What are composites?

Introduction

Composite materials are the most advanced and adaptable engineering materials known to man.

In its most basic form a composite material is one which is composed of at least two elements working together to produce material properties that are different to the properties of those elements on their own. Composites are thus an entirely new and unique material family.

History

Composite materials occur naturally: obvious examples include wood and bone. Indeed natural composites (and man-made composites derived from natural materials, such as paper and straw-reinforced clay bricks) were the predominant engineering materials in use before the Industrial Revolution. Then steel and other metals effectively took over.

However with the rapid development of light, strong and durable man-made engineering materials – especially since the 1960s – synthetic, rather than natural, composites have enjoyed a spectacular rise in popularity as ‘engineering solutions providers’.

Composites Today

Advanced polymer composites consist of long or continuous fibre reinforcement embedded in a polymer matrix. The primary aim of the fibre reinforcement is to carry the loads or stress whilst the resin binds the reinforcement together and protects the fibres from the environment. The resulting advanced polymer composite material then has all the strength and stiffness of metals, combined with the benefits of polymers – namely light weight, corrosion resistance and durability.

Typical fibre reinforcements include carbon, glass or aramid and these can be presented in a number of forms. Examples include mats, uni-directional rovings, bi-directional woven fabrics and multi-axial fabrics.

Typical polymer matrices include chemical-based thermosetting resins such as polyester, vinylester and epoxy and thermoplastic resins such as polypropylene, nylon, PBT, PVDF or PEEK. Thermosetting resins are liquid at room temperature and solidify through irreversible chemical reactions. Thermoplastic resins, on the other hand, are chemically inert and solid at room temperature and are processed by heating to melt temperature, applying pressure and then cooling to solidify. This process is reversible, making these materials more environmentally sustainable (ie recyclable) than equivalent thermosetting resin systems.

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