Laboratory Manual
for
ME F216
MATERIALS SCIENCE & ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
BITS PILANI, HYDERABAD CAMPUS
1
LIST OF EXPERIMENTS
CYCLE-A: MECHANICS OF SOLIDS
EXPERIMENT 1. UNI-AXIAL TENSILE TESTING
EXPERIMENT 2. DEFLECTION OF BEAMS
EXPERIMENT 3. IMPACT TESTING
EXPERIMENT 4(a). TORSION TEST
EXPERIMENT 4(b). SPRING TEST
CYCLE-B: MATERIALS SCIENCE AND ENGINEERING.
EXPERIMENT 5. HARDNESS TESTING
EXPERIMENT 6. JOMINY END QUENCH TEST
EXPERIMENT 7 - OPTICAL MICROSCOPY
EXPERIMENT 8 – FATIGUE TEST
DEMONSTRATIONS
DEMO 1: X-RAY DIFFRACTION
DEMO 2: ELECTRON MICROSCOPY
DEMO 3: NON-DESTRUCTIVE TESTING
DEMO 4: SHAPE MEMORY ALLOYS
MINI PROJECT
2
Experiment 1: Uni-axial Tensile Testing
Aim: - To conduct a simple tension test on a flat specimen of Al/Steel on UTM to observe the
load-displacement graph and to calculate the various mechanical properties.
Apparatus: - Universal testing machine (UTM)
Tensile test specimen: - Al or Steel
ASTM standard: - E8
Theory: - Universal testing machine is used for conducting tensile tests with which one can
determine various mechanical properties of a material like Young’s Modulus, Toughness,
Resilience, Ductility, Yield stress and Ultimate tensile strength. Specimens used in this test are
chosen as per the ASTM E8 standards as provided below.
Once the test is conducted on the UTM, the stress vs. strain diagram can be plotted. A typical
tensile test curve for mild steel is shown in figure 2. The curve in the solid line is called as the
engineering stress-strain curve and the curve in the dotted line is called the true stress-strain
curve.
Figure 2: Stress-strain diagram of steel
3
Engineering stress-strain diagram: In an engineering stress-strain curve, original area of the
specimen and original gauge length are used for the calculation of engineering stresses and
engineering strain, respectively. Whereas, in true stress- true strain diagram, stresses and strains
are calculated based on actual cross-sectional area and actual gauge length. The relationship
between true stress and engineering stress, as well as true strain and engineering strain, are
provided in equations (1) & (2) below.
𝜎𝑇 = 𝜎𝑒 (1+εe) ……..(1)
εT = ln (1+ εe) ……..(2)
where, σe is the engineering stress, σT is the true stress, εe is the engineering strain and εT is
true strain.
Procedure: 1) Collect the UTM test specimen and measure the gauge length and the cross-sectional area
of the dog-bone specimen
2) Mount the specimen in the bottom pin holder/gripper first and then add the upper pin
holder/gripper by slowly adjusting the upper grip or pin holder down by keeping the knob in
the “manual” position. Once the specimen is mounted, turn the knob to the “auto” position.
3) Open the UTM software in the computer and give all the initial data as per specimen
material, dimensions, geometry, type of loading, speed of testing etc.
4) It is essential to conduct the test at slow speeds of pulling for most tests unless we are
studying the effect of strain rate.
5) Before beginning the tension test set the displacement and load to zero by using the “tare”
function and reset the displacement function.
6) Then click on start test and observe the test specimen as it is pulled by the upper grip/holder
system while the lower/holder system stays stationary.
7) Also observe the load-displacement graph being dynamically built and updated on the
computer screen. Even if the scales for the horizontal axis (displacement) and vertical axis
(load) scales are approximately set in the input data, the software automatically rescales them
as per the maximum values achieved for each of them by the end of the test.
8) Once the test is finished, the specimen would have necked and fractured down in to two
pieces roughly midway the gauge length, the upper gripper/holder assembly automatically
stops moving and the final load-displacement with data is shown on the computer screen.
9) Remove the two pieces of specimen join them together carefully to measure the final
distance between the gauge points.
10) Enter that data into the software to obtain the percentage elongation. Note that the value of
the Young’s modulus cannot be ascertained in a load-displacement graph. For it, we need a
stress-strain diagram.
4
11) Plot the respective graphs:
a. Load vs. Displacement
b. Engineering Stress vs. Engineering Strain
c. True Stress vs. True Strain
12) For calculation of strain hardening coefficient plot the graph of ln of true stress & ln of true
strain and take the slope of it.
Observation table: Specimen:
Al
Gauge
length
(mm)
Crosssectional
Area
(mm2)
Elastic
Modulus
(MPa)
Ductility
(%)
Yield
Strength
(MPa)
1
2
3
Results: Inferences: -
5
UTS
(MPa)
Toughness
(J/m3)
Resilience
(J/m3)
Strain
hardening
exponent
(n)
Experiment 2: Deflection of Beams
Aim: - To find the deflection of a simply supported beam and a cantilever beam.
Apparatus: 1. Deflection measuring device
2. Dial Gauges
Figure 1: Experimental setup for measuring the deflection of beams.
Description: - The purpose of deflection of beams is to analyse the nonlinear behaviour of
deformable bodies, such as beams, plates and shells, when the relationship between the external
strains and shear strains, on the one hand, and the displacement, on the other, is taken to be
nonlinear, resulting in nonlinear strain-displacement relations. As a consequence of this fact,
the differential equations governing this system will turn out to be nonlinear. The relationship
between curvatures and displacements is assumed to be linear, the experiment will allow
exploring the deflections of a loaded simply supported and cantilever beam to observe in a
simple way the nonlinear behaviour of the beam. The line diagrams of the simply supported
and cantilever beam with deflection are shown in figure 2.
Cantilever beam subjected to
point load at the end.
6
Simply supported beam subjected
to point load at the centre.
Figure 2: Line diagrams of simple supported and cantilever beams
Deflection of simply supported beam = WL3/48EI
Deflection of cantilever beam = WL3/3EI
Moment of Inertia, I = bh3/12
where W is the load in N, L is the length in mm, E is the Elastic modulus in GPa
Procedure: 1) Position the deflection indicator and set it to zero
2) Mount the beam on the panel in the form of a simply supported/cantilever method
3) Fix the load pan and apply load step by step
4) Measure the deflection and tabulated in the observations.
Observations: Material: Steel
S. No.
Load (N)
Theoretical
deflection (mm)
Experimental
deflection (mm)
Load (N)
Theoretical
deflection (mm)
Experimental
deflection (mm)
Load (N)
Theoretical
deflection (mm)
Experimental
deflection (mm)
Material: Al
S. No.
Material: Composite
S. No.
Results: Inference: 7
Experiment 3: Impact Toughness
Aim: - To determine the energy absorbed by mild steel due to impact testing.
Apparatus: (i)
(ii)
Izod and Charpy Impact tester
Drop weight impact tester
Introduction to Izod & Charpy Test: - Impact testing is a method of determining the impact
resistance of materials. Impact tests are used in studying the toughness of material when
exposed to high strain rates. In these tests, a pivoting arm is raised to a specific height and then
released. The arm swings down hitting a notched sample, breaking the specimen. The energy
absorbed by the sample is calculated from the height the arm swings to after hitting the sample.
A notched sample is generally used to determine impact energy. The Izod impact test differs
from the Charpy impact test in that the sample is held in a cantilevered beam configuration as
opposed to a three-point bending configuration. Some of the differences between the two
impact tests are as follows:
SI. No.
1
2
3
4
5
Feature
Initial
angle
of
striker
Striker shape
Distance
b/w
supports
Specimen mounting
configuration
Charpy Method
142ᵒ
Izod Method
90ᵒ
Bar
40.2 mm
Wedge
Simply
supported
beam, notch facing
opposite side to the
striker
Specimen Shape and 55 mm length, 40
size
mm overhang, 10
mm * 10 mm square
cross-section prism,
5 mm deep and 2 mm
wide U- notch, 45ᵒ V
notch in the middle
of the specimen.
A cantilever beam,
notch facing on the
side exposed to the
striker
75 mm length, 28
mm overhang in
vertical
cantilever
position, 10 mm* 10
mm square crosssection prism, 2mm
deep, 45ᵒ V-notch at
28mm from top of
the specimen
In the Charpy specimen, the presence of a notch produces a triaxial state of stress. The relative
values of the three principal stresses depend strongly on the dimension of the bar and the
geometry of the notch. The amount of energy absorbed by the specimen till fracture is treated
as equal to the toughness of the material of the specimen. The energy absorbed by the notched
specimen before fracture can be obtained directly from the dial.
8
Experimental procedure: 1. Prepare the specimen as per the requirements and place it in the appropriate configuration.
2. Raise the pendulum- hammer assembly and latch it at an appropriate angle depending on
the type of test, for Charpy (142ᵒ) and Izod (90ᵒ).
3. For the Charpy test, place the specimen in such a way that notch is opposite to the direction
of the impact of the pendulum.
4. Release the lever of the latch such that the pendulum is released and performs its swing.
5. After impacting apply the pendulum brake using the pedal brake handle.
Observations: Material: Steel (Notched specimen)
S. No.
Izod/Charpy
Weight
of
the Impact Energy (J)
pendulum and striker
assembly (N)
Introduction to drop weight impact test: - Drop weight impact tests are also used to measure
the impact energy by determining the materials resistance to fracture due to a sudden external
force. In this test the impact load is applied by dropping a weighted striker towards the
specimen or part. The striker used is an instrumented striker and hence it is possible to
determine the load at which penetration occur. The photograph of the instrument is provided
below.
Figure 1: Photograph of the drop weight impact tester
9
Procedure: 1.
2.
3.
4.
5.
6.
7.
First a sample of 60 mm x 60 mm x 2 mm of aluminium is placed in between the clamping
plates. Press the ‘on clamp’ button to fix the plate between the clamps.
On the display screen, set the striker's height. The system will estimate the energy that
the striker will acquire and the velocity that the striker will reach. Close the door.
Press the ‘Destn’ button. It will take the striker to the set height chosen in the step 2.
Press ‘Ready’ and followed by the ‘impact’ button. The striker will be released from the
set position and hits the specimen.
After the test ‘Grasp Hammer’ button is pressed striker holder will come and grasp the
striker.
Moving the striker up, press ‘release clamp’ button.
Take out the sample and observe the failure.
Results: Inferences:-
10
Experiment 4(a): Torsion Test
Aim: - To find the modulus of rigidity and maximum torsional shear stress
Apparatus: - A torsion test apparatus
Specimen: - Mild steel
Figure 1 Experimental setup for torsion studies
Description: - A torsion test instrument is used in determining the value of the modulus of
rigidity (G) of a metallic specimen. In the torsion test twisting torque is applied on the circular
cross-section specimen from zero to maximum till fracture. Further, the modulus of rigidity
and maximum torsional shear stress is determined using the following equations.
G=
τ=
32 𝐿 𝑇
𝜋𝐷4 𝜃
16 𝑇𝑚𝑎𝑥
𝜋𝐷3
…………(1)
……………(2)
where, G = Modulus of rigidity, (GPa)
T = Torque applied, (Nm)
L = Gauge length, (mm)
D = Diameter at gauge length, (mm)
θ = Angle of twist, (radians)
𝜏 = Maximum torsional shear stress, (MPa)
Procedure: a) Measure the diameter and length of the specimen at gauge length
b) Fix the specimen in between two jaws of the equipment
c) Enter the inputs of the specimen and tare the load and displacement (angle) in software to
zero.
11
d) Start the motor to twist the specimen, note down the ultimate torque and the angle of twist.
e) Substitute the values in the formula and calculate the modulus of rigidity and maximum
torsional shear stress for the given material.
f) While determining the modulus of rigidity consider the elastic part of the curve.
Observations: S. No. Torque
applied (Nm)
1.
2.
3.
Angle of twist Modulus
(radians)
(GPa)
Results: Inference: -
12
of
Rigidity Maximum torsional
shear stress (MPa)
Experiment 4(b): Spring Test
Aim: - Determine the stiffness of the spring for both series and parallel connections.
Apparatus: Spring testing apparatus.
i)
ii)
iii)
iv)
A spring
Vernier calliper,
Scale
Micrometer.
Theory: Springs are elastic members which distort under load and regain their original shape when the
load is removed. They are used in railway carriages, motor cars, scooters, motorcycles,
rickshaws, governors etc. The functions of springs are:
1) To absorb shock or impact loading as in carriage springs.
2) To store energy as in clock springs.
3) To apply forces and control motions as in brakes and clutches.
4) To measure forces as in spring balances.
5) 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 and brass. 18/8 stainless steel and Monel and other metal alloys are
used for corrosion resistance springs. Several types of springs are available for different
applications. Springs may be classified as helical springs, leaf springs and flat springs
depending upon their shape. In several cases, it is essential to idealize complex structural
systems by suitable springs. The stiffness of the spring is defined as per the following equation
Stiffness (k) = Load / Deflection
Procedure: 1) Measure the diameter of the wire of the spring by using the micrometer.
2) Measure the diameter of spring coils by using the Vernier calliper
3) Count the number of turns.
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.
5) Increase the load and take the corresponding axial deflection readings.
6) Plot a curve between load and deflection.
13
Observation: Diameter of the spring wire, d
=……… mm (Mean of three readings)
Diameter of the spring coil, D
= ………mm (Mean of three readings)
Mean coil diameter, Dm
= D – d =……… mm
Number of turns, n
=………
𝟏
𝟏
𝟏
For Series, 𝒌𝐞𝐪 = 𝒌𝟏 + 𝒌𝟐
S.No.
Load W (N)
Deflection 𝛿 (mm)
Stiffness k
Load W (N)
Deflection 𝛿 (mm)
Stiffness k
Mean k (Series) = ……
For Parallel, keq = k1 + k2
S.No.
Mean k (Parallel) = ……
Result: - The value of spring constant k is found to be
1. For Series _________ N/ mm.
2. For Parallel _________ N/ mm.
Inferences: -
14
Experiment 5: Hardness Testing
PART A- Micro-Vickers Hardness Test
Aim: - To determine the Vickers Hardness Number (HV) of the given specimen.
Equipment: - Micro-Vickers hardness tester (Mitutoyo)
Specimen: - Mild Steel
Figure 1: Photograph of the Vickers Hardness Testing Machine
Introduction: - In Vickers hardness testing a diamond indenter with square pyramidal
geometry is used to test the hardness of the material. This can measure a wide range of materials
and has a maximum loading capacity of 1 kgf. The unit of hardness obtained from this test is
Vickers Hardness Number (HV). The full load is normally applied for 10 to 15 seconds which
leaves the indentation behind as shown in the figure. The produced impression is projected
onto a focusing screen and the diagonals of the impression are measured by means of the
measuring equipment. The Vickers hardness of the specimen is measured as per the following
equation.
HV = 1.854 F/d2 …….(1)
F= Load in kgf
d = Arithmetic mean of the two diagonals, d1 and d2 in mm
HV = Vickers Hardness Number
15
Figure 2: Vickers hardness measurement scheme
Procedure: 1) Clean the surface of the specimen to be tested to remove dirt and oil, if any. Polish the test
spot, which is flat, by Emery sheet. The top and bottom surfaces of the specimen should be
parallel to each other.
2) Place the standard specimen on the test table and turn the main nut (hand wheel) in the
clockwise direction until a sharp display of the surface of the specimen is obtained on the
focusing screen of the measuring device.
3) Calibrate the scale by aligning the measuring bars in one line before applying load and
clicking on the zero setting.
4) Select the load from the main menu and allow the load to be applied for 10 secs, and then
press Run.
5) Once the load is released, measure the diagonal of the square indentation using the scale
with micrometre present on the screen itself once in horizontal and other in the vertical
direction by tilting the gauge.
6) Determine the Vickers hardness number (HV) using equation 1.
Observations: S. No. Specimen
Material
Length of the diagonal (μm)
Vickers
D1 (μm)
D2 (μm)
Average D Number
(μm)
1.
2.
3.
16
Hardness
PART B- Brinell Hardness Test
Aim: - To determine the Brinell hardness number of the given Specimen using Brinell hardness
tester.
Introduction: - In Brinell Hardness testing an indenter with a spherical ball geometry having
a diameter of 10 mm is used. The indenter material is hardened steel and hence materials harder
than steel cannot be tested by the Brinell hardness tester. Brinell hardness number (BHN) is
obtained by the ratio of the calculated load and the spherical area of the indentation or
impression made on the specimen by the corresponding Indenter Ball.
Figure 2. Brinell hardness measurement scheme
Procedure: 1. Keep the loading and unloading lever at position “A” which is the unloading position.
2. Place the specimen on the testing table anvil.
3. An adjusting wheel on the indenter column enables the ball holder to be brought in contact
with the specimen.
4. Load, P (3000 kgf) is applied by means of a simple lever mounted on the knife edges
5. Turn the lever from the unload position to the load position, so that load is applied to the
specimen.
6. Till the dial gauge reaches a steady position, the load is applied continuously (10-15 sec).
7. Release the load by bringing the lever to the unload position and weights are lowered and
the indicator comes to rest.
8. Measure the diameter of the indentation (d) using a stereomicroscope.
9. Determine the Brinell Hardness Number (BHN) as per the equation mentioned below.
BHN =
2𝑃
𝜋 𝐷 √𝐷−(𝐷2 −𝑑2 )
………….(2)
Where, P is the load applied in kgf, D is the diameter of the spherical ball in mm, d is the
diameter of the indentation in mm,
17
Observations: S. No. Specimen
Material
Diameter of indent (mm)
Brinell
Hardness
D1 (mm)
D2 (mm)
Average D Number (BHN)
(mm)
1.
2.
3.
Results: Inferences: -
18
Experiment 6: Jominy End Quench Test
Aim:- To determine the hardenability of steels.
Apparatus: High-temperature furnace
End-quenching set-up
Rockwell hardness tester
Specimen: - High Carbon Steel
Introduction: (a) Jominy end quench test: -The Jominy end quench test is used to measure the hardenability
of steel, which is a measure of the capacity of the steel to harden in depth under a given set of
conditions. Knowledge about the hardenability of steel is necessary to be able to select the
appropriate combination of alloy steel and heat treatment to manufacture components of
different sizes to minimize thermal stresses and distortion. In the Jominy test, a standard
specimen is heated then water quenched from one end of the specimen, later a series of
Rockwell hardness tests are performed along the length of the specimen. It is the influence of
the steel’s chemical makeup (Carbon and Alloying elements) that determines how deeply a
grade of steel will transform to martensite for a particular quenching treatment. This means
that for each grade being heat treated, mechanical properties are a result of the cooling rate
(quench). Martensite is formed in carbon steels by the rapid cooling (quenching) of the
austenite form of iron at such a high rate that carbon atoms do not have time to diffuse out of
the crystal structure in large enough quantities to form cementite (Fe3C). Austenite is a solid
solution of carbon in gamma iron. It is stable above 727oC and below 1493℃. The structure
of the steel transforms from body centred cubic (bcc) to face centred cubic (fcc) above 727℃.
Figure 1. Illustration of the setup of the Jominy end quench set up showing the hard end
(quenched part) and softer end (unquenched part) of the sample.
(b) Rockwell hardness test: - Principle: A standard load (Based on type of material) is applied
through a standard indenter (cone or ball indenter) for a standard duration of time. The hardness
number is directly obtained from the instrument.
19
Practical importance: Hardness is the property of the material by which it offers resistance to
scratch or indentation. It is the most important property, as the material is subjected to friction
and scratch. By this experiment, we can determine the Hardness of the given material. The
hardness of a material is generally defined as resistance to permanent indentation under static
and dynamic loads. When a material is required to use under direct static or dynamic loads,
only the indentation hardness test will be useful to find out resistance to indentation. This test
is an indentation test used for smaller specimens and harder materials. In this test indenter is
forced into the surface of a test piece in two operations, measuring the permanent increase in
depth of an indentation from the depth increased from the depth reached under a datum 24 load
due to an additional load. Measurement of indentation is made after removing the additional
load. The indenter used is the cone having an angle of 120 degrees made of black diamond.
Procedure:  The specimen is a cylindrical bar with a 25-mm diameter and 100 mm length.
 The specimen is placed in the furnace at 750℃ for 1 hour.
 After the sample has reached sufficient temperature, it is removed from the furnace and
placed directly into the quenching setup.
 The water flow, in the setup used for quenching, is adjusted so that the water column is
approximately the distance 50 mm above the end of the pipe when water is flowing freely.
 A jet of water is quickly splashed at one end of the specimen.
 After the entire sample has cooled to room temperature, the scale oxidation is removed.
 For comparative purposes, one more specimen is heated to 750 ℃ but it is cooled in the air
after taking out from the furnace.
 Hardness measurements are then made every 5mm for both cases and these readings are
recorded.
 The hardness data point is plotted vs. the distance from the quench.
Observations: Rockwell hardness scale used: S. No. Distance from one end of the Rockwell Hardness (HRC)
quenched specimen
1.
2.
3.
4.
5.
Inferences: -
20
Experiment 7: Optical Microscopy
Aims: Get acquainted with the functioning of an optical microscope.
Observe and interpret the microstructure of the steel.
Determine the ASTM grain size number.
Equipment: 1. Optical microscope
2. Double disc polishing machine and SiC emery papers
Specimen: -Mild steel
Etching reagent: - Methanol (98%) + Nitric acid (2%)
Figure 1: Photograph of the Optical Micrscope (Max. magnification: 500 X)
Metallography: - Metallography is the study of the structure of materials using optical and
electron microscopes. Mild steel at room temperature has a microstructure consisting of ferrite
(α) and pearlite (P). A representative optical microstructure of mild steel is shown in figure 1.
Figure 2: A representative micrograph of mild steel showing the ferritic and pearlitic regions
Following is the sequence of operations that need to be performed to reveal the microstructure
of the steel.
21
1) Selection of specimen: The specimens for the microstructure study are mounted using a
either cold or hot mounting process.
2) Obtaining a flat surface of specimen: It is first necessary to obtain a reasonably flat surface
on the specimen. This is achieved by using a fairly coarse file or machining or grinding.
3) Intermediate and Fine Grinding: Intermediate and fine grinding are carried out using emery
papers of progressively finer grades.
4) Fine Polishing: The polishing compound used is alumina (Al2O3) powder placed on a clothcovered rotating wheel. Distilled water is used as a lubricant. Fine polishing removes fine
scratches and very thin distorted layers remaining from the rough polishing stage.
5) Final Polishing: A very small quantity of diamond paste is oil-soluble is placed on the nylon
cloth-covered surface of a rotating polishing wheel. The specimen is pressed against the cloth
of the rotating wheel with considerable pressure and is moved around the wheel in the direction
opposite to the rotation of the wheel to ensure a more uniform action.
6) Etching: Necessity- The purpose of etching is to make visible the many structural
characteristics of the metal and alloy. The main purpose of etching is to clearly differentiate
the various parts of the microstructure (e.g. Grains, Grain Boundaries etc). This step is achieved
by using the appropriate reagents (Nital for steel) which will react chemically with the surface
of the material and disclose the grains when seen using the microscope.
Grain size measurement: 1. Determine the magnification: To determine the magnification first we capture the
microstructure of the specimen using a metallurgical microscope. Now we take the print of the
microstructure and measure either the width or height of the picture.
Magnification (M) = print width / real width
Real width can be found from the microscope.
Number of grains = Whole Grains + 0.5 (Partial Grains). True area = print height x print width
/M
2. Find the ASTM grain size number N = 2(n-1) N- no. of grains per square inch area at 100X
magnifications, n- ASTM Grain size number, M- Magnification number. After few calculations
we can find the grain size number for our ‘M”.
3. Calculate the average grain size diameter
Average Grain Diameter = Total true length / no. of grains intercepted
Total true length = Total length of the lines / M
A number of grains intercepted refer to the grains intercepting between two vertical lines.
Observations: -
22
The ASTM grain size of the specimen is: _________________
The average grain size diameter of the specimen is: ______________
Inferences: -
23
Experiment 8: Fatigue Test
Aim: - To determine the fatigue life of a non-ferrous material subjected to a rotating bending
test.
Equipment: - Fatigue testing equipment
Specimen: - Aluminium
Figure 1. Rotating bending testing equipment
Introduction: - Fatigue failure because of the cyclic loading conditions and is the most
common type of failure in structural applications. Rotating Fatigue Machine (SM 1090) has
two main parts: the main unit and a separate control and instrumentation unit (Figure 1). The
main unit has a motor unit that rotates a specimen under constant load (stress). The motor turns
a coupling and a short driveshaft. The driveshaft turns a collet chuck that grips the ‘driven end’
of the test specimen with uniform pressure around its circumference. At the ‘loading end’ of
the specimen an adjustable dead weight applies a vertical (downwards) load on the specimen.
It does this through a self-aligning bearing inside the gimble. The gimble is important as it
allows movement but also ensures vertical loading even when the specimen deflects. The
driving end and the loading end make the specimen an axially rotating cantilever with a point
load near its end.
A sensor counts the rotations (cycles) of the specimen and a load cell measures the force that
you apply to the specimen (determined by the dead weight position). A separate control box
contains an electronic motor drive and a display that shows the load speed of rotations (cycle
rate) and the number of rotations (cycle count) since the start of the test. A socket on the control
box allows you to connect the fatigue Testing Machine to VDAS for automatic data acquisition.
A transparent safety guard protects the user in case small parts of the specimen fly off when it
fractures. An interlock switch disconnects the motor power if the guards are not lifted.
When the specimen breaks, a switch at the loading end switches off the motor power and the
display stops counting so you know how many cycles the specimen has done up to the point of
failure.
24
Procedure: 1) Load the aluminium specimen to the machine.
2) Adjust the dead weight to the furthest right-hand position on the load arm to give the
maximum allowable stress level.
3) Start and run the motor.
4) Note the cycle count when the specimen breaks.
5) Repeat the test for at least four more stress amplitude levels, moving the dead weight to the
left by the five notches for each stress amplitude.
6) Plot the graph for stress amplitude (MPa) vs. no of cycles to get the S-N curve for the
aluminium material
Observations: S.No
Load (N)
Frequency (Hz)
Stress
(MPa)
1
2
3
4
5
6
7
8
Inferences: -
25
Amplitude Number
cycles
failure
of
to
Demonstration 1: X-ray Diffraction
Aims: Demonstrate the method of evaluating the crystal structure of a metallic specimen using X-ray
diffraction.
Determine the crystal structure of an unknown metallic sample and its lattice parameters using
the X-ray diffraction technique.
Equipment: - X-ray diffractometer (Rigaku)
X-ray Source: - Cu Kα
Figure 1: X-ray diffratometer
Introduction: - X-ray diffraction can be used to determine the crystal structure of materials
and lattice parameters. It works on the principle of Bragg’s law. As per Braggs’ law, when a
crystal is bombarded with X-rays of a fixed wavelength (similar to the spacing of the atomicscale crystal lattice planes) and at certain incident angles, intense reflected X-rays are produced
when the wavelengths of the scattered X-rays interfere constructively. In order for the waves
to interfere constructively, the differences in the travel path must be equal to integer multiples
of the wavelength. When this constructive interference occurs, a diffracted beam of X-rays will
leave the crystal at an angle equal to that of the incident beam. A representative XRD plot of a
crystalline material is figure 2.
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Figure 2. XRD plot of a crystalline material
The general relationship between the wavelength of the incident X-rays, angle of incidence and
spacing between the crystal lattice planes of atoms is given in equation 1.
nλ = 2dhkl Sinθ
………………(1)
where, n is the order of diffraction (take n =1), d is the interplanar spacing between (h k l)
planes, λ is the wavelength of X-rays (0.154 nm) and θ is the angle of incidence. For pure
metals having cubic crystal structure the relationship between interplanar spacing and lattice
parameter ‘a’ is given by
dhkl =
a
√ℎ2 +𝑘 2 +𝑙 2
…………..(2)
Combining equations (1) and (2) it is possible to determine the crystal structure and lattice
parameters of a cubic crystal as per the following equation.
𝜆2
4𝑎2
=
𝑆𝑖𝑛2 𝜃
ℎ2 +𝑘 2 +𝑙 2
… … … … … … (3)
Procedure: Peaks
2θ
Sinθ
Sin2θ
Normalize
Sin2θ/ Sin2θ1
#1
#2
#3
#4
#5
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Convert to integers
(hkl)
1. Construct a table similar to that shown above.
2. From the (hkl) determine the crystal structure using the selection rules for reflection in
cubic crystal.
Simple cubic
All planes will reflect
Body centred cubic
Only planes with h+k+l is even will
reflect
Face centred cubic
Those planes where h,k,l are either all
odd or even will reflect.
3. Determine the lattice parameter using equation 3.
4. Using the relation between the lattice parameter and atomic radius, determine the
atomic radius of the atom.
5. Identify the material having the corresponding atomic radius.
Results: Inferences: -
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Demonstration 2: Electron Microscopy
Aims: 

Demonstrate the working of field emission scanning electron microscope (FE-SEM).
Conduct a fractography study and determine the type of failure.
Equipment: - Field Emission Scanning Electron Microscopy , FEI (Apreo LoVac)
Electron Source: - Tungsten filament with a pointed sharp tip for field emission
Figure 1. Photograph of SEM
Introduction: - Electron microscopes are powerful techniques for the characterization of a
wide range of materials. Electron microscopes can capture far higher resolution images than
the light microscopes, providing information that would otherwise be very difficult to obtain.
Their versatility and extremely high spatial resolution render them a very valuable tool for
many applications. The two main types of electron microscopes are the transmission electron
microscope (TEM) and the scanning electron microscope (SEM). Figure 2 shows the major
differences between these imaging techniques.
Main difference: The main difference between SEM and TEM is that SEM creates an image
by detecting reflected or scattered or knocked-off electrons, while TEM uses transmitted
electrons (electrons that are passing through the sample) to create an image. As a result,
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TEM offers valuable information on the inner structure of the sample, such as crystal structure,
morphology and stress state information, while SEM provides information on the sample’s
surface and its composition. SEM can magnify images up to 2 million times and it provides
insight into the topography and elemental composition of a sample. While TEMs have an
incredible magnification capability of 10-50 million times and able to provide details at the
atomic level, which is the highest resolution of any electron microscope. TEM samples are
usually very thin <150 nm, facilitating the travel of electrons through the specimen, producing
an image that details its morphology, composition, and crystal structure etc.
Fractography examination: The specimens tested under tensile test in the UTM machine will
have three types of fracture morphology (surface features) as shown in Figure 3, based on the
material’s fracture behaviour. It can be either very ductile (i.e. gold, copper), moderately
ductile (i.e. Steel) and brittle (i.e. cast iron, high carbon steel, ceramics). The objective of this
demonstration is to examine the fractured surfaces of the specimens tested in UTM machine
under tensile loading. This involves identifying the presence of dimples or cleaved morphology
in the fractographs. The presence of dimples indicates the fracture is ductile and cleavage or
faceted morphology indicates the fracture is brittle (Figure 4).
Figure 2. Schematic showing the difference between optical microscopy (OM), SEM and TEM.
(Source: microbiologyinfo.com).
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Operating Procedure:
1.
2.
3.
4.
5.
6.
7.
8.
Vent the sample exchange chamber of SEM
Open the chamber door and place your sample in the sample holder
Push the holder inside and close the chamber door
Switch on the vacuum pump to create 10-2 Pa vacuum in the chamber (If air is there, it
would disturb the electrons and simply ionize the air. The electrons will not hit the
target sample.)
Switch on the electron gun and apply the voltage
Now, in the screen, you will be able to see the images of your samples
Brightness/contrast adjustment, beam adjustment and other adjustments will be done to
optimize the imaging conditions
Note: For conductive samples (i.e. Metals), we don’t have to coat the samples. For nonconductive samples (i.e. polymers, ceramics, tissues), gold or platinum coating is
necessary for electronic conduction.
Figure 3 Schematic showing the different types of fractures.
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Figure 4: Representative SEM micrographs showing the ductile and brittle fracture in metals.
Inferences:-
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Demonstration 3: Non-Destructive Testing
Aims: - To determine the crack in the material by using an ultrasonic flaw detector
Equipment: - Ultrasonic flaw detector
Introduction: - Ultrasonic-testing is one of the non-destructive testing techniques that is
widely being used for testing the presence of inclusions, porosity and other discontinuities in
the material. It can also be used for thickness gauging of materials, requiring access from only
one side of the test piece. High-frequency sound (ultrasonic sound) waves are introduced into
the test material/part from a transducer/probe that is usually coupled to the test piece by water
or other suitable coupling liquid. The transducer converts electric signals to ultrasound and vice
versa. A short burst of ultrasound of frequency close to MHz range is introduced into the test
material so that some or all of the energy is reflected by the discontinuities. The reflection of
the ultrasound energy is a function of the ratio between the acoustic impedance of the
discontinuity and the base material. The greater the impedance ratio the more sound energy
will be reflected. The principle of ultrasonic testing is shown in fig. 1. This principle utilizes
the precise timing of the transit time of a short burst of ultrasound energy, through a material
under test. The ultrasound waves travel to the far side of the test piece and reflect back to the
transducer/probe and measurement is obtained.
Figure 1. Ultrasonic flaw detector principle.
Basically different type of transducers/probes are available for different types of applications:
1. Straight beam Probe: This probe introduces ultrasound normal to the test piece
surface utilizing longitudinal or compression waves. Normal beam probe is used mostly
for flaw detection and thickness gauging (refer figure 1.)
2. Transmitter-Receiver probe:
This probe contains separate transmitting and receiving elements as showing in figure
2 usually mounted
on delay lines. This design improves near surface resolution
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by separating the initial pulse from the received echoes. TR probe is suitable for the
thickness gauging of pitting and corrosion and also for a better surface resolution.
Procedure: 1. Clean the surface of the specimen to be tested and apply couplant.
2. Press the transducers gently onto the material surfaces, and hold for a while to allow readings
to be taken, wait until a consistent reading appears on the display screen of the instrument.
3. Record the stable reading, which is the time (T) in microseconds (μs) for the ultrasonic pulse
to travel the path length and pulse velocity (V) in m/s.
4. Special attention should be paid on the location where possible cracks exist.
5. A discontinuity like a crack produces a peak on the screen.
6. Attention should also be given to the movement of the possible peak caused by the cracks
on the specimen.
S. No
Distance (mm)
Time (µs)
Pulse Velocity (m/s)
Crack width (mm)
if any
1
2
3
4
5
6
7
8
9
10
Advantages
Low cost, Fast test, simple and well established, No damage to the material.
Inferences: -
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Demonstration 4: Shape Memory Alloys
Aim: - To demonstrate the shape memory effect of Nitinol alloy.
Apparatus: - Furnace, mould to train the material.
Material: - Nitinol (50% Ni -50% Ti alloy)
Theory: Smart materials can significantly alter one or more of their inherent properties owing
to the application of external stimuli in a controlled fashion. Smart materials are sensitive to
stress, temperature, moisture, pH, and electric and magnetic fields. Shape memory alloys come
under the category of smart materials. Shape memory alloy is an alloy which can revert to its
original shape & size up to a specific deformation range if any external source of excitation
medium is provided by undergoing phase transformations. The principle of the shape memory
effect is given in figure 1 below. Initially, the material is in the martensitic phase at room
temperature. Then the material has to be trained for the shape memory effect. At this stage, the
material is deformed in the desired shape and is trained at austenitic transformation
temperature. The austenite phase transforms into a martensitic phase at the sudden quenching
in the water and will remain in the trained shape. The most commonly used shape memory
alloy is Nitinol with a near equiatomic composition of Ni and Ti.
Figure 1 Principle of shape memory effect
Procedure:
1.
2.
3.
4.
5.
Prepare the mould of the desired shape for which the material has to be trained.
Fix the Nitinol wire in the mould and keep the assembly in the furnace at 525 °C for 15
min (Austenitic transformation).
Quench the assembly into the water (Martensitic transformation). The material is
trained into the desired shape.
Deform the shape and put it into hot water at ~ 80 °C.
The material will regain its trained shape.
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Figure 2 Shape Memory Effect
Applications: - Actuators with potential applications in aircraft and space vehicles,
bioengineering such as dental braces, stents to help open clogged arteries and veins, flexible
spectacle frames, bridge structures to dampen vibrations, decreasing aeroplane noise by
changing the size of exhaust nozzles etc.
Inferences: -
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Mini Project
Aim: - To develop an overall understanding of the various concepts discussed in the course by
doing a group activity.
Project characteristics: 





The project is a group activity (max 10 students in a team) and it should address the
concepts discussed in the Solid Mechanics or Materials Science and Engineering
courses. It is highly recommended to choose a topic that addresses both the courses
simultaneously. We welcome project themes related to your external student activities
also.
Given the time constraints the project must be simple and implementable.
The project theme should be limited to the experimental facilities and materials
available in the Materials Testing Lab. We could offer you support from Workshop as
well. However, we strongly advise that the teams begin the experimental work as soon
as the project topic is fixed.
The projects may usually sound easy on paper but may be extremely hard to implement
in practice. So be aware of that to avoid difficulties later.
The project involving the analytical and computational part in addition to the
experimental part is also promoted.
The teams and the project topics have to be decided by 30th September and the team is
expected to give a final presentation of the project (demonstration/ppt) before the
comprehensive exam. The weightage for the project will be 10 marks.
Examples: 1. Mechanical properties of fibre-reinforced plastics.
2. Ductile to a brittle transition temperature of metals.
3. Testing of 3D printed materials
4. Smart material behaviour
5. Metamaterials as acoustic dampers
6. Energy absorption of foams
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