In an advanced society like ours we all depend on composite materials in some aspect of our lives. Fiberglass, developed in the late 1940s, was the first modern composite and is still the most common. It makes up about 65 per cent of all the composites produced today and is used for boat hulls, surfboards, sporting goods, swimming pool linings, building panels and car bodies. You may well be using something made of fiberglass without knowing it. Over the last thirty years composite materials, plastics, and ceramics have been the dominant emerging materials. The volume and number of applications of composite materials have grown steadily, penetrating and conquering new markets relentlessly. Modern composite materials constitute a significant proportion of the engineered materials market ranging from everyday products to sophisticated niche applications.
Composites are emerging with an increasing role in building materials to replace timber, steel, aluminum, concrete etc. Composites are being used for prefabricated, portable and modular buildings as well as for exterior cladding panels. Composites also find extensive applications in shuttering supports, special architectural structures imparting aesthetic appearance, ergonomics, large signages etc. besides longer life, low maintenance, fire retardancy etc. Their benefits of corrosion resistance and lightweight have proven attractive in many low stress applications. The use of high performance FRP in primary structural applications, however, has been slower to gain acceptance although there is much development activity.
In pursuit of developing advanced performance materials for building and construction, railways, automobiles, bio-medical etc., the Advanced Composites Programme was launched by Technology Information, Forecasting & Assessment Council (TIFAC), an autonomous organization under the Department of Science & Technology (DST), Govt. of India.
What makes a material a composite?
Combining two or more materials that have quite different properties forms composite materials. The different materials work together to give the composite unique properties, but within the composite you can easily tell the different materials apart - they do not dissolved or blended into each other.
Composites exist in nature. A piece of wood is a composite, with long fibers of cellulose (a very complex form of starch) held together by a much weaker substance called lignin. Cellulose is also found in cotton and linen, but it is the binding power of the lignin that makes a piece of timber much stronger than a bundle of cotton fibers.
Not a new idea
Humans have been using composite materials for thousands of years. Take mud bricks for example. A cake of dried mud is easy to break by bending, which puts a tension force on one edge, but makes a good strong wall, where all the forces are compressive. A piece of straw, on the other hand, has a lot of strength when you try to stretch it but almost none when you crumple it up. But if you embed pieces of straw in a block of mud and let it dry hard, the resulting mud brick resists both squeezing and tearing and makes an excellent building material. Put more technically, it has both good compressive strength and good tensile strength.
Another well-known composite is concrete. Here aggregate (small stones or gravel) is bound together by cement. Concrete has good strength under compression, and it can be made stronger under tension by adding metal rods, wires, mesh or cables to the composite (so creating reinforced concrete).
Making a composite
Most composites are made up of just two materials. One material (the matrix or binder) surrounds and binds together a cluster of fibbers or fragments of a much stronger material (the reinforcement). In the case of mud bricks, the two roles are taken by the mud and the straw; in concrete, by the cement and the aggregate; in a piece of wood, by the cellulose and the lignin. In fiberglass, fine threads or fibres of glass, often woven into a sort of cloth, provide the reinforcement and the matrix is a plastic.
The threads of glass in fiberglass are very strong under tension but they are also brittle and will snap if bent sharply. The matrix not only holds the fibers together, it also protects them from damage by sharing any stress among them. The matrix is soft enough to be shaped with tools, and can be softened by suitable solvents to allow repairs to be made. Any deformation of a sheet of fiberglass necessarily stretches some of the glass fibres, and they are able to resist this, so even a thin sheet is very strong. It is also quite light, which is an advantage in many applications.
Over recent decades many new composites have been developed, some with very valuable properties. By carefully choosing the reinforcement, the matrix, and the manufacturing process that brings them together, engineers can tailor the properties to meet specific requirements. They can, for example, make the composite sheet very strong in one direction by aligning the fibers that way, but weaker in another direction where strength is not so important. They can also select properties such as resistance to heat, chemicals, and weathering by choosing an appropriate matrix material.
Composite as Building Materials
Composites present immense opportunities to play increasing role as an alternate material to replace timber, steel, aluminum and concrete in buildings. Their benefits of corrosion resistance and low weight have proven attractive in many low stress applications. The use of high performance FRP in primary structural applications, however, has been slower to gain acceptance although there is much development activity.
Composite is being used for the manufacture of prefabricated, portable and modular buildings as well as for exterior cladding panels, which can simulate masonry or stone. In interior applications, composites are used in the manufacture of shower enclosures and trays, baths, sinks, troughs and spas. Cast composite products are widely used for the production of vanity units, bench tops and basins.