In the true definition, a composite material is simply a material that has two components which total strength combined, is greater than the sum of their individual components. For composites, 1+1 does not equal 2, but rather much, much more. There are many examples of composite materials, for example, particleboard is technically a composite. (wood and glue).
However, in the modern world, composites is the broad term which encompasses “fiber reinforced composites”, or FRP for short. This is the material that is changing our lives, and is opening doors to new possibilities.
FRP composite materials combine two primary components, a resin and an structural fiber. There are a variety of fiber reinforcements that are used in FRP composites. Glass fiber (fiberglass) has long been the low cost workhorse of the composites industry. Aramid fiber, the best known being Kevlar, a DuPont trademarked product, is used due to it’s high tensile strength which is ideal in ballistic and impact applications. Carbon fiber is another primary reinforcing fiber used today, it’s high modulus to weight ratio provides the ability to make lightweight yet stiff structures.
Although there are other fibers commonly used in composites today, such as basalt, thermoplastic fibers, natural fibers, and others. The three primary fibers used today are glass, aramid, and carbon.
The fibers alone are soft and flexible. Using traditional and modified textile weaving and knitting machinery, these fibers are woven or stitched together into fabrics and cloth. When saturated with resins these cloths become the backbone to the composite and provide the strength to the new materials.
The resins are design for composites. Alone, most resins used in composites are brittle or too flexible. Resins are either thermoset, or thermoplastic. Traditionally, composite resins are thermoset but thermoplastic is gaining popularity.
Thermoset resins include epoxy, polyester, vinyl ester, urethane, phenolic, and others. These resins start as a liquid, go through a chemical reaction fully cross linking the molecules, and finish as a solid. In composites, the resin will wet out the structural fibers encapsulating and curing around them.
This curing process is done in a mold, around a mandrel, or through a die, giving the finished composite the shape. It could be in the shape of a boat, a pipe, or simply a flat sheet. Once cured, not only can the composite have an excellent strength to weight ratio, but the resin and fiber can be selected to provide properties tailored to the application.
Possible Properties of FRP Composites
- Non corrosive
- Fire and flame resistance
- Toughness / Impact resistance
- Tailored flex properties
- Attractive Cosmetics
- Non conductive or extremely conductive
- Water resistance
Beyond the properties, processing and manufacturing products with composites allow the ability to make complex parts and shapes. There are many reasons manufacturers are looking to composites to build their widgets both large and small. For any application the designer has the flexibility to tailor the properties to the specific need of the product. This unique design ability is what gives the true value to the composite. The possibilities are truly endless.