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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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2
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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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Cast iron is a brittle material
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Malleability
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A malleable material should be plastic but it is not essential to be so
strong
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It is the property of a material to resist fracture due to high impact loads like

hammer blows
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It is measured by the

amount of energy that a unit volume of the material has absorbed after being stressed upto the
point of fracture
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It is the property of a material which refers to a relative case with which a
material can be cut
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It
may be noted that brass can be easily machined than steel
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Resilience
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It is measured by the amount of energy absorbed per unit volume within elastic limit
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When a part is subjected to a constant stress at high temperature for a long period of
time, it will undergo a slow and permanent deformation called creep
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When a material is subjected to repeated stresses, it fails at stresses below the yield
point stresses
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The failure is caused by
means of a progressive crack formation which are usually fine and of microscopic size
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It is a very important property of the metals and has a wide variety of meanings
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It also means the ability of a metal to cut another metal
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The
hardness of a metal may be determined by the following tests :
(a) Brinell hardness test,

(b) Rockwell hardness test,

(c) Vickers hardness (also called Diamond Pyramid) test, and
(d) Shore scleroscope

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The ferrous metals commonly used in engineering practice are cast iron,

wrought iron, steels and alloy steels
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The
principal iron ores with their metallic contents are shown in the following table :

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It is primarily an alloy of iron and carbon
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7 per cent to 4
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It also contains small amounts of silicon, manganese, phosphorous
and sulphur
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Free carbon or graphite, and 2
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Since the cast iron is a brittle material, therefore, it cannot be used in those parts of machines
which are subjected to shocks
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The compressive strength of cast iron is much
greater than the tensile strength

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