Showing papers on "Sandwich-structured composite published in 1989"

Modelling the mechanical behavior of cellular materials

Abstract: Materials with a cellular structure are widespread; they include natural materials such as wood and cork as well as man-made honeycombs and foams. Their cellular structure gives rise to unique properties which can be exploited in engineering design. The selection of a specific honeycomb or foam for a particular engineering application is guided by models which describe their mechanical behavior in terms of the cell geometry and the mechanisms of deformation and failure. In this review, models for the mechanical behavior of cellular materials are first described and then used to select the optimum foam for two engineering applications, the design of packaging and of light-weight structural sandwich panels.

Impact Resistance of Composite Sandwich Plates

Abstract: The impact resistance of sandwich panels with [±45/0] s Hercules AS4/3501-6 graphite/epoxy face-sheets manufactured with different types of cores (aluminum honeycomb, Nomex honeycomb and Rohacell plastic foam with three different core thicknesses, 3.2 mm, 6.4 mm and 9.6 mm) was studied at low energy levels (less than 10 joules). X-ray photos were taken to determine the extent of delamination damage, and the panels were sectioned so the location and lengths of delaminations, debonds, and core damage could be determined

Laminates, panels and means for joining them

Abstract: This invention discloses sandwich panels, i.e., laminates which comprise two metal sheets (5, 14) with a filled, reinforced resin core (11) between a bonded metal sheet, which are useful for structural and other uses. This invention discloses combinations of metal skins, resins, fillers, and reinforcement bonded together in the sandwich structure to provide a laminate having a flexural modulus of at least 2.5 million psi (17.24 X 103 MPa), a rigidity index of at least about 2,000 and other unique properties which enable the laminates to be particularly useful for thin wall trailer body construction, as well as other uses. This invention discloses a rigidity index property for sandwich structures and panels and a falling ball impact test, both of which are used to characterize the properties of sandwich laminates. This invention discloses methods of making the above sandwich laminates. This invention also discloses a means for joining sandwich laminates and panels which is particularly useful in the trailer body construction as well as other uses.

Debonding in foam-core sandwich panels

Abstract: The strain energy release rate is used to give a criterion for debonding in structural sandwich beams with isotropic faces and a foam core. The critical strain energy release rate of the interface is measured on double-shear specimens and the results of the debonding analysis are compared with experiments on sandwich beams with aluminium faces and foamed polyurethane cores. The analysis describes debonding failure well. Comparison of the load for bebonding with that for other failure modes shows that debonding occurs only if relatively large cracks exist at the interface between the face and the core.

Closeout configuration for honeycomb core composite sandwich panels

Abstract: This invention is directed to a high strength, lightweight honeycomb core composite sandwich panel Typical composite sandwich panels comprise a honeycomb panel disposed between upper and lower composite panels In this invention, a shim is disposed between the upper and lower composite panels around a portion of the periphery of the composite sandwich The shim is disposed over an inner layer of foaming adhesive

Instrumented Impact Testing of Composite Sandwich Panels

Abstract: The impact response of various composite sandwich panels has been investigated These composite sandwich panels, consisting of various fabric facesheet materials and different densities of poly(vin

Thermoplastic composite plate material and products molded from the same

Abstract: A thermoplastic composite plate material (4) having a quasi isotropy comprises a thermoplastic resin having a melt viscosity of 1,000-15,000 poise and strip pieces (1) each constructed of unidirectionally orientated reinforcing fibers and each having the ratio of the width to the length thereof within specific ranges. The strip pieces (1) are randomly distributed in the plane parallel to a surface of the composite plate material (4). Since the composite plate material (4) has good quasi-isotropic and high mechanical properties such as flexural strength, flexural modulus and impact strength, a composite product having good quasi-isotropic and high mechanical properties can be obtained by using the composite plate materials (4). Moreover, since the composite plate material (4) can be easily fitted into a mould, a composite product having a complicated shape can be easily moulded.

Method for forming a composite structure

Abstract: A method of forming a three-dimensional composite structure. Uncured portions of the composite structure are first assembled between a initially rigid heat-softening inner layer of ABS plastic and a hard outer mold surface. Prior to curing of the composite structure, pressure and heat is applied to the ABS layer to soften the layer. Thereafter, pressure is applied to the side of the ABS layer opposite from the composite structure, thereby to compact the uncured portions of the composite structure against the hard outer mold. Stiffening beams may be incorporated into the composite structure, so as to yield a lightweight, strong composite structure that can be used as a pressure vessel in an aerospace vehicle.

Test Methods and Performance of Structural Core Materials -1. Static Properties

Abstract: The first in a series, this presentation describes the static mechanical test methods and response of structural core materials used in sandwich construction. The concept of sandwich construction is introduced wherein high strength facings are lami nated around lightweight cores. Benefits of this method of fabrication include higher strength and stiffness per unit weight compared with more traditional, homogeneous materials. A series of standardized test methods for characterizing the performance of structural cores is presented and the procedures, apparatus and relevance of each is dis cussed in detail. The core compressive, tensile, shear and flexural properties thus gener ated are necessary to the proper design of sandwich panels which may be subjected to static loading conditions. Three of the more prominent core types are compared on the basis of micro-structure and composition. These include end-grain balsa, hexagonal honeycombs constructed of aluminum or aramid fiber-paper and the polyvinyl cellula...

Connecting element for sandwich panels

Abstract: In order to reduce to a minimum the number of profiles necessary for the different requirements when connecting sandwich panels, in particular for vehicle bodies made of sandwich panels, as connecting element a single rail (1) is proposed as a hollow profile which contains essentially all of the individual elements required for receiving the body parts.

Light building material and process and installation for the production of honeycomb structures from this material

Abstract: Panels having a honeycomb structure, for example of polyamide paper, are used as core material for sandwich panels having outer layers of plastics reinforced with carbon fibre or glass fibre or of aluminium. The new light building material is to be used for producing honeycomb structures which are distinguished in comparison with the known honeycomb structures by a greater strength and rigidity, an improved energy absorption and an improved fire behaviour. The light building material consists of a fibre-thermoplastic composite sheet which contains fibres of carbon, silicon carbide, whiskers or the like in the form of woven, laid or matted structures, and the fibres are embedded in a matrix of a high-temperature thermoplastic such as polyetheretherketone, polyethersulfone or polysulfone. Applications for sandwich panels with honeycomb core are in aviation and aerospace, in mechanical engineering and in the construction of rail and water vehicles as well as of sports and leisure equipment.

Passenger seat for an airplane

Abstract: To make the passenger seat for the airplane as light as possible while satisfying safety requirements, some or all the essential components are made with a sandwich-like structure, especially from sandwich panels These sandwich panels can be made from a plurality of covering layers with a light but strong supporting core (eg with a honeycomb structure) interposed between pairs of covering layers

Process for the production of sandwich panels using semi-finished products made of high-performance composites with polymeric matrices

Abstract: Process for the production of sandwich panels using semi-finished products made of high-performance composites with polymeric matrices, characterised in that the cut-to-size semi-finished product, comprising polymeric outer layers and the core material, is heated between two heating plates of a resistance heating system, is subsequently pressed and cooled.

Method for producing an insulating container

Abstract: The invention relates to a method for producing an insulating container in the region of the longitudinal edge between container bottom and a container side wall, both bottom and side wall being a sandwich construction with cover panels and rigid foam located between the cover panels and bonded to the two said cover panels. The invention is characterised in that both the bottom (1) and the side wall (10) are foamed sandwich panels such that the cover panels (2,3 and 11,12) protrude beyond the rigid foam region, in that the inner cover panels (3,11) of bottom and side wall on the one hand and the outer cover panels (2,12) of bottom and side wall on the other hand are firmly bonded to each other and in that, adjoining thereto, the one-part cavity, bounded by the rigid foam regions of bottom and side wall as well as the cover plates, is completely filled in one operation with a foam of which the components and production conditions correspond to those of the rigid foams of bottom and side wall, so that during foaming the rigid foam components enter into a bond with the rigid foams of bottom and side wall as well as their cover panels (Fig. 3). The invention also shows a bottom longitudinal profile, which permits a particularly rigid connection of a side wall of a container to its bottom panel.

Thermal stresses in sandwich panels with interlayer slips

Abstract: Analytic solutions for sandwich panels subjected to temperature changes are obtained, taking into account the effects of finite bounding stiffnesses. The numerical results show that the bonding stiffness, up to a certain level, has a strong effect on the panel response. The answer to what constitutes “ perfect” bonding is best answered in terms of the ratio of the core stiffness to the bonding stiffness, rather on the individual constituent material. A heat chamber is designed and used to test sandwich specimens under different temperature changes. The experimental values for normal stresses in the skins are in a good agreement with the present theory

3D-Fabrics for Composite Sandwich Structures

Abstract: The skin-to-core adhesion strength in sandwich panels is very often the weak link in composite structures. For this problem, a novel solution has been developed, based on a new type of fabric. A three-dimensional fabric is woven in one step; pile threads connect the top and bottom twodimensional fabric. When the 3D-fabric is impregnated, cured and filled with a PU-foam, a sandwich structure with interconnected skins is created. Preliminary mechanical test results are encourageing.

Connection of sandwich panels

Abstract: In order to connect directly to one another sandwich panels which butt one against the other and comprise two outer layers and a core lying in between, it is proposed to design the sandwich panels in such a way that the outer layers with the core form steps into which the end of the respectively adjoining sandwich panel fits. In this way, all the components can be connected together, preferably adhesively bonded, uninterruptedly in such a way that the interconnection ensures a uniform distribution of forces.

Mechanical properties characterization of composite sandwich materials intended for space antenna applications

Abstract: The composite materials proposed for use in the Advanced Communications Technology Satellite (ACTS) Program contains a new, high modulus graphite fiber as the reinforcement. A study was conducted to measure certain mechanical properties of the new fiber-reinforced material as well as of a composite-faced aluminum honeycomb sandwich structure. Properties were measured at -157, 22, and 121 C. Complete characterization of this material was not intended. Longitudinal tensile, picture-frame shear, short-beam shear, and flexural tests were performed on specimens of the composite face-sheet materials. Unidirectional, cross-plied, and quasi-isotropic fiber composite ply layup designs were fabricated and tested. These designs had been studied by using NASA's Integrated Composite Analyzer (ICAN) computer program. Flexural tests were conducted on (+/- 60/0 deg) sub s composite-faced sandwich structure material. Resistance strain gages were used to measure strains in the tensile, picture-frame, and sandwich flexural tests. The sandwich flexural strength was limited by the core strength at -157 and 22 C. The adhesive bond strength was the limiting factor at 121 C. Adhesive mechanical properties are reflected in sandwich structure flexural properties when the span-to-depth ratio is great enough to allow a significant shear effect on the load-deflection behavior of the sandwich beam. Most measured properties agreed satisfactorily with the properties predicted by ICAN.

Fold and Bond Construction of Cement Laminate Structural Shapes

Abstract: The ease with which fabric‐reinforced cement mortar laminates can be folded leads to studying the behavior of folded plate structural shapes made by this method. Sandwich panels having fabric‐reinforced cement mortar faces and rectangularly folded cores have been designed to maximize flexural stiffness per unit material cost. Folded‐core, fabric‐reinforced, cement laminate sandwich panels have been fabricated by scoring and folding the core laminate, then adhesively bonding the folded core to the face laminates. A design example illustrates a way to maximize panel bending stiffness per unit of material cost. Stiffness/weight ratios are compared with the ratios for some precast concrete panel sections. Potential applications include lightweight panels for building walls, roofs, and floors.

Structural analog for sandwich panels with finite deflections

Abstract: The solution of sandwich plate problems by the framework method is proposed. The technique is demonstrated by application to a simple framework analog for rectangular sandwich pannels with very thin faces and an antiplane core

Finite deflections of sandwich beams and plates by finite element method

Abstract: A finite element capab?lity is described for the geometrically nonlinear analysis of arbitrarily curved sandwich panels with thick dissimilar faces. Each layer may have orthotropic properties of its own and may deform locally. Examples of bending and buckling problems are solved which illustrate the effectiveness of the proposed technique.

Sandwich panels with crosslinked foamed polyethylene core - are flame treated for surface activation prior to adhesive bonding of facing layers

Abstract: Sandwich panels are made by flame treating the surface of a crosslinked polyethylene core under oxidising conditions, applying an adhesive to the treated surface, applying the outer layer and pressing Pref the adhesive used is a heat activatable adhesive film eg of modified ethylene copolymer and pressing is carried out at a temp at which the adhesive film softens or melts Pref before the flame treatment the surface of the polyethylene core is provided with ridges 15-20 mm deep and 05-10 mm wide, or with slots 20-40 mm deep USE/ADVANTAGE - The flame treatment activates the surface of the polyethylene core and allows self supporting composite sandwich panels to be prepd having bonded outer layers of metal, plastics, fibre reinforced polyester or epoxy resin etc The panels have good heat-, sound- and vibration insulating properties and are usefuleg for construction of delivery vans, etc

Design and testing of thermal-expansion-molded graphite-epoxy hat-stiffened sandwich panels

Abstract: Minimum weight configurations for two types of graphite-epoxy hat-stiffened compression-loaded panels fabricated by the thermal-expansion-molding (TEM) manufacturing process were evaluated analytically and experimentally for designs with load index Nx/L values ranging from 100 to 800. The two types of panels contain graphite-epoxy face sheets with a foam core and hat stiffeners which are either open or filled with foam. Constraints on the extensional and shear stiffnesses are imposed on the design so that the panels will satisfy typical constraints for aircraft wing structures. Optimal structurally efficient TEM panels are compared to commercially available aluminum aircraft structures. Predicted load-strain relationships agree well with experimental results. Significant impact damage to the unstiffened face sheet and foam core does not noticeably reduce the load carrying ability of the panels, but damage to the stiffened face sheet reduces the failure load by 20 percent compared to unimpacted panels.