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UNIVERSITY OF NAIROBI
DEPT OF MECHANICAL ENGINEERING
FME 251: MATERIAL SCIENCE AND ENGINEERING 1
LAB EXP NO
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2
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4
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F18/2309/2021:
F18/143041/2021:
F18/1411/2018:
F18/2319/2021:
F18/2324/2021:

DATE OF EXPERIMENT:

13TH DECEMBER 2022

DATE OF SUBMISSION:

13TH JANUARY 2023

ABSTRACT
The purpose of this experiment is to study indentations made on metal surfaces
with regards to their hardness
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The experiment involves pressing a ball
sphere on a metal surface for a predetermined time
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OBJECTIVE:
To examine the deformation of a metal specimen when a hardened steel ball is
pressed on to it under different normal loads and to determine how such
indentations should be used to give an indication of the properties of the
specimen
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Hardness refers to the resistance of a metal to the penetration of another harder
body
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A hardness test usually involves loading a pointed diamond or hardened steel ball
and pressing it on the surface of the material being examined
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True
hardness can then be defined as load divided by the projected area of the indent
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A relation between hardness and tensile strength can be established but is not
sufficiently reliable
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This is due to its
simplicity and the non-destructive nature of the hardness indenter as it is so small
that it scarcely damages the material
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The steel
ball is pressed for a predetermined time-period and then removed
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The diameter of the
left indentation is measured and used to determine the Brinell hardness number
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Hardened steel ball indenter
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Test specimen: Steel, Aluminum
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i
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iii
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Load the testing machine with the appropriate weights
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Press the indenter for 30 seconds then lower the test specimen
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RESULTS
Table 1: A variation of load and Brinell’s hardness Number for steel
d (mm)

Load, P (kg)

2
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4
3
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6
4
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45
4
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Mm)
7
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18
14
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06
26
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82
41
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mm

64
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91
133
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43
148
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35
145
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mm)

BHN kg/sq
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25
2
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65
4
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45
4
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06
12
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47
21
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05
32
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19

62
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58
138
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41
137
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35
145
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Plot a load against curved surface area of the impression and derive the
gradients of the graphs
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Examine results more closely for;
a) BHN against diameter of impression
b) BHN against applied load

Fig 1: A graph of load against curved surface area of Steel

Fig 2: A graph of Load against curved surface area (Steel)

DISCUSSION
The calculated values of curved surface area when plotted against load gives
graphs of straight lines
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508 for Aluminum and 82
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CONCLUSION
The BHN values for materials can be determined by use of the Brinell hardness
testing machine
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Hardness of the material to set
standards
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REFERENCES
1
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A
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London: E
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2
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M
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Moscow: MIR
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Department of Mechanical Engineering
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FME 251 Lab Manual
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