AIM
To conduct hardness test on mild steel, carbon steel, brass and aluminum specimens.
APPARATUS
Hardness tester, soft and hard mild steel specimens,brass, aluminum etc.
THEORY
The hardness of a material is resistance to penetration
under a localized pressure or resistance to abrasion. Hardness tests provide an
accurate,rapid and economical way of determining the resistance of materials to deformation.
There are three general types of hardness measurements depending upon the test is conducted:
a. Scratch hardness measurement,
b. Rebound hardness measurement
c. Indention hardness measurement.
a. Scratch hardness measurement,
b. Rebound hardness measurement
c. Indention hardness measurement.
- In scratch hardness method the material are rated on their ability to scratch one another and it is usually used by mineralogists only.
- In rebound hardness measurement, a standard body is usually dropped on to the material surface and the hardness is measured in terms of the height of its rebound.
- The general means of judging the hardness is measuring the resistance of a material to indentation. The indenters are usually a ball cone or pyramid of a material much harder than that being used.
Hardened steel, sintered tungsten carbide or diamond indenters are generally used in indentation tests; a load is applied by pressing the indenter at right angles to the surface being tested.
The hardness
of the material depends on the resistance which it exerts during a small amount of yielding or plastic. The resistance depends on friction, elasticity, viscosity
and the intensity and distribution of plastic strain produced by a given tool
during indentation
PROCEDURE
1. Place the specimen securely upon the anvil.
2. Elevate the specimen so that it come into contact with the penetrate and put the specimen under a preliminary or minor load of 100+2N without shock
3. Apply the major load 900N by loading lever.
4. Watch the pointer until it comes to rest.
5. Remove the major load.
6. Read the Rockwell hardness number or hardness scale.
1. Place the specimen securely upon the anvil.
2. Elevate the specimen so that it come into contact with the penetrate and put the specimen under a preliminary or minor load of 100+2N without shock
3. Apply the major load 900N by loading lever.
4. Watch the pointer until it comes to rest.
5. Remove the major load.
6. Read the Rockwell hardness number or hardness scale.
|
SL.NO |
Specimens |
Reading (HRC/) |
Mean |
||
|
1 |
2 |
3 |
|||
|
1 |
Mild
Steel |
|
|
|
HRB = |
|
2 |
High
Carbon steel |
|
|
|
HRC = |
|
3 |
Brass |
|
|
|
HRB = |
|
4 |
Aluminum
|
|
|
|
HRB = |
RESULT:- The hardness of the metal is found to be
i) Hard steel =
ii) Unhardened Steel =
i) Hard steel =
ii) Unhardened Steel =
PRECAUTION:-
1. Brielle test should be performed on smooth, flat specimens from which dirt and scale have been cleaned.
2. The test should not be made on specimens so thin that the impression shows through the metal, nor should impression be made too close to the edge of a specimen.
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