What are the different forms of composites?

1. Unidirectional lamina:
• It is basic form of continuous fiber composites.
• A lamina is also called by ply or layer.
• Fibers are in same direction.
• Orthotropic in nature with different properties in principal material directions.
• For sufficient number of filaments (or layers) in the thickness direction, the effective properties in the transverse plane (perpendicular to the fibers) may be isotropic. Such a composite is called as transversely isotropic.
2. Woven fabrics:
• Examples of woven fabric are clothes, baskets, hats, etc.
• Flexible fibers such as glass, carbon, aramid can be woven in to cloth fabric, can be impregnated with a matrix material.
• Different patterns of weaving are shown in Figure 1.13.

Typical weaving patterns are shown in Figure 1.13.

Figure 1.13: Types of weave

3. Laminate:
1. Stacking of unidirectional or woven fabric layers at different fiber orientations.
2. Effective properties vary with:
1. orientation
2. thickness
3. stacking sequence

A symmetric laminate is shown in Figure 1.14.

Figure 1.14: A symmetric laminate

4. Hybrid composites:
   
   The hybrid composite are composites in which two or more types of fibres are used. Collectively, these are called as hybrids. The use of two or more fibres allows the combination of desired properties from the fibres. For example, combination of aramid and carbon fibres gives excellent tensile properties of aramid and compressive properties of carbon fibers. Further, the aramid fibres are less expensive as compared to carbon fibres.