Showing papers on "Sandwich-structured composite published in 1981"

Method of fabricating a reinforced composite structure

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.

Bending of Thick Rectangular Plates Laminated of Bimodulus Composite Materials

Abstract: A mixed finite-element analysis is presented for static behavior of rectangular plates laminated of composite materials having finite transverse shear moduli and different elastic properties depending upon whether the fiber-direction strains are tensile or compressive. As a benchmark to assess the validity and accuracy of the finite-element analysis, a closed-form solution is given for a two-layer, cross-ply plate having all edges simply supported without in-plane restraint and subjected to sinusoidally distributed normal pressure. Numerical results obtained by the two methods are compared and found to agree quite well.

A foam composite material impregnated with resin

Abstract: The invention relates to a foam composite material which comprises a material in web form impregnated with a curable resin. The resin in the foam composite material is in the B-stage. The foam composite material further contains expanded thermoplastic particles which are essentially uniformly distributed in the resin and in the web material. The invention also relates to laminates prepared by use of the foam composite material and a method for the manufacture of such laminates.

Some physical defects arising in composite material fabrication

Abstract: A fairly wide range of physical defects arising during the processing of composite materials is surveyed. The kinds of composites discussed are fibre-reinforced materials, metal-matrix composites, ceramic-matrix composites and bonded sandwich (clad, rolled) materials. The list of defects considered is not exhaustive but the defect phenomena described exemplify the practical value of a knowledge of the difficulties encountered in composite material processing.

Dynamic Analysis of Unbalanced Anisotropic Sandwich Plates

Abstract: The modified stiffness method of unbalanced anisotropic sandwich plates is extended and applied to the dynamic analysis of sandwich plates consisting of an orthotropic core and two equal thickness anisotropic face plates. The formulation allows for the dynamic analysis of certain types of sandwich plates that were not amenable to rigorous solutions due to the existence of anisotropic coupling stiffnesses, such as those with inbalanced angle-ply faces. The method is independent of the boundary conditions and can be combined with a variety of analysis techniques. Using a series solution, results are generated for simply-supported sandwich plates with unbalanced cross-ply and angle-ply face plates. In addition, the effect of coupling in the static and dynamic responses is presented. Coupling can influence the structural response significantly.

The effect of impact damage on the tension-compression fatigue properties of sandwich panels with face sheets of carbon epoxy

Abstract: An experimental investigation was performed to examine the effect of low energy impact damage on tension-compression fatigue properties of sandwich panels. The specimens consisted of a 9 mm thick Nomex honeycomb and face sheets of (0,± 45) and (± 45,0) Carbon/epoxy. Drop weight impact was applied to create internal laminate damage. In order to select an appropriate impact energy an impact investigation preceded the fatigue tests. For the fatigue specimens an impact energy was chosen which resulted in a barely visible damage. Constant amplitude fatigue tests were carried out at a stress ratio of R = -1 to determine the fatigue strength of impacted specimens. Damage propagation from the location of impact consisted of a combination of interlaminar delamination, fibre breakage and debonding of the laminate from the honeycomb.

Method for manufacturing a sandwich panel structure

Abstract: A method for manufacturing sandwich panels of the type in which a pair of facing sheets 12 are separated by a multiplicity of pins 14 is disclosed. Concepts and techniques for fabricating the structure in a leachable matrix are discussed. Selective roll bonding and cutting are employed to form pins of accurate dimension contour and spacing.

Stress Distribution in Sandwich Beams in Uniform Bending

Abstract: The three-dimensional elastic stress state in a sandwich beam in uniform bending is given. The analysis is carried out numerically through use of a finite-difference formulation of the exact equations of elasticity. The beam is proportioned similar to one used in the characterization of composite materials and composed of [′45] s composite face sheets laminated to a typical honeycomb core. It is shown that interlaminar stresses are confined to boundary regions near the free edges and that the in-plane stresses converge to the laminate theory solutions in the interior of the beam despite the fact that the beam is deeper than it is wide. Importantly, the core/face sheet tractions are found to be insignificant.

Development and demonstration of manufacturing processes for fabricating graphite/LARC 160 polyimide structural elements

Abstract: The development and demonstration of manufacturing technologies for the structural application of Celion graphite/LARC-160 polyimide composite material is discussed. Process development and fabrication of demonstration components are discussed. Process development included establishing quality assurance of the basic composite material and processing, nondestructive inspection of fabricated components, developing processes for specific structural forms, and qualification of processes through mechanical testing. Demonstration components were fabricated. The demonstration components consisted of flat laminates, skin/stringer panels, honeycomb panels, chopped fiber compression moldings, and a technology demonstrator segment (TDS) representative of the space shuttle aft body flap.

Curved foam core sandwich panels - where panels are bent after receiving saw cuts on inner face at bend area

Abstract: Curved sandwich-construction panels are produced and fixed to flat sandwich panels for use in caravans etc.; they utilise foam core material and the core can incorporate stiffening profiled sections. As a first operation a flat sandwich panel receives parallel saw cuts through the inner skin at the area to be bent, the panel is then bent, and finally fixed to the straight panel at the straight part adjacent to the bend. Suitable for roof or wall components, low cost, eliminate need for aluminium coverings for timber or metal members.

Minimum Weight Design of Flat Sandwich Panels under Edgewise Compression Loads.

Abstract: : An approach to the optimum design of flat, rectangular sandwich panels subjected to edgewise compression loading has been developed. Using a nonlinear programming method called the Sequential Unconstrained Minimization Technique, the design parameters characteristic of sandwich construction are determined so that the final panel configuration is not just an acceptable design, but is the best acceptable design as far as total panel weight is concerned. The design parameters are the individual thicknesses of the top and bottom face sheets and of the core, the cell size and foil thickness of honeycomb core, and the density of foam core. The acceptable ranges of the design parameters are limited by constraints which ensure, for example, that the thicknesses are within minimum and maximum limits, that the faces do not yield, wrinkle, or dimple, and that the panel does not buckle. Possible panel loads are edgewise compression in two directions.

Nonlinear Finite Element Analysis of Sandwich Composites.

Abstract: : Finite element analysis techniques are developed for the solution of nonlinear problems involving sandwich composite materials. Each layer of a sandwich panel is represented explicitly so that multicore panels and other configurations are easily considered. The finite element discretization is performed using arbitrary-shaped, fully compatible shell and continuum elements, as well as special elements representing full-depth and/or face sheet stiffeners. Each of these elements is capable of representing arbitrarily large displacements and rotations, since no simplifying assumptions are made in the theoretical formulation. Elastic-plastic effects may also be considered. An associated computer program is described which may be used to perform linear or nonlinear solutions for mechanical and thermal loading, linear natural frequency calculations. Several example problems are solved to demonstrate the capabilities of the program. (Author)

Parametric results for heat transfer across honeycomb sandwich panels

Abstract: The problem of heat transfer across honeycomb sandwich panels is theoretically investigated. The basic objective is to predict the rear surface temperature as a function of time when the front surface is exposed to a prescribed heat flux; the faces are bounded by planar sheets so that the air circulation in the honeycomb cells is bounded and contained. The influence of the air circulation on convective heat transfer is explicitly included. Drawing upon previous investigators' results that indicated various relations for the Nusselt numbers vs Rayleigh numbers in different regimes of the aspect ratio (defined as the ratio of the cell height to cell width), parametric calculations are performed to predict the rear surface temperatures. Chemical degradation of the material, especially the glue holding the face material on the end, is important but has not yet been included. The results indicate that decreasing the cell width, increasing the cell wall thickness and increasing the cell height all have beneficial effects upon the heat transfer; i.e., all of these variations reduce rear surface temperature for a given time for a prescribed heat flux on the front surface.

Edge effect in laminate composite materials

Abstract: In other studies dealing with the edge effect in composite materials [1-5] each layer was regarded as an anisotropic homogeneous one, all layers rigidly joined together and the entire specimen in a state of generalized plane strain under tension or flexure. The equations of anisotropic elasticity were solved by the finite-difference method [i, 2], by the finite-element method [3, 4], or by expansion into a double series of Legendre polynomials [5]. In the way these methods have been used, however, they hardly yield a true description of the edge effect with respect to stresses, because they are efficacious only when a bounded function will be the solution and not when the stresses can have singularities, as in the case of composite materials. In the application of these methods, the edge stresses remain bounded, but their maximum increases with increasing accuracy of the method (e.g., with an increasing number of terms retained in the series of orthogonal polynomials [5]) and this indirectly confirms the existence of a singularity. Here it will be demonstrated that in composite materials with characteristics close to real, there may appear a stress singularity, then there will be given examples of calculating the degree of such a singularity as a function of the reinforcement factor and of the fiber lay angle in adjacent layers of the composite

Opportunities for structural improvements for an advanced supersonic transport vehicle

Abstract: The superplastically formed diffusion-bonded (SPF/DB) program has developed successfully and far enough to recommend that a major structural program to validate the weight and cost of SPF/DB sandwich titanium structure should be initiated. The NASA Langley study of wing and fuselage SPF/DB sandwich panels shows that this process is potentially structurally efficient. The Douglas SPF/DB expanded sandwich process that utilizes a welded core sheet that expands to face sheets proves to be very efficient. The theoretical weight optimization design charts for the wing and fuselage concepts were validated by small-scale tests. Mnay design applications were fabricated. Projecting the results of an SPF/DB sandwich airframe structure to a MDC AST design shows significant weight and cost savings. A 6 percent lower direct operating cost was calculated. A growth AST utilizing composites, metal matrices, and SPF/DB sandwich shows future promise for a post-1990 technology readiness. Titanium SPF/DB sandwich, compared to presently available aluminum structure, is superior for application to a Mach 2.2 supersonic transport.

Response of stiffened sandwich panels

Abstract: An increasingly important part of the design of skin-stringer systems, such as those found in flight vehicles, is the ability to reduce surface vibration levels when they are subjected to the dynamic loads of jet, or propeller noise One common method of reducing the response of these structures is by layered construction using viscoelastic materials Thus analytical methods to describe such systems are essential

Buckling of sandwich plate layer method by finite

Abstract: fully in the free vibration analysis of thick plate1201 and static analysis of pavement [21]. In this study, the model is extended to the stability analysis of sandwich plate, and the results are compared with the published results. The study of the buckling behaviour of sandwich panels subject to axial compression is important for the design and analysis of such panels under gravity, wind or other loading systems. On the other hand, shear stability problem under edgewise shear forces occurs when the panel is under wind or racking loads.

Analysis of the effective heat conduction of honeycomb sandwich panels

Abstract: A method of analyzing the effective heat conduction of sandwich panels with different kinds of filler cells is elucidated.