Core materials sandwich construction

Honeycomb ho-ne- kom (before 12c) n. Manufactured product consisting of sheet metal or resin-impregnated sheet material (paper, fibrous glass, etc.) that has been formed into a network of open-ended, hexagonal cells, each cell s walls being shared with its immediate neighbors. Honeycombs are used as cores for sandwich constructions. 

Honeycomb cores n. Plastic impregnated woven or non-woven fiber fabric material that serves as a core in sandwich construction. 

In the usual building and construction practice a structural sandwich construction is a special case of a laminate with flat, curved, or otherwise two thin facings. The facings are of relatively stiff, hard, dense, strong material that are bonded to a relatively thick core of a lightweight material that is considerably less dense, stiff, and strong than the facings. Structural sandwiches can be all plastics, all metals, or combination of plastic and metal, etc. 

Since the stiffness of a laminate varies as a cubic relationship with the thickness, there are alternate methods employed to achieve thickness - and hence stiffness - than by using multiple layers of fiberglass and resin. Lightweight core materials, such as end-grained balsa wood, high-density polyurethane foam, PVC foam, and honeycombed materials, are available. These materials are sandwiched in between layers of unsaturated polyester resin to achieve increased laminate stiffness. The common terminology used for this technique is sandwich construction . 

A similar specimen design uses a sandwich construction with a dissimilar material bonded between the two cylindrical halves of the button specimen. This design is commonly used to measure the tensile strength of adhesives between dissimilar materials or if the adherend does not have the strength or characteristics to be machined into the shape of the button specimen. With some modifications in the dimensions, the button tensile test has also been adapted for testing adherence of honeycomb-cover sheets to the core (ASTM C 297). 

MIL-A-8576 MIL-A-9117 MIL-A-12850 MIL-C-14064 MIL-C-15705 MIL-C-18255 MIL-C-18969 MIL-C-23092 MIL-C-27315 MIL-C-27725 MIL-C-5539 MIL-C-7438 Adhesive, Acrylic Monomer Base Synthetic Elastomeric Sealant Natural Liquid Rubber Cement Grinding Disk Cement Caulking Compound Caulking Compound with Synthetic Rubber Base Caulking Compound—Watertight Exterior Hull Seams of Vessels Cement, Natural Rubber Coating Systems, Elastomeric Coating, Corrosion, Preventative, Air Fuel Tanks Natural Rubber Cement Core Material, Aluminum, for Sandwich Construction... 

The most widely used applications reported in 1973 included rib structures in the fabrication of lightweight reinforced-plastic parts and as a core material in sandwich construction, bonded to metal, wood, or glass. Other applications are as reinforcements for aircraft-control surfaces, radome housings, fUler blocks under fuel cells, tank floats for indicating devices, and ribs, posts, and framing in houses and shelters. Due to its buoyancy characteristics cellulose acetate foam has been used in lifeboats, buoys, and other flotation devices (21). 

Densities of syntactic foams range from 10 to 40 Ib/ft (160 to 640 kg/m ). Syntactic foams are being used as core materials in sandwich structures in construction of aircraft and hulls and decks of boats, and are being investigated for use in roofing structmes (2). 

ASTM C 271-61 (1988) Standard Test Method for Density of Core Materials for Structural Sandwich Constructions, 2 pp (Comm F-7)... 

MIL-STD-401B Sandwich Constructions and Core Materials General Test Methods, 26 September 1967, 35 pp (FSC 5680) (AS)... 

Foamed carbon has 600 times the thermal insulation capacity of the same weight of firebrick and is therefore used as a self-supporting thermal insulation material in furnaces or in fire-retarding sandwich-constructions. Foamed carbon cores are used in foundry technology, because they are easily produced and can be easily removed by combustion from inaccessible cavities. Furthermore foamed carbon is utilized as a filter material for the filtration of corrosive materials, as sintered plugs in gas inlets, as an electrode material and as a catalyst support. 

Figure 4.28 shows that the card comprises a symmetrical, sandwich-like structure. At the center of the card is a core sheet (16) made from a relatively rigid plastic material, such as polyvinyl chloride. In practice, the core can be constructed of two PVC layers (16a, 16b). Each layer can have a thickness of about... 

A sandwich structure is composed of two skins and a core material. The same or different materials are combined in the form of sandwich construction (Figure 7.46). They can be used in products with an irregular distribution of the different materials, and in the form of large structures or sub-structures. Overall load-carrying capabilities depend on average local sandwich properties, but materials failure criteria depend on local detailed stress and strain distributions. Design analysis procedures for sandwich materials composed of linear elastic constituents are well developed. In principle, sandwich materials can be analyzed as RP structures, but incorporation of viscoelastic properties will be subject to the limitations discussed throughout this book. 

For RP-faced sandvdch structures the design approaches includes both the unique characteristics introduced by sandwich construction and the special behavior introduced by RP materials. The overall stiffness provided by the interaction of the faces, the core, and their interfaces must be sufficient to meet deflection and deformation limits set for the structures. Overall stiffness of the sandwich component is also a key consideration in design for general instability of elements in compression (Figure 7.47). 

With most typical sandwich constructions, the faces provide primary stififhess under in-plane shear stress resultants (Nxy), direct stress resultants (N, Ny), and bending stress resultants (Mx, My) (Figure 7.48). Also as important, the adhesive and the core provide primary stiffness under normal direct stress resultants ( z), and transverse shear stress resultants (Q, Qy). Resistance to twisting moments (T, TyJ that is important in certain plate configurations, is improved by the faces. Capacity of faces is designed not to be limited by either material strength or resistance to local buckling. 

The following review relates to the performance of sandwich constructions such as those with RP skins and honeycomb core. For an isotropic material with a modulus of elasticity (E), the bending stiffness factor (El) of a rectangular beam 6 wide and 11 deep is ... 

Gas-assist injection moulding is becoming a frequently-used process for forming hollow, stiff parts. Foamed material, sandwich structures with compatible core and face sheets, and sandwich constructions with recycled material are other examples of how intelligent material utilisation can lead to source reduction. 

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