Continuous Assessment Cover Sheet
Faculty of Engineering
Module Details
Module Code
MT1011
Engineering Materials
Module Title
Program: SLIIT
Course: BSc
Stream: Mechanical
Assessment details
Impact Toughness of a Metal
Title
Group assignment
NO
If yes, Group No.
Lecturer/ Instructor
Mr. Zhakib
Date of Performance
19 March 2025
Due date
9 April 2025
Date submitted
9 April 2025
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EN24300156
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Gamage A.D.
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1
SRI LANKA INSTITUTE OF
INFORMATION TECHNOLOGY
Faculty of Engineering
MT1011 – Engineering Materials
Hardness Testing of Metals
Practical Date: 19 March 2025
Field of Study: Mechanical Engineering
Submission Date: 9 April 2025
Instructor’s Name: Mr. Zhakib
2
1 Objectives
The objective of this practical is to determine the hardness of a metal using the Rockwell
hardness test.
2 Introduction
Hardness can be simply defined as the ability of a material to resist deformation. Testing the
hardness of materials is a common practice in various fields and industries mainly due to the
simple procedure and since hardness testing can be performed without damaging the material.
Hardness testing can be carried out in one of three manners – Rockwell, Vickers, and Brinell
hardness tests. In this practical, the Rockwell hardness test was used to determine the hardness
of a 9 mm thick specimen of hard steel.
3 Theory
The Rockwell hardness test utilizes either a diamond spheroconical indenter, or a tungsten
carbide or steel ball (the former was used in this practical) driven into the material by a
calibrated hardness testing machine – as shown in Figure 1. The hardness is determined by
measuring the difference in depth of the indentation as the load is increased from a certain
preliminary test force to a specific total test force and then returned back to the preliminary test
force. A preliminary test force is used both as a reference (i.e. to minimize the effect of surface
imperfections) and to stabilize the specimen. The loading time refers to the time taken to apply
a load while the dwell time refers to the time period the load is fully applied before removal.
When conducting the Rockwell hardness test, it is important to ensure that the temperature is
between 10 and 35 ⁰C and that the thickness of the material being tested is at least 10 times the
depth of the indentation. The Rockwell hardness 𝐻𝑅 is calculated using the following
equations:
For a diamond spheroconical indenter,
𝐻𝑅 = 100 −
ℎ
0.002
For a tungsten carbide or steel ball indenter,
ℎ
0.002
Where ℎ denotes the difference in indentation depth in millimeters, respectively.
𝐻𝑅 = 130 −
3
Figure 1 – Rockwell Hardness Testing Machine (Source: Penn Tool Co.)
The Rockwell hardness testing machine has three scales on a dial face – HRA, HRB, and HRC
– which must be selected depending on the indenter being used and the type of material being
tested. According to Table 1, the HRC must be used in this practical.
Scale Preliminary
Indenter
Test Force
kgf
N
HRA
10
98 Diamond (120⁰), 0.2 mm tip radius
HRB
10
98 WC ball ϕ1/16 in (1.588 mm)
HRC
10
Total Test
Force
kgf
N
60
589
100 981
98 Diamond (120⁰), 0.2 mm tip radius
150 1471
Table 1 – Scales and Test Forces for Rockwell Hardness Test
4
Example
Materials
Thin steels
Non-ferrous,
soft steels
Hard steels
4 Materials and Apparatus
The following materials and apparatus was used when conducting this practical:
(1) 9 mm thick specimen of hard steel
(2) Rockwell hardness testing machine
(3) Sandpaper
5 Procedure
The following procedure was followed when conducting this practical:
(1) Initially, the specimen was polished to obtain a smooth finish and cleaned of any foreign
material such as dust or rust using sandpaper.
(2) Whereafter, it was ensured that the crank was at the unload position.
(3) A total test force of 150 kgf (1471 N) was then set using the load wheel. (See Table 1)
(4) Afterwards, the large pointer position was set to 0 or C. (See Table 2)
(5) The specimen was then placed on the anvil and brought into contact with the indenter
by raising the anvil by slowly rotating the hand wheel clockwise. Movement of the large
pointer indicates proper contact.
(6) In order to apply the preliminary test force of 10 kgf, the anvil was raised until the large
pointer made three rotations or the small pointer was at the red spot. (See Table 2)
(Dwell time: 0.1 – 4 s)
(7) Whereafter, the total test force was applied by slowly moving the crank to the load
position. (Loading time: 1 – 8 s, dwell time: 2 – 6 s)
(8) The specimen was then unloaded by moving the crank to the unload position and the
dial was read. (See Table 2)
(9) The preliminary test force was then removed by lowering the anvil.
Scale
HRA
HRB
HRC
Dial
Large Pointer Position
Small Pointer Position (Or Large
Figures
(Initial)
Pointer Revolutions)
Black
0 or C
Red spot (3)
Red
30 or B
2 divisions (2)
Black
0 or C
Red spot (3)
Table 2 – Pointer Adjustments for Rockwell Hardness Test
5
6 Observations
6
7 Discussion
7
8
8 Conclusion
The hardness of a 9 mm thick piece of hard steel at 24 ⁰C was measured using the Rockwell
hardness test. However, a somewhat significant discrepancy was observed between the results
obtained here and published data. Possible causes of this discrepancy were discussed. One
possible explanation is that various forms of hard steels can be found with different alloy
compositions and strengthening mechanisms. Moreover, the possibility of experimental error
causing these discrepancies was investigated although the former appears to be more likely. In
addition, the importance of hardness testing were discussed. Furthermore, the shortcomings of
the Rockwell test and way to overcome them were discussed.
9
9 References
[1] Low, S.R., Gettings, R.J., Liggett Jr, W.S. and Song, J., 1999. Rockwell hardness. In Proc.
1999 Workshop and Symp.(Charlotte, NC).
[2] Penn Tool Co., Inc. (2025). Penn Tool Co. [online] Available at:
https://www.penntoolco.com/spi-dial-rockwell-scale-hardness-testers/ [Accessed 5 Apr.
2025].
[3]. Steels, H.S.L.A., ASM Handbook, Volume 1, Properties and Selection: Irons, Steels, and
High Performance Alloys Section: Carbon and Low-Alloy Steels.
[4] ASTM, A.D., 2013. A276-13: standard specification for stainless steel bars and shape.
USA: ASTM International.
10