A cubic triangular finite element for flat plates with shear

This paper presents the development of a straightforward displacement type triangular finite element for bending of a flat plate with the inclusion of transverse (or lateral) shear effects. The element has twenty two degrees of freedom consisting of ten for the lateral displacement of the midplane and six for rotations of the normal to the undeformed midplane of the plate. The latter are taken as independent of the slopes of the deformed midplane in order to include deformation due to transverse shear. The element is fully conforming and may be orthotropic. At interelement boundaries, the element matches adjacent elements both with respect to lateral displacement of the midplane and the rotations of the normal. The result is an efficient ‘linear moment’ triangular element but with transverse shear deformation included. Numerical computations for a number of examples are presented. The results show the element to be more flexible than most other finite element models and agree closely with those from a numerical solution of the three dimensional elasticity equations. The results also converge to those from thin plate theory when the thickness to length ratio becomes small or when the transverse shear moduli are artificially increased.     

A triangular finite element for thin plates and shells

A finite element modelling technique which utilizes a triangular element with 45 degrees-of-freedom and seven-point integration has been tested for analysis of thin plate and shell structures. The element is based on the degenerate solid shell concept and the mixed formulation with assumed independent inplane and transverse shear strains. Numerical result indicates effectiveness of the present modelling technique which features combined use of elements with kinematic modes and those without kinematic modes in an attempt to eliminate both locking and spurious kinematic modes at global structural level.     

Unilateral buckling of thin elastic plates by the boundary integral equation method

The unilateral buckling of thin elastic plates, according to Kirchhoff's theory, is studied by using a boundary integral method. A representation for the second member of the equation is given. In the matrix formulatiea, boundary unknowns are eliminated; therefore, the unilateral buckling problem reduces to compute the eigenvalues and the eigenvectors of a matrix depending on the contact zone with the rigid foundation. An iterative process allows this zone and the buckling load to be computed. The capacities of the proposed method are illustrated by four examples.     

Closed-form analysis of the buckling loads of symmetrically laminated orthotropic plates considering elastic edge restraints

The initial buckling loads of symmetrically laminated rectangular orthotropic plates under uniaxial compression are determined in a closed-form analytical manner. The considered laminates are simply supported at all edges and furthermore subjected to elastic rotational restraints at the unloaded edges. The analysis approach which is based on the assumptions of Classical Laminate Plate Theory employs a representation for the transverse displacements consisting of a system of trigonometric functions in both inplane coordinate directions. Due to its simplicity, a closed-form solution for the critical buckling load is possible which is useful for preliminary design purposes. The presented approach is compared to closed-form analytical and numerical data available in the literature and is found to be in favorable agreement.     

Hierarchic finite elements for moderately thick to very thin plates

We consider the numerical solution of Reissner-Mindlin plates. The model is widely used for thin to moderately thick plates. Generally low order finite elements (with degree one or two) are used for the approximation. Unfortunately the solution degenerates very rapidly for small thickness (locking phenomenon). Non standard formulations of the problem are usually combined with low order finite elements to weaken or possibly eliminate the locking of the numerical solution. We introduce a family of hierarchic finite elements and we present a set of numerical results for the plate problem in its plain formulation. We show that reliable solutions are achieved for all thicknesses of practical interest by using high order finite elements. Moreover, the hierarchic structure allows a low cost assessment of the quality of the solution.     

Consistent multiscale analysis of heterogeneous thin plates with smoothed quadratic Hermite triangular elements

A consistent multiscale formulation is presented for the bending analysis of heterogeneous thin plate structures containing three dimensional reinforcements with in-plane periodicity. A multiscale asymptotic expansion of the displacement field is proposed to represent the in-plane periodicity, in which the microscopic and macroscopic thickness coordinates are set to be identical. This multiscale displacement expansion yields a local three dimensional unit cell problem and a global homogenized thin plate problem. The local unit cell problem is discretized with the tri-linear hexahedral elements to extract the homogenized material properties. The characteristic macroscopic deformation modes corresponding to the in-plane membrane deformations and out of plane bending deformations are discussed in detail. Thereafter the homogenized material properties are employed for the analysis of global homogenized thin plate with a smoothed quadratic Hermite triangular element formulation. The quadratic Hermite triangular element provides a complete C¹ approximation that is very desirable for thin plate modeling. Meanwhile, it corresponds to the constant strain triangle element and is able to reproduce a simple piecewise constant curvature field. Thus a unified numerical implementation for thin plate analysis can be conveniently realized using the triangular elements with discretization flexibility. The curvature smoothing operation is further introduced to improve the accuracy of the quadratic Hermite triangular element. The effectiveness of the proposed methodology is demonstrated through numerical examples.     

Unsteady response of thin elastic plates subjected to time-dependent loads and external damping

Summary The problem of the forced vibration of a thin elastic plate of arbitrary shape, and resting on an elastic foundation with damping, is solved for time-dependent loading- and boundary-conditions and under arbitrary initial-conditions. By use of the classical theory of bending of flat plates, infinite series expressions are derived for the deflection field, and various forms of the solution are noted. An example of a circular plate is included.

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Zusammenfassung Das Problem der erzwungenen Schwingung einer dünnen, elastischen Platte beliebigen Umrisses, die auf einer elastischen Bettung mit Dämpfung ruht, wird für zeitabhängige Belastungen und Randbedingungen und für beliebige Anfangsbedingungen gelöst. Mittels der klassischen Biegetheorie der Platten wird das Durchbiegungsfeld durch unendliche Reihen ausgedrückt. Verschiedene Gestalten der Lösung werden angegeben. Ein Beispiel einer Kreisplatte ist eingeschlossen.

     

The elasto-plastic analysis of plates using hybrid finite elements

An elasto-plastic plate-bending analysis is developed based on the finite element method and utilizing an assumed-stress hybrid (Pian) element. Plasticity is incorporated using the Prandtl–Reuss relations and isotropic hardening theory together with an incremental residual force technique. Several example solutions are included to demonstrate the ability of this approach in elasto-plastic plate-bending problems.     

Vibration of circular and annular plates using finite elements

The finite element method is applied to the free transverse vibration of circular and annular plates of varying thickness. An annular element is derived which incorporates the number of diametral modes in the deflection function. This results in an element having only four degrees of freedom, these being the deflection and slopes at the inner and outer radii of the element at an anti-node of the particular vibration mode. Thickness variation in the radial direction is readily introduced, and stiffness and inertia matrices are presented for elements with linear and parabolic variations in thickness. The method is checked with several numerical examples. Calculations of free vibration of circular and annular plates of constant, linear and parabolic thickness variation are compared with available exact solutions.     

Buckling of triangular plates with elastic edge constraints

Summary This paper presents the first-known investigation on the buckling behavior of triangular plates with both translational and rotational elastic edge constraints. The energy functional of a general triangular plate with elastic edge supports is derived, and thep-Ritz method is utilized to derive the governing eigenvalue equation for the buckling problem. Convergence and comparison studies are carried out to verify the validity and accuracy of the solution method. Extensive buckling factors are presented for several selected isosceles and right-angled triangular plates of various edge support conditions and subjected to isotropic inplane compressive load. The influence of elastic edge supports on the buckling factors for triangular plates of various vertex angles (aspect ratios) and boundary conditions is examined.     

On buckling of crosswise rigid elastic cantilever plates

Summary The classical two-dimensional equations for the buckling of thin elastic anisotropic plates are reduced, on the basis of an assumption of crosswise rigidity, to a system of one-dimensional equations. The reduction pre-supposes that the crosswise dimension of the plate is small compared to it's spanwise dimension and leads, effectively, to a system of beam buckling equations which automatically associates a warping stiffness effect with the classical beam bending and twisting stiffness effects. In the event that inertia load terms are to be considered the system is of the eight order with respect to the spanwise space coordinate. In the absence of such load terms the system can be reduced to the sixth order, with further reductions possible for suitably specialized load conditions.     

A simple class of finite elements for plate and shell problems. I: Elements for beams and thin flat plates

This is the first paper of a pair which together discuss the development of a class of overlapping hinged bending finite elements which are suitable for the analysis of thin-shell, plate and beam structures. These elements rely on a simple physical analogy, involving overlapping hinged facets. They are based on quadratic overlapping assumed displacement functions. Only translational nodal degrees of freedom are necessary, which is a significant simplification over most other currently available beam, plate and shell finite elements which employ translational, rotational and higher-order nodal variables. In this paper the hinged bending element concept is introduced, and the hinged beam bending (HBB) and hinged plate bending (HPB) elements are formulated. In paper II these concepts are extended to develop a hinged shell bending (HSB) element. The HSB element can be readily combined with the constant strain triangular (CST) plane stress finite element for the modelling of thin-shell structures.     

Buckling of composite plates using simple shear flexible finite elements

An eight-noded, shear flexible quadratic rectangular element with five degrees of freedom per node is developed in this paper, to study the effects of transverse shear on the stability of layered composite plates, under uni-axial and bi-axial compression for various boundary conditions. Green's nonlinear strain tensor is used to formulate the initial stress matrix (K_σ). The validity of the element is demonstrated by comparing the results from the present formulation with those existing in the literature.     

Optimal shape remodelling of linearly elastic plates using finite element methods

The optimality conditions for the optimal shape remodelling of linearly elastic plates are obtained by introducing the total variation of a function defined on a variable domain, although the variation of a function has been taken on a fixed domain in most literature on calculus of variations. Using these optimality conditions, a solution scheme involving an iterative algorithm is proposed, together with several numerical examples.     

Elastic-plastic buckling analysis of rectangular plates subjected to biaxial loads

In order to calculate the buckling load of a rectangular plate, the analytical approach is used in this study. The plate is assumed to be simply supported on four edges and loaded by uniform stresses along the edges. If the plate is slender, the buckling is elastic. However, if the plate is sturdy, it buckles in the plastic range. Then, the instantaneous moduli in the constitutive equations depend on the external loading. In this study, the elastic and plastic buckling equations are derived for rectangular plates under biaxial loading, and the corresponding interaction curves are presented. The influences of aspect ratios, load ratios and hardening factors on the buckling stresses are investigated for rectangular plates. From the plastic buckling analysis, the optimal combination of loads is given for the buckling strength.     

Elastic-plastic buckling analysis of rectangular plates subjected to biaxial loads

In order to calculate the buckling load of a rectangular plate, the analytical approach is used in this study. The plate is assumed to be simply supported on four edges and loaded by uniform stresses along the edges. If the plate is slender, the buckling is elastic. However, if the plate is sturdy, it buckles in the plastic range. Then, the instantaneous moduli in the constitutive equations depend on the external loading. In this study, the elastic and plastic buckling equations are derived for rectangular plates under biaxial loading, and the corresponding interaction curves are presented. The influences of aspect ratios, load ratios and hardening factors on the buckling stresses are investigated for rectangular plates. From the plastic buckling analysis, the optimal combination of loads is given for the buckling strength.     

Numerical simulation of crack problems using triangular finite elements with embedded interfaces

The aim of this paper is to propose numerical aspects for the modeling of discrete cracks in quasi-brittle materials using triangular finite elements with an embedded interface based on the formulation in [Computational Mechanics 27 (2001) 463]. The kinematics of the discontinuous displacement field and the variational formulation applied to a body with an internal discontinuity is given. The discontinuity is modeled by additional global degrees of freedom and the continuity of the displacement jumps across the element boundaries is enforced. To show the performance of the model, a single element test and two examples for mode-I dominated fracture, namely a tension test and a three-point bending beam, are discussed.     

A linearized analysis of buckling of thin rotational shells using the finite element method

An isoparametric shell element has been developed capable of linear response to the imposed loads. The original formulation, which was written for static and dynamic analyses, was extended to embrace linear buckling problems. A variety of numerical examples were attempted in order to assess the adaptability of the element to different geometrical representations. Despite serious size limitations of the computer, the accuracy of the predicted buckling loads was found to be satisfactory.     

Behaviour of Lagrangian triangular mixed fluid finite elements

The behaviour of mixed fluid finite elements, formulated based on the Lagrangian frame of reference, is investigated to understand the effects of locking due to incompressibility and irrotational constraints. For this purpose, both linear and quadratic mixed triangular fluid elements are formulated. It is found that there exists a close relationship between the penalty finite element approach that uses reduced/selective numerical integration to alleviate locking, and the mixed finite element approach. That is, performing reduced/ selective integration in the penalty approach amounts to reducing the order of pressure interpolation in the mixed finite element approach for obtaining similar results. A number of numerical experiments are performed to determine the optimum degree of interpolation of both the mean pressure and the rotational pressure in order that the twin constraints are satisfied exactly. For this purpose, the benchmark solution of the rigid rectangular tank is used. It is found that, irrespective of the degree of mean and the rotational pressure interpolation, the linear triangle mesh, with or without central bubble function (incompatible mode), locks when both the constraints are enforced simultaneously. However, for quadratic triangle, linear interpolation of the mean pressure and constant rotational pressure ensures exact satisfaction of the constraints and the mesh does not lock. Based on the results obtained from the numerical experiments, a number of important conclusions are arrived at.