Ravi Agarwal 09003017 Hardness

8/4/2019 Ravi Agarwal 09003017 Hardness

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SOLID MECHANICS LAB

HARDNESS TEST

Vickers and Rockwell Hardness

Name : Ravi Agarwal

Roll No : 9003017


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Objective:

To determine hardness number of metal specimen by Vickers and Rockwell

hardness test.

Introduction:

Hardness is usually defined as the resistance of a material to plastic penetration of

its surface. There are three main types of tests used to determine hardness:

Scratch tests are the simplest form of hardness tests. In this test, various materials

are rated on their ability to scratch one another. Mohs hardness test is of this type.

This test is used mainly in mineralogy.

InDynamic Hardness tests, an object of standard mass and dimensions is bounced

back from a surface after falling by its own weight. The height of the rebound isindicated. Shore hardness is measured by this method.

Static Indentation tests are based on the relation of indentation of the specimen by

a penetrator under a given load. The relationship of total test force to the area or

depth of indentation provides a measure of hardness. The Rockwell, Brinell,

Knoop, Vickers, and ultrasonic hardness tests are of this type.

For engineering purposes, mostly the static indentation tests are used.

About Vickers Hardness Test:-

The Vickers hardness is widely employed as a measure or indicator of materialproperties and performance. For example the sensitivity of the steel weld HAZ (

Heat Affected Zone) to hydrogen delayed cracking, a major factor controlling the

weldability of high strength steel, is a function of maximum Vickers hardness of

HAZ, which is limited below 300 HV in many cases. However the application of

the Vickers hardness test has a limit coming from the size of the residual

impression.


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Procedure:

1. Place the specimen on anvil of Vickers machine and adjust the focus of themicroscope, so that surface of the specimen is clearly visible from the microscope.

2. Bring the indenter (diamond, in this case) over the specimen and apply the load.

3. Again, bring the microscope exactly over the position the of indentation.

4. Measure the diagonals of the square shaped indentation visible on the screen

with the help of cross hairs.

Observations and Calculations:

(where the diameter, d is in mm

force, F=9.807 kg-f)


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Sample-A

Sr.No D1(m) D2(m) Davg(m) HRV(by

formula)

HRV(by

Machine)

HRB

1 413.8 418.0 415.9 107.2 107 59.9

2 410.2 419.7 415.0 107.6 108 60.4

3 425.5 418.6 422.0 104.1 104 58.3

4 426.6 419.7 423.2 103.5 104 58.3

5 420.1 420.1 420.1 105.1 105 58.8

Average 105.5 105.6

Sample-B

Sr.No D1(m) D2((m) Davg(m) HRV(by

formula)

HRV(by

machine)

HRB

1 283.5 283.0 283.2 231.1 231.0 96.7

2 278.0 281.9 280.0 236.4 237.0 97.6

3 284.2 284.5 284.3 229.4 229.0 96.4

4275.9 277.4 276.6 242.3 242.0

-5 275.1 279.5 277.3 241.1 241.0 -

Average 236.0 236.0

Sample-C


formula)

HRV(by

machine)

HRB

1 361.8 362.0 361.9 141.5 142.0 75.52 359.9 359.5 359.7 143.3 143.0 75.9

3 370.0 371.5 370.7 134.9 135.0 72.7

4 350.0 354.4 352.2 149.4 149.0 78.3

5 362.2 363.1 362.6 141.0 142.0 75.5

Average 142.0 142.2


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Sample-D


formula)

HRV(by

machine)

HRB

1 413.7 412.7 413.2 108.6 109 60.9

2 416 415 415.5 107.4 107 59.9

3 423.7 421 422.3 103.9 104 58.3

4 427.5 422.5 425 102.6 103 57.8

5 413 428.7 420.8 104.7 106 59.3

Average 105.4 105.8

Sample-E


formula)

HRV(by

machine)

HRB

1 327.3 325.2 326.2 174.2 174.0 85.4

2 340.4 340.4 340.4 160.0 160.0 81.5

3 331.2 334.4 332.8 167.4 168.0 83.7

4 346.2 331.4 338.8 161.5 162.0 82.1

5 299.8 312.5 306.1 197.8 198.0 91.1

Average 172.2 172.4

Sample-F


formula)

HRV(by

machine)

HRB

1 312.3 304.1 308.2 195.2 195.0 90.4

2 312.3 316.0 314.1 187.9 188.0 88.9

3 318.6 318.5 318.5 182.7 183.0 87.84 317.6 326.0 321.8 179.0 179.0 86.8

5 319.6 322.5 321.0 179.9 180.0 87.1

Average 184.9 185.0


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Sample-G


formula)

HRV(by

machine)

HRB

1 327.2 318.4 322.8 177.9 177.0 86.3

2 348.1 338.7 343.4 157.2 157.0 80.7

3 329.8 341.1 335.4 164.8 165.0 82.9

4 328.9 351.0 340.0 160.4 161.0 81.8

5 316 316.4 316.2 185.4 186.0 88.4

Average 169.1 169.2

Result:

Sample

No.

A B C D E F G

Vickers

Hardness

Number

105.5 236.0 142.0 105.4 172.2 184.9 169.1

Standard

Deviation

1.62 5.21 4.44 2.135 13.60 5.90 10.74

Discussions:

The specified value of duration taken by Vickerss hardness test fordifferent materials is as shown below:


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Steel, copper and copper alloys 10 to15 seconds

Lighter metals and their alloys 302 seconds

Grey cast iron 15 to 30 seconds

The indenter used is a diamond in the shape of a right circular pyramidwith square base.

(where the diameter, d is in mm

force, F=9.807 kg-f)

Looking at the mathematical results obtained above, specimen B is thehardest and specimens A and D are least hard.

Surface observations of the materials:-

Sample no A B C D E F G

Surface

appearance

Smooth

Finished

Smoot

h

Polishe

d

Rough

Finished

Mirror

smooth

finishedS

hiny

Rough

compare

d to E

Unpolis

d

Probable

material

Aluminiu

m

Cast

Iron

Brass Aluminiu

m

Mild

Steel

Mild

Steel

Brass


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Uncertainty of the results:The uncertainties of the results are grouped into two main categories:-

Parameters depending on the Vickers hardness testing machine(including the uncertainty of the verification of the testing

machine and of calibration of the reference blocks );

Parameter depending on the application of the test method(variation of operating condition).

Conclusions:-

On the basis of mathematical values, B is the hardest and A and D arethe least hard materials. So, we can say that B is Cast Iron, E and F are

Mild Steel, C and G are Brass, A and D are aluminium.

The mathematical arguments are also supported by the ASTM standardsas we can observe the same pattern in them also.

Also as observed in the lab the surface properties of the specimen predictB to be Cast Iron, E and F to be Mild Steel, C and G to be brass, A and

D to be Aluminium. However it should be noted that this is not the only

criteria to categorise a material, it just give a mere indication of thementioned material.

The mathematical and the surface observation argument also supporteach other. Hence we can predict the materials to be:-

Sample no A B C D E F G

Material Aluminiu

m

Cast

Iron

Brass Aluminiu

m

Mild

Steel

Mild

Steel

Brass


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Rockwell Hardness Test

About the Test:-

This hardness test uses a direct reading instrument based on the principle of

differential depth measurement. Rockwell testing differs from Brinell testing in

that the Rockwell hardness number is based on an inverse relationship to the

measurement of the additional depth to which an indenter is forced by a heavy

(major) load beyond the depth resulting from a previously applied (minor) load.

Initially a minor load is applied, and a zero datum position is established. The

major load is then applied for a specified period and removed, leaving the minor

load applied. The resulting Rockwell number represents the difference in depth

from zero datum position as a result of the application of major load.The entire

procedure requires only 5 to 10 s.

1. Depth of indentation under preliminary load (10 kg)

2. Increase in depth of indentation under additional load (140 kg)

3. Permanent increase of depth of indentation under preliminary load afterremoval of additional load, the increase being expressed in units of 0002 mm

4. Rockwell hardness HRC = 100e


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Procedure:

Place the specimen on the anvil and apply the minor load so as to ensureproper holding of the load to the specimen.

Adjust the pointer at set position and set the dial to zero position. Apply major load by operating handle without any interference. Read the position of the pointer on the appropriate dial, which gives the

Rockwell hardness number.

Sample No A B C D E F G

Machine

Reading(HRB)

51.1 94.1 71.1 50.1 88.2 84.8 70.2

57.4 94.5 70.9 50.5 89.1 85.1 72.1

50.4 94.7 71.9 50.3 82.2 80.7 72.450.9 94.5 70.6 50.8 91.3 79.9 73.7

52.0 93.8 71.2 50.7 88.7 84.5 72.3

Average(HRB) 51.9 94.5 71.1 50.5 87.7 83.6 72.1

Standard

Deviation

2.61 0.37 0.43 0.27 3.01 2.30 1.12

Calculations:

Take the average of the values obtained and tabulate them.

Results:

Sample A B C D E F G

HRB 51.9 94.5 71.1 50.5 87.7 83.6 72.1

Discussion:

There are 30 different Rockwell scales, defined by the combination of theindenter and minor and major loads. The suitable scale is determined due to

the type of the material to be tested. The majority of applications are covered

by the Rockwell C and B scales for testing steel, brass, and other materials.


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Scale Major Load Indenter Typical applications

of scale

A 60 Diamond Cone Cemented Carbides

thin steel, shallow

depth case-hardenedsteel

B 100 1.588mm dia

steel ball

Copper alloys, soft

steels,aluminium

alloys, malleable

iron

C 150 Diamond cone Steel, hard cast iron

D 100 Diamond cone Thin steel, medium

depth case-hardened

steel

E 100 3.175mm diasteel ball

Cast iron,aluminiumand magnesium

alloys

F 60 1.588mm

dia,steel ball

Annealed copper

alloys,thin soft sheet

metals

G 150 1.588mm dia

steel ball

Phosphor

bronze,beryllium

copper

H 60 3.175mm diasteel ball

Aluminium,lead zinc

Typically, most Rockwell hardness testing problems can be separated intothree categories accuracy, repeatability, and correlation and traced to

five main causes machine, operator, environment, sample preparation,

and calibration.

Fig. 1 Left: Broken Rockwell diamond indenter. Note interrupted radius and angle, which will

create greater resistance to penetration. Right: Unbroken diamond indenter. Note nicely formed

radius and smoothed edges to form angle.


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Conclusion:

Advantages of the Rockwell hardness method include the direct Rockwell

hardness number readout and rapid testing time. Disadvantages include many

arbitrary non-related scales and possible effects from the specimen support

anvil.

Bibliography:

Strength of Materials Laboratory Manual, Nirma University of Science andTechnology

Common Problems in Rockwell Hardness Testing by Doughlas.B.Mcghee Advanced Hardness Testing Technologies by Qualitfest

(www.worldoftest.com) Mechanical Testing of Materials, A. J. Fenner, Philosophical Library Inc.,

1965

Pollack, H. W.,Materials Science and Metallurgy, Reston Pub. Co.,Reston:1981

Van Vlack, L. H.,Materials Science for Engineers, Addison Wesly Pub.Co., Mass:1970

Galvinfonote 5.1 by GalvinfoCenter Web Links:-

www.google.com www.osun.org

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Ravi Agarwal 09003017 Hardness