composite materials

Composites are materials formed from a mixture of two or more components which, when combined, produce a material with properties or characteristics which are superior to those of the individual materials. Most composites are comprised of two parts, namely the polymer matrix component and the reinforcement component(s). The polymer matrix components are the materials which encapsulate the reinforcing material. The resulting matrix with reinforcements in place and distributing the load among the reinforcements. Since reinforcements are usually stiffer than the matrix material, they are the primary load-carrying component within the composite. Reinforcements may come in many different forms ranging from fibers, to fabrics, to particles imbedded into the matrix that form the composite.

Composite structures have existed for millions of years in nature. Wood is a wonderful example. Examination of the microstructure of wood reveals the composites material found in nature and suggests that modern composite materials have essentially evolved mimicking structures found in nature. A prefect example of a composite would be concrete. If you look at the different forms of concrete you will quickly get the idea of how reinforcements work. The cement acts as the matrix, which holds the concrete together, while the sand, gravel, and steel, serve as reinforcements. Concrete made with only sand and cement isn't nearly as strong as concrete made from cement, sand, gravel, which, in turn, is not as strong as concrete reinforced with steel, sand and gravel. The matrix and reinforcement materials of concrete are blended, poured and molded, typically in a form structure. In the generation of parts made with other composite materials, the shape of a composite part is determined by the shape or geometry of the mold, die of other tooling used in the part forming.

There are many different types of composites, including plastic composites. Each plastic resin has its own unique properties, which when combined with different reinforcements create composites with differing mechanical and physical properties. If one considered the number of plastic polymers in existence today and multiplied that figure by the number of reinforcements available, the number of potential composite materials is staggering. Of all the available plastic composites, there are two primary categories: Thermoset and Thermoplastic composites.

In the case of Thermoset composites, after application of heat and pressure, Thermoset resins undergo a chemical change, which cross-links the molecular structure of the material. Once cured, a Thermoset part cannot be remolded.

Thermoplastic materials are not as constrained as Thermoset materials and can be recycled and reshaped to create a new part. Thermoplastics that are reinforced with high-strength, high-modulus fibers provide dramatic increases in strength and stiffness, as well as toughness and dimensional stability. The performance gain achieved from Thermoplastic materials is often justification that compensates for the increased costs of most Thermoplastic materials.

Composite materials are used in numerous applications across a broad range of industries. Typically, composites are used to replace products made of metal alloys. Composites can offer comparable or better strength than metal parts, while providing a reduction in weight. This is particularly important in industries such as automotive and aerospace, where the use of composite materials results in lighter, faster and more fuel-efficient aircraft and automobiles.

Thermoplastic composites may also be designed to replace wood, fiberglass, concrete and other more traditional materials. The following is a partial list of industries that may have application for the use of long-fiber reinforced structural parts made from thermoplastic composites:

  • Aerospace
  • Automotive
  • Construction
  • Home Appliance
  • Marine
  • Material Handling
  • Medical
  • Military
  • Telecommunications
  • Transportation
  • Waste Management
  • Specialty Products
In general, among other attributes, composite materials are corrosion resistant and offer long fatigue lives, which has made them particularly attractive for many manufacturers. The fatigue life refers to the period of time the part will last prior to exhibiting material wear or significant stress. Typically, composites are substituted for conventional materials where there is a desire to reduce the weight of a particular part while providing the required strength and other performance criteria.

Numerous parts, particularly in the aerospace industry, have been and are being made from "advanced" thermoset composite materials, which are very expensive. These types of advanced composite parts are typically in the military and aerospace industries.

As a result of the previously noted issues and due to advances in thermoplastic composites, many product development engineers and design engineers believe that composite materials will play an ever-increasing role in modern technological development. New thermoplastic resins are regularly developed and more innovative methods of manufacturing are being introduced bringing down the costs of manufacturing parts. As costs for reinforced thermoplastic production are lowered, the use of thermoplastics composites becomes more and more viable in many commercial and industrial applications.




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