Showing papers on "Sandwich-structured composite published in 1993"

Method of production of reinforced foam cores

Abstract: Rigid foam insulation boards and thin flexible fibrous sheets or strips are stacked in alternating layers with adhesive between the layers, and the stack is compressed while the adhesive cures to form a rectangular core panel or billet. In one embodiment, the parallel spaced sheets or strips extend diagonally of the panel or billet, and each billet is cut through the alternate layers of foam and fibrous sheets and along parallel spaced planes to form a plurality of core panels. The core panels are adhesively bonded between skins of rigid sheet materials to form laminated sandwich panels with the fibrous strips connecting the skins. The above stacking and curing steps are also performed with core panels in place of insulation boards to form a billet which is cut to form core panels with grid-like webs, and grid-like core panels are used to form a billet with the webs extending in X-Y-Z directions. Billets are also formed with core panels stacked in a step-like manner and then cut along inclined parallel planes to provide core panels with truss-like webs, and billets are formed with adjacent rigid foam boards having different densities and thicknesses, Resilient foam panels are used in place of or with the fibrous sheets for producing core panels which may be curved, and the foam between the webs of grid-like core panels is recessed to expose the webs for bonding surface materials such as stucco to the core panels.

Impact-Damaged Graphite-Thermoplastic Trapezoidal-Corrugation Sandwich and Semi-Sandwich Panels

Abstract: The results of a study of the effects of impact damage on compression-loaded trapezoidal-corrugation sandwich and semi-sandwich graphite-thermoplastic panels are presented. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered in this study. Panels were designed, fabricated and tested. The panels were made using the manufacturing process of thermoforming, a less-commonly used technique for fabricating composite parts. Experimental results for unimpacted control panels and panels subjected to impact damage prior to loading are presented. Little work can be found in the literature about these configurations of thermoformed panels.

Shear buckling response of tailored, rectangular, composite plates

Abstract: The concept of stiffness tailoring for improved shear buckling resistance of rectangular composite plates is investigated analytically. The tailoring involves only the redistribution of the given material with given orientations to create beneficial stiffening patterns across the planform of the plate. The resulting local nonuniformities in thickness and membrane and bending stiffness combine to change the buckling response of the plate. The weight and average membrane shear stiffness are essentially unaffected by the tailoring. Practical limitations on the degree to which the tailoring may be carried out are shown to govern most designs. Improvements in the shear buckling load on the order of 50 percent are shown possible with monolithic tailoring. Tailored sandwich concepts, in which a light-weight core material is added to keep both plate surfaces flat, can produce improvements well over 100 percent in specific buckling loads compared with uniform composite plates.

Structural analysis and design of sandwich panels with cold-formed steel facings

Abstract: Superior structural efficiency, ease of erection, mass-production capabilities and thermal-insulation qualities are making sandwich panels with flat or thin-walled cold-formed steel facings and rigid foamed insulating core increasingly popular as enclosures for system buildings. In this paper the structural behavior — including flexural stresses, deflections, vibration and thermal stresses — is presented, summarizing more than two decades of research. Methods used are analytical (boundary-value approaches), numerical (finite-strip, finite-layer, finite-prism approaches) and experimental (full-scale testing). Key equations are formulated, and results by different methods are compared. Design guidelines are also suggested.

Flexural and impact properties of sandwich panels used in surfboard construction

Abstract: Surfboards represent a particularly simple example of sandwich panel construction and are conventionally made from a preshaped low density polyurethane foam core encased in an E-glass/polyester skin. They are made to minimum weight and thickness and as a result suffer durability problems. The boards are particularly prone to denting due to impact damage, causing principally cosmetic problems. More importantly, they frequently snap under normal service conditions. Recently, there has been considerable interest in the use of higher performance materials for the skins, notably S-glass and epoxy resin, to improve the durability of surfboards. This work examines the failure of simple parallel faced panels fabricated to simulate a section of a surfboard. It is shown that when loaded in four point bending, the panels fail by compression of the core and that this mode of failure produces the same characteristics as seen in service failures. Further, the flexural strength is dominated by the behavior of the core and is not improved appreciably by the use of S-glass or epoxy resin. On the other hand, the impact resistance is improved by the use of S-glass and further improved if epoxy resin is used as the matrix.

Mechanical and thermal buckling analysis of sandwich panels under different edge conditions

Abstract: By using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system, combined load (mechanical or thermal load) buckling equations are established for orthotropic rectangular sandwich panels supported under four different edge conditions. Two-dimensional buckling interaction curves and three dimensional buckling interaction surfaces are constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide easy comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. Thermal buckling curves of the sandwich panels also are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory. In sandwich panels, the effect of transverse shear is quite large, and by neglecting the transverse shear effect, the buckling loads could be overpredicted considerably. Clamping of the edges could greatly increase buckling strength more in compression than in shear.

Local buckling of composite corrugated compression panels

Abstract: This paper investigates the problem of local instability of corrugated panels fabricated from composite materials and subjected to in-plane compressive loading. The panels are considered as a series of linked plate strips with rotationally restrained unloaded edges. At buckling, the moments and slopes at each common edge are related in such a way as to satisfy equilibrium and compatibility conditions. The local buckling coefficient for various geometries and different composites are obtained. It is concluded that unidirectional composite corrugated panels have lower local buckling resistance than panels made of isotropic materials, and hence layers of angle-ply fibers should be included in the laminates in order to improve the local buckling strength.

Cold-formed steel in tall buildings

Abstract: Structural members decking and sandwich panels shear diaphragms connections functional requirements for tall buildings stainless steel and corrosion resisting steel sections.

A simplified method for ultimate load prediction of all-steel sandwich panels

Abstract: This paper is concerned with the ultimate load prediction of a sandwich panel manufactured from a steel plate assembly. The panel essentially consists of two facing plates, spot welded onto a corrugated steel core. All the plates of a panel have identical thickness. Three groups of panels with varying plate thicknesses were examined. The typical panel considered in this study had plan dimensions of 2·1 m × 1·0 m with a core consisting of top-hat stiffeners of depth 60 mm, placed side by side. The panel was simply supported across its y-direction boundaries and subjected to uniform lateral loading over its entire surface. The plastic hinge theory is used to evaluate the ultimate collapse load of the panel. In this respect, two approaches are compared: one based on fullsection properties and the other based on the effective width concept. It is shown that the effective section gives more reliable collapse-load predictions than the full section. Theoretical collapse-load predictions agree very well with the experimental collapse load for a series of 13 panels. To accentuate the salient features of the technique, a numerical example is presented.

The response of various ships hull plating materials to pressure loads caused by slamming

Abstract: Various materials are used for the hull plating in modern fast ships and yachts. Beam (or strip) and linear flat plate analysis are often used to predict the response of curved hull panels. This paper demonstrates that these methods are inappropriate for all materials with the possible exception of plywood panels. Use of beam (or strip) and linear flat plate analysis for curved panels could results in unexpected catastrophic failure. This paper details beam bending and panel static pressure tests of various metal, wooden, composite and sandwich panels. It also includes preliminary plans for dynamic drop tests of various rigid and elastic hull panel samples and a dimensional analysis of the scaling laws for the slamming of curved hull models and prototypes.

Machine for the manufacture of sandwich panels.

Abstract: The invention is a new machine for the manufacture of roofing panels consisting of an upper sheet, a foam polystyrene insulating layer and, if required, a lower protection sheet. The polystyrene sintering takes place directly on the upper sheet, that serves also as a die in the sintering phase. The polystyrene granules that are introduced in the chamber obtained between the upper sheet, previously treated with a bonding agent, and the fixed mould are heated and foamed by means of steam, thus realizing a rigid panel of the necessary thickness. The panel is used, in particular, for the roofing of industrial buildings or for the realization insulated curtain walls.

Composite laminate and sandwich optimization with applications

Abstract: The design optimization problem of composite laminate structures is addressed with a decomposition into a structural and laminate optimization process. Emphasis is given on the latter, with specifics such as the determination of the fibre/matrix system in parallel to fibre angles and lamina thicknesses. The nonconvexity of the problem is highlighted. Practical examples are taken from high precision space reflector design and the design of a large composite cylindrical shell structure of the Ariane launcher.

Processing and Properties of Fiber Reinforced Article with Sandwich Structure in Simultaneous Composite Injection Molding

Abstract: A simultaneous composite injection molding (SCI. molding) process is a new process of molding composite parts in which two different melts are injected into one mold cavity simultaneously through two channels. This molding process has the outstanding advantages of high resin/resin bonding strength and low production cost compared with the conventional two-color injection molding. The sandwich injection molding process as well as two-color injection molding uses two injection units. However, since they use one common nozzle, some problems remain such as the limitation in the selection of materials. The SCI. molding process can solve these problems with the conventional sandwich injection molding.In this study, we fabricated fiber reinforced thermoplastics articles with sandwich structures using the SCI. molding process. The effect of molding conditions on the sandwich structure was discussed. Two different materials with large differences in melting temperature can be fabricated. Bending tests were carried out, and composite beam theory and laminated beam theory were applied to predict the bending modulus. It was confirmed that sandwich composite injection molding has various unique properties i.e. high strength, low cost, low weight etc. The bending modulus of the sandwich beam showed good agreement with the theoretical value obtained by composite beam theory. This result suggested that a very strong interface could be formed between two different materials.

Acoustic Transmission Loss and Structureborne Noise Transmission Tests on a LASCOR and a Reference Steel Panel

Abstract: : LASCOR is a laser welded corrugated steel sandwich developed as a lightweight construct for ship superstructures. Tests were performed to measure acoustic transmission loss and structureborne noise transmission for both a LASCOR panel and a reference conventional rib-stiffened steel panel. This report outlines the test methods used and compares the results for the two panels. LASCOR, Laser Welded Corrugated Steel, Sandwich, Sound Pressure, Driving Point Mobility

Packaging, deployment, and panel design concepts for a truss-stiffened 7-panel precision deployable reflector with feed boom

Abstract: A concept is presented for achieving a remotely deployable truss-stiffened reflector consisting of seven integrated sandwich panels that form the reflective surface, and an integrated feed boom. The concept has potential for meeting aperture size and surface precision requirements for some high-frequency microwave remote sensing applications. The packaged reflector/feed boom configuration is a self-contained unit that can be conveniently attached to a spacecraft bus. The package has a cylindrical envelope compatible with typical launch vehicle shrouds. Dynamic behavior of a deployed configuration having a 216-inch focal length and consisting of 80-inch-diameter, two-inch-thick panels is examined through finite-element analysis. Results show that the feed boom and spacecraft bus can have a large impact on the fundamental frequency of the deployed configuration. Two candidate rib-stiffened sandwich panel configurations for this application are described, and analytical results for panel mass and stiffness are presented. Results show that the addition of only a few rib stiffeners, if sufficiently deep, can efficiently improve sandwich panel stiffness.

System for the manufacture of insulating panels and the respective panels

Abstract: The invention concerns a machine for the manufacture of flat or curved sandwich panels for the thermal insulation of buildings. The insulating layer, which is made of polystyrene, is injected directly between two flat or curved metal and/or plastic sheets. This invention refers to the covering panels for buildings and in particular panels for curved or flat walls and roofing. At present, in the buildings to be insulated, panels are used with polyurethane foam injected into the gaps, or polystyrene panels are used.

Investigation of Advanced Lightweight Sandwich Structural Concept.

Abstract: : Although the sandwich panels fabricated of honeycomb core bonded between two face-sheets are very weight-efficient, their application causes many problems such as moisture retention, extensive corrosion, ineffective edge seals, unbonding of face-sheets, and time consuming and expensive repair. In an attempt to eliminate these detrimental factors, new sandwich structural concepts are introduced. These structural concepts include bidirectionally-corrugated, lattice-core, offset-corrugated, and cross-corrugated sandwich. They are variations of corrugated sandwich. The new features of all the sandwich are the provision of passageways from cell to cell for moisture drainage to reduce corrosion. The lattice-core, offset-corrugated, and cross-corrugated sandwich can be fabricated of fiber-reinforced composite materials in single cure operation without any secondary bonding. Sample specimens of lattice-core and offset-corrugated sandwich panels have been fabricated and tested to obtain their flexural and transverse shear stiffnesses. The predicted flexural and transverse shear stiffnesses of lattice-core and cross-corrugated sandwich panels are comparable to that of honeycomb sandwich panels. (MM)

The Impact Behavior of Composite Sandwich Used in Ship Structures

Abstract: The impact behavior of composite sandwich panels subjected to a cylindrical impactor is investigated numerically and experimentally. Three kinds of facesheets and two different core densities of sandwich panels are considered in the impact analysis. During the experiment, the impact force and strain history are measured, and the failure is inspected by visual observations. The experimental results show that the impact behavior is mainly controlled by core material. The ABAQUS finite element software is used to analyze the impact responses of sandwich panels. Because of line load conditions, the sandwich panels impacted by the cylindrical impactor is modeled as a 2-D plane strain problem. The numerical results of impact force and strain history are compared with those measured in experiment, it is shown that the experimental results are in good agreement with the finite element solutions. Further, the stresses of sandwich panels are examined. The maximum stress failure criterion is used to estimate the fracture initiation of sandwich panels. Then the experimental and numerical results are compared and discussed.