engineering materials

Engineering Materials

Since the earliest days of the evolution of mankind , the main distinguishing features between human begins and other mammals has been the ability to use and develop materials to satisfy our human requirements. Nowadays we use many types of materials, fashioned in many different ways, to satisfy our requirements for housing, heating, furniture, clothes, transportation, entertainment, medical care, defense and all the other trappings of a modern, civilised society. Most materials doesn't exist in its pure shape , it is always exist as a ores . During the present century the scope of metallurgical science has expanded enormously ,  so that the subject can now be studied under the following headings :

a) Physical metallurgy

b) Extraction metallurgy

c) Process metallurgy

In the recent years studying the metallurgy science gave to humanity an ever growing range of useful alloys. Whilst many of these alloys are put to purposes of destruction, we must not forget that others have contributed to the material progress of mankind and to his domestic comfort.

This understanding of the materials resources and nature enable the engineers to select the most appropriate materials and to use them with greatest efficiency in minimum quantities whilst causing minimum pollution in their extraction, refinement and manufacture.

Selection of materials :

Let’s now start by looking at the basic requirements for selecting materials that are suitable for a particular application. For example a connecter joining electric cables. The plastic casing has been partly cut away to show the metal connector. Plastic is used for the outer casing because it is a good electrical insulator and prevents electric shock if a person touches it. It also prevents the conductors touching each other and causing a short circuit. As well as being a good insulator the plastic is cheap, tough, and easily moulded to shape. It has been selected for the casing because of these properties – that is, the properties of toughness, good electrical insulation, and ease of moulding to shape. It is also a relatively low cost material that is readily available. The metal joining piece and its clamping screws are made from brass. This metal has been chosen because of its special properties. These properties are good electrical conductivity, ease of extruding to shape, ease of machining (cutting to length, drilling and tapping the screw threads ), adequate strength and corrosion resistance. The precious metal silver is an even better conductor, but it would be far too expensive for this application and it would also be too weak and soft.

Another example as in  the connecting rod of a motor car engine. This is made from a special steel alloy. This alloy has been chosen because it combines the properties of strength and toughness with

the ability to be readily forged to shape and finished by machining.

Thus the reasons for selecting the materials in the above examples can be summarized as :

 1 Commercial factors such as:

Cost, availability, ease of manufacture.

2 Engineering properties of materials such as:

Electrical conductivity, strength, toughness, ease of forming by extrusion, forging and casting, machinability and corrosion resistance.

classification of engineering materials

1. Metals
1.1 Ferrous metals
 These are metals and alloys containing a high proportion of the element iron.
 They are the strongest materials available and are used for applications where high strength is required at relatively low cost and where weight is not of primary importance.
 As an example of ferrous metals such as : bridge building, the structure of large buildings, railway lines, locomotives and rolling stock and the bodies and highly stressed engine parts of
road vehicles.
 The ferrous metals themselves can also be classified into "families'.

1.2 Non – ferrous metals

 These materials refer to the remaining metals known to mankind.

 The pure metals are rarely used as structural materials as they lack mechanical strength.

 They are used where their special properties such as corrosion resistance, electrical conductivity and thermal conductivity are required. Copper and aluminum are used as electrical conductors

and, together with sheet zinc and sheet lead, are use as roofing materials.

 They are mainly used with other metals to improve their strength.

 Some widely used non-ferrous metals and alloys are classified as shown in figure 

2. Non – metallic materials
2.1 Non – metallic (synthetic materials ) These are non – metallic materials that do not exist in nature, although they are manufactured from natural substances such as oil, coal and clay. Some typical examples are classified  They combine good corrosion resistance with ease of manufacture
by moulding to shape and relatively low cost.
 Synthetic adhesives are also being used for the joining of metallic
components even in highly stressed applications.
2.2 Non – metallic (Natural materials ) Such materials are so diverse that only a few can be listed here to give a basic introduction to some typical applications.
 Wood: This is naturally occurring fibrous composite material used for the manufacture of casting patterns.
 Rubber :This is used for hydraulic and compressed air hoses and oil seals. Naturally occurring latex is too soft for most engineering uses but it is used widely for vehicle tyres when it is compounded with carbon black.
 Glass : This is a hardwearing, abrasion-resistant material with excellent weathering properties. It is used for electrical insulators, laboratory equipment, optical components in measuring instruments
etaand, in the form of fibers, is used to reinforce plastics. It is made by melting together the naturally occurring materials : silica (sand), limestone (calcium carbonate ) and soda (sodium carbonate).
 Emery : This is a widely used abrasive and is a naturally occurring
aluminum oxide. Nowadays it is produced synthetically to maintain
uniform quality and performance.
 Ceramic: These are produced by baking naturally occurring clays
at high temperatures after moulding to shape. They are used for
high – voltage insulators and high – temperature – resistant cutting
tool tips.
 Diamonds: These can be used for cutting tools for operation at high speeds for metal finishing where surface finish is greater importance. For example, internal combustion engine pistons and
bearings. They are also used for dressing grinding wheels.
 Oils : Used as bearing lubricants, cutting fluids and fuels.
 Silicon : This is used as an alloying element and also for the manufacture of semiconductor devices. These and other natural, non-metallic materials can be classified.

Composite materials (composites )

These are materials made up from, or composed of, a combination of different materials to take overall advantage of their different properties. In man-made composites, the advantages of deliberately combining materials in order to obtain improved or modified properties was understood by ancient civilizations. An example of this was the reinforcement of air-dried bricks by mixing the clay with straw.this helped to reduce cracking caused by shrinkage stresses as the clay dried out. In more recent times, horse hair was used to reinforce the plaster used on the walls and ceiling of buildings. Again this was to reduce the onset of drying cracks. Nowadays, especially with the growth of the plastics industry and the development of high-strength fibers, a vast range combinations of materials is available for use in composites. For example, carbon fiber reinforced frames for tennis rackets and shafts for golf clubs have revolutionized these sports.