New Conservation Laws of Energy and C-D Inequalities in Continua Without Microstructure

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Stability of sandwich plates by mixed,higher-order analytical formulation

A unified mixed, higher-order analytical formulation has been presented in this paper to predict general buckling as well as wrinkling of a general multi-layer, multi-core sandwich plate having any arbitrary sequence of stiff layers and cores. Assumptions of thin stiff layers and anti-plane core, which are usually made in the analysis of sandwiches, have been eliminated in the present formulation. Displacements as well as the transverse stress continuities have been enforced in the formulation by incorporating them as the degrees-of-freedom. The modal transverse stresses have been obtained directly as eigen vectors and thus their separate calculations have been advantageously avoided. Two sets of mixed models have been proposed on the basis of individual layer as well as equivalent single layer (ESL) theories by selectively incorporating non-linear components of Green’s strain tensor. Solutions from the models have been shown to be in excellent agreement with the available three-dimensional elasticity solutions as well as with the available experimental results. It has been demonstrated that the ESL theories cannot accurately evaluate the overall buckling as well as the wrinkling loads of sandwiches. Limitations of the typical simplifying assumptions have also been highlighted.     

Streak interferometric measurements of transient displacements

A program was designed to demonstrate and evaluate the use of streak interferometry as a method for collecting temporally and spatially resolved transient-deformation data on the surfaces of metallic solids. The study has shown that the technique can resolve displacement histories with times as short as 70 nsec and measure surface velocities as large as 80 ips. These capabilities appear adequate for the intended applications. Representative data are shown and analyzed.     

Drained and Undrained Poroelastic Properties of Healthy and Pathological Bone: A Poro-Micromechanical Investigation

Poro-micromechanics allows for the quantification of poroelastic properties such as the Biot and Skempton coefficients, once a continuum micromechanics model for the material under consideration has been developed and validated. Employing such a model for the transversely isotropic elasticity of cortical and trabecular bone, we determine the tensors of Biot and Skempton coefficients as functions of the volume fractions of mineral, collagen, and the micropore space (Haversian and Volkmann canals, and the inter-trabecular space). Increase of microporosity, as experienced in osteoporosis, as well as decrease of mineral content, as experienced in osteomalacia, lead to an increase of Biot and Skempton coefficients, i. e. to magnification of the mechanical role of the marrow filling the micropore space. For quantification of the marrow pressure rise upon downfall, undrained conditions are appropriate, as can be shown by model predictions of non-destructive impact experiments.     

On mechanics of saturated granular materials

A continuum theory of saturated granular materials is formulated. The basic balance laws for the solid phase as well as for the fluid phase are presented. The constitutive equations are derived and the basic equations of motion of the solid and fluid continua are obtained. Several cases of interest, such as incompressible granules saturated with liquids are discussed. It is shown that the theory contains, as its special cases, the Mohr-Coulomb criterion for a granular material as well as Darcy's law of flow through porous media.     

四面体无定型无氢非晶碳膜的制备及其摩擦学性能研究

采用磁过滤阴极真空弧系统分别在硅片[Si(100)]、W18Cr4V高速钢和Cr18Ni9不锈钢基体上沉积了一系列sp3键含量较高的四面体无定型无氢非晶碳膜(ta-C),研究了所合成薄膜的结构、硬度、附着强度和摩擦磨损性能,考察了基体和薄膜厚度对薄膜摩擦系数的影响,简要分析了相应ta-C膜的失效机理.结果表明,在高速钢基体上沉积的ta-C膜的显微硬度为76 GPa,结合力Lc值达42 N,具有优良的摩擦学性能,其摩擦系数为0.12,且摩擦系数可以在16 000 r范围内保持稳定.     

New Principles of Work and Energy as Well as Power and Energy Rate for Continuum Field Theories

Ｉｎｔｒｏｄｕｃｔｉｏｎ1 999ｉｓｔｈｅ 90ｔｈａｎｎｉｖｅｒｓａｒｙｏｆｔｈｅｐｕｂｌｉｃａｔｉｏｎｏｆＥ .Ｆ .Ｃｏｓｓｅｒａｔ’ｓｂｏｏｋ“ＴｈｅｏｒｉｅｄｅｓＣｏｒｐｓＤｅｆｏｒｍａｂｌｅ”[1],ｗｈｉｃｈｗａｓｔｈｅｆｏｕｎｄａｔｉｏｎｓｔｏｎｅａｎｄｎｏｗｉｓｓｔｉｌｌａｇｕｉｄｉｎｇｍｏｎｏｇｒａｐｈｉｎｔｈｅｓｔｕｄｙｏｆｇｅｎｅｒａｌｉｚｅｄｃｏｎｔｉｎｕｕｍｆｉｅｌｄｔｈｅｏｒｉｅｓ.Ｈｏｗｅｖｅｒ,ｉｔｗａｓｎｏｔｔｉｌｌｔｈｅｐｕｂｌｉｃａｔｉｏｎｏｆｐａｐｅｒｓｏｆＥｒｉｃｋｓ…     

稀土铈有机配合物添加剂的制备及其摩擦学性能

采用水热合成法分别制备了含1，10-菲啰啉和油酸两种配体的稀土铈配合物，以及作为对照组的只含一种配体的配合物. 利用傅里叶变换红外光谱仪、紫外-可见分光光度仪和热重分析仪对配合物的组成及结构进行了表征和分析，利用SRV-IV型微动摩擦磨损试验机对含有不同质量分数目标产物的润滑油的摩擦学性能进行了研究. 结果表明:以Ce3+为中心离子，1，10-菲啰啉作为第一配体，油酸作为第二配体所制备的稀土有机配合物可以显著提高基础油(PAO8)的极压性能和抗磨损性能，并且使润滑油的使用寿命得以延长.      

Periodic motions of coupled simple pendulums with periodic disturbances

Several theorems on the existence of oscillatory, rotary, and mixed periodic motions of n, coupled simple pendulums are proved. These theorems are very general and include subharmonic and ultraharmonic type solutions as well as harmonic type solutions and cover cases of large coupling and disturbances as well as small. The results are also extended to include more general systems of nonlinear oscillators.     

Large deflection analysis of plates on elastic foundation by the boundary element method

A boundary element method is developed for the large deflection analysis of thin elastic plates resting on elastic foundation. The subgrade reaction may depend linearly (Winkler-type) or nonlinearly on the deflection as well as on the point coordinates (nonhomogeneous subgrade). Moderately large deflections are examined as described by the von Karman equations. The plate may have arbitrary shape and its boundary may be subjected to any type of boundary condition. The proposed method uses the fundamental solution of the linear plate theory and treats the nonlinearities as well as the subgrade reaction as unknown domain forces. Numerical results are presented to illustrate the method and demonstrate its effectiveness and accuracy.     

我国航空航天结构强度事业的开拓者——黄玉珊

黄玉珊先生是我国著名的力学家、航空航天科学家,新中国航空高等教育的奠基人.他不满14岁考入大学,不满23岁时师从国际著名力学大师铁摩辛柯获博士学位,随即义无反顾地回到战火连绵的祖国,受聘中央大学教授.新中国成立后,面对航空工业初建时期技术基础薄弱、人才储备不足、教育体系不完善的困境,他呕心沥血,鞠躬尽瘁,建立新学科,开创新局面,毕生致力于祖国航空航天教育和科技事业.他被认为是我国旧飞机疲劳定寿和延寿、损伤容限评定和新飞机损伤容限设计最早的创始人之一,也是我国飞机自激励振动研究和航天结构环境强度事业的开拓者.本文通过回顾黄玉珊先生在固体力学、航空航天结构强度领域的主要学术成果和卓越贡献,缅怀其坚定不移的报国情怀、严谨求实的治学态度、勇于开拓的创新精神、高瞻远瞩的学术视野以及求真务实的教育思想.     

Numerical computations of internal flows for axisymmetric and two-dimensional nozzles

MacCormack's explicit time-marching scheme is used to solve the full Navier–Stokes unsteady, compressible equations for internal flows. The requirement of a very fine grid to capture shock as well as separated flows is circumvented by employing grid clustering. The numerical scheme is applied for axisymmetric as well as two-dimensional flows. Numerical predictions are compared with experimental data and the qualitative as well as the quantitative agreement is found to be quite satisfactory. © 1997 John Wiley & Sons, Ltd.     

Happiness and Deep Ecology: On Noise,Harmony, and Beauty in the Mind

This article represents a reflection about the new perspectives opened by chaos theory in the relationships between ethics and esthetics within the philosophy of psychology. The roots of these perspectives can be traced from the foundations of Western philosophy: Plato and Aristotle, Kant and Hegel. The epistemological changes embedded in chaos theory can be as strong as the ones related to the Scientific Revolution represented by Galilei and Newton. Fractal thinking and physical phenomena, such as studies on the different types of noise, can start new approaches in the dialectics between ethics and esthetics, as well as their impact on human relations.     

Constitutive modeling of cyclic plasticity and creep,using an internal time concept

Using the concept of an internal time as related to plastic strains, a differntial stress-strain relation for elastoplasticity is rederived, such that (i) the concept of a yield-surface is retained; (ii) the definitions of elastic and plastic processes are analogous to those in classical plasticity theory; and (iii) its computational implementation, via a “tangent-stiffness” finite element method and a “generalized-midpoint-radial-return” stress-integration algorithm, is simple and efficient. Also, using the concept of an internal time, as related to both the inelastic strains as well as the Newtonian time, a constitutive model for creep-plasticity interaction, is discussed. The problem of modeling experimental data for plasticity and creep, by the present analytical relations, as accurately as desired, is discussed. Numerical examples which illustrate the validity of the present relations are presented for the cases of cyclic plasticity and creep.     

Nonlinear pedagogy: a constraints-led framework for understanding emergence of game play and movement skills

Team sport competition can be characterized as a complex adaptive system in which concepts from nonlinear dynamics can provide a sound theoretical framework to understand emergent behavior such as movement coordination and decision making in game play. Nonlinear Pedagogy is presented as a methodology for games teaching, capturing how phenomena such as movement variability, self-organization, emergent decision making, and symmetry-breaking occur as a consequence of interactions between agent-agent and agent-environment constraints. Empirical data from studies of basketball free-throw shooting and dribbling are used as task vehicles to exemplify how nonlinear phenomena characterize game play in sport. In this paper we survey the implications of these data for Nonlinear Pedagogy, focusing particularly on the manipulation of constraints in team game settings. The data and theoretical modeling presented in this paper provide a rationale in nonlinear dynamics for the efficacy of a prominent model of game play teaching, Teaching Games for Understanding approach.     

Network Dynamics: Tools and Examples

Some mathematical tools and results are presented which may be used to study the dynamics of agents living on a network as well as the networks themselves as evolving dynamical systems. They include decomposition of differential dynamics, ergodic techniques, estimates of invariant measures, etc. Some examples are discussed as an application of the dynamical tools.     

THE MIXED BOUNDARY-VALUE PROBLEM FOR NON-LOCAL ASYMMETRIC ELASTICITY

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