Cores sandwich materials

It is interesting to note that foamed composites are suitable sandwich core materials for FRP boats (8). Cross-ties (or sleepers) for railroads, especially for use in tunnels and subways, are very promising applications. Japanese National raUways carried out a long-term test in a tunnel, and the results were excellent. 

ASTM C 394-62 (1988) Standard Method of Test for Shear Fatigue of Sandwich Core Materials, 2 pp (Comm F-7)... 

Shear properties of sandwich core materials can be determined by a similar technique described in ASTM C273-94 [24]. In this method the support plates may be adhered directly to the facings of the sandwich or the core materials. The recommended speed of jaw separation is 0.50 mm/minute. 

ASTM C275 94. Shear properties of sandwich core materials. 

ASTM-Intemational, editor. Standard practice for shearography of polymer matrix composites, sandwich core materials and filament-wound pressure vessels in aerospace apphcations 2007. 

Ji, G. and Li, G. (2013) Impact tolerant and healable aluminum miUitube reinforced shape memory polymer composite sandwich core. Materials and Design, 51, 79-87. 

Table 3.4 Properties of PVC foam cores (Divinycell H Sandwich Core Material, reference 3.6).

The Plate Constitutive equations can be used for curved plates provided the radius of curvature is large relative to the thickness (typically r/h > 50). They can also be used to analyse laminates made up of materials other than unidirectional fibres, eg layers which are isotropic or made from woven fabrics can be analysed by inserting the relevant properties for the local 1-2 directions. Sandwich panels can also be analysed by using a thickness and appropriate properties for the core material. These types of situation are considered in the following Examples. 

This type of analysis could also be used for a sandwich structure with solid skins and a foamed core. It is simply a matter of using the appropriate values of E, G 2,Ei,v 2 for the skin and core material. This is illustrated in the following Example. 

What kinds of configurations are possible for composite structures The most obvious is that of a fiber-reinforced laminate. With a laminate, we can change laminae orientations, stacking sequence, and laminae materials to arrive at a suitable structure. We can stiffen the laminate, or we can put a sandwich core in the middle of those laminae. We can do all of those possibilities, but recognize that we will also have, in vir-tuaiiy any structure, some kind of hoie or a cutout for some reason. Thus, we must have a procedure to place an appropriate amount of reinforcement around those cutouts so that ioad can be transferred around them. Without that reinforcement, the structure cannot do the job it is required to do. These various possibie configurations are shown in Figure 7-38. 

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 . 

Structural sandwich panels represent what is probably one of the most common applications for structural adhesives. Facing materials can be made to adhere to core materials, such as aluminum or paper honeycomb, to give a high composite strength-to-weight ratio. 

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). 

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

Making more economical material by sandwiching a less costly core material between two more expensive materials. 

Component parts with PTFE polyamide materials as the skin component and reinforced polyamides as the core materials made by sandwich moulding will lower the material and processing costs and reduce the amount of PTFE polyamide... 

Corrosion can be brought about as a result of water ingress or the coupling of anodic metals and carbon fiber composites in the absence of a barrier coating [29], If the adhesive layer is improperly coated or sealed, it absorbs moisture and may corrode. The core material in honeycomb sandwich materials is prineipally subject to bondline corrosion [29]. Coupling a cathodic material such as carbon with an anodic metal can cause galv anic corrosion if a protective barrier is not present. 

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