What is the Definition of a Composite Material?

Fiberglass Cloth
Fiberglass cloth commonly used in composites. Todd Johnson

Loosely defined, a composite is a combination of two or more different materials that results in a superior (often stronger) product. Humans have been creating composites for thousands of years to build everything from simple shelters to elaborate electronic devices. While the first composites were made from natural materials like mud and straw, today's composites are created in a lab from synthetic substances. Regardless of their origin, composites are what have made life as we know it possible.

A Brief History

Archaeologists say humans have been using composites for at least 5,000 to 6,000 years. In ancient Egypt, bricks made from mud and straw to encase and reinforce wooden structures such as forts and monuments. In parts of Asia, Europe, Africa and the Americas, indigenous cultures build structures from wattle (planks or strips of wood) and daub (a composite of mud or clay, straw, gravel, lime, hay, and other substances).

Another advanced civilization, the Mongols, were also pioneers in the use of composites. Beginning around 1200 A.D., they began building reinforced bows out of wood, bone, and natural adhesive, wrapped with birch bark. These were far more powerful and accurate than simple wooden bows, helping Genghis Khan's Mongolian Empire to spread across Asia.

The modern era of composites began in the 20th century with the invention of early plastics such as Bakelite and vinyl as well as engineered wood products like plywood. Another crucial composite, Fiberglas, was invented in 1935. It was far stronger than earlier composites, could be molded and shaped, and was extremely lightweight and durable. 

World War II hastened the invention of still more petroleum-derived composite materials, many of which are still in use today, including polyester. The 1960s saw the introduction of even more sophisticated composites, such as Kevlar and carbon fiber. 

Modern Composite Materials

Today,  the use of composites has evolved to commonly incorporate a structural fiber and a plastic, this is known as Fiber Reinforced Plastics or FRP for short. Like straw, the fiber provides the structure and strength of the composite, while a plastic polymer holds the fiber together. Common types of fibers used in FRP composites include:

  • Fiberglass
  • Carbon fiber
  • Aramid fiber
  • Boron fiber
  • Basalt fiber
  • Natural fiber (wood, flax, hemp, etc.)

In the case of fiberglass, hundreds of thousands of tiny glass fibers are compiled together and held rigidly in place by a plastic polymer resin. Common plastic resins used in composites include:

  • Epoxy
  • Vinyl Ester
  • Polyester
  • Polyurethane
  • Polypropylene

Common Uses and Benefits

The most common example of a composite is concrete. In this use, structural steel rebar provides the strength and stiffness to the concrete, while the cured cement holds the rebar stationary. Rebar alone would flex too much and cement alone would crack easily. However, when combined to form a composite, an extremely rigid material is created.

The composite material most commonly associated with the term "composite" is Fiber Reinforced Plastics. This type of composite is used extensively throughout our daily lives. Common everyday uses of fiber reinforced plastic composites include:

  • Aircraft
  • Boats and marine
  • Sporting equipment (golf shafts, tennis rackets, surfboards, hockey sticks, etc.)
  • Automotive components
  • Wind turbine blades
  • Body armor
  • Building materials
  • Water pipes
  • Bridges
  • Tool handles
  • Ladder rails

Modern composite materials have a number of advantages over other materials such as steel. Perhaps most importantly, composites are much lighter in weight. They also resist corrosion, are flexible and dent-resistant. This, in turn, means they require less maintenance and have a longer lifespan than traditional materials. Composite materials make cars lighter and therefore more fuel efficient, make body armor more resistant to bullets and make turbine blades that can withstand the stress of high wind speeds.

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