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Brinell Hardness Test Kalla Rohit, KVS Aditya, Kavya S, Kesava Vishnu, Khagesh Bharadwaj, Pravallika Yadav, Lipi Roy IIST Department of Aerospace (Dated: August 12, 2016; Experiment number 1) Hardness of a material is it’s resistance to plastic deformation. In the Brinell Hardness test, the indentation was caused when a hardened mild steel ball was subjected to loading on a specimen and the diameter of the indents was measured using a microscope. This test was done with two sample specimens, Aluminium and Cast Iron, and their Brinell hardness number was calculated. Brinell hardness number is one of the methods to determine the hardness of a specimen. It is found that Cast Iron is harder than Aluminium The findings are tabulated and shown.

I. Introduction

II. Apparatus

Hardness is the property of a material by virtue of its ability to resist abrasion, indentation (or penetration). It is the resistance of the metal to permanent plastic deformation. The Brinell Hardness number (BHN) is a hardness index, calculated by pressing an indenter into test specimen under standardized loading [1]. Equation 1 gives the formula for the calculation of BHN.

The experimental apparatus consists of a Brinell hardness tester, appropriate loads, test specimens, sandpaper and a microscope.

BHN =

applied load (kg) area of indentation

BHN =

2F √ πD(D − D2 − d2 )

Figure 2 shows the schematic of a Brinell hardness tester. It uses lever mechanism to magnify load, which is applied on the test specimen. It has two loads, major load and minor load. Minor load is 250 Kg (for the present model of Brinell hardness tester) which is applied manually by rotating a shaft which rises the test table and brings the specimen in contact with indenter. Major load is applied when weights are hanged behind the machine.

(1)

where F is the load applied in Kg, D is the diameter of indenter in mm and d is the diameter of the indent in mm. BHN for different materials is shown in Appendix. Figure 1 shows the application of load on the specimen. In this, the load is applied on indenter which is on specimen thereby causing an indent on the surface of specimen.

FIG. 1. (a) Brinell specimen setup (b) Specimen after indent was made [2]

FIG. 2. The Brinell Hardness tester [2]

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IV Results

III. Procedure III.1. Indent formation

IV.1. Aluminium

The test specimens (Aluminium and Cast Iron blocks) were given and their base face and the face to be indented was made smooth using a sandpaper. The Brinell hardness tester was switched on after the specimen was placed on it. The handle of the machine was moved to A and a minor loading of 250 kg was given by manually rotating a shaft which rises the test table and the handle was moved to B and a major load of 250 kg was given to the Aluminium block. When we apply the major load, the pointer in the dial rotates for some time and then it halts, indicating that the indentation was done. Then the diameter of the indent was measured using a microscope. The above process was repeated to produce four indents, each at different places in the same specimen block. Then the Cast Iron block was taken and the above process was repeated except that the major loading was 2750 kg since Cast Iron is harder than Aluminium.

The force applied (major and minor loads) on Aluminium to make an indentation is 500 Kgf and the diameter of indenter is 10mm. BHN is calculated using equation 1. Table I tabulates the observations and calculations made. S.no 1

d 2.29 mm

Average d

BHN

2.255 mm

123.41 Kgf

2.305 mm

117.92 Kgf

2.305 mm

120.60 Kgf

2.22 mm 2

2.20 mm 2.41 mm

3

2.30 mm 2.27 mm

TABLE I. Calculations for Aluminium specimen where d is the diameter of indent in mm, BHN is the Brinell Hardness number in Kgf. From the table, the average BHN is 120.64 Kgf/mm2 and the standard deviation was calculated to be 2.241 Kgf/mm2 .

III.2. Determining the diameter of indent Figure 3 shows the view of diameter through a microscope. While measuring the diameter, zero on the scale of the microscope was aligned tangent to the indent. The thimble was set to zero. The main scale reading ( MSR ) was measured as the distance on the scale between two points on the circle and taken to the nearest 0.5 mm. Then the thimble was adjusted till the peripheri of the mark came. Equation 2 gives the formula for the reading (diameter) d. d = M SR + (0.01 × reading on thimble) (2)

IV.2. Cast Iron The force applied on Cast Iron to make an indentation is 3000 Kgf and the diameter of indenter is 10mm. Table II tabulates the observations and calculations made. S.no 1

d 5.190 mm

Average d

BHN

5.185 mm

131.780 Kgf

5.165 mm

132.695 Kgf

5.100 mm

136.487 Kgf

5.185 mm 2

5.130 mm 5.20 mm

3

5.090 mm 5.185 mm

TABLE II. Calculations for Cast Iron specimen where d is the diameter of indent in mm, BHN is the Brinell Hardness number in Kgf. From the table, the average BHN is 133.65 Kgf/mm2 and

FIG. 3. Indent through a microscope [2] 2

the standard deviation was calculated to be 2.037 Kgf/mm2 .

results depend on all these parameters. The Aluminium specimen showed indentation on applying a smaller amount of load as compared to Cast Iron. 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. This is one of the tests for hardness.

V. Discussion Brinell hardness test was performed for Aluminium and Cast Iron. In each specimen four indentations were made by constant loading and the diameter for each indentation was measured twice in different angles (Refer to Table I, II). From the experiment,

VII. References [1] Harry Chandler, Hardness Testing, 2nd Edition, ASM International, The Materials Information Society. ISBN-13: 978-1-61503-832-9.

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BHN for Aluminium is 120.64 Kgf/mm BHN for Cast Iron is 133.65 Kgf/mm2

[2] D.Tabor, The Hardness of metals, Clarendon Press, Oxford, ISBN-0-19-850776-3.

The result implies that Cast Iron is more resistant to local deformation than Aluminium. Also, as BHN represents hardness, the tensile strength of a material is directly proportional to its brinell hardness [1]. As Cast Iron has more hardness compared to Aluminium, Cast Iron can be used in pipes, machines, automotive industry parts [3].

[3] Donald R. Askeland , Pradeep P.Phule, The Science and Engineering of materials, 5th Edition, Cengage Learning, ISBN-13: 978-81-315-0321-8.

VIII. Appendix

Possible errors in the experiment are : surface of the specimen might contain some irregularities even though it is cleaned, errors made while reading diameter of the indentation using the microscope.

VI. Conclusion After performing the Brinell Hardness test, the average Brinell hardness number of the Aluminium and Cast Iron were found to be 120.64 Kgf /mm2 and 133.65 Kgf /mm2 respectively. The BHN is found to give a good approximation of the hardness of the material and its strength, as both these properties are in inverse relation [3]. Since the experiment depends upon point of indentation, loading measurements and surface cleaning, the

FIG. 4. BHN for different materials [3]

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