This document discusses hardness testing methods. It defines hardness as resistance to indentation, scratching, or wear. Common hardness tests include indentation hardness using Brinell, Vickers, and Rockwell tests which measure the resistance of a material to permanent indentation from static or dynamic loads. Rebound hardness measures energy absorption under impact loads using a scleroscope. Scratch and wear hardness measure resistance to scratching and abrasion. Relationships between hardness values and material properties like tensile strength are provided. Test procedures, calculations, and applications of different hardness tests are described.

1. HARDNESS TEST

2. Hardness: It is the resistance of material surface to occurs any
variation on it under loads as scratch, indentation, abrasion. No
single measure of hardness, universally applicable to all
materials, has yet been devised.
 Indentation hardness: Resistance of a material to permanent
indentation under static or dynamic load.
 Rebound hardness: Energy absorption under impact loads.
 Scratch hardness: Resistance of a material to scratching.
 Wear hardness: Resistance of a material to abrasion.
 Machinability: Resistance of a material to cutting or drilling.
HARDNESS TEST
2

3. HARDNESS TEST
3
STATIC INDENTATION HARDNESS TESTS
Because of the simplicity of the indentation hardness
tests, they have become one of the important quality
control tests of metals and they are considered as
non-destructive tests. The Brinell, Vickers and Rockwell
tests are the most commonly used as the static
indentation hardness tests.
1- Brinell hardness test
In this test, the hardness of a
metal is obtained from the
dimensions of the impression
made by a steel ball after the
ball has been pressed into the
metal under a known load.
Hydraulic Brinell hardness
testing machine

4. HARDNESS TEST
4
Brinell hardness number (BHN) =
D is the diameter of the indenter in mm,
d is the diameter of the indentation in mm,
P is the load on a ball in kg,
h is the depth of the indentation in mm, and
A is the spherical area of indentation = Dh
Then, Brinell hardness number (BHN) = P/A
2
kg/mm
)
2
d
2
D
πD(D
2P


BHN =
When the depth of indentation is to be measured,
a hardness number is computed from the depth of
the indentation by using the following equation:
BHN =
Then,
2
d
2
D
2
1
2
D
h 


Where
D
P
d
h
Indentation
Indenter
Specimen
Schematic representation of
Brinell Indentation

5. 5
There is an empirical relationship, for steels, between the tensile
strength and BHN which may be expressed as follows:
u = BHN x 0.36 (kg/mm2)
u = BHN x 0.22 (ton/in2)
u = BHN x 500 (psi)
In spite of the Brinell test is a simple one to make, several
precautions are necessary in order to obtain good results. These
precautions are as follows:
 It is not adapted to testing extremely hard materials, because the
ball itself may deform.
 It is not satisfactory for testing thin pieces such as razor blades,
because the usual indentation may be greater than the thickness of
the piece.
 It is not adapted to testing case hardened surfaces, because the
depth of the indentation may be greater than the thickness of the
case and because the yielding of the soft cores.
HARDNESS TEST

6. 6
HARDNESS TEST
.
 Thickness of test specimen should be at least 10 times the depth
of indentation (h).
 Specimen surface should be cleaned and polished
 Full load must be applied for 15-30 sec.
Relation between hardness number and tensile strength of some metals

7. 7
If an indentation is made too near the edge of the specimen or too close
to a previous one, it may be too large owing to lack of sufficient
supporting material. However, tests have shown that the error may be
neglected if the distance of the center of the indentation from the edge
of the specimen or from the center of adjacent indentations is equal to
or greater than 2.5 times or 4 times the diameter of the indentation
respectively.
The size of the balls used is: 10, 5, 2 and 1 mm diameters according to:
- The structure of the metal,
- Size of indentation and dimensions of specimen
- Load applied.
The relation between the applied load P (kg) and the diameter of
the ball D (mm) according to: d/D= 0.25-0.5 and P/d2= const., then
HARDNESS TEST
.)
(
2
const
K
D
P

2.5d 4d

8. 8
HARDNESS TEST
Material
Load (kg) for indicated ball diameter
BHN
D=1 mm D=2 mm D=5 mm D=10 mm
Steel & materials of similar
hardness
30 30 120 750 3000 >160
Copper alloys & materials of
similar hardness (light)
10 10 40 250 1000 60-160
Copper & materials of
similar hardness (very light)
5 5 20 125 500 20-60
Lead, tin & materials of
similar hardness (soft)
1 1 4 25 100 < 20
2
D
P
The specifications specify particular sizes of D balls and certain
values for the constants are shown in this table

9. 9
HARDNESS TEST
2- Vickers hardness test
The Vickers hardness tester is somewhat similar to the Brinell in
that an indentation is made and the hardness number is determined
from the ratio P of the load exerted by a mass P ( in kgs) to the
contact surface area A of the indentation ( in mm2) .
Vickers Hardness Number (VHN)
Where
d is the arrange length of the two diagonals
of the impression in mm,
 is the angle of apex = 136, and
P is the load in kg.
2
2
2
/
8544
.
1
2
sin
2
VHN mm
kg
d
P
d
P



The indenter is a square-based diamond
pyramid in which the angle between the
opposite face is 136º. The mass may be
carried from 1 to 120 kg

10. 10
HARDNESS TEST
2- Vickers hardness test
The hardness number is determined from the ratio P of the load exerted
by a mass P ( in kgs) to the contact surface area of the indentation A ( in
mm2) . The indention is a square-based pyramid in which the angle
between the opposite face is 136º.
Area = 4× area of triangle ABC
= 4× ½ × AB × CD
= 4× ½ × ×
=
Sin(θ/2)  DF/CD
CD = DF/ Sin(θ/2) 
A
B
D F
C
2
2
2
/
8544
.
1
2
sin
2
VHN mm
kg
d
P
d
P




11. 11
HARDNESS TEST
One advantage of the Vickers machine over the Brinell machine lies
in the shape of the indentation: A much more accurate reading can
be taken from the diagonal of a square than can be taken from the
diameter of a circle, where the measurement must be made between
two tangents. The Vickers machine provides a fairly rapid method of
measuring hardness and can be used on metal as thin as 0.15 mm. It
is said to be accurate for hardness as high as 1300 (about 850 BHN).
This method is useful for obtaining hardness for case hardened
surfaces.
3- Rockwell hardness test
The indenter or "penetrator" may be either a steel ball of diameter
1/16" (1.41 mm) or a diamond cone with somewhat rounded of 0.2
mm radius.
The Rockwell test differs from the Brinell test in that the indenters
and the loads are smaller (the masses being 60, 100, 150 kg), and
that the resulting indentation is smaller and shallower. It is faster
because it gives direct readings. Therefore the Rockwell test is
widely used in industrial work.

12. Several different scales may be utilized from possible combinations
of various indenters and different loads, which permit the testing
of virtually all metal alloys (as well as some polymers). Each scale
is represented by a letter of the alphabet; several are listed with the
corresponding indenter and load in this table.
12
HARDNESS TEST
Scale Penetrator
Major
load
Material for which scale is used
Rockwell A
Diamond
Cone
60 kg
Hardness steel and extremely hard metal
when small impressions are required.
Rockwell B
Steel ball
1/16
diameter
100 kg
Mild steel, medium carbon steel, sheet
steel, soft steel and bars hardness steels,
hardened and tempered.
Rockwell C
Diamond
Cone
150 kg
Steel, alloy steel, material harder than
Rockwell B 100.

13. 13
HARDNESS TEST
A Rockwell test is made by slowly elevating a specimen against the
indenter until a minor load has been applied; as indicated by an index
hand on a dial gage, minor load = 10 kg. Dial of apparatus is then set
at zero. A major load is then applied by releasing a load lever system
(major load = 50, 90 or 140 kg) as shown in Figure. The major load is
removed and, while the minor load still acting, the Rockwell hardness
number is read on the dial gage. The utilization of a minor load causes
initial indentation that sets the indenter on the material and holds it
in position, thus enhances test accuracy

14. 14
HARDNESS TEST
Dynamic hardness
The hardness measured by this instrument is often referred to as
rebound hardness. Scleroscope hardness is expressed by a number
given by the height of rebound of small pointed hammer after
falling within a glass tube from a height of 10 in (254 mm) against
the surface of the specimen. The height of rebound is measured
against a scale graduated into 140 equal parts.
Scratch hardness
The materials are arranged with respect to their ability to scratch
each other. Scale is set up in terms of several materials, each of
which will just scratch the material of next lower hardness number.
Moh was the first to give mineralogists a scratch hardness scale,
talc being at one end and diamond at the other.
Wear hardness
The wear hardness is the resistance of the material surface to
abrasion or wear and it measured by abrasion test, which is
performed by pressing the sample against the surface of a rotating
table to which an abrasive powder is applied in specific time.
The weight loss indicate the wear resistance.

15. 15
HARDNESS TEST
Example 1
Machinability
It is the resistance of the material to cutting or drilling; the hardness
is measured as the depth of a hole made by a special drill in a given
time, while running at a constant speed and pressure.
A Brinell test was carried out on a steel specimen using a ball of 10 mm in
diameter, if the diameter of indentation was 4.26mm. Calculate the BHN
and tensile strength of the test specimen (K= 30)
Kg/mm2
200.55
)
26
.
4
(
)
10
(
10
(
10
2
3000
2
2








2
2
2
/
)
(
2
mm
kg
d
D
D
D
P



D = 10 mm, d = 4.26 mm,
K = P/D2 = 30 P = 30 × 100 = 3000 Kg
BHN =
σu (kg/mm2) = BHN × 0.36 = 0.36 × 200.55 = 72.2 Kg/mm2
Solution

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