Showing papers on "Sandwich-structured composite published in 1991"

Characterization of Face Sheet/Core Shear Fracture of Composite Sandwich Beams

Abstract: Debonding failure of cored composite materials is investigated herein. A new test method that subjects the bondline between the core and face sheets to a shear stress singularity is presented and studied analytically by laminated beam shear deformation theory and experimentally on glass/polyester face sheets on balsa wood core sandwich beams.

Laminates, panels and methods for making them

Abstract: Sandwich panels and methods of making them, i.e., laminates which comprise two metal sheets with a filled resin core between a bonded metal sheets, which are useful for structural and other uses wherein the laminates utilize combinations of metal skins, metal surface preparation, resins, fillers, and reinforcement bonded together in the sandwich structure to provide a laminate having a flexural modulus of at least 1.7 million psi, 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 structural and non-structural uses. A rigidity index property for sandwich structures and panels and a falling ball impact test are disclosed and used to characterize the properties of sandwich laminates. A laminate of plywood core or a reconstituted wood product core, such as hardboard, particleboard or flakeboard, bonded to prepared metal surfaces with the resin also has properties suitable for structural uses.

Structural analysis methods for lightweight metallic corrugated core sandwich panels subjected to blast loads

Abstract: Since the early 1980s, the U.S. Navy, in conjunction with industry, has continued to develop and test innovative lightweight structural concepts with the purpose of seeking alternative replacements for conventional plate beam metallic structures. One commercially available concept currently under investigation is lightweight metallic corrugated core sandwich panels. This paper presents both elastic and plastic design methods for lightweight metallic corrugated core sandwich panels subjected to air blast loading. The equations presented in this paper, while not a complete solution to the complicated dynamic, elastic plastic phenomena of blast wave-rigid body interaction, are offered as a set of relatively simple analytical expressions that can be used in preliminary design. Because of the closed form nature of the equations the designer has the capability to quickly identify the most important parameters effecting the response of lightweight metallic corrugated core sandwich panels to air blast loads.

Combined Compressive and Shear Buckling Analysis of Hypersonic Aircraft Structural Sandwich Panels.

Abstract: The combined-load (compression and shear) buckling equations were established for orthotropic sandwich panels by using the Rayleigh-Ritz method to minimize the panel total potential energy. The resulting combined-load buckling equations were used to generate buckling interaction curves for super-plastically-formed/diffusion-bonded titanium truss-core sandwich panels and titanium honeycomb-core sandwich panels having the same specific weight. The relative combined-load buckling strengths of these two types of sandwich panels are compared with consideration of their sandwich orientations. For square and nearly square panels of both types, the combined load always induces symmetric buckling. As the panel aspect ratios increase, antisymmetric buckling will show up when the loading is shear-dominated combined loading. The square panel (either type) has the highest combined buckling strength, but the combined load buckling strength drops sharply as the panel aspect ratio increases. For square panels, the truss-core sandwich panel has higher compression-dominated combined load buckling strength. However, for shear dominated loading, the square honeycomb-core sandwich panel has higher shear-dominated combined load buckling strength.

Process for making honeycomb sandwich panels

Abstract: The invention relates to a process for making an aminoplast-impregnated sandwich panel consisting of a honeycomb (6) and facing by means of an autoclave (1), characterized in that at least one of the honeycomb (6) and facing (5) is impregnated with aminoplast and the sandwich panel is placed in an autoclave under a sheet of flexible material (7), which flexible material is at least partially gas tight and is sealed at its edges, over which flexible material a first pressure is applied and under which flexible material a second pressure is applied, that is lower than the first pressure whereby the second pressure is at least as high as the vapour pressure of water at the curing temperature of the aminoplast. Honeycomb sandwich panels made by applying a process according to the invention are particularly suited for being used in applications with high demands imposed in respect of strength and rigidity in combination with high demands in respect of fire resistance. Examples are aircraft, house building, trains, automotive vehicles and ships.

Flexural behavior of ferrocement sandwich panels

Abstract: The flexural behavior of ferrocement sandwich panels has been studied. The parameters considered in the experimental investigation were the number of wire mesh layers, the skeletal steel, the web mesh reinforcement and the number of webs. Ultimate moment capacities were computed analytically using conventional reinforced concrete theory. The analytical results are compared with the experimental results by tests on 12 sandwich panels. Cracking behavior and failure patterns for all panels were also obtained and compared.

Combined-load buckling behavior of metal-matrix composite sandwich panels under different thermal environments

Abstract: Combined compressive and shear buckling analysis was conducted on flat rectangular sandwich panels with the consideration of transverse shear effects of the core. The sandwich panel is fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that the square panel has the highest combined load buckling strength, and that the buckling strength decreases sharply with the increases of both temperature and panel aspect ratio. The effect of layup (fiber orientation) on the buckling strength of the panels was studied in detail. The metal matrix composite sandwich panel was much more efficient than the sandwich panel with nonreinforced face sheets and had the same specific weight.

Optimization of composite sandwich cover panels subjected to compressive loadings

Abstract: An analysis and design method is presented for the design of composite sandwich cover panels that include the transverse shear effects and damage tolerance considerations. This method is incorporated into a sandwich optimization computer program entitled SANDOP. As a demonstration of its capabilities, SANDOP is used in the present study to design optimized composite sandwich cover panels for for transport aircraft wing applications. The results of this design study indicate that optimized composite sandwich cover panels have approximately the same structural efficiency as stiffened composite cover panels designed to satisfy individual constraints. The results also indicate that inplane stiffness requirements have a large effect on the weight of these composite sandwich cover panels at higher load levels. Increasing the maximum allowable strain and the upper percentage limit of the 0 degree and +/- 45 degree plies can yield significant weight savings. The results show that the structural efficiency of these optimized composite sandwich cover panels is relatively insensitive to changes in core density. Thus, core density should be chosen by criteria other than minimum weight (e.g., damage tolerance, ease of manufacture, etc.).

Nonlinear behaviour of single-skin and sandwich hull panels

Abstract: In context with research aiming at improved structural design methods for boats and small-craft, the behaviour of typical hull panels has been studied at the VTT Ship Laboratory. The bending behaviour of FRP hull panels is characterised by remarkable geometric nonlinearities due to large panel size and high lateral loads. The importance of performing nonlinear analysis is demonstrated as well for single-skin as sandwich panels. The geometric nonlinearity of a laterally loaded single-skin FRP-plate becomes significant if the deflection exceeds half of the plate thickness. This is common in structures designed for the allowed stress rather than the maximum deflection. The analysis of the plate bending problem must then be extended to include membrane stresses. The influence of the boundary conditions and the panel geometry as well as laminate orientation on the stress distribution and the maximum deflection are investigated. These were studied with a calculation method based on the direct minimisation of the total potential energy. The results for a typical rectangular panel show the significance of the membrane effects even at low loading levels. The influence of curvature of sandwich panels on the bending behaviour, the face strain and the transverse shear strain distributions is studied using the geometric nonlinear finite element methods. The results show that the bending behaviour varies depending on the curvature of the panel. Transverse shear strains decrease significantly with increasing curvature, except for panels with very small curvature, where snap-through occurs. For typical flat sandwich panels, the membrane effects become significant if the deflection exceeds about twice the thickness of one face.

Assessment of long term effects of slamming loads on frp sandwich panels

Abstract: High speed craft are subjected to repeated dynamic loads caused by slamming. Some rescue vessels having sandwich hulls with GRP laminates and foamed polymer cores have experienced damage that is believed to have been caused by extreme and/or repeated slamming loads exceeding the design load levels. The mode or failure has been predominantly shear cracking of the core followed by delamination. As part of the NTNF Fast Craft Programme, a laboratory test procedure has been developed to simulate single and repeated slamming loads on sandwich panels. This procedure is based on four-point bending of various sandwich beam specimens. Experimental results are presented on the shear properties of sandwich beams subjected to simulated slamming loads. Particular attention is paid to the influence of adhesive joints within the core. A range of core/adhesive combinations is considered. In the case of beams having adhesive joints in the core, the experimental work is supplemented by evaluation of stresses in the core and adhesive using finite element analyses. By this means the influence of the adhesive's mechanical properties on crack initiation is studied. A possible basis for minimising the effect of adhesive joints on static and fatigue performance is thereby established. The experimental test procedure combined with finite element analyses provide a basis for assessing the long-term effects of repeated slamming loads on sandwich panels.

Creep Mixture Rules of Polymer Matrix Fiber-Reinforced Composite Materials

Abstract: Creep mixture rules of polymer matrix fiber-reinforced composite materials are studied systematically in this paper. Two kinds of micromechanical models of composite materials with fibers in two directions at right angles are advanced. The comparisons of the predictions of creep behavior for the composite by the creep mixture rules in this paper with the experimental data show that this theory is very precise for predicting the linear creep behavior of composite materials.

Study 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. Optimal structurally efficient TEM panels are compared to commercially available aluminum aircraft structures

Fabric‐Reinforced, Mortar‐Faced, Foam‐Core Sandwich Panels

Abstract: This paper describes the construction of structural sandwich panels by wrapping reinforcing fabric around a foam board, then dipping it in a mortar slurry and screeding away excess mortar. A design procedure is described for obtaining the relative face, core, and reinforcing thicknesses to satisfy panel structural constraints at minimum material cost and at minimum weight for these faces, which have unequal tensile and compressive stiffnesses. Design is illustrated for a panel bending stiffness constraint. Stiffness/weight and stiffness/material cost ratios have been studied as a function of the amount of mineral wool added as a supplementary reinforcement stiffener. Stiffness/weight ratios are compared to those of pre‐stressed hollow‐core concrete decks. Potential applications include lightweight insulated panels for foundation walls and for walls and roofs of small buildings. Potential advantages include the elimination of concrete footing and foundation‐wall insulation costs as well as the reduction of...

Method of manufacturing plastic composite panels

Abstract: The invention concerns a method of manufacturing a plastic composite panel from a substrate containing solid recycled-plastic material and coated on at least one side with a decorative panel made of a different material.

Joint structure of wall

Abstract: PURPOSE:To easily carry out a construction work and increase a fitting strength, water-proof and heat-insulating characteristics, by fitting a joint cover on a wall after fixing sandwich panels on a base body with a fitting tool, making edge faces of both of the sandwich panels abut on each other. CONSTITUTION:Heat-insulating members 8, 8 made of light plastic form are interposed as a unit between metallic surface materials 1, 1 and metallic rear face materials 9, 9 to constitute sandwich panels A1, A2. And respective pane A1, A2 are fixed to a base body alpha with a fixing tool beta, making edge faces of both sandwich panels A1, A2 abut on each other. Next, a joint cover B having nearly a T-form in the section is fixed in such a way that the fitted part 19 thereof is inserted into a recessed fitting part to form a wedge at the end of the panels A1, A2.

Composite material technology - 1991; Proceedings of the Symposium, 14th Annual Energy-sources Technology Conference and Exhibition, Houston, TX, Jan. 20-23, 1991

Abstract: Consideration is given to damping in composite structures, material and mechanical properties of composite materials, strength damage and failure in composite materials, manufacturing and design of composite structures, and micro- and macromechanics of composite materials and structures. Particular attention is given to the vibrational damping behavior of composite materials, improved composite material damping using high damping graphite fibers, mechanical behavior of viscoelastic solids, a study of flexural stiffness in delaminated composite plates, and quasi-static and dynamic axial crushing of foam-filled FRP tubes. Also discussed are drilling of fiber and particle reinforced aluminum, a reliability analysis of composite plates for eigenvalue problems, creep buckling of asymmetric laminated columns, and stationary and nonstationary responses of nonlinear dynamic instability of laminated angle-ply composite beams.

Polyurethane rigid foam systems for metal-faced sandwich panels for the 1990s

Abstract: Sandwhich panels with polyurethane rigid foam cores are important building elements for a wide variety of applications. They are used for the cost effective construction of industrial and commercial buildings and in many stages of the food chain, including cold storage, cold rooms and refrigerated transport containers and trucks

Projection device with breaking of the thermal bridge for a system essentially for fastening sandwich panels

Abstract: The present invention relates to a protection device essentially designed for elements for fastening sandwich panels. It solves two problems which are well known to the professionals: the absence of satisfactory sealing and heat insulation of systems for fastening, and the condensation and erosion which result therefrom. According to one embodiment of the invention, the device is composed of a component (1) forming a container, the edges (2) of which are curved so that they match the shape of the sandwich panel (3). The end (4) of this container includes an opening (5) allowing the passage of the screw (6); the head (7) of the screw (6) rests on the end (4). The container (1) is filled with polyurethane (8) and hermetically sealed by a cap (9) provided with anchor means (10). Neoprene seals (11) supplement the system.