复合材料薄壁结构连接件细节内力分析的有限元方法

为得到复合材料薄壁结构机械连接件中各承力元件的内力和变形情况,确定各承载紧固孔的旁路载荷（ＰＰＬ）和钉传载荷（Ｐｄｃ）,以便合理地进行连接件的细节设计和强度分析,本文基于迭层板“等效弹性模量”概念,提出了一套工程实用的复合材料结构连接件细节内力分析的有限元方法。所编制的计算程序适用于对实际结构中各种机械连接型式和各种平面受载情况的内力计算和分析。     

Finite plane and anti-plane elastostatic fields with discontinuous deformation gradients near the tip of a crack

In this paper the fully nonlinear theory of finite deformations of an elastic solid is used to study the elastostatic field near the tip of a crack. The special elastic materials considered are such that the differential equations governing the equilibrium fields may lose ellipticity in the presence of sufficiently severe strains.The first problem considered involves finite anti-plane shear (Mode III) deformations of a cracked incompressible solid. The analysis is based on a direct asymptotic method, in contrast to earlier approaches which have depended on hodograph procedures.The second problem treated is that of plane strain of a compressible solid containing a crack under tensile (Mode I) loading conditions. The materials is characterized by the so-called Blatz-Ko elastic potential. Again, the analysis involves only direct local considerations.for both the Mode III and Mode I problems, the loss of equilibrium ellipticity results in the appearance of curves (elastostatic shocks) issuing from the crack-tip across which displacement gradients and stresses are discontinuous.The results communicated in this paper were obtained in the course of an investigation supported by Contract N00014-75-C-0196 with the Office of Naval Research.     

The viscoelastic behavior of linear elastic materials with voids

It is shown that the constitutive equations for a linear elastic material with voids imply a viscoelastic stress-strain relation known as the standard linear solid in the case of quasi-static, homogeneous deformations in the absence of self-equilibrated body forces. It is noted that, even for deformations that are dynamic and/or inhomogeneous the viscoelastic behavior is still qualitatively similar to that predicted by the standard linear solid model.     

New method for solving the one-dimensional problem of the displacement of petroleum by water taking account of capillary forces

The article describes a method for the solution of the one-dimensional problem of the displacement of petroleum by water taking account of capillary forces; on the basis of the method, in the equations of two-phase filtration it is proposed to use a new, soughtfor function, i.e., the fraction of water in the total flow of liquid. As a result, the problem is simplified, the labor consumption of the calculations is reduced, and it becomes possible to make a qualitative evaluation of the behavior of the solutions, including the analytical justification of a solution with a stabilized zone.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 83–91, May–June, 1975.     

Hydroelastic behavior of a floating plate in waves

The behavior of a floating semiinfinite plate in surface waves incident normally to the edge of the plate is studied. We used an analytical solution of this problem obtained earlier by the Wiener–Hopf technique. In this paper, we study the distributions of displacements, deformations, and pressure over the plate as functions of the dimensionless parameters of the problem (reduced rigidity and depth) and their asymptotic distributions for large and small wavelengths.     

Zur Berechnunǵ ǵroßer Verformunǵen von ǵekrümmten Stäben

Übersicht Es wird ein Verfahren zur Berechnung beliebig großer Verformungen von ebenen, schwach gekrümmten, dünnen Stäben vorgestellt. Die Gültigkeit der Ersten Love'schen Näherung für die Verzerrungsenergie wird vorausgesetzt. Kennzeichnend für das Verfahren ist die exakte Berechnung von Restschnittgrößen als Differenz von Schnittgrößen, die sich einerseits aus den Gleichgewichtsbedingungen und andererseits aus den Stabverzerrungen ergeben. Das Berechnungsverfahren wird am Beispiel eines Kragträgers, der am freien Ende mit einem Einzelmoment bzw. mit einer Einzellast belastet ist, getestet.

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Summary A method is presented to calculate unlimited large deformations of plane, initially curved, slender beams. It is assumed that Love's first approximation for the strain energy is valid. Main aspect of the method is the derivation of residual internal forces and moments based on exact strain-displacement relations and equilibrium equations. The method has been used to calculate the deformations of a straight cantilever beam under end moment and end force.

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Über diese Arbeit wurde im Rahmen des 16th Annual Meeting of the Society of Engineering Science, Inc., Northwestern University, Evanston, Illinois, USA, 5.–7. September 1979, berichtet     

Displacement of a liquid from a horizontal circular tube by another liquid

We consider the axisymmetric problem of expulsion of one liquid from a horizontal circular pipe by another for the laminar flow regime.Studies of Taylor [1], Cox [2, 3], and others have been devoted to the experimental investigation of the displacement of a liquid from a capillary. Experiments on the displacement of mutually immiscible liquids show that the length of the combined flow region and the amount of displaced liquid remaining in this region are determined primarily by the magnitude of the interphase tension forces at the leading edge of the interface. The equilibrium of these forces and the hydrodynamic differential, established some time after the beginning of displacement, give rise to the rigid bullet-shaped form of the interface leading edge. This portion of the interface, whose stiffness is achieved as a result of the force balance, is termed the head of the interface between the liquids. The radius of the head-the relatively small autonomous portion of the interface-defines the dimensions and deformations of the entire remaining interface.The existence of a rigid autonomous interface head is the basis of the physical displacement model used in this article.     

Dynamics of an Elastic Four Bar Linkage Mechanism with Geometric Nonlinearities

The geometric nonlinearity due to the large elastic deformations of three flexible links is considered in setting up the dynamic equation of elastic linkages. It is shown that both the quadratic nonlinear terms and the cubic nonlinear terms are included in the model. The analyses with the method of multiple scales demonstrate that the superharmonic resonances caused by the quadratic and cubic nonlinearities, as well as the multi-frequency nature of the inertial force are the reasons causing the critical speed to take place. They also demonstrate that the combination resonances caused by the combined effects of internal resonance in the form of ₂ 2₁, the cubic nonlinearity and the multi-frequency nature of the inertial forces is the reason causing the production of the nonsynchronism of the lower order harmonic resonances of elastic linkages. Meanwhile, the influences of important system parameters on the resonances are investigated.     

Contact problems for a finitely deformed incompressible elastic halfspace

This paper examines the class of problems related to the interaction between a finitely deformed incompressible elastic halfspace and contacting elements that include smooth, flat rigid indenters with elliptical and circular shapes and a thick plate of infinite extent. The contact between the finitely deformed elastic halfspace and the contacting elements is assumed to be bilateral. The interaction between both the rigid circular indenter and the finitely deformed halfspace is induced by a Mindlin force that acts at the interior of the halfspace regions and by exterior loads. Similar considerations apply for the contact between the flexible plate of infinite extent and the finitely deformed elastic halfspace. The theory of small deformations superposed on large deformations proposed by Green et al. (Proc R Soc Ser A 211:128–155, 1952) is used as the basis for the formulation of the problem, and results of potential theory and integral transform techniques are used to develop the analytical results. In particular, explicit results are presented for the displacement of the rigid elliptical indenter and the maximum deflection of the flexible plate induced by the Mindlin forces, when the finitely deformed halfspace region has a strain energy function of the Mooney–Rivlin form.     

Bifurcation analysis of an arch structure with parametric and forced excitation

The subharmonic bifurcation and universal unfolding problems are discussed for an arch structure with parametric and forced excitation in this paper. The amplitude–frequency curve and some dynamical behavior have been shown for this class of problems by Liu et al. Here, by means of singularity theory, in the case of strict 1:2 internal resonance, the bifurcation behavior of the amplitude with respect to a parameter (which is related to the amplitude of the live load imposed on the arch structures) is studied. The results indicate that it is a high codimensional bifurcation problem with codimension 5, and the universal unfolding is given. From the mechanical background, 20 forms of two parameter unfoldings with some constraints are studied. The transition sets in the parameter plane and the bifurcation diagrams are plotted. The results obtained in this paper present some new dynamic buckling patterns and abundant bifurcation phenomena.     

Effect of elastomer slight compressibility

This paper is concerned with the constitutive equation for slightly compressible elastic material under finite deformations. We show that material slight compressibility can be effectively taken into account in the case of high hydrostatic pressure or highly confined material. In all other situations the application of the incompressible and nearly incompressible material theories gives practically the same results. Therefore it is of interest to consider the problem in which allowing for material slight compressibility leads to results essentially different from those obtained with help of the incompressible material model. In the present paper this difference has been demonstrated for the problem of high hydrostatic pressure causing an increase of the ‘bulk’ and ‘shear’ material moduli. The behavior of a long hollow cylinder of real material under finite deformations is analyzed. The cylinder is subjected to internal pressure and axial and circular displacements at the outer surface. This problem has been solved analytically using the small parameter method. The solution obtained predicts a decrease of the axial and circular displacements of the outer surface under fixed shear (axial and circular) forces when the internal pressure is applied.     

The method of composite expansions applied to boundary layer problems in symmetric bending of the spherical shells

In this paper,the method of composite expansions which was proposed by W. Z. Chien (1948)[5]is extended to investigate two-parameter boundary layer problems.For the problems of symmetric deformations of the spherical shells under the action of uniformly distribution load q, its nonlinear equilibrium equations can be written as follows: where ε and δ are undetermined parameters.If δ=1 and ε is a small parameter, the above-mentioned problem is called first boundary layer problem; if ε is a small parameter, and δ is a small parameter, too, the above-mentioned problem is called second boundary layer problem.For the above-mentioned problems, however, we assume that the constants ε, δ and p satisfy the following equation: εp=1-ε In defining this condition by using the extended method of composite expansions, we find the asymptotic solution of the above-mentioned problems with the clamped boundary conditions.     

Measurement of surface displacements in a tribological application

Laser-speckle photography is used to measure deformations which occur on the lateral surface of a rectangular-section pin which is in dry sliding contact against a counterface disk. The side of the pin is illuminated by a pulsed ruby laser. A double-exposure specklegram is made to obtain deformations which occur between laser pulses. So, by appropriately sequencing pulses, deformation histories can be obtainedin situ.Since the exposed side of the thin pin specimen represents the cover layer under which subsurface sections lie, the deformation history observable through the laser-speckle method reflects the deformation behavior which is occurring on subsurface planes. The strain fields associated with the deformations are also calculated by the usual methods which include nonlinear terms (Lagrangian formulation). Moreover, this paper presents results obtained for the extent of the plastically deformed zone for different materials.These fundamental data, obtained by laser-speckle photography, yield direct displacement or strain histories for wear specimens. Such data are important for understanding wear phenomena, and for the development of engineering models for wear.     

Exact solution of the non-linear differential equation concerning the elastic line of a straight rod due to terminal loading

In this paper a closed-form solution of the differential equation

related to the elastic line of a straight thin rod due to a terminal co-planar loading, is obtained. Based on this solution, the problem of eccentric buckling of the same rod, taking into account the influence of transverse shear deformations, is examined.     

水下航行体螺栓法兰连接结构可靠性分析

螺栓法兰连接结构中的摩擦、接触、间隙及预紧力等因素,会导致水下航行体结构在复杂载荷环境中出现非线性的动力学响应特性,甚至破坏连接结构.目前,常取指定时段内的各类内力最大值同时施加于连接结构进行可靠性分析,导致结构设计偏于保守.为解决此问题,本文基于随机水动力载荷作用下水下航行体结构内力响应数据,分析螺栓法兰连接结构在端面内力组合作用下的最大Mises应力,由此建立连接结构端面内力组合的极限状态面,利用最大熵方法开展螺栓法兰连接结构可靠性分析.为提高分析效率,根据连接结构端面各类内力在塑性极限状态面附近的线性相关性,提出以端面等效弯矩为指标的工程可靠性分析方法,并通过数值仿真分析对可靠性分析结果精度进行校核.     

不同模量理论弹性支承连续梁及框架

弹性支承连续梁及框架结构的内力不仅与各杆件的刚度有关，而且与支承结构的刚度有关．当引入拉压不同模量后，各杆件的抗弯刚度EI不再为常数(与经典力学不同)，而是内力的函数，使结构内力计算成为非线性问题．用分段积分法推导出不同模量弹性支承连续梁及框架的中性轴公式和内力计算表达式并编制非线性内力计算迭代程序．通过实例计算对比分析不同模量与经典力学相同模量两种方法计算结果的差异，最后提出对该类结构计算的合理建议以及利用不同模量对结构进行优化的结论．     

A variational approach to a micro-structured theory of solid-fluid mixtures

Summary In this paper, we present a micro-structured model for describing global deformations of heterogeneous mixtures. In particular, for a saturated solid-fluid mixture, we regard the solid volume fraction as a microstructural parameter so as to enlarge the space of admissible deformations with respect to the classical theory of mixtures. According to the variational approach, the governing equations are obtained as the stationarity of a suitable action functional. The micro-structured model is then forced to establish a second-gradient mixture theory, by introducing among the considered state parameters a suitable internal constraint. Finally, we determine under which (integrability) conditions the additional balance laws, typically employed to close the theory of porous media endowed with the volume fraction, can fit the variational framework. The authors wish to thank Prof. Francesco dell'Isola from University of Rome La Sapienza for his constructive criticism about the variational approach to continuum mechanics and the interpretation of the volume-fraction balance law.     

Hydrodynamics in weak force fields onset of steady thermocapillary convection in a spherical fluid layer under zero-g conditions

In the study of cellular convection in an infinite plane fluid layer with a free surface, both the Archimedes and thermocapillary forces [1–3] have been cited as reasons for the onset of convection. This has also been confirmed experimentally [4], When mass forces are absent or negligibly small it is natural to pose the question of the onset of pure thermocapillary convection or convection caused only by the surface tension gradients (see [2–3]). In the present paper, this problem is examined for a spherical fluid layer under zero-g conditions.     

The improvement of the general expression for the stress function Φ of the two-dimensional problem

In this paper, it is pointed that the general expression for the stress function of the plane problem in polar coordinates is incomplete. The problems of the curved bar with an arbitrary distributive load at the boundries can’t he solved by this stress function. For this reason, we suggest two new stress functions and put them into the general expression. Then, the problems of the curved bar applied with an arbitrary distributive load at r=a,b boundaries can be solved. This is a new stress function including geometric boundary constants.