The document discusses various aspects of material hardness, including definitions, measurement techniques, and applications. It defines hardness as a material's resistance to plastic deformation from scratching, penetration, or cutting. Hardness depends on properties like ductility, elastic stiffness, plasticity, and toughness. Common hardness tests include scratch, penetration, rebound, and cutting hardness. Specific tests described include Brinell, Rockwell, Vickers, and Knoop hardness tests. Factors that influence hardness include grain size, work hardening, solid solution strengthening, precipitation hardening. Hardness is important for applications requiring wear/fatigue resistance like cutting tools, bearings, armor.

1. HARDNESS OF MATERIALS
MECHANICS OF MATERIAL AND MACHINE DESIGN
PRESENTED TO: PROF. SYED SAQIB
PRESENTED BY:
2015-CE-78 2015-CE-64 2015-CE-51 2015-CE-72 2015-CE-73

2. HARDNESS:
The property of a material to
resist plastic deformation. The
resistance may be against:
• Scratching
• Penetration
• Cutting
Figure: Hardness

3. HARDNESS DEPENDS UPON:
• Ductility
• Elastic stiffness
• Plasticity
• Strain
• Toughness
• Viscosity

4. SCRATCH HARDNESS(ABRASSION HARDNESS):
Scratch hardness is the measure of how
resistant a sample is to fracture or
permanent plastic deformation due to
friction from a sharp object.

5. PENETRATION HARDNESS(INDENTATION HARDNESS):
This measures the resistance of a
sample to material deformation due to a
constant compression load from a sharp
object.

6. REBOUND HARDNESS(DYNAMIC HARDNESS):
This measures the height
of the "bounce" of a diamond-
tipped hammer dropped from
a fixed height on to a material.

7. CUTTTING HARDNESS:
This measures the
resistance of the sample
to material deformation
due to cutting by any
means.

8. HARDNING PROCESS
• There are five hardening processes:
• Hall-Petch strengthening
• Work hardening
• Solid solution strengthening
• Precipitation hardening

9. Hall-Petch Strengthening
• Hall-Petch hardening, also known as grain-
boundary hardening
• a method of strengthening materials by
changing their average crystallite (grain) size
• It is based on the observation that grain
boundaries impede dislocation movement
and that the number of dislocations within
a grain Figure: Hall–Petch Strengthening is limited
by the size of dislocations. Once the grain
size reaches about 10 nanometres
(3.9×10−7 in), grain boundaries start to
slide.

10. HALL-PETCH STRENGTHENING
• dislocation-dislocation interactions.
• Dislocation creates stress fiels around them given by
𝜎 𝛼 𝐺𝑏/𝑟

11. WORK HARDENING
• Work hardening, also known as strain
hardening or cold working
• It is the strengthening of a metal by plastic
deformation.
• This hardness occur due to dislocation
movement and dislocation generation
within a crystal structure of material
Figure : A phenomenological uniaxial
stress-strain curve showing typical work
hardening plastic behavior of materials
in uniaxial compression.

12. PRECIPITATION HARDENING
• Precipitation hardening, also called age
hardening
• It is a heat treatment technique used to
increase the yield strength and hardness
of malleable materials
• Precipitation hardening relies on changes
in solid solubility with temperature to
produce fine particles of an
impurity phase, which impede the
movement of dislocations, or defects in
a crystal's lattice
Figure:
precipitation hardening

13. SOLID SOLUTION STRENGTHENING
• Solid solution strengthening is a type
of alloying that can be used to
improve the strength of a pure metal.
• The technique works by adding atoms
of one element (the alloying element)
to the crystalline lattice of another
element (the base metal), forming
a solid solution
Figure :Solid Solution
Strengthening

14. HARDNESS TEST
• Brinell Hardness Test
• Rockwell Hardness Test
• Vickers Hardness Test
• Knoop Hardness Test
ME101: Materials Science and Technology

15. CLASSIFICATION OF HARDNESS TEST
• Macro Hardness Test
load applied by indenter>=9.8N
diameter of indentation>=19 μm
e.g.
Brinell Hardness Test
Rockwell Hardness Test

16. CLASSIFICATION OF HARDNESS TEST
• Micro Hardness Test
load applied by indenter< 9.8N
diameter of indentation< 19 μm
e.g.
Vickers Hardness Test
Knoop Hardness Test

17. BRINELL HARDNESS
A spherical indenter (1 cm diameter) is shot
with a load of 500, 1000 or 3000kg
• The indenter is steel, but for harder
materials it is replaced with a tungsten
carbide sphere
Formula :
𝐵𝐻𝑁 =
𝑙𝑜𝑎𝑑
𝑎𝑟𝑒𝑎 𝑜𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑒𝑛𝑡𝑎𝑡𝑖𝑜𝑛 Figure: Brinell Hardness
Figure: Brinnel Harness

18. LIMITATIONS OF THE BRINELL HARDNESS TEST
• Sample must be ten times thicker than the indentation depth
(sample usually should be at least 3/8" thick).
• Test is most accurate if the indentation depth is 2.5 - 5.0 mm.
Adjust load to achieve this.
• It gives hardness between 50 HB to 750HB.
• BHN evaluates the hardness of metallic materials

20. BHN PROS & CONS
• Widely used and well accepted
• Large ball gives good average
reading with a single test.
• Accurate
• Easy to learn and use
• Destructive
• Non-portable
• High initial cost ($5,000)
• Error due to operator reading
Brinell Microscope (10% max)
ME101: Materials Science and Technology

21. ME101: Materials Science and Technology
ROCKWELL HARDNESS TEST (HRB,HRC,ETC.)

22. ROCKWELL HARDNESS
The shape of indentor is either steel
ball or conical diamond point
Formula :
BHN=
𝑙𝑜𝑎𝑑
𝑑𝑒𝑝𝑡ℎ 𝑜𝑓 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑖𝑛𝑑𝑒𝑛𝑡𝑜𝑟
Figure: Rockwell Hardness

23. ROCKWELL HARDNESS METHOD
• Select Scale - load and indentor
depending on the scale
• Press a point into material
• - Diamond Point (Brale)
• - 1/16" ball
• - 1/8" ball
• - ¼” ball

24. Symbol Minor(Pre-) Major(Total)
Indenter Load, kg Load, kg C1 C2mm-1
Coefficients in
R = C1 – C2 Δ t
Normal Scales
RB, 1/16 ball*
RC, cone +
RA, cone
RD, cone
RE, 1/8 ball
RF, 1/16 ball
RG, 1/16 ball
Superficial Sales
R15N, cone+
R30N, cone
R45N, cone
R15T, 1/16 ball
R30T, 1/16 ball
R45T, 1/16 ball
10 100 130 500
10 150 100 500
10 60 100 500
10 100 100 500
10 100 130 500
10 60 130 500
10 150 130 500
3 15 100 1000
3 30 100 1000
3 45 100 1000
3 15 100 1000
3 30 100 1000
3 45 100 1000
Load levels and indenter sizes for Rockwell hardness tests.

25. ROCKWELL TEST LIMITATIONS
 Sample must be ten times thicker than the indentation depth (sample usually should be at
least 1/8" thick).
 Need 3 tests (minimum) to avoid inaccuracies due to impurities, hard spots.
 Test is most accurate if the Rockwell Hardness is between 0 and 100. Adjust scale to achieve
this.
For Steel:
If HRa > 60, use HRc scale
If HRa < 60, use HRb scale
ME101: Materials Science and Technology

26. PROS & CONS (RHT)
• Widely used and well accepted
• Little operator subjectivity
• Accurate
• Fast
• Destructive
• Non-Portable
• Initial cost ($5,000)
ME101: Materials Science and Technology

27. VICKERS HARDNESS
• The indenter is square based pyramid
• Formula
VH = 2PSin(θ/2)/L2
P: applied load in kg
L: average diagonal length
θ: angle between opposite faces of indenter=136⁰
𝑽𝑯 =
𝑷∗𝟐
𝑫 𝟐 𝒔𝒊𝒏 𝟏𝟑𝟔/𝟐
𝑽𝑯 = 𝟏. 𝟖𝟓𝟒
𝑷
𝑫 𝟐

28. PROS AND CONS
• It provides a continuous scale of hardness for a given load from very
soft to hard metals
• Measurement of diagonal length also subjects to human error
• The Micro hardness methods are used to test on metals, ceramics, almost
any type of material.
• Small indentation compared to BHN

30. KNOOP HARDNESS TEST
 Shape of indenter:
Diamond tip tool
 P : Applied load = 0.1 kg – 1 kg
 Ap : Unrecovered Proj. area of indentations, mm2
 L : Length of long diagonal, mm
 C : A constant supplied by the manufacturer
(C=0.07028 for 172° 30' between long edges and 130° 0'
between short edges)

ME101: Materials Science and Technology

31. PROS & CONS (KHN)
• Accurate
• Any material which is extremely soft
or hard can be used to evaluate its
hardness using knoop hardness .
• Requires load to be normal to
surface plane parallel surfaces.
• Independent to ductility of material
• Slow
• Sensitive to surface condition
• Subject to error in diagonal
measurement
ME101: Materials Science and Technology

32. ME101: Materials Science and Technology

33. COMPARISON OF HT METHODS
ME101: Materials Science and Technology

34. SCLEROMETER:
• Used to measure scratch hardness
• Handheld instrument
• Consists of a tungsten carbide tip with
spring inside
• Tip touched to material and spring pressed
• Load increased by pressing spring until
surface is scratched
• Hardness measured by gauge attached
TOOLS OF HARDNESS

35. SCLEROSCOPE:
• Used to measure rebound
hardness
• A diamond tipped hammer is
dropped from a height
• Rebound height gives a
measure of hardness

36. BRINELL HARDNESS TESTER:
• Used to measure indentation hardness
• A steel ball of 10mm diameter is used as
indenter
• Load is applied for 10-15 seconds
• Formula:
𝐵𝐻𝑁 =
𝐹
𝜋
2
𝐷 𝐷 − 𝐷2 − 𝐷𝑖
2
• Gives a range of values rather than one value

37. VICKERS HARDNESS TESTER:
• Used to measure micro-indentation
hardness
• Indenter is a diamond pyramid with
136o apex angle
• Used to measure micro indentation
• Small loads applied
• Formula:
𝐻𝑉 =
1.85𝐹
𝐷2

38. OTHER TOOLS:

39. SCALES OF HARDNESS

40. MOHS SCALE:
• Developed by Friedrich Mohs,
a German geologist in the 19th
century.
• The Mohs scale of mineral
hardness is based on the
ability of one natural sample of
mineral to scratch another
mineral visibly.

41. THE ROCKWELL SCALE IS A HARDNESS SCALE
BASED ON INDENTATION HARDNESS OF A
MATERIAL.
ROCKWELL SCALE:(MACROINDENTATION)

42. ROCKWELL SCALE:(MICROINDENTATION)

43. VICKERS SCALE:

44. BRINELL SCALE:

45. APPLICATION OF HARDNESS

46. • Material hardening is required for many applications:
• Construction materials - High strength reduces the need for
material thickness which generally saves weight and cost.
• Machine cutting tools (drill bits, taps, lathe tools) need be much
harder than the material they are operating on in order to be
effective.
• Knife blades – a high hardness blade keeps a sharp edge.

47. • Bearings – necessary to have a very hard surface that will
withstand continued stresses.
• Armor plating - High strength is extremely important both for
bullet proof plates and for heavy duty containers for mining and
construction.
• Anti-fatigue - (Martensitic) case hardening can drastically improve
the service life of mechanical components with repeated
loading/unloading, such as axles and cogs.

48. ANY QUESTION?????