Non-traditional crack problem for transversely-isotropic body

The published traditional crack problem solutions usually consider cracks located in the planes, parallel to the plane of isotropy, which is usually denoted as z = 0. We consider here case of a crack located in the plane x = 0 and subjected to arbitrary normal or tangential loading. The case of elliptic crack is considered in detail. Complete solution for the fields of displacements and stresses is presented single contour integrals of elementary integrands. Stress intensity factors are computed explicitly.     

Degenerate scale problem for plane elasticity in a multiply connected region with outer elliptic boundary

This paper investigates the degenerate scale problem for plane elasticity in a multiply connected region with an outer elliptic boundary. Inside the elliptic boundary, there are many voids with arbitrary configurations. The problem is studied on the relevant homogenous boundary integral equation. The suggested solution is derived from a solution of a relevant problem. It is found that the degenerate scale and the non-trivial solution along the elliptic boundary in the problem are same as in the case of a single elliptic contour without voids. The present study mainly depends on integrations of several integrals, which can be integrated in a closed form.     

Motion of a deformed contour in a flow of an ideal incompressible liquid with a constant vorticity

The article gives a solution to the plane problem of the motion of a deformed contour in a flow of an ideal incompressible liquid with a constant vorticity. An explicit expression is obtained for the hydrodynamic force when the velocity of the external flow depends linearly on the coordinates. In the case of a contour of small dimensions, this expression is valid also for an arbitrary external flow.     

Singular solutions for an anisotropic plate with an elliptical hole

A solution of the bending problem for a plate with an elliptical hole subjected to a point force (a singular solution) is obtained using the engineering theory of thin anisotropic plates and Lekhnitskiis complex potentials. The solution is constructed by conformal mapping of the exterior of the elliptical hole onto the exterior of a unit circle with evaluation of the Cauchy-type integrals over closed contours. Different versions of the boundary conditions on the holw contour are considered. In the limiting case where the ellipse becomes a slot, the solution describes the bending of a plate with a rectilinear crack or a rigid inclusion.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 144–152, January–February, 2005.     

Construction of asymmetric nozzles of maximum moment given additional conditions on the geometrical and force characteristics

A solution is given to the variation problem of constructing asymmetric plane nossles which realize the maximum moment relative to some point. The contours of the nozzle are assumed to be noninteracting. The method of the undetermined control contour is used [1]. The solution of this problem contains as a special case the solution to the problem of constructing a nozzle of maximum thrust, including also the case of a given lifting force [1–3]. It is shown that the construction of a nozzle of maximum moment under additional conditions on the thrust and the lifting force, or on the moment relative to another point, reduces to the construction of a nozzle of maximun moment relative to some auxiliary point.Translated from Izvestiya Akademi Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 148–152, September–October, 1984.The author thanks A. N. Kraiko for useful discussions and for his appraisal of the study.     

A tri-material elastodynamic solution for a transversely isotropic full-space

A linear elastic full-space composed of an upper half-space, a lower half-space and a layer of three different transversely isotropic materials under an internal load is considered. The axes of symmetry of the different regions are assumed to be normal to the planar interfaces of the regions and are thus parallel. An arbitrary load in the frequency domain is allowed on a finite patch located at the interface of the upper half-space and the adjacent layer. By means of the complete displacement potentials, the displacements and stresses in the three regions are determined in Fourier–Hankel space in the form of line integrals. The solution can be degenerated to the solution for (i) a full-space under an arbitrary buried load, (ii) a half-space contain a layer bonded to the top of it under an arbitrary surface force, (iii) a half-space under an arbitrary surface load, (iv) a two layer half-space under an arbitrary force applied at the interface of two regions, (v) a half-space under an arbitrary buried force, (vi) a layer of finite thickness fixed at the bottom and under an arbitrary surface load, and (vii) a bi-material full-space under an arbitrary load at the interface of two materials. Examples of the displacements and stresses are obtained numerically and compared to existing solutions.     

Conservation of the resultant force vector in the plane of the angle of attack for slender star-shaped bodies in supersonic flows

At high supersonic flight speeds bodies with a star-shaped transverse and power-law longitudinal contour are optimal from the standpoint of wave drag [1–3]. In most of the subsequent experimental [4–6] and theoretical [6–9] studies only conical star-shaped bodies have been considered. For these bodies in certain flow regimes ascent of the Ferri point has been noted [10]. In [11] the boundary-value problem for elongated star-shaped bodies with a power-law longitudinal contour was solved for the case of supersonic flow. The present paper deals with the flow past these bodies at an angle of attack. It is found that for arbitrary star-shaped bodies with any longitudinal (in particular, conical) profile the aerodynamic forces can be reduced to a wave drag and a lift force, the lateral force on these bodies being equal to zero for any position of the transverse contour.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 135–141, November–December, 1989.     

Time-harmonic Green’s functions for anisotropic magnetoelectroelasticity

Two-dimensional (2-D) and three-dimensional (3-D) time-harmonic Green’s functions for linear magnetoelectroelastic solids are derived in this paper by means of Radon-transform. Displacement field and electric and magnetic potentials in a fully anisotropic magnetoelectroelastic infinite solid due to a time-harmonic point force, point charge and magnetic monopole are obtained in form of line integrals over a unit circle in 2-D case and surface integrals over a unit sphere in 3-D case. This dynamic fundamental solution is then split into the sum of regular dynamic plus singular terms. The singular terms coincide with the Green’s functions for the static problem and may be further reduced to closed form expressions. The proposed Green’s functions can be used in the corresponding boundary element method (BEM) formulation.     

Solution of De Saint Venant flexure-torsion problem for orthotropic beam via LEM (Line Element-less Method)

In this paper the numerical technique, labelled Line Element-less Method (LEM), is employed to provide approximate solutions of the coupled flexure-torsion De Saint Venant problem for orthotropic beams having simply and multiply-connected cross-section. The analysis is accomplished with a suitable transformation of coordinates which allows to take full advantage of the theory of analytic complex functions as in the isotropic case.A boundary value problem is formulated with respect to a novel complex potential function whose real and imaginary parts are related to the shear stress components, the orthotropic ratio and the Poisson coefficients. This potential function is analytic in all the transformed domain and then expanded in the double-ended Laurent series involving harmonic polynomials.The solution is provided employing an element-free weak form procedure imposing that the squared net flux of the shear stress across the border is minimum with respect to the series coefficients.Numerical implementation of the LEM results in system of linear algebraic equations involving symmetric and positive-definite matrices. All the integrals are transferred into the boundary without requiring any discretization neither in the domain nor in the contour.The technique provides the evaluation of the shear stress field at any interior point as shown by some numerical applications worked out to illustrate the efficiency and the accuracy of the developed method to handle shear stress problems in presence of orthotropic material.     

Green functions for an incompressible linearly nonhomogeneous half-space

Summary Time-harmonic vibrations of an incompressible half-space having shear modulus linearly increasing with depth are studied. The half-space is subjected to a surface load which has vertical or hovizontal direction. The general solution of the time-harmonic, in the vertical direction nonhomogeneous problem is constructed for arbitrary angular distribution in the horizontal plane. Numerical results concerning surface displacements due to a point force are given for the case of nonzero shear modulus at the surface. These results show that nonhomogeneity can considerably increase amplitudes at large distances from the applied force.     

Radiation and scattering from bodies of revolution

The problem of electromagnetic radiation and scattering from perfectly conducting bodies of revolution of arbitrary shape is considered. The mathematical formulation is an integro-differential equation, obtained from the potential integrals plus boundary conditions at the body. A solution is effected by the method of moments, and the results are expressed in terms of generalized network parameters. The expansion functions chosen for the solution are harmonic in ø (azimuth angle) and subsectional in t (contour length variable). Because of rotational symmetry, the solution becomes a Fourier series in ø, each term of which is uncoupled to every other term.Illustrative computations are given for radiation from apertures and plane wave scattering from bodies of revolution. The impedance elements, currents, radiation patterns, and scattering patterns for a conducting sphere are computed both from the general solution and from the classical eigenfunction solution. The agreement obtained serves to check the general solution. Similar computations for a cone-sphere illustrate the application of the general solution to problems not solvable by classical methods.     

Elastic Displacement in a Half-Space Under the Action of a Tensor Force. General Solution for the Half-Space with Point Forces

The elastic displacement in an isotropic elastic half-space with free surface is calculated for a point tensor force which may arise from the seismic moment of seismic sources concentrated at an inner point of the half-space. The starting point of the calculation is the decomposition of the displacement by means of the Helmholtz potentials and a simplified version of the Grodskii-Neuber-Papkovitch procedure. The calculations are carried out by using generalized Poisson equations and in-plane Fourier transforms, which are convenient for treating boundary conditions. As a general result we compute the displacement in the isotropic elastic half-space with free surface caused by point forces with arbitrary structure and orientation, localized either beneath the surface (generalized Mindlin problem) or on the surface (generalized Boussinesq-Cerruti problems). The inverse Fourier transforms are carried out by means of Sommerfeld-type integrals. For forces buried in the half-space explicit results are given for the surface displacement, which may exhibit finite values at the origin, or at distances on the surface of the order of the depth of the source. The problem presented here may be viewed as an addition to the well-known static problems of elastic equilibrium of a half-space under the action of concentrated loads. The application of the method to similar problems and another approach to the starting point of the general solution are discussed.     

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.     

Optimal control of the dynamic response of an anisotropic plate with various boundary conditions

The problem of minimising the dynamic response of an anisotropic rectangular plate with minimum possible expenditure of force is presented for various cases of boundary conditions. The plate has a principal direction of anisotropy rotated at an arbitrary angle relative to the coordinate axes. This orientation angle has been taken as an optimisation design parameter. The control problem is formulated as an optimisation problem by using a performance index, which comprises a weight sum of the control objective and penalty function of the control force. The explicit solutions for the closed-loop distributed control function is obtained by means of Liapunov-Bellman theory. To assess the present solution, numerical results are presented to illustrate the effect of anisotropy ratio, orientation angle, aspect ratio and boundary conditions on the control process.     

Steady crack propagation followed by non-steady growth—Mode I solution

A mode I crack moves under steady-state conditions. At some time instant the velocity of propagation changes in some arbitrary way. By use of known solutions to other elastodynamic crack problems, the stress-intensity factor for this non-steady growth is obtained. It is given in the form of convolution integrals over quantities known from the steady-state solution. For the case of a momentaneous velocity jump an explicit equation is derived. Generalization of the results to the problem of arbitrary growth after an initial self-similar propagation is outlined.     

Structure of polynomial solutions of elasticity equations in stresses

For an isotropic elasticity problem in stresses in three-dimensional space minus the origin, we study solutions that have the singularity 1/r ² and, after the multiplication by r ², polynomially depend on the direction cosines. In this polynomial class, for the equilibrium equation we write out the general solution that is a statically admissible (in the sense of Castigliano) solution of the Kelvin problem. We show that if one or several Beltrami equations are not satisfied, then the classical Kelvin solution becomes nonunique. A method for constructing nonunique solutions of this kind is given. The equivalence of various statements of the elasticity problem in stresses is discussed. For the problem on the action of a lumped force at the vertex of an arbitrary conical elastic body, we write out the exact solution in stresses for the case of an incompressible material. The solution for a compressible material is represented in the form of series in a parameter characterizing the deviation of the Poisson ratio from 1/2. We obtain iterative chains of problems in stresses and conditions for the finiteness of these chains. We also analyze the realizability of a linear-fractional dependence of the solution in stresses on the Poisson ratio.     

Plane Elastic Boundary Value Problem Posed by Displacement and Force Orientations on a Closed Contour

A boundary value problem (BVP) of the plane elasticity posed in terms of the orientations of forces and displacements is considered. The main aim of the present paper is to investigate the solvability of BVPs of this kind. Firstly, analysis of two cases is performed: the case of a circle with special orientations of force and displacement vectors on the circumference and the case of an arbitrary contour with coaxial orientations of these vectors. The solutions obtained indicate that the problem can have a certain number of solutions or be unsolvable. Then the BVP is reduced to a boundary integral equation and its solvability is investigated for the general case of a smooth simple-connected closed contour. As a result, the number of linearly independent solutions is determined. This number only depends upon the angle between the force and displacement vectors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differentiation of energy functionals in the problem on a curvilinear crack with possible contact between the shores

We consider the N-dimensional (N = 2 or 3) model of a one-dimensional anisotropic elastic body containing a curvilinear or surface crack. On the crack shores, the nonpenetration conditions in the form of inequalities (Signorini type conditions) are posed. For the general form of a sufficiently smooth perturbation of the domain, we obtain the derivative of the energy functional with respect to the perturbation parameter. We derive sufficient conditions for the existence of invariant integrals over an arbitrary closed contour. In particular, we obtain an invariant Cherepanov-Rice integral for curvilinear cracks.     

Elastic fields of dislocation loops in three-dimensional anisotropic bimaterials

By applying semi-analytical point-force Green's functions obtained via the Stroh formulism, we derive simple line integrals to calculate the elastic displacement and stress fields for a three-dimensional dislocation loop in an anisotropic bimaterial system. The solutions for the case of anisotropy are more convenient for treating an arbitrary dislocation loop compared with traditional area integration. With this new formulation, we numerically examine the displacement, stress, and energy due to the interaction between a dislocation loop and the bimaterial interface in an Al–Cu system. The interactive image energy due to the elastic moduli mismatch across the interface is then numerically evaluated. The result shows that a dislocation loop is subjected to an attractive force by the interface when it lies in the stiff material, and a repulsive force when it lies in the soft material. Moreover, the dependence of the interactive image energy of a dislocation loop on the position and size of the dislocation loop are also demonstrated and discussed. Significantly, it is found that the interactive image energy for a dislocation loop depends only on the ratio d/a, where a is the loop diameter and d is its distance to the interface. The examples studied provide benchmark solutions for anisotropic bimaterial dislocation problems.