1. 6.0 Hardness Used to designate several qualities of the materials.
Hardness may indicate resistance to abrasion, scratching, cutting or shaping.
Hardness of material usually implies the resistance to deformation or indentation. It is an easily measured quantity.
Hardness tester
Brinell,
Rockwell
Vickers
Knoop
Mohr
Indenter=penakuk
differ in the shape, size and type of indenter used, the load applied and the method of measuring the diameter or depth of the impression.

2. HARDNESS • Resistance to permanently indenting the surface.
• Large hardness means:
--resistance to plastic deformation or cracking in
compression.
--better wear properties.
Adapted from Fig. 6.18, Callister 6e. (Fig is adapted from G.F. Kinney, Engineering Properties
and Applications of Plastics, p. 202, John Wiley and Sons, 1957.) 21

3. Hardness Testing Techniques

4. 6.1 Brinell Hardness Test
The test consists in forcing a steel ball of diameter, D under a load, P into the test piece & measuring the mean diameter d of the indentation left in the surface under test, after removal of the load.
The Brinell hardness number (BHN) is obtained by dividing the test load P (in kilogram) by the curved surface area of the indentation (in square millimeter).

5. Brinell Hardness Test where P = Load applied, kg
D = Diameter of indenter ball, mm
d = Diameter of impression, mm
Side view Top view

6. 6.2 Rockwell Hardness Test
Several different scales may be utilized from possible combinations of various indenters and different loads.
Indenters include spherical and hardened steel balls having diameters of 1/16, 1/8, 1/4 & 1/2 in and a conical diamond (Brale) indenter, which is used for the hardest materials.
Two type of tests;
Rockwell and
Superficial Rockwell
are differentiate by the magnitude of both major and minor loads.

7. Rockwell hardness scales
Superficial Rockwell hardness scales

8. Rockwell Hardness Test
Both hardness number and scale symbol must be indicated when specifying the hardness value.
The scale is designated by the symbol HR followed by the appropriate scale identification.
For example,
80 HRB represents a Rockwell hardness of 80 on the B scale
60 HR30W indicates a superficial hardness of 60 on the 30W scale.
Side view Top view

9. Knoop & Vickers Microhardness Test
Two microhardness testing technique widely used are Knoop and Vickers.
The resulting impression is observed under a microscope and measured. This measurement is then converted into a hardness number
The Knoop and Vickers hardness numbers are designated by HK and HV, respectively

10. 6.3 Vickers Microhardness Test
Vickers hardness (HV)
Side view Top view

11. 6.4 Knoop Microhardness Test
Knoop hardness (HK)
Side view Top view

12. Hardness Conversion
From a practical standpoint it is important to be able to convert the results of one type of hardness test into those of a different test.
The most reliable conversion data exist for steels as shown in Figure 7.30 for Knoop, Brinell and two Rockwell scales, including also the Mohs scale.

13. Figure 7.30: Comparison of several hardness scales

14. Correlation Between Hardness & Tensile Strength
Both tensile strength and hardness are indicators of a metal’s resistance to plastic deformation.
The same proportionality relationship does not hold for all metals.
For most steels, the HB and the tensile strength are related according to:
TS (MPa) = x HB or
TS (psi) = 500 x HB

15. Relationship between hardness and tensile strength for steel, brass and cast iron.

16. Example 1
A 10 mm diameter Brinell Hardness indenter produced an indentation 2.50 mm in diameter in a steel alloy when a load of 1000 kg was used. Compute the HB of this materials
Solution:
We are asked to compute the Brinell hardness for the given indentation. It is necessary to use the equation for HB, where P = 1000 kg, d = 2.50 mm, and D = 10 mm. Thus, the Brinell hardness is computed as

17. Example 2
What will be the diameter of an indentation to yield a hardness of 300 HB when a 500 kg load is used ?
Solution:
This part of the problem calls for us to determine the indentation diameter d which will yield a 300 HB when P = 500 kg. Solving for d from this equation in Table 6.4 gives

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