Engineering Materials

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Engineering Materials

Msc. Shaymaa Mahmood

Introduction to Eng. 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 figure 1 shows 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

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Engineering Materials

Msc. Shaymaa Mahmood

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.

Figure 1. The electrical connector.

Another example as in figure 2 shows 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.

Figure 2. The connecting rod of motor car engine.

Thus the reasons for selecting the materials in the above examples can be summarized as :  Commercial factors such as: Cost, availability, ease of manufacture.  Engineering properties of materials such as: Electrical conductivity, strength, toughness, ease of forming by extrusion, forging and casting, machinability and corrosion resistance.

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Engineering Materials Engineering materials:

Msc. Shaymaa Mahmood

Almost every substance known to man has found its way into the engineering workshop at some time or other. The most convenient way to study the properties and uses of engineering materials is to classify them into ‘families’ as shown in figure below:

Figure 3. classification of engineering materials.

1. Metals
1.1 Ferrous metals  These are metals and alloys containing a high proportion of the element...
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