1. Unit 2
Mechanical Properties & their Testing
Tensile Test
(tension testing )
is a basic destructive test
of materials science and engineering
in which
a sample is put to a controlled
tension until failure

2. Materials testing
Measurement of the
characteristics and behaviour of substances
as metals, ceramics, or plastics
under various conditions
The data is used to see the
suitability of materials for various applications
—e.g., building or aircraft construction,
machinery, or packaging etc.

3. .

4. Tensile Test

5. .

6. Tensile Test
• A tensile test pulls (or stretches) a sample until it breaks (Destructive Test)
• It measures force
which can be translated to tensile properties
or terms like tensile strength, tensile ‘break point’, elongation,
burst point, yield / fracture stress & strain, etc.
• It measures Elongation
which can be translated to change in length or distance
• Stress (force per unit area) to stretch &
Strain (per cent change in length) or the distance it can be stretched to,
are measured, throughout the test until the sample breaks
Procedure
• A sample is held in between two grips (which are a set distance apart ) –
this is uniaxial tension
• The loading arm (attached to the top grip) moves up at a constant speed
to deform the sample,
first elastically then plastically

7. .
Stress F/A भर (जेर) दाब
Strain tension, to stretch, Resist tense, tighten
ताणणे ओढाताण करणे
Yield commit, resign, surrender
घेऊ देणे ताब्यात देणे
शरण जाणे
Deform विकृ त करणे
विरूप करणे
चे स्िरूप बबघडिणे

8. .
axial normal Stress VS axial normal Strain
curve of materials measured in a tension test

9. True stress–strain curve
& Engineering stress–strain curve

10. Engineering stress and strain
Consider a bar of
original cross sectional area A0
under equal and opposite forces F pulling at the ends
So the bar is under tension
The material experiences a stress
Ratio of the force to the cross sectional area of the bar &
Ratio of axial elongation
Subscript 0 denotes the original dimensions of the sample
SI unit
σ = F / A0 Stress Pa = N/m2
ε = L-L0 /LO = ΔL /LO Strain Unitless

11. Engineering stress and strain
Stress-strain curve for the material
The sample is elongated
The stress variation with strain is recorded
until the sample fractures
Strain - x axis & Stress – y axis
For engineering we
assume the cross-section area of the material does not change
in the deformation process
This is not true
The actual area decreases while deforming,
due to elastic and plastic deformation
The curve based on the original cross-section and gauge length
is called the engineering stress-strain curve
Unless stated, engineering stress-strain is used

12. True stress and strain
The curve based on the
instantaneous (actual) cross-section area & length
is called the true stress-strain curve
Due to the shrinking of the section area
& the ignored effect of
developed elongation to further elongation,
true vs engineering stress and strain are different

13. True stress and strain
• σt = F / A
• εt = ∫δL / L Here the values are instantaneous (actual)
• The true stress and strain can be expressed by engineering stress
and strain
• Equation between true stress and strain,
σt =K (εt)^n
K is the strength coefficient
n is the strain-hardening coefficient &
n shows the material's work hardening behavior
Materials with a higher n have a greater resistance to necking
Metals at room temperature have n ranging from 0.02 to 0.5

14. Types of
stress-strain curves

15. Types of stress-strain curves
Materials are of two categories
• 1 . Ductile materials
structural steel and many alloys of other metals,
yield at normal temperatures
& have linear stress–strain curve up to yield point
• The linear portion of the curve is the elastic region
• Beyond yield point , work hardening commences
• After the yield point, the curve decreases
• As deformation continues,
the stress increases on account of strain hardening until
it reaches the ultimate tensile stress
& the cross-sectional area decreases uniformly
• Then it starts necking & finally fractures
• In ductile materials
the appearance of necking is work-hardening

16. Types of stress-strain curves
• 2 . Brittle materials
which includes cast iron, glass, and stone,
• rupture occurs without any noticeable prior change in
the rate of elongation
• or they fracture before yielding
• Brittle materials do not have a well-defined yield
point, and do not strain-harden.
• Therefore, the ultimate strength and breaking strength
are the same
• Brittle materials like glass do not show any plastic
deformation
but fail while the deformation is elastic
• There will be NO neck formation like in the case of
ductile materials
• Stress–strain curve for a brittle material will be linear

17. Compression Test

18. Compression test
• To determine a material's behavior
under applied crushing loads
• Compressive pressure is applied
to a test specimen
• Specimen is cuboid or cylindrical
• Platens or Fixtures are used
• On Universal testing machine UTM

19. Compression test
Place the test specimen between two plates
Apply a force to the specimen
by moving the crossheads together
During the test
the specimen is compressed &
deformation vs the applied load is recorded

20. Compression Test
The maximum stress a material can sustain
over a period
under a load (constant or progressive)
is determined
Compression testing is done
upto a break (rupture) or to a limit

21. Bend Test

22. .

23. .
• A bending test (bending tensile test)
tests the bending strength
& other important properties
• It is destructive materials test
• Performed on a universal testing machine
• Place specimen on two support anvils
• Bend it by applied force until failure
• Measure its properties
• It is simple & inexpensive
• It is qualitative test
• Used to evaluate ductility & soundness of a
material

24. .
• Bend testing
(flexure testing or transverse beam testing)
measures the behavior of materials under
simple beam loading
• It measures stiffness and yield
• Bend tests for ductility
evaluates the materials’ ability to resist cracking or other
surface irregularities
during one continuous bend
• The bend test can determine tensile strength
• Bend tests are common in linear failure behaviors ,
like in springs and brittle materials i.e.
• Concrete/stone
• Wood/plastic
• Glass/ceramics
• Powder metallurgy-processed metals and materials
• Bend tests are also known as bending tests

25. Universal Testing Machine

26. Torsion Test

27. Torsion test
Sample is twisted along an axis to measure
• torsional shear stress
• maximum torque
• shear modulus
• breaking angle of a material
• the interface between two materials
• evaluates the properties under stress from
angular displacement

28. Torsion Test
• Apply only a rotational motion
or apply both
axial (tension or compression) & torsional
forces
• Determine shear properties in a material
when twisted, or under torsional forces,
due to applied moments that cause shear stress
about the axis

29. .
Example of torsion
• Twisting a piece of blackboard chalk between
ones fingers until it snaps is an example of a
torsional force in action
• A transmission drive shaft
(such as in an automobile)
receives a turning force from its power source
(the engine)

30. Formability
Materials Formability Testing

31. Formability
• Formability is the ability of a given metal workpiece to undergo
plastic deformation without being damaged. The plastic
deformation capacity of metallic materials, however, is limited to a
certain extent, at which point, the material could experience tearing
or fracture
• The formability is the capability of a material to undergo plastic
deformation to a given shape without defects. Formability limits
are a hard constraint when sheet metal parts are manufactured, but
also in bulk metal forming, formability limits can be reached leading
to faulty parts
• estimation of formability is usually based on total elongation,
measured from the tensile test
• refers to the ease with which a material can be formed while
satisfying quality requirements
• the capacity of a material, as sheet steel, to be readily bent,
stamped, shaped, etc.

32. Formability
• A metal with a large elongation has good
formability because the metal is able to
undergo a large amount of strain (work)
hardening.

33. Hardness testing
A test to determine
the resistance of a material
to permanent deformation by
penetration of another harder material
in relation to the given load on the indenter

34. Hardness testing
Hardness is a characteristic of a material
not a fundamental physical property
It is the resistance to indentation
For Indentation hardness value
measure the parmanent depth or the area of the
indentation
When using a fixed force (load) & a given indenter,
the smaller the indentation, the harder the
material
One of over 12 different test methods is used

35. Vickers hardness test
The indenter shape should give geometrically
similar impressions, irrespective of size
The impression should have well-defined points
of measurement
The indenter should have high resistance to self-
deformation
A diamond in the form of a square-based
pyramid satisfied these conditions

36. .
Vickers test scheme Pyramidal diamond indenter
Difference in
length of both diagonals & the illumination gradient
Out-of-level sample This is not a good indentation
A good indentation

37. Vickers Hardness test
• It is easier than other hardness tests as the
• calculations are independent of the size of the indenter,
• The indenter can be used for all materials irrespective of hardness
• Basic principle (as with all common measures of hardness) is
to observe from a standard source;
a material's ability to resist plastic deformation
• The Vickers test can be used for all metals
• Widest scales among hardness tests
• The unit of hardness we get is Vickers Pyramid Number (HV)
or Diamond Pyramid Hardness (DPH)
• The hardness number can be converted into units of pascals
• Should not be confused with pressure, which uses the same units
• The hardness number is determined by
the load over the surface area of the indentation &
not the area normal to the force, & is therefore not pressure

38. Vickers Hardness test
• This gives an angle of 22° on each side
from each face normal to the horizontal plane
normal
• Varied loads are applied to a flat surface,
depending on the hardness of the material to
be measured
• The HV number is F/A,
• F --- force applied to the diamond in
kilograms-force
• A --- surface area of the resulting indentation
in square millimeters

39. Vickers hardness test
Calculation
• d --- average length of the diagonal left by the indenter in mm
• HV =F/A = approx 1.8544F/d^2 kgf/mm^2
• F is in kgf d is in millimeters
• Unit of HV is kilogram-force per square millimeter (kgf/mm²) or HV number
• F is in N d in mm HV in the SI unit of Mpa
• For (VHN) in SI units
the force applied is converted from N to kgf
by dividing by 9.806 65 (standard gravity)
• HV = approx 0.1891F/d^2 kgf/mm^2
• F is in N d is in mm
• A common error is that the above formula to calculate the HV number does
not result in a number with the unit Newton per square millimeter (N/mm²),
but results directly in the Vickers hardness number (usually given without
units), which is in fact one kilogram-force per square millimeter (1 kgf/mm²)

40. Vickers hardness test
• Vickers hardness numbers are reported as xxxHVyy
• e.g. 440HV30
• or xxxHVyy/zz if duration of force differs from 10 s
to 15 s
• e.g. 440HV30/20, where:
• 440 is the hardness number,
• HV gives the hardness scale (Vickers)
• 30 indicates the load used in kgf
• 20 indicates the loading time
if it differs from 10 s to 15 s

41. Vickers hardness test
Examples of HV values for various materials
Material Value
• 316L Stainless steel 140HV30
• 347L Stainless steel 180HV30
• Carbon steel 55–120HV5
• Iron 30–80HV5
• Martensite 1000HV
• Diamond 10000HV

42. Vickers hardness test
Estimating tensile strength
If HV is expressed in N/mm2 (i.e. in MPa)
then the tensile strength (in MPa) ≈ HV/3

43. Vickers hardness test
Application example
• The fin attachment pins and sleeves
in the Convair 580 airliner were specified by the
aircraft manufacturer
to be hardened to a Vickers Hardness specification of
390HV5,
the '5' meaning five kiloponds
• However, on the aircraft flying Partnair Flight 394 the pins
were later found to have been replaced with sub-standard
parts, leading to rapid wear and finally loss of the aircraft
• Accident investigators found that the
sub- standard pins had a hardness value of only 200-
230HV5

44. Rockwell Test
• It measures the depth of penetration of an indenter
under a large load (major load)
compared to the penetration made by a
preload (minor load)
• There are different Rockwell scales
• The hardness scale is based on
indentation hardness of a material
• Denoted by a single letter, that use different loads or
indenters
• We get a dimensionless number as HRA, HRB, HRC, etc.
• The last letter is the respective Rockwell scale
• Indentation hardness is linear with tensile strength

45. Rockwell Test
• To find Rockwell hardness of a material
• Apply a minor load . It establishes the zero position
• Apply a major load
• Remove the major load but keep the minor load
• Measure the depth of penetration from the zero datum
from a dial
• Harder material gives a lower penetration depth
• These are inversely proportional
• Rockwell hardness gives value of hardness directly
• No calculations as in other hardness measurement
techniques
• Equation for Rockwell Hardness is HR=N-hd,
• d --- depth in mm (from the zero load point),
• N & h --- scale factors
that depend on the scale of the test being used

46. Rockwell Test

47. .
Scale Abbreviation§ Major
Load* (kgf)
I n d e n t e r U s e N h
A HRA 60
spheroconical
diamond
Cemented carbides, thin steel, shallow case-hardened steel 100 500
B HRB 100 1⁄16 in (1.59 mm) ball Copper alloys, soft steels, aluminum alloys, malleable iron 130 500
C HRC 150
spheroconical
diamond
Steel, hard cast irons, pearlitic malleable iron, titanium, deep
case-hardened steel, other materials harder than 100 HRB
100 500
D HRD 100
spheroconical
diamond
Thin steel, medium case-hardened steel, pearlitic malleable iron 100 500
E HRE 100 1⁄8 in (3.18 mm) ball CastIron, Alu & magnesium alloy,bearing metal,thermoset plastic 130 500
F HRF 60 1⁄16 in (1.59 mm) ball Annealed copper alloy, thin soft sheet metals 130 500
G HRG 150 1⁄16 in (1.59 mm) ball Phosphor bronze, beryllium copper, malleable irons 130 500
H HRH 60 1⁄8 in (3.18 mm) ball Aluminum, Zinc, Lead 130 500
K HRK 150 1⁄8 in (3.18 mm) ball Bearing alloy, tin, hard plastic materials 130 500
L HRL 60 1⁄4 in (6.35 mm) ball Bearing metals and other very soft or thin materials. 130 500
M HRM 100 1⁄4 in (6.35 mm) ball Thermoplastics, bearing metals & very soft or thin materials 130 500
P HRP 150 1⁄4 in (6.35 mm) ball Bearing metals and other very soft or thin materials 130 500
R HRR 60 1⁄2 in (12.70 mm) ball Thermoplastics, bearing metals, & very soft or thin materials 130 500
S HRS 100 1⁄2 in (12.70 mm) ball Bearing metals and other very soft or thin materials 130 500
V HRV 150 1⁄2 in (12.70 mm) ball Bearing metals and other very soft or thin materials 130 500

48. Brinnel Hardness Test

49. Brinnel Hardness Test

50. Brinnel Hardness Test
• For softer materials,
• 10 mm diameter steel ball as an indenter is used
• A smaller force 3,000 kgf (29.42 kN) is used
• For harder materials
• A tungsten carbide ball indenter is used
• The indentation is measured & hardness calculated as:
BHN = 2P / pi D [ D- sqrt {D^2 - d^2} ]
• BHN = Brinell Hardness Number (kgf/mm2)
• P = applied load in kilogram-force (kgf)
• D = diameter of indenter (mm)
• d = diameter of indentation (mm)

51. Brinnel Hardness Test
• Brinell hardness is sometimes in megapascals
• BHN x g ( 9.80665 ) m/s2 converts it to megapascals
• BHN is converted to the ultimate tensile strength (UTS)
by Meyer's law
• If Meyer's index < 2.2 then UTS / BHN = 0.36
• If Meyer's index > 2.2, then UTS / BHN increases
• BHN is shown as HBW
• H --hardness B --brinell W --indenter material ,
tungsten (wolfram) carbide
• HBW = 0.102 x 2F / pi D (D- sqrt {D^2-d^2} )
• F = applied load (newtons)
• D = diameter of indenter (mm)
• d = diameter of indentation (mm)

52. Impact Tests
IZOD CHARPY

53. Impact Test
• Test of
the ability of a material to withstand impact
• To predict its behaviour under actual conditions
• Many materials fail suddenly
under Impact, Shock at flaws, cracks, or notches
• A swinging pendulum strikes a notched bar;
heights before and after impact
are used to compute the
energy required to fracture the bar

54. Impact Test - Types
• Charpy test, (V or U notch)
the test piece is held horizontally
between two vertical bars, like the lintel over a door
• Izod test (V-notch)
the specimen stands erect like a fence post
• Striking a standard specimen
with a controlled weight pendulum travelling at a
set speed
• Energy absorbed in fracturing the test piece is
measured
• Notch toughness of the test material is counted

55. Impact strength calculation
Impact energy in J / Thickness of the specimen
( area under notch )
• The test result is average of 5 specimens
• ISO impact strength is expressed in kJ/m2

56. Fatigue testing
Cyclic Loading

57. Fatigue testing
• Process of
• progressive localized permanent structural
• change occurring in a material
• subjected to conditions that
• produce fluctuating stresses and strains
• at some point or points and that may
• results in cracks or complete fracture
• after a sufficient number of fluctuations
थकिा Fatigue, weariness

58. Fatigue testing
• Mechanical testing
• Apply cyclic loading to structure
• Generate fatigue life & crack growth data,
• identify critical locations or
• demonstrate the safety of a structure
• that may be at risk to fatigue

59. Creep testing

60. Creep testing
• Conducted using a tensile specimen
• A constant stress is applied
• at a constant temperature
• by the simple method of
• suspending weights from it
• The test is recorded
• on a graph of strain vs time
राांगणे रेंगाळणे , creep, crawl, to crawl

61. Creep testing
• Creep is the tendency of a material
• to change form over time
• after facing high temperature and stress
• Creep increases with temperature
• it is more common
when a material is
exposed to high temperatures for a long time
or at the melting point of the material

62. Creep testing

63. Assignment 2
1. What is Material Testing ; Tensile test & it’s procedure
2. Plot True vs Engineering Stress-Strain curves
3. Write a note on Compression Test
4. Explain a) Bend Test b) Torsion Test
5. What is formability
6. Explain Hardness Testing.
Enlist the types & write a detailed note on any one of it
7. What is impact testing. Explain in brief
8. What is Fatigue Testing
9. Briefly write about Creep Test
Use sketch & table wherever possible