01.

Composite materials are not new. They have been used since antiquity. Wood, straw and mud have been everyday composites.
As the term indicates, composite material reveals a material that is different from its heterogeneous materials. Currently ‘composite materials’ refers to materials having strong fibers - continuous or non-continuous – surrounded by a weaker matrix material. The matrix serves to distribute the fibers and also to transmit the load to the fibers.

02.

A structural composite is a material system consisting of two or more phases on a macroscopic scale, whose mechanical performance and properties are designed to be superior to those of the constituent materials acting independently. One of the phases is usually discontinuous, stiffer, and stronger and is called the ‘matrix’. Sometimes, because of chemical interactions or other processing effects, an additional distinct phase called an ‘interphase’ exist between the reinforcement of the matrix. The properties of a composite material depend on the properties of the constituents, their geometry, and the distribution of the phases. One of the most important parameters is the volume fraction of reinforcement or fiber volume ratio. The distribution of the reinforcement determines the homogeneity or uniformity of the material system. The more non-uniform the reinforcement distribution, the more heterogeneous the material, and the higher the scatter in properties and probability of failure in the weakest areas. The geometry and orientation of the reinforcement affect the anisotropy of the system.

Phases of a composite material

Effect of the Orientation of Impurities

Different Fiber Forms

03. Fibers

Short Fibers have lengths as small as fractions of millimeters or as big as a few centimeters. Some general examples are felts, mats, and short fibers used in injection molding.

Long Fibers are cut during time of fabrication of the composite material and are used as cut, or woven

Some fiber materials are:

• Glass
• Aramid or Kevlar (very light)
  
• Carbon (high modulus or high strength)
• Boron (high modulus or high strength)
• Silicon carbide (high temperature resistant)

Fiber assembly for the fabrication of a composite material can take 3 forms:

• Unidimensional: unidirectional tows, yarns, or tapes
• Bidimensional: woven or nonwoven fabrics
• Tridimensional: fabrics with fibers oriented along many directions

Prior to creating the composite material te fibers are treated in order to:

• Decrease the abrasion action of fibers when passing through the forming machines
• Improve the adhesion with the matrix material
  

04. Matrix Materials

• Polymeric Matrix: thermoplastic resins and thermoset resins.
• Mineral Matrix: silicon carbide, carbon. They can be used at high temperatures.
• Metallic Matrix: aluminum alloys, titanium alloys, oriented eutectics.