The document discusses the hardness of materials, defining it as the resistance to scratching, abrasion, or plastic deformation. It outlines three principal testing methods: scratch testing, rebound hardness, and indentation testing, along with several hardness measurement units and specific tests such as Brinell, Rockwell, Vickers, Mohs, and Scleroscope tests. Each test method has its procedures and suits different material types, providing various scales of hardness measurement.

1. Hardness
Measurement
Peeyush Mishra
Material Science and Engineering
Materials Characterization

2. Introduction
• Those properties of a material that define its behaviour under applied forces
are known as mechanical properties
• Hardness is defined as the ability of a material to resist scratching abrasion
or wear on it
• It may also be defined as the ability of material to resist plastic deformation.

3. Introduction
• Example of such hard materials: ceramics, concrete, and superhard
materials.
A hard material, such as this metal
will not undergo wear and tear
easily.

4. Testing hardness of a material
• There are three principal methods of testing the hardness of a material –
scratch testing, rebound hardness and indentation testing
• Scratch Testing:
o Scratches are narrow continuous lines on surface of materials.
o It is defined as ability of a material to resist scratches on surface
o Used for brittle materials like ceramic
o By performing a scratch hardness test, it can be considered hard if the
material will withstand the friction and not lose its smooth
surface.

5. Testing hardness of a material
• There are three principal methods of testing the hardness of a material –
scratch testing, rebound hardness and indentation testing
• Rebound Hardness:
o Also called dynamic hardness, it is more of elastic hardness than plastic hardness.
o The material used as an indenter already has a known hardness which machinists
compare to that of the material measured.
o measure the rebound or dynamic hardness of a material by dropping a
diamond-tipped hammer on it.

6. Testing hardness of a material
• There are three principal methods of testing the hardness of a material –
scratch testing, rebound hardness and indentation testing
• Indentation Testing:
o Use indentation hardness to determine the hardness of a material to deformation.
o Requires indenting the examined material with a continuous load until it forms an
impression
o Can be used on both microscopic and macroscopic scale.
o Measuring the indentation value of material helps to know how much load the
material can bear before it deforms.

7. Units for measuring hardness
• SI unit of N/mm², this is called Unit Pascal
• Each of the different types of hardness discussed has different scales of
measurement. The units are derived from each measurement method
• Common units of Hardness: Brinell Hardness Number (HB), Rockwell
hardness number (HRA, HRB, HRC, etc.), Leeb hardness value (HLD, HLS,
HLE, etc.), and Vickers hardness number (HV).

8. Units for measuring hardness
• We can use a conversion table that can be used to
compare between different units of hardness.
• They are not 100% accurate

9. Brinell Test
• One of the most common hardness test
• Principle involves a steel ball of 10 mm diameter to create an impression on
the test piece. The impression is then calculated.
• Machine lowers the ball on the material to form an indentation and left for
about 30 seconds. The machinist then applies a force to the ball.
• Metals may require load between 500-3000 kg
• The values noted are used to calculate Brinell hardness using formula

10. Brinell Test
Pressure Gage
Penetrator
Anvil
Elevating Screw

11. Rockwell Test
• The kind of material tested determines the sort of scale used. There are 30 kind
of scales.
• A minor load is applied before testing load.
• Indenter is lowered into the material to create an impression by applying the
major load. Then, the impression to determine the hardness is measured.
• Following that, increase in dent is measured.

12. Rockwell Test
Dial Face
Penetrator
Wheel
Anvil

13. Vickers Diamond Test
• It is more suitable for soft materials that require lesser loads.
• Vickers uses a single diamond indenter for all materials, making its
calculations easier.
• Specimen is placed on the machine to find a suitable height using the
microscope. The correct place can be determined by checking the images on
the screen.
• Diamond indenter is lowered to the part and allowed to stay for a specified
period. Then it’s lifted and indentation value is measured

14. Vickers Diamond Test
Working Panel
Power Source
Working Table
Eyepiece Lens
Manual / Auto Turret

15. Mohs hardness test
• If scratch hardness is to be measured, this is the ideal method to proceed
with.
• This test is performed by scratching the material against a reference
material with a known hardness.
• The Mohs hardness test uses ten reference materials with different
hardness.
• A Rockwell diamond indenter is used for the modern Mohs hardness test.
The working principle of the machine is similar to this of the traditional
method.

16. Scleroscope Test
• Scleroscope test can be used to determine the rebound hardness of materials
• A hollow vertical glass tube is connected to a stand. Then, a diamond
hammer will be dropped through the tube onto the test piece
• The hammer will bounce, and the height of the bounce will be measured and
recorded
• Materials with higher hardness will have higher bounce while soft materials
will have low bound.