How materials are classified and the most important properties of the engineering materials are listed with brief explanations. The properties covered here are especially those properties, which are important in manufacturing processes.
Engineering Materials and Their Properties
Classification of Engineering Materials
A. Metals and Alloys: Inorganic materials composed of one or more metallic elements. They usually have a crystalline structure and are good thermal and electrical conductors. Many metals have high strength and high elastic module. They maintain their good strength at high and low temperatures. They also have sufficient ductility, which is important for many engineering applications. They can be strengthened by alloying and heat treatment. They are least resistant to corrosion.
B. Ceramics and Glasses: Inorganic materials consisting of both metallic and non- metallic elements bonded together chemically. They can be crystalline (ceramics), non-crystalline (glasses) or mixture of both (glass-ceramics). Generally they have high melting points and high chemical stabilities. They have high hardness, high moduli and high temperature strength. But since they are very brittle they cannot be used as good as metals. Ceramics are usually poor electrical conductors. Ceramics have a high strength on compression
C. Polymers: Organic materials which consist of long molecular chains or networks containing carbon. Most polymers are non-crystalline, but some consist of mixtures of both crystalline and non-crystalline regions. They generally have low densities and low rigidity. Their mechanical properties may vary considerably. Most polymers are poor electrical conductors due to the nature of the atomic bonding. Most of them are corrosion resistant, but cannot be used at high temperatures. They generally have a good strength to weight ratio.
D. Composites: Materials where two or more of the above materials are brought together on macroscopic level. Usually they consist of a matrix and a reinforcement. They are designed to combine the best properties of each of its components.