Sandwich Plate Structures Research Articles

The dynamic response of edge clamped plates loaded by spherically expanding sand shells

The dynamic deformation of both edge clamped stainless steel sandwich panels with a pyramidal truss core and equal mass monolithic plates loaded by spherically expanding shells of dry and water saturated sand has been investigated, both experimentally and via a particle based simulation methodology. The spherically expanding sand shell is generated by detonating a sphere of explosive surrounded by a shell of either dry or water saturated synthetic sand. The measurements show that the sandwich panel and plate deflections decrease with increasing stand-off between the center of the charge and the front of the test structures. Moreover, for the same charge and sand mass, the deflections of the plates are significantly higher in the water saturated sand case compared to that of dry sand. For a given stand-off, the mid-span deflection of the sandwich panel rear faces was substantially less than that of the corresponding monolithic plate for both the dry and water saturated sand cases. The experiments were simulated via a coupled discrete-particle/finite element scheme wherein the high velocity impacting sand is modeled by interacting particles while the plate is modeled within a Lagrangian finite element setting. The simulations are in good agreement with the measurements for the dry sand impact of both the monolithic and sandwich structures. However, the simulations underestimate the effect of stand-off in the case of the water saturated sand explosion, i.e. the deflections decrease more sharply with increasing stand-off in the experiments compared to the simulations. The simulations reveal that the momentum transmitted into the sandwich and monolithic plate structures by the sand shell is approximately the same, consistent with a small fluid–structure interaction effect. The smaller deflection of the sandwich panels is therefore primarily due to the higher bending strength of sandwich structures.

Dynamic response analysis of light weight pyramidal sandwich plates subjected to water impact

ABSTRACTThe fluid-solid interaction (FSI) dynamic responses for a Light Weight Pyramidal Sandwich Plate Structure(LWPSPS) under different water-entry velocities (1m/s-6m/s) are investigated numerically and theoretically.The characteristics of impact pressure and structure deformation are obtained by using LS-DYNA codebased on the proposed 3D multi-physics (air-water-solid) FEM model. Numerical results show that theaverage water impact pressure of LWPSPS is much lower than that of the monolithic plate with same mass.Moreover, a phenomenon called “local air cushion” is observed for LWPSPS which does not exist fora monolithic plate. Theoretical hydroelasticity analysis demonstrates that the FSI effect of LWPSPS is weakwhen the ratio of water impact duration time to wet natural vibration period is greater than 4. In the study,an engineering estimation method to predict the maximum deformation of the LWPSPS is proposed, in whichthe total deformation is divided into two parts, i.e. local field deformation and global field deformation,and they are both computed using analytical model. Good agreement between the numerical results andones obtained from the proposed engineering estimation method is achieved. Furthermore, the geometricvariation sensitiveness analysis is also conducted.

Analysis of functionally graded sandwich plate structures with piezoelectric skins, using B-spline finite strip method

Functionally graded materials are composite materials wherein the composition of the constituent phases can vary in a smooth continuous way with a gradation which is function of its spatial coordinates. This characteristic proves to be an important issue as it can minimize abrupt variations of the material properties which are usually responsible for localized high values of stresses, and simultaneously providing an effective thermal barrier in specific applications. In the present work, it is studied the static and free vibration behaviour of functionally graded sandwich plate type structures, using B-spline finite strip element models based on different shear deformation theories. The effective properties of functionally graded materials are estimated according to Mori–Tanaka homogenization scheme.These sandwich structures can also consider the existence of outer skins of piezoelectric materials, thus achieving them adaptive characteristics. The performance of the models, are illustrated through a set of test cases.

Prediction of inter-laminar stresses in composite honeycomb sandwich panels under mechanical loading using Variational Asymptotic Method

This work focuses on the formulation of an asymptotically correct theory for symmetric composite honeycomb sandwich plate structures. In these panels, transverse stresses tremendously influence design. The conventional 2-D finite elements cannot predict the thickness-wise distributions of transverse shear or normal stresses and 3-D displacements. Unfortunately, the use of the more accurate three-dimensional finite elements is computationally prohibitive. The development of the present theory is based on the Variational Asymptotic Method (VAM). Its unique features are the identification and utilization of additional small parameters associated with the anisotropy and non-homogeneity of composite sandwich plate structures. These parameters are ratios of smallness of the thickness of both facial layers to that of the core and smallness of 3-D stiffness coefficients of the core to that of the face sheets. Finally, anisotropy in the core and face sheets is addressed by the small parameters within the 3-D stiffness matrices. Numerical results are illustrated for several sample problems. The 3-D responses recovered using VAM-based model are obtained in a much more computationally efficient manner than, and are in agreement with, those of available 3-D elasticity solutions and 3-D FE solutions of MSC NASTRAN.

The Optimization Design of Laser Welded Sandwich Plate Structure

Height lightweight is one of key technology to dock structure that is made up of the sandwich composite board and satisfy requirements of bending rigidity feature. This paper proposes a new engineering optimization method which is both precision and economical. First, through theoretical calculation, to get bending stiffness( , ) and twist stiffness( ). Afterwards ,based on structures bending theory ,we could get the stiffness equation of the model , and calculate the quality equation of the model equations. Supposed the maximal stiffness as objective function ,height(h) of rib and space of rib(a) as design variable.Using MATLAB software and ABAQUS finite element software, we could get the Optimized design program that is to meet the requirements of the structural characteristics of sandwich composite panels of the dock structure. In 100 tons load, when the length of plate is 1m, thickness of plate is 4mm, the height of the rib is 40 mm, the spacing of the rib is 75 mm, and when the height is 45 mm, the spacing is 95 mm, the bending performance of the whole mode lis betterand the quality is more lighter.

On the use of discontinuous elastomer patches to optimize the damping properties of composite sandwich plates

This study investigates the optimization of a hybrid composite/elastomer sandwich plate structure using a periodical pattern of viscoelastic material. Design variables consist in the thicknesses of the layers, their fiber orientations, the position of the elastomer patches and their geometrical distribution. Damping properties of the hybrid structure are calculated by the Method of Strain Energy (MSE) and the constrained optimization maximizes these properties using the active-set algorithm. Two optimized plates containing patterns embedded or not in a composite matrix are compared with a plate damped by a continuous viscoelastic layer. Results show that optimizing composite plates with patches gives interesting results: damping properties are about ten times the properties of the plates with continuous viscoelastic layers, the patches can be sticked on the external layers of the plate and not internally, and all the strain components in elastomer are involved in damping.

Analysis of Active-Passive Plate Structures Using a Simple and Efficient Finite Element Model

In this work a simple and efficient finite element model is developed for vibration analysis of active-passive damped multilayer sandwich plates, with a viscoelastic core sandwiched between elastic layers, including piezoelectric layers. The elastic layers are modeled using the classical plate theory and the core is modeled using Reddy’s third-order shear deformation theory. The finite element is obtained by assembly of N “elements” through the thickness, using specific assumptions on the displacement continuity at the interfaces between layers. To achieve a mechanism for the active control of the structural dynamics response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers. The dynamic analysis of active-passive damped multilayer sandwich plate structures is conducted in frequency domain to obtain the natural frequencies and respective loss factors, and in time domain for steady state harmonic motion. For both analyses, a finite element code is implemented. The model is applied in the solution of some illustrative examples and the results are presented and discussed.

Simultaneous geometrical and material optimal design of hybrid elastomer/composite sandwich plates

The paper presents the complete optimization of a hybrid elastomer/composite sandwich plate structure: design variables consist in the total number of layers of the structure, their respective thicknesses, their fiber orientations, the position(s) of the viscoelastic core(s) and the stacking sentence. The damping of the hybrid structure is calculated by the Method of Strain Energy (MSE). The constrained optimization maximizes the damping loss factor using the linear search algorithm. As an example, the method is applied to a simple structure and the results demonstrate the capabilities of our tool.

Theory and Practice of New Types of Long-Span Building Structures Developed at Guizhou University

This paper presents the theory and practice of new types of long-span building structures developed at Guizhou University for the recent 25 years. The new structural systems include RC open-web sandwich plate structures, steel/RC composite open-web sandwich plate structures, prestressed RC open-web sandwich plate structures, and cast-in-place concrete round eye hollow plate structures. The mechanical characters and technical indexes of each system are described. The application of the structures is detailed in tables and photos.

633 ロケット衛星フェアリング内の音圧低減化の一試み

A trial study to examine if the sound reduction effects in the rocket fairing are obtained or not was carried out by using, so to speak, Sound Decreasing Structure, considering that concerned Structure is very similar to the structure of existing rocket faring. Specimens are honeycomb sandwich plate structures composed of outer thin Al skin and inner porous Al of sound absorbing material in stead of Al skin. They were excited acoustically by white random noise in the rectangular acoustic tube and the transmitted SPL was measured in the anechoic chamber and compared with the excitation SPL. As a result, it turned out that sound decreasing effects were actually observed if the SPL is normalized by the velocity SPL of specimens. And besides if the sound absorbing effects of reflection sounds from the inner walls of faring model are added in addition to the above decreasing ones by setting the concerned models on all surrounding walls in the chamber, it was observed that SPL reduction effects were remarkably large in the low frequency range that is important from the practical point-of- view of breakage of satellite components.

Lightweight composite structures in the forewings of beetles

In order to develop lightweight biomimetics composite structures, research was done on the structural characteristics of the forewings of two beetles, Allomyrina dichotoma and Prosopocoilus inclinatus, with these characteristics to be further expounded upon. The structural models of both forewings and trabeculae were also established. As a result, (1) the beetle forewing is of a sandwich plate structure with the central void layer of trabeculae and this is one of typical lightweight composite structures. The forewing of A. dichotoma is of an economic design, while the forewing of P. inclinatus is of a more durable design; (2) the chitin fibers in trabeculae connect continuously in a curvular shape to the chitin fibers on the upper and lower laminations, and it is clear that this structure greatly increases resistance against peeling for laminated composite structures.

Use of the finite strip method in predicting the behaviour of composite laminated structures

A description is given of the use of the finite strip method (FSM) in determining the behaviour of composite laminated, prismatic plate and shell structures, with emphasis placed on relatively recent work conducted at The University of Birmingham. Both the semi-analytical and the spline variants of the method are described, and some attention is also paid to “exact” strips. Consideration is given to analyses conducted in the contexts of first-order shear deformation theory and of classical, or thin, theory. The calculation of buckling stresses and natural frequencies of vibration is discussed in detail for single span structures and then, using the spline finite strip approach with variable knot spacings, for multi-span structures and stepped structures. An account is given of the use of the FSM in predicting the post-buckling response of plate structures to progressive end-shortening strain. Brief description is given of the use of the method in predicting the thermal buckling and the transient response to dynamic loading of flat plates. Finally, the calculation of buckling stresses and natural frequencies of sandwich plate structures is considered, based on the adoption of a three-zone plate theory. Numerous examples of the application of the FSM are included in the paper.

The Galerkin element method applied to the vibration of rectangular damped sandwich plates

The Galerkin element method (GEM), which combines Galerkin orthogonal functions with the traditional finite element formulation, has previously been applied successfully to the vibration analysis of damped sandwich beams, and an improved iteration method was developed for its eigen solution. In the current paper, this promising method is extended to the vibration of damped sandwich plates. A quite different model is formulated which has both nodal coordinates and edge coordinates, while in the case of beams, there are only nodal coordinates. Displacement compatibility over the interfaces between the damping layer and the elastic layers is taken account of in order to ensure a conforming element and thereby guarantee good accuracy. The seed matrix method is proposed for simplifying the building of the element mass, stiffness and damping matrices. Numerical examples show that the application of the GEM to sandwich plate structures is computationally very efficient, while providing accurate estimates of natural frequencies and modal damping over a wide frequency range.

Integral finite element method for dynamical analysis of elastic–viscoelastic composite structures

Four types of integral finite elements have been developed and used to estimate the dynamical characteristics of elastic–viscoelastic composite structures, namely sandwich beam, plate and shell structures with viscoelastic materials as core layers. The results of the integral finite element prediction are compared with those from the direct frequency response method and experiment, showing that the numerical stability, convergence and accuracy of the integral finite elements are satisfactory in terms of engineering applications.

Sound radiation from a line forced perforated elastic sandwich panel

Composite barriers, consisting of thin plates separated by light matrix structures, are widely used for fuselage construction in the aircraft industry, and in partitions in the building trade. The acoustical properties of such materials can vary considerably by altering the interior geometry, and perforations can be added to one or both sides. With perforations the interior cavities can act as Helmholtz resonators, causing a substantial modification to the overall transmission and reflection properties of such barriers. Leppington [Proc. R. Soc. London, Ser. A 427, 385–399 (1990)] devised an effective boundary condition for a perforated sandwich plate structure, valid in the limit of low frequency (acoustical waves long compared with the typical dimensions of the hole/cavity construction), and obtained transmission and reflection coefficients for infinite planar structures. This article investigates the radiation properties of perforated sandwich plates by examining a simple infinite one-dimensional model (employing Leppington’s effective boundary condition) which is loaded by a line force or moment. The radiated far field, and unattenuated subsonic plate wave coefficients, are found explicitly, and are plotted over a range of frequencies for two physical configurations, namely an aluminum plate in water and in air. It is revealed that, unlike the usual thin plate equation, the model discussed herein has two bi-directional unattenuated plate waves, and for the structure in air the two waves are of similar magnitude over most frequencies. Surprisingly, these amplitudes are shown to become very large at a frequency below that of the structure’s Helmholtz resonance frequency. Further, the field radiating into air is also significantly modified by the cavity/perforations well away from the Helmholtz frequency.

Identification of composite material parameters of plates using vibration test data

Two methods for identifying the material parameters of laminated plates are presented, differing with respect to the type of residual vectors to be minimized. Both methods used eigenvalue residuals. In addition either weighted eigenequation residuals (method 1) or mode shape residuals (method 2) were used. The finite element model of the plate was assembled from four-noded rectangular elements with four degrees of freedom (DOF) per node. The stiffness matrix was based on Reissner-Mindlin plate theory which includes shear deformation effects. An approximate two step condensation procedure was used, instead of the dynamic condensation which is normally used in the first identification method for the large order problem. The two methods were applied to free-free composite sandwich beam and plate structures using simulated and real modal test data.

Finite element analysis of sandwich plates: An overview

Many finite element models have been proposed for the analysis of sandwich plates. In general, these elements can be classified into two broad streams. The first is based on the assumed displacement approach, and the second on the assumed-stress hybrid approach. Within each stream, the characteristics of the elements vary greatly in terms of the formulation complexity, accuracy and applicability. An overview is given of the state-of-the-art finite element analysis applied to sandwich plate structures.

Rectangular hybrid elements for the analysis of sandwich plate structures

The structural behaviour of sandwich plate structures are characterized by transverse shear deformations in the core. The assumed stress hybrid finite element technique is particularly suitable for developing sandwich plate bending elements. In the present study, rectangular three-layer sandwich plate elements have been formulated using simple assumed stress functions. Numerical test problems have been solved to examine the convergence property and suitability of these elements. The results are compared with that of a complete quadratic stress mode element and with analytical solutions. Six degrees of freedom per node shell elements are formulated by combining the plate bending elements with membrane elements. A folded plate sandwich panel roof has been analyzed using these elements and the results are compared with the experimental values. The use of simple stress function gives satisfactory results and reduces the size of the matrices to be used, the length of the program, and the computation time for the formulation of element stiffness matrices. Key words: sandwich panel, structural analysis, finite element method, stress hybrid approach, folded plates.