Realizing the Willis equations with pre-stresses

This paper proves that the linear elastic behavior of the material with inhomogeneous pre-stresses can be described by the Willis equations. In this case, the additional terms in the Willis equations, compared with the classical linear elastic equations for homogeneous media, are related to the gradient of pre-stresses. In this way, the material length scale is naturally incorporated in the framework of continuum mechanics. All these findings also coincide with the results of transformation elastodynamics, so that they can meet the requirement of the principle of material objectivity and the principle of general invariance.     

THE GENERALITY OF THE GENERAL EQUATIONS OF DYNAMICS 1)

理论力学中动力学普遍方程,在分析力学中称为d'Alembert--Lagrange原理。动力学普遍方程之普遍在于,由它不仅可导出动力学普遍定理,可导出完整约束系统和非完整约束系统的运动微分方程,还可导出积分变分原理。     

On the dynamic bending of layered plates

The dynamic bending of layered metallic plates is studied. Their layers are reinforced with wires, and there are interfacial layers between the contact surfaces. A general approach to solving the corresponding dynamic problems is proposed. It is the principle of virtual work. A system of ordinary differential constitutive equations is obtained and used to determine the amplitude coefficients of the series of coordinate functions that approximates the deflections. The constitutive equations are reduced to Volterra equations of the second kind. Algorithms are developed to calculate the coefficients of the constitutive equations depending on the coordinate functions and on the reinforcement pattern. Possible methods to set up coordinate functions and solve integral equations are indicated     

A new approach to the vakonomic mechanics

The aim of this paper was to show that the Lagrange–d’Alembert and its equivalent the Gauss and Appel principle are not the only way to deduce the equations of motion of the nonholonomic systems. Instead of them we consider the generalization of the Hamiltonian principle for nonholonomic systems with non-zero transpositional relations. We apply this variational principle, which takes into the account transpositional relations different from the classical ones, and we deduce the equations of motion for the nonholonomic systems with constraints that in general are nonlinear in the velocity. These equations of motion coincide, except perhaps in a zero Lebesgue measure set, with the classical differential equations deduced with the d’Alembert–Lagrange principle. We provide a new point of view on the transpositional relations for the constrained mechanical systems: the virtual variations can produce zero or non-zero transpositional relations. In particular, the independent virtual variations can produce non-zero transpositional relations. For the unconstrained mechanical systems, the virtual variations always produce zero transpositional relations. We conjecture that the existence of the nonlinear constraints in the velocity must be sought outside of the Newtonian mechanics. We illustrate our results with examples.     

Theory of nonlinear dynamic stability for composite laminated plates

In this paper,the general equations of dynamic stability for composite laminatedplates are derived by Hamilton principle.These general equations can be used to considerthose different factors that affect the dynamic stability of laminated plates.The factors aretransverse shear deformation,initial imperfections,longitudinal and rotational inertia,andply-angle of the fiber,etc.The solutions of the fundamental equations show that someimportant characteristics of the dynamic instability can only be got by the considerationand analysis of those factors     

机器人粘弹性手臂的动力学有限元分析

本文用动力学虚功原理建立了一般粘弹性大阻尼结构机器人手臂的动力学有限元模型,该模型是时变的Voterra型微分积分方程。文中还提出了以结构动力学中响应计算的逐步积分法为基础的递推求解方法,从而解决了机器人粘弹性手臂动力学建模和分析的理论难题。     

RESTUDY OF THEORIES FOR ELASTIC SOLIDS WITH MICROSTRUCTURE

ＩｎｔｒｏｄｕｃｔｉｏｎＵｐｔｏｎｏｗｔｈｅｒｅｈａｓｂｅｅｎｖｅｒｙｍｕｃｈｗｒｉｔｔｅｎｗｏｒｋｏｎｔｈｅｓｕｂｊｅｃｔｓｏｆｃｏｎｔｉｎｕｕｍｔｈｅｏｒｉｅｓｉｎｗｈｉｃｈｔｈｅｄｅｆｏｒｍａｔｉｏｎｉｓｄｅｓｃｒｉｂｅｄｎｏｔｏｎｌｙｂｙｔｈｅｕｓｕａｌｖｅｃｔｏｒｄｉｓｐｌａｃｅｍｅｎｔｆｉｅｌｄ ,ｂｕｔｂｙｏｔｈｅｒｖｅｃｔｏｒｏｒｔｅｎｓｏｒｆｉｅｌｄｓａｓｗｅｌｌ.Ｉｎａｆａｍｏｕｓｍｏｎｏｇｒａｐｈ ,Ｅ .ＣｏｓｓｅｒａｔａｎｄＦ .Ｃｏｓｓｅｒａｔ[1]ｇａｖｅａｓｙｓｔｅｍａｔｉｃ…     

On the fundamental equations of electromagnetoelastic media in variational form with an application to shell/laminae equations

The fundamental equations of elasticity with extensions to electromagnetic effects are expressed in differential form for a regular region of materials, and the uniqueness of solutions is examined. Alternatively, the fundamental equations are stated as the Euler–Lagrange equations of a unified variational principle, which operates on all the field variables. The variational principle is deduced from a general principle of physics by modifying it through an involutory transformation. Then, a system of two-dimensional shear deformation equations is derived in differential and fully variational forms for the high frequency waves and vibrations of a functionally graded shell. Also, a theorem is given, which states the conditions sufficient for the uniqueness in solutions of the shell equations. On the basis of a discrete layer modeling, the governing equations are obtained for the motions of a curved laminae made of any numbers of functionally graded distinct layers, whenever the displacements and the electric and magnetic potentials of a layer are taken to vary linearly across its thickness. The resulting equations in differential and fully variational, invariant forms account for various types of waves and coupled vibrations of one and two dimensional structural elements as well. The invariant form makes it possible to express the equations in a particular coordinate system most suitable to the geometry of shell (plate) or laminae. The results are shown to be compatible with and to recover some of earlier equations of plane and curved elements for special material, geometry and/or effects.     

On the method of equivalent inclusions in elastodynamics and the scattering fields of two ellipsoidal inhomogeneities

Gurtin’s variational principle is used to derive the equivalence equalions for general linear elastodynamical problems of multiple inhomogeneities. An approximate expression on scattering field of two ellipsoidal inhomogeneities is obtained by the method of equivalent inclusions. And some numerical examples are presented.     

SOME PROBLEMS IN ELECTROSTRICTIVE AND MAGNETOSTRICTIVE MATERIALS

Some of the previous theories in the electrostrictive and magnetostrictive materials and their differences are discussed in this paper.A variational principle in the general thermody- namic sense is given and the governing equations can be derived from this principle.Illustrational examples are given.     

New scalar-type equilibrium equations of the general space force system

ＩｎｔｒｏｄｕｃｔｉｏｎＬｉｋｅｔｈｅｃｏｐｌａｎａｒｆｏｒｃｅｓｙｓｔｅｍ ,ａｎｙｇｅｎｅｒａｌｓｐａｃｅｆｏｒｃｅｓｙｓｔｅｍＦｉ(ｉ =1 ,2 ,… ,ｎ)ｃａｎｂｅｒｅｄｕｃｅｄｔｏａｐｏｉｎｔＯａｎｄｒｅｐｌａｃｅｄｂｙａｐｒｉｎｃｉｐａｌｖｅｃｔｏｒＲａｎｄａｐｒｉｎｃｉｐａｌｍｏｍｅｎｔＬ0 .Ｓｏｔｈａｔｔｈｅｖｅｃｔｏｒ＿ｔｙｐｅｎｅｃｅｓｓａｒｙａｎｄｓｕｆｆｉｃｉｅｎｔｃｏｎｄｉｔｉｏｎｓｆｏｒｅｑｕｉｌｉｂｒｉｕｍｏｆｔｈｅｇｉｖｅｎｆｏｒｃｅｓｙｓｔｅｍａｒｅＲ =0 ,　Ｌ0 =0 . (1 )…     

On the Equations of Capillarity

Some conceptual ambiguities in the derivation of the equations of capillarity on the basis of the principle of virtual work are addressed, and hypotheses are proposed toward obtaining a physically correct characterization in general circumstances. It is shown that under the hypotheses, the classical equations of capillarity for an interface of an incompressible fluid with a fluid of negligible density can be obtained on the basis of global phenomenological reasoning, without recourse to consideration of intermolecular attractions. More generally, the procedure is applied to derive the specific equations arising from a compressible fluid configuration with idealized pressure-density relationship in a capillary tube, and a general necessary condition for existence of a solution is established. It is shown that for symmetric domains, the condition is also sufficient for existence of a unique symmetric solution.     

GURTIN VARIATIONAL PRINCIPLE AND FINITE ELEMENT SIMULATION FOR DYNAMICAL PROBLEMS OF FLUID-SATURATED POROUS MEDIA

Based on the theory of porous media,a general Gurtin variational principle for theinitial boundary value problem of dynamical response of fluid-saturated elastic porous media isdeveloped by assuming infinitesimal deformation and incompressible constituents of the solid andfluid phase.The finite element formulation based on this variational principle is also derived.Asthe functional of the variational principle is a spatial integral of the convolution formulation,thegeneral finite element discretization in space results in symmetrical differential-integral equationsin the time domain.In some situations,the differential-integral equations can be reduced to sym-metrical differential equations and,as a numerical example,it is employed to analyze the reflectionof one-dimensional longitudinal wave in a fluid-saturated porous solid.The numerical results canprovide further understanding of the wave propagation in porous media.     

RESTUDY OF COUPLED FIELD THEORIES FOR MICROPOLAR CONTINUA (Ⅱ)-THERMOPIEZOELECTRICITY AND MAGNETOTHERMOELASTICITY

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｏｒｙｏｆｍｉｃｒｏｐｏｌｏａｒｔｈｅｒｍｏｅｌａｓｔｉｃｉｔｙｐｒｅｓｅｎｔｅｄｂｙＷ .Ｎｏｗａｃｋｉｉｓｒｅｓｔｕｄｉｅｄｉｎｏｕｒｐａｐｅｒ[1].Ｔｈｉｓｐａｐｅｒｉｓａｄｉｒｅｃｔｃｏｎｔｉｎｕａｔｉｏｎｏｆｒｅｆｅｒｅｎｃｅ [1 ] .Ｔｈｅｐｒｏｂｌｅｍｓｏｃｃｕｒｒｉｎｇｉｎｔｈｅｔｈｅｏｒｉｅｓｏｆｔｈｅｒｍｏｐｉｅｚｏｅｌｅｃｔｒｉｃｉｔｙａｎｄｍａｇｎｅｔｏｔｈｅｒｍｏｅｌａｓｔｉｃｉｔｙｆｏｒｍｉｃｒｏｐｏｌａｒｃｏｎｔｉｎｕａａｒｅｓｉｍｉｌａｒｔ…     

GIBBS-APPELL’S EQUATIONS OF VARIABLE MASS NONLINEAR NONHOLONOMIC MECHANICAL SYSTEMS

In this paper,the Gibbs-Appell’s equations of motion are extended to the most generalvariable mass nonholonomic mechanical systems.Then the Gibbs-Appell’s equations ofmotion in terms of generalized coordinates or quasi-coordinates and an integral variationalprinciple of variable mass nonlinear nonholonomic mechanical systems are obtained.Finally,an example is given.     

基于哈密顿原理的两种材料界面裂纹奇性研究

研究了两种材料组成的弹性体在交界面上含裂纹时的裂纹尖端奇异场。通过变量代换及变分原理，将平面弹性扇形域的方程导向哈密体系，从而可通过分离变量及共轭辛本征函数展开法解析法求解扇形域方程，得到求解双材料界面裂纹尖点奇性的一般表达式，由此为该类问题的求解开辟了一条新途径。     

Thermodynamical bounds to the elastic behaviour of elastic materials

We propose to exploit the second principle of thermodynamics in a different way from that usually followed in continuum mechanics. We study the consequences of this approach as far as the path-dependent character of the constitutive equations is concerned. The analysis leads us to infer that for materials capable of thermoelastic behaviour there are, in general, states of deformation beyond which a deformation process cannot occur without violating the second principle of thermodynamics. The relation between these states of deformation and those relevant to the yield limit is considered.     

流体饱和多孔介质的动力学Gurtin型变分原理和有限元模拟

基于多孔介质理论。在两相不可压和小变形的假设下，建立了流体饱和弹性多孔介质的动力学Gurtin型变分原理，并导出了以此变分原理为基础的有限元离散公式，由于Gurtin型变分原理是卷积型的空间积分泛函，空间的有限元离散导致一个关于时间的对称微分—积分方程组，在一般条件下。该积分—微分方程组可转化为对称的微分方程组，这组方程有别于标准Galerkin有限元的非对称离散方程组，作为数值例子，分析了流体饱和弹性多孔介质中一维纵向波的传播和反射，其结果进一步揭示了饱和多孔介质中波的传播特性。     

哈密顿体系下机电耦合问题的基本方程

利用多变量变分原理,针对具有机电耦合特性的压电材料,在哈密顿体系下推导出了机电耦合问题的对偶方程．求出了问题的零本征解和非零本征解的一般表达式。并就“二维压电平板对边受均布载荷”这一具体问题进行了完整的分析计算,得出了应力和电位移的具体解答,结果与一般弹性力学所得的结论相吻合,而且精度极高。表明哈密顿体系适用于压电材料的力学分析。