Postbuckling behavior of an ideal bar on an elastic foundation

Novosibirsk. Translated from Prikladnaya Mekhanaika i Tekhnicheskaya Fizika, No. 2, pp. 130–142, March–April, 1994.     

Natural motion density of elastic shells under intensive dynamic loading

The question of the natural motion density in dynamics problems of elastic shells is considered. Motions are studied for which an exponential growth in amplitude with time occurs. The number of natural motions incident in a given range of variation of the exponent is computed by using an idea of R. Courant. The governing natural motions and condensation points at which the natural motion density tends to infinity are found. The condensation points and governing motions are compared in specific examples.     

Unsteady behavior of an elastic beam floating on shallow water under external loading

A solution is derived for the twodimensional unsteady problem of the behavior of an elastic beam of finite dimensions floating on the free surface of water under external loading. It is assumed that the fluid is ideal and incompressible and its depth is well below the beam length. The simultaneous motion of the beam and the fluid is considered within the framework of linear theory, and the fluid flow is assumed to be potential. The behavior of the beam under various loadings with and without allowance for the inertia of the load is studied.     

Buckling analysis of an elastic bar using the Bubnov-Galerkin method

The factors responsible for the errors often encountered in the stability analysis of elastic systems are found by testing the Bubnov-Galerkin method for the buckling problem of a single-layer flexible elastic bar. Refined formulas are obtained for the maximum deflection of a longitudinally compressed hinged three-layer bar. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 148–156, January–February, 2008.     

Asymptotic models for optimizing the contour of multiply-connected cross-section of an elastic bar in torsion

An asymptotic solution is obtained for the problem of maximizing the torsional rigidity of elastic, multiply-connected cylindrical bars for a given area of cross-section. The shapes of the inner contours of the multiply-connected cross-section are specified while the outer contour is determined as a result of the shape optimization. We apply the method of matched asymptotic expansions to construct a first-order asymptotic model. The conditions for unique solvability of the asymptotic model have been established under some restrictions imposed on the location of the inner contours and their polarization matrices. The economy achieved by optimization is estimated.     

Global analysis of secondary bifurcation of an elastic bar

In a three dimensional framework of finite deformation configurations, this paper investigates the secondary bifurcation of a uniform, isotropic and linearly elastic bar under compression in a large range of parameters. The governing differential equations and finite dimensional equations of this problem are discussed. It is found that, for a bar with two ends hinged, usually many secondary bifurcation points appear on the primary branches which correspond to the maximum bending stiffness. Results are shown on parameter charts. Secondary modes and branches are also calculated with numerical methods. The project supported in part by the National Natural Science Foundation of China     

基于三维Hopkinson杆的混凝土动态力学性能研究

混凝土、岩石类材料在复杂应力状态下的动态力学性能研究一直备受关注,但鉴于动态实验的复杂性,对真三轴应力状态下材料的动态加载一直未曾实现。本文中研制了一套真三轴静载作用下混凝土、岩石类材料的“三维Hopkinson杆”动态力学实验系统,为冲击载荷作用下材料动态各向异性特性的研究提供了一种有效的实验测试技术。该系统采用液压伺服控制对立方体试件施加三向独立的0~100 MPa真三轴静载,再利用分离式Hopkinson压杆对试件施加冲击动载,具体研究了C30混凝土材料在不同真三轴静载条件下的动态压缩性能,得到了不同条件下X、Y、Z方向上的动态应力应变关系。     

Dynamic behavior of the interface between two solid phases in an elastic bar

Using the continuum mechanical model of solid-solid phase transitions of Abeyaratne and Knowles, this paper examines the large time dynamical behavior of a phase boundary. The problem studied concerns a semi-infinite elastic bar initially in an equilibrium state that involves two material phases separated by a phase boundary at a given location. Interaction between the phase boundary and the elastic waves generated by an impact at the end of the bar and subsequent reflections is studied in detail, and an exact solution of the dynamical problem, which is governed by a nonlinear resursive formula, is obtained. It is shown that the phase boundary reaches a new equilibrium state for large time. Numerical calculations based on the recursive formula are carried out to illustrate analytical results.Address after August 15, 1995: Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA24061, USA.     

Approximation of yield condition for the hysteretic behavior of a bar under repeated axial loading

This paper is concerned with the hysteretic behavior of a prismatic bar subjected to repeated axial loading. Elastic-perfectly plastic behavior is assumed in the analysis under the combined action of axial force and bending moment. The fully plastic states in pure bending and in pure tension and compression are bilinearly interpolated to serve as the yield condition; linearly interacted regimes are combined with interactionless regimes of pure bending to form the yield hexagon, which is a modification of a previously assumed yield quadrangle. Basic equations are derived through the analysis, expressed in a simple analytic closed form, and are able to determine the load-deformation relationship of the bar for any specified history of axial loading.As a result of the analysis it follows that due to the load cycle of tension and compression an initially straight and plastically bent bar undergoes a plastic extension upon the recovery of the straight configuration. This is the balanced axial deformation at a yield hinge between extension and contraction, taking place during the cycle of hinge rotation. Another characteristic feature found is that cyclic alternate displacement loading with large amplitude leads to a steady state after some repeated deterioration of processes. Comparison is made of the load-axial displacement relation between the analytical and experimental results to show reasonable agreement, with discussions extended to the appropriateness of the form of the yield condition.     

Nonlinear vibration modes of an elastic panel under periodic loading

The dynamic instability and nonlinear behavior of a nonshallow thin elastic cylindrical panel with simply supported rectilinear edges under uniformly distributed periodic load is studied. The regions of regular and chaotic dynamics are determined for symmetric and nonsymmetric bending modes of the panel. It is shown that depending on the external load frequency, the nonsymmetric buckling. which occurs when the load amplitude reaches a critical value, can lead to two different dynamic modes. Institute of Mechanics and Mechanical Engineering, Kazan' Science Center, Russian Academy of Sciences, Kazan' 420111. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 1, pp. 186–191, January–February, 2000.     

Variational analysis of gradient elastic flexural plates under static loading

Gradient elastic flexural Kirchhoff plates under static loading are considered. Their governing equation of equilibrium in terms of their lateral deflection is a sixth order partial differential equation instead of the fourth order one for the classical case. A variational formulation of the problem is established with the aid of the principle of virtual work and used to determine all possible boundary conditions, classical and non-classical ones. Two circular gradient elastic plates, clamped or simply supported at their boundaries, are analyzed analytically and the gradient effect on their static response is assessed in detail. A rectangular gradient elastic plate, simply supported at its boundaries, is also analyzed analytically and its rationally obtained boundary conditions are compared with the heuristically obtained ones in a previous publication of the authors. Finally, a plate with two opposite sides clamped experiencing cylindrical bending is also analyzed and its response compared against that for the cases of micropolar and couple-stress elasticity theories.     

Asymptotic method for analysis of a conical shell under local loading

Differential equations of the general theory describing the stress-strain state of conical shells are very complicated, and when computing the exact solution of the problem by analytic methods one encounters severe or even so far insurmountable difficulties. Therefore, in the present paper we develop an approach based on the method of asymptotic synthesis of the stressed state, which has already proved efficient when solving similar problems for cylindrical shells [1, 2]. We essentially use the fourth-order differential equations obtained by Kan [3], which describe the ground state and the boundary effect. Earlier, such equations have already been used to solve problems concerning force and thermal actions on weakly conical shells [4–6]. By applying the asymptotic synthesis method to these equations, we manage to obtain sufficiently accurate closed-form solutions.     

Asymptotic analysis of layered elastic beams

We consider an elastic beam formed by three layers, fixed at one end and loaded at the free end. We call adherents the upper and lower layers ${\Omega }_{+}^{?}$ and ${\Omega }_{?}^{?}$ and an adhesive layer ${\Omega }_m^{?}$. We denote by $?h_{\pm ,m}$ the thickness of each layer and we suppose that the stiffness of the adhesive layer is ${?}^2$, with respect to that of the adherents. By an asymptotic analysis we obtain the zeroth order limit problem and the form of the second order displacements. To cite this article: M. Serpilli, C. R. Mecanique 333 (2005).     

Dynamic buckling mode of an elastic bar

The conception of buckling relative initial imperfection is presented in this paper. According to Boulli-Euler beam equation, the dynamic buckling mode of an elastic bar under the homogeneous boundary conditions can be derived by applying the preferred mode analytical method. As an example, the dynamic buckling mode of an elastic bar clamped at both ends is discussed.     

On axisymmetric motion of an incompressible elastic medium under impact loading

The method of matched asymptotic expansions was employed to obtain approximate solutions to the one-dimensional boundary-value problems of nonlinear dynamic elasticity theory of impact loading on the surface of a cylindrical cavity of an incompressible medium that causes antiplane motion or torsion of the medium. The expansion of the solution in the near-front region is based on solutions of evolution equations different from the equations for quasi-simple waves. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 144–151, November–December, 2006.     

Strength analysis of an elastic plane containing a square lattice of circular holes under mechanical loading

The strength characteristics of an elastic plane weakened by a square lattice of circular holes are considered. The stress concentrations in three distinct lattices under the conditions of uniaxial tension/compression in various directions are studied. The minimum and maximum values of the stress concentrations are calculated, and the stress fields in various lattices are considered. We show that under the compression conditions fracture can occur inside the material rather than on the hole boundaries. It is demonstrated that in dense lattices the stress concentrations exhibit power-law dependence on the structure parameter equal to the ratio of the length of the interval between the holes to the hole radius.     

The elastic sphere under nonsymmetric loading

Existing solutions to boundary value problems arising from an elastic sphere subjected to a body force have been primarily restricted to axisymmetric, conservative loading. In this paper, a method for solving the displacement equations governing the static equilibrium of an elastic sphere subjected to an arbitrary body force and surface displacement is presented. The solutions are obtained in terms of three vector spherical harmonics and expressions for the displacement and stress fields are presented. Additionally, a short discussion indicating extension of these solutions to dynamic problems is included.This research was supported in part by an Organized Research Grant, Southwest Texas State University, 1979.     

Asymptotic theory for static behavior of elastic anisotropic I-beams

End effects for prismatic anisotropic beams with thin-walled, open cross-sections are analyzed by the variational-asymptotic method. The decay rates for disturbances at the ends of prismatic beams are evaluated, and the most influential end disturbances are incorporated into a refined beam theory. Thus, the foundations of Vlasovs theory, as well as restrictions on its applicability, are obtained from the variational-asymptotic point of view. Vlasovs theory is proved to be asymptotically correct for isotropic I-beams. The asymptotically correct generalization of Vlasovs theory for static behavior of anisotropic beams is presented. In light of this development, various published generalizations of Vlasovs theory for thin-walled anisotropic beams are discussed. Comparisons with a numerical 3-D analysis are provided, showing that the present approach gives the closest agreement of all published theories. The procedure can be applied to any thin-walled beam with open cross-sections.     

Stability of an elastic cube under dead loading: Two equal forces

A cube of incompressible neo-Hookean material undergoes a pure homogeneous deformation and is held in equilibrium by three specified pairs of equal and opposite forces, two of which are the same, applied normally to its faces and uniformly distributed over them. The possible equilibrium states are determined and the stability of each is studied with respect to arbitrary superposed infinitesimal deformations. The stability limits are found to be different from those obtained when only infinitesimal deformations having the same principal directions as those of the basic equilibrium state are considered. The differences arise from rotational and shearing types of instabilities that may occur in the general case. A critical inference is drawn concerning the nature of the dead loading conditions employed.