Finite Element Analysis of Axisymmetric Elastic Body Problems

Linear form functions are commonly used in a long time for a toroidal volume element swept bya triangle revolved about the symmetrical axis for general axisymmetrical stress problems.It is diffi-cult to obtain the rigidity matrix by exact integration,and instead,the method of approximate in-tegration is used.As the locations of element close to the symmetrical axis,the accuracy of this ap-proximation deteriorates very rapidly.The exact integration have been suggested by various authorsfor the calculation of rigidity matrix.However,it is shown in this paper that these exact integrationscan only be used for those axisymmetric bodies With central hole.For solid axisymmetric body,itcan be proved that the calculation fails due to the divergent property of rigidity matrix integration.In this paper a new form function is suggested.In this new form function,the radial displacementu vanishes as radial coordinates r approach to zero.The calculated rigidity matrix is convergenteverywhere,including these triangular     

Justification of the Cauchy–Born Approximation of Elastodynamics

We present sharp convergence results for the Cauchy—Born approximation of general classical atomistic interactions, for static problems with small data and for dynamic problems on a macroscopic time interval.     

DISCUSSIONS On "Finite Element Analysis of Axisymmetric Elastic Body Problems

Regarding the calculdtion of the rigidity matrix of the linear triangular elements, there is really the existence of the nonconvergent terms. But the corresponding rows and columns of these terms     

An Experimental–Numerical Methodology for a Rapid Prototyped Application Combined with Finite Element Models in Vertebral Trabecular Bone

In the present study, a novel evaluation method involving rapid prototyped (RP) technology and finite element (FE) analysis was used to study the elastic mechanical characteristics of human vertebral trabecular bone. Three-dimensional (3D) geometries of the RP and FE models were obtained from the central area of vertebral bones of female cadavers, age 70 and 85. RP and FE models were generated from the same high-resolution micro-computed tomography (μCT) scan data. We utilized RP technology along with FE analysis based on μCT for high-resolution vertebral trabecular bone specimens. RP models were used to fabricate complex 3D objects of vertebral trabecular bone that were created in a fused deposition modeling machine. RP models of vertebral trabecular bone are advantageous, particularly considering the repetition, risks, and ethical issues involved in using real bone from cadaveric specimens. A cubic specimen with a side length of 6.5 mm or a cylindrical specimen with a 7 mm diameter and 5 mm length proved better than a universal cubic specimen with a side length of 4 mm for the evaluation of elastic mechanical characteristics of vertebral trabecular bones through experimental and simulated compression tests. The results from the experimental compression tests of RP models closely matched those predicted by the FE models, and thus provided substantive corroboration of all three approaches (experimental tests using RP models and simulated tests using FE models with ABS and trabecular bone material properties). The RP technique combined with FE analysis has potential for widespread biomechanical use, such as the fabrication of dummy human skeleton systems for the investigation of elastic mechanical characteristics of various bones.     

The Electronic Structure of Smoothly Deformed Crystals: Wannier Functions and the Cauchy–Born Rule

The electronic structure of a smoothly deformed crystal is analyzed for the case when the effective Hamiltonian is a given function of the nuclei by considering the regime when the scale of the deformation is much larger than the lattice parameter. Wannier functions are defined by projecting the Wannier functions for the undeformed crystal to the space spanned by the wave functions of the deformed crystal. The exponential decay of such Wannier functions is proved for the case when the undeformed crystal is an insulator. The celebrated Cauchy–Born rule for crystal lattices is extended to the present situation for electronic structure analysis.     

A Study of Crack–inclusion Interactions and Matrix–inclusion Debonding Using Moiré Interferometry and Finite Element Method

Failure behavior of composite materials in general and particulate composites in particular is intimately linked to interactions between a matrix crack and a second phase inclusion. In this work, surface deformations are optically mapped in the vicinity of a crack–inclusion pair using moiré interferometry. Edge cracked epoxy beams, each with a symmetrically positioned cylindrical glass inclusion ahead of the tip, are used to simulate a compliant matrix crack interacting with a stiff inclusion. Processes involving microelectronic fabrication techniques are developed for creating linear gratings in the crack–inclusion vicinity. The debond evolution between the inclusion–matrix pair is successfully mapped by recording crack opening displacements under quasi-static loading conditions. The surface deformations are analyzed to study evolution of strain fields due to crack–inclusion interactions. A numerical model based on experimental observations is also developed to simulate debonding of the inclusion from the matrix. An element stiffness deactivation method in conjunction with critical radial stress criterion is successfully demonstrated using finite element method. The proposed methodology is shown to capture the experimentally observed debonding process well.

The Fundamental Equations in Finite Element Method of Coupled Thermo-elastic Plane Problem

The fundamental equations in finite element method for unsteady temperature field elasticplane problem are derived on the bases of variational principle of coupled thermoelastic problems.In these derivations,elastic plane is divided into three nodes triangular elements,and time interval isdivided into linear time elements,in which all the variables,including displacements and temperaturesat various nodal points,are varied linearly with time.Two coupled sets of linear algebraic equations ofall the unknown displacements and temperatures at every nodal point in every instant(i.e.the terminalvalues of time elements)are obtained.They are the fundamental equations of the said problem.     

A New Stable Bubble Element for Incompressible Fluid Flow Based on a Mixed Petrov–Galerkin Finite Element Formulation

A new mixed Petrov–Galerkin formulation employing the MINI element with a non-confirming bubble function for an incompressible media governed by the Stokes equations, which is equivalent to the stabilized finite element by P ¹-P ¹ approximation, is proposed. The new formulation possesses better stability properties than the conventional Bubnov–Galerkin formulation employing the MINI element. In this aspect, the stabilizing effect of this formulation is evaluated by a stabilizing parameter determined by both shapes of the trial and the weighting bubble functions.     

Weakly Nonlinear-Dissipative Approximations of Hyperbolic–Parabolic Systems with Entropy

Hyperbolic–parabolic systems have spatially homogenous stationary states. When the dissipation is weak, one can derive weakly nonlinear-dissipative approximations that govern perturbations of these constant states. These approximations are quadratically nonlinear. When the original system has an entropy, the approximation is formally dissipative in a natural Hilbert space. We show that when the approximation is strictly dissipative it has global weak solutions for all initial data in that Hilbert space. We also prove a weak-strong uniqueness theorem for it. In addition, we give a Kawashima type criterion for this approximation to be strictly dissipative. We apply the theory to the compressible Navier–Stokes system.     

Engineering Models for Numerical Analysis of Composite Bending Members∗

Abstract

ABSTRACT The two-step numerical analysis of a composite beam structure is presented in this paper. The first step, based on the idea of dividing the cross section into laminas, leads to the estimation of the moment-curvature relation for different types of cross sections used in composite beams. The second step adopts this constitutive relation, which is expressed in the space of generalized stresses and strains, into finite element nonlinear code. Some numerical examples are given, to show the agreement of numerical calculations with results of the authors' experiments, when the shrinkage of a concrete encasement and stresses due to welding processes in steel beams are considered. In addition, the numerical concept presented here seems to reduce the sensitivity of the final results obtained to finite element discretization error.     

On (Andersen–)Parrinello–Rahman Molecular Dynamics, the Related Metadynamics, and the Use of the Cauchy–Born Rule

It is shown that the Parrinello–Rahman Lagrangian is obtained by assuming that (i) the cell inertia tensor is spherical and constant in time, and that (ii) the cell fluctuation motions are irrotational. A slightly different Lagrangian is suggested, arrived at by dropping the sphericity assumption in (i). A related metadynamics is also proposed, based on replacing by (ii) the various no-cell-rotation assumptions that are customarily used. Finally, a zero-temperature, scale-bridging relation is proposed between the intermolecular potential and the macroscopic stored-energy mapping.     

Finite Element Implementation of the Microplane Theory for Simulating a Rigid Concrete Pavement-Vehicle Interaction∗

Abstract

This paper presents an approach for modeling concrete pavement, based on the constitutive implementation of Bazant's microplane theory, for the purpose of predicting pavement response due to complex loading by vehicles. This includes implementation of the microplane theory in a three dimensional finite element code and verification of its numerical accuracy. The analytical method is then verified. The program's accuracy under simple static loading is verified by comparison with two of the most widely used pavement design codes. Experimental data from the literature are used to verify the approach developed for both cyclic response and prediction of material softening, a critical feature of the Portland Cement Concrete (PCC) concrete material used in pavement. The analysis is also verified against experimental influence function data for a single axle, Finally, the analytically predicted pavement response is verified for dynamic multi-axle truck loading. Based on agreement with experimental data, the model developed captures the essential characteristics of concrete pavement subjected to complex     

Stability Properties of POD–Galerkin Approximations for the Compressible Navier–Stokes Equations

Fluid flows are very often governed by the dynamics of a mall number of coherent structures, i.e., fluid features which keep their individuality during the evolution of the flow. The purpose of this paper is to study a low order simulation of the Navier–Stokes equations on the basis of the evolution of such coherent structures. One way to extract some basis functions which can be interpreted as coherent structures from flow simulations is by Proper Orthogonal Decomposition (POD). Then, by means of a Galerkin projection, it is possible to find the system of ODEs which approximates the problem in the finite-dimensional space spanned by the POD basis functions. It is found that low order modeling of relatively complex flow simulations, such as laminar vortex shedding from an airfoil at incidence and turbulent vortex shedding from a square cylinder, provides good qualitative results compared with reference computations. In this respect, it is shown that the accuracy of numerical schemes based on simple Galerkin projection is insufficient and numerical stabilization is needed. To conclude, we approach the issue of the optimal selection of the norm, namely the H ¹ norm, used in POD for the compressible Navier–Stokes equations by several numerical tests. Received 21 April 1999 and accepted 18 November 1999     

Atomistic–continuum coupled model for nonlinear analysis of single layer graphene sheets

In this paper, atomistic–continuum coupled model for nonlinear flexural response of single layer graphene sheet is presented considering von-Karman geometric nonlinearity and material nonlinearity due to atomic interactions. The strain energy density function at continuum level is established by coupling the deformation at continuum level to that of at atomic level through Cauchy–Born rule. Strain and curvature dependent tangent in-plane extensional, bending–extension coupling, bending stiffness matrices are derived from strain energy density function constructed through Tersoff–Brenner potential. The finite element method is used to discretize the graphene sheet at continuum level and nonlinear bending response with and without material nonlinearity is studied. The present results are also compared with Kirchhoff plate model and significant differences at higher load are observed. The effects of other parameters like number of atoms in the graphene sheet, boundary conditions on the central/maximum deflection of graphene sheet are investigated. It is also brought out that the occurrence of bond length exceeding cutoff distance initiates at corners for CFCC, CFCF, SFSS, SFSF graphene sheets and near center for SSSS and CCCC graphene sheets.     

A Variational Framework for Spectral Approximations of Kohn–Sham Density Functional Theory

We reformulate the Kohn–Sham density functional theory (KSDFT) as a nested variational problem in the one-particle density operator, the electrostatic potential and a field dual to the electron density. The corresponding functional is linear in the density operator and thus amenable to spectral representation. Based on this reformulation, we introduce a new approximation scheme, termed spectral binning, which does not require smoothing of the occupancy function and thus applies at arbitrarily low temperatures. We prove convergence of the approximate solutions with respect to spectral binning and with respect to an additional spatial discretization of the domain.     

Limit Design in the Absense of a Given Layout: A Finite Element,Zero-One Programming Approach∗

Limit design in three dimensions is discussed and formulated as a constrained minimax problem in kinematic and geometric variables. A finite element discretization is proposed which, combined with piecewise linearization of the yield surfaces, reduces the minimum weight design to a pair of dual problems in linear mixed zero one programming. The relevant duality theory is shown to be useful for the theoretical frame of the mechanical problem. Various ways of reducing the number of variables and constraints are pointed out, in order to make available algorithms economically applicable to practical situations.