Glass-reinforced plastic
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Glass-reinforced plastic (GRP), is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine fibers made of glass. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass). The plastic is most often polyester or vinylester, but other plastics, like epoxy (GRE), are also sometimes used. The glass is mostly in the form of chopped strand mat (CSM), but woven fabrics are also used.
As with many other composite materials (such as reinforced concrete), the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the glass fibers are very strong in tension but have no strength against compression. By combining the two materials together, GRP becomes a material that resists well both compressive and tensile forces. The two materials may be used uniformly or the glass may be specifically placed in those portions of the structure that will be experience tensile loads.
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[edit] Applications
GRP/GRE is a versatile material with many uses. Although GRP was originally developed in the UK during the Second World War as a replacement for the molded plywood used in aircraft radomes (GRP being transparent to microwaves) its first main civilian application was for building of boats, where it gained acceptance in the 1950s, and now plays a dominant role. But its use has broadened over the years, and it is used extensively within the automotive and sport equipment sectors, although its use there is being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight. GRE is also used to make hot tubs, pipes for drinking water, sewers, chemicals, and so on.
Advanced manufacturing techniques such as pre-pregs and fiber rovings extend the applications and the tensile strength possible with fiber-reinforced plastics.
GRP is also widely used in the telecommunications industry for shrouding the visual appearance of antennas, due to its RF permeability and low signal attenuation properties. It may also be used to shroud the visual appearance of other equipment where no signal permeability is required, such as equipment cabinets and steel support structures, due to the ease with which it can be molded, manufactured, and painted to custom designs, to blend in with existing structures or brickwork.
GRP is also manufactured in sheet form and used for manufacturing electrical insulators and other structural components commonly found in the power industries. GRP materials for these uses are marketed under the trade name Glastic, or referred to generically as GPO materials like GPO-3. Parts manufactured from these materials are generally machined instead of formed to guarantee dielectric consistency from part to part.
[edit] Chopped strand mat
Chopped strand mat or CSM is a form of reinforcement used in glass-reinforced plastic. It consists of glass-fibers laid randomly across each other and held together by a binder.
It is typically processed using the hand lay-up technique, where sheets of material are placed in a mold and brushed with resin. Because the binder dissolves in resin, the material easily conforms to different shapes when wetted out. After the resin cures, the hardened product can be taken from the mold and finished.
Using chopped strand mat gives a glass-reinforced plastic with isotropic in-plane material properties.
- See also: Fiberglass molding
[edit] Examples of GRP use
- Thorpe Park's 'Tidal Wave' ride uses reinforced GRP for its 4-ton boats.
- Sailplanes have been built almost exclusively of reinforced plastic since the mid-1960s, with carbon, aramid and other fibers taking the place of glass in modern competition sailplanes, and with extensive use of high strength rovings.
- The hollow rotor blades of large wind turbines are usually made of GRP.
- Kayaks are often made of chopped strand mat and polyvinylester because they are strong, durable, and are easily shaped.
