Showing papers on "Sandwich-structured composite published in 1978"

Reinforced composite structure and method of fabrication thereof

Abstract: A composite structure has two composite panels which are bonded together at a joint. The joint is reinforced by composite thread being sewn in a series of stitches through the panels. Sewing the panels while they are in a staged condition allows the structure to be co-cured as assembled.

Thermal insulation for aircraft fuselage

Abstract: Thermal insulating apparatus for an aircraft fuselage of the type utilizing a sandwich panel construction. A foam insulation panel is provided which includes a plurality of standoffs for contacting the inwardly-facing skin of the sandwich panel. The standoffs may be arranged in a grid pattern, molded integrally with the rest of the panel, and bonded to the skin of the sandwich panel. The insulation panel may be used with or without a trim panel between it and the fuselage compartment, and in either case a sheet of metal foil may be attached to the inside face of the insulation panel. The foam may be of the self-skinning type so as to resist penetration of moisture into the foam panel and help direct condensate away from the fuselage compartment.

Method of fabricating sandwich panels

Abstract: Sandwich panels comprising a top skin and a bottom skin and a connecting core of a plurality of strand connectors are fabricated by applying viscous liquid core material to one of the skins, providing particles with the viscous core material, and reciprocating the particles between the top and bottom skins to form the strand connectors. The strand connectors are permitted to solidify to complete the formation of the sandwich panel. The particles are preferably of a ferrous metal and are driven between the top and bottom skins by a controlled magnetic field. Compound curved and tubular sandwich panels can be formed by the method.

An evaluation of the sandwich beam in four-point bending as a compressive test method for composites

Abstract: The experimental phase of the study included compressive tests on HTS/PMR-15 graphite/polyimide, 2024-T3 aluminum alloy, and 5052 aluminum honeycomb at room temperature, and tensile tests on graphite/polyimide at room temperature, -157 C, and 316 C. Elastic properties and strength data are presented for three laminates. The room temperature elastic properties were generally found to differ in tension and compression with Young's modulus values differing by as much as twenty-six percent. The effect of temperature on modulus and strength was shown to be laminate dependent. A three-dimensional finite element analysis predicted an essentially uniform, uniaxial compressive stress state in the top flange test section of the sandwich beam. In conclusion, the sandwich beam can be used to obtain accurate, reliable Young's modulus and Poisson's ratio data for advanced composites; however, the ultimate compressive stress for some laminates may be influenced by the specimen geometry.

Buckling and Structural Efficiency of Sandwich-Blade Stiffened Composite Compression Panels.

Abstract: The minimum mass structural efficiency curve was determined for sandwich blade stiffened composite compression panels subjected to buckling and strength constraints. High structural efficiencies are attainable for this type of construction. A method of analysis is presented for the buckling of panels of this configuration which shows that buckling of such panels is strongly dependent on the through-the-thickness transverse shearing of the stiffener. Experimental results are presented and compared with theory.

Composite joint system including composite structure of carbon fibers embedded in copper matrix

Abstract: A composite joint system is disclosed in which a composite structure containing carbon fibers embedded in a copper matrix in any configuration, e.g. in one direction, in random directions, in mesh form, spirally or radially is joined to another structure through a brazing material such as solder, Al brazer or Ag brazer. A film of metal such as Ni, Cr, Mo, W, Ta, Ti, Zr, V, an alloy of one or some of such metals, or the combination of some thereof is interposed between the composite structure and the brazing material. The metal film has a good wettability to both the composite structure material and the brazing material.

High heat flux actively cooled honeycomb sandwich structural panel for a hypersonic aircraft

Abstract: The results of a program to design and fabricate an unshielded actively cooled structural panel for a hypersonic aircraft are presented. The design is an all-aluminum honeycomb sandwich with embedded cooling passages soldered to the inside of the outer moldline skin. The overall finding is that an actively cooled structure appears feasible for application on a hypersonic aircraft, but the fabrication process is complex and some material and manufacturing technology developments are required. Results from the program are summarized and supporting details are presented.

Study of advanced composite structural design concepts for an arrow wing supersonic cruise configuration

Abstract: Based on estimated graphite and boron fiber properties, allowable stresses and strains were established for advanced composite materials. Stiffened panel and conventional sandwich panel concepts were designed and analyzed, using graphite/polyimide and boron/polyimide materials. The conventional sandwich panel was elected as the structural concept for the modified wing structure. Upper and lower surface panels of the arrow wing structure were then redesigned, using high strength graphite/polyimide sandwich panels, retaining the titanium spars and ribs from the prior study. The ATLAS integrated analysis and design system was used for stress analysis and automated resizing of surface panels. Flutter analysis of the hybrid structure showed a significant decrease in flutter speed relative to the titanium wing design. The flutter speed was increased to that of the titanium design by selective increase in laminate thickness and by using graphite fibers with properties intermediate between high strength and high modulus values.

Compression Fatigue of Impact Damaged Graphite Epoxy Sandwich Beams.

Abstract: : The resistance of composite aircraft structures to handling and impact loadings is an important consideration in assessing their suitability for long term operational service. The specific threat addressed in this study is that of low speed (0 to 30m/s), hard object, transverse normal impact (dropped tool, runway stones, etc.). The objective is to characterize the damage which occurs to composite faced sandwich structures under realistic impact conditions and determine the effect of this damage on residual compression fatigue properties. The sandwich construction selected for study consisted of AS/3501-6 graphite/epoxy face sheets of (0/+ OR - 45/0) SUBS CONSTRUCTION BONDED TO HRP-3/16-5.5 honeycomb core. This construction is representative of sandwich construction generally used in flaps, spoilers, and access doors. Static indentation tests were conducted on sandwich panels supported on a rigid foundation, and dropped weight impact tests were performed on simply supported sandwich beams. Comparison of the results of these tests indicates that static tests in conjunction with a simple 2-degree-of-freedom dynamic model can be used to accurately simulate low velocity, hard object impacts on sandwich structures for impact velocities up to 6.1 m/s. Test results of indentation versus static load is used in the dynamic model to predict the indentation which would occur for any particular impact case.

Finite Element Method for the Finite-Displacement Analysis of Sandwich Composite Panels.

Abstract: : A finite element method is presented for the large deflection analysis of flat, layered sandwich panels having arbitrarily-shaped boundaries Fully compatible isoparametric elements based upon Hermite bicubic interpolation are formulated, and requirements for the satisfaction of both displacement and slope compatibility are discussed As special cases, the analysis can be applied to thin laminated plates and multicore sandwich, as well as elastically-supported plates Solutions for geometrically nonlinear behavior are obtained by either the conjugate gradient or variable metric method Applications presented include rectangular, skewed, annular and circular geometries The analysis is shown to maintain displacement and stress accuracy for elements having extremely large aspect ratios, or edges which degenerate to a single point (Author)

Bismaleimide resins for flame resistant honeycomb sandwich panels

Abstract: Bismaleimide resins are prime candidates for nonflammable aircraft interior panels. Three resin types with different structures and processing characteristics were formulated. Resin M 751 was used to fabricate 100 kg of glass fabric prepregs which were used for the preparation of face sheets for honeycomb sandwich panels. Prepreg characteristics and curing cycles for laminate fabrication are provided. In order to advance beyond the current solvent resin technology for fibre and fabric impregnation, a hot melt solvent-less resin system was prepared and characterized. Preliminary tests were performed to develop a wet bonding process for the fabrication of advanced sandwich honeycomb panels by use of polybismaleimide glass fabric face sheets and polybismaleimide Nomex honeycomb core. B-stage material was used for both the core and the face sheet, providing flatwise tensile properties equivalent to those obtained by the state-of-the-art 3-step process which includes an epoxy adhesive resin.

The response of the Space Shuttle Orbiter graphite/epoxy sandwich panels to exposure to moisture and heat

Abstract: The Shuttle Orbiter Payload Bay Door is covered with graphite/epoxy sandwich panels. Their interaction with ground environments causes a moisture absorption of approximately 1.0% by weight at the time of launch. During the reentry phase the temperature of the outer facesheets rises to 177 C and their moisture content diminishes to 0.65%. In this condition the facesheet strength deteriorates significantly. Also, desorption of moisture produces an internal pressure in the panels of ca. 345 kPa. The paper discusses the prediction of expected moisture levels in the constituent parts of the sandwich panels. It describes further the test program necessary to assess the residual strength of the facesheets and the internal pressure capability of the sandwich panels.

Enhancing the Damping of Slabs by Viscoelastic Layers

Abstract: A study is presented of the potential of constrained viscoelastic layers in enhancing the damping of two-way slab floor systems with simply supported and clamped boundary conditions subjected to dynamic loading. The finite strip method is extended to the analysis of the resulting sandwich structures. The damping of the sandwich system is mainly due to the shear deformation of the viscoelastic layers and is described by a composite loss factor. Results are presented which demonstrate the effect of the elastic, damping, and geometric properties of the attached layers as well as their location in the domain of the slab, on the damping of the structures considered. Substantial damping can be achieved by proper choice of these parameters.