Hardness is a material property that describes resistance to indentation. It is influenced by factors like carbon content in steel. Common hardness tests include Brinell, Rockwell, Vickers, and microhardness Knoop testing. Brinell testing involves indenting a specimen with a hard ball under load and measuring the diameter. Rockwell uses an indenting cone to measure depth. Vickers and Knoop are for very hard materials and measure indention diagonal length. Hardness values correlate to other properties like tensile strength. Hardness testing is used to evaluate properties but is not the only factor in assessing mechanical behavior.

2. Hardness Test
Definition: Hardness is a very important but hard to
define property of materials.
“Hardness is the resistance offered by a material
to indentation.”

3. IES-1992
Hardness as a function of carbon content is shown
in
(a) Fig-A
(b) Fig-B
(c) Fig-C
(d) Fig-D

4. IAS-2001
With the increase of percentage of carbon in the
steel, which one of the following properties does
increase?
(a) Modulus of elasticity (b) Ductility
(c) Toughness (d) Hardness

5. Moh’s Scale of Hardness
Material Moh’s hardness
Talc 1
Gypsum 2
Calcite 3
Fluorite 4
Apatite 5
Orthoclase 6
Quartz 7
Topaz 8
Corundum 9
Diamond 10

6. Brinell Hardness test
 Most commonly used tests.
 A 10 mm tungsten carbide or hardened steel ball
intended.
 Gradually applied load.
 Load applied at right angle to the specimen surface
 Indentation diameter made on the specimen is
measured.
Contd…
 
2
2 2
/
2
;
Load P
BHN kgf mm
Surface Area of Indentation D D d
D
P Kgf D and d in mm

 
 



7.  It cannot be used on very hard or very soft material.
 It is best if the thickness of the material is at least 10
times the depth.
 Tensile strength = k×BHN MPa
k = 3.296 for alloy steel
= 3.342 for Plain Carbon steel.
 For steel, flexural endurance limit e
1.75 BHN MPae  
  VHN BHN
BHN
Rc


x
10

8. IES 2010
The hardness of lathe bed material should be
measured by
(a) Rockwell tester
(b) Brinell hardness tester
(c) Shore Scleroscope
(d) Vickers hardness tester

9. IES-1992
A carbon steel having Brinell Hardness
number 100 should ultimate tensile
strength closer it
(a) 100 N/mm2 (b) 200 N/mm2
(c) 350 N/mm2 (d) 1000 N/mm2

10. Rockwell Hardness test
 A sphere – conical diamond cone of 120º angle and a
spherical apex of radius 0.2 mm is used
 Depth of indentation t is measured.
 Gradually applied load,
 Load is applied at right angle to the specimen surface.
 R = 100 – 500 × t
 Depending on the load used a scale A, B, C, etc. used.
 Rockwell test should not be used on thin materials
(generally less than 0.16 mm, on rough surface or on
materials that are not homogeneous).

11. IAS-1999
A measure of Rockwell hardness is the
(a) Depth of penetration of indenter
(b) Surface area of indentation
(c) Projected area of indentation
(d) Height of rebound

12. Vickers hardness test
(i) A square based diamond pyramid having 136º
between the opposite faces is used.
(ii) Average Diagonal of the indention (D) is
measured.
(iii) Even a light load will produce plastic deformation
that so why we may use VHT on very hard material
likes Tungsten Carbide.
p
VHN
D
 2
p in kgf1.854
,
D in mm.

13. The Scleroscope
(i) Based on the rebound height of a ball from the
specimen.
(ii) Harder the material, higher is the height to which
the ball rebounds.
(iii) Scleroscope hardness numbers are comparable
only among similar materials. A comparison between
steel and rubber would not be valid.

14. Knoop Test (Micro Hardness Test)
 Various micro hardness tests have been developed for
application where it is necessary to determine the
hardness of a very precise area of material, or where
the material or surface layer is exceptionally thin.
 Special machine have been developed for this purpose.
The location for this test is select in the high
magnification.
 A small diamond penetrator is then loaded with a
predetermined load ranging fm 25g to 3000g.

15. IES-1992
Which of the following would you prefer for
checking the hardness of very thin sections?
(a) Hebert cloud burst test
(b) Shore's Scleroscope
(c) Knoop hardness test
(d) Vickers hardness test

16. Durometer
 When testing soft, elastic materials, such as
rubbers and non rigid plastics, a durometer is
use
Herbert Cloudburst hardness test:
 It is used to know the uniformity of hardness
over a surface.

17. IES-1992
Herbert cloudburst Hardness test is conducted to
know
(a) Uniformity of hardness over a surface
(b) Softness of non-metallic components
(c) Hardness of non-metallic components
(d) Hardness at specified depth inside the surface.

18. Charpy and Izod test
 Toughness of a material is measured by means of impact
tests.
 Notched bar prepared as per standard from the test
material, is held in a vice and a weight is allowed to swing
from a known height in such a way that it hits the notched
bar in its path and breaks it.
 Since the material has absorbed some amount of energy
during its fracture, the swinging mass loses part of its
energy and therefore will not be able to reach the same
height from where it started.
 The loss in height (h) multiplied by the weight represents
the energy absorbed by the specimen during fracture,
which can be directly measured from the indicator on the
tester. Contd…

19.  In the Charpy impact test, the specimen is held between
two grips whereas in the Izod impact test the specimen is
held at one end like a cantilever .
 The standard test specimens used in the izod and Charpy
impact tests are made of bars with a square cross section of
10 mm.
 The impact resistance is dependent upon the material
composition as well as the heat treatment process given to
it.
 The annealed materials normally would have better
toughness than the corresponding normalized or
quenched specimens. Coarse-grained structure would tend
to have higher ductility compared to fine grain structure
and consequently better toughness.

20. Sheet Formability Tests
 During the various sheet metal forming processes, the
stresses and strains developed in the material are quite
complex. So, any measure of the formability of the
sheet metal on the basis of material properties derived
from a simple tension test( for example, % elongation
as an index of ductility of the material) is not very
accurate.
 So cupping tests have been developed to evaluate the
formability of the sheet metals.

21. GATE-2006
Match the items in Column I and Column II.
Column I Column II
P. Charpy test 1. Fluidity
Q. Knoop test 2. Micro hardness
R. Spiral test 3. Formability
S. Cupping test 4. Toughness
5. Permeability
(a) P - 4, Q - 5, R - 3, S – 2 (b) P - 3, Q - 5, R - 1, S - 4
(c) P - 2, Q - 4, R - 3, S – 5 (d) P- 4, Q - 2, R - 1, S – 3

22. IES-2002
Assertion (A): The hardness test is a slow, expensive
method of assessing the mechanical properties of
materials.
Reason (R): The hardness is a function of yield stress
and the work hardening rate of material.
(a) Both A and R are individually true and R is the correct
explanation of A
(b) Both A and R are individually true but R is not the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

23. The End