力学进展

2002, 32(3): . doi: 10.6052/1000-0992-2002-3-J2002-088

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2002, 32(3): . doi: 10.6052/1000-0992-2002-3-J2002-089

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2002, 32(3): . doi: 10.6052/1000-0992-2002-3-J2002-090

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2002, 32(3): . doi: 10.6052/1000-0992-2002-3-J2002-091

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MICRO-SCALE GAS FLOWS

2002, 32(3): 321-336. doi: 10.6052/1000-0992-2002-3-J2002-009

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Understanding the features of micro-scale gas flows is essential to designing and optimizing micro-electro-mechanical systems(MEMS). Research on micro-scale gas flows originated from the famous experiments carried out by Knudsen and Millikan, respectively, i.e. the measurements of mass flux through a plane channel and drag coefficient of a small sphere, at the beginning of the 20th century. The experimental results revealed the significant effects of scale influence (rarefaction) on the gas flow characteristics. In the slip and transition regimes, the similar parameters of gas flows are the Knudsen number and Mach number, and therefore, there is a possibility to utilize the principle of similarity, i.e. increasing the geometric scale while decreasing the pressure, to solve the difficulty associated with the measurement in MEMS experiments. An information preservation(IP) technique was proposed by us to address the serious statistical scatter encountered in Monte Carlo direct simulation of low-speed gas flows. The IP technique may reduce the statistical scatter efficiently, and has been successfully applied to many micro-scale gas flows.

A SURVEY OF THE MODIFYING TECHNIQUES OF STRUCTURE DYNAMIC MODELS

2002, 32(3): 337-348. doi: 10.6052/1000-0992-2002-3-J2001-003

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Full-scale test method were used to find out themechanical characters in spacecraft design. With powerfulcomputers and the accurate FEM technology, this method seems too expensive and time-concuming. FEM analysis and model updating technique can to replace most of the full-scale test. So, this paper summarized the development of structural dynamic model updating methodologies since 1970s, including the matrix updating methodology and design parameters updating methodology developed from the early 1990s. Then, this paper discussed the iterative method, perturbation method and optimization method, emphasized the statistical method which takes into account the error of test data and heredity method which could be used in complex spacecraft structure. After that, this paper mentioned the freedom accordance technique between test model and analysis model, sensitivity analysis of eigen-value and the validation criteria of the updatingresults. At last, this paper presented some key questions that need to be solved in this field.

DEVELOPMENTS AND APPLICATIONS OF NANO-HARDNESS TECHNIQUES

2002, 32(3): 349-364. doi: 10.6052/1000-0992-2002-3-J2001-041

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Great strides have been made over the past two decades in the development of techniques for studying the mechanical properties of materials on the micron and submicron levels. In this review paper, first, several definitions, classifications and their scopes used for hardness are introduced. Secondly, developments for nanoindentation techniques are summarized, especially the measuring principles of nanoindentation, CSM(Continuous Stiffness Measurement), high resolution load/displacement sensors, several typical tips, sample preparation, reference to the point of contact, experimental methods, instrument calibration and so on. With nanoindentation systems, quantitative data can be obtained: hardness, elastic modulus, fracture toughness, storage and loss modulus, stress exponent. Finally, advances in nanoscratch techniques are briefly discussed.

A REVIEW OF STUDIES ON THE MECHANICAL BEHAVIOR OF MICROCELLULAR PLASTICS

2002, 32(3): 365-378. doi: 10.6052/1000-0992-2002-3-J2001-013

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A review of studies on the mechanical properties ofmicrocellular plastics is given in this paper. The fabrication and characterization of microcellular plastics are introduced brietly and the emphasis is placed on the studies on into mechanical properties of microcellular plastics, including some author's work in this field. They are mainly concerned with the compressive behavior, tensile behavior, impact behavior, fatigue and visco-elasticity of these materials. Finally, some discussions and future development trends are also presented.

MATHEMATICAL MODEL OF ALLOY SOLIDIFICATION PROCESSES

2002, 32(3): 379-390. doi: 10.6052/1000-0992-2002-3-J2001-042

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Numerical study of alloy solidification processes has seen great developments since the 1980's. The major mathematical models applied to macroscopic processes are discussed. The basic ideas, numerical methods, relative merits and disadvantages of those models are presented. This paper indicates that microscopic processes have a very important influence on the macroscopic transport phoenomena and the two aspects must be considered at the same time while building themathematical model. The relevant engineering applications and future directions are also discussed.

MICROSCOPIC AND MACROSCOPIC THEORY OF THE FATIGUE DAMAGE OF METAL

2002, 32(3): 391-401. doi: 10.6052/1000-0992-2002-3-J2000-056

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There are different stages of the fatigue damage in an engineering component where defects may nucleate in an initially undamaged section and propagate in a stable manner until catastrophic fracture ensues. For this most general situation, the progression of the fatigue damage can be broadly classified into the following stages: (1) substructural and microstructural changes which cause the nucleation of permanent damage, and the creation of microscopic cracks; (2) the growth and coalescence of microscopic flaws to form `dominant' cracks; (3) stable propagation of the dominant macrocrack; (4) structuralinstability or complete fracture. A review of the microscopic and macroscopic theory of the fatigue damage of metal is given in the present paper. The mechanism of the evolution of the fatigue damage is discussed firstly, and the recent advances of the research of the fatigue damage are then presented. Emphasis is given on the application of dislocation mechanics to evaluating the propagation of the fatigue cracks, and the role of dislocation-free zone in the process of the fatigue crack propagation.

ADVANCES OF STUDY ON RESIDUAL STRENGTH OF DELAMINATED COMPOSITE SANDWICH PLATES AFTER LOW VELOCITY IMPACT

2002, 32(3): 402-414. doi: 10.6052/1000-0992-2002-3-J2001-028

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This article to reviews the progress achieved in the study of damage behavior of composite sandwich plates after low velocity impact. Emphasis is placed on the residual tensile and/or compressive strength of the damaged sandwich plates in composite engineering structures. The contents of the article are as follows: (1) Analysis theory, model and corresponding finite element method of the composite sandwich.(2) Damage and failure configurations and classifications for the composite sandwich plates. (3) Residual tensile strength.(4) Residual compressive strength. (5) Related problems and perspective for developing new analysis methods. There are 90 recent references included in this article.

A REVIEW ON DOUBLE-DIFFUSIVE CONVECTION

2002, 32(3): 415-424. doi: 10.6052/1000-0992-2002-3-J2001-043

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Convection may occur in fluid because of the simultaneous buoyancy forces due to instability of gradients of two properties with different molecular diffusivity, which is usually called double-diffusive convection. It is a common phenomenon in nature and engineering. As more careful control and a higher quality manufacture are required for solidification processes of metallic alloys and semiconductor crystal growth, etc, double-diffusive convection problems have received more attention in recent years. The emphasis of this paper is on research work on double-diffusive convection with widely used models and methods, such as box models, two-dimensional Boussinesq model, k-e model, numericalmethods and some famous experimental methods.

UNSTEADY LIFT MECHANISMS IN INSECT FLIGHT

2002, 32(3): 425-434. doi: 10.6052/1000-0992-2002-3-J2001-051

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Recently, interest has been directed to small autonomous flying vehicles, largely motivated by the need for aerial reconnaissance robots inside buildings and confined spaces. In military and commercial fields, there are similarpotential demands for such micro-air vehicles (MAVs). Thelinear dimension of the intended MAVs ranges from 10 cm to 1 cm or even smaller. At such a size, the fixed- or rotary wing aerodynamic configuration would not work because the Reynolds number (Re) of the wing is so low that enough lift and control forces could not be produced. Novel aerodynamic configuration must be sought. However, there already exist such autonomous MAVs in nature: the insects. In the design of small flying machines, it would be very helpful to understand first how these small animals fly. In this article, we review recentachievements in the field of insect flight aerodynamics. We first summarize the kinematics of the flapping motion of insects. Next we present issues related to the unsteady lift mechanisms of flapping wings of the fruit fly and similar insects. Then we discuss the lift (and thrust) and power requirements of hovering and forward flight in the fruit fly. Recent work on insects with two pairs of wings is also discussed.

ADVANCE IN HEMODYNAMICS NUMERICAL SIMULATION AND ATHEROSCLEROSIS

2002, 32(3): 435-443. doi: 10.6052/1000-0992-2002-3-J2002-005

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Hemodynamic factors are thought to have close relevance to arterial pathological changes, such as atherosclerosis. The simulated objects of hemodynamics are mainly on the arteries with geometry of bifurcation, curvature and stenosis, because atheroselerosis is prone to develop at these particular arterial positions. Accurate numerical simulations of hemodynamics must rely on the anatomically realistic vascular geometrical model and thephysiologically realistic nonlinear transient fluid-solid interaction between blood flow and vessel deformation. Only based on the `virtual vascular flow', and with the wall shear stress, particle residence time and oxygen mass transfer across vessel wall being duly taken into consideration, can the numerical results of hemodynamics be useful in understanding the physiology and pathology of atherosclerosis, and be used in surgery planning for relevant vascular diseases.

CONTIMUUM MESOMECHANICAL FINITE ELEMENT MODELING IN MATERIALS DEVELOPMENT: A STATE-OF-THE-ART REVIEW

2002, 32(3): 444-466. doi: 10.6052/1000-0992-2002-3-J2002-082

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Advanced finite element techniques for the simulation of materials behavior under mechanical loading are reviewed. Advantages, limitations and perspectives of different approaches are analyzed for the simulation of deformation, damage and fracture of materials taking into account their micro- and mesostructure. Devlopment of simulation methods fordifferent aspects of materials behavior (such as the unit cell approach, real structure simulation, cohesive zone model, etc) is described includng the simple versions of the methods as well as the advanced, highly efficient models. Possibilities of using the finite element method in the development of new materials are analyzed. This review article contains 131 references.

THE MEASURES OF SUPPRESSING EXPLOSION WAVES

2002, 32(3): 467-470. doi: 10.6052/1000-0992-2002-3-J2001-068

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Suppressing pressure waves produced by combustion and explosion is a very important problem. The present measures about suppressing explosion waves are described in this paper. Theoretical results on suppressing explosion waves using mesh or compressive materials are introduced. The suggestion of how to solve the key problems is provided.

2002 Vol. 32, No. 3

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