Practical No.

09:
Hardness Testing On Relevant Hardness Testers of given Aluminum
Specimens.
I. Practical Significance
Hardness Testing provides useful information, which can be correlated to tensile strength,
wear resistance, ductility, and other physical characteristics. Hardness testing is therefore
useful for monitoring quality control and for the materials selection process. Versatile for
both micro and macro hardness testing. Each hardness testing method provides unique
insights into the mechanical properties of aluminum specimens, with practical applications
ranging from industrial quality control to advanced materials research. The choice of test
depends on the specific requirements of the application, such as the size and type of the
aluminum sample, the precision needed, and whether the testing process should be non-
destructive. Understanding the significance of these tests helps in selecting the right
method to ensure material performance and reliability in various engineering applications.

II. Industry/Employer Expected Outcome (s)

This practical is expected to develop the following skills for the industry/Employer
1. Implement standard operating procedures for hardness testing.
2. Evaluate the performance and suitability of aluminum materials for different industrial
applications.
3. Develop solutions to improve material properties based on hardness test results.
VI. Minimum Theoretical Background with diagram
Hardness of a material is generally defined as resistance to the permanent indentation under
static and dynamic load. When a material is required to use under direct static or dynamic
loads, only indentation hardness test will be useful to find out resistance to indentation.
Brinell hardness test a hard steel or carbide ball indenter is pressed into the material under a
specified load. The diameter of the indentation is measured, and the hardness is calculated
using the formula:
2𝑃
BHN=
𝜋𝐷(𝐷−√𝐷2 −𝑑 2
Where:
P is the applied load (in kgf).
D is the diameter of the indenter (in mm).
d is the diameter of the indentation (in mm).
Alloying and heat treatment can significantly affect the hardness and other mechanical properties
of aluminum. The choice of indenter and load depends on the Rockwell scale suitable for the
aluminum specimen being tested. Different Rockwell scales (e.g., B and E) are used for aluminum:
Rockwell B (HRB): Uses a 1/16-inch steel ball indenter and a 100 kgf major load. Rockwell E
(HRE): Uses a 1/8-inch steel ball indenter and a 100 kgf major load. Measures the depth of
penetration of an indenter under a minor and a major load. Indenters used Diamond Cone for harder
materials and Steel Ball for softer materials like aluminum. Apply a minor load (usually 10 kgf)
to seat the indenter. Use hardness values to determine the suitability of aluminum for specific
applications, such as automotive components, aerospace structures, and consumer goods.
VII. Experimental setup

1. Power switch
2. Test scale scroll key
3. Indenter
4. Indenter display
5. Major load (kg) display
6. Weight selector dial
7. Anvil
8. Specimen
9. Capstan hand wheel
10. Minor load (kg) display

Fig 9.1 Rockwell

Hardness Tester

Fig 9.2 Indentation

 Fig 9.3 Brinell hardness testing Machine

VIII. Required Resources /Apparatus/Equipment with specification

sr. Instrument
Specification Quantity
/Components
No.
Brinell hardness 1) Test loads - 500 to 3000 Kgf. in steps of 250 01
tester Kg. 2)Magnification of objective - 14 X 3)
1. Maximum test height - 380 mm. 4) Least count -
0.001 mm. 5) Throat depth - 200 mm.
Rockwell hardness 1) Test loads - 60, 100 & 150 kgf 2) Minor load - 01
tester 10 kg3) Max test height - 230 mm 4) Throat depth
2. - 133 mm along with essential accessories

Aluminium Specimen Rectangular shape 25 mm x 25 02

3.
c/s area or circular shape 25 mm diameter or as per
the availability
IX.Precautions to be Followed
● Ensure the surface of the specimens is clean, smooth, and free from any contaminants,
oxides, or surface irregularities. Polishing the surface to a mirror finish is often
recommended.
● The specimens should have an adequate thickness to prevent deformation of the material
during the test. Typically, the thickness should be at least ten times the depth of the
indentation.
● Perform the test at a standard room temperature, avoiding extreme temperatures that could
affect the material properties.
● Conduct the test in a clean environment to avoid any contamination of the specimens or
the testing machine.
● Ensure the hardness testing machine is properly calibrated before starting the test. Regular
calibration checks are essential for accurate results.
● Verify that the indenters are in good condition, with no wear or damage. Use the
appropriate indenter for the specific hardness test (e.g., Brinell, Rockwell).
● Apply the test load smoothly and without impact to avoid any additional stresses on the
material.
● Align the specimen correctly under the indenter to ensure a perpendicular application of
the load.
● Adhere to the specified load holding time for the test being performed. Different hardness
tests have different requirements for load application and duration.
● Conduct multiple hardness measurements on different areas of the specimen to obtain an
average value, reducing the effect of localized material anomalies.
● Due to copper's high ductility, avoid using excessive loads that could cause plastic
deformation. Ensure the surface is well-polished to reduce the influence of surface
roughness on the test results
● Brass is more susceptible to dezincification, which can affect its hardness. Ensure that the
specimens are free from any surface corrosion or degradation before testing.
● Do not apply excessive load on specimen. Use 50.0 kg load for hardness testing of soft
alloys using Brinell hardness tester.
● Select the appropriate scale if using Rockwell hardness tester
● Specimen thickness should be 10 times higher than the depth of the indenter
● The spacing between the indentations should be 3 to 5 times of the indentation diameter
● Loading speed should be standardized.

X. Procedure
For Rockwell hardening Test
1. Ensure the surface of the specimen is clean, smooth, and free of any contaminants,
oxides, or debris. Polishing to a mirror finish is recommended to achieve a consistent
surface.
2. Ensure that the specimen is of adequate thickness, generally at least ten times the depth
of the indentation to avoid any substrate influence on the measurement.
3. Verify that the Rockwell hardness tester is properly calibrated according to the
manufacturer’s specifications. Regular calibration checks are essential to maintain
accuracy.
 4. Select the appropriate indenter (diamond cone for Rockwell C scale or steel ball for
Rockwell B scale) and ensure it is in good condition without any wear or damage.
5. Secure the specimen on the testing anvil, ensuring it is stable and aligned
perpendicularly under the indenter.
6. Apply the preliminary test load (typically 10 kgf) to the specimen. This initial load helps
seat the indenter and establishes a zero reference position.
7. After the preliminary load is applied, incrementally apply the major test load (an
additional load, typically 100 kgf for Rockwell B scale or 150 kgf for Rockwell C scale)
smoothly and without impact.
8. Hold the major load for a specified duration to ensure accurate indentation. The hold
time is typically around 2 to 6 seconds.
9. After holding the major load for the required duration, release it smoothly while
maintaining the preliminary load. The Rockwell hardness number is then automatically
indicated by the machine.
10. Record the hardness value displayed by the Rockwell hardness tester. This value is
based on the depth of indentation caused by the applied loads.
11. To ensure reliability, perform multiple hardness measurements at different locations on
the specimen, especially if the material is suspected to have in homogeneities. Typically,
at least three measurements are recommended, and then calculate the average hardness
value.
12. Check for any signs of cracking or deformation around the indentation, which could
affect the hardness reading.
13. Copper is relatively soft and ductile, so it is typically tested using the Rockwell B scale
(steel ball indenter, 100 kgf major load). Ensure the surface is well-prepared to minimize
the effect of surface roughness.
14. Brass can vary in hardness based on its composition (e.g., alpha brass, alpha-beta brass).
Typically, the Rockwell B scale is used, but for harder brass alloys, the Rockwell C
scale might be appropriate. Check for any signs of dezincification, which can affect
hardness.
For Brinell Test
1. Ensure the specimen surface is clean, free from dirt, oil, and other contaminants.
2. Polish the surface to remove any scratches or irregularities. A smooth, uniform surface is
essential for accurate readings.
3. Ensure the specimen is thick enough to prevent the indenter from contacting the back of
the specimen. The thickness should be at least ten times the depth of the indentation.
4. Verify that the Brinell hardness tester is properly calibrated according to the manufacturer’s
specifications. Use standard reference blocks to check for accuracy.
5. Use a hardened steel or carbide ball indenter, typically 10 mm in diameter.
6. For copper and brass, a common load is 500 kgf, but this can vary depending on the specific
material properties and standards being followed. For soft materials like copper, lighter
loads (e.g., 250 kgf) might be used.
7. Place the specimen on the anvil of the Brinell hardness tester. Ensure it is stable and
properly aligned under the indenter.
 8. Gradually apply the test load (e.g., 500 kgf) to the specimen. Ensure the load is applied
smoothly to avoid shock loading.
9. Maintain the load for a specific duration (typically 10 to 15 seconds) to allow for a
consistent indentation
10. After the dwell time, smoothly release the load.
11. After the load is released, examine the indentation for consistency and clarity. The
indentation should be well-defined and free from irregularities.
12. Use a microscope with a calibrated scale or an optical measuring system to measure the
diameter of the indentation. Take two measurements at right angles to each other and
average them to obtain the final diameter.
13. Conduct multiple hardness measurements at different locations on the specimen to account
for any material inconsistencies. Calculate the average BHN from these measurements.
14. Copper is relatively soft, so lighter loads (e.g., 250 kgf) might be used to prevent excessive
indentation and ensure accuracy.
15. Brass hardness can vary depending on its composition. Use appropriate loads to ensure
clear, accurate indentations without causing material deformation or work hardening.

XI.Observation Tables-

Brinell hardness measurement

SR Specimen Indenter Diameter Total Diameter of Avg. BHN

No (D) Load(P) Indentation (d) Diameter
Kgf mm d avg.
1 2 3

1 Copper hardened steel or

Specimen carbide ball indenter
10 mm in diameter
2 Brass hardened steel or
Specimen carbide ball indenter
10 mm in diameter

Rockwell harness number

SR Specimen Type of Rockwell Hardness Number(RHN) Avg. RHN
No Indenter 1 2 3

1 Copper diamond cone for C

Specimen scale or steel ball
for B scale
 2 Brass diamond cone for C
Specimen scale or steel ball
for B scale

Calculations
For Brinell Hardness-

2𝑃
BHN=
𝜋𝐷(𝐷−√𝐷2 −𝑑 2

The formulas used for calculating Rockwell Hardness values are as follows:
For regular Rockwell Hardness using spheroconical "Brale" Indenter
HR [Scale] = 100 - h/0.002
Where Scale is A, C, D and h is the depth penetrated in mm. For regular Rockwell
Hardness using a steel ball
HR [Scale] = 130 - h/0.002
Where Scale is B, E, F, G etc. and his in mm
OR
In Rockwell B (HRB) and Rockwell C (HRC):

HR=E−e
Where:
 E is a constant based on the Rockwell scale used (e.g., 130 for HRC, 100 for
HRB).
e is the depth of indentation under the major load, measured in units of 0.002 mm
(0.00008 inches).
For Rockwell C scale (HRC):
HRC=100−h
Where h is the depth difference in 0.002 mm units after applying the major load.
For Rockwell B scale (HRB):
HRB=130−h
Where h is the depth difference in 0.002 mm units after applying the major load.
XII. Results
The hardness of aluminum is 1) BHN---------------- 2) RHN-----------------

XIII. Interpretation of Results

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XIV.Conclusions and Recommendation
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XV. Practical Related Questions
 Note: Below given are few sample questions for reference. Teachers must design more such
questions so as to ensure the achievement of identified CO.

1. Explain common hardness testing methods used for assessing the hardness of aluminum
materials.
2. Explain factors considered when selecting an appropriate indentation load for hardness
testing aluminum materials.
3. Explain how does the thickness of aluminum specimens affect the choice of hardness
testing method.
4. Explain key differences between the Brinell and Rockwell hardness testing methods, and
which is more suitable for assessing the hardness of aluminum components.
5. Explain a scenario where an inappropriate hardness tester was used for aluminum and the
impact it had on the results. What was the correct choice of tester in that scenario?
6. Explain how can the results obtained from hardness testing of aluminum materials be
correlated with their mechanical properties and performance characteristics.
7. Considering the use of aluminum in industries like aerospace, automotive, and
construction, how does the choice of hardness testing method vary based on the specific
requirements of each industry.
8. Explain role of industry standards, such as ASTM or ISO, play in guiding the selection
and execution of hardness testing procedures for aluminum.