9m404.8 to 9

9M404.8TO 9 1

Department of Technical Education Andhra Pradesh

Name :V.SureshDesignation : LecturerBranch :Mechanical Engineering.Institute :Govt.polytechnic, VisakhapatnamYear/semester :IV semesterSubject :Engineering materialsSubject code :M 404Major Topic : Testing of MaterialsDuration :100 min.SubTopic : Hardness testsTeaching aids : PPT & DiagramsRevised by : K.Vijaya Bhaskar

9M404.8TO 9 2

Recap

In the previous class, we have discussed about• Conducting of shear test, impact test

• Calculating the shear strength, impact strength of the

material

9M404.8TO 9 3

Objectives

On completion of the topic you would be able to understand

• How to conduct Hardness test on Brinell Hardness

testing machine

• Precautious, Advantages and limitations of Hard ness

test (Brinell)

• How to conduct Vicker’s hardness test

• How to conduct Rockwell’s hardness test

9M404.8TO 9 4

Hardness Testing

Hardness:-

• Hardness of the material indicate resistance to

abrasoin, scratching, cutting or shaping, when it is

subjected to external load

• The hardness can be determined by any one of the

following tests.

i . Brinell

ii . Vicker's

iii . Rockwell

9M404.8TO 9 5

Brinell Hardness Test

• Specimen is placed on the anvil and the hand wheel is

rotated so that the specimen along with the anvil

moves up and contacts with the steel ball

• The desired load is applied and the steel ball pressed

into the specimen.

• The diameter of the indentation on the specimen is

measured by the use of microscope

9M404.8TO 9 6

Brinell Hardness Testing Machine

Elevating screw

Hand wheel

Indenter holder

Micrometer

Fig 1

9M404.8TO 9 7

Indentation For Brinell Test

Fig2

9M404.8TO 9 8

Brinell hardness number is found out by the following equation.

BHN = =

Where P = load applied on inventor, kg D = Diameter of steel ball, mm d = diameter of Indentation, mm

(


9M404.8TO 9 9

• Less load is applied for measuring hardness of soft

materials and vice versa.• But the required load is selected from the following relations.

= 30 for steel = 10 for copper = 5 for aluminium = 1 for lead, tin and their alloys.

2DP


9M404.8TO 9 10

• The table shows different loads for different materials with the carbide ball of 10 mm diameter .

• The time of loading is in between10 and15 seconds, i.e., depending upon the alloy being examined.

Ball diameter D , mm

Load , P kg Materials

10 3000 Steel 10 1000 Copper

10 500 Aluminium

Table:1


9M404.8TO 9 11

Precautions

1.The Brinell test should be performed on smooth, flat

specimens from which dirt and scale have been cleaned.

2.Successive impression made too close to one another to

produce high reading because of work hardening.

9M404.8TO 9 12

Advantages

1. Its results can correlate well with tensile properties.

2. Careful surface preparation is not required.

3. The impression made by the Brinell machine is

large enough to give a fairly representative

hardness, not often affected by small soft spots and

small hard spots

9M404.8TO 9 13

Limitations

1. The Brinell test produces so large an impression that it is considered to be a destructive test under some circumstances

2. The test of the piece which can be tested is limited to the opening between the anvil and penetrator

3. Brinell hardness testing take much time compared to the Rockwell hardness testing

9M404.8TO 9 14

Vicker’s Hardness Test

Vicker’s test aims at determining the hardness of

specimen of

• Small cross section

• Surface hardened elements

• Specimen having very high hardness

9M404.8TO 9 15

Vicker’s Hardness Testing

P

Fig.3

9M404.8TO 9 16


Fig.4

9M404.8TO 9 17

Computerised Vicker’s Testing Machine

Fig.5

9M404.8TO 9 18

• Here a polished square based pyramid diamond tool with an angle of 1360 between the faces is used• This tool under gradual load makes an impression on the specimen• The load when divided by the area of indentation in mm2 gives what is known pyramid hardness number (D.P.N)


9M404.8TO 9 19

• Pyramid hardness number:-

D.P.N =

Where, P = Load in kg, θ = Angle between the opposite faces

d = Mean length of the two diagonals in mm.


9M404.8TO 9 20

• The load on the plunger carrying the diamond is

applied by a cam

• Which is rotated by a drum on which a wire carrying a

weight is wound

• The load and time during which it is applied are thus

mechanically controlled


9M404.8TO 9 21

Advantages

1. It gives greater precision in measurement of hardness

as compared to the Brinell test

2. The Vicker’s tester can also be used for testing

harder materials because it uses a diamond

9M404.8TO 9 22

Disadvantages / limitations

Disadvantages:-

Vicker’s hardness testers are much more

complicated and expensive than either Rockwell or Brinell

machines

Limitations:-

They may be considered as semi – micro

hardness testers because of the small size of the

impression

9M404.8TO 9 23

Rockwell Hardness Test

• Rockwell hardness test is probably the most widely

used method of hardness testing in industries

• Rockwell testers use much smaller penetrators and

small loads than does the Brinell tester

• Rockwell testers uses of hard ball from 1/16 in. to

1/12 in. in diameter as well as a cone shaped

diamond

9M404.8TO 9 24

• For testing metallic materials the 1/16 in. ball and the

diamond penetrator are most commonly used

• The penetrator chuck is mechanically connected to a

dial indicator with respect to vertical motion of the

penetrator

• The test has several scales of hardness (A, B, C, N, T).

But B, C scales are widely used

Rockwell Hardness Test

9M404.8TO 9 25

Rockwell Hardness Tester

Rockwell hardness tester fig.6

9M404.8TO 9 26

Rockwell Hardness

Tester

Fig7

9M404.8TO 9 27

Test Procedure

• The specimen is placed on the anvil of the machine

and penetrator seated by means of 10 kg minor load

• Keep the dial indicator is zero and then a major load of

60, 100, 150 kg is applied, forcing the penetrator into

the specimen

• Upon removal of the major load, the final depth of

penetration is recorded directly on the dial indicator as

a hardness number

9M404.8TO 9 28

Hardness Number On B Scale

• B – scale is marked in red and uses a steel ball indicator

• It is used for soft material and its working range of

this scale is from 0 to 100

• Rockwell number is obtained mathematically

= 130 -

9M404.8TO 9 29

Rockwell Testing Machine Penetrators

Rockwell machine penetration fig.8

9M404.8TO 9 30

Hardness Number On C- Scale

• C – scale is marked in black and uses a diamond cone indenter with 120o apex angle

• It is used for hard materials for testing materials

harder than B100

• With a diamond cone indicator and a total load of 150 kg

• C – Scale number is obtained

R c = 100 – (d / 0.002)

9M404.8TO 9 31

Rockwell Hardness Testing

• Minor load 10 kg and major load 140 kg applied and

removed as shown below

Fig 9

9M404.8TO 9 32

• It is more flexible than the Brinell hardness test

• A large number of combinations of indenter and

loads make it more useful to test wider range of

materials

• Rockwell testers fitted with a number of fixtures for

testing different sizes and shapes of metal parts

Advantages

9M404.8TO 9 33

• A greater care is required in preparation of

samples

• More sensitive as compared to Brinell test

Limitations

9M404.8TO 9 34

Summary

In this class, we have discussed about

• Conducting hardness test on Brinell Hardness

testing machine, its advantages and disadvantages

• Conducting hardness test on vicker’s hardness

testing machines, its advantages and

disadvantages

• Conducting hardness test on Rockwell hardness

testing machine, its advantages and disadvantages

9M404.8TO 9 35

Quiz

1. The lower loads are applied for measuring hardness of ….?

a. Brittle material

b. Hard material

c. Soft material

d. None of the above

9M404.8TO 9 36

2. The time of loading the indenter important…

seconds for ferrous metals

a. 10 – 15 seconds

b. 5 – 10 seconds

c. 15 – 20 seconds

d. 1- 5 seconds

Quiz

9M404.8TO 9 37

Quiz

3. The Vicker’s hardness number is given by,

a).

b).

c).

d). None

9M404.8TO 9 38

4. The testing machine uses a square based diamond pyramid indenter with an included angle of….

a) 1200 b). 180o c). 136o d). 145o

Quiz

9M404.8TO 9 39

Quiz

5. B – Scale is uses a ……ball indenter for

soft material

a) Brass

b) Steel

c) Iron

d) Copper

9M404.8TO 9 40

6. What type of scales are widely used in Rockwell

hardness test?

a) A and D scale

b) B and E scale

c) B and C scale

d) H and K scale

Quiz

9M404.8TO 9 41

Frequently Asked Questions

1. Explain how hardness is tested on Brinell’s

hardness testing machine

2. Give the brief account of Vicker’s hardness test?

3. List out the advantages and disadvantages of

Vicker’s hardness test

4. Write the applications of the Vicker's pyramid

9M404.8TO 9 42

Frequently Asked Questions

5. Explain Rockwell hardness test? Distinguish the B –

scale and C- scale ?

6. List out the advantages and limitations of Rockwell

hardness test

9m404.8 to 9

Documents