Mathematical modelling and the study of the influence of initial stresses on the SIF and ERR at the crack tips in a plate-strip of orthotropic material

A plate-strip fabricated from the orthotropic material and containing a crack whose edges are parallel to the face planes of the plate is considered. It is assumed that the strip is stretched (or compressed) initially along the crack edges by uniformly distributed external normal forces acting on the simply supported ends of the plate-strip. After this initial stretching (or compression) the crack edges are loaded by additional uniformly distributed normal (opening) forces. As a result of the action of these additional forces the stress concentration characterized by the stress intensity factor (SIF) of mode I or by the energy release rate (ERR) of mixed mode arises at the crack tips. In this paper, the influence of the initial stresses on the SIF or ERR is modelled mathematically by the use of the three-dimensional linearized theory of elasticity. The aim of the present investigations is to study the effect of the mechanical–orthotropic properties of the plate-strip material on this influence by the use of the finite element method (FEM) modelling of the corresponding boundary-value problem.     

Three-Dimensional Stress Analysis for a Thick Plate of a Composite Material with a Spatially Locally Curved Structure

The stress distribution in a thick rectangular plate of a multilayered composite with a spatially locally curved structure is investigated with the use of three-dimensional exact equations of elasticity theory. The investigations are carried out within the framework of the continuum approach proposed by Akbarov and Guz'. It is supposed that the plate edges are clamped and uniformly distributed normal forces are applied to its upper face. The corresponding boundary-value problem is solved by employing the three-dimensional FEM modeling. Numerical results for the normal stresses acting in the thickness direction of the plate are given. The influence of the spatial local curving on the distribution of these stresses is analyzed.     

Torsional wave propagation in a pre-stressed circular cylinder embedded in a pre-stressed elastic medium

Within the framework of the piecewise homogeneous body model with utilization of the three-dimensional linearized theory of elastic waves in initially stressed bodies, the mathematical modeling of the torsional wave propagation in the initially stressed infinite body containing an initially stressed circular solid cylinder (case 1) and circular hollow cylinder (case 2) are proposed. In these cases, it has been assumed that in the constituents of the considered systems there exist only the normal homogeneous tensional or compressional initial stress acting along the cylinder, i.e. in the direction of wave propagation. In the case where the mentioned initial stresses are not present, the proposed mathematical modeling coincides with that proposed and investigated by other authors within the classical linear theory of elastic waves. The mechanical properties of the cylinder and surrounding infinite medium have been described by the Murnaghan potential. The numerical results related to the torsional wave dispersion and the influence of the mentioned initial stresses on this dispersion are presented and discussed.     

On an Approach to the Solution of the Bending Problem for Laminated Plates

The paper presents a method for determining the three-dimensional state of stresses and strains in a moderately thick rectangular plate composed of isotropic layers unlimited in number and arranged symmetrically about the midplane of the plate. The method is based on a variant of Timoshenko theory [1, 2] and allows one to calculate the stresses and displacements in a shear-compliant plate for various types of boundary conditions and various external loads. According to it, the displacement field in the plate is represented as a sum of products of two unknown functions one of which is defined on the midplane and the second one depends on the thickness coordinate and satisfies the layer contact conditions. As an example, a rectangular laminated plate clamped at all its edges and loaded on the upper surface by a sinusoidal load is considered.     

Elastic equilibrium of an anisotropic plate of arbitrary thickness with an elliptic cavity

We study the stressed state of an anisotropic plate of arbitrary thickness weakened by a cylindrical elliptic cavity and subject to forces that are independent of the thickness coordinate. The results of numerical computations are described. Four figures. Bibliography: 2 titles. Translated fromTeoreticheskaya i Prikladnaya Mekhanika, No. 28, 1998, pp. 76–80.     

A dynamical model of storm surges along island coasts

A time-independent dynamical model of storm surge along island coasts using orthogonal curvilinear coordinates is presented. The curved annulus between an island coast and an arbitrary deep-water boundary is mapped conformally onto a rectangular image. Two configurations of island coasts are investigated; circular and elliptic coasts. The corresponding coordinates are circular polar and elliptic respectively. The linearized vertically-integrated equations of motion are used to model storm surges with two assumptions: (i) bottom stress is proportional to horizontal transport, and (ii) storm forces are shear stresses on water surface. Analytical solutions are presented for three dynamical cases: (i) a constant-depth basin acted upon by a uniform storm stress, (ii) variable-depth basin acted upon by a uniform-direction variable-magnitude stress, and. (iii) a basin with closed depth contours acted upon by vortex-shaped storm stress. The obtained solutions clarify the relative importance of the various parameters and variables that affect surge height distribution along island coasts. These solutions may be used to test a time-dependent, numerical dynamical storm model.     

Delamination buckling of a rectangular orthotropic composite plate containing a band crack

The delamination buckling problem for a rectangular plate made of an orthotropic composite material is studied. The plate contains a band crack whose faces have an initial infinitesimal imperfection. The subsequent development of this imperfection due to an external compressive load acting along the crack is studied through the use of the three-dimensional geometrically nonlinear field equations of elasticity theory for anisotropic bodies. A criterion of initial imperfection is used in determining the critical forces. The corresponding boundary-value problems are solved by employing the boundary-form perturbation technique and the FEM. Numerical results for the critical force are presented.     

FEM Analysis of the Three-Dimensional Buckling Problem for a Clamped Thick Rectangular Plate Made of a Viscoelastic Composite

The buckling instability of a thick rectangular plate made of a viscoelastic composite material is studied. The investigation is carried out within the framework of the three-dimensional linearized theory of stability. The plate edges are clamped and the plate is compressed through the clamps. Moreover, it is assumed that the plate has an initial infinitesimal imperfection, and, as a buckling criterion, the state is taken where this imperfection starts to increase indefinitely at fixed finite values of external compressive forces. From this criterion, the critical time is determined. The corresponding boundary-value problems are solved by employing the three-dimensional FEM and the Laplace transform. The material of the plate is assumed orthotropic, viscoelastic, and homogeneous. Numerical results related to the critical time are presented.     

Stressed state of an anisotropic body with elliptical holes, elastic inclusions, and cracks

A method is proposed for studying the two-dimensional stressed state of a multiply connected anisotropic body with cavities and elastic and rigid inclusions, as well as planar cracks and rigid laminar inclusions. Generalized complex potentials, conformal mapping, and the method of least squares are used. The problem is reduced to solving a system of linear algebraic equations. Formulas are given for finding the stress intensity factors in the case of cracks and laminar inclusions. For an anisotropic plate with a single elliptical hole or a crack and an elastic (rigid) inclusion, some numerical results are presented from a study of the effect of the rigidity of the inclusion and the closeness of the contours to one another on the distribution of stresses and the stress intensity factor. Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 30, pp. 175–187, 1999.     

Dispersion of lamb waves in a three-layer plate made from compressible materials with finite initial deformations

A three-layer plate made from compressible elastic materials with finite initial deformations caused by compressive forces applied to their faces is considered. By using the three-dimensional linearized theory of propagation of elastic waves in bodies with initial stresses, the propagation of Lamb waves in this plate is investigated.     

任意形状孔口双边裂纹平板的应力强度因子计算

本文采用Muskhclishvili弹性力学的复变函数和边界配位方法对不同形状孔口双边裂纹问题进行了研究,计算了圆孔、椭圆孔、矩形孔、菱形孔等不同形状孔口双边裂纹,以及Ⅰ型和复合型等不同类型断裂试件的应力强度因子,本文方法简单方便,精度较高,与某些已有计算结果的问题比较,本文方法所得的结果是令人满意的.同时,本方法可以应用于不同几何形状和加载条件下的孔口双边裂纹有限大板的计算,是解这一类问题的一致有效方法.     

Energy release rate in a prestressed sandwich plate-strip containing interface cracks

Within the framework of a piecewise homogeneous body model, by utilizing the three-dimensional linearized theory of elasticity, the problem of opening of interface cracks in an initially stressed sandwich plate-strip is studied. To solve the corresponding boundary-contact problem, the FEM is employed. Numerical results for the influence of the initial stresses on the energy release rate (ERR) at various values of problem parameters are presented and discussed. In particular, it is established that the ERR in creases (de creases) with growing initial tension (compression) of the plate-strip.     

Torsion of prismatic elastic bodies containing screw dislocations

The problem of the stressed state of a prismatic anisotropic rod containing screw dislocations, the axes of which are parallel to the rod axis, is considered. Such defects may arise during the growth of filamentary crystals (metal “whiskers”), and may also exist in multiply connected cylindrical structures. The torsion of an anisotropic elastic bar with a multiply connected cross-section is investigated initially, assuming that the stresses and strains are single-valued but dispensing with the requirement that the warping function should be single-valued. The boundary-value problem is formulated in terms of the Prandtl stress function, which, unlike the warping function, is single-valued in a multiply connected region. A variational formulation of the boundary-value problem for the stress function is given. From the variational principle obtained a torsion boundary-value problem is formulated when there are lumped or continuously distributed dislocations. A modification of the membrane analogy for the torsion problem is proposed which takes into account the presence of dislocations. General theorems of the theory of the torsion of a rod containing dislocations are formulated. An effective formula is derived for the angle of torsion of a bar due to a specified dislocation distribution. Problems on dislocations in a thin-walled rod and a rectangular anisotropic bar are solved.     

无限非均质横观各向同性黏弹性介质中具有圆柱孔洞时的振动

在无限介质中,研究了横截面为圆的柱形孔洞表面上瞬时径向力或扭转引起的扰动,讨论了高阶黏弹性和横观各向同性弹性参数的非均匀性对扰动产生的影响．根据高阶黏弹性Voigt模型,将非零应力分量简化为径向位移分量项表示,这对横观各向同性和高阶黏弹性固体介质是合宜的．导出了含有弹性和黏弹性参数以幂律变化时的应力方程．在瞬时力和扭转边界条件下,求解该方程,求得径向位移分量以及和它相关的应力分量,用修正的Bessel函数项来表示．对瞬时径向力作用问题进行了数值分析,并给出了不同阶的黏弹性和非均质性时的位移和应力变化图形．扭转作用时扰动的数值解可以用类似的方法研究,这里不再深入讨论．     

任意形状孔口单边裂纹问题的边界配位解法

本文提出了一组复应力函数,采用边界配位方法对不同形状孔口(包括圆、椭圆、矩形及菱形孔口)的单边裂纹平板的应力强度因子进行了计算.计算结果表明,对长度和宽度远大于孔口和裂纹几何尺寸的试件,配位法与用其他方法所得的无限大板含圆或椭圆孔边裂纹问题的解符合得很好.同时,对其他孔口问题,特别是有限大板情形,本文给出了一系列计算结果.本文所提出的函数及计算过程可以应用于任意形状孔口单边裂纹平板的计算.     

Stress Concentration in an Anisotropic Half Space with Cylindrical Cavities and Plane Cracks

A method is proposed for determining the two-dimensional stressed state of a half space with a general rectilinear anisotropy. General representations of the complex potentials are obtained and studied, as well as expressions for the stresses and displacements, along with the boundary conditions for determining these functions. As an example, we solve for the stressed state of and calculate the stress intensity factors for a half plane (in the presence of a single elastic symmetry plane) with a circular (elliptical) hole and edge cracks. It is shown how the crack length, the closeness of a hole with a crack to the boundary, and the anisotropy of the material affect the stress concentration and stress intensity factors.     

The problem of an interface crack with a rigid patch plate on part of its edge

A mixed boundary-value problem is solved for a piecewise-homogeneous elastic body with a rectilinear semi-infinite crack on the line where the materials are joined. A rigid patch plate (a reinforcing plate) of specified shape is attached to the upper edge of the crack on a finite interval adjacent to the crack tip. The edges of the crack are loaded with specified stresses. The body is stretched at infinity by a specified longitudinal stress. External forces with a given principal vector and moment act on the patch plate. The problem reduces to a Riemann-Hilbert boundary-value matrix problem with a piecewise-constant coefficient, the solution of which is explicitly constructed using a Gaussian hypergeometric function. The angle of rotation of the patch plate and the complex potentials describing the stress state of the body are found and the stress state of the body close to the ends of the patch plate, one of which is also simultaneously the crack tip, is investigated. Numerical examples are presented that illustrate the effect of the initial force parameters, the length of the patch plate and other parameters of the body on the angle of rotation of the patch plate and the stress state of the body.     

Continual model of deformation of graphene

A single-layer graphene sheet is studied. It is assumed that the total potential energy of the system under consideration consists of four parts. First, the energy of stretching of the bond between two neighboring atoms (the Morse potential). Second, the energy of variations in the angle between three neighboring atoms (the Brenner potential). Third, the energy needed to remove an atom from the plane defined by three neighboring atoms. Fourth, the energy of the torsion of four neighboring atoms. The van der Waals forces are neglected. Only small strains are considered. In the long-wavelength approximation, the two-dimensional extension and flexion energy is derived. As a result, an equivalent plate with corresponding extension and flexion moduli is obtained. The free vibration frequencies of a rectangular plate are found. The stability under the compression in the plane of the plate is studied. To that end, the tangential stresses are complemented with nonlinear terms depending on the transverse displacements. The results of this work are compared with the results of other authors obtained by the methods of molecular dynamics.     

The dynamic contact problem for a prestressed cylindrical tube filled with a fluid

The radial harmonic oscillations of a rigid bandage on the thin-walled elastic cylindrical tube filled with an ideal compressible fluid under a high static pressure are investigated. The problem is reduced to an integral equation, the kernel symbol of which is constructed in numerical form. The properties of the integral equation are investigated, a method of solving it is proposed, and the effect of the presence of the fluid and the initial stresses of the pipeline on the stress state in the contact area for dynamic actions are investigated. It is shown that when monitoring the initial stresses at high frequencies it is essential to take into account the presence of the fluid.     

A consistent solution of the problem of one-sided tension of an elastic plane with an astroidal hole

We consider the stress-strain state of an elastic plate with a hole in the form of an astroid under one-sided tension. The contact of edges of the hole near two opposite tips of the astroid is taken into account, which eliminates the contradiction with the classical solution concerning the overlapping of edges of the hole. We determined both the length of the regions of contact pressure and the distribution of contact stresses. For two contact-free tips of the hole, the value of the stress intensity factor is calculated.