Loading restrictions for the Blatz-Ko hyperelastic model—application to a finite element analysis

In this paper, we consider the Blatz-Ko constitutive model for compressible elastic solids. It is shown that the Cauchy stress tensor leads to a normal loading limitation. This limitation induces slow convergence of the Newton-Raphson algorithm near the maximum authorized normal loading value and divergence if this value is exceeded. In addition, convergence of the Newton-Raphson scheme also depends on ellipticity and strong ellipticity conditions. These various points are discussed in the case of a rectangular specimen subjected to a tensile load and modeled with finite elements.     

Nonlinearly Elastic Shell Models: A Formal Asymptotic Approach II. The Flexural Model

This paper is the sequel of Part I, in which the limiting displacement field of a thin shell when its thickness approaches zero is identified as the solution of a two‐dimensional nonlinear membrane shell model. When the geometry of the middle surface of the shell and the boundary conditions allow non‐zero “inextensional displacements”, the previous membrane limit model is not relevant. In this case, we show how to “update” the assumptions on the applied forces acting on the shell so that a limiting model can be derived by an asymptotic analysis. Furthermore, we identify this limit as the two‐dimensional nonlinear flexural shell model. (Accepted January 13, 1997)     

A variational differential quadrature solution to finite deformation problems of hyperelastic shell-type structures: a two-point formulation in Cartesian coordinates

A new numerical approach is presented to compute the large deformations of shell-type structures made of the Saint Venant-Kirchhoff and Neo-Hookean materials based on the seven-parameter shell theory. A work conjugate pair of the first Piola Kirchhoff stress tensor and deformation gradient tensor is considered for the stress and strain measures in the paper. Through introducing the displacement vector, the deformation gradient, and the stress tensor in the Cartesian coordinate system and by means of the chain rule for taking derivative of tensors, the difficulties in using the curvilinear coordinate system are bypassed. The variational differential quadrature (VDQ) method as a pointwise numerical method is also used to discretize the weak form of the governing equations. Being locking-free, the simple implementation, computational efficiency, and fast convergence rate are the main features of the proposed numerical approach. Some well-known benchmark problems are solved to assess the approach. The results indicate that it is capable of addressing the large deformation problems of elastic and hyperelastic shell-type structures efficiently.     

Rheological relationships for concentrated polymer solutions

Using a network model for concentrated polymer solutions, an expression is calculated for the stress tensor, defined in terms of the moments of the distribution function and the kinetic equation for these moments. In the limiting case the results obtained coincide with known results for normal Newtonian liquids.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 126–132, March–April, 1976.     

拉压性能不同材料厚壁圆筒和厚壁球壳的极限压力分析

本文用广义双剪应力强度理论对拉压性能不同的材料制成的厚壁圆筒和厚壁球壳进行了弹塑性应力分析，得出与拉压比有关的弹性极限内压力、塑性极限内压力、弹塑性区的应力以及弹塑性内压力与弹塑性半径之间的关系式．     

Convergence of Peridynamics to Classical Elasticity Theory

The peridynamic model of solid mechanics is a nonlocal theory containing a length scale. It is based on direct interactions between points in a continuum separated from each other by a finite distance. The maximum interaction distance provides a length scale for the material model. This paper addresses the question of whether the peridynamic model for an elastic material reproduces the classical local model as this length scale goes to zero. We show that if the motion, constitutive model, and any nonhomogeneities are sufficiently smooth, then the peridynamic stress tensor converges in this limit to a Piola-Kirchhoff stress tensor that is a function only of the local deformation gradient tensor, as in the classical theory. This limiting Piola-Kirchhoff stress tensor field is differentiable, and its divergence represents the force density due to internal forces. The limiting, or collapsed, stress-strain model satisfies the conditions in the classical theory for angular momentum balance, isotropy, objectivity, and hyperelasticity, provided the original peridynamic constitutive model satisfies the appropriate conditions.      

Derivation of a dual-mixed <Emphasis Type="Italic">hp</Emphasis>-finite element model for axisymmetrically loaded cylindrical shells

The two-field dual-mixed Fraeijs de Veubeke variational formulation of three-dimensional elasticity serves as the starting point of the derivation of a dimensionally reduced shell model presented in this paper. The fundamental variables of this complementary energy-based variational principle are the not a priori symmetric stress tensor and the skew-symmetric rotation tensor. The tensor of first-order stress functions is applied to satisfy translational equilibrium, while the rotation tensor plays the role of a Lagrange multiplier to ensure rotational equilibrium. The volumetric locking-free shell model uses unmodified three-dimensional constitutive equations, and no classical kinematical hypotheses are employed during the derivation. The numerical performance of the related low-order h-, and higher-order p-version finite elements developed for axisymmetrically loaded cylindrical shells is investigated by two representative model problems. It is numerically proven that no negative effect can be experienced when the thickness is small and tends to zero.     

Statics and kinematics of discrete Cosserat-type granular materials

A theoretical framework is presented for the statics and kinematics of discrete Cosserat-type granular materials. In analogy to the force and moment equilibrium equations for particles, compatibility equations for closed loops are formulated in the two-dimensional case for relative displacements and relative rotations at contacts. By taking moments of the equilibrium equations, micromechanical expressions are obtained for the static quantities average Cauchy stress tensor and average couple stress tensor. In analogy, by taking moments of the compatibility equations, micromechanical expressions are obtained for the (infinitesimal) kinematic quantities average rotation gradient tensor and average Cosserat strain tensor in the two-dimensional case. Alternatively, these expressions for the average Cauchy stress tensor and the average couple stress tensor are obtained from considerations of the equivalence of the continuum force and couple traction vectors acting on a plane and the resultant of the discrete forces and couples acting on this plane. In analogy, the expressions for the average rotation gradient tensor and the average Cosserat strain tensor are obtained from considerations of the change of length and change of rotation of a line element in the two-dimensional case. It is shown that the average particle stress tensor is always symmetrical, contrary to the average stress tensor of an equivalent homogenized continuum. Finally, discrete analogues of the virtual work and complementary virtual work principles from continuum mechanics are derived.     

Stress and fabric in granular material

It has been well recognized that, due to anisotropic packing structure of granular material, the true stress in a specimen is different from the applied stress. However, very few research efforts have been focused on quantifying the relationship between the true stress and applied stress. In this paper, we derive an explicit relationship among applied stress tensor, material-fabric tensor, and force-fabric tensor; and we propose a relationship between the true stress tensor and the applied stress tensor. The validity of this derived relationship is examined by using the discrete element simulation results for granular material under biaxial and triaxial loading conditions.     

On an analogy between the deformation gradient and a generalized shell shifter tensor

This short paper deals with an analogy between the deformation gradient in three-dimensional continuum mechanics and a generalized shell shifter tensor being employed in volume shell formulations. This analogy is very well suited to derive relations between the line, area and volume elements in the shell continuum and those located at the reference surface of the shell. Furthermore, strain and stress tensors can be derived in a very elegant way. Finally, the three-dimensional and two-dimensional strain-energy density is obtained in a very clear manner. The analogy found therefore gives a new and very powerful interpretation of the shell shifter tensor.     

基于SE(3)群局部标架的5/6 Dofs CB壳单元

基于李群局部标架(local frame of Lie group,LFLG)的多柔体系统动力学建模方法可自然消除刚体运动带来的几何非线性,使系统的广义弹性力、广义惯性力及其雅可比矩阵满足刚体运动的不变性.本文融合李群局部标架思想和基于连续体(continuum-based,CB)的壳理论,提出基于SE(3)群局部标架...     

Theorems on the limit analysis dealing with the yield condition expressed by the sum of the homogeneous linear form of stress tensor and the homogeneous quadratic form of stress tensor

In this paper a generalized variational principle on the limit analysis dealing with the yield condition expressed by the sum of the homogeneous linear form of stress tensor and the homogeneous quadratic form of stress tensor is suggested.This variational principle can be applied to the limit analysis in rock mechanics and it takes the situation, in which the yield condition is expressed by the homogeneous linear form of stress tensor or the homogeneous quadratic form of stress tensor, as its special case.     

Assessment of the modulated gradient model in decaying isotropic turbulence

A recently introduced nonlinear model undergoes evaluations based on two isotropic turbulent cases: a University of Wiscosion-Madison case at a moderate Reynolds number and a Johns Hopkins University case at a high Reynolds number. The model uses an estimation of the subgrid-scale (SGS) kinetic energy to model the magnitude of the SGS stress tensor, and uses the normalized velocity gradient tensor to model the structure of the SGS stress tensor. Testing is performed for the first case through a comparison between direct numerical simulation (DNS) results and large eddy simulation (LES) results regarding resolved kinetic energy and energy spectrum. In the second case, we examine the resolved kinetic energy, the energy spectrum, as well as other key statistics including the probability density functions of velocities and velocity gradients, the skewness factors, and the flatness factors. Simulations using the model are numerically stable, and results are satisfactorily compared with DNS results and consistent with statistical theories of turbulence.     

Tensor-orientierte Formulierung nichtlinearer,finiter Schalenelemente

Übersicht In unmittelbarer Anlehnung an die Tensorformulierung geometrisch nichtlinearer Flächentrag-werkstheorien werden besonders genaue, finite Weggrößenmodelle hergeleitet. Sie sind für beliebige Schalen-formen einsetzbar und dienen insbesondere zur Simulation kritischer und überkritischer Systemantworten. Der vorliegende Aufsatz beschreibt die Herleitung der Elemente und überprüft deren Konvergenzverhalten und Leistungsfähigkeit.

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Tensor-oriented formulation of nonlinear, finite shell elements

Summary In accordance with the tensor formulation of geometrically nonlinear shell theories high precision finite displacement models will be developed. They can be applied to arbitrarily curved shell shapes and are especially able to simulate critical and supercritical mechanical responses. The paper describes the derivation of the elements and investigates their convergence behavior and efficiency.

     

On the Müller paradox for thermal-incompressible media

In his monograph Thermodynamics, I. Müller proves that for incompressible media the volume does not change with the temperature. This Müller paradox yields an incompatibility between experimental evidence and the entropy principle. This result has generated much debate within the mathematical and thermodynamical communities as to the basis of Boussinesq approximation in fluid dynamics. The aim of this paper is to prove that for an appropriate definition of incompressibility, as a limiting case of quasi-thermal-incompressible body, the entropy principle holds for pressures smaller than a critical pressure value. The main consequence of our result is the physically obvious one that for very large pressures, no body can be perfectly incompressible. The result is first established in the fluid case. In case of hyperelastic media subject to large deformations, the approach is similar, but with a suitable definition of the pressure associated with a convenient stress tensor decomposition.     

Mesh Discretization of the Vector Relations of Shell Theory in a Curvilinear Coordinate System

Mesh methods for discretization of the differential vector relations are generalized as applied to problems of shell theory. In the finite-difference method, covariant derivatives are replaced by vector differences, which are then projected on the vectors of a local basis. In the finite-element method, vector functions are approximated by a Taylor series with tensor coefficients. It is shown that such schemes satisfy the condition of rigid displacement for a deformable body, which improves considerably the convergence of the solution. The proposed schemes, which are sensitive to approximation uncertainties, were tested by solving problems on deformation of shells     

An Optimal Condition of Compactness for Elasticity Problems Involving one Directional Reinforcement

This paper deals with the homogenization of a homogeneous elastic medium reinforced by very stiff strips in dimension two. We give a general condition linked to the distribution and the stiffness of the strips, under which the nature of the elasticity problem is preserved in the homogenization process. This condition is sharper than the one used in Briane and Camar-Eddine (J. Math. Pures Appl. 88:483–505, 2007) and is shown to be optimal in the case where the strips are periodically arranged. Indeed, a fourth-order derivative term appears in the limit equation as soon as the condition is no more satisfied. In the periodic case the influence of oscillations in the medium surrounding the strips is also considered. The homogenization method is based both on a two-scale convergence for the strips and the use of suitable oscillating test functions. This allows us to obtain a distributional convergence of two of the three entries of the stress tensor contrary to the Γ-convergence approach of Briane and Camar-Eddine (J. Math. Pures Appl. 88:483–505, 2007).     

Stokes flow past an assemblage of axisymmetric porous spherical shell-in-cell models: effect of stress jump condition

The quasisteady axisymmetrical flow of an incompressible viscous fluid past an assemblage of porous concentric spherical shell-in-cell model is studied. Boundary conditions on the cell surface that correspond to the Happel, Kuwabara, Kvashnin and Cunningham/Mehta-Morse models are considered. At the fluid-porous interfaces, the stress jump boundary condition for the tangential stresses along with continuity of normal stress and velocity components are employed. The Brinkman’s equation in the porous region and the Stokes equation for clear fluid are used. The hydrodynamic drag force acting on the porous shell by the external fluid in each of the four boundary conditions on the cell surface is evaluated. It is found that the normalized mobility of the particles (the hydrodynamic interaction among the porous shell particles) depends not only on the permeability of the porous shells and volume fraction of the porous shell particles, but also on the stress jump coefficient. As a limiting case, the drag force or mobility for a suspension of porous spherical shells reduces to those for suspensions of impermeable solid spheres and of porous spheres with jump.     

An iterative data-driven turbulence modeling framework based on Reynolds stress representation

Data-driven turbulence modeling studies have reached such a stage that the basic framework is settled, but several essential issues remain that strongly affect the performance. Two problems are studied in the current research: (1) the processing of the Reynolds stress tensor and (2) the coupling method between the machine learning model and flow solver. For the Reynolds stress processing issue, we perform the theoretical derivation to extend the relevant tensor arguments of Reynolds stress. Then, the tensor representation theorem is employed to give the complete irreducible invariants and integrity basis. An adaptive regularization term is employed to enhance the representation performance. For the coupling issue, an iterative coupling framework with consistent convergence is proposed and then applied to a canonical separated flow. The results have high consistency with the direct numerical simulation true values, which proves the validity of the current approach.