Plastics skin-core structures

Plastic composites are more or less inhomogeneous particularly due to the anisotropy of filler concentration. Plastic processing methods involving shear flow can lead to separation of the fillers and polymer matrix. For instance, a skin-core structure can be formed where the outer surface has a lower filler concentration than the inner part of the specimen. This phenomenon generates samples with a nonconductive surface (although the conductivity of the core may be high). Typically, the conductivity... 

In addition to developing solid RP structures, work has been conducted on sandwich structures such as filament-wound plastic skins with low-density foamed core or a plastic honeycomb core to develop more efficient strength-to-weight structures. Sandwich structures using a syntactic core have been successfully tested so that failures occurred at prescribed high-hydrostatic pressures of 28 MPa (4,000 psi). 

W J Cantwell, G Broster and P Davies, The influence of water immersion on skin-core debonding in GFRP-balsa sandwich structures , / Reinf Plastics Compos 1996 15(11) 1161-1172. 

The plastic insulants are rigid, homogeneous materials, suitable as the core of sandwich panels. Such a method of fahrication is facilitated when using foamed rigid polyurethane, since the liquids can he made to foam between the inner and outer panel skins and have a good natural adhesion, so making a stiff structural component [40]. 

They range from structural foam molded products (which come from the mold as completed molded products) incorporating low density cores and high density skins of the same materials to products vacuum formed of a plastics material, the core of which becomes cellular during the heating process (Chapter 8). RP translucent structural panels for curtain wall building construction using... 

The type of shelf design is the next consideration. The shelf can be a solid plate of plastic material, an inverted pan-like structure with reinforcing ribs, a sandwich-type structure with two skins and an expanded core, or even a lattice type sheet that has a series of openings. The choice between these is dictated by a number of factors. One is appearance or aesthetics. 

The lattice-type shelf is functionally as good as the others, but it may not look appropriate for a book shelf in the context of a library. A second consideration is a combination of physical requirements and appearance. A simple plastic beam that will function adequately in terms of strength and stiffness may be rather thin. A shelf of this type can look flimsy even if it is functional. This impression is useful to the designer since the solid plate is probably an uneconomical use of material. A requirement was added that the design should look like a wood shelf since this is the context in which it is to be used. To produce the desired thickness appearance either a lipped pan with internal reinforcement can be used or, alternatively, a sandwich-type structure with two skins and a separator core. In either case the displacement of the material from the plane of bending will improve the stiffness efficiency of the product. The appropriate procedure is to... 

The simply supported beam has a load applied centrally. The upper skin go into compression while the lower one goes into tension, and a uniform bending curve will develop. However, this happens only if the shear rigidity or shear modulus of the cellular core is sufficiently high. If this is not the case, both skins will deflect as independent members, thus eliminating the load-bearing capability of the plastic composite structure. 

SF is characterized as a plastic structure with a nearly uniform density foam core and integral near-solid skins (facings). When these structures are used in load-bearing applications, the foam bulk density is typically 50 to 90% of the plastic s unfoamed bulk density. Most SF products (90wt%) are made from different TPs, principally PS, PE, PVC, and ABS. Polyurethane is the primary TS plastic. Unfilled and reinforced SFs represent about 70% of the products. The principal method of processing (75%) is modified low-pressure injection molding. Extrusion and RIM account for about 10% each. 

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