The subject matter discussed in chapter seventeen focuses mainly on understanding various types of composites, however to fully understand the properties and characteristics of composites, we need to know about the different types of fabrication techniques. The fabrication techniques that will be discussed herein are: pultrusion, prepreg, filament winding, and resin transfer molding. But first, the rule of mixtures will be discussed.
A composite material is made of two or more materials, for example fiber and matrix.
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Fiber and matrix each have different properties. When combined, the properties of the composite material is some combination of the properties of the two constituent materials.
For certain properties (including density, modulus, coefficient of thermal expansion, dielectric constant and cost), the resulting composite property can be predicted by the "Rule-of-Mixtures". The composite property depends on how much of each of the original materials was mixed together -- hence rule-of-mixtures.
The composite property equals:.
the amount of the fiber property multiplied by the volume percentage of fiber plus the amount of matrix property multiplied by the volume percentage of matrix.
For example, the density of an S-2 Glass ® fiber/epoxy composite material is:.
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Two mathematical equations have been derived for the dependence of the elastic modulus on the volume fraction of the constituent phases for a two-phase composite. These rule-of-mixtures expressions predict that the elastic modulus should fall between an upper bound represented by:.
Ec(u) = Em*Vm + Ep*Vp.
And a lower bound represented by:.
Ec(l) = Em*Ep/(Vm*Ep+Vp*Em).
Now that the rule-of-mixtures has been explained, the fabrication techniques can be discussed.
The first of the four to be introduced will be the method of pultrusion. Pultrusion is used for the manufacture of components having continuous lengths and a constant cross-sectional shape (i.