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Engineering Materials and their Properties
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The machine elements should be made of such a material which has properties suitable for the
conditions of operation
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In this note, we shall discuss the commonly used engineering materials and their properties in
Machine Design

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2 Classification of Engineering Materials
The engineering materials are mainly classified as :
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The metals may be further classified as :

(a) Ferrous metals, and (b) Non-ferrous metals
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The non-ferrous metals are those which have a metal other than iron as their main
constituent, such as copper, aluminum, brass, tin, zinc, etc
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The best material is one which serve the desired objective at the
minimum cost
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Availability of the materials,
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The cost of the materials
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We shall now discuss
the physical and mechanical properties of the material in the following article
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4 Physical Properties of Metals
The physical properties of the metals include luster, colour, size and shape, density, electric and
thermal conductivity, and melting point
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These mechanical properties of the metal include
strength, stiffness, elasticity, plasticity, ductility, brittleness, malleability, toughness, resilience,
creep and hardness
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Strength
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The internal resistance offered by a part to an externally applied force is called
*stress
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Stiffness
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The modulus of
elasticity is the measure of stiffness
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Elasticity
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This property is desirable for materials used in tools and
machines
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It is property of a material which retains the deformation produced under load
permanently
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It is the property of a material enabling it to be drawn into wire with the

application of a tensile force
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The ductility is
usually measured by the terms, percentage elongation and percentage reduction in area
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Note : The ductility of a material is commonly measured by means of percentage elongation
and percentage reduction in area in a tensile test
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Brittleness
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It is the property of breaking
of a material with little permanent distortion
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(b) keeping the metal at this temperature for a considerable time, depending upon its thickness
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It may be noted that the low carbon steels cannot be hardened appreciably, because of the
presence of ferrite which is soft and is not changed by the treatment
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Notes :

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The steel hardened by rapid quenching is very hard and brittle
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The tempering (also known as drawing) is, therefore, done for the following
reasons :

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The tempering process consists of reheating the hardened steel to some temperature below the
lower critical temperature, followed by any desired rate of cooling
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In many engineering applications, it is desirable that
a steel being used should have a hardened surface to resist wear and tear
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This is

achieved by hardening the surface layers of the article while the rest of it is left as such
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Following are the various *surface or case hardening processes by means of which the surface
layer is hardened:

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Cyaniding, 3
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Induction hardening, and 5
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The non-ferrous metals are usually employed in industry
due to the following characteristics :

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Resistance to corrosion,

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Weight
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and their alloys
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27

Aluminum

It is white metal produced by electrical processes from its oxide (alumina), which is prepared

from a clayey mineral called bauxite
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7 and melting
point 658°C
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In its pure state, the metal would be weak and soft for most purposes, but when mixed with
small amounts of other alloys, it becomes hard and rigid
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Its good electrical conductivity is an important property and is
widely used for overhead cables
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It is extensively used in aircraft and automobile components where
saving of weight is an advantage
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Aluminum Alloys

The aluminum may be alloyed with one or more other elements like copper, magnesium,

manganese, silicon and nickel
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The
main aluminum alloys are discussed below:

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It is an important and interesting wrought alloy
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5 – 4

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