002年第2期18卷 405-416页

作者： WONG George y.c. Strang cancer Prevention center.428 E 72nd Street.New york.Ny 10021.USA

consider a linear regression model y=β'X+*** y may be right censored and the cdf F+o of e is *** show that a modified semi-parametric *** by .is strongly consistent under certain regularity *** F_o is discontinuous,then P(≠βi.o.)=0, which means that P(=βif the sample size is large)=*** latter property has not been reported for the existing *** contrast,most estimators,such as the Buckley-James estimator and M-estimators .satisfy that P(≠βi.o.)=1.

关键词： consistency Super-efficiency Semi-parametric MLE

A Hybrid Joining Technology for Aluminum/Zinc coated Steels in Vehicles

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Journal of Materials Science & Technology 2010年第9期26卷 858-864页

作者： c.y.choi D.c.Kim D.G.Nam y.D.Kim y.D.Park School of Materials Science and Engineering Pusan National UniversityBusan Advanced Welding & Joining R&D Division Institute of Industrial Technology Incheon Dongnam Technology Service Division Korea Institute of Industrial TechnologyBusan Department of Advanced Materials Engineering Dong-Eui UniversityBusan

currently,in the automotive industry,joining of the aluminum alloys with the steel is a crucial problem to be *** joining techniques including resistance spot and gas metal arc welding are not acceptable for those applications due to a number of metallurgical *** investigation was carried out to develop the hybrid joining process combining the resistance spot welding and *** this study,an attempt was made to apply hybrid process to the joining of dissimilar sheet metals,Al-Mg-Si（6000 series） alloy and low carbon steel *** process（resistance spot weld/brazing） using filler metal was found to be effective to overcome the incompatibility between aluminum alloy and *** hybrid joining process of Al alloy sheet and steel sheet did not produce acceptable bond strength,it was proved to have reasonable interfacial bond layer if the optimal process condition was applied.

关键词： Hybrid joining Aluminum alloy Steel Resistance welding Brazing

Enhancement of Sinter Densification of SrO-BaO-Nb_2O_5-SiO_2 Tungsten-Bronze Glass-ceramics by Doping with P_2O_5

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Journal of Materials Science & Technology 2013年第8期29卷 731-736页

作者： J.c.chen y.Zhang Shenyang Research and Development centre for Advanced Materials Institute of Metal ResearchChinese Academy of Sciences State Key Laboratory of New ceramics and Fine Processing Institute of Nuclear and New Energy TechnologyTsinghua University

Densification behaviors of SrO-BaO-Nb2O5-SiO2 based glass-ceramics prepared by conventional sintering were investigated with an emphasis on the influence of P2O5 content. Although P2O5 dopant did not modify the surface crystallization mechanism, it resulted in a decrease of the glass transition temperature, which facilitates the viscous glass flow necessary for sintering. However, premature crystallization of （Sr, Ba）Nb2O6 induced by addition of excess amount of P2O5 essentially retarded sintering due to the formation of closed pores in the matrix. The SrO-BaO-Nb2O5-SiO2 glass with 1.0 mol% P2O5 （SBN-1P） showed the best sinter densification, which was accomplished at about 850 ℃.

关键词： Sintering densification DieLectric properties Glass-ceramic