There can be many secondary reasons why polymer composites may be chosen for the manufacture of particular articles or components, but the primary reason is because of weight saving for their relative stiffness and strength. As an example we can compare a carbon fibre reinforced composite with its steel counterpart. The carbon fibre composite can be five times stronger than 1020 grade steel while having only one fifth the weight. Aluminium (6061 grade) is much nearer in weight to carbon fibre composite (though still somewhat heavier), but the composite can have twice the modulus and up to seven times the strength.
When should you use composites?
Polymeric composites are one class of engineering material. As with all other engineering materials, they have particular strengths and particular weaknesses. The matrix protects the strong stiff fibres and together the composite material improves on the properties of either the matrix material or the fibres alone. A major driving force behind the development of composites has been to produce materials with improved specific mechanical properties over existing materials. Specific stiffness can be defined as the stiffness of a material divided by the density of material and specific strength can be defined as the strength of a material divided by the density of the material. It is these good specific properties of composites that allow the design of high performance structural components. Polymer composite material structures can also be engineered so that the directionality of the reinforcement material is arranged so as to match the loading on a given component or structure. In addition, polymer composites are useful in applications where the environment would be detrimental to other materials. A wide selection of resins and coatings are available to match appropriate environmental conditions. Cost is ever present in the engineering equation and it is the balance of cost and performance that determine whether or not to use polymer composites over an alternative structural material option.