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MECHANICAL ENGINEERING DEPARTMENT
LAB MANUAL
Material Testing Lab
(Subject Code: KME 352)
List of Experiments:
Objectives:


To understand the principles and performance characteristics different materials.
To know about material properties.
1. Strength test of a given mild steel specimen on UTM with full details and stress versus
strain plot on the machine.
2. Other tests such as shear, bend tests on UTM.
3. Impact test on impact testing machine like Charpy, Izod or both.
4. Hardness test of given specimen using Rockwell and Vickers/Brinell testing machines.
5. Spring index test on spring testing machine.
6. Fatigue test on fatigue testing machine.
7. Creep test on creep testing machine.
8. Experiment on deflection of beam, comparison of actual measurement of deflection with
dial gauge to the calculated one, and or evaluation of young’s modulus of beam.
9. Torsion test of a rod using torsion testing machine.
10.Study of NDT (non-destructive testing) methods like magnetic flaw detector, ultrasonic
flaw detector, eddy current testing machine, dye penetrant tests.
Course Outcomes: The students who have undergone the course will be able to measure various properties of
materials.
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Experiment 1 (Tensile Test)
OBJECTIVE: Strength test of a given mild steel specimen on UTM with full details and stress versus strain
plot on the machine.
APPARATUS USED:
1. Universal Testing Machine (UTM) Capacity: 400 KN
2. Mild steel specimens
3. Graph paper
4. Scale
5. Vernier Caliper
SPECIMEN: Tensile test specimen has been prepared in accordance with Bureau of Indian standards as
shown in the figure below
THEORY:- Various machine and structural component are subjected to tensile loading in numerous
applications. For safe design of these components ,their ultimate tensile strength and ductility are to be
determined before actual use. For that the above test is conducted .Tensile test can be conducted on U.T.M.
A material when subjected to a tensile load, resists the applied load by developing internal resisting force.This
resistance comes due to atomic bonding between atoms of the material .The resisting force per unit normal
cross-sectional area is known as stress.The value of stress in material goes on increasing with an increase in
applied tensile load, but it has a certain maximum (finite) limit too. The maximum stress at which a material
fails,is called ultimate tensile strength
Definitions:
Limit of proportionality (A): It is the limiting value of the stress up to which stress is proportional to
strain.
Elastic limi(B)t: This is the limiting value of stress up to which if the material is stressed and then released
(unloaded), Strain disappears completely and the original length is regained.
Upper Yield Point (C): This is the stress at which, the load starts reducing and the
extension increases. This phenomenon is called yielding of material.
Lower Yield Point (D): At this stage the stress remains same but strain increases for some time.
Ultimate Stress (E): This is the maximum stress the material can resist. At this stage cross sectional area at
a particular section starts reducing very fast (fig.1). This is called neck formation.
Breaking Point (F): The stress at which finally the specimen fails is called breaking point.
Hooks law: Within the elastic limit, the stress is proportional to the strain for an Isentropic material.
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Fig. 1 Stress-strain graph of Mild Steel




Fig. 2 Stress-strain graphs of different materials.
Curve A shows a brittle material. This material is also strong because there is little strain for
a high stress. The fracture of a brittle material is sudden and catastrophic, with little or no
plastic deformation. Brittle materials crack under tension and the stress increases around the
cracks. Cracks propagate less under compression.
Curve B is a strong material which is not ductile. Steel wires stretch very little, and break
suddenly. There can be a lot of elastic strain energy in a steel wire under tension and it
will “whiplash” if it breaks. The ends are razor sharp and such a failure is very dangerous
indeed.
Curve C is a ductile material
Curve D is a plastic material. Notice a very large strain for a small stress. The material will
not go back to its original length.
PROCEDURES:
1. Observe the specimen. Measure the total length and parallel length of the specimen. Also
measure the diameter of the specimen. Calculate the gauge length. Mark the gauge length
on the central portion of the specimen.
2. Fix the specimen in-between the upper and middle cross heads using the gripping devices. Take
precautions to fix the test specimen in such a way as to ensure that the load is applied axially.
3. Fix the extensometer in its position over the gauge points. Adjust the extensometer and the linear
scale to read zero initially.
4. Select proper range of loading (i.e. 0 to 40 tonnes).
5. Switch on the machine. Apply the axial tensile load on the specimen gradually. Record the
extensometer readings at a constant load increment of 400 kg.
6. The yield point can be observed either:
a. by the kickback of the live needle of the load indicating dial. OR
b. by the rapid movement of extensometer dial needle at constant load reading.
Record the yield load(s), and remove the extensometer.
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Continue the axial loading.
7. At one stage, the live needle begins to return, leaving the dummy needle there itself. Note down
the load at that point as the ultimate load. Also, observe the neck formation on the specimen.
8. Note down the load at the point of failure of the specimen.
9. Switch off the machine; Remove the failed specimen; Observe the type of fracture.
10. Measure the final gauge length on the tested specimen, if the failure has occurred within the
gauge length portion and also, the diameter at the neck.
NOTE:
a)
b)
c)
d)
e)
f)
The above procedure is valid for steel bar of diameter equal to or greater than 4 mm,
or of thickness equal to or greater than 3 mm.
For test pieces of rectangular section, a ratio of width to thickness of 8 : 1 should not
be exceeded.
The gauge length can be calculated from the equation L0 √ A = 5.65D.
where A is the initial cross sectional area of the test specimen. It is rounded off to nearest
multiple of 5 mm. However, test pieces with other gauge lengths may be used, for technical
or economical reasons.
Some specimens exhibit both upper and lower yield points, and some specimens
exhibit only one yield point.
Some materials may not exhibit any yield point at all. For such materials, 0.2% proof
stress is to be determined.
If the failure occurs outside the gauge length, the value of the percentage of
elongation can not be calculated.
OBSERVATION: Following data are recorded for conducting a tensile test.
Type of fracture =
Material of the specimen =
Intial gauge length of the specimen lo =
Intial gauge diameter of the specimendo =
Extended gauge length at fracture lf =
Reduced gauge diameter at the broken end df =
Load at Yield point =
Ultimate Load=
Breaking Load=
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S. No.
Load P (N)
TABLE
Extension (δ l)
mm
Stress =P/Ao
(MPa)
Strain
(l/ lo
1
2
3
4
5
CALCULATION:
Initial cross sectional area A0=/4 d02
Final cross sectional area Af=/4 df2
Percentage elongation % (l) = ( lf-lo)/lo
Percentage reduction in cross sectional area = (A–a) x 100 / A=
Young‟s modulus of elasticity of Mild Steel in tension =
Slope of the straight lineportion of the stress vs. strain curve = Et =………………N/mm2
Upper yield stress =σyu =
Load at upper yield point / A = ……………..N/mm2
Lower yield stress =σyu =
Load at lower yield point / A = ……………..N/mm2
OR
Yield stress(σy) = Load at yield point / A ……………….N/mm2
Tensile strength (Ultimate strength) (σult) = Ultimate Load / A
Failure or breaking stress(σf) = Breaking load / A =……….N/mm2
RESULTS:
 Young‟s Modulus of specimen =
 Yield stress =
 Ultimate stress =
 Breaking stress =
 % reduction in Area =
 % Elongation=
VIVA VICE QUESTIONS
1. Which modulus did you find from the initial portion of the stress-strain curve? If did not
use an extensometer but determined strain from the crosshead movement, would the
initial slope still allow you to determine an accurate modulus? Explain.
2. Write the definition using symbols for shear modulus, bulk modulus and Poisson's ratio.
Write the equations relating these two modulus to Young's modulus.
3. What is the approximate value of Poisson's ratio for metals? What is the physical
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significance of Poisson's ratio, i.e. what does it represent resistance to?
4. What is the area under the stress-strain curve equivalent to? What does the area under
the elastic portion of the stress-strain represent?
5. What % elongation and % reduction in area measures of?
6. Explain the different deformation mechanisms which are active in the different regions of
the tensile stress-strain curve. (elastic, yielding, strain hardening, necking etc.)
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EXPERIMENT NO: 2 (Shear Test)
OBJECTIVE: To conduct shear test on given specimen under double shear.
APPARATUS: i) Universal testing machine.
ii) Shear test attachment.
iii) Vernier
iv) Specimens.
DIAGRAM:-
THEORY:-Place the shear test attachment on the lower table, this attachment consists of cutter. The specimen
is inserted in shear test attachment & lift the lower table so that the zero is adjusted, then apply the load such
that the specimen breaks in two or three pieces. If the specimen breaks in two pieces then it will be in single
shear & if it breaks in three pieces then it will be in double shear.
PROCEDURE:
1. Insert the specimen in position and grip one end of the attachment in the upper portion
and one end in the lower portion.
2. Switch on the main switch of universal testing machine machine
3. The drag(red) indicator in contact with the main(black) indicator.
4. Select the suitable range of loads and space the corresponding weight in the pendulum
and balance it if necessary with the help of small balancing weights.
5. Operate (push) buttons for driving the motor to drive the pump.
6. Gradually apply the pressure through pressure valve till the specimen shears.
7. Note down the load at which the specimen shears.
8. Stop the machine and remove the specimen
Repeat the experiment with other specimens.
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OBESERVATIONS:Diameter of the Rod, D = ….. mm
Cross-section area of the Rod (in double shear) = 2x π/4x d2 mm2
Load taken by the Specimen at the time of failure , W
Newton
2
Strength of rod against Shearing = τ x 2x πd /4
Shear Stress (τ) = W / 2.πd2/4
N/mm2
RESULT: The Shear strength of mild steel specimen is found to be = ……………… N/mm2
PRECAUTIONS:1. The measuring range should not be changed at any stage during the test.
2. The inner diameter of the hole in the shear stress attachment should be slightly greater
than that of the specimen.
3. Measure the diameter of the specimen accurately.
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Experiment 3
IZOD and CHARPY TEST
OBJECTIVE:-To conduct the impact test (Izod / Charpy) on the impact testing machine.
APPARATUS USED -Impact testing machine, Izod and charpy test specimen of mild steel and/or aluminum,
vernier caliper.
THEORY- An impact test signifies toughness of material that is ability of material to absorb energy during
plastic deformation In manufacturing locomotive wheel, coin, connecting rods etc., the component are
subjected to impact (shock) load. These load are applied suddenly. The stress induced in these component are
many times more than the stress produced by gradual loading. Therefore impact tests are performed to assess
shock absorbing capacity of materials subjected to suddenly applied loads. These capabilities are expressed
as (i) rupture energy (ii) modulus of rupture, and (iii) notch impact strength.
Two types of notch impact test are commonly conducted these are
1-Charpy test
2-Izod test
In both tests, standard specimen is in the form of a notched beam. In charpy test, the specimen is placed as
‘simply supported beam’ while in izod test it is kept as a ‘cantilever beam’. The specimens have V shape notch
of 45Degree in izod test and U shaped notch in charpy test. The notch is located on tension side of specimen
during Impact loading. Depth of notch is generally taken as t/5 to t/3 where t is the thickness of the specimen.
TEST SET UP AND SPECIFICATIONS:
Capacity Energy Range
Charpy 0-300 J
Izod 0-164 J
Model ITM 300
Mfd. By ::
1.
Pendulum type impact testing machine. The machine consists of:
2.
3.
4.
5.
6.
7.
8.
A pendulum of mass 18.748 kg, length = 825 mm with an angle of swing of 160o.
Specimen holder (different for Izod and Charpy tests)
Striking edge (different for Izod and Charpy tests)
Lock lever and pendulum releaser.
Pendulum brake.
A calibrated dial to measure the Impact energy, with red and black indicators.
Slide Calipers and Scale
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Standard Specimen for CHARPY test:
Standard specimen for IZOD test
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PROCEDURE:



Check the specimen for the its standard dimensions.
Depending upon the type of test, fix the corresponding striking edge to the hammer.
To find the frictional loss:
a) Raise the pendulum to its highest position where it gets locked. At this position,
the potential energy stored in the pendulum is 30 Nm.
b) Set the dial to read 30 Nm with the indicator showing black colour.
c) Press the lock lever first and then the pendulum releaser to release the pendulum.
d) Stop the oscillations of the pendulum using the damper plate / brake.
e) Record the reading on the dial which indicates the frictional loss directly.
Note: Read the black or red scale according as the indicator is black or red respectively.
Fix the specimen in its holder.
a)
For Izod Test: The specimen should be placed vertically as a cantilever with the
shorter end of the specimen projecting above the holder and V-Notch on the
tension side.
b)
For Charpy Test: The specimen should be placed horizontally as a simple beam
and the U-notch on the tension side.
Note: Use the appropriate centraliser to keep the specimen in its proper position.
ii)
iii)
iv)
v)
vi)
Raise the pendulum to its highest position where it gets locked. Set the dial to read 30
Nm with the indicator showing black colour.
Release the pendulum by pressing down the lock lever first and then the pendulum
releaser to strike the specimen.
Use the damper plate / brake to stop the oscillations of the pendulum.
Record the dial reading on the red or black scale depending upon whether the
indicator is red or black respectively.
Observe whether the specimen has broken completely or not.
OBSERVATION:
Material of the specimen =
Mass of the pendulum = 187.5 kg
Length of the pendulum = 825 mm
Angle of swing = 90o (IZOD Test) & 160o (CHARPY Test)
Frictional Loss = Uf
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Izod Impact Test
Specimen
Specimen
No.
Dimension
Charpy Test
Specimen
Specimen
No.
Dimension
Enrgy
Observed
Uo N m
Impact Enrgy Ui=
Uo-Uf
Impact
Strength =
KU = UI/A
Nm/mm2
Remarks
Enrgy
Observed
Uo N m
Impact Enrgy Ui=
Uo-Uf
Impact
Strength =
KU = UI/A
Nm/mm2
Remarks
RESULTS:
The energy absorbed for given material ………… in Izod test is found out to be (K) ---------------- Joules.
The energy absorbed for given material ………… in Charpy test is found out to be (K) ---------------- Joules.
Impact strength of the specimen (Izod Test) (K/A) = ------------------J/mm2
Impact strength of the specimen (Charpy Test) (K/A) = ------------------- J/mm2
PREACAURIONS:
1. Hold the specimen (lzod test) firmly.
2. Utmost care must be taken to see that no person is present in the line of oscillation of
the pendulum.
3. Use the damper plate / brake to stop the oscillations of the pendulum.
4. During the test, if the test piece is not completely broken, the impact value obtained is
indefinite. Then the test report should state that the test piece was unbroken by
joules, in case of Izod test, and the test report should state that the test piece was not
broken by the striking energy of the testing machine, in case of Charpy test.
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EXPERIMENT NO. 4 (Hardness Test)
OBJECT-To determine the hardness of a given specimen using Brinell / Rockwell / Vicker testing machine
APPARATUS USED – Brinell / Rockwell / Vicker testing machine, specimen of mild steel/cast iron/ non –
ferrous metal, optical microscope
THEORY- Hardness is a surface property. It is defined as the resistance of material against permanent
deformation of the surface in the form of scratch, cutting, indentation, or mechanical wear. The need of
hardness test arises from the fact that in numerous engineering applications, two components in contact are
made to slide or roll over each other. In due course, their surfaces are scratched and they may fail due to
mechanical wear. This result in not only a quick replacement of both parts but also incurs a big loss in terms
of money.
For example, piston ring of an I.C ingine remains in sliding contact with the cylinder body when the
piston reciprocates within the cylinder. If proper care is not taken in selection of materials for then, The piston
rings and cylinder will wear soon.
In this case the replacement or repairing of cylinder block will involve much time, trouble and money.
Therefore, the material of piston rings and cylinder block should be taken such that the wear is least on the
cylinder. Thus in case of repairing, comparatively cheaper piston rings can be easily replaced. This envisages
that material of cylinder block should be harder than the material of piston rings so that the cylinder wears.
The least. This can be ascertained by conduct of a hardness test. That is why it is essential to known as to how
this test can be conducted.
There are three general types of hardness measurements depending upon the manner in which the
test is conducted:
A. Scratch hardness measurement,
B. Rebound hardness measurement
C. Indention hardness measurement.
In scratch hardness method the material are rated on their ability to scratch one another and it is usually
used by mineralogists only.
In rebound hardness measurement, a standard body is usually dropped on to the material surface and the
hardness is measured in terms of the height of its rebound.
The general means of judging the hardness is measuring the resistance of a material to indentation. The
indenters usually a ball cone or pyramid of a material much harder than that being used. Hardened steel,
sintered tungsten carbide or diamond indenters are generally used in indentation tests; a load is applied by
pressing the indenter at right angles to the surface being tested. The hardness of the material depends on
the resistance which it exerts during a small amount of yielding or plastic. The resistance depends on
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friction, elasticity, viscosity and the intensity and distribution of plastic strain produced by a given tool
during indentation
Material
Ball Indenter diameter (mm)
5
2.5
Mild steel
750 kgf
Cast Iron
Brass
Gun Metal
Aluminum
BRINELL HARDNESS TEST:
750 kgf
250 kgf
250 kgf
125 kgf
187-5
kgf
187.5 kgf
62.5 kgf
62.5 kgf
31.25 kgf
In Brinell‟s hardness test, a hard steel ball, under specified conditions of load and time, is
forced into the surface of the material under test and the diameter of the impression is
measured. Hardness number is defined as the load in kilograms per square millimeters of
the surface area of indentation. This number depends on the magnitude of the load
applied, material and geometry of the indentor.
LOAD RANGE FOR BRINELL HARDNESS TEST:
The load to be applied can be obtained by the formula P = KD2 kgf.
where K = Constant for a given metal (listed in Table-1)
D = Diameter of the ball indenter in mm.
Table 1: Values of „K‟ and range of hardness for different metals (for Brinell Hardness
Test)
Sl.
No.
Metal
Value of K
1.
Mild steel
30
2.
Cast Iron
30
3.
Brass
10
4.
Gun Metal
10
5.
Aluminum
5
Range of Brinell hardness
number
(HB)
67-500 kgf/mm2
67-500 kgf/mm2
22-315 kgf/mm2
22-315 kgf/mm2
11-158 kgf/mm2
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Example:
Brinell’s hardness number (HB) is given by
=
Load on ball in kg
Curved surface area of indentation in sq.mm
=
Where:
2P / { πD [D - (D 2 – d 2) ] }
P=load Applied in Kgf
D=diameter of indentor in mm
d=average diameter of impression in mm
PROCEDURE:
1. Select the proper diameter of the indentor and load.
2. Start the machine by pushing the green button of starter and allow oil to
circulate for few minutes.
3. Keep the hand lever in position A.
4. Place the specimen securely on the testing table. Turn the hand wheel in
clockwise direction, so that the specimen will push the indentor and will show a
reading on dial gauge. The movement will continue until the long pointer will
stop at „0‟ and small pointer at red dot when the initial load of 250kg is applied. If
little error exists the same can be adjusted by rotating the outer ring dial gauge.
5. Turn the handle from position „A‟ to „B‟ so that the total system sibrought into action.
6. When the long pointer of dial gauge reaches a steady position, the load may be
released by taking back the lever to position „A‟.
7. Turn back the hand wheel and remove the specimen.
8. The diameter of the impression can be found by using optical microscope.
9. Read the hardness number from the tables.
Note:
a) The thickness of the test piece should not be less than 10 times the depth of indentation.
b) The distance of the centre of the indentation from the edge of the test piece are from
the circumference of the adjacent indentation should not be less than 3 times the
diameter of the indentation.
c) The Brinell hardness number is calculated using the formula
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OBSERVATIONS:
TABLE
Material
of the
specime
n
Diamete
r of the Load
indenter P, kg
D, mm
Load
P,N
Diameter of the
indentation
d2, mm d = (d1 +
d1,
d2)/2,
mm
mm
Brinell
hardne
s
s
value
Cast Iron
Mild Steel
Brass
Gun Metal
Aluminum
CALCULATION: For the given
specimen,
RESULT: The Brinell‟s hardness number of …………………
.=
………………
PRECAUTIONS:
1. Operate the hand lever from A to B several times to raise and lower the weights
in order to eliminate air from the hydraulic system.
2. Operate it slowly for accurate results.
3. Brinell test should be performed on smooth, flat specimens from which dirt and scale have been
cleaned
ROCKWELL HARDNESS TEST:
The specimen is subjected to a major load for about 15 seconds after the minorl load. ASTM says 13 scales for
testing of wide range of materials. These scales are A,B, C… etc.
Table-: Commonly used Rockwell hardness scales.
Scale
Indenter Type
A
D
C
Diamond Brale
Diamond Brale
Diamond Brale
IMajor Load
(kgf)
60
100
150
Typical Applications
Tool Materials
Cast Irons, Sheet Steels
Hardened steels and cast irons, Ti Alloys
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B
E
F
M
R
1/16" Diameter Ball
1/8" Diameter Ball
1/16" Diameter Ball
1/4" Diameter Ball
1/2" Diameter Ball
100
100
60
100
60
Annealed steels, Cu and Al Alloys
Al and Mg alloys, reinforced Polymers
Soft sintered products
Very soft metals, polymers
Very soft metals, polymers
For Rockwell – B Test: Steel ball indenter of diameter (1/16)th inch.
Indenters:
i)
For Rockwell – C Test: Rockwell diamond cone of vertex angle 120o and tip
radius 0.2 mm.
Standard Loads:
Sl.
No.
1.
2.
3.
4.
5.
Material
Cast Iron
Mild Steel
Brass
Gun Metal
Aluminum
For Rockwell – B Test
Load, kgf
For Rockwell – C Test
Load, kgf
–
–
100
100
100
150
150
–
–
–
PROCEDURE:
1. Smoothen the surface of the specimen to be tested, and clean it to remove dirt and oil, if any.
2. Fix the appropriate indenter to the thrust member or penetrator.
3. Depending upon the material of the specimen and type of the indenter, select and set the required
load stage, and see that the load lever is in position “A”.
4. Place the standard specimen on the test table, and turn the main nut (hand wheel) in the clockwise
direction to have contact between specimen and the penetrator. Continue turning until the small
pointer of the dial gauge reaches the red spot and the long pointer comes to “0” mark on the dial
gauge. This also indicates the application of a preload of 10 kg.
5. Turn the load lever from position “A” to position “B” to apply the main load on the specimen.
6. Wait for the long needle of the dial gauge to reach a steady position.
7. Release the main load by bringing back the load lever from position “B” to position “A” slowly.
8. Record the reading shown by the long pointer
a. on red scale for Rockwell – B Test
b. on black scale for Rockwell – C Test.
9. Turn the main nut in the counter clock wise direction and remove the specimen.
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Note:
One division of Rockwell B or C scale is equal to a depth of indentation of 2 micron.
Rockwell hardness should be designated by HR, preceded by the hardness
value and supplemented by a letter indicating the scale.
Ex: 60 HRC indicates Rockwell hardness of 60 on C scale.
OBSERVATIONS:
Rockwell – B Test
a)
b)
Type of indenter. Steel ball of diameter (1/16)th inch.
Specimen
Load
P, kg
Load
P, N
Red scale
reading ‘n’
Hardnes
s value,
n
Depth of
indentatio
n
= (130n)x2,
Microns
Brass
Gun Metal
Aluminum
Rockwell – C Test Type of indenter. Rockwall diamond cone of vertex angle 120o
Specimen Load P, kg
Load P, N Black
Hardnes
scale
s value,
reading ‘n’ n
Depth of
indentation (100-n)
2,
microns
Cast Iron
Mild Steel
RESULTS: The rock well hardness number for ………
PRECAUTIONS:
1. Select the proper indentor and load to suit the material under the Test.
2. Surface to be tested must be sufficiently smooth and free from any defects.
3. The surface under the test must be at right angle to the axis of the indentor.
4. Diamond indentor has highly polished surface and is Susceptible
to damage if not handled properly.
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EXPERIMENT NO. 5 (Spring Test)
OBJECTIVE: To determine the stiffness and modulus of rigidity of the spring wire.
APPARATUS USED: 1.
2.
3.
4.
Spring testing machine.
A spring
Vernier caliper, Scale.
Micrometer.
DIAGRAM:THEORY: - Springs are elastic member which distort under load and regain their original shape when load is
removed. They are used in railway carriages, motor cars, scooters, motorcycles, rickshaws, governors etc.
According to their uses the springs perform the following Functions:
1) To absorb shock or impact loading as in carriage springs.
2) To store energy as in clock springs.
3) To apply forces to and to control motions as in brakes and clutches.
4) To measure forces as in spring balances.
To change the variations characteristic of a member as in flexible mounting of motors. The spring is
usually made of either high carbon steel (0.7 to 1.0%) or medium carbon alloy steels. Phosphor
bronze, brass, 18/8 stainless steel and Monel and other metal alloys are used for corrosion
resistance spring. Several types of spring are available for different application. Springs may
classified as helical springs, leaf springs and flat spring depending upon their shape. They are
fabricated of high shear strength materials such as high carbon alloy steels spring form elements of
not only mechanical system but also structural system. In several cases it is essential to idealize
complex structural systems by suitable spring.
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PROCEDURE:
1. Measure the outer diameter (D) and diameter of the spring coil (d) for the given
compression spring.
2. Count the number of turns i.e. coils (n) in the given compression specimen.
3. Place the compression spring at the center of the bottom beam of the spring testing
machine.
4. Insert the spring in the spring testing machine and load the spring by a suitable
weight and note the corresponding axial deflection in tension or compression.
5. Note down the initial reading from the scale in the machine.
6. Increase the load and take the corresponding axial deflection readings.
7. Find the actual deflection of the spring for each load by deducting the initial scale
reading from the corresponding scale reading.
8. Calculate the modulus of rigidity for each load applied.
9. Plot a curve between load and deflection. The shape of the curve gives the stiffness
of the spring.
FORMULA : Modulus of rigidity, G =64 WR3n / δd4 Where
W = Load in N
R = Mean radius of the spring in mm (D –(d /2))/2
d = Diameter of the spring coil in mm
δ = Deflection of the spring in mm
D = Outer diameter of the spring in mm.
OBESERVATIONS:
1. Material of the spring specimen =
2. Diameter of the spring wire, d =………mm (Mean of three readings)
3. Diameter of the spring coil, D = ……...mm (Mean of three readings)
4. Number of turns, n =
S.No
Load in Kgf
Scale
readings
in mm
Deflection
in mm
Rigidity Stiffness
modulu
in
s
N/mm
2
in N/mm
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RESULT:
The modulus of rigidity of the given spring =
------------------- GPa
The stiffness of the given spring = ------------------- N/mm2
GRAPH: Load Vs Deflection
PRECAUTIONS:1. Dimensions should be measure accurately with the help of Vernier Calipers.
2. Deflection from the scale should be noted carefully and accurately.
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Experiment No. 6 (Fatigue Test)
Objective :To study the fatigue testing machine and to determine the fatigue limit and fatigue strength.
Equipment: Fatigue testing machine and micrometer caliper.
Theory:
Failure due to repeatedly applied load is known as fatigue. The physical effect of a
repeated load on a material is different from that of a static load, failure always being brittle
fracture regardless of whether the material is brittle or ductile. Mostly fatigue occur at stress
well below the static elastic strength of the material. If the applied load changes from any
magnitude in one direction to the same magnitude in the opposite direction, the loading is
termed completely reversed, whereas if the load changes from one magnitude to another
(the direction does not necessarily change), the load is said to be a fluctuating load. Fatigue
testing machine is shown in figure.
A specimen of circular cross-section is held at its ends in special holders and loaded
through 2 bearings equidistant from the center of the span. Equal loads on these bearings
are applied by means of weights that produce a uniform bending moment in the specimen
between the loaded bearings. The specimen is rotated by a motor. Since the upper fibers in
tension, it is apparent that a complete cycle of reversed stress in all fibres of the beam is
produced during each revolution. A revolution counter is used to find the numberof cycles
the specimen is repeatediy subjected to the load. For simply supported beam, maximum
bending moment is at the centre. Bending moment M=FL/4 and bending stress S=M/z
Where L is the length of the specimen and z is the sectional modulus. In rotating
cantilever beam type, the specimen is rotated while a gravity load is applied to the free end
by means of a bearing. For cantilever specimen the maximum bending moment is at the fixed
end.
M=FL and S=M/z
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The testing technique is subjected to a series of identical specimens to loads of
different magnitude and note the number of cycles of stress ( or load) N necessary to fracture
the specimen. The data are plotted on a graph sheet, the stress S being plotted on y-axis and
the number of cycles N on X-axis.
This is known as stress-cycle (S-N) diagram and the fatigue limit can be determined
from the diagram fatigue limit or endurance limit is the stress below which a material can be
stressed cyclically an indefinitely large number of times without failure. The fatigue strength
is the stress at which a metal fails by fatigue after a certain number of cycles. Fig. shows the
S-N diagram for MS.
Specimens:
All specimen should be taken from the same rod, each specimen should receive same
kind of amchining and heat treatment. The specimens for tests of the metal have no sharp
stress raisers. The surface of the specimen is polished.
Fracture Appearance:
Under repeated loading, a small crack forms in a region of high localized stress, and
very high stress concentration accompanies the crack. As the load fluctuates, the crack opens
and insufficient cross section left to carry the load and the member ruptures, the failure
being fatigue failure. Therefore fractured surface shows two sufraces of distinctly different
appearance. 1. A smooth surface where the crack has spread slowly, and the walls of the
crack are polished by repeated opening and closing. This surface usually shows
characteristic beach or clam shellmarkings. 2. A crystalline or fibrous surface wherer sudden
failure occurred.
Procedure:
Measure the diameter d and the length L of the specimen. Securely fasten the specimen in
the chucks of the testing machine. Set the maximum load. Set the counter to zero, the start the
machine. Note the number of cycles N the specimen experiences before fracture. Repeat the
above test on the other specimens with gradually reduced loads. Draw the S-N diagram and
obtain the endurance limit.
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Observations and Tabulation:
Material
=
Diameter of the specimen d(mm) =
Length of the specimen L (mm) =
Section modulus Z (mm3)= Пd3/32=
Sl.
Load F
No. of Cycles
No.
N(kgf)
N
Bending
Stress
moment
S=M/
M=FL/4
z
N/mm2(kgf/m
m2)
N-mm(kgf-mm)
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Fatigue Testing Machine.
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Experiment: Creep testing
Objective : To determine the creep point in the plastic material.
Apparatus required:
1.
2.
3.
4.
5.
6.
Creep machine
dial gauge
stop watch
weight
Specimen
Thermometer.
Formula:
Elasticity = change in length / original length
Specification:
Length = 700mm
Width = 350mm
Height = 510mm
Weight = 23Kg
Sample 1= Lead
Sample 2 = Plastic
Thermometer measurement range = 1 C to
300 C. Dial gauge = 0 to 10 mm.
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Tabular column
S.N
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Time (sec)
Change in
Elasticity
length (mm)
(mm)
Temperatur
e in C
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Procedure:
1. Locate the sample specimen in the holder.
2. Insert the thermometer in the climatic chamber.
3. Locate the dial gauge and set to zero above the coolant chamber
which touches the beam of the specimen.
4. Release the lock net and apply the load as per the required needs.
5. Observe the time taken and change in length which takes places in
the experiment with the help of stopwatch.
Result:
Thus the creep point has been indentified for the corresponding material.
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EXPERIMENT NO: - 8 (Deflection test on simply supported beam)
OBJECT:-To find the values of bending stresses and young‟s modulus of elasticity of the
material of a beam simply supported at the ends and carrying a concentrated load at the center.
APPARATUS: 1. Deflection of beam apparatus
2. Pan
3. Weights
4. Beam of different cross-sections and material (say wooden and Steel beams)
DIAGRAM:-
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THEORY:-If a beam is simply supported at the ends and carries a concentrated load at its center,
the beam bends concave upwards. The distance between the original position of the beams and its
position after bending at different points along the length of the beam, being maximum at the
center in this case. This difference is known as „deflection‟ In this particular type of loading the
maximum amount ofdeflection (δ) is given by the
𝑾𝑳𝟑
𝜹=
𝟒𝟖𝑬𝑰
𝑬=
𝑾𝑳𝟑
𝟒𝟖 𝜹𝑰
W = Load acting at center, N
L = Length of the beam between the supports mm
E = Young‟s modulus of material of the beam, N/mm2
I = Second moment of area of the cross- section (i.e, moment of Inertia) of the
beam, about the neutral axis, mm.4
BENDING STRESS
As per bending equation
Where
M = Bending Moment N-mm; I = Moment of inertia mm4
σ b = Bending stress, N/mm2 , and
Y = Distance of the top fibre of beam from the neutral axis
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PROCEDURE:
1
2
3
4
5
6
7
Adjust cast- iron block along the bed so that they are symmetrical
with respect to the length of the bed.
Place the beam on the knife edges on the block so as to project
equally beyond each knife edge. See that the load is applied at the
center of the beam
Note the initial reading of Vernier scale.
Add a weight of 20N (say) and again note the reading of the Vernier scale.
Go on taking readings adding 20N (say) each time till you have
minimum six readings.
Find the deflection (δ) in each case by subtracting the initial
reading of Vernier scale.
Draw a graph between load (W) and deflection (δ). On the graph
choose any two convenient points and between these points find the
corresponding values of W and δ. Putting these Values in the relation
=
Calculate the value of E
8. Calculate the bending stresses for different loads using relation
As given in the observation table.
𝑀𝑦
𝜎𝑏 =
𝐼
OBESERVATION TABLE:-
Sl No
RESULT:
Load
W (N)
Bending Moment
Bending
Stress (σb)
Deflection
(δ)
Young‟s Modulus
of elasticity
=
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1.
2.
The young‟s modulus for steel beam is found to be----- N/mm2.
The young‟s modulus for wooden beam is found to be----- N/mm2
PRECAUTION
1. Make sure that beam and load are placed a proper position.
2. The cross- section of the beam should be large.
3. Note down the readings of the Vernier scale carefully
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EXPERIMENT NO. 9 (Torsion Test)
OBJECTIVE: To study the behaviour of Mild steel when subjected to a gradually increasing torsional
load and to determine the rigidity modulus & modulus of rupture (torsion).
APPARATUS:
1. A torsion test machine along with angle of twist measuring attachment.
2. Standard specimen of mild steel or cast iron.
3. Steel rule.
4. Vernier caliper or a micrometer.
M/C SPECIFICATIONS:
Torsion machine
Capacity:
Torque Range: 0-10 Kg. m
Model: TTM-10.
SR.No: 2001/1012.
Mfd. By.
It has the following parts:
 Arrangement to twist the specimen – It consists of end blocks, specimen holder,
a worm gear arrangement and a heavy weight pendulum.
 A circular scale with a vernier to record the angle of twist.
 A calibrated scale mounted on a rack and pinion arrangement to record the
torque in Nm. The capacity of the machine is 50 Nm.
 The machine can be operated either manually by means of a crank or
mechanically with the help of an electric motor.
 Slide calipers/micrometer, scale.
PROCEDURE:
1. Observe the specimen. Measure its diameter and initial length.
2. Mark a straight line parallel to the longitudinal axis of the specimen with a piece
of chalk to observe the twisting of the specimen and to measure the percentage
elongation.
3. Place the two enlarged ends of the specimen inside the two end blocks and place
the whole assembly in the specimen holder. See that the specimen is fixed with
no slack.
4. Adjust the circular scale and the torque scale to read zero. See that the screw
provided in the torque scale arrangement is in contact with the main scale and
that the vernier of the circular scale is in contact with the pendulum frame,
initially.
5. To begin with, operate the machine manually. Record the torque scale readings
at regular intervals of 1o twist up to 10o and at every 2o intervals up to 30o.
6. Now, remove the crank used for manual operation and connect the machine to
an electric motor through a clutch arrangement.
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7. Note down the torque scale readings at 60o and afterwards at an interval of 60o up to the
8. failure of the specimen.
9. At the instant of failure, disengage the clutch. Record the angle of twist as well
as the torque at the instant of failure.
10. Remove the tested specimen. Observe the type of fracture.
11. With the help of a thread, measure the length of the chalk mark on the specimen.
THEORY: For transmitting power through a rotating shaft it is necessary to apply a turning force. The
force is applied tangentially and in the plane of transverse cross section. The torque or twisting moment
may be calculated by multiplying two opposite turning moments. It is said to be in pure torsion and it
will exhibit the tendency of shearing off at every cross section which is perpendicular to the longitudinal
axis.
Torsion equation:
T/J = τ/R= Gθ/L
G = T L/J θ N/mm2
T= maximum twisting torque (N mm)
J = polar moment of inertia (mm4) = π d4/32
τ = shear stress N/mm2)
G = modulus of rigidity (N/mm2)
θ = angle of twist in radians
L= length of shaft under torsion (mm)
OBESERVATIONS AND CALCULATIONS:Gauge length of the specimen, L = ………
Diameter of the specimen, d = ………
Polar moment of inertia, J = π d4/32 = ......
Modulus of rigidity of the material of the specimen = G= TL/ J θ =……
Modulus of rapture (Torsion) = 16 T max/ πD3= …………
Sl. No.
Torque,
Torque,
Kg-cm
N - mm
TABLE :
Angle of twist
Degrees
Radians
Modulus
Rigidity, G
N/mm2
Average
G,
N/mm
2
RESULT:-Thus the torsion test on given mild steel specimen is done and the modulus of rigidity is ------N/mm2 and modulus of rupture is ------------
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GRAPH: Torque Vs Angle of Twist
PRECAUTIONS:1) Measure the dimensions of the specimen carefully
2) Measure the Angle of twist accurately for the corresponding value of
torque. 3)The specimen should be properly to get between the jaws.
5) After breaking specimen stop to m/c.
Viva Questions
1.
2.
3.
4.
Define torque.
Give the expression for torque.
Define modulus of rigidity.
Give the values of G for different materials.