Showing papers in "European Journal of Mechanics A-solids in 2009"

Analytical modelling of spur gear tooth crack and influence on gearmesh stiffness

Abstract: Due to excessive service load, inappropriate operating conditions or simply end of life fatigue, damage can occur in gears. When a fault, either distributed or localised, is incurred by gears, the stiffness and consequently vibration characteristics of the damaged tooth will change. In this work an analytical formulation of the time varying gearmesh stiffness was derived. An original analytical modelling of tooth cracks is presented and the gearmesh stiffness reduction due to this fault is quantified. A comparison with finite element model is presented in order to validate the analytical formulation.

Free vibrations of four-parameter functionally graded parabolic panels and shells of revolution

Abstract: Basing on the First-order Shear Deformation Theory (FSDT), this paper focuses on the dynamic behaviour of moderately thick functionally graded parabolic panels and shells of revolution. A generalization of the power-law distribution presented in literature is proposed. Two different four-parameter power-law distributions are considered for the ceramic volume fraction. Some symmetric and asymmetric material profiles through the functionally graded shell thickness are illustrated by varying the four parameters of power-law distributions. The governing equations of motion are expressed as functions of five kinematic parameters. For the discretization of the system equations the Generalized Differential Quadrature (GDQ) method has been used. Numerical results concerning four types of parabolic shell structures illustrate the influence of the parameters of the power-law distribution on the mechanical behaviour of shell structures considered.

Micromechanical approach to the strength properties of frictional geomaterials

Abstract: The present paper describes a micromechanics-based approach to the strength properties of composite materials with a Drucker–Prager matrix in the situation of non-associated plasticity. The concept of limit stress states for such materials is first extended to the context of homogenization. It is shown that the macroscopic limit stress states can theoretically be obtained from the solution to a sequence of viscoplastic problems stated on the representative elementary volume. The strategy of resolution implements a non-linear homogenization technique based on the modified secant method. This procedure is applied to the determination of the macroscopic strength properties and plastic flow rule of materials reinforced by rigid inclusions, as well as for porous media. The role of the matrix dilatancy coefficient is in particular discussed in both cases. Finally, finite element solutions are derived for a porous medium and compared to the micromechanical predictions.

A nonlinear homogenization procedure for periodic masonry

Abstract: The present paper deals with the problem of the determination of the in-plane behavior of masonry material. The masonry is considered as a composite material composed by a regular distribution of blocks connected by horizontal and vertical mortar joints. The overall constitutive relationships of the regular masonry are derived by a rational micromechanical and homogenization procedure. Linear elastic constitutive relationship is considered for the blocks, while a new special nonlinear constitutive law is proposed for the mortar joints. In particular, a mortar constitutive law, which accounts for the coupling of the damage and friction phenomena occurring during the loading history, is proposed; the developed model is based on an original micromechanical analysis of the damage process of the mortar joint. Then, an effective nonlinear homogenization procedure, representing the main novelty of the paper, is proposed; it is based on the transformation field analysis, using the technique of the superposition of the effects and the finite element method. The presented methodology is implemented in a numerical code. Finally, numerical applications are performed in order to assess the performances of the proposed procedure in reproducing the mechanical behavior of masonry material.

A finite-strain model for anisotropic viscoplastic porous media: I – Theory

Abstract: In this work, we propose an approximate homogenization-based constitutive model for estimating the effective response and associated microstructure evolution in viscoplastic (including ideally-plastic) porous media subjected to finite-strain loading conditions. The proposed model is based on the "second-order" nonlinear homogenization method, and is constructed in such a way as to reproduce exactly the behavior of a "composite-sphere assemblage" in the limit of hydrostatic loading and isotropic microstructure. However, the model is designed to hold for completely general three-dimensional loading conditions, leading to deformation-induced anisotropy, whose development in time is handled through evolution laws for the internal variables characterizing the instantaneous "ellipsoidal" state of the microstructure. In Part II of this study, results will be given for the instantaneous response and microstructure evolution in porous media for several representative loading conditions and microstructural configurations.

A theoretical analysis of smart moderately thick shear deformable annular functionally graded plate

Abstract: Based on Mindlin's plate theory, free vibration analysis of moderately thick shear deformable annular functionally graded plate coupled with piezoelectric layers is presented in this paper. A consistent formulation that satisfies the Maxwell static electricity equation is presented so that the full coupling effect of the piezoelectric layer on the dynamic characteristics of the annular FGM plate can be estimated based on the free vibration results. The differential equations of motion are solved analytically for various boundary conditions of the plate through the transformation of variable method. The applicability of the proposed model is analyzed by studying the effect of varying the gradient index of FGM plate on the free vibration characteristics of the structure. For some specific cases, obtained results were cross checked with those existing literatures and furthermore, verified by those obtained from three-dimensional finite element (3D FE) analyses.

Generalized thermoelastic functionally graded orthotropic hollow sphere under thermal shock with three-phase-lag effect

Abstract: This problem deals with the determination of thermo-elastic interaction due to step input of temperature on the boundaries of a functionally graded orthotropic hollow sphere in the context of linear theories of generalized thermo-elasticity. Using the Laplace transformation the fundamental equations have been expressed in the form of vector–matrix differential equation which is then solved by eigenvalue approach. The inverse of the transformed solution is carried out by applying a method of Bellman et al. Stresses, displacement and temperature distributions have been computed numerically and presented graphically in a number of figures. A comparison of the results for different theories (TEWOED(GN-II), TEWED(GN-III) and three-phase-lag model) is presented. When the material is homogeneous, isotropic and outer radius of the hollow sphere tends to infinity, the corresponding results agree with that of existing literature for GN-III model.

On the anti-plane shear of an elliptic nano inhomogeneity

Abstract: The elastic field of an elliptic nano inhomogeneity embedded in an infinite matrix under anti-plane shear is studied with the complex variable method. The interface stress effects of the nano inhomogeneity are accounted for with the Gurtin–Murdoch model. The conformal mapping method is then applied to solve the formulated boundary value problem. The obtained numerical results are compared with the existing closed form solutions for a circular nano inhomogeneity and a traditional elliptic inhomogeneity under anti-plane. It shows that the proposed semi-analytic method is effective and accurate. The stress fields inside the inhomogeneity and matrix are then systematically studied for different interfacial and geometrical parameters. It is found that the stress field inside the elliptic nano inhomogeneity is no longer uniform due to the interface effects. The shear stress distributions inside the inhomogeneity and matrix are size dependent when the size of the inhomogeneity is on the order of nanometers. The numerical results also show that the interface effects are highly influenced by the local curvature of the interface. The elastic field around an elliptic nano hole is also investigated in this paper. It is found that the traction free boundary condition breaks down at the elliptic nano hole surface. As the aspect ratio of the elliptic hole increases, it can be seen as a Mode-III blunt crack. Even for long blunt cracks, the surface effects can still be significant around the blunt crack tip. Finally, the equivalence between the uniform eigenstrain inside the inhomogeneity and the remote loading is discussed.

Static analysis for functionally graded piezoelectric actuators or sensors under a combined electro-thermal load

Abstract: Based on the theory of piezoelasticity, a functionally graded piezoelectric sandwich cantilever under an applied electric field and/or a heat load is studied. All materials may be arbitrary functional gradients in the thickness direction. The static solution for the mentioned problems is presented by the Airy stress function method. As a special case, assuming that the material composition varies continuously in the direction of the thickness according to a power law distribution, a comprehensive parametric study is conducted to show the influence of electromechanical coupling (EMC), functionally graded index, temperature change and thickness ratio on the bending behavior of actuators or sensors. The distribution of electric field or normal stress in present FGPM actuators is continuous along the thickness, which overcomes the problem in traditional layered actuators. The solution facilitates the design optimization for different piezoelectric actuators and has another potential application for material parameter identification.

The dynamic response of clamped rectangular Y-frame and corrugated core sandwich plates

Abstract: The dynamic response of fully clamped, monolithic and sandwich plates of equal areal mass has been measured by loading rectangular plates over a central patch with metal foam projectiles. All plates are made from AISI 304 stainless steel, and the sandwich topologies comprise two identical face-sheets and either Y-frame or corrugated cores. The resistance to shock loading is quantified by the permanent transverse deflection at mid-span of the plates as a function of projectile momentum. At low levels of projectile momentum both types of sandwich plate deflect less than monolithic plates of equal areal mass. However, at higher levels of projectile momentum, the sandwich plates tear while the monolithic plates remain intact. Three-dimensional finite element (FE) calculations adequately predict the measured responses, prior to the onset of tearing. These calculations also reveal that the accumulated plastic strains in the front face of the sandwich plates exceed those in the monolithic plates. These high plastic strains lead to failure of the front face sheets of the sandwich plates at lower values of projectile momentum than for the equivalent monolithic plates.

Delay effects in shimmy dynamics of wheels with stretched string-like tyres

Abstract: The dynamics of wheel shimmy is studied when the self-excited vibrations are related to the elasticity of the tyre. The tyre is described by a classical stretched string model, so the tyre-ground contact patch is approximated by a contact line. The lateral deformation of this line is given via a nonholonomic constraint, namely, the contact points stick to the ground, i.e., they have zero velocities. The mathematical form of this constraint is a partial differential equation (PDE) with boundary conditions provided by the relaxation of deformation outside the contact region. This PDE is coupled to an integro-differential equation (IDE), which governs the lateral motion of the wheel. Although the conventional stationary creep force idea is not used here, the coupled PDE-IDE system can still be handled analytically. It can be rewritten as a delay differential equation (DDE) by assuming travelling wave solutions for the deformation of the contact line. This DDE expresses the intrinsic memory effect of the elastic tyre. The linear stability charts and the corresponding numerical simulations of the nonlinear system reveal periodic and quasi-periodic self-excited oscillations that are also confirmed by simple laboratory experiments. The observed quasi-periodic vibrations cannot be explained in single degree-of-freedom wheel models subject to a creep force.

Effects of inter-fibre spacing on damage evolution in unidirectional (UD) fibre-reinforced composites

Abstract: A three dimensional (3D) micromechanical study has been performed in order to investigate local damage in UD composite materials under transverse and longitudinal tensile loading. In particular, the influence of non-uniform distribution of fibres in RVEs (representative volume element) with a hexagonal packing array and the effects of thermal residual stresses has been investigated. To examine the effect of inter-fibre spacing and residual stress on failure, a study based on the Maximum Principal Stress failure criterion and a stiffness degradation technique has been used for damage analysis of the unit cell subjected to mechanical loading. Results indicate a strong dependence of damage onset and its evolution from the fibres position within the RVE. Predicted mechanical properties, damage initiation and evolution are also clearly influenced by the presence of residual stress.

A finite-strain model for anisotropic viscoplastic porous media: II – Applications

Abstract: In Part I of this work, we have proposed a new model based on the "second-order" nonlinear homogenization method for determining the effective response and microstructure evolution in viscoplastic porous media with aligned ellipsoidal voids subjected to general loading conditions. In this second part, the new model is used to analyze the instantaneous effective behavior and microstructure evolution in porous media for several representative loading conditions and microstructural configurations. First, we study the effect of the shape and orientation of the voids on the overall instantaneous response of a porous medium that is subjected to principal loading conditions. Secondly, we study the problem of microstructure evolution under axisymmetric and simple shear loading conditions for initially spherical voids in an attempt to validate the present model by comparison with existing numerical and approximate results in the literature. Finally, we study the possible development of macroscopic instabilities for the special case of ideally-plastic solids subjected to plane-strain loading conditions. The results, reported in this paper, suggest that the present model improves dramatically on the earlier "variational" estimates, in particular, because it generates much more accurate results for high triaxiality loading conditions.

Circumferential wave in magneto-electro-elastic functionally graded cylindrical curved plates

Abstract: Piezoelectric-piezomagnetic functionally graded materials (FGM), with a gradual change of the mechanical and electromagnetic properties, have greatly applying promises. Based on Legendre orthogonal polynomial series expansion approach, a dynamic solution is presented for the propagation of circumferential harmonic waves in piezoelectric-piezomagnetic FGM cylindrical curved plates. The materials properties are assumed to vary in the direction of the thickness according to a known variation law. The dispersion curves of the piezoelectric-piezomagnetic FGM cylindrical curved plate and the corresponding non-piezoelectric and non-piezomagnetic cylindrical curved plates are calculated to show the influences of the piezoelectricity and piezomagnetism. Electric potential and magnetic potential distributions are also obtained to illustrate the different influences of the piezoelectricity and piezomagnetism. Finally, a cylindrical curved plate at a different ratio of radius to thickness is calculated to show the influence of the ratio on the piezoelectric effect and piezomagnetic effect.

Analysis of micropolar elastic beams

Abstract: In this paper, a linear theory for the analysis of beams based on the micropolar continuum mechanics is developed. Power series expansions for the axial displacement and micro-rotation fields are assumed. The governing equations are derived by integrating the momentum and moment of momentum equations in the micropolar continuum theory. Body couples and couple stresses can be supported in this theory. After some simplifications, this theory can be reduced to the well-known Timoshenko and Euler–Bernoulli beam theories. The nature of flexural and longitudinal waves in the infinite length micropolar beam has been investigated. This theory predicts the existence of micro-rotational waves which are not present in any of the known beam theories based on the classical continuum mechanics. Also, the deformation of a cantilever beam with transverse concentrated tip loading has been studied. The pattern of deflection of the beam is similar to the classical beam theories, but couple stress and micro-rotation show an oscillatory behavior along the beam for various loadings.

Static analysis of an infinite beam resting on a tensionless Pasternak foundation

Abstract: This paper addresses the static response of an infinite beam supported on a unilateral (tensionless) two-parameter Pasternak foundation and subjected to complex transverse loads, including self weight. The transfer displacement function method (TDFM) is employed to determine the initially unknown lengths that remain in contact. In contrast to a Winkler Foundation System (WFS), the lift-off points in a PFS (Pasternak Foundation System) are not necessarily at zero displacement but may be determined sequentially through considering the compatibility conditions at the junctions of contact and non-contact segments. After the response of the whole system including the beam and foundation is expressed through the displacement constants of the initial segment, the contact problem is reduced to two nonlinear algebraic equations with two unknowns. The foundation reactions and the internal actions of the beam may also be determined from the displacement response of the system. Two simple cases are solved to illustrate the influence of the foundation stiffness factors and finally, a third example of a beam with several contact segments is presented to demonstrate the application of the TDFM.

Dynamic analysis of beams on viscoelastic foundation

Abstract: This study is intended to analyze dynamic behavior of beams on Pasternak-type viscoelastic foundation subjected to time-dependent loads. The Timoshenko beam theory is adopted in the derivation of the governing equation. Ordinary differential equations in scalar form obtained in the Laplace domain are solved numerically using the complementary functions method to calculate exactly the dynamic stiffness matrix of the problem. The solutions obtained are transformed to the real space using the Durbin's numerical inverse Laplace transform method. The dynamic response of beams on viscoelastic foundation is analyzed through various examples.

A theoretical analysis of the dynamic response of metallic sandwich beam under impulsive loading

Abstract: The objective of this paper is to analytically study the dynamic response of a fully clamped metallic sandwich beam under impulsive loading. The membrane factor method is employed to derive the solutions for large deflections and time responses of the sandwich beam, in which the interaction of bending and stretching is considered. Moreover, tighter ‘bounds’ of the solutions are obtained. It is shown that the present solutions are in good agreements with the previous finite element results and lie in the bounds of the solutions. It is clear that core strength and membrane force induced by large deflections have significant effects on the dynamic response of sandwich beam with increasing the transient deflections. The present method is efficient and simple for the dynamic response analysis of large deflections of metallic sandwich structures.

Axisymmetric bending analysis of thick functionally graded circular plates using fourth-order shear deformation theory

Abstract: In the present article, axisymmetric bending and stretching of functionally graded (FG) circular plates subjected to uniform transverse loading based on fourth-order shear deformation plate theory (FOST) have been studied. Using a fourth-order shear deformation theory, the solutions for deflection and rotation functions of FG plates are presented in terms of the corresponding quantities for a homogeneous plate using the classical plate theory (CPT), from which solutions one can easily obtain the FOST solutions for axisymmetric bending of FG circular plates. It is assumed that the effective mechanical properties of the functionally graded plates through the thickness are continuous functions of the volume fractions of the constituent parts which are themselves defined by a power-law function. Numerical results for maximum deflection and shear stress are presented for various percentages of ceramic–metal volume fractions. These results are also compared with those obtained from the first-order shear deformation plate theory of Mindlin (FST), the third-order shear deformation plate theory of Reddy (TST) as well as the exact three-dimensional elasticity solution. It is found that although the maximum deflections obtained using FOST and TST are close to each other, the through-thickness shear stress is predicted more accurately by the FOST formulation than by the TST.

Non-linear vibrations of imperfect free-edge circular plates and shells

Abstract: Large-amplitude, geometrically non-linear vibrations of free-edge circular plates with geometric imperfections are addressed in this work. The dynamic analog of the von Karman equations for thin plates, with a stress-free initial deflection, is used to derive the imperfect plate equations of motion. An expansion onto the eigenmode basis of the perfect plate allows discretization of the equations of motion. The associated non-linear coupling coefficients for the imperfect plate with an arbitrary shape are analytically expressed as functions of the cubic coefficients of a perfect plate. The convergence of the numerical solutions are systematically addressed by comparisons with other models obtained for specific imperfections, showing that the method is accurate to handle shallow shells, which can be viewed as imperfect plate. Finally, comparisons with a real shell are shown, showing good agreement on eigenfrequencies and mode shapes. Frequency-response curves in the non-linear range are compared in a very peculiar regime displayed by the shell with a 1:1:2 internal resonance. An important improvement is obtained compared to a perfect spherical shell model, however some discrepancies subsist and are discussed.

Stress–strain curve and stored energy during uniaxial deformation of polycrystals

Abstract: The subject of this paper is an attempt to obtain information about the energy stored during plastic deformation from experimentally measured stress–strain curve. Theoretical analysis of the stress–strain curve for elastic-perfectly plastic polycrystalline material has shown that only the part of stored energy can be calculated from the stress–strain curve. This part is the energy stored during non-homogeneous plastic deformation. The results of such calculation have been compared with the total stored energy determined experimentally. It has been shown that part of total stored energy related to non-homogeneous plastic deformation of investigated materials is much lower than that corresponding to homogeneous one.

Out-of-plane modulus of semi-auxetic laminates

Abstract: Materials that possess negative Poisson's ratio are termed “auxetic solids” The out-of-plane modulus of a laminate consisting of alternating positive and negative isotropic laminas (semi-auxetic laminate) is investigated in this paper It is herein shown that the use of the inverse rule-of-mixture for obtaining the out-of-plane Young's modulus of a laminate is valid only for conventional laminates and fully auxetic laminates The Young's modulus by inverse rule-of mixture significantly underestimates the out-of-plane Young's modulus of a semi-auxetic laminate It is also shown that under certain conditions, the out-of-plane Young's modulus of a semi-auxetic laminate exceeds even the direct rule-of-mixture A correction term is developed herein for incorporation into the inverse rule-of-mixture

Plane waves and vibrations in the theory of micropolar thermoelasticity for materials with voids

Abstract: The present paper concerns with the linear theory of micropolar thermoelasticity for materials with voids. Some basic properties of wave numbers of the longitudinal and transverse plane harmonic waves are treated. The existence theorems of non-trivial solutions and eigenfrequencies of the interior homogeneous boundary value problems of steady vibrations are proved. The connection between plane harmonic waves and eigenfrequencies of the aforementioned problems is established.

Mixed method and convex optimization for limit analysis of homogeneous Gurson materials: a kinematical approach

Abstract: A fully kinematical, mixed finite element approach based on a recent interior point method for convex optimization is proposed to solve the limit analysis problem involving homogeneous Gurson materials. It uses continuous or discontinuous quadratic velocity fields as virtual variables, with no hypothesis on a stress field. Its modus operandi is deduced from the Karush-Kuhn-Tucker optimality conditions of the mathematical problem, providing an example of cross-fertilization between mechanics and mathematical programming. This method is used to solve two classical problems for the von Mises plasticity criterion as a test case, and for the Gurson criterion for which analytical solutions do not exist. Using only the original plasticity criterion as material data, the method proposed appears robust and efficient. providing very tight bounds on the limit loadings investigated. (C) 2008 Elsevier Masson SAS. All rights reserved.

Influence of hardening type on self-heating of metallic materials under cyclic loadings at low amplitude

Abstract: For several years, some authors have worked on the rapid estimation of the High-Cycle Fatigue (HCF) properties of metallic materials based upon temperature measurements under cyclic loadings. This method is so-called "self-heating tests". More recently, the development of a two-scale probabilistic model has shown that self-heating tests permit to identify, not only, the mean fatigue limit, but also, the scatter of classical fatigue results. So, it is proposed, in this paper, to extend the previous approach for materials with different kinds of hardening and different kinds of hardening evolution (i.e., cyclic hardening or cyclic softening) and to show the influence of the hardening type on self-heating and on the partition of the plastic energy (i.e., dissipated and stored energies). The identification and the validation of the proposed approach have been performed on two different metallic materials (i.e., a dual-phase steel and a chrome-cobalt alloy).

Overspeed burst of elastoviscoplastic rotating disks - Part I: Analytical and numerical stability analyses

Abstract: Burst of rotating disks in case of overspeed is investigated. The certification of turbo-engines requires to demonstrate the integrity of disks at higher rotation speeds than the maximum rotation speed reachable in service. The determination of the burst speed by analysis can help to reduce the number of tests required for the certification. This prediction can be established by non-linear stability analyses of finite element simulations. Non-linearities originate from (i) the material behaviour described by elastoviscoplastic constitutive equations, (ii) geometric changes accounted for by the finite strain formulation. In this work, loss of uniqueness and loss of stability criteria from [Hill, R., 1958. A general theory of uniqueness and stability in elastic-plastic solids. J. Mech. Phys. Solids 6, 236–249] are applied. The loss of stability criterion is restricted to the case of rotating disks and compared to several simple widely used material based failure criteria. 3D simulations of rotating metal disks are performed for a given elastoviscoplastic behaviour and the stability criteria are evaluated. The sensitivity of disk stability to material parameters, such as yield criterion, hardening and viscosity is evaluated in the case of a nickel based superalloy.

Torsion of functionally graded hollow tubes

Abstract: An analytical formulation is presented for torsional analysis of functionally graded hollow tubes of arbitrary shape. Moreover, relatively simpler formulas are presented for torsional analysis of functionally graded hollow tubes of polygonal shape. Thicknesses of all segments of the cross section are the same. Shear modulus of rigidity changes continuously across the thickness between two phases according to a power law distribution. Governing equations in terms of Prandtl's stress function are used to derive the formulas. Several examples are presented to show the accuracy and efficiency of the formulation. The obtained results are verified by accurate finite element solutions. Effects of changing thickness and volume fraction of constituent materials are also investigated. Derived formulas can be useful for analysis of thin to moderately thick-walled hollow tubes.

Effect of geometric nonlinearity on dynamic pull-in behavior of coupled-domain microstructures based on classical and shear deformation plate theories

Abstract: This paper investigates the dynamic pull-in behavior of microplates actuated by a suddenly applied electrostatic force. Electrostatic, elastic and fluid domains are involved in modeling. First-order shear deformation plate theory and classical plate theory are used to model the geometrically nonlinear microplates. The equations of motion are descritized by the finite element method. The effects of nonlinearity, fluid pressure, initial stress and different geometric parameters on dynamic behavior are examined. In addition, the influences of initial stress and actuation voltage on oscillatory behavior of microplates are evaluated.

Numerical implementation and assessment of the GLPD micromorphic model of ductile rupture

Abstract: Just like all constitutive models involving softening, Gurson's classical model for porous ductile solids predicts unrealistic, unlimited localization of strain and damage. An improved variant of this model aimed at solving this problem has been proposed by Gologanu, Leblond, Perrin and Devaux (GLPD) on the basis of some refinement of Gurson's original homogenization procedure. The GLPD model is of “micromorphic” nature since it involves the second gradient of the macroscopic velocity and generalized macroscopic stresses of “moment” type, together with some characteristic “microstructural distance”. This work is devoted to its numerical implementation and the assessment of its practical relevance. This assessment is based on two criteria: absence of mesh size effects in finite element computations and agreement of numerical and experimental results for some typical experiments of ductile fracture. The GLPD model is found to pass both tests. It is therefore concluded that it represents a viable, although admittedly complex solution to the problem of unlimited localization in Gurson's model of ductile rupture.

Some analytical solutions for Saint-Venant torsion of non-homogeneous cylindrical bars

Abstract: The Saint-Venant torsion problem of linearly elastic cylindrical bars with solid and hollow cross-section is treated. The shear modulus of the non-homogeneous bar is a given function of the Prandtl's stress function of considered cylindrical bar when its material is homogeneous. The solution of the torsional problem of non-homogeneous bar is expressed in terms of the torsional and Prandtl's stress functions of homogeneous bar having the same cross-section as the non-homogeneous bar.