Chapter 1 Mechanical Engineering Materials( 22343)

Program: Diploma(Mechanical)
Class: SYME
Course: Mechanical Engineering Materials(22343)
Unit 1: Basics of Engineering Materials
Lecture 01: Classification Engineering Materials

1. Name of the Trainer :- Prof. S. B. Deshmukh
2. Years of Experience :- 8 Years
3. Domain Expertise :- Mechanical Engineering
www.sandipuniversity.edu.in
Presented By 02
https://www.sandipfoundation.org/
Department Of Mechanical Engineering,Sandip Polytechnic,Nashik

Mechanical Engineering
Materials(22343)
01
Basics of Engineering
Materials – 10 Marks
Cast Iron – 10 Marks
03
Heat Treatment
Processes – 14 Marks
06
Steel and its Alloys – 14 Marks
02
Non ferrous Metals and Alloys –
10 Marks
04
Non metallic and Advanced
Materials – 12 Marks
05
03
Syllabus

Course Title- Basics of Engineering Materials (22343)
Course code-ME-3I
Teaching & Examination Scheme 04
Teachin
g
Scheme Credi
t
(L+T+
P)
Examination Scheme
L T P Theory Practical
Paper
Hrs
ESE PA Total ESE PA Total
Max Mi
n
Ma
x
Mi
n
Ma
x
Mi
n
Ma
x
Mi
n
Ma
x
Mi
n
Ma
x
Min
3 - 2 5 3 70*#
^
28 30
*
00 10
0
40 25# 10 25 10 50 20

At the end of the course, student should able to
1. CO1:Identify properties of materials.
2. CO2: Select relevant ferrous materials for mechanical
components.
3. CO3: Select relevant cast iron for the engineering
application.
4. CO4: Use non-ferrous metals for mechanical components..
5. CO5: Suggest relevant advanced materials for mechanical
components.
6. CO6:Select relevant heat treatment process.
Course Outcomes(COs) : 05

Learning resources for students 06
Sr.
No
Title of Book Author Publication
1 Engineering Material Sharma, C. P.
PHI Learning, New Delhi 2015
ISBN 978-81-203-2448-0
2 Engineering Material Agrawal, B. K.
McGraw Hill Education, New Delhi
ISBN 978-00-745-1505-1
3
Material Science and
metallurgy
Kotgire, V. D.
Everest publishing House, New
Delhi 2015; ISBN 81 86314 008
4
Material Science and
metallurgy
Khanna, O. P.
Dhanpat Rai and sons, New Delhi
2015; ISBN- 978-81-899-2831-5
5
Material Science for
polytechnic
Rajput, R. K
. S K Katariya and sons; New Delhi
2015; ISBN- 81-85749-10-8

Suggested Software/Learning Websites 07
http://vimeo.com/32224002
http://www.substech.com/dokuwiki/doku.php?id=iron-carbon_phase_diagram
http://www-g.eng.cam.ac.uk/mmg/teaching/typd/
http://www.ironcarbondiagram.com/
http://www.youtube.com/watch?v=fHt0bOfj3T0andfeature=related
http://www.youtube.com/watch?v=cN5YH0iEvTo
http://www.youtube.com/watch?v=m9l1tVXyFp8
http://www.studyvilla.com/electrochem.aspx
http://www.sakshat.ac.in/

Unit – 1 Basics of Engineering Materials 08
Topic to be covered
1.1 Classification of engineering materials.
1.2 Crystal structure, Unit cell and space lattice
1.3 Microstructure, types of microscopes
1.4 Sample preparation, etching process, types of etchant.
1.5 Properties of metals Physical Properties, Mechanical Properties.
1.6 Hardness testing procedure on Brinell and Rockwell tester

Introduction 09
WHY STUDY THE CHEMISTRY OF MATERIALS?
A standard place setting includes metal cutlery, a
polymer napkin, and a ceramic dish.
Traditionally the three major classes of materials
are metals, polymers, and ceramics.
Examples of these are steel, cloth, and pottery.
These classes usually have quite different
sources, characteristics, and applications

Introduction 10
Early humans Stone age
~9000 BCE Copper age
~3000 BCE Bronze age
~1200 BCE Iron age

Introduction 11
Material is anything made of matter, constituted of one or more substances.
Wood, cement, hydrogen, air and water are all the examples of materials.
Materials science is an interdisciplinary field applying the properties of matter
to various areas of science and engineering.
Metallic alloys are those of aluminum, titanium, copper and magnesium
The study of metal alloys is a significant part of materials science. Of all the
metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool
steel, alloy steels) make up the largest proportion both by quantity and
commercial value
Raw materials are first extracted or harvested from the earth and divided into
a form that can be easily transported and stored, then processed to produce
semi-finished materials.

12
Selection of material
Selection of material based on following criterion
Product shape: a) sheet, strip, plate, (b) bar, rod, wire, (c) tubes, (d) forging
(e) casting
Mechanical properties-tensile, fatigue, hardness, creep, impact test
Physical & chemical properties-specific gravity, thermal & electrical
conductivity, thermal expansion
Metallurgical consideration - hardenability of steel, grain size & consistency
of properties
Processing castability-castability, formability, machinability
Sales appeal-color, luster
Cost & availability

13
Classification of Engineering Materials
Most engineering material may be classified in four broad groups according to
their mode of occurrence
Metals 1.Ferrous metals
2.Non-ferrous metals
Ceramics
Polymer
Composites

14
Classification of Engineering Materials

15
Metals
Metals account for about two thirds of all the elements and about 24% of
the mass of the planet.
Metals have useful properties including strength, ductility, high melting
points, thermal and electrical conductivity, and toughness
A metal is a chemical element that is a good conductor of both electricity
and heat and forms ionic bonds with non-metals
Pure Metals- 1.A pure metal only consists of a single element
2. It only has one type of atom in it.
3. common pure metals are:-aluminium, copper, iron, and
lead, zinc, tin, silver and gold.
Common Metallic Materials
1. Iron/Steel - Steel alloys are used for strength critical applications
2. Aluminum - Aluminum and its alloys are used because they are easy to
form, readily available, inexpensive, and recyclable.

16
Metals
3. Copper - Copper and copper alloys have a number of properties that make them
useful, including high electrical and thermal conductivity, high ductility, and good
corrosion resistance.
4. Titanium - Titanium alloys are used for strength in higher temperature (~1000° F)
application, when component weight is a concern, or when good corrosion resistance
is required
5. Nickel - Nickel alloys are used for still higher temperatures (~1500-2000° F)
applications or when good corrosion resistance is required
6. Refractory materials are used for the highest temperature (> 2000° F) applications.
Ferrous metal: The term "ferrous" is derived from the Latin word meaning
"containing iron". It contains iron as a base metal E.g. Iron and steel etc
Non-ferrous: It does not contain iron as a base metal.
E.g. Aluminium, copper, zinc and magnesium etc

17
Metals
FERROUS NON FERROUS METAL

18
Periodic Table of Elements
Department of Mechanical Engineering

19
Periodic Table of Elements

20
Ceramics
Ceramic has traditionally been defined as “an inorganic, non-metallic solid that is
prepared from powdered materials, is fabricated into products through the
application of heat, and displays such characteristic properties as hardness,
strength, low electrical conductivity, and brittleness."
The word ceramic comes the from Greek word "keramikos", which means
"pottery.“
They are typically crystalline in nature and are compounds formed between
metallic and non-metallic elements such as aluminium and oxygen (alumina-Al2O3),
calcium and oxygen (calcia - CaO), and silicon and nitrogen (silicon nitride-Si3N4).
Depending on their method of formation, ceramics can be dense or lightweight.
Typically, they will demonstrate excellent strength and hardness properties;
however, they are often brittle in nature

21
Ceramics
Ceramics can also be formed to serve as electrically conductive materials or
insulators
Some ceramics, like superconductors, also display magnetic properties
They are also more resistant to high temperatures and harsh environments than
metals and polymers
The broad categories or segments that make up the ceramic industry can be classified as
Structural clay products (brick, sewer pipe, roofing and wall tile, flue linings,etc.)
White wares (dinnerware, floor and wall tile, electrical porcelain, etc.)
Refractories (brick and monolithic products used in metal, glass, cements, ceramics,
energy conversion, petroleum, and chemicals industries)
Glasses (flat glass (windows), container glass (bottles), pressed and blown glass
(dinnerware), glass fibers (home insulation), and advanced/specialty glass (optical
fibers)

22
Ceramics
Abrasives (natural (garnet, diamond, etc.) and synthetic (silicon carbide, diamond,
fused alumina, etc.) abrasives are used for grinding, cutting, polishing, lapping, or
pressure blasting of materials)
Cements (for roads, bridges, buildings, dams, and etc.)
Advanced ceramics
Structural (wear parts, bioceramics, cutting tools, and engine components)
Electrical (capacitors, insulators, substrates, integrated circuit packages, piezoelectric,
magnets and superconductors)
Coatings (engine components, cutting tools, and industrial wear parts)
Chemical and environmental (filters, membranes, catalysts, and catalyst supports)

23
Ceramics

24
Summary
In this lesson, We have learned
Introduction
Classification of engineering materials.
Metal
Non metal
Ceramic

25

Class: SYME
Lecture 02: Polymer ,Composite, Crystal structure, Unit cell and
space lattice

27
Polymers
A polymeric solid can be thought of as a material that contains many chemically
bonded parts or units which themselves are bonded together to form a solid
The word polymer literally means "many parts”
Two industrially important polymeric materials are plastics and elastomers
Plastics are a large and varied group of synthetic materials which are processed by
forming or moulding into shape
Elastomers or rubbers can be elastically deformed a large amount when a force is
applied to them and can return to their original shape (or almost) when the force is
released.
Polymers have many properties
Are less dense than metals or ceramics
Resist atmospheric and other forms of corrosion
Offer good compatibility with human tissue
Exhibit excellent resistance to the conduction of electrical current.

28
Polymers
The polymer plastics can be divided into two classes, thermoplastics and thermosetting
plastics, depending on how they are structurally and chemically bonded
Thermoplastic polymers comprise the four most important commodity materials –
polyethylene, polypropylene, polystyrene and polyvinyl chloride
The term ‘thermoplastic’ indicates that these materials melt on heating and may be
processed by a variety of molding and extrusion techniques
‘thermosetting’ polymers can not be melted or remelted
Thermosetting polymers include alkyds, amino and phenolic resins, epoxies, polyurethanes,
and unsaturated polyesters
Rubber is a natural occurring polymer.
Polymers are created by engineering the combination of hydrogen and carbon atoms and
the arrangement of the chains they form.
Polymers are primarily produced from petroleum or natural gas raw products but the use of
organic substances is growing

29
Polymers
The super-material known as Kevlar is a man-made polymer
Kevlar is used in bullet-proof vests, strong/lightweight frames, and underwater cables
that are 20 times stronger than steel.

30
Composites
A composite is commonly defined as a combination of two or more distinct materials,
each of which retains its own distinctive properties, to create a new material with properties
that cannot be achieved by any of the components acting alone
For example-concrete is a composite because it is a mixture of Portland cement and
aggregate, Fiberglass sheet is a composite since it is made of glass fibers imbedded in a
polymer.
Composite materials are said to have two phases
The reinforcing phase is the fibers, sheets, or particles that are embedded in the matrix
phase
Reinforcing material and the matrix material can be metal, ceramic, or polymer.
Reinforcing materials are strong with low densities while the matrix is usually a ductile,
or tough, material.

31
Composites
Common classifications of composites are
1. Reinforced plastics
2. Metal-matrix composites
3. Ceramic-matrix composites
4. Sandwich structures
5. Concrete
Three categories based on the strengthening mechanism.
1. Dispersion strengthened :- Dispersion strengthened composites have a fine distribution of
secondary particles in the matrix of the material .These particles impede the mechanisms
that allow a material to deform
2. Particle reinforced :- . Particle reinforced composites have a large volume fraction of
particle dispersed in the matrix and the load is shared by the particles and the matrix
3. Fiber reinforced :- The fiber is the primary load-bearing component. Fiberglass and
carbon fiber composites are examples of fiber-reinforced composites.

32
Composites
Composite is designed and fabricated correctly, it combines the strength of the
reinforcement with the toughness of the matrix to achieve a combination of desirable
properties not available in any single conventional material
Composites are often more expensive than conventional materials
GLASS FIBER
METAL FIBER

33
Crystal structure, Unit cell and space lattice
Crystal Structure
Structure means geometric relationship of material components
Structure means the arrangement of the internal components of matter or atoms.
“The arrangement of multiple unit cells together is called crystal structure”.
For example:- electron structure, crystal structure and microstructure.
In nature, 14 different types of crystal structures or lattices are found.
Unit Cell
The smallest representation of geometry
of crystal structure of a material is called unit cell
The unit cell is defined as, “The smallest repeating
unit in space lattice which when repeated over again,
results in a crystal of the given substance”.
The unit cell is simply a box with an atom at each corner.

34
Crystal structure, Unit cell and space lattice
Space Lattice
“A space lattice is an array of points showing how particles (atoms, ions or molecules)
are arranged at different sites in three dimensional spaces.”
The Lattice structure represents arrangement of unit cells in 3- dimensional axes.
Lattice constant.
The constant distance between
adjacent atoms of unit cell is called
as Lattice constant. GLSS FIBER

35
Crystal structures Classification
Crystal structures are classified according to Geometry of unit cell
Body-Centered Cubic (BCC) Structure
The body-centered cubic unit cell has atoms at each of the eight corners
of a cube (like the cubic unit cell) plus one atom in the center of the cube
as shown in Fig.
Each of the corner atoms is the corner of
another cube so the corner atoms are shared among eight unit cells &
one in the centre In this structure, the average number of atoms per unit
cell is 2.
The volume of atoms in a cell per the total volume of a cell is called the
packing factor. The bcc unit cell has a packing factor of 0.68.
E.g. lithium, sodium, potassium, chromium, barium, vanadium, alpha-iron
and tungsten
Metals which have a bcc structure are usually harder and less malleable
than close-packed metals such as gold

36
Face Centered Cubic (FCC) Structure
The face centered cubic structure has atoms located at each of the
corners and the centre's of all the cubic faces (as shown in Fig.)
Each of the corner a toms is the corner of another cube so the corner
atoms are shared among eight unit cells. Additionally, each of its six face
centered atoms is shared with an adjacent atom.
The FCC unit cell consists of a net total of four atoms; eight eighths from
corners atoms and six halves of the face atoms as shown in the Fig
The packing factor (the volume of atoms in a cell per the total volume of
a cell) is 0.74 for FCC crystals
E. g aluminium, copper, gold, iridium, lead, nickel, platinum and silver

37
Hexagonal Close Packed (HPC) Structure
The hexagonal structure of alternating layers is shifted so its
atoms are aligned to the gaps of the preceding layer
In each the top and bottom layer, there are six atoms that
arrange themselves in the shape of a hexagon and a seventh atom
that sits in the middle of the hexagon.
The packing factor is 0.74, which is the same as the FCC unit
cellE.g. beryllium, cadmium, magnesium, titanium, zinc and
zirconium.

38
Microstructure
The term ‘Microstructure’ is refers to the surface structure of materials such as thin foil
that can be revealed under magnification higher than 25×.
It is Used to describe the appearance of the material on the nanometer- to centimeter-
length scale.
Microstructure is:“The arrangement of phases and defects within a material.”
Microscopic method provides information about Impurities in a metal
A material’s microstructure can be classified into the following:
1. Composite
2. Metallic
3. Ceramic
4. Polymeric
This can immensely affect properties that determine the application of materials, like -
Corrosion, Wear resistance, Hardness, Ductility, Toughness
The structure of a material can be described through its microstructure and crystal
structure

39
Types of Microscopes
The three main types of microscopes are
Sr.
No.
Category Types
1 Electron
microscope
Transmission electron
microscope (TEM),
scanning electron microscope
(SEM), etc.
2 Scanning
probe
microscope
(SPM)
Atomic force microscope (AFM),
scanning near-field optical
microscope (SNOM), etc.
3 Others X-ray microscope, ultrasonic
microscope, etc.

40
Sample preparation
Sample preparation refers to the ways in which a sample is treated prior to its analysis
Sample preparation is a commonly used technique for preparing metallographic
samples for microscopic analysis.

41
Etching Process
Etching is the process of using strong acid to cut into the unprotected parts of a metal
surface to create a image is created by cutting, carving or engraving into a flat surface in
the metal
Steps of Etching process:
1. The artist draws with a needle on to a copper, zinc or steel plate that has been covered
with an acid resistant wax. When the plate is immersed in acid, the bare metal, exposed
by the lines of the drawing, is eroded. The depth of the `etch’ is controlled by the
amount of time the acid is allowed to `bite’ the metal. The longer in acid, the deeper
the line and the darker it will print.
2. In order to obtain a print, a viscous greasy ink is pushed into the etched grooves, then
the surface is wiped clean with muslin, leaving only the etched areas retaining ink. The
actual impression is made with a copper plate press which is similar to an old washing
mangle with a large plank or `bed’ between the rollers. The plate is placed on the bed,
covered with dampened paper and backed with three or four felt blankets.

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Etching Process
3. These are then passed through the press under high pressure; the malleable paper is
forced into the cuts and ridges in the plate and thus picks up the ink. When the paper is
finally peeled off, it reveals a faithful mirror image of the etched drawing. This inking
procedure is then repeated for each print
Types of etchant:
The two fundamental types of etchants are
1. Liquid-phase ("wet")
2. plasma-phase ("dry")

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Summary
Polymer.
Composite
Crystal structure
Unit cell
space lattice
Microstructure
Sample preparation
Etching process
Microscope

44

Class: SYME
Lecture 03: Properties of metals, Hardness testing procedures

46
Properties of metals
Physical Properties :-
A physical property is any measurable property the value of which describes a
physical system's state
Physical properties can be observed or measured without changing the composition
of matter
Physical properties include: Structure, appearance, texture, color, odor, melting point,
boiling point, density, solubility, polarity, and many others
The three states of matter are: solid, liquid, and gas. The melting point and boiling
point are related to changes of the state of matter. All matter may exist in any of three
physical states of matter.
Density :-
The mass density or density of a material is defined as its mass per unit volume
The symbol most often used for density is ρ (Greek letter rho)
The SI unit for density is: kilograms per cubic meter (kg/m³).

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Density :-
Mass can be thinly distributed as in a
pillow, or tightly packed as in a block of lead.
The space the mass occupies is its volume,
and the mass per unit of volume is its density.
Water in the liquid state has a density of 1
g/cm3 = 1000g/m3 at 4o C. Ice has a density of
0.917 g/cm3 at 0oc, and it should be noted that
this decrease in density for the solid phase is
unusual
Chart shows density of various substances.
Substance Density (g/cm3)
Air 0.0013
Wood 0.85
Water (ice) 0.92
Water (liquid) 1.0
Aluminum 2.7
Steel 7.8
Silver 10.5
Lead 11.3
Mercury 13.5
Gold 19.3

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Melting point:-
The melting point of a solid is the temperature at which it changes state from solid to
liquid or we may define it as,the temperature at which the solid melts to become a
liquid
Melting point of the material is related
to the bonding forces in solid.
Materials having stronger bonds tend to have higher melting point
Melting points: Mild steel : 1500 OC , Copper : 1080 OC, Aluminium: 650 OC
Boiling Point:-
When a liquid is heated, it eventually reaches a temperature
at which the vapour pressure is large enough that bubbles form inside
the body of the liquid. This temperature is called the boiling point.
Once the liquid starts to boil, the temperature remains
constant until all of the liquid has been converted to a gas

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Mechanical properties:-
In mechanical properties of material, their strength, rigidity and ductility, are of vital
importance in determining their fabrication and possible mechanical applications
For proper selection one should know the mechanical properties of metals.
Eg. ductility of pure copper to the hardness of diamond
The some of the mechanical properties are.
1. Strength 2.Elasticity 3.Ductility 4.Malleability 5.Plasticity
6. Toughness 7.Hardness 8.Hardenability 9.Brittleness 10.Fatigue
11. Creep 12.Thermal conductivity 13.Electrical conductivity
14. Thermal coefficient of linear expansion

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1. Strength:
The ability of the material to resist stress without failure is called strength
strength of a material is its ability to withstand an applied stress without failure
Some types of strengths
a. Tensile strength or Ultimate tensile strength-
It is the ratio of maximum load to original
cross sectional area. It is measured in kg per sqr.cm.
it is defined as the ability of a material to stretch without breaking or snapping
b. Yield strength-
When metals are subjected to tensile force, they stretch or elongates as the stress
increased. The point where the stress suddenly increases is known yield strength of
material.
When metals are subjected to tensile force, they stretch or elongates as the stress
increased. The point where the stress suddenly increases is known yield strength of
material.

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a. Impact Strength
The capacity of material to resist or absorbs shock energy before it fractures.
2. Elasticity:
When a material has a load applied to it, the load causes the material to deform.
Elasticity is the ability of a material to return to its original shape after the load is
removed
The elastic limit of a material is the limit to which a material can be loaded and still
recover its original shape after the load is removed.
The loss of strength in compression with simultaneous gain
in strength in tension due to overloading
is known as inelasticity
Eg.Rubber, copper, plastics etc.
Youngs Modulus or Modulus of elasticity :- It is the ratio of stress at elastic limit to strain
at elastic limit.

52
Following table shows
values of Modulus of elasticity
of some important metals
3.Ductility:
Ductility is a solid material's ability to deform under tensile stress.
Ductility is the property that enables a material to stretch, bend, or twist without
cracking or breaking
This property makes it possible for a material to be drawn out into a thin wire.
Eg.Aluminium,copper,etc.
Ductility may be expressed as percentage elongation (%EL) from a tensile test
Metals Modulus of elasticity( GN/m2)
Lead 18
Tin 42
Aluminium 72
Cast Iron 98
Mild Steel 210
Molybdenum 350
Tungsten 430

53
Ductility may be expressed as percentage elongation (%EL) from a tensile test
Fracture length - original gauge length
Percentage elongation =--------------------------------------- X 100
original gauge length
Following table shows values of Ductility of some important metals.
Metals Ductility (%EL) In 50 mm
Copper 45
Iron 45
Aluminium 45
Nickel 40
Titanium 30

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4.Malleability:
Malleability of a material is its ability to
be flattened in to their sheets without
cracking by pressing, rolling, hammering
etc.
It can be also defined as the property
that enables a material to deform by
compressive forces without developing
defects
A malleable material is one that can be
stamped, hammered, forged, pressed, or
rolled into thin sheets
Following table shows common metals in
order to their ductility and malleability
Ductility Malleability
Gold Gold
Silver Silver
Platinum Lead
Iron Copper
Nickel Aluminium
Copper Tin
Aluminium Platinum
Zinc Zinc
Tin Iron
Lead Nickel

55
5. Plasticity :-
Plasticity is the ability of a material to deform permanently
without breaking or rupturing. Plastic deformation will take place
only after the elastic range has been exceeded.
By careful alloying of metals, the combination of plasticity and
strength is used to manufacture large structural members.
Eg, should a member of a bridge structure become overloaded,
plasticity allows the overloaded member to flow allowing the
distribution of the load to other parts of the bridge structure
Gold and lead have highest plasticity
Plasticity is of importance in coining, forming, shaping,
stamping images on coins and extruding operations

56
6. Toughness or Tenacity:-
This describes the amount of energy a material
can absorb without breaking
This is the opposite of brittleness.
Toughness may be considered as a combination
of strength and plasticity.
Eg. Copper, steel are extremely tough but cast iron is less tough
7. Hardness:-
Hardness may represent the ability of a material to resist scratching, abrasion,
cutting, or penetration
Hardness is also measure by resistance to wear of a material
Rockwell, Vickers, or Brinell are some of the methods
of testing hardness
Following chart shows Hardness test and their units.
Hardnesstest Unit
Rockwell HRC
Brinell BHN
Vickers HV
6
7

57
8. Hardenability :-
The hardenability of a metal alloy is its capability to be
hardened by heat treatment.
Hardness is associated with strength, while hardenability is
connected with the transformation characteristics of steel
9. Brittleness
The brittleness of a material is the property of breaking or
shattering without much permanent distortion
Brittle failures are caused by high tensile stresses, high carbon
content, rapid rate of loading, and the presence of notches
Brittleness is the opposite of the property of plasticity
A brittle metal is one that breaks or shatters before it deforms.
Brittle metals are high in compressive strength but low in tensile strength
E.g.Materials such as glass, cast iron, and concrete.
9
8

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10. Fatigue :-
Materials subjected to a repetitive or fluctuating stress will fail at a stress much lower
than that required to cause fracture under steady loads, This behavior is called fatigue
and is distinguished by three main features:
1.Loss of strength.
2.Loss of ductility.
3.Increased uncertainty in strength and service life.
Fractures usually start from small nicks or scratches
or fillets which cause a localized concentration of stress
Failure can be influenced by a number of factors including
size, shape and design of the component, condition of the surface or operating
environment
Stress relaxation is- the phenomenon in which deformation tends to loosen the
joint and produces a stress reduced

59
11. Creep :-
Creep is the permanent plastic deformation of
materials when subjected to constant stress or
prolonged loading usually at high temperature
Creep leads to a fracture in the material at static
stresses.
In the Gas turbine blades, consideration of creep
is important
There are three stages of creep,
1.Primary creep
2.Secondary creep
3.Tertiary creep

60
1.Primary creep:
It represents the region of decreasing creep rate. Primary creep is a decreasing
creep rate because of the work hardening process resulting from the deformation.
2.Secondary creep
It is a period of nearly constant creep rate which results from a balance between
the work hardening effect and annealing effect.
3.Tertiary creep
In tertiary creep mainly occur at an accelerated rate resulting in an immediate
fracture of the material

61
12. Thermal conductivity
Thermal conductivity (λ) is the intrinsic property of
a material which relates its ability to conduct heat
Heat transfer by conduction involves transfer of energy
within a material without any motion of the material as a whole
Conductive heat flow occurs in the direction of decreasing
temperature because higher temperature equates to higher
molecular energy or more molecular movement.
Thermal conductivity is defined as the quantity of heat (Q) transmitted through
a unit thickness (L) in a direction normal to a surface of unit area (A) due to a unit
temperature gradient (ΔT) under steady state conditions and when the heat
transfer is dependent only on the temperature gradient.
Thermal Conductivity = heat × distance / (area × temperature gradient)
λ = Q × L / (A × ΔT)

62
13. Electrical conductivity
Electrical conductivity is that electrical property of a
material owing to which the electrical current flows easily
through the material, that is material provides an easy
path for the flow of electricity through it
Electrical conductivity permits the movement of
electric charge from one location to another
When thermal energy is added to a material, a change in its dimensions occurs
For example, if a 10 cm long road of mild steel is heated it increases in length. This
phenomenon is thermal expansion and the property of the material, responsible for
this is known as coefficient of thermal expansion.
It is the ratio of change in length (Dl) to the total starting length (li) and change in
temperature (DT).

63
Hardness testing procedures
Brinell hardness Tester:
Most commonly it is used to test materials that have a structure that is too coarse or
that have a surface that is too rough to be tested using this test
Method e.g., castings and forgings
A number expressing Brinell hardness and denoting the load applied in testing in
kilograms divided by the spherical area of indentation produced in the specimen in
square millimeters
The indenter used in Brinell hardness test is a cone.
BHN is designated by the most commonly used test standards (ASTM E10-14 and ISO
6506–1:2005) as HBW (H from hardness, B from Brinell and W from the material of the
indenter, tungsten (wolfram) carbide)
In former standards HB or HBS were used to refer to measurements made with steel
indenters. Brinell testing often use a very high test load (3000 kgf) and a 10mm
diameter Steel ball is used as indenter

64
Brinell hardness Test
Brinell hardness Procedures:
1. Insert ball of dia ‘D’ in ball holder of the m/c.
2. Make the specimen surface clean by removing dust, dirt, oil and grease etc.
3. Make contact between the specimen surface and the ball by rotating the jack
adjusting wheel.
4. Push the required button for loading.
5. Pull the load release level and wait for minimum 15 second. The load will
automatically apply gradually.
6. Remove the specimen from support table and locate the indentation so made.
7. View the indentation through microscope and measure the diameter ‘d’ by
micrometer fitted on microscope.
8. Repeat the entire operation, 3-times.

65
9. Observation And Calculation :- Following
observation are recorded from a test on steel
specimen using a hardened steel ball as indenter
BHN = Load Applied (kg.)/
Spherical surface area indentation (in mm.)
= 2P/πD(D-√D2 – d2)
S.
No.
Ball diameter
‘D’ in mm.
Load
applied P
in kg
Diameter of
indentation ‘d’
(mm)
P/D2 BHN

66

67
Rockwell Hardness Test
Rockwell Hardness Tester: :
The Rockwell scale is a hardness scale based on indentation hardness of a material
The result is a dimensionless number noted as HRA, HRB, HRC, etc., where the last
letter is the respective Rockwell scale.
When testing metals, indentation hardness correlates linearly with tensile strength
In C- scale of Rockwell hardness testing, the shape of indenter used is Diamond cone.
HRC: An abbreviation for Rockwell Hardness measured on the C scale.
Full form of HRC is high rupture capacity.

68
Rockwell Hardness Procedures:
1. Insert ball of dia. ‘D’ in ball holder of the m/c.
2. Make the specimen surface clean by removing dust, dirt, oil and grease etc.
3. Make contact between the specimen surface and the ball by rotating the jack
adjusting wheel.
4. Push the required button for loading.
5. Pull the load release lever wait for minimum 15 second. The load will automatically
apply gradually.
6. Remove the specimen from support table and locate the indentation so made.
7. Repeat the entire operation, 3-times
8. Observation And Calculation :- Following observation are recorded are from a test on
steel specimen using a hardened steel ball as indenter
9. Test piece material =-----------HRA = 100-(t/0.002)
HRB = 130-(t/0.002)
RC = 100-(t/0.002)

69

70
Summary
Physical properties of metal.
Mechanical properties of metal
1. Strength 2.Elasticity 3.Ductility 4.Malleability 5.Plasticity
6. Toughness 7.Hardness 8.Hardenability 9.Brittleness 10.Fatigue
11. Creep 12.Thermal conductivity 13.Electrical conductivity
Hardness test – Rockwell & Brinell

71

Chapter 1 Mechanical Engineering Materials( 22343)

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