Dynamics of a system of remote punches on an elastic half-space

The dynamic interaction (contact) between an elastic half-space and several smooth punches is studied. It is assumed that the dimensions of the contact regions Ω_i are much smaller than the distances between them and the scale of time of the process considered is comparable with the time required for an elastic wave to travel from one region to another. An asymptotic approach to the solution of the problem is proposed and the first two terms of the asymptotic representation of the displacement in the contact region and its neighborhood are constructed. Institute of Problems of Machine Science, Russian Academy of Sciences, St. Petersburg 199178. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 204–210, November–December, 1999.     

Homogenization of a contact problem for a system of densely situated punches

A linear contact problem of an elastic half space with rigid punches ε-periodically situated on a bounded part of the boundary of the elastic solid is investigated. Using the method of homogenization theory and the method of matched asymptotic expansions, the leading terms of the asymptotic solution are constructed as ε→0. The general capacity of the contact spot is introduced and some its properties are described.     

Interaction of slowly moving punches with an elastic half-space

The problem of slow dynamic contact interaction of a system of punches remote from each other with an elastic half-space surface in the absence of friction is studied under the assumptions that the diameters of the contact areas are smaller than the minimum distance between the punches and the time required for the shear wave to travel the distance equal to the punch diameter is comparable to the time scale of the process. A first-order asymptotic model is constructed. As an example, the case of steady-state vibrations of a system of two punches is considered. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 198–206, November–December, 2008.     

Indentation of a Punch with a Fine-Grained Base into an Elastic Foundation

The linear contact problem for a system of small punches located periodically on a part of the boundary of an elastic foundation is studied. An averaged contact problem is derived using the Marchenko–Khruslov averaging theory. An asymptotic formula is obtained for the translational capacity of a smooth punch with a fine-grained flat base.     

Solution of the plane Hertz problem

The paper considers the problem of onesided frictionless compression of plane elastic bodies that are initially in contact with each other at a point. The first terms of an asymptotic solution of the problem are constructed by the method of joined asymptotic expansions. Determination of the approach of the bodies as a function of the pressing force reduces to calculating socalled of local compliance. The problems of contact of an elastic ring and elastic circular disks with punches and an elastic disk compressed between two elastic strips are considered. An asymptotic model for the quasistatic collision of plane elastic bodies is proposed.     

Galin’s problem for a spatial elastic wedge

We study a three-dimensional contact problem on the indentation of an elliptic punch into a face of a linearly elastic wedge. The wedge is characterized by two parameters of elasticity and its edge is subjected to the action of an additional concentrated force. The other face wedge is free from stresses. The problem is reduced to an integral equation for the contact pressure. An asymptotic solution of this equation is obtained which is effective for a given contact region fairly remote from the edge. Calculations are performed that allow one to evaluate the effect of a force applied outside the contact region on the contact pressure distribution. The problem under study is a generalization of L. A. Galin’s problem on a force applied outside a circular punch on an elastic half-space [1, 2]. In a special case of a wedge with an opening angle of 180° and zero contact ellipse eccentricity, the obtained asymptotic relation coincides with the expansion of Galin’s exact solution in a series. Problems of indentation of an elliptic punch into a spatial wedge with the face not loaded outside the contact region have been studied previously. For example, the paper [3] dealt with the case of a known contact region (asymptotic method) and the paper [4] considered the case of an unknown contact region (numerical method). The solution of Galin’s problem allowed the authors of [2] to reduce the contact problem on the interaction of several punches applied to a half-space to a system of Fredholm integral equations of the second kind (Andreikin-Panasyuk method). A topical direction in contact mechanics is the model of discrete contact as well as related problems on the interaction of several punches [2, 5–8]. The interaction of several punches applied to a face of a wedge can be treated in a similar manner and an asymptotic solution can be obtained for the case where a concentrated force is applied at an arbitrary point of this face beyond the contact region rather than on the edge.     

Electromechanical behaviour of a finite piezoelectric layer under a flat punch

This paper solves the problem of a smooth and frictionless punch on a piezoelectric ceramic layer. Different electrical boundary conditions that employ conducting or insulating punches are presented. The stress and electric displacement intensity factors are used to characterize the electromechanical fields at the punch tip. The field intensity factors are obtained numerically for finite layer thickness. Effects of the thickness of the piezoelectric layer on the stress and electric displacement, and the stress and electric displacement intensity factors at the punch tip are discussed. Solution technique for two identical and collinear surface punches on the piezoelectric layer is also provided and the effect of relative distance between the punches is investigated. Numerical results for some interesting special cases, such as conducting punch and insulating punch, and infinite piezoelectric layer thickness, are presented.     

Abnormal long wave dispersion phenomena in a slightly compressible elastic plate with non-classical boundary conditions

A two parameter asymptotic analysis is employed to investigate some unusual long wave dispersion phenomena in respect of symmetric motion in a nearly incompressible elastic plate. The plate is not subject to the usual classical traction free boundary conditions, but rather has its faces fixed, precluding any displacement on the boundary. The abnormal long wave behaviour results in the derivation of non-local approximations for symmetric motion, giving frequency as a function of wave number. Motivated by these approximations, the asymptotic forms of displacement components established and long wave asymptotic integration is carried out.     

Complete Asymptotic Expansions of Solutions of the System of Elastostatics in the Presence of an Inclusion of Small Diameter and Detection of an Inclusion

We consider the system of elastostatics for an elastic medium consisting of an imperfection of small diameter, embedded in a homogeneous reference medium. The Lamé constants of the imperfection are different from those of the background medium. We establish a complete asymptotic formula for the displacement vector in terms of the reference Lamé constants, the location of the imperfection and its geometry. Our derivation is rigorous, and based on layer potential techniques. The asymptotic expansions in this paper are valid for an elastic imperfection with Lipschitz boundaries. In the course of derivation of the asymptotic formula, we introduce the concept of (generalized) elastic moment tensors (Pólya–Szegö tensor) and prove that the first order elastic moment tensor is symmetric and positive (negative)-definite. We also obtain estimation of its eigenvalue. We then apply these asymptotic formulas for the purpose of identifying with high precision the order of magnitude of the diameter of the elastic inclusion, its location, and its elastic moment tensors.     

On indentation of a pair of rigid punches connected by an elastic beam into an elastic half-plane with regard to the friction and adhesion forces in the contact region

The contact problem of indentation of a pair of rigid punches with plane bases connected by an elastic beam into the boundary of an elastic half-plane is considered under the conditions of plane strain state. The external load is generated by lumped forces applied to the punches and a uniformly distributed normal load acting on the beam.It is assumed that the contact between the punch and the elastic half-plane can be described by L. A. Galin’s statement, i.e., it is assumed that the adhesion acts in the interior part of each of the contact regions and the tangential stresses obeying the Coulomb law act on their boundaries.With the symmetry taken into account, the problem is stated only for a single punch, and solving this problem is reduced to a system of four singular integral equations for the tangential and normal stresses in the adhesion region and the contact pressure in the sliding zones. The solution of the constitutive system together with three conditions of equilibrium of the system of punches connected by a beam is constructed by direct numerical integration by the method of mechanical quadratures.As a result of the numerical analysis, the contact stress distribution functions were constructed and the values of the sliding zones and the punch rotation angle were determined for various values of the geometric, elastic, and force characteristics.     

Contact Problems for Prestressed Elastic Bodies and Rigid and Elastic Punches

Contact problems for prestressed bodies and rigid and elastic punches are discussed. The influence of the prestresses on the contact characteristics is analyzed numerically     

Asymptotic models of contact interaction among elliptic punches on a semiclassical foundation

Consideration is given to the contact without friction among an arbitrary number of elliptic punches or punches in the form of an elliptic paraboloid and an elastic half-space with Young's modulus as a power-law function of the distance from the edge. Asymptotic models of contact interaction are designed assuming that the distance between punches is large compared with their dimensions __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 1, pp. 78–96, January 2006.     

Derivation of the Linear Elastic String Model from Three-Dimensional Elasticity

We derive a one-dimensional model for the displacement and torsion of an elastic string starting from a cylindrical three-dimensional linearized prestressed elastic body with small diameter. The prestress is due to the prior elastic deformation of an isotropic, homogenous, elastic body. We deduce the scaling of forces by a formal asymptotic expansion. Then we prove that the family of solutions of three-dimensional problems converges to a limit that is the unique solution of the string model. Coefficients of the string model depend on the three-dimensional elasticity coefficients and the tension due to the predeformation.     

有限变形下线弹性裂尖场的渐近分析

对有限变形下线弹性Ⅰ型裂纹场建立了无需分区的统一控制方程并进行了渐近分析, 利用“打靶法”得到位移场在物质描述与空间描述下的渐近阶次分别为3／4和1,Green应变、第二类P－K应力及Cauchy应力在物质描述与空间描述下的渐近阶次分数为－1／2和－2／3;对不同泊松比,裂尖有限变形线弹性场的位移均以UⅡ或u2为主导,裂纹张开角为π,现时构形中的大变形区为一垂直初始构形中裂纹表面的狭长带状区,应力则处于由σ22主导的单向拉伸状态,角分布函数U^-Ⅱ（0）及σ22^-(0)具有奇异性,但UL^-‘(Θ）／UⅡ^－‘(0)及σij^-(θ）/σ22^-(0)均趋于有限值。     

Decay and other estimates for a semi-infinite magnetoelastic cylinder: Saint-Venant''s principle

An analogue of the well known Toupin's version of Saint-Venant's principle is proved for a semi-infinite magnetoelastic cylinder under very mild assumptions on the asymptotic behaviour of the Dirichlet integral of the magnetic field and of the elastic energy. With regard to the elastic fields, we assign on the base either the stress or the displacement vector while we assume that the lateral surface is either traction free or held fixed at zero displacement. We make use of the first Korn inequality and estimate the total energy of the conductor in terms of the data for all the problems considered.     

Boundary Perturbations Due to the Presence of Small Linear Cracks in an Elastic Body

In this paper, Neumann cracks in elastic bodies are considered. We establish a rigorous asymptotic expansion for the boundary perturbations of the displacement (and traction) vectors that are due to the presence of a small elastic linear crack. The formula reveals that the leading order term is ε ² where ε is the length of the crack, and the ε ³-term vanishes. We obtain an asymptotic expansion of the elastic potential energy as an immediate consequence of the boundary perturbation formula. The derivation is based on layer potential techniques. It is expected that the formula would lead to very effective direct approaches for locating a collection of small elastic cracks and estimating their sizes and orientations.     

Asymptotic analysis of an impermeable crack in an electrostrictive material subjected to electric loading

The simple asymptotic problem of an impermeable crack in an electrostrictive ceramic under electric loading is analyzed. Closed form solutions of elastic fields are obtained by using the complex function theory. It is found that the K_I-dominant region is very small compared to the electric saturation zone. A fracture parameter for an electrostrictive material subjected to electric loading is discussed. In order to investigate the influence of the transverse electric displacement on fracture behavior under the small-scale conditions, we also consider the modified boundary layer problem of a crack in an electrostrictive material. Analytic solutions of electric displacement fields for the asymptotic problem are obtained based on the nonlinear dielectric theory from a modified boundary layer analysis. The shape of the electric displacement saturation zone is shown to depend on the transverse electric displacement. Stress intensity factors induced by the electrostrictive strains are evaluated using the nonlinear solution of the electric displacements. It is found that the transverse electric displacement affects strongly the variation of the mode mixity.     

Asymptotic stability in nonlinear elastic materials with dissipation

This paper is concerned with the effects of dissipation on classical solutions of the displacement and mixed initial-boundary value problems for a nonlinear elastic material. A proof of the asymptotic stability of the null solution in three dimensions is presented and the necessary assumptions are carefully discussed. The derivation of an analogous result for non-zero equilibrium solutions of the one-dimensional problem completes this work.     

Mixed-mode stress intensity factors for graded materials

In this paper, we present a general method for the calculation of the various stress intensity factors in a material whose constitutive law is elastic, linear and varies continuously in space. The approach used to predict the stress intensity factors is an extension of the interaction integral method. For this type of material, we also develop a systematic method to derive the asymptotic displacement fields and use it to achieve better-quality results. A new analytical asymptotic field is given for two special cases of graded materials. Numerical examples focus on materials with space-dependent Young modulus.     

Inclined semi-elliptical crack for predicting crack growth direction based on apparent stress intensity factors

Linear elastic criterion of the inclined semi-elliptical crack growth direction is elaborated on the basis of the strain energy density theory. Stress and displacement fields are presented for higher order terms asymptotic expansion. Solutions for elastic stress intensity factors are accounting for the function describing of the crack tip fields near the free surface of plate. The mixed mode behavior of crack growth direction angle along the semi-elliptical crack front for different combination of biaxial loading, inclination crack angle and surface flaw geometry is determined.