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tafila technical university

Faculty engineering

Exp. Name: Brinnel Hardness Test # (3).

Vickers Hardness Test # (4).

Name: Mohammad Nashat Abu-Sabbah.

Lecturer name: Eng. Mohannad Tamimi.

Date of doing this exp.: 17/11/2014.

.

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1.

Objectives :1. To measure the hardness of material using Brinrell Micro hardness tester.

2. To measure the hardness of material using Vickers hardness tester.

2.

Introduction

2.1.

HardnessIt is a common practice to test most materials before they are accepted for processing, and

before they are put into service to determine whether they meet the specifications required or

not. One of these tests is for hardness. (Rockwell, knoop, Brinnel, Vickers are the most

common types of hardness tests).If we look up for the meaning of hardness we will find a various definitions, for example

hardness could be defined as the relative resistance of a metal or other material to denting,

scratching, bending, or the comparative ability of a substance to scratch or be scratched byanother.But the most precise and accurate meaning for it's the measure of a materials

resistance to localized plastic deformation (e.g., a small dent or a scratch).There are two types of tests classified upon the destruction criteria:

1- Destructive test. 2- Nondestructive test.And in our experiment we use hardness test which is nondestructive test (e.g. the specimen

neither fractured nor excessively deformed; a small indentation is the only deformation.)

By using an indentation with a fixed load, the size of the indentation is proportional to the

material's hardness.And note that these tests are considered to be relative tests; so after we use the empirical

formulas to calculate the hardness of the material the unit of the value conducted is the

hardness test type (HB, KB.etc.), so care is needed when we compare two test results andthis involve that we should combine test type for different tested materials.

2.1.1 Rockwell Hardness TestThe Rockwell tests are established as the most common method used to measure hardness

because they are not complicated to perform. Several different scales may be utilized from

possible combinations of various indenters and different loads, which permit the testing of

virtually all metal alloys (as well as some polymers).Indenters include spherical and hardened steel balls and a conical diamond (Brale) indenter,

which is used for the hardest materials.

fig.1:Rockwell Hardness Tester

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There are different scales, denoted by a single letter, that use different loads or indenters.

The result is a dimensionless number noted as HRA, where A is the scale letter.

For example, 20HRC refers to the C scale of the Rockwell Hardness with the value of 20 and

60HR30W refers to the Rockwell Hardness of the value of 60 in the 30W scale.

2.1.2

Brinnel Hardness TestDr. J. A. Brinell Swedish researcher invented the Brinell test in Sweden in 1900. Brinell

hardness is determined by forcing a hardened steel or carbide sphere of a specified diameterDunder a specified load Finto the surface of a material and measuring the diameter of theindentation left after the test D1.

Fig.2: Brinnel ball and its impression

The Brinell hardness number, or simply the Brinell number, is obtained by dividing the loadused, in kilograms, by the actual surface area of the indentation, in square millimeters. The

result is a pressure measurement, but the units are rarely stated.

The Brinell hardness test uses a desktop machine to press a (1, 2.5, 5.0, 10) mm diameter of

hardened steel ball into the surface of the test specimen.The machine applies a load of 500 kilograms for light metals such as copper, brass and thin

stock. A 1500-kilogram load is used for aluminum castings, and a 3000-kilogram load is used

for materials such as iron and steel. The load is usually applied for 10 seconds. After theimpression is made, a measurement of the diameter of the resulting round impression is

taken. It is measured using a low magnification portable microscope.

2.1.3 Knoop Micro hardness TestThe Knoop hardness test is a microhardness test use a very small diamond indenter with

pyramidal geometry which is pressed into the polished surface of the specimen with appliedloads varying from 1 and 1000 g (often 100g) for a certain time.

The resulting impression caused by the pyramidal indenter is measured by microscope afterthat we convert it to hardness number HK using the following formula:

=14.2

^2

Where:

P is the applied load in Kg.L is the larger diagonal of the indenter.

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Knoop test is used for particularly for very brittle materials (ceramics) or thin sheets, where

only a small indentation may be made for testing purposes.

The test was developed by Frederick Knoop and colleagues at the National Bureau of

Standards (now NIST) of the USA in 1939, and is defined by the ASTM E384 standard. Theadvantage of the test is we need only a very small sample of material, and that it is valid for awide range of test forces. But in the other hand the main disadvantages are the difficulty of

using a microscope to measure the indentation (with an accuracy of 0.5 micrometer), and the

time needed to prepare the sample and apply the indenter. Temperature, load and theenvironment may affect this procedure, which have been examined in detail.

fig.3: Knoop diamond indenter and its indentation.

.

2.1.4 Vickers Micro hardness TestIn fact Vickers microhardness test is similar to Knoop microhardness test. The Vickers

hardness test was developed in 1921 by Robert L. Smith and George E. In his method we

determine the hardness of steel whereby a diamond pyramid is pressed into the polished

surface of the specimen and the diagonals of the impression are measured with a microscopefitted with a micrometer eye piece. The rate of application and duration are automatically

controlled and the load can be varied (1 to 2000g).

There are many reasons that we perform Vickers microhardness test instead of Brinrell

hardness test, for example if the thickness of the specimen is too small and it have a smallareas or even if it was very hard like high speed steel (H.S.S) and we use it also for brittle

materials.Two types of indenters are generally used for the Vickers test family, a square base pyramid

shaped diamond for testing in a Vickers hardness tester and a narrow rhombus shaped

indenter for a Knoop hardness test.

The Knoop and Vickers hardness numbers are designated by HK and HV, respectively, andhardness scales for both techniques are approximately equivalent.

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fig.4: Vickers diamond indenter and its indentation.

3.Materials , Equipment and Experimental procedure3.1

Materials

3.1.1

Materials Brinnel Hardness TestSpecimen of low carbon steel.

3.1.2 Materials Vickers Micro hardness TestPolished specimen of low carbon steel

3.2

Equipment

3.2.1 Equipment for Brinnel Micro hardness TestSimple microscope and Brinell hardness testing machine:

1. User load.

2. Brinell ball holder.3. Device body.

4. Specimen holding stand.

Fig.3: Brinnel hardness test machine.

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3.2.2

Equipment for Vickers Microhardness TestVickers microhardness test machinewith a diamond indenter in the form square pyramid

with angle of 136between its opposite faces.

Fig.3: Vickers hardness test machine.

3.3

Experimental Procedure

3.3.1

Experimental Procedure for Brinnel Microhardness Test

The Brinell hardness test method consists of indenting the test material with a 5mm diameterhardened steel or carbide ball subjected to a load of 7350N (750 kg).

1. Choose the indenter and place it in the hole of main rod according to the requirement of

the test.

2. Choose a force test according to the type of tested specimen.3. Slowly pull the control handle to apply the load. And maintain to 10 sec.

4. The control handle is pushed backward to remove the load.

5. The test piece is remover after lowering the anvil.

6. We use readout microscope is used to measure the diameter of the indentation d.

The Brinell hardness number, or simply the Brinell number, is obtained by dividing the load

used, in kilograms, by the actual surface area of the indentation, in square millimeters.

=

=

= 2

. #1

Where: F = applied force (kg)

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D = diameter of indenter (mm)

d = diameter of indentation (mm)

It was conducted that the load is 24.5 Kg, diameter of indenter was 5.00 mm and the impression orindentation diameter was 1.85 mm.

3.3.2

Experimental Procedure for Vickers Microhardness Test1. The load of the indenter according the material of the specimen should be selected. In

the experiment, the load is equal to 500 gf (ferrous material).

2. Then we prepare the surface of the sample to be examined hardness by fine grindingand polishing.

3. Place the sample on the vise of the tester and the arm of the machine is rotated so that

the distance between the upper surface of the sample and the object lens surface is 0.5

mm where the surface of the specimen is scene with a magnification of 400x.4. Diamond pyramid is placed above the surface of the sample then running the test.

5. The lengths of indentation diagonals are measured then the average d is calculated and

applied in the Vickers hardness equation.The Brinell hardness test method consists of indenting the test material with a diamond

indenter subjected to load of (1 to 2000g) for 10 seconds. After we measure the two diagonal

of the indentation using the microscope we take the average value for them.

Then we calculate the area of slopping surface of the indentation. The Vickers hardnessobtained by the following relation:

=2 2

^2 =

1.8544 ^2

Where: p is the load in gf.

d is the average of the diagonals of the indentation in m

isthe angle between the opposite faces of the diamond pyramid which equals 136.

We must prove that there is no difference between the two formulas which used to calculate

the Vickers hardness. To do this, we adopt a certain measurement units and turn all the units

in the equations to these units. The adopted units are millimeter for diagonal length and Kgf

for load. The two equations are:1- HV=1.8544F/d^2, where F in Kgf and d in mm.

2- HV=1854.4F/d^2, where F in gf and d in m.

And when we convert the units the formula would be:

HV=1854.4*10-3F*106*10-3/d2=1.8544F/d^2 , where F in Kgf and d in mm.

4.

Results and Discussion4.1

Results and Discussion for Brinell Hardness Test

HB equation:

=

=

= 2

. = 2

750

3.14 5(5 5 1.85)= 269.25

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Table 1.HB Brinell hardness number according the diameter of indenter and the diameter of indentation.

Diameter of the indentation (mm)

: 2: 5.HB

3.7 278

According to the table the diameter of indenter is 5mm and the relation is 2thediameter of the indentation is 1.85 mm why multiply by 2 according to relation so it 3.7and by using the table we get HB equal to 278 .

Error =.

. 100% = 3.249%

4.2Results and Discussion for Vickers Micro Hardness TestTable 2.HV Vickers hardness number according the diameter of indenter.

# d1 d2 davg HV

1 54.5 53.2 53.85 319.74

2 54.6 53.9 54.25 315.0459

3 52.4 54.9 53.45 324.54

Average ----- ------- ------ 319.78

5. References:www.farasia.com.cn

www.apmtesting.comwww.substech.com