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Composite Design
The first known applications of composite design can already be found in the first millennium before Christ in Egypt. The Egyptians used parchment which was glued in layers to create coffins. An unimposing composite design application hides within old walls, made of clay. To reinforce the wall they were filled with straw as a fiber material. Clay pots and bricks were supported in the same way. Until today this technology is applied in ferroconcrete. Composite design is also commonly used in car wheels with integrated steel wires, plywood and flake boards.
Modern composite technology developed parallel to the aerospace business and the increased necessity of simultaneous gradual weight reduction and higher stability. In the beginning only glass fibers were used to substitute metal in planes. These fibers have a comparably low specific stiffness and because of that can not be utilized in heavily loaded structures. Boat building is only one of the areas in which this technique still plays an important role today. Other important materials are carbon and aramid fibers.
The contents of composite design are easily displayed. By combining a matrix material with a fiber material a composite material is created. In this combination the fiber material gradually improves the stiffness-weight relation. In the twenties A. A. Griffith formulated the following rule based on this relation: "The strength of a material in fiber form is many times higher than that of the same material in another form, and the thinner the fiber, the greater the strength." A reduction of the diameter of fibers leads to a higher orientation of the molecules within the fibers and consequently strengthens them. Hence, the heavier component is substituted by a lighter one under the creation of a high specific strength. In a composite material many fibers are stacked up with a high density. The mutual fixation of all fibers is achieved by the matrix material, which also distributes forces from one fiber to another. The contact area between fiber and matrix is called interface. Therefore the condition of the interface has a great influence on the mechanical properties of the composite material.
Depending on the used matrix material (curable plastics, thermoplastics), the product shape and the necessary mechanical properties different production methods are available. For example manual lamination, prepreg methods or resin injection methods are known methods in case curable plastics are utilized. For the use of thermoplastics injection moulding and transfer moulding are common examples.
Fibers which guarantee tensile strength are highly flexible due to their slenderness. Mutual sliding between fibers is inhibited by gluing them together in the lamination process. A number of connected layers form a highly stiff and buckling resistant structure. The shape of a so produced structural element needs to be self contained (closed, enclosed) to reach high structural impact resistance. A skeletal structure comparable to the insect body is created. Following this principle monocoques of Formula 1 cars are produced.
