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Types and Classification of the Composites

Posted on 18 Feb 2016 in Blog | 0 comments

There was an evolution. That is a fact. Man could create fire, the wheel, invented agriculture, and a lot of other things. What was prevalent throughout history was the fact that we humans were purists. We used a single element and made a product out of it. This approach was essentially flawed, as it created objects that had properties of the constituent material. So, an aluminum box would be lightweight, and still be sturdy. An iron box on the other hand, would be heavier, sturdier, but more prone to corrosion. These were essential flaws that could not be removed from the objects, because these were inherent to the material used in them.

This changed slowly, when we reached the idea of using different materials to achieve a similar goal. The different materials would be incompatible, in many cases, but a combined use of them would give rise to features and properties that were not present in the base materials at all. These combined materials were called composites, and they have taken the world by storm. They are used everywhere, from cars to wearing gear. And they have properties that set them apart from purist objects. They make up for something more exquisite.

The composite materials are of numerous types, and classifications are done on the following basis:

1. Matric constituent

Based on the constituent of matrix of the materials, they are of the types:

Organic Matrix Composites: These consist of polymers and resins that have organic origins, and have thermosets and thermoplastics under their banner. They are very cheap to manufacture, and we can fine-tune the characteristics of these composites by carefully choosing (or even manufacturing) the component materials in the first place. This is something that other forms of composites do not offer.
Metal Matrix Composites: Although these are not as widely used as their plastic counterparts (which come under organic composites), they are widely known for their high strength, tensile nature, toughness and stiffness: something which organic matrix polymers do not possess. Since these are metals and have very high melting points, they can withstand high temperatures and sustain their shape under adverse conditions. They are resistant to corrosion and non-reactive in most cases (as opposed to the individual metals that form the components). Some common metal components used are Titanium, Magnesium and Aluminum, which have major applications in aerospace industry.
Ceramic Matric Composites: Ceramics are usually sturdy solids that have strong ionic bonding, or in a few cases, strong covalent bonding as well. They have some very good properties such as very high melting point, superior corrosion resistance, stability and compressive strength in adverse situations, and the like. Thus, ceramics are materials which are preferred if the operating temperatures could get as high as 1500 degrees Celsius.

2. Reinforcements

The composites might need reinforcements, which could be fibers, or particles of fibers, or whiskers. Fibers are materials that have a thin and long structure, where one axis is long while other is circular or almost circular in nature. The following classifications are possible:

Fiber reinforced composites: Fibers are very good components and transfer strength and other desirable properties to the composites. Fibers are not very ideal for use in composites, as the properties that they bring to the composite material can depend on their length, shape, orientation and composition, and these vary a lot. Especially, orientation of fibers can matter a lot in strength of the composite. During formative stages of the matrix, there can be some randomness and optimum strengths might not be reached.
Laminar composites: These are present in “lamina”, that is, layers of material bonded together. They are used in clad and sandwich laminate formats, which have numerous applications.
Particulate reinforced composites: These are microstructures of metal and ceramic composites, which have one phase of material strewn into another, to form numerous particles, which may have different shapes like triangle, square and the like. The dispersed size of these particles is of the order of few microns, and they can get in volumes of as much as 28%.
Whiskers: These are single crystals with almost no defects in their structure. They are not continuous, and are short in structure, and made from materials such as graphite, silicon carbide, and the like. The lengths of these whiskers is of the range of 3 to 55 nanometers. They have a length to width ratio greater than one, and therefore, are elongated, as opposed to the particles.
Flakes: These can be used in place of fibers, and can usually be densely packed into the composite. They can provide numerous characteristics to the composite. Metal flakes can make the material conductive, while mica and glass flakes can make it highly resistive. Although these are very helpful, flakes can fall short in case of uniformity of the material. They can have differing shapes and sizes, and can have notches or cracks, etc.
Filled composites: They come by adding filler material to plastic components, to change the properties of the composite. They enhance the properties and reduce the weight as well, as they are simply filler materials that “fill” up the space.
CerMets: These are composites composed of ceramics and metals. They take up the best properties of each, such as high strength, high tolerance to temperature, better stability, and the like. They are usually used to manufacture resistors, capacitors and numerous electrical components that have specific properties, and might have to work under high temperatures. They are used in dentistry for filling the tooth cavities and the like, as well as in machining and cutting tools. They are somewhat pricier than the other composites.

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