Composite material

A composite material is defined as a mixture of 2 or more material that results in improved properties than those of the individual components used. In comparison to metallic alloy, each material retains its separate electrical, physical, and mechanical properties. The 2 materials are reinforcement and a matrix is developed. The main advantages of composite materials are their high strengths and stiffness, combined with less density, when compared with bulk material, resulting in a weight reduction in the finished part. In maximum cases, the reinforcement is harder, stronger, and stiff than matrix. The reinforcement is usually a fibre. Particulate composites have dimensions that are uniformly equal in all directions. They are spherical, platelets, straight or any other irregular geometry. Composites tends to be weaker and less stiff than continuous fibre composites, they are much less expensive. Particulate reinforced composites usually contains less reinforcements due to processing difficulties and brittleness. A fibre has a length that is much higher than its diameter. The length to diameter (l/d) ratio is known as the aspect ratio and can vary greatly in its field. Continuous fibre have really long aspect ratios, while discontinuous fibre have short ratios. Continuous-fibre composites normally have a standard orientation, while discontinuous fibre generally have a random orientation. Continuous-fibre composites are often made into laminates or sheets set by stacking single sheets of continuous fibre in different orientations to achieve the desired strength and stiffness properties with higher fibre volumes. Fibre produce high-strength composites due to their small diameter; they contain very less defects compared to the material produced in bulk. In general, the smaller the diameter of the fibre higher will be the strength but often the cost increases as the diameter becomes smaller. In addition, less-diameter high-strength fibre have greater flexibility and are easier to fabricate such as weaving or forming over radius. Typical fibre include glass and carbon, which may be continuous or discontinuous. The continuous phase is a matrix, which is a polymer or ceramic. Polymers have low strength and stiffness, metals have medium strength and stiffness but highly ductile, and ceramics have high strength and stiffness but are case brittle. The matrix performs several functions, including maintaining the fibre in the proper orientation and proper spacing and protecting them from abrasion. In the polymer and MMC that form a strong bond between the fibre and the matrix, the matrix transmits load from the matrix to the fibre through shear loading at the point of interface. In ceramic matrix composites, the objective is to increase the toughness value rather than strength and stiffness; therefore, a low strength bond is desirable. The type and quantity of the reinforcement shows the final properties.
Need for Composites:
A composite is something made from 2 or more components-in our case here, a fibre (Jute+ Bamboo) and a resin (PVC). Composites are not a new idea. Moses floated down the Nile in a basket made from papyrus coated with pitche. Papyrus form of the paper with a visible fibrous reinforcement would not have been difficult to produce a water-proof basket out of it. From ancient days, it is known that bricks are stronger if filled with chopped straws. African soil buts were re-in forced with greases and thin sticks. Although the concept is old, the materials have changed eventually. Carbon and glass fibre are very expensive compared to straw, and epoxy resins are costlier compared to the composition of cow dung and mud. Fortunately, the performance for the prescribed weight is much higher. There are natural composites such as wood, hemp & jute. The structure of a tree consists of long & strong cellulose fibre bonded together by a protein-like substance called G-lignin. The fibre that runs up the trunk and along the branches are thus aligned by the property in the optimum way to resist the stresses from gravity and wind forces. Large radii are provided at the trunk to branch end and branch to branch joint points to reduce a stress concentrations at high-load points.
A higher performance for a given weight leads to fuel saving. Excellent strength to weight & stiffness to weight ratios can be achieved by composite material. This is usually expressed as strength divided by density & stiffness divided by density. These are so called specific strength and specific modulus characteristic. Laminates patterns and ply side build-up in a part that can be made to give the required mechanical properties in various different directions. It is easier to achieve smooth aerodynamic profiles for reduction. Complex curvature parts with a smooth surface finish can be made in a manufacturing operation. Production cost is drastically reduced. Composites may be made by a wide range of processes/ products. Composites offer excellent resistance to corrosions, chemical attacks, and outdoor weathering; however some chemicals are damaging to composites and new types of paints and stripper are being developed to deal with this. Some thermoplastics are not very resistant to solvents.

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