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Showing papers on "Sandwich panel published in 2008"


Journal ArticleDOI
TL;DR: In this paper, an air blast simulation code was used to determine the blast loads at the front surfaces of the test panels, and these were used as inputs to finite element calculations of the dynamic response of the sandwich structure.

359 citations


Journal ArticleDOI
TL;DR: In this article, a wave/finite element (WFE) method is described by which the dispersion relations for a two-dimensional structural component can be predicted from a finite element (FE) model.

306 citations


Journal ArticleDOI
TL;DR: In this article, a large number of experiments have been conducted to investigate the structural response of sandwich panels loaded by blasts, and the experimental results are reported and discussed in this paper.

215 citations


Journal ArticleDOI
TL;DR: In this article, a self-healing sandwich panel was designed and manufactured, which consists of vascular networks carrying the two liquid components of an epoxy resin system, and tested in edgewise compression-after-impact to prove the concept.

158 citations


Journal ArticleDOI
TL;DR: In this paper, an investigation into whether incremental sheet forming (ISF) would be mechanically feasible alternative means to form sandwich panels is presented, which is shown that ISF can be applied to sandwich panels which have ductile and largely incompressible cores.

141 citations


Journal ArticleDOI
TL;DR: In this paper, the structure and mechanical properties of honeycomb sandwich panels are introduced and the satisfying weight condition of the honeycomb core weight is 50-66.7% of the weight of the whole honeycomb composite panels by theoretical analysis.

122 citations


Journal ArticleDOI
TL;DR: In this article, a preliminary study has been conducted to investigate the ballistic behavior of a model lattice and to explore the effect of filling the lattices void spaces with polymers and ceramics.
Abstract: Sandwich panels with lattice cores have attracted significant interest as multifunctional structures. The lattices consist of 3D repeating unit cells constructed from plates or trusses oriented to efficiently support applied stresses. These systems show promise for supporting structural loads and mitigating the blast effects of explosions. Here, a preliminary study has been conducted to investigate the ballistic behavior of a model lattice and to explore the effect of filling the lattices void spaces with polymers and ceramics. A sheet folding and brazing method has been used to fabricate pyramidal lattice truss structures from 304 stainless steel. The impact response of the various panels was assessed after impact by spherical, 12 mm diameter, 6.9 g projectiles with an incident, zero obliquity velocity of ∼600 m/s. Empty lattice sandwich panels with an areal density of 27.7 kg m−2 do not prevent the perforation of the sandwich panel. The impact with proximal face sheet reduced the projectile velocity to ∼450 m/s (by about 25%). Interactions with the lattice trusses and the distal face sheet further slowed the projectile resulting in an exit velocity at the distal face sheet of ∼360 m/s. The projectiles energy was dissipated by face sheet plastic dishing and fracture by petaling, and by truss plastic deformation. Infiltration of the lattice with polyurethane elastomers further reduced the projectile exit velocity. The strength of the effect depended upon the modulus of the polymer (and therefore its glass transition temperature, Tg). Only high modulus (high Tg) elastomers fully arrested the projectile. The energy of the projectile in this case was dissipated by a combination of face sheet stretching and polymer deformation and fracture. Low modulus elastomers reduced the projectile exit velocity by about 45% (to ∼250 m/s) and also resulted in resealing of the projectile path within the sandwich panel core. The incorporation of ballistic fabric within the polymer infiltrated systems had little effect on the ballistic resistance. A hybrid sample containing metal encased Al2O3 prism inserts provided the greatest resistance to penetration. In this case the projectiles were arrested within a sphere diameter of the sample front surface. Several of these hybrid systems offer promise as multifunctional, ballistic resistant, load-bearing structures.

91 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental investigation into the response of square sandwich panels with an aluminium foam core under blast loading is presented, followed by a corresponding FE simulation using LS-DYNA.
Abstract: This paper first presents an experimental investigation into the response of square sandwich panels with an aluminium foam core under blast loading, followed by a corresponding FE simulation using LS-DYNA. In the simulation, the loading process of explosive and response of the sandwich panels have been investigated. The blast loading process includes both the explosion procedure of the charge and interaction with the panel. The simulation result shows that the deformation/failure patterns observed in the tests are well captured by the numerical model, and quantitatively a reasonable agreement has been obtained between the simulation and experiment. Finally, a parametric study has been carried out to investigate the energy absorption performance of sandwich panels.

86 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe the results of an experimental investigation on the low-velocity impact response of four different types of sandwich structures considered as the structural materials of the Korean low floor bus.

86 citations


Journal ArticleDOI
TL;DR: In this paper, a multifunctional heat pipe sandwich panel combining efficient structural load support and thermal management characteristics has been designed and experimentally assessed, which is based upon a truncated, square honeycomb sandwich structure.

82 citations


Journal ArticleDOI
TL;DR: In this paper, the responses of metallic plates and sandwich panels to localized impulse were examined by using a dynamic plate test protocol supported by simulations. Butler et al. found that the honeycomb panel is superior to a solid plate when subjected to a planar impulse, but inferior when localized.
Abstract: The responses of metallic plates and sandwich panels to localized impulse are examined by using a dynamic plate test protocol supported by simulations. The fidelity of the simulation approach is assessed by comparing predictions of the deformations of a strong-honeycomb-core panel with measurements. The response is interpreted by comparing and contrasting the deformations with those experienced by the same sandwich panel (and an equivalent solid plate) subjected to a planar impulse. Comparisons based on the center point displacement reveal the following paradox. The honeycomb panel is superior to a solid plate when subjected to a planar impulse, but inferior when localized. The insights gained from an interpretation of these results are used to demonstrate that a new design with a doubly-corrugated soft core outperforms solid plates both for planar and localized impulses.

Journal ArticleDOI
TL;DR: In this article, a new empirical Ballistic Limit Equation (BLE) was derived from an existing Whipple-shield BLE, which provided a good level of accuracy in predicting the ballistic performance of stand-alone sandwich panels.

Journal ArticleDOI
TL;DR: In this paper, the stiffness and strength of 6061-T6 aluminum tetrahedral lattice structures are shown to be comparable to those of conventional 5052-H38 aluminum closed cell hexagonal honeycombs and more than 40% stiffer and stronger than flexible honeycombbs used for the cores of curved sandwich panels.
Abstract: Age hardenable 6061 aluminum tetrahedral lattice truss core sandwich panels have been fabricated by folding perforated sheets to form highly flexible cellular cores Flat or curved sandwich panels can be fabricated by furnace brazing the cores to facesheets Flat sandwich panels with core relative densities between 2 and 10% have been fabricated and tested in the σ ±13 shear orientation (minimum shear strength orientation for a tetrahedral lattice) in the fully annealed (O) and aged (T6) conditions The shear strength of the lattices increased with relative density, parent alloy yield strength and work hardening rate Analytical stiffness and strength predictions agree well with measured values for all relative densities and parent alloy heat treatments investigated The stiffness and strength of 6061-T6 aluminum tetrahedral lattice structures are shown to be comparable to those of conventional 5052-H38 aluminum closed cell hexagonal honeycombs and more than 40% stiffer and stronger than flexible honeycombs used for the cores of curved sandwich panels

Journal ArticleDOI
TL;DR: In this paper, the authors presented the geometrical non-linear response of unidirectional sandwich panels with a soft core subjected to thermally induced deformation type of loading, which may be fully distributed or localized.
Abstract: The paper presents the geometrical non-linear response of unidirectional sandwich panels with a “soft” core subjected to thermally induced deformation type of loading, which may be fully distributed or localized. The mathematical formulation incorporates the effects of the flexibility of the core in the vertical direction as well as the effects of the temperature dependent mechanical properties of the constituent materials on the non-linear behavior. The non-linear governing equations are derived using a variational approach following the approach of the high-order sandwich panel theory (HSAPT). The features of the non-linear response are presented through a numerical study that discusses the effects of localized reinforced cores and the mismatch of the coefficients of thermal expansion of the constituent core materials; the effects of continuous panels in the presence of immovable supports; the effects of localized thermal loading with temperature dependent material properties and, finally, the interaction of mechanical and thermal loading on the response with and without immovable supports and temperature dependent material properties. An important conclusion of the study is that the interaction between mechanical loads, temperature induced deformations, and degradation of the mechanical properties due to elevated temperatures, may seriously affect the structural integrity.

Journal ArticleDOI
TL;DR: In this article, the authors compared the Fourier-Galerkin method, the higher-order theory, and the finite element analysis for one-dimensional sandwich panels with functionally graded core.
Abstract: This study investigates several available sandwich beam theories for their suitability of application to one-dimensional sandwich plates with functionally graded core. Two equivalent single-layer theories based on assumed displacements, a higher-order theory, and the Fourier-Galerkin method are compared. The results are also compared with the finite element analysis. The core of the sandwich panel is functionally graded such that the density, and hence its stiffness, vary through the thickness. The variation of core Young's modulus is represented by a differentiable function in the thickness coordinate, but the Poisson's ratio is kept constant. A very good agreement is found among the Fourier-Galerkin method, the higher-order theory, and the finite element analysis.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the nonlinear dynamic response of a shallow sandwich shell subject to blast loading with consideration of core compressibility and proposed a new nonlinear compressible core model by means of Hamilton's principle in combination with the Reissner-Hellinger variational principle.
Abstract: This paper investigates the nonlinear dynamic response of a shallow sandwich shell subject to blast loading with consideration of core compressibility. The shallow shell consists of two laminated composite or metallic face sheets and an orthotropic compressible core. Experimental results and finite element simulations in literature have shown that the core exhibits considerable compressibility when a sandwich panel is subjected to impulse loading. To address this issue properly in the analysis, a new nonlinear compressible core model is proposed in the current work. The system of governing equations is derived by means of Hamilton's principle in combination with the Reissner-Hellinger's variational principle. The analytical solution for the simply supported shallow shell is formulated using an extended Galerkin procedure combined with the Laplace transform. Numerical results are presented. These results demonstrate that this advanced sandwich model can capture the transient responses such as the stress shock wave effect and the differences in the transient behaviors of the face sheets and the core when a sandwich shadow shell is subjected to a blast loading. However, in the steady state dynamic stage, all the displacements of the face sheets and the core tend to be identical. This model can be further used to study the energy absorption ability of the core and the effects of different material and geometrical parameters on the behaviors of sandwich structures subject to blast loading.

Journal ArticleDOI
TL;DR: In this paper, a full-scale dynamic test of a single storey building constructed on a shaking table by a prefabricated 3D sandwich panel method is carried out under several ground motions.

Journal ArticleDOI
TL;DR: In this article, the theoretical modal properties of the sandwich panel can be predicted from the stiffness and damping properties of its constituent components using the basic laminate theory, a first-order shear deformation theory and a simple discretization method.
Abstract: Currently, there is incomplete knowledge of the damping level and its sources in satellite structures and a suitable method to model it constitutes a necessary step for reliable dynamic predictions. As a first step of a damping characterization, the damping of honeycomb structural panels, which is identified as a main contributor to global damping, has been considered by ALCATEL SPACE. In this work, the inherent vibration damping mechanism in sandwich panels, including those with both aluminium and carbon fibre-reinforced plastic (CFRP) skins, is considered. It is first shown how the theoretical modal properties of the sandwich panel can be predicted from the stiffness and damping properties of its constituent components using the basic laminate theory, a first-order shear deformation theory and a simple discretization method. Next, a finite-element transcription of this approach is presented. It is shown to what extent this method can be implemented using a finite-element software package to predict the overall damping value of a sandwich honeycomb panel for each specific mode. Few of the many theoretical models used to predict natural frequencies of plates are supported by experimental data and even fewer for damping values. Therefore, in a second, experimental part, the Rayleigh–Ritz method and NASTRAN (finite-element software used by ALCATEL SPACE) predicted modal characteristics (frequency and damping) are compared with the experimentally obtained values for two specimens of typical aluminium core honeycomb panels (aluminium and CFRP skins) used by ALCATEL SPACE as structural panels. It is shown through these results that the method (theoretical and finite element) is satisfactory and promising.

Journal ArticleDOI
TL;DR: In this article, the authors derived the nonlinear governing equations of the prebuckling and postbuckling states of a unidirectional sandwich panel with a soft core using a variational approach following the principles of the high-order sandwich panel theory.
Abstract: This paper deals with thermally induced deformation buckling and postbuckling of a unidirectional sandwich panel with a soft core. The mathematical formulation is based on the high-order sandwich-panel approach and it incorporates the effects of the flexibility of the core in the vertical direction, along with its expansion or contraction in the vertical direction as a result of the imposed thermal field. The nonlinear governing equations are derived using a variational approach following the principles of the high-order sandwich-panel theory. The governing equations of the prebuckling and buckling states are determined through linearization following a perturbation approach. The effects of the vertical thermal core normal strains of the core, which are usually ignored by various computational models, are studied at the buckling and the postbuckling stages, with emphasis on the differences in the mechanical behavior. A comparison with results obtained using a classical elastic foundation approach is conducted, and the differences are presented and discussed. The postbuckling behavior of thermally loaded sandwich panels in the vicinity of the temperatures that cause buckling, based on a simplified model, is presented through numerical examples involving a uniform temperature field, along with finite element results using ANSYS that compare very well. In addition, the results for a gradient thermal field are described. The results are presented through various structural quantities along the panel and through equilibrium path curves of temperature vs extreme values of these structural quantities. An important conclusion of the study is that the postbuckling behavior of a heated sandwich panel with a soft core is of a stable type for the cases investigated (i.e., that of a plate rather than of a column or a shell).

Journal ArticleDOI
TL;DR: In this article, a static analysis of sandwich panels with a square honeycomb core is performed using the finite element approach applied to the plate theories, and the constitutive behavior of an equivalent continuum to the core is obtained using the strain energy approach.
Abstract: Static analysis of sandwich panels with a square honeycomb core is performed using the finite element approach applied to the plate theories. The constitutive behavior of an equivalent continuum to the core is obtained using the strain energy approach. The displacement field of the sandwich panel modeled using the equivalent continuum is then compared with results obtained from a highly detailed finite element method created in ABAQUS. The comparison shows the results of the higher-order shear deformation theory in error of 7.6% compared with the detailed model results. An equivalent single layer finite element method for the sandwich panel was then created in ABAQUS and the displacement results of this equivalent single layer model are compared with those obtained from the detailed finite element method. This comparison reveals an error of 6.1% in the results between the two models. A comparison between the equivalent single layer model and the highly detailed model is presented for different core relative densities at two locations of the sandwich panel. A detailed finite element method analysis of the unit cell of the square honeycomb was next performed using ABAQUS and the flexibility approach. Comparison between the equivalent strain energy approach and flexibility approach applied to detailed ABAQUS models of the unit cell proved the equivalent strain energy approach to be efficient.

Patent
15 Aug 2008
TL;DR: In this article, a combination of composite sandwich topology concepts with hard, strong materials to provide structures that efficiently support static and fatigue loads, mitigate the blast pressure transmitted to a system that they protect, and minimizes shock (stress wave) propagation within the multi-layered armor sandwich structure.
Abstract: The armor system according to the present invention also exploits synergistic multi-layering to provide different properties as a function of depth within a sandwich panel Various embodiments of the invention include a combination of composite sandwich topology concepts with hard, strong materials to provide structures that (i) efficiently support static and fatigue loads, (ii) mitigate the blast pressure transmitted to a system that they protect, (iii) provides very effective resistance to projectile penetration, and (iv) minimizes shock (stress wave) propagation within the multi-layered armor sandwich structure By using small pieces of highly constrained ceramic, the concept has significant multi-hit potential

Journal ArticleDOI
01 Jan 2008
TL;DR: In this article, a multi-functional structure based on the secondary power system is proposed to save mass from a spacecraft by incorporating other functional subsystems into the structure, and the feasibility of the proposed multifunction structure is demonstrated though vibration testing on a single cell and successful manufacture of a test panel.
Abstract: A multi-functional structure saves mass from a spacecraft by incorporating other functional subsystems into the structure. By using the structural properties of a non-structural element, inert structure may be eliminated, and the requirement to allot internal volume to the subsystem in question is removed. The current paper describes a multi-functional structure based on the secondary power system. By using commercially available plastic lithium-ion cells to form the core of a sandwich panel, inert mass is eliminated from both the structure and from the battery enclosure. The feasibility of the proposed multi-functional structure is demonstrated though vibration testing on a single cell, and the successful manufacture of a test panel. The work goes on to quantify the potential mass savings that may be achieved by using a multi-functional structure of this type. By varying a set of spacecraft attributes, the study identifies that small spacecraft with high power requirements have the potential to gain the most benefit from using a multi-functional structure of this type. © IMechE 2008.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new zone width equation for use in the current zone method to compute the R-value of precast concrete sandwich panels containing the metal wythe connectors.
Abstract: Metal wythe connectors are used in a typical precast concrete sandwich panel to tie concrete wythes together and to keep the panel intact during handling and in service. Connectors interrupt the continuous insulation layer, reducing the effectiveness of the insulation. In current practice, thermal resistance (R-value) of such a panel is calculated from the zone method. However, the zone width parameter W used in the zone method was originally developed for metal-frame structures and an accurate R-value cannot be estimated for precast concrete sandwich panels containing metal wythe connectors. This paper proposes a new zone-width equation for use in the current zone method to compute the R-value of precast concrete sandwich panels containing the metal wythe connectors. The proposed zone width W n was derived from the results of a series of finite element heat-transfer analyses intended to quantify the influence of several key parameters on W n . It was found that the zone method with the proposed zone-width equation can accurately estimate R-value of a precast concrete sandwich panel containing metal wythe connectors. Also the proposed zone-width equation can effectively consider the effects of metal wythe connector sizes and spacing, material conductivities, and panel thicknesses in the zone method of R-value computation.

Patent
Christian Thomas1, Ralph Gerstner1
17 Dec 2008
TL;DR: An aircraft cabin panel for sound absorption, with a sandwich construction, comprising a core layer that comprises a plurality of tube-like or honeycomb-like cells that extend in an open manner across the thickness of the core layer and that are separated from each other by cell walls, is described in this paper.
Abstract: An aircraft cabin panel for sound absorption, with a sandwich construction, comprising a core layer that comprises a plurality of tube-like or honeycomb-like cells that extend in an open manner across the thickness of the core layer and that are separated from each other by cell walls and that are uniform in design. A first cover layer faces away from the sound field, as well as a second cover layer that faces towards the sound field and that comprises a plurality of perforation holes and adjacent cells are interconnected by way of apertures in the cell walls. The perforation of the second cover layer comprises a distance (b) between holes, which distance exceeds the opening width (c) of the cells of the core layer, wherein the first cover layer is closed and wherein the cell walls comprise a perforation so that they are acoustically transparent in the direction parallel to the cover layers.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the transmission of sound through all-metallic sandwich panels with corrugated cores using the space-harmonic method and found that the inclination angle has a significant effect on sound transmission loss.
Abstract: The transmission of sound through all-metallic sandwich panels with corrugated cores is investigated using the space-harmonic method. The sandwich panel is modeled as two parallel panels connected by uniformly distributed translational springs and rotational springs, with the mass of the core sheets taken as lumped mass. Based on the periodicity of the panel structure, a unit cell model is developed to provide the effective translational and rotational stiffness of the core. The model is used to investigate the influence of sound incidence angle and the inclination angle between facesheet and core sheet on the sound transmission loss (STL) of the sandwich structure. The results show that the inclination angle has a significant effect on STL, and sandwich panels with corrugated cores are more suitable for the insulation of sound having small incidence angle.

Proceedings ArticleDOI
07 Apr 2008
TL;DR: In this article, the authors used finite element analyses to construct response surface approximations (RSA) of the critical constraints, including maximum bottom facesheet temperature, maximum deflection, maximum stresses and buckling loads.
Abstract: For space vehicles traveling at hypersonic speeds through a planetary atmosphere, the aerodynamic forces may result in high aerodynamic heating. A Thermal Protection System (TPS) protects the vehicle structure from damage due to this heating. TPS occupies a large acreage on vehicle exteriors and accounts for a significant part of the launch weight. One potential way of saving weight is to have a load-bearing TPS that performs some structural functions. One such concept called the Integrated Thermal Protection System (ITPS) is a corrugated-core sandwich structure. A previous study on this corrugated core sandwich panel developed an optimization procedure for finding the optimal geometry leading to low mass design. The procedure used finite element analyses to construct response surface approximations (RSA) of the critical constraints, including maximum bottom facesheet temperature, maximum deflection, maximum stresses and buckling loads. The RSAs obtained are of high fidelity, however they require too much computational time. In parallel, an analytical model of the ITPS was developed based on homogenization of the panel for calculating displacements and stresses. This model, though relatively inexpensive, is not accurate enough for design optimization. In the present paper we combine the two models into a multi-fidelity model, which can be used for the design optimization of the ITPS panel. We fit the low fidelity analytical model with a high quality surrogate, which is then corrected by the use of a small number of high fidelity finite element analyses. Fitting the difference or the ratio between the high fidelity analyses and the low fidelity surrogate with a response surface approximation allows constructing a so-called correction response surface. The approach is known as multi-fidelity or variable-complexity modeling, and usually allows using significantly fewer high fidelity analyses for given accuracy.

Journal ArticleDOI
TL;DR: In this article, a multi-layer piezoelectric actuator (MPA) was used for active vibration control of a cantilever honeycomb sandwich panel (CHSP).

Journal ArticleDOI
TL;DR: In this article, a multi-layer piezoelectric actuator (MPA) was developed and used to control the vibration of honeycomb sandwich panel (HSP).

Journal ArticleDOI
TL;DR: In this paper, the authors presented the solution of symmetrical face sheet wrinkling problem for sandwich panel with composite facings and an orthotropic core, which takes into account compressive and shear stiffnesses as well as nonlinear change of transverse displacement over the core thickness at wrinkling.
Abstract: The article presents the solution of symmetrical face sheet wrinkling problem for sandwich panel with composite facings and an orthotropic core. The new model is proposed for elastic core that takes into account compressive and shear stiffnesses as well as nonlinear change of transverse displacement over the core thickness at wrinkling. The governing buckling equation is derived using energy method. Analysis of cylindrical face wrinkling is performed for sandwich strips subjected to compressive loads applied to the two opposite simply supported edges. The effects of elastic and geometric parameters on the critical buckling stresses and wrinkling waves' formation are examined.

Dissertation
01 Jan 2008
TL;DR: In this paper, the authors present a solution to the brittleness of the composites in tubular form and introduce a composite tube that shows the same strength, stiffness and failure strain as its high grade Aluminum 7075-T6 counterpart tube.
Abstract: Composites have proved their great potentials for many aerospace applications, where the high performance can justify the high cost. However, the brittleness of the composites has been a main drawback for many applications that require large deformation, high failure strain and extensive energy absorption before final fracture. The objective of this research is to present a solution to the brittleness of the composites in tubular form and to introduce a composite tube that shows the same strength, stiffness and failure strain as its high grade Aluminum 7075-T6 counterpart tube. One application of this research can be in the development of composite landing gear for helicopters. Up to date, almost all helicopter landing gears are made of high strength aluminum, and despite their major issues in maintenance and fabrication, aluminum landing gears have remained the only choice for the helicopter manufacturing industry. Substitution of aluminum landing gear for helicopters with a thermoplastic composite landing gear is really a challenge, but if this can be done, it would be for the first time in the world! Through this research, the mechanical behavior of flat plate Carbon AS4/PEKK is characterized, and the potential mechanisms for large deformation of composite laminates are sought. The outcomes are used to design a composite tube that shows the same strength, stiffness and deformability as its high grade aluminum counterpart. The accuracy of the design is verified through progressive failure by ANSYS analysis and experimental work. Strain Controlled Design is introduced as a new design technique to substitute for the traditional stiffness-controlled techniques whenever large deformation from composite laminates is expected. The analytical techniques for stress analysis of composite tubes are reviewed, and the cumbersomeness of the method is highlighted. Finally, a simplified technique is presented to analyze composite tubes as a sandwich panel model. The results of the analysis are compared with the ANSYS and experimental results. Agreement between three methods is demonstrated. Moreover, guidelines for the design of composite tubes that exhibit large deformation before failure are presented