STRENGTH OF MATERIALS

HARDNESS TEST

GROUP A4

GROUP MEMBERS:

1) NUR SABRINA BINTI NOR JAEMAN (174874)

2) SITI NUR AIDA BINTI DAMANHURI (174873)

3) SITI NUR AISYAH BINTI MOHAMAD OTHMAN (174831)

LECTURERS NAME:

DR. NUR ISMARRUBIE BINTI ZAHARI

INSTRUCTORS NAME:

MRS. NOR AINI BINTI ADNAN

DATE:

29th NOVEMBER 2014

Objective:

1. To determine the hardness of various engineering material using Rockwell hardness

test.

2. To develop an understanding of suitable scale for hardness test specimens.

Theory:

Brinell Test Method:

All Brinell tests use a carbide ball indenter. The test procedure is as follows:

The indenter is pressed into the sample by an accurately controlled test force. The force is

maintained for a specific dwell time, normally 10 - 15 seconds. After the dwell time is complete,

the indenter is removed leaving a round indent in the sample. The size of the indent is

determined optically by measuring two diagonals of the round indent using either a portable

microscope or one that is integrated with the load application device. The Brinell hardness

number is a function of the test force divided by the curved surface area of the indent. The

indentation is considered to be spherical with a radius equal to half the diameter of the ball. The

average of the two diagonals is used in the following formula to calculate the Brinell hardness.

The Brinell number, which normally ranges from HB 50 to HB 750 for metals, will increase as

the sample gets harder. Tables are available to make the calculation simple. A typical Brinell

hardness is specified as follows:

356HBW

Where 356 is the calculated hardness and the W indicates that a carbide ball was used. Note-

Previous standards allowed a steel ball and had an S designation. Steel balls are no longer

allowed.

Vickers Hardness Test:

All Vickers ranges use a 136 pyramidal diamond indenter that forms a square indent.

The indenter is pressed into the sample by an accurately controlled test force. The force is

maintained for a specific dwell time, normally 10 15 seconds. The dwell time is complete; the

indenter is removed leaving an indent in the sample that appears square shaped on the surface.

The size of the indent is determined optically by measuring the two diagonals of the square

indent. The Vickers hardness number is a function of the test force divided by the surface area

of the indent. The average of the two diagonals is used in the following formula to calculate the

Vickers hardness.

HV = Constant x test force / indent diagonal square.

The constant is a function of the indenter geometry and the units of force and diagonal. The

Vickers number, which normally ranges from HV 100 to HV1000 for metals, will increase as the

sample gets harder. Tables are available to make the calculation simple, while all digital test

instruments do it automatically. A typical Vickers hardness is specified as follows:

356HV0.5

Where 356 are the calculated hardness and 0.5 is the test force in kg.

Rockwell hardness Test:

The Rockwell hardness test method consists of indenting the test material with a diamond cone

or hardened steel ball indenter. The indenter is forced into the test material under a preliminary

minor load FO. When equilibrium has been reached, an indicating device, which follows the

movements of the indenter and so responds to changes in depth of penetration of the indenter,

is set to a datum position. While the preliminary minor load is still applied an additional major

load is applied with resulting increase in penetration. When equilibrium has again been reach,

the additional major load is removed but the preliminary minor load is still maintained. Removal

of the additional major load allows recovery, so reducing the depth of penetration. The

permanent increase in depth of penetration, resulting from the application and removal of the

additional major load is used to calculate the Rockwell hardness number.

HR =E - e

Fo= preliminary minor load in kgf

F1= additional major load in kgf

F = total load in kgf

e= permanent increase in depth of penetration due to major load F1 measured in units of 0.002

mm

E= a constant depending on form of indenter: 100 units for diamond indenter, 130units for steel

ball indenter HR = Rockwell hardness number

D= diameter of steel ball

Specimen and Equipment:

1. Rockwell hardness tester- Mitutoyo ATK-600

2. Ball and diamond indenters.

3. Calibration block.

4. Hardness specimens: steel, brass, aluminium.

Procedure:

1. The power switch was turned ON.

2. The total load sequence switch was set to the AUTO position in the side panel.

3. The minor load from selector ring was set to S (Rockwell Superficial) or R (Rockwell).

4. Table 1 was referred for selecting a desired indenter.

5. The indenter was fixed.

6. The specimen was placed on the anvil.

7. The total load value was set by turning the selector knob.

8. Preparation was completed :

Loading navigator rapidly flashing (from outer to inner)

Indicator 100 (diamond indenter); 130 (ball indenter)

9. The minor load was applied by raising the anvil by rotating clockwise the elevating

handle slowly until the tip of indenter touched the specimen.

10. During minor load application

Loading navigator slowly flashing (from outer to inner)

11. When the hardness indicator displayed as below, the handle was stopped operation.

Indicator 620 to 640 (Rockwell Superficial); 360 to 370 (Rockwell)

12. After applied appropriate minor load, minor load application was completed.

Loading navigator 4 LEDs light up

13. The START switch was pressed. The measurement process was automatically

performed from step 14-17.

14. Presenting :

Indicator 4 LEDs lighted up

Loading lamp lighted up

Indicator 100 (diamond) ; 130 (ball intender)

15. During total load application :

Loading navigator flashing (from outer to inner)

Loading lamps lighted up

Indicator rapid to slow count-down (duration time 3 to 60 seconds)

16. During total load was removed :

Loading navigator flashing (from inner to outer)

Loading lamps lighted up

Indicator rapid count up

17. Measurement was completed :

Indicator hardness value displayed

OK/NG lamps OK lighted up

18. The hardness value was read and recorded from the hardness indicator.

19. The elevating handle was turned in the reversed direction to lower the anvil and

removed the specimen.

20. Step 3 to 19 was repeated for specimens of other methods and specimens.

21. Three readings on each test specimen and method (refer Table 2) was taken.

Results:

Method Indenter Scale Specimen

Reading

Average

1 2 3

Rockwell

Superficial

Ball

30Y Brass 93.6 95.4 94.4 94.5

30Y Aluminium 93.0 93.4 93.6 93.3

30Y Steel 89.0 95.8 96.2 93.7

Rockwell

Superficial

Diamond

45N Brass 7.8 6.0 6.4 6.7

30N Aluminium 9.2 10.6 11.2 10.3

45N Steel 17.8 14.8 13.0 15.2

Rockwell Diamond S Brass 28 29 27.3 28.1

S Aluminium 6.1 8.4 11.7 8.7

S Steel 34.7 35.5 31.4 33.9

Table 2: Experimental results

Discussion:

Brass specimen:

For brass, the value given when tested using Rockwell Superficial with ball indenter

for 30Y scale is 94.5. The value given for Rockwell Superficial test using diamond indenter

using 45N scale is 6.7 while for Rockwell test with diamond indenter with S scale is 28.1.

However, brass did not give reading when tested using Rockwell with ball indenter because

the test is not suitable for brass.

Aluminium specimen:

As for aluminium, the value given when tested using Rockwell Superficial with ball

indenter for 30Y scale is 93.3. The value given for Rockwell Superficial test using diamond

indenter using 45N scale is NG so we change it to 30N and the value given is 10.3. As for

Rockwell test with diamond indenter with S scale is 8.7. However, as same as brass, aluminium

did not give reading when tested using Rockwell with ball indenter because the test is not

suitable for aluminium.

Steel specimen:

As for aluminium, the value given when tested using Rockwell Superficial with ball

indenter for 30Y scale is 93.7. The value given for Rockwell Superficial test using diamond

indenter using 45N is 15.2. As for Rockwell test with diamond indenter with S scale is 33.9.

However, as same as brass and aluminium, steel also did not give reading when tested using

Rockwell with ball indenter because the test is not suitable for steel too.

Hardness test need to be performs in engineering practice because it is a vital to test

most materials before they are accepted for processing, and before they are put in to use to

determine whether they meet the specifications required or not. Besides that, other mechanical

properties often may be estimated from hardness data, such as tensile strength. Other than

that, hardness test are simple and inexpensive and no special specimen is needed to be

prepared before conducting the test. Other than that, this test could save cost as the testing

apparatus is inexpensive, the test conducted is non-destructive, and the specimen is neither

fractured nor excessively deformed, a small indentation is the only deformation.

To compare the hardness values of tested specimens with values from reference

sources or manufacturers data, it is complicated and cannot be made mathematically as

different methods and scales used is not exact for a wide range of materials. Different loads,

different shape of indenters, mechanical properties of the specimen all complicate the problem.

All tables and charts should be considered as giving approximate equivalents, particularly when

converting to a method or scale which is not physically possible for the particular test material

and thus cannot be verified.

The importance of hardness test in engineering practice are when it is needed to

localised plastic deformation of materials, the hardness test is used to measure the materials

resistance. Other than that, it is based on natural materials with a scale fabricated solely on the

ability of one material to graze another that was softer. Other than that, the clear-cut and

meticulousness of a hardness test require following strict hardness etiquette and observance to

standards.

Conclusion:

By using Rockwell Superficial with ball indenter of 30Y scale, it is shown that brass is

the hardest specimen, followed by steel and aluminium. When using Rockwell Superficial with

diamond indenter of 45N scale, steel give highest value followed by brass and aluminium. As for

the Rockwell test using diamond indenter with S scale, steel is the hardest followed by brass

and aluminium. So it can be said that steel is the hardest among the specimen tested in this

experiment while aluminium is the softest. As for the Rockwell test using ball indenter, the

result shown for all specimens is NG, which means the indenter cannot calculate the hardness

reading. It is a vital to test most materials before they are accepted for processing, and before

they are put in to use to determine whether they meet the specifications required or not. One of

these tests is for hardness. Hardness is the most important property. Therefore, we should learn

to measure the hardness accurately. Rockwell hardness testing process is most simple and

widely used. Therefore, we should learn it perfectly.