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A new design of dual-constituent triangular lattice metamaterial with unbounded thermal expansion

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Acta Mechanica Sinica 2019年第3期35卷 507-517页

作者： y.C.Zhang y.J.Liang S.T.Liu y.d.Su State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of TechnologyDalian 116024China New Functional Structural design and Verification Key Laboratory of Aeronautical Technology Shenyang 110035China

Triangular lattice metamaterials composed of bi-layer curved rib elements (called the Lehman-Lakes lattice) possess unbounded thermal expansion, high stiffness and impossibility of thermal buckling, which are highly desirable in many engineering structural applications subjected to large fluctuations in temperature. However, the requirement of such lattice metamaterial is that it must be a hinged joint in order to achieve the bending deformation upon heating freely, which directly leads to poor manufacturability, especially in small dimensions. In this study, a new design of dual-constituent triangular lattice metamaterial (dTLM) with good manufacturability is proposed to achieve the identical unbounded thermal expansion. In this lattice, a special bi-layer curved rib element where layer one is partially covered by layer two is presented, where the hinge joints are not necessary because the flexural rigidity in the single-layer part is much smaller than that in the bi-layer part, and the desirable thermal bending deformation can be achieved. A sample fabricated by additive manufacturing is given in order to show the good manufacturability;simultaneously, the multifunctional performance of the tailored dTLM with zero, large positive or negative coefficient of thermal expansion (CTE) can remain excellent, as well as the Lehman-Lakes lattice. Examples illustrate that the dTLM with zero CTE has about 34.2% improvement in stiffness and meanwhile has 17% reduction in weight compared with the Lehman-Lakes lattice. The stiffness of the dTLM has a moderate reduction when achieving the same large positive or negative CTE. In addition, the thermomechanical properties of the dTLM are given by the closed-form analytical solution and their effectiveness is verified by the detailed numerical simulation.

关键词： Metamaterial Zero thermal expansion Lattice material Multifunctional design Additive manufacturing

Physical scientists research biomedicine: a call for caution

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Chinese Journal of Cancer Research 2015年第1期27卷 94-95页

作者： yì-Xiáng J.Wáng department of Imaging and Interventional Radiology Faculty of Medicine The Chinese University of Hong Kong Prince of Wales Hospital

It is noticeable that nowadays there are more and more scientists with physical science or engineering background working on or started to work on biomedical projects, but rarely vice versa. This reflects the multi-discipline nature of some projects, however, also at least partially can be explained that biomedical research is seen as trendy, fundable, and likely to get more citations and with results more publishable in high impact journals （1,2）. It is also apparent with some publications and lectures that not all these physical scientists/engineers are well-prepared to work on projects which do not align with their own expertise. Some studies are against very basic principles of pharmacology or biology, while others try to solve medical problems which do not exist clinically. I reviewed a number of submissions including a few from prestigious American universities to Nature journals which made no sense with the study design. Much of manpower and financial resource are being wasteful spent. There are also examples of clinical trials which were ill-planned right from the start and in the end only causing much inconvenience to patients to say at the least. In addition, ample examples exist where experienced physical scientists worked with inexperienced medical scientists and resulted in avoidable failures.

关键词： a call for caution very Physical scientists research biomedicine

STUdy ON dyNAMIC J-INTEGRAL OF MECHANICAL HETEROGENEOUS WELdEd JOINT

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Acta Metallurgica Sinica(English Letters) 2004年第6期17卷 934-939页

作者： F.Q.Tian d.y.He X.y.Li y.W.Shi d.Zhang InstituteofCompositeMaterials ShanghaiJiaotongUniversityShanghai200030China SchoolofMaterialsScienceandEngineering BeijingPolytechnicUniversityBeijing100022China

Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are com- puted. dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia, dynamic load response curve of computed model waves periodically. dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.

关键词： virtual crack extension welded joint dynamic response curve dynamic J-integral

Shape Memory Alloy-Reinforced Metal-Matrix Composites:A Review

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Acta Metallurgica Sinica(English Letters) 2014年第5期27卷 739-761页

作者： d.R.Ni Z.y.Ma Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

Metal-matrix composites reinforced with shape memory alloys （SMA, including long fiber, short fiber, and particle） are ＂intelligent materials＂ with many special physical and mechanical properties, such as high damping property, high tensile strength, and fatigue resistance. In this review article, the fabrication method, microstructure, interface reaction, modeling, and physical and mechanical properties of the composites are addressed. Particular emphasis has been given to （a） fabrication and microstructure of aluminum matrix composites reinforced with SMAs, and （b） shape memory effect on the physical and mechanical properties of the composites. While the bulk of the information is related to aluminum matrix composites, important results are now available for other metal-matrix composites.

关键词： Metal-matrix composites Shape memory alloy Fabrication method Microstructure Interface reaction Mechanical properties

Improved GaN grown on Si(111) substrate using ammonia flow modulation on SiN_x mask layer by MOCVd

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Science China(Technological Sciences) 2009年第9期52卷 2758-2761页

作者： ng KaiWei LAU KeiMay department of Electrical and Electronic Engineering Hong Kong University of Science & Technology Clear Water BayKowloon Hong Kong China

In this paper,1 μm n-GaN was grown by using varied and fixed ammonia flow (NH3) on SiNx mask layer on Si(111) substrate using metal organic chemical vapor deposition (MOCVd). In-situ optical reflectivity traces of GaN growth show that the three-to two-dimensional process has been prolonged by using varied ammonia flow on SiNx mask layer method compared with that grown by fixing ammonia flow. Structural and optical properties were characterized by high-resolution X-ray diffraction and photolu-minescence,and compared with the sample grown by fixing ammonia flow,GaN grown using the varied ammonia flow on SiNx mask layer showed better structure and optical quality. It was assumed that the low NH3 flow in the initial growth stage considerably increased the GaN island density on the nano-porous SiNx layer by enhancing vertical growth. Lateral growth was significantly favored by high NH3 flow in the subsequent step. As a result,the improved crystal and optical quality was achieved utilizing NH3 flow modulation for GaN buffer growth on Si(111) substrate.

关键词： GaN epilayer MOCVd NH3 modulation

ON INTEGRITy ASSESSMENT OF AXISyMMETRIC COMPONENTS OPERATIng WITHIN CREEP REGIME

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Chinese Journal of Mechanical Engineering 2006年第4期19卷 492-495页

作者： ZARRABI K LAWRENCE ng School of Mechanical and Manufacturing Engineering University of New South Wales Sydney NSW 2052 Australia

A multiaxial paradigm for predicting creep damage/lives of components is described. Although in principle the paradigm is general, it is verified using axisymmetric experimental data. It is shown that the proposed paradigm is capable of predicting creep lives with an error of less than 2%. It is also shown that the proposed paradigm is more accurate than the reference stress method.

关键词： Creep damage Creep life

PSEUdO ALMOST PERIOdIC SOLUTIONS OF dIFFERENTIAL EQUATIONS WITHPIECEWISE CONSTANT ARGUMENT

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Chinese Annals of Mathematics,Series B 1999年第4期20卷 489-494页

作者： PIAOdAX10ng yUANROng SchoolofMathematicalSciences PekingUniversityBeijing100871China. dpaRmentofMathematics BeijingNormniUniversityBejLug100875China

The authors discuss the existence of pseudo almost periodic solutions of differential equations with piecewise constant argument by means of introducing new concept, pseudo almost periodic sequence.

关键词： Pseudo almost periodic functions Pseudo almost periodic sequences Piecewise constant arguments Ergodic perturbation

State-to-state Photoionization dynamics of Vanadium Nitride by Two-color Laser Photoionization and Photoelectron Methods

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Chinese Journal of Chemical Physics 2013年第6期26卷 669-678,I0003页

作者： Huang Huang Zhi-hong Luo yih Chung Chang Kai-Chung Lau C. y. ng department of Chemistry University of California Davis CA 95616 USA department of Biology and Chemistry Oty University of Hone Kong Kowloon Hone Kong China

We have conducted a two-color visible-ultraviolet （VIS-UV） resonance-enhanced laser pho- toionization and pulsed field ionization-photoelectron （PFI-PE） study of gaseous vana- dium mononitride （VN） in the total energy range of 56900-59020 cm-1. The VN molecules were selectively excited to single rotational levels of the intermediate VN（d3H0, v＇=0） state by using a VIS dye laser prior to photoionization by employing a UV laser. This two-color scheme allows the measurements of rovibronically selected and re- solved PFI-PE spectra for the VN＋（X2A; v＋=0, 1, and 2） ion vibrational bands. By simulating the rotationally resolved PFI-PE spectra, J＋=3/2 is determined to be the lowest rotational level of the ground electronic state, indicating that the symmetry of the ground VN＋ electronic state is 2A3/2. The analysis of the PFI-PE spectra for VN＋ also yields accurate values for the adiabatic ionization energy for the formation of VN＋（X2A3/2）, IE（VN）=56909.5＋0.8 cm-1 （7.05588±0.00010 eV）, the vibrational fre- quency wc＋=1068.0±0.8 cm-1, the anharmonicity constant wc＋Xe＋=5.8±0.8 cm-1, the rotational constants Be＋=0.6563±0.0005 cm-1 and ae＋=0.0069±0.0004 cm-1, and the equi-librium bond length, re＋=1.529A, for VN＋（X2A3/2）; along with the rotational constants Bc＋=0.6578i0.0028 cm-1 and a＋=0.0085±0.0028 cm-1, and the equilibrium bond length re＋=1.527A for VN＋（X2As/2）, and the spin-orbit coupling constant A=153.3±0.8 cm-1 for VN＋（X2/k5/2,3/2）. The highly precise energetic and spectroscopic data obtained in the present study are valuable for benchmarking the predictions based on state-of-the-art ab initio quantum calculations.

关键词： Vanadium nitride Vanadium nitride cation Photoionization dynamics Two- color photoionization Pulsed field ionization-photoelectron Ionization energy Bond disso- ciation energy

WATER WAVES IN AN ELASTIC VESSEL

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Acta Mechanica Sinica 1997年第4期13卷 289-303页

作者： d. y. Hsieh department of Mathematics Hong Kong University of Science and Technology Hong Kong

Linear and nonlinear analyses of water waves in an elastic vessel are carried out to study the dramatic phenomena of dragon Wash as well as related controllable experiments. It is proposed that the capillary edge waves are generated by parametric resonance, which is shown to be a possible mechanism for both rectangular an circular vessels. For circular vessel, the normal geometric resonance is also operating, thus greatly. enhance the dramatic effect. The mechanism of nonlinear mode-mode interaction is proposed far the generation of axisymmetric low-frequency gravity waves by the high-frequency external excitation. A simple model system is studied numerically to demonstrate explicitly this interaction mechanism.

关键词： water waves elastic vessel dragon Wash