Honeycomb sandwich panels examples

Figure 1.17 Another major use of structural adhesives in the aerospace industry is in making honeycomb sandwich panels where the face skins are bonded to the honeycomb core. This example is from a section of the rudder of Concorde and consists of aluminium alloy core and skins. More recently one has seen the increased use of non-metallic core and skin materials, i.e. carbon-fibre reinforced plastic (CFRP) skins. 

Figure 6.12 shows an example of a sandwich panel made from an extruded polypropylene honeycomb core (from Tubulam, Bagneux, France). 

A typical layered structure consists of two thin, glass-fibre-reinforced polymer skins bonded to a thick, lightweight honeycomb core (Fig. 4.5a). Such sandwich panels are used in railway carriages and aircraft there are similar structures inside many skins. Other examples are less obvious the space between the outer container and the toughened polystyrene liner of a refrigerator is filled with rigid polyurethane foam. 

Producing airplanes at lower costs is another aspect of advanced RP structural applications. In many cases, the carbon and aramid fiber RP components compare fevorably with the cost of conventional component structures, in spite of the rather high material costs. An important aspect here is the possible simplification of the design. For example, the complicated leg fairing of the Airbus was replaced by a simple all-RP sandwich (honeycomb core) panel reinforced by two RP beams. Besides a weight savings of about 30%, the production hours were reduced by 27%. 

The possibilities for making bonded structural sandwich elements in a variety of materials are very real. However, whilst there exist structural examples such as aluminium honeycomb panels (used in aircraft and transport applications) and metal skinned foam sandwich panels (used as the monocoque chassis in refrigerated transport applications), these composite constructions are normally utilised in non- or semi-structural ways. Typical skin materials are steel, aluminium, GRP and plywood, and common core materials are rigid foam polystyrene, polyurethane, polyisocyanurate, PVC, and honeycombed aluminium. In some instances the foam core is injected between the skins and adheres to them in others, adhesives are used to bond the separate components together. The nature of the manufaeturing process depends on the type of structure to be made, and the degree of investment in produetion maehinery. Both flat and eomplex eurved forms ean be made by a hand lay-up process as well as in an automated way. 

Figures 8-3, 8-4 and 8-5 show some of the parts which incorporate the sandwich panel concept to improve stiffness. They range from structural foam molded parts (which come from the mold as completed parts) incorporating low density cores and high density skins of the same materials to parts vacuum formed of a plastics material, the core of which becomes cellular during the heating process for forming. Reinforced plastic structural panels for curtain wall building construction that have honeycomb cores or decorative cores are examples...

One specific example concerns the sound-deadening, so-called acoustic panels . These are fitted to the front (position B in Fig. 76) and the rear of the engine and comprise a structurally bonded sandwich panel where a perforated aluminium, titanium or stainless steel top skin is bonded to the honeycomb core. 

Figure 1-7. Examples of plastics in the electrical and electronics field a) snap-in cable set of plugs and adapters, using Amoco s Ardel D-lOO polyarylate b) plastic parts in a sixty-ft.-diameter high-precision, high-frequency antenna c) schematic of a reinforced plastics/ composite radome that protects a 150-ft.-diameter radar antenna from its Maine environment view of reinforced plastics sandwich geodesic radome being assembled the completely assembled radome d) space-communication antenna. The horn of plenty uses an RP sandwich in its reflective panels (glass-fiber-TS polyester skins with a kraft paper-phenolic honeycomb core). It has a two-ply air-inflated Du Pont Hypalon/Dacron fabric elastomeric radome that will protect the antenna from the outside environment for many decades and uses other plastics. This site in Maine was the world s first ground-to-ground conununication satellite.

Thickness of the adhesive is varied to suit the specific application. For example, when the substrates to be bonded are smooth and uniform in thickness a light weight adhesive of about 5 mils in thickness is usually selected. For assemblies having large or variable gaps, adhesives up to 15 mils or higher in thickness are utilized. Examination of the honeycomb panel pictured in Fig. 1 makes it obvious that adhesive thickness is a critical factor that must be considered in the design of sandwich structure. The size of the adhesive fillets and thickness of the face bond adhesive determine the... 

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