Showing papers on "Sandwich panel published in 2006"

Multifunctional periodic cellular metals

Abstract: Periodic cellular metals with honeycomb and corrugated topologies are widely used for the cores of light weight sandwich panel structures. Honeycombs have closed cell pores and are well suited for thermal protection while also providing efficient load support. Corrugated core structures provide less efficient and highly anisotropic load support, but enable cross flow heat exchange opportunities because their pores are continuous in one direction. Recent advances in topology design and fabrication have led to the emergence of lattice truss structures with open cell structures. These three classes of periodic cellular metals can now be fabricated from a wide variety of structural alloys. Many topologies are found to provide adequate stiffness and strength for structural load support when configured as the cores of sandwich panels. Sandwich panels with core relative densities of 2-10% and cell sizes in the millimetre range are being assessed for use as multifunctional structures. The open, three-dimensional interconnected pore networks of lattice truss topologies provide opportunities for simultaneously supporting high stresses while also enabling cross flow heat exchange. These highly compressible structures also provide opportunities for the mitigation of high intensity dynamic loads created by impacts and shock waves in air or water. By filling the voids with polymers and hard ceramics, these structures have also been found to offer significant resistance to penetration by projectiles.

Thermal insulation properties of wood-based sandwich panel for use as structural insulated walls and floors

Abstract: Thermal insulation and warmth-keeping properties of thick plywood-faced sandwich panels with low-density fiberboard (plywood-faced sandwich, PSW), which were developed as wood-based structural insulation materials for walls and floors, are comprehensively clarified. The properties focused on were thermal conductivity (λ), thermal resistance (R), and thermal diffusivity (D). The results for PSW panels were compared with those for commercial wood-based boards, solid wood, and commercial insulators. The λ values were measured for PSW panels and their core and face elements. As a result, the composite theory of λ was found to be appropriate for PSW composites, because the calculated/experimental λ ratios were approximately 90%. The λ values for PSW panels with densities of 340 kg/m3 (PSW350) and 410kg/m3 (PSW400) were 0.070 and 0.077W/mK, respectively. The R values for PSW350 and PSW400 were 1.4 and 1.2m2K/W, and the D values were 0.00050 and 0.00046m2/h, respectively. Consequently, the PSW provided thermal insulation properties superior to those of the boards and in terms of warmth-keeping properties were greatly advantageous over the insulators. These advantages were due to the moderate densities of PSW panels. The PSW panel with sufficient thickness showed remarkably improved thermal resistance compared with those of the boards.

Use of Inorganic Polymer to Improve the Fire Response of Balsa Sandwich Structures

Abstract: The study presented in this paper deals with the fire performance of balsa sandwich panels made using inorganic Geopolymer resin and high-strength fiber facings. A thin layer of a fire-resistant paste composed of Geopolymer and hollow glass microspheres was applied to the facings to serve as a protective fire barrier and to improve the fire resistance of the sandwich panels. Using 17 sandwich panel specimens, the primary objective of this program was to establish the minimum amount of fireproofing necessary to satisfy the Federal Aviation Administration (FAA) requirements for heat and smoke release. The influence of this fireproofing insulation on the increase in mass of the panels was also evaluated. The system is simple and inexpensive to manufacture, and a 1.8-mm-thick layer of fireproofing satisfies the FAA requirements for both heat release and smoke emission.

Study on the Collapse of Pin-Reinforced Foam Sandwich Panel Cores

Abstract: New fabrication technologies now allow for hybrid sandwich structures, known as X-core, to be manufactured. The X-core panels consist of a pin reinforced polymer foam core with carbon fiber face sheets. Carbon fiber or metallic (Titanium/Steel) pins are inserted into the foam core in the out-of-plane direction and extend from face sheet to face sheet. The through thickness three-point simply supported bending behavior of these panels is used to evaluate the collapse characteristics of the panels. Explicit experimental observations are used to calibrate analytical energy balance models describing the panel collapse as a function of geometry and properties. The mechanical response of X-core sandwich panels is compared to current sandwich materials for material selection.

Response of a Sandwich Panel Subject to Fire or Elevated Temperature on One of the Surfaces

Abstract: The paper presents the analysis of deformations and stresses in a large aspect ratio sandwich panel subject to fire or another source of elevated temperature. The panel, assumed to bend into a cylindrical surface, is simply supported at the edges. The edges are also prevented from in-plane displacements providing an elastic restraint as the panel stretches due to bending. The solution is obtained in a closed form when the deformations are small and when geometrically nonlinear effects are incorporated into the analysis. The solution is open to modification with arbitrary temperature and property distributions through the thickness of the panel, enabling a designer to incorporate the results from a multitude of heat transfer scenarios so long as the structural problem can be treated as quasi-static.

A triangular plate element for thermo‐elastic analysis of sandwich panels with a functionally graded core

Abstract: A sandwich construction is commonly composed of a single soft isotropic core with relatively stiff orthotropic face sheets. The stiffness of the core may be functionally graded through the thickness in order to reduce the interfacial shear stresses. In analysing sandwich panels with a functionally gradient core, the three-dimensional conventional finite elements or elements based on the layerwise (zig-zag) theory can be used. Although these elements accurately model a sandwich panel, they are computationally costly when the core is modelled as composed of several layers due to its grading material properties. An alternative to these elements is an element based on a single-layer plate theory in which the weighted-average field variables capture the panel deformation in the thickness direction. This study presents a new triangular finite element based on (3, 2}-order single-layer theory for modelling thick sandwich panels with or without a functionally graded core subjected to thermomechanical loading. A hybrid energy functional is employed in the derivation of the element because of a C 1 interelement continuity requirement. The variations of temperature and distributed loading acting on the top and bottom surfaces are non-uniform. The temperature also varies arbitrarily through the thickness.

Strength and stiffness optimization studies on honeycomb core sandwich panels

Abstract: The optimization of strength and stiffness properties of sandwich panels is a critical area of study in the effective design of sandwich panels in view of their potentialities in weight critical applications. G. R. Froud in his article aptly named 'Your sandwich order, Sir' (Froud, G. R. (1980). Your Sandwich Order, Sir, Composites, 133-138), shows theoretically how a sandwich construction can be optimally designed for a stiffness or a strength criterion. This article has triggered the interest and has prompted the authors, to carry out experimental studies, to verify the applicability of this theory to sandwich panel specimens made out of glass/epoxy skins with honeycomb core. The optimum core to skin weight ratios for maximum stiffness and strength of the sandwich panels are experimentally found to be 2.04 and 0.96 as against the theoretical values of 2.0 and 1.0.

Fabrication of lightweight structural panels through ultrasonic consolidation

Abstract: A fundamental investigation of the feasibility of producing lightweight structural panels using ultrasonic consolidation (UC) was undertaken. As a novel solid freeform fabrication technology, UC utilizes both additive ultrasonic joining and subtractive CNC milling to enable the creation of complex aluminum structures with internal geometry at or near room temperature. A series of experiments were performed to understand the issues associated with sandwich structure fabrication using UC, including peel test experiments which evaluated the bond strength for various geometric configurations. The honeycomb lattice was found to offer the best core configuration due to its ability to resist vibration from the sonotrode and provide adequate support for pressure induced by the sonotrode. UC was found to be capable of producing lightweight and stiff structures, including honeycomb and other sandwich panels, without the use of adhesives. An effective manufacturing process plan for fabricating structural panels was ...

Vibro-acoustic behaviors of flat sandwich composite panels

Abstract: The main objective of this paper is to present a theoretical approach to model the vibro-acoustic behavior of flat sandwich composite panels. Two models are studied: symmetrical laminate composite and sandwich composite panel. The theories are developed in a wave approach context. It is shown that a discrete layers sandwich composite panel modeling type leads to a 12th order relation of dispersion while a laminate composite panel modeling leads to a 6th order relation of dispersion. The two models give similar results at low frequencies but the modeling of a sandwich panel using the laminate panel theory leads to inaccuracies at high frequencies. The dispersion relations are first solved in the context of generalized polynomial complex eigenvalues problems. Next, the dispersion relations are used to derive the analytical expression of the critical frequencies and to calculate the natural frequencies of the panel. Using the dispersion relation’s solutions, the study is then focused on the numerical computa...

Sandwich panel including honeycomb structure body and method of producing the sandwich panel

Abstract: The breadth and width of a sheet-like filler material before it is placed in a cell of a honeycomb material is set greater than those of the honeycomb material, and after the placement, peripheral edges of the honeycomb material are fringed with filler materials to prevent a filler material from falling out of an end section cell. A liquid adhesive agent is applied to the top of cell walls facing one surface of the honeycomb material, and a surface material is pressed to that surface of the honeycomb material to which the adhesive agent is applied. Then, before the adhesive agent hardens, water-absorbing foam materials are placed in cell spaces by pressing them into the cell spaces from the other surface of the honeycomb material until they are in contact with the adhesive agent. The foam material is quickly adhered to the honeycomb material.

Parameter optimization of the dynamic behavior of inhomogeneous multifunctional power structures

Abstract: For next generation microsatellites and nanosatellites, new design approaches will be required to significantly increase their payload to mass fraction. One proposed technology is the multifunctional design concept that incorporates spacecraft subsystems into the load carrying structure. The focus of the research is the multifunctional power structure which replaces conventional battery systems in a spacecraft. An analytical and finite element analysis of ten multifunctional sandwich structures is presented. The out-of-plane material properties are discussed and a parameter optimization of the ten sandwich panels is carried out to optimize their frequency to density ratio. The best configuration for an optimized multifunctional power structure is then identified from the analytical and finite element investigation. The optimized design provides a similar predicted dynamic response as a conventional honeycomb sandwich panel, and can be considered a serious alternative for future spacecraft. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Elastic moduli and stiffness optimization in four-point bending of wood-based sandwich panel for use as structural insulated walls and floors

Abstract: Several wood-based sandwich panels with low-density fiberboard core were developed for structural insulated walls and floors, with different face material, panel thickness, and core density. The elastic moduli with and without shear effect (E L, E 0) and shear modulus (Gb) were evaluated in four-point bending. Generally, the stiffer face, thicker panel, and higher core density were advantageous in flexural and shear rigidity for structural use, but the weight control was critical for insulation. Therefore, optimum designs of some virtual sandwich structures were analyzed for bending stiffness in relation to weight for fixed core densities, considering the manufactured-panel designs. As a result, the plywood-faced sandwich panel with a panel thickness of 95 mm (PSW-T100), with insulation performance that had been previously confirmed, was most advantageous at a panel density of 430 kg/m3, showing the highest flexural rigidity (E L I = 13 × 10−6 GNm2) among these panels, where E L, E 0, and G b were 3.5, 5.5, and 0.038 GN/m2, respectively. The panel was found to be closest to the optimum design, which meant that its core and face thickness were optimum for stiffness with minimum density. The panel also provided enough internal bond strength and an excellent dimensional stability. The panel was the most feasible for structural insulation use with the weight-saving structure.

Analysis of sandwich panels for an energy efficient and self-supporting residential roof

Abstract: The structural and thermal feasibility of a self-supporting sandwich panel for energy efficient residential roof applications is assessed. The assessment is limited to symmetric sandwich panels comprising two face sheets and an insulating core. Feasible panel designs are presented for loading conditions, corresponding to southern and northern climates in the United States. The base case panel is 5.5 m long for a nominal 4.6 m horizontal span and an 8/12 roof pitch. Face sheet materials considered are oriented strand board, steel, and fiber reinforced plastic. Core materials considered are expanded polystyrene, extruded polystyrene, polyurethane, and poly(vinyl-chloride) foams. A wide range of material options meet building code limits on deflection and weight and prevent face sheet fracture and buckling, and core shear failure. Panels are identified that have structural depths similar to conventional wood rafter construction. Shortening the overall panel length provides greater choice in the use of materials and decreases the required panel thickness. Suggestions for improved panel designs address uncertainty in the ability of the plastic core to withstand long term loading over the expected life of residential buildings.

Crushing of a Textile Core Sandwich Panel

Abstract: A class of textile core sandwich structure is investigated with respect to their ability to absorb transverse compressive load. To this end, experimental observations are compared to numerical simulations for cores made from precrimped woven wire cloth laminated together via transient liquid-phase bonding. The experimental observations show that this structure exhibits key properties for being a promising load-absorbing structure, for example, impact and blast protection. Matching numerical simulations show that the behavior can be captured with simulations and that a relatively simplified scheme can be used. The simulations also suggest sensitivity to the local topology in absorbing energy, as well as explaining the somewhat unexpected deformation behavior observed experimentally. Multifunctionality, owing to the accessible open space between cells, coupled with attractive compressive behavior is achieved. Nomenclature d = diameter of the truss (wire diameter) E = Young’s modulus of the material comprising the trusses G c = shear modulus of the truss core R = radius of the truss, d/2 r = radius of the connecting element in the woven structure w = opening width (distance between wires) ¯ ρcore = relative density of the truss core σY = yield strength of the material comprising the trusses σ c Y = compressive strength of the truss core τ c Y = shear strength of the truss core

Response of In-plane Linearly Prestressed Composite Sandwich Panels with Transversely Flexible Core to Low-velocity Impact

Abstract: The problem of transverse low-velocity impact on a linearly in-plane prestressed sandwich panel has been considered in this article. The panel may be subjected to initial in-plane biaxial normal and shear stresses along the edges of the panel. Impact is assumed to occur normally over the top or the bottom face-sheets, at arbitrary location. The boundary conditions of the top and the bottom face-sheets are independent. The interaction between the impactor and the panel is modeled with the help of the system having three-degrees-of-freedom (TDOF) consisting of springs-masses-dashpot (SMD) or springs-masses (SM). The effects of initial biaxial stresses and transverse flexibility of the core are considered analytically. In order to determine all components of the displacements, stresses and strains in the face-sheets and the core, a numerical procedure based on improved higher-order sandwich plate theory (IHSAPT) and Galerkin’s method, are employed. The deflections and the corresponding stresses in the panel ...

Analytical Prediction of Low-velocity Impact Response of Composite Sandwich Panels using New TDOF Spring-mass-damper Model

Abstract: A new equivalent three-degree-of-freedom (TDOF) spring–mass– damper (SMD) model has proposed to predict the low-velocity impact response of composite sandwich panels with transversely flexible core. Impacts are assumed to occur normally over the top face-sheet with the arbitrary different impactor masses and initial velocities. The interaction between the impactor and the panel is modeled with the help of a new proposed system having TDOF consisting of springs, damper, and masses. An analytical procedure that includes the transverse flexibility and structural damping of the core has not yet been dealt with. In the present model, the effects of transverse flexibility of the core and structural damping of the panel are considered analytically. The analysis yields analytic functions describing the history of contact force, displacements of the impactor and the panel in the transverse direction etc. The effects of some physical and geometrical parameters such as initial potential energy of the impactor, the a...