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2.1 Composite Material
A composite material is a combination of a strong material usually as a fiber embedded in a weaker matrix. The combination produces a new material with properties
that can greatly outperform the properties of either component [1].
2.1.1 Composite background
The principals of composite materials can be found all around us. Reinforced concrete is one example of a material in which various elements combine to create a
stronger, tougher material than the sum of its individual components. Typically the term ‘advanced composites’ refers to carbon, Kevlar or other highly engineered fibers
embedded in an epoxy matrix. The epoxy matrix in composites serves to distribute stress loads evenly between the embedded fibers. The epoxy also stiffens the composite when
cured into the desired form. [1]. The properties of certain fibers make them extremely strong in tension. Glass
fibers, carbon fibers and Kevlar have very high tensile strength. Though strong and light weight these fibers lack stiffness on their own. Also, imperfections on the surface of the
fibers can cause stress points, which will open to fractures under strain. When fibers are woven together the multiple fibers act to divide strain so that it is not concentrated in
any one fiber. The combination of composite strength and low weight has been applied where
high material performance is paramount. Initial applications of advanced composite technology were for military and space programs, where high strength to weight ratios
were a necessity and cost was not critical. Since then, advanced composites have found their way into a variety of everyday uses.
The Kevlar in bulletproof vests is incredibly tough. High performance sporting goods have been made from composites for decades and in addition to outperforming
other materials they have produced more affordable and graceful shapes.
6 Fiberglass watercrafts are a mature technology that has dramatically changed the boat
building industry. As composites have become better understood they have become preferred materials for aircraft.
There are five key factors that determine the weight and cost of composite structures: 1 Labor content
2 Cost of machinery 3 Cost of materials
4 Tooling and assembly requirements 5 Curing requirements
Early composite fabrication techniques used dry-fiber broad goods laid up by hand with resins applied by hand. Most current composites manufacturing relies on fiber
broad goods that are pre impregnated with resin. These pre impregnated are still laboriously laid up by hand. These techniques use expensive materials and are very labor
intensive, limiting their practical commercial application. Composite parts made using the current state-of-the-art methods typically
include core stiffeners, including various kinds of specialized foams or honeycombs. These materials represent a significant cost in materials and labor for their application in
addition to increasing weight and reducing usable volume. Spectrum’s processes drastically reduce the need for core stiffeners. [2]
Curing high performance composite parts generally requires applying both external heat and pressure to the part. This is typically accomplished using expensive
autoclaves. With traditional composite fabrication techniques it can also be difficult to control the
manufacturing process with verifiable precision. This and other ‘knock-down’ factors force manufacturers to add weight and cost to load bearing parts in order to meet FAA
certification requirements. This has tended to make testing, process controls and certification procedures expensive, limiting the use of composites in civil aircraft.
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2.1.2 Composite Structure
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