Introduction to Composite Materials
What is a Composite?
A composite material can be defined as a combination of a matrix and a reinforcement, which when combined gives properties superior to the properties of the individual components.
In the case of a composite, the reinforcement is the fibres and is used to fortify the matrix in terms of strength and stiffness.
The reinforcement fibres can be cut, aligned, placed in different ways to affect the properties of the resulting composite.
The matrix, normally a form of resin, keeps the reinforcement in the desired orientation. It protects the reinforcement from chemical and environmental attack, and it bonds the reinforcement so that applied loads can be effectively transferred.
Type of Composites
The term ‘composite’ can be used for a multitude of materials. Composites UK uses the term composite, or reinforced polymers to encompass:
Carbon fibre-reinforced polymers (CFRP)
Glass fibre-reinforced polymers (GFRP)
Aramid products (e.g. Kevlar)
Bio-derrived polymers (or biocomposites as they are sometimes referred)
Why Use Composites?
The primary reason composite materials are chosen for components is because of weight saving for its relative stiffness and strength. For example, carbon-fibre reinforced composite can be five times stronger than 1020 grade steel while having only one fifth of 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?
As with all engineering materials, composites have particular strengths and weaknesses, which should be considered at the specifying stage. Composites are by no means the right material for every job.
However, a major driving force behind the development of composites has been that the combination of the reinforcement and the matrix can be changed to meet the required final properties of a component. For example, if the final component needs to be fire-resistant, a fire-retardant matrix can be used in the development stage so that it has this property.
Stiffness and strength can also be influenced at the development stage. The material structure can be engineered so that the directionality of the reinforcement material is arranged so as to match the loading on a given component.
A wide range of coatings and paints are available to match appropriate environmental conditions, which can be highlighted in the initial development stage or applied later should it be decided that a particular property or standard needs to be met further down the line.
Cost is ever present in the engineering equation and it is the balance of cost, performance and life-cycle analysis that should determine whether or not to use polymer composites over an alternative structural material option.