Various Material testing techniques for basic mechanical and materials analysis- Rishal Kashyap

1. MATERIALS TESTING

2. Presented by-
 Rishal Kashyap

3. Contents -
 TensileTest.
 CompressionTest.
 BendTest.
 HardnessTest.
 TorsionTest.

4. Why are metals tested ?
 Ensure quality
 Test properties
 Prevent failure in use
 Make informed choices in using materials
Factor of Safety is the ratio comparing the
actual stress on a material and the safe
useable stress.

5. Two forms of testing
 Mechanical tests – the material may be
physically tested to destruction.Will normally
specify a value for properties such as
strength, hardness, toughness,etc
 Non-destructive tests (NDT) – samples or
finished articles are tested before being used.

6. Tensile Test
The following MATERIAL PROPERTIES can be
evaluated / determined by TENSILE TESTING:
 STRENGTH.
 DUCTILITY.
 ELASTICITY.
 STIFFNESS.

7. Tensile Test
In this Test, we simply apply Tension to a
Specimen in a Controlled manner till the
specimen attains failure.

8. Tensile Test
specimen
machine
8

9. Extensometer

10. Equipment Used
 Universal Testing Machine.
 Extensometer.
 Data Acquisition Unit.

11. Tensile Tester Data Acquisition Unit

13. This device, called an
EXTENSOMETER,
measures the distance
between the two prongs
very precisely while the
test is in progress.

14. So what happens to the Specimen during the
Test ?
Lets see ……..

15. 15
Elastic Deformation
F

bonds
stretch
return to
initial
1. Initial 2. Small load 3. Unload
Elastic means reversible.

16. 16
Plastic Deformation (Metals)
1. Initial 2. Small load 3. Unload
Plastic means permanent.
F

linear
elastic
linear
elastic
plastic

17. PLASTIC DEFORMATION REGION
ELASTIC DEFORMATION REGION

18. 18

19. Till what point do we have to continue
to test the specimen ???
Obviously , Till it gets Stressed out
…..;)..

20. “Necking” occurs as
the sample leaves
the elastic
deformation region
and begins to
deform plastically.
i.e. at the Ultimate
Tensile Stress.
Necking

21. The classic cup &
cone shape of a
fairly ductile tensile
fracture is visible
here.

22. •INTRODUCTION
•LENGTHTO DIAMETER RATIO OF
SPECIMEN
•FRACTURES IN COMPRESSIONTEST
•LIMITATIONS OF COMPRESSION TEST
22

23.  Simply, compression testing is the opposite of tensile
testing. Compression results from forces that push
toward each other.
 Compression test is also carried in the same
machine in which the tensile test is carried i.e.
Universal testing machine.
 Generally ,brittle materials are good in compression
as compared to tension and hence they are used for
compressive loads.
 Materials, such as concrete, brick, and some
ceramic products, are more often used in
applications for their compressive loading properties
and are, therefore, tested in compression. 23

24. Universal Testing Machine
24

25.  TEST SPECIMENSCAN BE OF ANY CROSS SECTOIN BUTWE PREFER
CIRCULARCROSS SECTION.
 THE LENGTHTO DIAMETER RATIO SHOULD NOT BE MORETHAN 10
TO AVOID BENDING OF SPECIMEN.
25

26.  BRITTLE MATERIALSCOMMONLY FRACTURE BY SHEAR EITHER
ALONGA DIAGONAL PLANE OR CONE OR PYRAMIDAL WHICH IS
CALLED HOURGLASS FRACTURE.
 THE SHEAR STRESS IS MAXIMUMAT 45 ͦTOTHE LOADAXIS,THE
FRACTURE SHOULDOCCUR IN PLANEAT 45 ͦTOTHE LOADAXIS .
 BUT BECAUSEOF INTERNAL FRICTION NON HOMOGENEITY INTHE
MATERIALAND FRICTIONATTHE ENDSOF SPECIMENTHE PLANE IS
BETWEEN 50 ͦTO 60 ͦ.
26

27.  Top and bottom faces of the specimen on which the load
is to be applied should be perfectly parallel otherwise an
eccentric loading occurs which results in wrong readings.
 Machine of high capacity cannot be used for testing
small samples and machine of lower capacity can not be
used for testing large samples .
 During loading a careful attention is required for
observation of fractures because after fracture if loading
is not stopped the specimen gets crushed.
 Since the length of specimen is kept short to avoid its
buckling it is difficult to obtain strain measurements
accurately.
27

28. A type of hardness test .
Hugh M. Rockwell (1890–1957) and Stanley P. Rockwell
(1886–1940) from Connecticut in the United States co-
invented the "Rockwell hardness tester," a differential-
depth machine.
ROCKWELL HARDNESS TEST

29. Introduction
 This test is probably the most widely
used method of hardness testing .
• It works on the principle of
resistance offered by the metal for
depth of indentation
• In case of Rockwell test we measure
the depth of indentation ( in Brinell
andVickers test we measure the
area of indentation
• The metal is said to be harder when
depth of indentation is less and vice
versa
• It is typically used in engineering
and metallurgy. Its commercial
popularity arises from its speed,
reliability, robustness, resolution
and small area of indentation.
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30. TestInstrument
 Two types of loads are used ,a
Minor load of 10kg and a major
loads of 50,100and 150 kg
 Minor load is used to break
surface film and to hold the
specimen in position
 Major load gives true
indentation on the surface
 Indenters used are also of two
types
1. Hardness steel ball indenters
2. Diamond cone indenter

31. TestProcedure
• After placing the specimen on the
anvil,the anvil is raised up till the
minor load of 10kg is applied,this
will be indicated by a small dial
and pointer situated on a big dial.
• Proper selection of indenter and
major load is done,this major load
is applied gradually and then
released.The hardness number can
be obtained on dial.
• Afterwards by taking the anvil
down a minor load can be released
with the help of handwheel.

32. Advantages
a) It is more flexible than Brinell hardness tester,
because more number of combinations of
indenters and major loads.
b) Highly polished,smooth surface is not required.
c) The test procedure is fast and quick.
d) As the impression is so small the test may be
considered as a non destructive test for certain
applications.
e) Less skilled operator is required.

33. Disadvantages
a) This test is not suitable
for porous bearings or
powder metallurgical
components.
b) Calibration is required
periodically.
c) Proper scale and
indenter should be
chosen otherwise
wrong hardness
number will obtain.

34. BENDTESTING

35. INTRODUCTION
BENDTESTING is also termed as FormabilityTest.
It is used to Determine Ductility Of Material
Types of BendTesting –
 Close bend test:
 Angle bend test:
 Reverse OR 180˚ Bend test:
 Cold BendTest

36. BEND TESTING
During Bending , Due to applied forces
One part of the material is subjected to
COMPRESSION And another part is subjected to
TENSION
IN beam cross section , the axis along which
the bending stresses are ZERO is called as
NEUTRAL AXIS.

37. CLOSE BEND TEST
 InThisType of test, one part of the specimen
is bend over another part and flattened.
If the specimen can bend completely without
failure , it means that it is acceptable BUT it
should not show SPRING BACKACTION .

38. ANGLE TEST
INThis Type ofTEST ,
A former is used which
is having standard
NOSEANGLE and
NOSE RADIUS , As
shown in above figure.
Here also after bending
, that specimen or
component should not
show SPRING BACK.
As this specimen is
bend at certain Angle it
is called as ANGLE
BENDTEST

39. 180˚ BEND
TEST or
REVERSIBLE
BEND TEST.InThis type ofTEST ,
The specimen is bend
on a former which is
having nose angle of
180˚.
 This type of test is
suitable for a
material having high
DUCTILITY
 This test is continued
for a number of times
, Until the crack is
Observed

40. COLD BEND TEST.
In this type of testing ,
The specimen is held at
two points and at the
centre the load is
APPLIED.
The diameter of Punch
which is used for
Application of load is
depends on-
• Thickness of specimen
• Width of Specimen .
• Distance between two
Supporting Points.

41. A torsion test measures the strength of any material against
maximum twisting forces. It is an extremely common test
used in material mechanics to measure how much of a twist
a certain material can withstand before cracking or breaking.
Torsiontest
Torsion-the action of twisting or the state of being twisted .

42. Whytoperformtorsiontest?
 Many products and
components are subjected to
torsion forces during their
operation. Products such as
biomedical catheter tubing,
switches, fasteners, and
automotive steering columns
are just a few devices subject
to such torsion stresses. By
testing these products in
torsion, manufacturers are
able to simulate real life
service conditions, check
product quality, verify
designs, and ensure proper
manufacturing techniques.

43. THEORY
 A shaft fixed at one end and twisted at the other end due to the
action of torque T. The radius of shaft is R and the length is L.
 Imagine a horizontal radial line drawn on the end face. When the
end is twisted, the line rotates through an angle @.
 G is one of the elastic constants of the material. The equation
is only true so long as the material remains elastic.
 Where
 T = Torque applied
 J = Polar moment of inertia of the shaft
 G = Rigidity modulus of the material(Shear Modulus)
 @ = Relative angle of twist in radians
 L = Length of shaft
 The Empirical formula for Shear Modulus
 G=TL/J@

44. Torsion testingequipment
Torsion testing equipment consist of
1)A twisting head with a chuck for gripping the specimen and
for applying the twisting moment to the specimen.
2)A weight head which grips the other end of the specimen
and measures the twisting moment of torque.
Specimen Used
A circular cross section specimen
is normally used since in the elastic
range, shear stress varies linearly
from a value zero at the centre of
the bar to a maximum value at the
Surface.

45. PROCEDURE
 1. Measure the overall length and the
diameter of the specimen .
 2. Draw a line down the length of the
test section of the specimen with a
chalk; this serves as a visual aid to the
degree of twist being put on the
specimen during loading.
 3. Set the maximum load pointer to
zero.
 4. Carry out straining by rotating the
hand wheel in either direction.
 5.Taking note of the torque and the
corresponding angle of twist.
 6. Calculate the value of G by using the
empirical formula.

46. ADVANTAGES
1.Yields shear strength and shear modulus.
2.Compatible with metals and composites.
3. Suitable for use under environmental conditions.
4.Suitable for cyclic/creep testing.

47. DISADVANTAGES
1.Special bonding fixture required
2.Accurate specimen machining required
3.Torsion facility required.
4.Stress concentrations present at end grips.
5.No international and national standards.

48. ANY QUESTIONS ???

49. THANK YOU