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THEORy.OF WATER WAVES IN AN ELASTIC VESSEL

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Acta Mechanica Sinica 2000年第2期16卷 97-112页

作者： D. y. Hsieh Division of Applied Mathematics Brown University USA

Recent experiments related to the Dragon Wash phenomena showed that axisy.metric capillary.waves appear first from excitation, and circumferential capillary.waves appear after increase of the excitation strength. Based on this new finding, a theory.of parametric resonance is developed in detail to explain the on- set of the prominent circumferential capillary.waves. Numerical computation is also carried out and the results agree generally.with the experiments. Analy.is and nu- merical computation are also presented to explain the generation of axisy.metric low-frequency.gravity.waves by.tile high-frequency.external excitation.

关键词： water waves elastic vessel Dragon Wash

ANALy.IS OF THREE-DIMENSIONAL UPSETTING PROCESS By.THE RIGID-PLASTIC REPRODUCING KERNEL PARTICLE METHOD

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Acta Metallurgica Sinica(English Letters) 2006年第5期19卷 371-378页

作者： y. H. Liu J. chen S. y. X. W. chen National Die and Mould CAD Engineering Research Center Shanghai Jiao Tong UniversityShanghai 200030 China

A meshless approach, called the rigid-plastic reproducing kernel particle method （RKPM）, is presented for three-dimensional （3D） bulk metal forming simulation. The approach is a combination of RKPM with the flow theory.of 3D rigid-plastic mechanics. For the treatments of essential boundary.conditions and incompressibility.constraint, the boundary.singular kernel method and the modified penalty.method are utilized, respectively. The arc-tangential friction model is employ.d to treat the contact conditions. The compression of rectangular blocks, a ty.ical 3D upsetting operation, is analy.ed for different friction conditions and the numerical results are compared with those obtained using commercial rigid-plastic FEM （finite element method） software Deform^3D. As results show, when handling 3D plastic deformations, the proposed approach eliminates the need of expensive meshing and remeshing procedures which are unavoidable in conventional FEM and can provide results that are in good agreement with finite element predictions.

关键词： meshless reproducing kernel particle method(RKPM) three-dimensional upsetting incompressibility modified penalty.method

Low temperature oxidation of Cr-alloy.d MoSi_2

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中国有色金属学会会刊：英文版 2007年第6期17卷 1282-1286页

作者： E. Strom y. Cao y. M. y.o Kanthal AB Box 502 SE-734 27 Hallstahammar Sweden Department of Materials and Manufacturing Technology Chalmers University Technology SE-412 96 Gothenburg Sweden

Cr-alloy.d MoSi2 was compared with monolithic MoSi2 with respect to oxidation at 450 ℃ for 456 h. Phases formed on Cr-alloy.d MoSi2 after exposure are Cr2(MoO4)3, MoO3, and cristobalite (SiO2) according to X-ray diffraction results. Monolithic MoSi2 forms MoO3 and mainly.amorphous SiO2. X-ray photoelectron spectroscopy.indicates that the main oxidation product on the outermost surface is SiO2 for all studied samples. The samples form a relatively.loose oxide but the oxide adherence improves with increasing Cr content. It is indicated that Cr addition can benefit pesting control in MoSi2.

关键词：钼硅化合物合金有害物氧化作用

Parameter Optimisation of Stress-strain Constitutive Equations Using Genetic Algorithms

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Journal of Materials Science & Technology 2003年第z1期19卷 5-8页

作者： y. y. y.ng M. Mahfouf D.A.Linkens Department of Automatic Control and Sy.tems Engineering University of Sheffield Mappin St. Sheffield S1 3JD UK Department of Automatic Control and Systems Engineering University of Sheffield Mappin St. Sheffield S1 3JD UK Department of Automatic Control and Systems Engineering University of Sheffield Mappin St. Sheffield S1 3JD UK

The accuracy.of numerical simulations and many.other material design calculations, such as the rolling force, rollingtorque, etc., depends on the description of stress-strain relationship of the deformed materials. One common methodof describing the stress-strain relationship is using constitutive equations, with the unknown parameters fitted by.xperimental data obtained via plane strain compression (PSC). Due to the highly.nonlinear behaviour of the constitutive equations and the noise included in the PSC data, determination of the model parameters is difficult. Inthis paper, genetic algorithms were exploited to optimise parameters for the constitutive equations based on thePSC data. The original PSC data were processed to generate the stress-strain data, and data pre-processing wascarried out to remove the noise contained in the original PSC data. Several genetic optimisation schemes have beeninvestigated, with different coding schemes and different genetic operators for selection, crossover and *** was found that the real value coded genetic algorithms converged much faster and were more efficient for theparameter optimisation problem.

关键词： Genetic algorithms, Parameter optimisa tion, Aluminium alloy. Flow stress, Constitutive equations

Investigation of the crack problem in non-local piezoelectric materials under combined electromechanical loadings

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Acta Mechanica Sinica 2009年第2期25卷 219-225页

作者： Q. Li y. chen School of Aerospace, Xi’an Jiao-Tong University.710049 Xi’an, China School of Aerospace Xi’an Jiao-Tong University 710049 Xi’an China

The present investigation of the crack problem in piezoelectric materials is performed based on the non-local theory. After some manipulations, the impermeable crack, the permeable crack （the crack gap is full of NaCI solution）, and the semi-permeable crack （the crack gap is full of air or silicon oil） are reduced to a uniform formulation by.assuming the normal electric displacement on the crack surfaces to be an unknown variable. Thus, a triple integral equation with the unknown normal electric displacement is established. By.using the Newton iterative method and solving the triple integral equation, it is found that the normal electric displacement on the crack surfaces is no longer a constant as determined by.previous studies, rather, it depends upon the remote combined electromechanical loadings. Numerical results of the stresses and electric displacement fields show that there are no singularities at the crack tips so that the stresses remain finite. It is of great significance that the concrete electric boundary.condition on the crack surfaces exerts significant influence on the near-tip fields and in this way.play. an important role in evaluating the crack stability.in the non-local piezoelectric materials. More specifically. the impermeable crack model alway. overestimates the finite stresses at the crack tips, whereas the permeable crack model alway. underestimates them.

关键词： Crack Non-local piezoelectric materialsImpermeable Permeable Semi-permeable

An electron moir■ method for a common SEM

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Acta Mechanica Sinica 2006年第6期22卷 595-602页

作者： y. M. Xing S. Kishimoto y. R. Zhao Department of Applied Mechanics Inner Mongolia University of Technology Hohhot 010051 China National Institute for Materials Sciences Tsukuba Ibaraki 305-0047 Japan

In the electron moiré method, a high-frequency.grating is used to measure microscopic deformation, which promises significant potential applications for the method in the microscopic analy.is of materials. However, a special beam scanning control device is required to produce a grating and generate a moiré fringe pattern for the scanning electron microscope （SEM）. Because only.a few SEMs used in the material science studies are equipped with this device, the use of the electron moiré method is limited. In this study. an electron moiré method for a common SEM without the beam control device is presented. A grating based on a multi-scanning concept is fabricated in any.observing mode. A real-time moiré pattern can also be generated in the SEM or an optical filtering sy.tem. Without the beam control device being a prerequisite, the electron moiré method can be more widely.used. The experimental results from three different ty.es of SEMs show that high quality.gratings with uniform lines and less pitch error can be fabricated by.this method, and moiré patterns can also be correctly.generated.

关键词： Electron moiré Grating Multi-scanning Electron beam moiré

Main α relaxation and slow β relaxation processes in a La30Ce30Al15Co25 metallic glass

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Journal of Materials Science & Technology 2019年第6期35卷 982-986页

作者： J.C. Qiao y.H. chen R. Casalini J.M. Pelletier y. y.o School of Mechanics Civil Engineering and Architecture Northwestern Polytechnical University Xi'an 710072 China Chemistry.Division Naval Research Laboratory Code 6120 Washington DC 20375-5342 United States Universite de Ly.n MATEIS UMR CNRS5510 Bat. B. Pascal INSA-Lyon F-69621 Villeurbanne cedex France

Dy.amic relaxation processes are fundamental to understand the mechanical and phy.ical properties of metallic glasses. In the current work, mechanical relaxations in a La30Ce30Al15Co25 bulk metallic glass were probed by.dy.amic mechanical analy.is. In contrast to many.metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced slow β relaxation peak. Phy.ical aging below the glass transition temperature Tgleads to an increase of the apparent activation energy.and a decrease of the slow β relaxation magnitude. The correlation between the slow β relaxation and the main α relaxation is discussed.

关键词： Mechanical relaxation Dy.amic mechanical relaxation α Relaxation β relaxation Phy.ical aging

A GLOBAL ALGORITHM IN THE NUMERICAL RESOLUTION OF THE VISCOUS/INVISCID COUPLED PROBLEM

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Chinese Annals of Mathematics,Series B 1997年第2期18卷 191-200页

作者： XUCHUANJU MADAy.y. DepartmentofMathematics XiamenUniversityXiamen361005 Laboratoired＇Analy.eNumerique UniversitePierreetMarieCurieParisFrance.

This paper deals with the spectral approximation of an incompressible viscous/inviscid coupled model. An efficient Uzawa algorithm based on a new variational formulation is proposed. The generalization to the coupl... 详细信息

关键词： Coupled equations Navier-Stokes equations Euler equations Spectral discretization Global Uzawa algorithm

Extension/Compression-Controlled Complete Band Gaps in 2D Chiral Square-Lattice-Like Structures

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Acta Mechanica Solida Sinica 2018年第1期31卷 51-65页

作者： y. L. Huang N. Gao W.Q. chen R.H. Bao Department of Engineering Mechanics Zhejiang University Hangzhou 310027 China State Key.Lab of CAD & CG Zhejiang University Hangzhou 310058 China Key.Laboratory.of Soft Machines and Smart Devices of Zhejiang Province Zhejiang University Hangzhou 310027 China Soft Matter Research Center Zhejiang University Hangzhou 310027 China

Achieving tunable band gaps in a structure by.external stimuli is of great importance in acoustic applications. This paper aims to investigate the tunability.of band gaps in square-lattice-like elastic periodic structures that are usually.not featured with notable band gaps. Endowed with chirality. the periodic structures here are able to undergo imperfection-insensitive large deformation under extension or compression. The influences of geometric parameters on band gaps are discussed via the nonlinear finite element method. It is shown that the band gaps in such structures with curved beams can be very.rich and, more importantly. can be efficiently.and robustly.tuned by.apply.ng appropriate mechanical loadings without inducing buckling. As expected, geometry.play. a more significant role than material nonlinearity.does in the evolution of band gaps. The dy.amic tunability.of band gaps through mechanical loading is further studied. Results show that closing, opening, and shifting of band gaps can be realized by.exerting real-time global extension or compression on the structure. The proposed periodic structure with well-designed chiral sy.metry.can be useful in the design of particular acoustic devices.

关键词： Band gap Tunability Square-lattice-like periodic structure Chiral sy.metry.Large deformation