Showing papers on "Sandwich-structured composite published in 2003"
TL;DR: The authors showed that truss and textile cores are superior to honeycombs at low relative densities, because of their superior buckling resistance and lower manufacturing cost as well as their multifunctionality.
725 citations
290 citations
TL;DR: In this paper, the effective properties of corrugated core sandwich panels are investigated, based on the asymptotic expansion method, and an equivalent Reissner-Mindlin homogeneous plate is derived.
211 citations
TL;DR: In this article, stitch-bonded sandwich structures have been developed using commercial close-cellular core and woven broadcloth, using tufting and weft insertion techniques derived from the textile industry.
133 citations
TL;DR: In this article, the performance of metal sandwich panels with textile cores has been analyzed subject to combined bending and shear and then designed for minimum weight, with emphasis on restricted optimizations that assure robustness and acceptable thinness.
120 citations
TL;DR: In this article, it was found that the foam core stabilises the pins against elastic buckling, and the pin-reinforced core has a strength and energy absorption capacity in excess of the individual contributions from the foam and unsupported pins.
119 citations
TL;DR: In this article, a composite front shield for a high speed train made of composite materials was considered, made of glass fiber epoxy face sheets with a polymeric foam core, and a series of static and dynamic impact tests were then run on the sandwich structure.
112 citations
TL;DR: In this article, a fatigue model based on the crack growth was developed and validated with experiments to develop a model for life prediction of foam core sandwich beams in a three-point flexure mode.
102 citations
TL;DR: In this article, the static and fatigue behavior of vacuum-assisted resin transfer molded sandwich panels has been experimentally investigated under flexural loading, and two core materials, D-100 balsa wood and H 250 PVC foam, were used to study the effect of core material on static failure in 3-point and 4-point bending.
100 citations
TL;DR: In this paper, a direct method using a strain energy-based RVE-procedure was proposed for the determination of the effective plate stiffness matrix for composite shells with microheterogeneous layers.
Abstract: The present study is concerned with the numerical determination of the effective plate stiffness matrix for composite shells with microheterogeneous layers. Contrary to the standard two-step procedure, where the effective plate or shell stiffness matrix is derived by a projection of the effective elasticity tensor onto the plate or shell reference surface, a direct method is proposed. This method uses a strain energy based RVE-procedure which assumes mechanical equivalence of a representative volume element for the given microstructure and a corresponding plate element if the strain energy in both elements is equal, provided that the effective deformation is equal in an average sense. In parametric studies concerning sandwich plates with hexagonal honeycomb cores, it is observed that the direct method and the two-step procedure are equivalent for the determination of the in-plane and the transverse shear properties while a significant deviation of the results obtained by both methods is found in case of the effective bending properties.
82 citations
TL;DR: In this paper, an advanced geometrically nonlinear shell theory of doubly curved structural sandwich panels with transversely compressible core is presented, based on the adoption of the Kirchhoff theory for the face sheets and a second/third order power series expansion for the core displacements.
TL;DR: In this article, semi-empirical numerical models are developed for predicting the residual strength of impact-damaged sandwich composites comprised of woven fabric carbon epoxy facesheets and Nomex honeycomb cores subjected to compression-after-impact loading.
TL;DR: In this paper, the damping behavior of a 0° laminated sandwich composite beam inserted with a viscoelastic layer is investigated, and a quantitative analysis of damping in the sandwich laminated composite beam has been conducted through the theoretical method.
TL;DR: In this paper, three variants of a novel steel sandwich sheet material have been studied and the geometrical arrangements of the steel fibres in the core have been characterised, and the beam stiffnesses of the sheets, and also their through-thickness Young's moduli have been measured.
TL;DR: In this paper, the classical and the high-order computational models of unidirectional sandwich panels with incompressible and compressible cores are presented and significant theoretical and practical differences are discussed and elaborated through some numerical examples of typical sandwich panels.
Abstract: The classical and the high-order computational models of unidirectional sandwich panels with incompressible and compressible cores are presented The significant theoretical and practical differences are discussed and elaborated through some numerical examples of typical sandwich panels The classical models considered for the incompressible panel consists of two variants of the well-known splitted rigidity approach The first one, due to Allen and Plantema and many others, assumes that the plane section of the shear substructure takes a specific ‘zigzag’ pattern with no in-plane deformation in the face sheets and a vertical one when the flexural rigidity of the faces is ignored The second model, due to Frostig, assumes that the plane section of the core in the shear substructure remains vertical and the face sheets are subjected to in-plane deformation as well as flexural ones They are compared with the accurate incompressible model, denoted as ordinary sandwich panel theory (OSPT) and with the high-order sandwich panel theory (HSAPT) based on a variational approach In case of a sandwich panel with a compressible core the elastic foundation models based are compared with the high-order one The governing equations and the appropriate boundary conditions of the classical models have been rederived to clarify the ambiguity involved in the definition of the boundary conditions of the various computational models The cases of simply supported panel, cantilevered and a two-span panel are used to demonstrate numerically the differences in the overall response of the panel as well as in the near vicinity of the localized loads and supports
TL;DR: In this article, the tensile bond strength between the facesheet and the core was determined through the flatwise tension test, and fracture toughness of the bond line was measured through the double cantilever beam test.
Patent•
14 Jan 2003
TL;DR: In this paper, the use of interchangeable laminate components in affording the capability of altering the coloring or other visual features of a reveal in a panel or panels is considered, as well as the application of an injection molding technique, such as Reaction Injection Molding, in establishing a foam or polymeric core between laminates in thin composite panels.
Abstract: Thin composite panels with interconnection schemes that are unitized with the panels, i.e., formed integrally and substantially simultaneously with the panels. Further contemplated is the application of an injection molding technique, such as reaction injection molding, in establishing a foam or polymeric core between laminates in thin composite panels. Additionally contemplated is the use of interchangeable laminate components in affording the capability of altering the coloring or other visual features of a reveal in a panel or panels.
TL;DR: In this paper, a theoretical and experimental study of the local effects that occur in the vicinity of intersections between cores of different stiffness in such sandwich panels is presented, and closed-form estimates of the stress/strain fields induced by local effects are presented for sandwich beams and panels loaded in cylindrical bending.
Abstract: Sandwich beams and panels with symmetric faces and cores of varying stiffness are investigated. The paper presents a theoretical and experimental study of the local effects that occur in the vicinity of intersections between cores of different stiffness in such sandwich panels. These local effects manifest themselves by a significant rise of the bending stresses in the faces in the vicinity of the core junctions. Closed-form estimates of the stress/strain fields induced by local effects are presented for sandwich beams and panels loaded in cylindrical bending. The accuracy of the derived closed-form estimates is verified experimentally for the case of a sandwich beam in three-point bending.
TL;DR: In this article, the fracture energy of a thin sandwich sheet was measured at about 340 J m−2, which is consistent with predictions from a model based on shear-lag theory, with a fibre-adhesive interfacial shear strength of about 5 MPa.
TL;DR: In this paper, failure modes and failure criteria for composite sandwich columns and beams were investigated and failure envelopes were developed for general two-dimensional states of stress, including bending moment, shear and axial loading and failure modes.
Abstract: An investigation was conducted of failure modes and criteria for their occurrence in composite sandwich columns and beams. The initiation of the various failure modes depends on the material properties of the constituents (facings and core), geometric dimensions and type of loading. The loading type or condition determines the state of stress throughout the sandwich structure, which controls the location and mode of failure. The appropriate failure criteria at any point of the structure account for the biaxiality or triaxiality of the state of stress. The specimens were made of unidirectional carbon-epoxy facings and aluminum honeycomb and PVC closed-cell foam cores. The constituent materials were fully characterized and, in the case of the foam core, failure envelopes were developed for general two-dimensional states of stress. Sandwich specimens were loaded under bending moment, shear and axial loading and failure modes were observed and compared with analytical predictions. The failure modes investigat...
TL;DR: In this paper, the authors investigated the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations, and the resin infusion time for each method was minimized through simulations.
Abstract: Vacuum-assisted resin transfer molding (VARTM) of sandwich panels can be facilitated by using high permeability layers (HPL) over the skins or adding channels in the surfaces of the core (CIC). The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. A cost model is developed, and the resin infusion time for each method was minimized through simulations. The design parameters are the number of high-permeability layers and the number and size of channels. A penalty function with equal weight on cost and time is used to find the optimum values of the design parameters. Under the conditions studied, the optimal HPL method is found to be better than the optimal CIC method. While the conclusion is limited to the present study, the proposed approach can be used to optimize manufacturing processes for larger sandwich panels under different conditions.
TL;DR: In this article, an analytic model is developed that deals with partition of the energy of absorption, allowing for quantitative estimation of the amount consumed via panel elastic response and the one consumed via irreversible damage.
TL;DR: In this article, the state-of-the-art carbon foams from various manufacturers were evaluated as core material in a sandwich construction, and the results showed that the carbon foam possessed highly anisotropic properties between in-plane and through-thethickness directions.
Abstract: To study suitability of the emerging ultralightweight carbon foams in load-carrying structures, the state-of-the-art carbon foams from various manufacturers were evaluated as core material in a sandwich construction. The carbon foams were firstly characterized by measuring compressive and shear mechanical properties. The carbon foam possessed highly anisotropic properties between in-plane and through-the-thickness directions. The foams aged at 316°C (600°F) for 100 h in air lost 0.6% of their weight and showed little degradation in the properties within the scatter range of test data. The carbon foams tested at an elevated temperature of 316°C (600°F) showed no degradation in the compressive modulus and strength as compared to the properties measured at a room temperature of 21°C (70°F). Sandwich beams with laminated composite facesheets were fabricated with a carbon foam core and tested under static and fatigue four-point bending loads. The beams under the static loadings showed nearly linear elastic beh...
01 Mar 2003
TL;DR: In this article, the impact damage in sandwich composites can be attributed to a number of fairly common discrete sources and may result in drastic reductions in composite strength, elastic moduli, and durability and damage tolerance characteristics.
Abstract: : Sandwich construction composites are used in a wide variety of structural applications largely because of their relative advantages over other designs in terms of improved stability, weight savings, and ease of manufacture and repair. While the design of sandwich structures is at a fairly mature stage of development, less progress has been made in understanding the effect of adverse in-service impact events on structural integrity. Foreign object impact damage in sandwich composites can be attributable to a number of fairly common discrete sources and may result in drastic reductions in composite strength, elastic moduli, and durability and damage tolerance characteristics. In this report, past work is summarized and synthesized to provide guidance for analysis, testing, and nondestructive inspection of impact-damaged composite structures.
Patent•
02 Dec 2003
TL;DR: In this article, a closed-cell foams are used as structural core materials in sandwich composites, which are amenable to vacuum-mediated resin bonding to composite skins to provide lightweight, high-strength structural sandwiches suitable for use in a variety of applications.
Abstract: High-strength, chemically and thermally stable, closed-cell foams, useful as structural core materials in sandwich composites. The core materials of the invention display anisotropic properties. The core materials of the invention are amenable to vacuum-mediated resin bonding to composite skins to provide lightweight, high-strength structural sandwiches suitable for use in a variety of applications, such as marine applications, construction, aviation, rapid transit, and recreational vehicles.
TL;DR: In this paper, a new arrangement of balsa blocks in a sandwich core was developed and numerically analyzed, which allowed the grains in various balsa block to be oriented for example at 45° to the normal of the core.
TL;DR: In this article, the cell wall arrangement of the honeycomb core was addressed in the context of maximizing resistance to either bending, torsion, or combined bending and torsions for given dimensions, face sheet thicknesses and core relative density.
Journal Article•
TL;DR: In this paper, three equivalent methods based on sandwich plate theory, honeycomb plate and equivalent plate theory were derived and analyzed by numerical comparisons, and the results show that all of the three equivalent method discussed in this paper are reliable and practical in the finite element analysis of satellite structures.
Abstract: The honeycomb sandwich panels have been widely used in the satellite structures, and the equivalent elastic constants for the sandwich panels directly influence the accuracy of computational results. Three equivalent methods based on sandwich plate theory, honeycomb plate and equivalent plate theory were derived and analyzed by numerical comparisons. Only the core is equivalent when using the sandwith plate theory while the whole honeycomb sandwich panel is equivalent when using the honeycomb plate and equivalent plate theory. By using the above three equivalent methods the natural frequencies of a honeycomb sandwich panel including two load cases were calculated. The computational results show that all of the three equivalent methods discussed in this paper are reliable and practical in the finite element analysis of satellite structures.
TL;DR: In this article, a multilayered and higher-order deformable finite element is developed for free vibration analysis of multilayer-deformable laminates such as laminated plates with constrained viscoelastic interlayers.
Abstract: In this article, a multilayered and higher-order-deformable finite element is developed for free vibration analysis of multilayer-deformable laminates such as laminated plates with constrained viscoelastic interlayers. The developed finite element (FE) is based both on the multilayer theory and on the higher-order theory, in which the cubic variations of the in-plane displacements and the quadratic of the out-of-plane displacements are assumed for each discrete layer. In the present multilayer FE, the displacement continuity constrains at the layer interfaces are enforced through the penalty function method. For numerically predicting modal loss factors as damping effectiveness of laminates, the modal strain energy method is also implemented into the present FE analysis. In addition to the FE development, well-devised experimental measurements are conducted to obtain dynamic properties of several actually fabricated laminated coupons and sandwich panels, which contain some viscoelastic layers for improvin...
Patent•
24 Jul 2003
TL;DR: In this paper, an improved, load bearing, modular design container structure assembled from thermoformed fiber reinforced thermmoplastic (FRTP) sandwich panels is presented. But the exact configuration of articles so thermo-formed is design optimized to overcome manufacturing, assembly, weight, in-service and structural performance shortcomings of prior art and FRP sandwich panel structures.
Abstract: A method is disclosed utilizing off the shelf constant cross section thickness sandwich panels comprised of Fiber Reinforced Thermoplastic (FRTP) resin skins and low density thermoplastic (TP) core material wherein the steps of selectively and controllably exposing the panels to heat and incrementally thermoforming the skin-core into a consolidated composite edge or intra-panel area in consideration of subsequent mating and attachment of the FRTP sandwich panel to other structures is achieved. The exact configuration of articles so thermoformed is design optimized to overcome manufacturing, assembly, weight, in-service and structural performance shortcomings of prior art and FRP sandwich panel structures. Further disclosed is an improved, load-bearing, modular design container structure assembled from such thermoformed FRTP sandwich panels in which is utilized the unique core-skin edge configuration of the present invention in consideration of improved: load bearing performance, useful load volume, reduced manufacturing costs, structural weight savings, impact and damage tolerance and repair and replace issues.