A finite crack in a semi-infinite strip of a graded piezoelectric material under electric loading

In this paper, the mixed-mode crack problem for a functionally graded piezoelectric material (FGPM) strip is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under in-plane electric loading. The problem is formulated in terms of a system of singular integral equations. The stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crack size, the crack location, and the material nonhomogeneity.     

Deflections and buckling of a bent elastica in contact with a flat surface

A straight elastica is bent until its ends are vertical and a fixed distance apart, and then it is pushed onto a flat rigid surface. The weight of the strip and friction between the strip and the surface are neglected. Planar equilibrium states of the strip are investigated, using either a shooting method or an integral formulation. Both symmetric and asymmetric configurations are possible. There may be a single point of contact, a flat region of contact, or two points of contact with a buckled section between them. Also, if the ends are pushed down sufficiently far, one or two loops may form when the upper portion of the strip makes contact with the lower portion on the surface. If the two ends are held together (vertically) and then pushed down, asymmetric configurations may occur in which there is a region of contact between the upper and lower portions of the strip near their ends. The properties of these various equilibrium shapes are investigated.     

Stress distribution in a strip fabricated from a composite material with small-scale curved structure

Summary Using FEM, the stress distribution in a strip fabricated from a composite material with curved structures is investigated. The constitutive relations of the strip material are considered within the framework of the continuum theory proposed by Akbarov and Guz'. The investigations are carried out using the exact equations of elasticity theory. The influence of a change in the structural parameters of the strip material on the stress distribution in the considered strip is studied using a concrete problem as an example.Published in Prikladnaya Mekhanika, Vol. 32, No. 9, pp. 32–39, September, 1996.     

Bending of a thin strip by a circular tool

We present a model of transverse bending of a wide thin elastic, elastoplastic, or rigid-plastic strip by a circular tool in the case of large displacements. The bending of the initial rectilinear strip is modeled by small increments in the load on the tool with analysis of the forces, moments, curvature, and the midline equation. The final form of the strip and the residual stresses are determined after elastic unloading. The model describes technological operations of sheet slab bending in dies and on roller-bending machines.     

Pressing a rigid-plastic strip through a curvilinear matrix channel

We develop a model that describes pressing a rigid-plastic strip through a curvilinear matrix channel; this model takes into account the material strengthening, the gap between the strip and the matrix channel, and the contact friction. We present examples of computations of the strip pressing through channels of various shapes. The model imitates the technological processes of a thin strip bending by pressing it through a curvilinear matrix channel.     

A piezoelectric material strip with a crack perpendicular to its boundary surfaces

A cracked piezoelectric material strip under combining mechanical and electrical loads is considered. The crack is vertical to the top and bottom edges of the strip. The edges of the strip are parallel to the x-axis and perpendicular to the z-axis. When a piezoelectric ceramic is poled, it exhibits transversely isotropic behavior. Among many possible poled axis orientations, a particular orientation when the poling direction lies parallel to x-axis is examined in this paper. Both impermeable crack and permeable crack assumptions are considered. Numerical results are included for three kinds of fracture mechanics specimens, namely an edge-cracked strip, a double edge-cracked strip, and a center-cracked strip, subjected to uniform tensions and uniform electric displacement loads simultaneously, at the far ends. In addition, an edge-cracked strip under pure bending and uniform electric displacement loads at the far ends is also investigated in this paper.     

Natural convection in a vertical strip immersed in a porous medium

In this work, the conjugated heat transfer characteristics of a thin vertical strip of finite length, placed in a porous medium has been studied using numerical and asymptotic techniques. The nondimensional temperature distribution in the strip and the reduced Nusselt number at the top of the strip are obtained as a function of the thermal penetration parameter s, which measures the thermal region where the temperature of the strip decays to the ambient temperature of the surrounding fluid. The numerical values of this nondimensional parameter permits to classify the different physical regimes, showing different solutions: a thermally long behaviour, an intermediate transition and a short strip limit.     

Conjugate free convection along a thin vertical plate with internal nonuniform heat generation in a porous medium

 The steady state heat transfer characteristics of a thin vertical strip with internal heat generation placed in a porous medium is studied in this work. The non-dimensional temperature distribution in the strip is obtained as a function of the intensity and distribution of the internal heat sources. Both the thermally thin as the thick wall approximations are considered in this paper. The mass flow rate of fluid induced by heating the strip decreases as the longitudinal heat conduction effects along the strip decreases. Received on 22 November 2000 / Published online: 29 November 2001     

Deformation and the strip necking zone in a cracked steel sheet

When a tensile stress is applied to a thin cracked plate, a strip necking region results ahead of a crack tip. The relative opening displacement between the crack surfaces and between the upper and lower boundaries of the strip necking region were measured by the moiré method. The strains ahead of the strip necking region and the thickness reduction (therein) were also measured. The measured relative opening displacements were compared with the calculated values using the Dugdale strip necking model. The thickness reduction in the strip necking region is equal to the relative opening displacement.     

An anti-plane propagating crack in a functionally graded piezoelectric strip bonded to a homogeneous piezoelectric strip

Summary A finite crack propagating at constant speed in a functionally graded piezoelectric strip (FGPS) bonded to a homogeneous piezoelectric strip is considered. It is assumed that the electroelastic material properties of the FGPS vary exponentially across the thickness of the strip, and that the bimaterial strip is under combined anti-plane mechanical shear and in-plane electrical loads. The analysis is conducted for the electrically unified crack boundary condition, which includes both the traditional permeable and the impermeable ones. By using the Fourier transform, the problem is reduced to the solution of Fredholm integral equations of the second kind. Numerical results for the stress intensity factor and the crack sliding displacement are presented to show the influences of the crack propagation speed, electric loads, FGPS gradation, crack length, electromechanical coupling coefficient, properties of the bonded homogeneous piezoelectric strip and crack location.     

Functionally graded piezoelectric strip with a penny-shaped crack under electromechanical loadings

In this paper, the mixed-mode penny-shaped crack problem for a functionally graded piezoelectric material (FGPM) strip is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under in-plane electromechanical loadings. The problem is formulated in terms of a system of singular integral equations. The stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crack size, the crack location, and the material nonhomogeneity.     

Heat transfer in a thin facing up horizontal strip with internal heat generation

The steady state heat transfer characteristics of a thin facing-up strip with internal heat generation is studied in this work. The nondimensional temperature distribution in the strip is obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the strip and (d) the Prandtl number of the fluid. Both the thermally thin and the thick wall approximations are considered in this paper. The total thermal energy or averaged temperature of the strip is found to decrease, as the influence of the longitudinal heat conduction effects in the strip decreases, in the thermally thin wall regime. After reaching a minimum, it increases again in the thermally thick wall regime. Received on 15 December 1998     

Equilibrium of a Prestressed Strip Reinforced with Elastic Plates

The contact problem for a prestressed elastic strip reinforced with equally spaced elastic plates is considered. The Fourier integral transform is used to construct an influence function of a unit concentrated force acting on the infinite elastic strip with one edge constrained. The transmission of forces from the thin elastic plates to the prestressed strip is analyzed. On the assumption that the beam bending model and the uniaxial stress model are valid for an elastic plate subjected to both vertical and horizontal forces, the problem is mathematically formulated as a system of integro-differential equations for unknown contact stresses. This system is reduced to an infinite system of algebraic equations solved by the reduction method. The effect of the initial stresses on the distribution of contact forces in the strip under tension and compression is studied     

The effect of nonlinearity on a principle of Saint-Venant type

Summary This paper establishes a principle of Saint-Venant type associated with finite anti-plane shear of a cylinder whose cross-section is a semi-infinite strip. The long sides of the strip are traction-free, and the short side carries an arbitrarily distributed shear traction. At the infinity in the strip, the deformation is prescribed to be one of simple shear, and the associated shear stress is uniform. The analysis is based on the fully nonlinear theory of finite elastostatics and is carried out for a special class of homogenous, isotropic incompressible materials. It is shown that, along the parallel sides of the strip, the nonvanishing component of shear stress differs from its average value (taken across the strip) by an exponentially decaying function of the distance from the end. A lower bound is given for the rate of decay.Paper presented at the 15th International Congress of Theoretical and Applied Mechanics, Toronto, Canada, August 1980.     

Crack nucleation in a strip of varying thickness under force loading

A mathematical model of crack nucleation in a strip of varying thickness under force loading is constructed. It is assumed that the loading of the strip by external forces gives rise to prefracture zones, which are modeled as regions of weakened interparticle bonds in the material. Solution of the problem of the equilibrium of an isotropic strip of varying thickness, with a crack nucleus reduces to solving a system of nonlinear singular integral equations with a Cauchy type kernel to determine the forces in the region of crack nucleation. The condition of crack nucleation in a strip of varying thickness is formulated using the criterion of the limiting stretching of material bonds.     

Interaction of a deformable patch with a stressed strip

We consider the plane problem on the contact interaction of an elastic patch with an elastic strip loaded at infinity by a tensile force parallel to the strip boundaries. We assume that the patch resists extension and does not resist bending. We determine the contact tangential stresses under the patch, the patch point displacements, and the strip strain distortion factor. The problem is solved by the regular asymptotic method of “large λ” and the method of special orthonormal polynomials.In plane problems, the method of “large λ” was first used in [1], and the method of special orthonormal polynomials was first used in [2].     

Flutter of an elastic strip in a longitudinal supersonic flow

An elastic strip in a longitudinal supersonic gas flow is considered. An excess pressure formula is obtained on the basis of the linearized theory of supersonic potential flow. It is shown that, in the case of high-speed supersonic flow, the critical flutter velocity is equal to the phase velocity of perturbation waves propagated along the strip. In the framework of the classical piston theory, the flutter problem is solved for the case of a rigidly fixed strip in a longitudinal flow.     

The conjugate heat transfer from an internal heated small strip in a forced laminar flow

 An asymptotic and numerical investigation was conducted for the cooling process, by a forced laminar flow, of a small strip with a non-uniform heat source. The nondimensional temperature distribution in the strip has been obtained as a function of the following parameters: (a) the intensity and distribution of the internal heat sources, (b) the aspect ratio of the strip, (c) the longitudinal heat conductance of the strip and (d) the Prandtl number of the fluid. Both the thermally thin as the thick wall approximations were considered in this paper. The total thermal energy or averaged temperature of the strip is found to decrease as the influence of the longitudinal heat conduction effects in the strip decreases in the thermally thin wall regime. After reaching a minimum, it increases again in the thermally thick wall regime. Received on 19 May 2000     

A first approximation of a mixed boundary value problem for a strip using Legendre polynomials

A mixed boundary value problem for a strip is studied to a first approximation using the Legendre polynomials. The boundary conditions given on the edges of the strip are considered.     

Maximum stress in a tensile strip with a large hole

Measurements were made to decide between two solutions of the title problem. In question was the limiting value of the stress-concentration factor at the edge of a large hole in a tensile strip as the hole diameter approached the strip width. The results indicate that the stress-concentration factor is near two and support one of the solutions with a minor qualification.