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.     

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

ＩｎｔｒｏｄｕｃｔｉｏｎＣｏｎｔｉｎｕｕｍｍｅｃｈａｎｉｃｓｉｓｎｏｔｏｎｌｙａｎｏｌｄａｎｄｂｕｔａｌｓｏａｙｏｕｎｇｓｃｉｅｎｔｉｆｉｃｄｉｓｃｉｐｌｉｎｅ.Ｉｔｃｏｎｓｉｓｔｓｏｆｓｏｍｅｆｕｎｄａｍｅｎｔａｌｌａｗｓ,ｗｈｉｃｈａｒｅｖａｌｉｄｆｏｒａｌｌｂｏｄｉｅｓｉｒｒｅｓｐｅｃｔｉｖｅｏｆｔｈｅｉｒｓｈａｐｅｓ,ｃｏｎｓｔｉｔｕｔｉｏｎｓａｎｄｃｏｎｓｔｉｔｕｔｉｖｅｒｅｌａｔｉｏｎｓ,ｗｈｉｃｈｍｕｓｔｒｅｆｌｅｃｔｔｈｅｎａｔｕｒｅｏｆｔｈｅｍａｔｅｒｉａｌａｎｄｔｈｅｃｏｎｓｔｉ…     

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.      

MOIRÉ INTERFEROMETRY WITH ENHANCED RESOLUTION

The implementation of this method is relatively simple. It does not require any modification to interferometric systems already in use. It can be used in the analysis of large as well as very small fields, including measurements under a microscope.
A fringe pattern with a carrier is recorded in a single exposure, just as in the standard procedure. As a consequence, any possible instability of the interferometer does not affect the accuracy of the measurements. Further, the spatial resolution of the measurements is not compromised.
Since only one exposure is needed for a given displacement component this method can be applied to dynamic as well as static measurements.
It should be emphasized that even though the number of electronically generated fringes can be arbitrary, the sensitivity is the same as in ordinary moire interferometry as long as the data are taken at the lines of minimum intensity. The improvement is in the increase of the number of data points taken at the locations of maximum resolution. In other words, all the data are taken at the maximum resolution.
This method applies not only to moire interferometry but to any experimental technique based on two-beam interference, as long as the fringe pattern has good contrast.     

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.     

??????????й????????

简单介绍了理性力学的目的、特点、学科内容、同其他学科的关系及发 展过程等;介绍了理性力学与力学中的方法专业(组)委员会的发展沿革;并围绕专业(组)委 员会的活动情况详细叙述了理性力学在中国的传播与发展,以此来说明钱伟长先生在推动理 性力学在中国的传播过程中所做出的重大贡献与理性力学在中国取得的成就.     

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.     

陶瓷摩擦学I．陶瓷的摩擦与磨损

根据大量文献调查结果，从影响陶瓷材料摩擦磨损性能的内因（主要包括陶瓷材料的力学性能及微观结构）和外因（主要包括载荷、速度、温度、环境气氛及偶件的化学活性等）出发，讨论了陶瓷材料的摩擦磨损行为及机制，以促进正确选择、设计和使用陶瓷材料，在对陶瓷摩擦学研究现状分析评论的基础上，提出了陶瓷摩擦磨损今后研究工作中值得重视的发展方向．     

Influence of specimen gage length and loading method on the axial compressive strength of a unidirectional composite material

Various compression test methods for composite materials have been developed during the past few years incorporating specimens of different gage lengths and modes of load introduction. Most of these test methods are not recognized as standards at the present time. Thus the question arises as to whether these various test methods produce similar results.Two commonly used test fixtures are compared in detail here, viz., the ASTM Standard D 3410 IITRI compression test fixture, and another often referred to as the Boeing-Modified D 695 compression test fixture. The IITRI fixture loads a specimen of 12.7-mm gage length via shear through end tabs and wedge grips. The Boeing-Modified D 695 fixture also uses a tabbed specimen, but with only a 4.8-mm gage length and loaded directly on its ends.Hercules S2/3501-6 glass/epoxy and AS4/3501-6 carbon/epoxy unidirectional composites were used as the primary material configurations in the present comparison. Highstrength, highly orthotropic materials such as these are among the most difficult composites to test successfully in compression. However, a carbon/epoxy quasi-isotropic laminate was tested as well.The results obtained are compared with similar data available in the literature. It is concluded that there is relatively little influence of specimen gage length as long as it is sufficiently small so that gross buckling does not occur. Also, the differences between shear loading and end loading of the specimen are small, as long as the ends of the end-loaded specimen do not crush, and that in either case the tabs do not debond.     

Cavitation in finite elasticity with surface energy effects

Cavity formation in incompressible as well as compressible isotropic hyperelastic materials under spherically symmetric loading is examined by accounting for the effect of surface energy. Equilibrium solutions describing cavity formation in an initially intact sphere are obtained explicitly for incompressible as well as slightly compressible neo-Hookean solids. The cavitating response is shown to depend on the asymptotic value of surface energy at unbounded cavity surface stretch. The energetically favorable equilibrium is identified for an incompressible neo-Hookean sphere in the case of prescribed dead-load traction, and for a slightly compressible neo-Hookean sphere in the case of prescribed surface displacement as well as prescribed dead-load traction. In the presence of surface energy effects, it becomes possible that the energetically favorable equilibrium jumps from an intact state to a cavitated state with a finite cavity radius, as the prescribed loading parameter passes a critical level. Such discontinuous cavitation characteristics are found to be highly dependent on the relative magnitude of the surface energy to the bulk strain energy.     

Measurement of the shear viscosity using a newly developed GRLDA-viscometer

A two-point laser-Doppler anemometer is used to determine velocity gradients. Measuring additionally the pressure drop in channel flow allows one to use this instrument as a viscometer. This is demonstrated by measuring two polymer solutions as well as water. Besides the velocity gradient, the system also furnishes the velocity as well as velocity fluctuations. For surfactant solutions the sudden increase in these fluctuations go hand-in-hand with the sudden shear thickening reported. This behavior thus seems to be caused by a change in type of flow field (structural turbulence) rather than a change in the rheology of the surfactant solutions.This paper is dedicated to Professor Hanswalter Giesekus on the occasion of his retirement as Editor of Rheologica Acta.     

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 hydrodynamic instabilities,chaos and phase transition

Ellipticity as the underlying mechanism for instabilities of physical systems is highlighted in the study of model nonlinear evolution equations with dissipation and the study of phase transition in Van der Waals fluid. Interesting results include spiky solutions, chaotic behavior in the context of partial differential equations, as well as the nucleation process due to ellipticity in phase transition.     

ℋ︁‐LU factorization in preconditioners for augmented Lagrangian and grad‐div stabilized saddle point systems

The (mixed finite element) discretization of the linearized Navier–Stokes equations leads to a linear system of equations of saddle point type. The iterative solution of this linear system requires the construction of suitable preconditioners, especially in the case of high Reynolds numbers. In the past, a stabilizing approach has been suggested which does not change the exact solution but influences the accuracy of the discrete solution as well as the effectiveness of iterative solvers. This stabilization technique can be performed on the continuous side before the discretization, where it is known as ‘grad‐div’ (GD) stabilization, as well as on the discrete side where it is known as an ‘augmented Lagrangian’ (AL) technique (and does not change the discrete solution). In this paper, we study the applicability of ??‐LU factorizations to solve the arising subproblems in the different variants of stabilized saddle point systems. We consider both the saddle point systems that arise from the stabilization in the continuous as well as on the discrete setting. Recently, a modified AL preconditioner has been proposed for the system resulting from the discrete stabilization. We provide a straightforward generalization of this approach to the GD stabilization. We conclude the paper with numerical tests for a variety of problems to illustrate the behavior of the considered preconditioners as well as the suitability of ??‐LU factorization in the preconditioners. Copyright © 2010 John Wiley & Sons, Ltd.     

Principles and application of velocimetry-based planar pressure imaging in compressible flows with shocks

The paper addresses the computation of pressure fields from velocimetry data, such as provided by Particle Image Velocimetry (PIV), with specific attention to its application in compressible flows with shocks. An essential extension with respect to incompressible flow is that in view of the variable density occurring in compressible flow, the velocimetry data has to be supplemented with additional relations, derived from the flow governing equations. Secondly, compressible flows display specific flow features, notably shocks but also thin shear layers, that pose particular difficulties for the flow velocity measurement itself, as well as for the subsequent determination of the pressure field. The present communication addresses the basic principles of the pressure-field extraction method, as well as its feasibility of application under realistic experimental conditions.     

桂林地区红土砾石层的工程地质特征及其应用

桂林地区的红土砾石层以其独特的工程地质特征引起了许多中外学者的注意, 对它的成因至今还存在争议。本文主要讨论红土砾石层的工程应用, 即不仅可作为一般低层建筑物的天然持力层, 而且可以作为沟、塘等低洼地带的回填土料 ;而且厚度较大的红土砾石层坚硬部分可作为桩端持力层。     

A self-destruction game

A simple model of a self-destructing society is presented. It can be interpreted as a game with two players: the society and its sub-set which tends to destroy the whole society, as well as itself. The main factor taken into account in the model is the progress of science and technology which provides the destruction tools (new weapons and killing techniques), as well as tools the society can use to defend itself. The modeling and simulation tool is discrete-event and can be treated as agent-oriented, though the agent capabilities are rather simple. The simulation experiments show that, in the near future, this progress will become extremely dangerous, and it may result in the total destruction of mankind. For the longer time period, however, the conclusion is not so pessimistic. If the society survives during a certain time interval, then the probability of survival becomes greater for a longer time span.     

微球制备的研究概况及发展

粉体加工生产中制备的颗粒有多种形态，其中微球具有很多不规则颗粒所没有的优异性能，如高的流动性、高的堆积密度、不易团聚、填充到复合材料中不易引起应力集中等，在生产和生活中受到越来越多的重视，就目前国内外微球制备的研究状况，综述了近年来实心微球、空心微球、多孔微球这3种微球的制备原理、方法及应用，并对微球制备技术的发展作了介绍．