Mechanical properties

1. UNIT -V -
TESTING OF MECHANICAL
PROPERTIES

2. ELASTICITY
• The ability of the material to regain its original
shape after releasing the load
• EXAMPLE: STEEL AND RUBBER

3. Plasticity
• The ability of the material not to regain its
original shape after releasing the load
• EXAMPLE: CLAY

4. Ductility
• The ability of the material to drawn into wire
EXAMPLE: Gold, platinum, silver

5. Malleability
• The ability of the material to drawn in to
sheets.
• EXAMPLE: gold

6. Brittleness
• The ability of the material fracture without
deformation
EXAMPLE: Cast iron and glass

7. Hardness
• The ability of the material to resist abrasion,
indentation , machining and scratching.
• EXAMPLE: DIAMOND, QUARTZ AND GLASS

8. Toughness
• The ability of the material to absorb energy
and plastically deform without fracturing.
• EXAMPLE: MILD STEEL

9. Stiffness
• The ability of a material to resist deformation
against bending or loading
• The ratio of stress to the strain below elastic
limit.

10. Resilience
• The ability of the material to store energy and
resist shocks or impacts.
• Proof resilience
The maximum energy which can be stored in a
body up to the elastic limit is called proof
resilience.
*The proof resilience per unit volume is called
modulus of resilience

11. Creep
• A slow and permanent deformation in a
material under a steady load at constant
temperature.
• EXAMPLE: the property is considered in
turbines and IC engines.

12. Strength
• The ability of the material to withstand or
support an external force or load without
rupture.
• Elastic strength : It’s the value of load
corresponding to transition from elastic to
plastic range.
• Plastic strength : It’s the value of the load
corresponding to plastic range and rupture.

13. FATIGUE
• It deforms under the fluctuating or repeated
loads

14. Technological properties
.

15. Machinability
• The ability of the material to allow and
undergo various machining operations.

16. Castability
• The ability of the material to cast into
different shape and size.

17. Weldability
• The ability of the material to accept the
joining of two similar or dissimilar materials
during welding.

18. Formability or Workability
• The ability of the material to accept and
undergo the changes in shape and sizes.

19. FACTORS AFFECTING
MECHANICAL PROPERTIES
.

20. FACTORS
• Grain size
• Heat treatment
• Atmospheric exposure
• Low and high temperature.

21. Hooks law
• The stress is directly proportional to strain
with in the elastic limit

22. DEFORMATION OF METALS

23. DEFORMATION OF METALS
• When force is applied on the metal piece,
then size and shape will be altered.
• Any changes in shape and size of metal is
called deformation of metal.
TYPES OF METAL DEFORMATION:
1. ELASTIC DEFORMATION
2. PLASTIC DEFORMATION

24. Elastic deformation
• It’s a deformation of a body which remains even
after removing the external load from the body.
• The plastic deformation may occur under the tensile,
compressive or torsional stresses.
Plastic deformation
It is the deformation of the body which completely
disappears as soon as the external load is removed.

26. Mechanism of plastic
deformation
.

27. Modes
• There are two modes of plastic deformation
• Slip
• twinning

28. Slip
• Sliding of blocks of the crystal over one another
along definite crystallographic planes called slip
planes
• i.e --- displacement of one part of
the crystal relative to another along
a particular plane and direction
The combination of slip plane and
slip direction is called slip system

32. Mechanism of slip
• When Shear stress applied exceeds the critical
value slip occur.

33. .

34. TWINNING
• The second important mechanism in the metal
deformation.
• Here the atoms in the part of a crystal subjected to
stress, rearrange themselves so that one part of the
crystal become the mirror to the other.

35. .
• twinning differs from slip in that every plane of
atoms suffers some movement, and the
crystallographic orientations of many unit cells are
altered.

36. .

37. .

38. Fracture
.

39. Fracture - definition
• Fracture is the mechanical failure of the
material which will produce the separation or
fragmentation of a solid into 2 or more parts
under the action of stress.

40. Types of fracture
• Brittle fracture
• Ductile fracture
• Fatigue fracture
• Creep fracture

41. Brittle fracture
• Fracture occur with out deformation in metal
• Mostly amorphous material like glasses having
this kind of fractures.
(crystalline material having deformation before brittle)
• Brittle fracture increased with decreasing temperature
and increasing strain rate.

42. .

43. .

44. Griffith theory
• There is a difference between material strength
to theoretical value of the ideal material. This is
due to fine cracks in the material. The stresses
applied on the material is concentrated more on
crack portions and lead it to fracture.
• i.e when the stress at the tips of a crack exceeds
the theoretical stress value, the crack expands
and fracture occurs.

45. Mechanism of brittle mechanism

46. .
• Now the tensile stress is applied at the both sides of the material.
• So the stress is maximum at the tip of the crack

48. .

49. DUCTILE FRACTURE

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51. .

52. .
• Formation of fine cavities
Formation of central crack

53. .
• Crack propagates perpendicular to the axis of the specimen
• Fracture occurred at the end

54. .

55. .

56. FATIGUE FAILURE
• Failure occur due to repeated or fluctuating load
This occur in components subjected to cyclic loading
such as motor shaft, bolts, springs, gear teeth ,
automobile parts, suspension bridges etc ….

57. Mechanism in fatigue failure.
• Due to crack , slip in metal the stress concentrated high
in that places.
• Due to cyclic loading the micro crack propagates and lead
to failure (fracture)
• In ductile material fatigue failure occur suddenly
• High temperature increase the mobility of atoms,
facilitating slip and hence the fatigue failure

58. .

59. CREEP
• It’s a slow and permanent deformation in metal under steady
load at constant temperature.
• Some materials such as zinc, lead and tin are having more
creep at room temperature.

60. .

61. Factors affecting creep
• Grain size
• Thermal stability of the micro- structure
• Chemical reactions

62. Mechanism of creep fracture
• (a)Dislocation climb
at high temperature, atomic movements permit the dislocation.

63. (b) Vacancy diffusion
• Due to applied stress a vacant places
(dislocations) takes place and it lead to
fracture.

64. ( c ) grain boundary sliding
• At low temperature creep fracture takes place due to
sliding of grain boundaries.

65. .