Choice of materials for a machine element depends very much on its properties, cost, availability and such other factors. It is therefore important to have some idea of the common engineering materials and their properties before learning the details of design procedure. Common engineering materials are normally classified as metals and nonmetals. Metals may conveniently be divided into ferrous and non-ferrous metals. Important ferrous metals for the present purpose are: (i) Cast iron (ii) wrought iron (iii) steel. Some of the important non-ferrous metals used in engineering design are:
(a) Light metal group such as aluminum and its alloys, magnesium and
(b) Copper based alloys such as brass (Cu-Zn), bronze (Cu-Sn).
(c) White metal group such as nickel, silver, white bearing metals e.g.
Selection criteria for engineering materials
The selection of material, for engineering purposes, is one of the most difficult problem for designer. The best material is one which serves the desired objective at the minimum cost. The following factors should be considered while selecting the material: 1. Availability of the materials. 2. Suitability of the materials for the working conditions in service. 3. The cost of the material. 4. Its susceptibility to corrosion. 5. Its physical, chemical as well as thermal stability. 6. Material must withstand service demands. Such as dimensional stability, adequate strength, toughness, thermal conductivity etc. 7. The extent of the stresses induced. 8. Factor of safety desired. 9. The initial stresses during the material processing. 10. Its density, melting point, boiling point at the working conditions. 11. The extent of surface finish required. 12. Fabrication requirement. 13. Ease of joining, repair by welding etc. 14. Disposability and recyclability. 15. The aesthetics of the material. 16. Chemical nature