Structural 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. 

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

Some special types of foams are (1) structural foams (2) syntactic foams and multifoams and (3) reinforced foams. Structural foams (Figure 2.58c and d), which possess full-density skins and cellular cores, are similar to structural sandwich constructions or to human bones, which have solid surfaces but cellular cores. Structural foams may be manufactured by high pressure processes or by low-pressure processes (Figure 2.61). The first one may provide denser, smoother skins with greater fidelity to fine detail in the mold than maybe true of low-pressure processes. Fine wood detail, for example, is used for simulated wood furniture and simulated wood beams. Surfaces made by low-pressure processes may, however, show swirl or other textures, not necessarily detracting from their usefulness. Almost any thermoplastic or thermosetting polymer can be formulated into a structural foam. 

The term structural foams designates components possessing full density skins and cellular cores, similar to structural sandwich constructions, or to bones, whose surfaces are solid but whose cores are cellular. For structural purposes, they have favourable strength and stlffness-to-welgh ratios, because of their sandwich type configuration. Frequently, they can provide the necessary structural performance at a reduced cost of materials. 

Laminated structures Sandwich construction Shoes, interUnings, belts, etc. 

For obtaining a low -weight, high-bending-stiffness structure, sandwich constructions are a conunon choice for composite components. To make a sandwich, low-density materials are inserted as sandwich cores between two faces of the structural material itself (so in this case between two stacks of prepreg plies). Commonly used core materials are plastic foams (for example, made from PVC, PS, or PET) and balsa wood. Examples of core materials for more sophisticated, structured sandwich cores are honeycombs (made from aluminium, or resin-impregnated paper sheets), or fibre-reinforced foams. 

A self-adhesive flame resistant, controlled flow epoxy for structural/sandwich construction. Cure temperature 80 - 125"C and hot-wet service operation to 80 C. Meets BMS 8079V and MIL-R-9300B, Type I. 

Core material, metallic, heat-resisting, for structural sandwich construction Honeycomb material, cushioning, paper... 

Military Specification MIL-A-25463 Adhesive, Film Form, Metallic Structural Sandwich Construction ... 

Sorenson, A., Sonic fatigue testing and development of aircraft panels. Symposium on Structural Adhesives and Sandwich Construction. Wright Air Development Center, Wright Patterson Air Force Base, Ohio, 1957. 

Applications All types of structural bonding Large area metal-to-metal bonds, sandwich construction General-purpose General-purpose... 

Plate 18 Structure of the NF-kB p50 homodimer bound to a 10 base pair kB- responsive DNA site. The structure of the DNA-binding p50 subunit of NF-kB complexed with DNA is an example how /3-sheets make specific contacts with the DNA. The p50 NF-kB subunit dimerizes. Both halves are folded as a /3-sandwich. The dimer wraps around the major groove of the unfolded DNA double helix, and the /3-sheets make the specific contacts. The N-termlnal part of NF-kB p50 is similar to the core domain of the tumour suppressor, p53 (see Chapter 15). (The ribbon structure was constructed with permission of the authors and Nature from data in ref. 23 of Chapter 9 see also ref. 24 of Chapter 9.)... 

Uniaxial compressive properties are important to the design engineer who can utilize the foams inherent high compressive strength in reinforcing other structural members. Sandwich construction is a typical example of such a use, as in submarine-hull construction. Syntactic-foam prepregs have been developed for this application (7). 

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). 

MII S-25392B(ASG) Sandwich Construction, Plastic Resin, Glass Fabric Base, Laminated Facings and Urethane Foomed-in-Place Core, for Structural Applications, 8 May 1968, 12 pp (FSC 9330) (AS)... 

Another important distinction is based on density. For flotation, sandwich construction, thermal insulation, and ecomsmy, very low-density foams are preferred, often as low as 1 Ib/ft or less. Vinyl, polyolefin, and syntactic foams are generally of medium density. Structural foams are of medium to fairly high density and have a graded structure from solid skin to fairly low-density core. RIM foams are similar, often exhibiting a fairly high density. 

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