Table of Contents

1 Question #1 “Titanic”..........................................................................................................................4

1.1 Brief Description:........................................................................................................................4

1.2 Design Requirements:..................................................................................................................4

1.2.1 Structural Design Considerations:........................................................................................4

1.2.2 Material Selection Considerations:......................................................................................4

1.2.3 Mechanical Design Considerations:.....................................................................................5

1.2.4 Safety Features:...................................................................................................................5

1.3 Selection of Materials:.................................................................................................................5

1.3.1 Mechanical Parts:.................................................................................................................5

1.3.2 Structural Parts:...................................................................................................................6

1.4 Engineering Material Requirements:...........................................................................................6

1.4.1 Material Requirements for Mechanical Parts:......................................................................6

1.4.2 Material Requirements for Structural Parts:.........................................................................7

1.5 Properties of Materials:................................................................................................................7

1.5.1 Mechanical Parts:.................................................................................................................7

1.5.2 Structural Parts:...................................................................................................................7

Mild Steel:...........................................................................................................................................7

Carbon Steel:.......................................................................................................................................7

1.5.3 Wood:..................................................................................................................................8

1.6 Atomic Structures:.......................................................................................................................8

1.6.1 Carbon Steel:.......................................................................................................................8

1.6.2 Mild Steel:...........................................................................................................................8

1.6.3 Wood:..................................................................................................................................9

1.7 Fatigue:........................................................................................................................................9

1.7.1 Fatigue in Mechanical Parts:................................................................................................9

1.7.2 Fatigue in Structural Parts:.................................................................................................10

1.8 Yield:.........................................................................................................................................10

1.8.1 Yield Point in Mechanical Parts:........................................................................................10

1.8.2 Yield Point in Structural Parts:..........................................................................................10

1.9 Modulus:....................................................................................................................................10

1

1.10 Linear Elasticity:........................................................................................................................11

1.11 Environment and Intended Condition of Use:............................................................................11

1.12 Creep and Oxidation:.................................................................................................................11

1.13 Thermodynamics:......................................................................................................................12

1.14 Heat Stress:................................................................................................................................12

2 Question # 2:.....................................................................................................................................13

2.1 Materials:...................................................................................................................................13

2.2 Properties of the Material:.........................................................................................................13

2.2.1 Case Material:....................................................................................................................13

2.2.2 Chuck Material:.................................................................................................................13

2.3 Heat Treatments:........................................................................................................................13

2.3.1 Case Material:....................................................................................................................13

2.3.2 Chuck Material:.................................................................................................................14

2.4 Formation of Drill Body:...........................................................................................................14

2.5 Corrosion Protection Treatments:..............................................................................................14

2.5.1 Atomic Absorption:...........................................................................................................14

2.5.2 Galvanizing:.......................................................................................................................14

3 Question # 3.......................................................................................................................................15

3.1 Annealing:.................................................................................................................................15

3.1.1 Advantages:.......................................................................................................................15

3.2 Normalizing:..............................................................................................................................15

3.2.1 Advantages:.......................................................................................................................15

3.3 Hardening:.................................................................................................................................15

3.3.1 Advantages:.......................................................................................................................15

3.4 Tempering:................................................................................................................................16

3.4.1 Advantages:.......................................................................................................................16

3.5 Quenching:................................................................................................................................16

3.5.1 Advantages:.......................................................................................................................16

4 Question No 4....................................................................................................................................16

4.1 Vickers Test...............................................................................................................................16

4.1.1 Procedure:..........................................................................................................................16

4.2 Brinell Test:...............................................................................................................................17

2

4.2.1 Procedure:..........................................................................................................................17

4.3 IZOD Test:.................................................................................................................................18

4.3.1 Procedure:..........................................................................................................................18

4.4 Charpy Test:..............................................................................................................................18

4.4.1 Procedure:..........................................................................................................................19

5 Question # 5:.....................................................................................................................................19

5.1 Points:........................................................................................................................................19

5.1.1 Proportional Limit: (σ pl).....................................................................................................19

5.1.2 Yield Stress: (σ y)..............................................................................................................19

5.1.3 Ultimate Stress: (σu)..........................................................................................................19

5.1.4 Fracture: (σ f)......................................................................................................................19

5.2 Regions:.....................................................................................................................................20

5.2.1 Elastic Region:...................................................................................................................20

5.2.2 Yielding Region:................................................................................................................20

5.2.3 Strain Hardening Region:...................................................................................................20

5.2.4 Necking:.............................................................................................................................20

6 Question # 6.......................................................................................................................................21

6.1 Limits:.......................................................................................................................................21

6.2 Advantages:...............................................................................................................................21

7 References:........................................................................................................................................22

3

1 Question #1 “Titanic”

1.1 Brief Description:

The Titanic is mainly a passenger as well as cargo ship. The ship should have complete

residential facilities for passengers because the ship is used for long journeys.

1.2 Design Requirements:

There is three types of design considerations which is used in the manufacturing of “Titanic”

which are stated as follows:

1.2.1 Structural Design Considerations:

The structural design requirements of the ship is as follows:

The design should be aero dynamically correct as the ship experience high wind speeds

during its journey.

The design should be according to the estimated maximum load and there should a proper

factor of safety.

The design should be compact according to the given dimensions.

The structure of the ship should be able to withstand the maximum load.

Beams and Columns used in the structure should up to certified standards.

Proper structural designs of the residential parts of the ship should be done.

1.2.2 Material Selection Considerations:

The material design requirements of the ship as follows:

The materials used for the manufacturing of ships must possess the minimum level of

corrosion because the water is involved.

Sensitive parts such as blades of propellers and engines must have a minimum level of

creep and induced stresses and least corrosion rates due to exposure of these parts to

water.

4

Proper heat treatment of the material which has exposure to water should be done so that

there should be no induced stresses in the material.

Processes should be done in order for the prevention of corrosion or to minimize the level

of corrosion.

There should be minimum level of creep and induced stresses in the material.

1.2.3 Mechanical Design Considerations:

The mechanical design requirements of the ship is as follows:

There should be proper buoyancy force calculation according to the load of ship.

Engines should be designed according to the demanded power as calculated from load.

Propeller should be designed according to the required power and propellers blades

should have a proper aerodynamic structure in order to give maximum power thrust.

In case of welding the welding is done according to standards and the stresses induced

due to welding must be calculated.

Proper air conditioning and proper heating of the ship is done.

1.2.4 Safety Features:

The safety requirements in the ship is as follows:

There must be an auxiliary power source for electricity.

There must be a Mustard Point in case of emergency.

There must be fire alarms and fire extinguishers in every room in the ship.

There must be an adequate of safety water jackets in the ship.

There must be a proper telecommunication system in the ship.

(Budynes & Nisbet, 2011)

(CALLISTER, 2012)

1.3 Selection of Materials:

1.3.1 Mechanical Parts:

The selection of material for mechanical parts of the ships should be done primarily on the basis

of the following factors:

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Rate of corrosion.

Rate of erosion.

Availability of the material.

Temperature points (Melting Point, Freezing Point, and Critical Point).

Thermal stress level.

Machinability of materials.

The materials that is used for the manufacturing of the mechanical parts are alloy steels mild

steels and high carbon steels.

1.3.2 Structural Parts:

The selection of the material for structural point of view will be done on the basis of the

following factors:

The load which needs to be applied.

Maximum allowable stress of the material.

Life of the material.

The materials that is used in the structure of the ship is carbon steel is used in the sheets beams

and columns. Wood is used for flooring of different portions of ship. Chequred plates of

aluminum is used in the flooring of the top floor which is exposed to sky. Rooms are made of

wooden walls because of the less weight of wood.

(Callister, 2012)

(Budynes & Nisbet, 2011)

1.4 Engineering Material Requirements:

The material required for the manufacturing of the ship should be very rigid and of high strength.

1.4.1 Material Requirements for Mechanical Parts:

In the designing of the mechanical parts of the ship material should have a higher melting point

and higher corrosion resistance because of higher temperature in the combustion chamber of the

engine and the exposure of propellers to the sea water. Moreover material should be machinable

6

so that desired design shapes can be obtained with ease. In the designing of the ship engines we

have used high carbon steel and other steel alloys for the manufacturing because these materials

have high melting points and by proper heat treatments and other corrosion reduction processes

these materials can be used effectively.

1.4.2 Material Requirements for Structural Parts:

The material used for should be resistance to wear and tear and it should be able to carry the

designed load of the ship. The beams and columns are made of carbon steels whereas mild steel

is used in the body manufacturing of the ship. Base plates which are used as a base material for

beams and column are made of mild steel and nuts and bolts are made of high carbon steel.

(Groover, 2010)

1.5 Properties of Materials:

1.5.1 Mechanical Parts:

High Carbon Steel (HSS) is used to make mechanical parts due to following reasons:

High Melting Point.

High Corrosion Resistance (due to coating Titanium Nitride).

Can stand at high temperature without losing structural integrity.

Smooth Surface.

Easily Malleable

1.5.2 Structural Parts:

Mild Steel:

Base plates for beams and column are made of mild steel due to following reasons:

Strong.

Ductile.

Malleable.

High Melting Point.

High value of allowable stress.

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Carbon Steel:

Carbon steel is used for manufacturing beams and columns for the following reasons:

High Strength and Density.

Easily machinable.

High structural integrity.

Resistant to wear.

Cheap

1.5.3 Wood:

The wood is used for in construction of rooms and floors due to following reasons:

Easily available.

Low weight.

Cheap.

Easily machinable.

Structurally strong.

(Groover, 2010)

1.6 Atomic Structures:

1.6.1 Carbon Steel:

Carbon steel is a metallic alloy. It contains iron and control amount of carbon. Other elements

are found in traces.Carbon content in the Carbon steel

increases the yield strength if the steel because they

settle into the interstitial crystal lattice sites of the BCC

arrangement of molecules as shown in the figure. This

carbon lessen the movements of the dislocations which

in return gives the hardening effect on the iron.

1.6.2 Mild Steel:

Mild steel is a type of carbon steel which contains 0.25% of Carbon, 0.4-0.7 % of Manganese

and 0.1 to 0.5 % of Silicon and traces of other elements in it. It has a BCC structure as carbon

steel.

8

Figure 1 Body Centered Cubic Structure of Steel

1.6.3 Wood:

The wood mainly consists of organic compounds in their structure. According to atomic

structural pint of view wood can be classified into two types:

(i) Soft Wood

(ii) Hard Wood

(i) Soft Wood:

Soft Wood mainly consists of long cells called “Tracheid” which are 20 – 80 µm.

(ii) Hard Wood:

Hard wood mainly consists of two type of cells “wood fibers” and “Vessel Elements”.

Wood fibers are elongated cells which are similar to tracheid cells except they are

small as compared to tracheid cells. The vessel element serve for fluid transport in a

living tree.

(Callister, 2012)

1.7 Fatigue:

When a material or a structure is subjected to repeated or cyclic load i.e. loading and unloading,

it causes the fatigue. In the case of Titanic Ship there is a fatigue in structural as well as

mechanical parts of the ship.

1.7.1 Fatigue in Mechanical Parts:

The engines of the ships are operating at high temperature and pressure and the combustion

phenomenon occurs periodically so there is chances of heat stress induced in the material due to

cyclic loads because the engines are operated at different speeds according to the desired

requirement. Due to this different stress level is obtained inside the combustion chambers of heat

engines.

In propellers which are exposed to sea water stress is induced due to the cyclic loads on the

propellers. As different speeds required under different conditions so the thrust given by

propellers is different according to the desired velocity requirements so there is a possible chance

of fatigue in the propellers too.

9

1.7.2 Fatigue in Structural Parts:

Fatigue in structural parts is induced due to the vibrations caused by mechanical parts which are

periodic that’s why structure should be designed in such a manner so that it could bear the

vibrations caused by mechanical parts.

(Budynes & Nisbet, 2011)

1.8 Yield:

Yield point is a point in a stress strain graph of a material above which the material deforms

plastically or permanently or you can see material is not obeying Hook’s law any more i.e. after

removal of the applied load material will not return to its original shape.

1.8.1 Yield Point in Mechanical Parts:

In order to have a safe and failure free design material should have operated below the yield

point. The yield stress of the material used in the manufacturing of the mechanical parts of the

ship must be determined by using different standard techniques. The stresses induced in the

material during the maximum load must be less than the yield stress of the material so that there

should be no probability of failure.

1.8.2 Yield Point in Structural Parts:

The shear stress and transverse stresses applied to the material under maximum load conditions

must be less than the yield point of the material. Once the yield point is crossed the shape of the

material changes which alters its structural stability and there is a possible chance of failure then.

(Callister, 2012)

1.9 Modulus:

The elastic modulus of a material is defined as the ratio of stress applied to the strain observed

due to that stress. It is denoted by the following formula:

E= StressStrain

(Pa)

In the designing considerations Elastic Modulus is readily used in different calculations of the

design parameters of both the mechanical parts as well as the structural parts.

10

(Callister, 2012)

1.10 Linear Elasticity:

When a stress is applied on a body or a material, corresponding strain is produced in it. As long

as the stress and the strain remains directly proportional i.e. Hook’s Law is obeyed the material is

said to be in the elastic region and the material will comes into its initial position when the load

is removed.

The region of the linear elasticity of a material varies from material to material. The stresses

produced in the combustion chamber of the reciprocating engines and propellers of the ship

should remain within the elastic limit so that the material remains its structural integrity and

don’t deform plastically.

Once the fuel starts to burn and ship starts to move the stresses will be generated in both

mechanical and structural parts. The material of the ship should be selected so that it can bear

both the thermal stresses induced due to high temperature gradient and shear stresses induced to

the loads of the ships without crossing the elastic limit. The maximum level of all types of

stresses should remain within the elastic region of the material.

(Callister, 2012)

1.11 Environment and Intended Condition of Use:

The ship is used in the normal atmospheric conditions except the wind speed is greater in the sea.

Due to higher value of wind speed the ship should be properly aerodynamically designed so that

the wind speed could not alters the equilibrium of the ship. There will be higher level of moisture

in the wind. The flue gasses coming from engine zone due to the burning of fuel is left into the

atmosphere via chimney.

1.12 Creep and Oxidation:

Creep is defined as affinity of a solid material to deform slowly under the influence of high

stresses. Creep occurred due to long term exposure of the stresses that are beyond the yield point

of the material. Materials subjected to high heat levels for long periods encounter severe

creep .This factor should be taken care of when designing the cylinder of the chamber of the

engine used in this ship to minimize the level of creep for the longer life of the engine. Creep is a

11

deformation mode which may or may not cause failure for example in beams and columns creep

is welcomed because it relieved tensile stresses which may cause cracks in the beams and

columns. Creep is “Time dependent” phenomenon.

At higher temperatures the material of the cylinder would become nascent to the oxygen and it

reacts with primary air (air require for complete burning of fuel) and oxidation would occur. This

will make a layer of metal oxides on the cylinder walls which may cause rusting and it will lower

the heating capacity of the fuel.

(Groover, 2010)

1.13 Thermodynamics:

The heat generated inside the cylinder walls of the engine would move towards the walls of the

furnace following the phenomenon of the forced convection. It is necessary to reduce heat loss as

much as possible .For this purpose the combustion chamber needs to be properly insulated so

that there should be no heat transfer to the atmosphere. Heat from the outer walls of the engine

cylinder move into the environment through convection and radiation as well while the heat

within the wall and the insulation through conduction. Proper calculations of temperature,

pressure and specific volume and enthalpy should be done during the different processes of the

heat engine cycle.

(Cengel & Boles, 2009)

1.14 Heat Stress:

Heat stresses are induced where there is high temperature and pressure. In the ship considering

the max temperature of 1200 o C a high level of heat stresses would be generated in the

combustion chamber of the reciprocating engine that is used. Maximum heat stress will be

induced at a point where the fuel will be initially ignited (the cylinder region). The heat stress

level would be based on the temperature gradient inside the combustion chamber. Once the fuel

would start burning in the combustion chamber stresses will be induced in the cylinder walls due

to heat rejection. These stresses would be localized as well as distributed along the cylinder

walls.

12

The stresses in the walls would vary depending on the temperature gradient in the furnace. Heat

stresses generated in any materials depends on the type of the application. In the case of

reciprocating engines of the ship the combustion chamber where the fuel burns would be

subjected to a constant heat flux as a result of the heat released by the combustion of the fuel.

The heat stresses generated in the cylinder walls also depends on the composition and heating

value of the fuel used. The energy released also depends on the heating value of the fuel and

mass flow rate of the fuel.

(Cengel & Boles, 2009)

2 Question # 2:

2.1 Materials:

The material used for case of a Hand Help Drill is a plastic named as “Poly Propylene”.

The material used for chuck is Hand Help Drill High Carbon Steel (HSS).

(Callister, 2012)

2.2 Properties of the Material:

2.2.1 Case Material:

As the Hand Help Drill is used for domestic purpose so there will be no such severe conditions

such as high temperature and pressure so plastic (Poly Propylene) is very safe to use as case

material.

2.2.2 Chuck Material:

In case of chuck material the material that is used is High Carbon Steel the reason for using this

material is that it can stand high temperatures without losing its mechanical reliability such as

hardness.

(Callister, 2012)

13

2.3 Heat Treatments:

2.3.1 Case Material:

In the Case material of the drill the drying of the plastic in ovens is done to remove internal

stresses and to remove moisture content from the material.

2.3.2 Chuck Material:

The heat treatment that is used in the chuck material is called “Hardening” in which the material

is heated to a temperature above its critical temperature and then it is held at this temperature for

some time and then cooled down at a specific rate by using some cooling mediums such as air,

water and oil. This process increases the durability and mechanical stability of the Chuck.

(Groover, 2010)

2.4 Formation of Drill Body:

The body of the drill is formed by “Injection Molding”. It is a manufacturing process to achieve

a desired mold. In this process a screw type plunger which pushes the molten plastic into the

mold cavity and then the molten material hardens into the desired shape.

(Callister, 2012)

2.5 Corrosion Protection Treatments:

The chuck surface can be prevented from corrosion by the following processes:

2.5.1 Atomic Absorption:

Nickel and Titanium alloys forms an oxide layer which protects the surface from corrosion

because both

these elements are corrosion resistant and thus prevent the surface.

2.5.2 Galvanizing:

In the galvanizing process the zinc coatings are formed on the chuck surface by the use of the

galvanic cell. These type of coatings gives us the most reliable and cost efficient way of

protecting steel from corrosion.

(Groover, 2010)

14

3 Question # 3

3.1 Annealing:

It is a process in which a material is first heated at a specified temperature for a specific time and

then it is slowly cooled using some medium.

3.1.1 Advantages:

Homogenize the structure of the material.

Increases the ductility of the material.

Increase the machining ability of the material.

Removes thermal stresses which occurs due to temperature gradient.

3.2 Normalizing:

It is a process in which a material is heated above the critical temperature (temperature above

which a material cannot be liquefied) for a specific amount of time and then it is air cooled at a

moderate rate.

3.2.1 Advantages:

Removes residual stresses in the material.

Control the dimensional variation during other heating processes.

Refines the grain size.

Improves the homogeneity of the microstructure.

3.3 Hardening:

It is a process in which a material is heated to a specific temperature above its critical point and

then it is cooled rapidly by some cooling medium i.e. air oil or water

3.3.1 Advantages:

Increases the durability of the material.

Increases the mechanical strength of a material.

Increases the hardness of the material.

Increase the machining capacity of a material

15

3.4 Tempering:

It is process in which a material is heated to a higher temperature below the melting point of a

material and then cooled using air at a specified rate.

3.4.1 Advantages:

It is used to lessen the brittleness of the material.

Reduces the internal stresses in the material.

Increases the structural stability of a material.

3.5 Quenching:

It is a process in which a material is heated up to a suitable temperature above the recrystallize

phase and then it is rapidly cooled by using some cooling medium such as water, air and oil.

3.5.1 Advantages:

Relieve induced stresses.

Increases structural stability.

Increases the mechanical strength of a material.

(Groover, 2010)

4 Question No 4

4.1 Vickers Test

Vickers test is used to determine the hardness of a test material and it is also called micro

hardness test method. The Vickers hardness test comprises of denting the test surface with a

diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees

between opposite faces subjected to a load of 1 to 100 kgf. Vickers tests are typically referred to

as macro indentation tests and are used on a wider variety of materials including case hardened

and steel components.

4.1.1 Procedure:

(i) The full load is usually applied for 10 to 15 seconds.

(ii) The two diagonals of the indentation left in the surface of the material after removal

of the applied force are measured using a simple microscope.

(iii) The average mean of the measured values is calculated.

16

(iv) The area of the sloping surface of the indentation is calculated.

(v) The Vickers hardness is the quotient obtained by dividing the kgf load by the square

mm area of indentation.

HV =Vickers Hardness=1.845 Fd2

F = load in kgf

d = Arithmetic mean of two diagonals in mm

4.2 Brinell Test:

Brinell hardness test is invented by Dr J A Brinell in 1900.It is used to measure the hardness of a

material. It is used mostly to test materials that have a too rough structure. Brinell test uses a

carbide ball indenter.

4.2.1 Procedure:

(i) A precisely controlled test force is applied and the carbide indenter is pressed into the

test material surface.

(ii) The force is applied for a specific amount of time called the Dwell Time usually the

dwell time isv10-15 sec.

(iii) The size of the indent is optically determined by microscope by measuring the size of

the two diagonals of the round indent.

(iv) The arithmetic mean of the diagonals is calculated and the Brinell hardness is

determined by the following equation:

HB= 2 FπD (D−√ D2−d2 )

F = Applied Force kgf

D = Carbide Ball Diameter in mm

D = Arithmetic Mean of the diagonals length in mm

17

It is required that the test load are restricted to a impression diameter in the range of 2.5 to 4.75

mm. The Brinell number is normally ranges from 50 HB to 750HB.

4.3 IZOD Test:

IZOD impact test is used to measure the impact resistance of the material. IZOD test is normally

used to evaluate the comparative toughness or impact toughness of a materials and it is mostly

used for quality control purposes.Factors that affect the IZOD impact energy of a specimen will

include:

Yield strength and ductility.

Notches.

Temperature and strain rate.

Fracture mechanism.

4.3.1 Procedure:

(i) Fix the test piece which is a cantilever in an anvil with v shaped notch at the

bottom part of the clamp.

(ii) The test specimen is hit by striker carried on a pendulum which is set to fall

freely from a fixed height.

(iii) After the test piece is fractured the height of the pendulum to which it rises is

measured by the slave pointer mounted on the dial.

(iv) The absorb amount of energy is read from the dial.

4.4 Charpy Test:

The Charpy impact test provides the measure of energy which is required to break a material

under impact loading. Charpy tests show whether a metal can be termed as being either brittle or

ductile. The arrangement of an Izod Test and Charpy Test is almost same and differentiate only

in the configuration of the sample in Izod Test the specimen is held in a Cantilever Beam

configuration whereas in Charpy test the specimen is held in a three point bending configuration.

There are two types of Charpy test:

(i) V notch Test

18

(ii) U notch Test

4.4.1 Procedure:

(i) The notched specimen is sustained at its two ends on an anvil

(ii) The specimen is hit by a pendulum on the opposite end of the notch.

(iii) The energy that is absorbed due to fracture is measured from the dial.

(iv) Three specimen are tested at a same temperature and the arithmetic mean is taken.

(Callister, 2012)

5 Question 5:

5.1 Points:

5.1.1 Proportional Limit: (σ pl)

Proportional limit is maximum amount of stress on the stress strain diagram up to which stress

and strain have a linear behavior.

5.1.2 Yield Stress: (σ y)

Yield Stress is defined as an maximum amount of stress that can be applied on a material without

causing plastic deformation.

5.1.3 Ultimate Stress: (σu)

It is a maximum amount of stress that material can with stand without fracturing.

5.1.4 Fracture: (σ f)

Fracture is an amount of stress at which material breaks into two separate parts.

19

(Callister, 2012)

5.2 Regions:

5.2.1 Elastic Region:

Elastic region is a region in which a material is obeying Hook’s Law which states that “up to

elastic limit stress is directly proportional to strain”. In this region the deformation is reversible

or u can say when the stresses are removed the specimen will come into its original state. It is

also noted that above the proportional limit the relation between stress and strain become

nonlinear as from the graph but the material is remained in the elastic region unless the yield

point is reached.

5.2.2 Yielding Region:

After the yield point the material will be permanently deformed and the Hook’s Law is in longer

obeyed. As you can see from the graph with a small change in the stress value the change in the

strain value is quite large. In this region the materials is deformed permanently and with the

removal of the applied stresses the material will not come to its original state. The deformation

occurred in this region is called plastic deformation.

5.2.3 Strain Hardening Region:

After the yielding region if the stress is increased further, corresponding to a nonlinear increase

in strain then the material becomes stronger and it is difficult to deform the material in this

region. In this region the dislocation density of the material increases. This implies that the

material is becoming stronger as the strain is increasing hence it is called “Strain Hardening

Region”. If a material does not exhibit the strain hardening region then it is called perfectly

plastic material.

5.2.4 Necking:

After the ultimate tensile stress (σ u) the material enters in the necking region where the cross

section area of the specimen starts to decrease in a localize region of the specimen instead of

along the length of the specimen. So a “Neck” is formed as the material is stretched further until

the specimen breaks into two separate pieces at fracture point.

20

(Callister, 2012)

6 Question No 6

6.1 Limits:

Relatively provides larger amount of indentation to the specimen.

The depth of the indenter impression should not be greater than the specimen thickness.

Size of the carbide ball indenter will give different readings.

The formula used in Brinell test will give less accurate values if the indentation is more.

Brinell Test has only one scale and only applied to small number of materials.

This test cannot be used for delicate materials

This test cannot be used for the testing of thin materials because of a sphere shaped

indenter. Cylindrical shaped specimen cannot be tested using this test.

The test has limitations on critically stressed parts where indentation could be a probable

cause of failure.

The geometry of the impression is not changed as the load is increased its impression

only changes.

(Callister, 2012)

6.2 Advantages:

Due to size of the indenter the Brinell test is used for measuring the hardness of the

bulk materials as compared to other techniques.

The result of the Brinell hardness test can be considered as force independent because

force can be adjusted for materials of different sizes or strengths and the results

cannot be altered. This is because a sphere divides its pressure equally on the surface.

It gives a linear scale hardness mostly used for design work.

In Brinell Test we use a carbide sphere for indenting instead of a cone shaped or a

point shaped indenter so this test can be used for wide specimen.

Brinell hardness test is less influenced y surface scratches and roughness as compared

to other hardness tests.

Suitable Hardness test on the materials which are inhomogeneous.

Most of the metals can be tested using Brinell Hardness Test.

21

(Callister, 2012)

7 References:CALLISTER, D.W. & RETHWITCH, D.G (2012), Materials Science and Engineering an

Introduction. 8th Edition. America: John Wiley & Sons

BORGNAKKE, C & SONNTAG, R.E (2009), Fundamentals of Thermodynamics. 7th

Edition. America: John Wiley & Sons

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