CE 3410

Mechanics of Materials Lab

Louisiana State University

Laboratory Report No. 1

Hardness Test

by

Joshua Board

Table of Contents Purpose:............................................................................................................................... 3

Introduction: ........................................................................................................................ 3

Apparatus and Test Procedures:.......................................................................................... 7

Results: .............................................................................................................................. 11

Discussion: ........................................................................................................................ 13

Sample Calculations: ........................................................................................................ 17

Brinell Hardness Test .................................................................................................... 17

Rockwell Hardness Test ............................................................................................... 18

Conclusion: ....................................................................................................................... 19

References ......................................................................................................................... 20

Appendix ........................................................................................................................... 21

Appendices A1 – Original Test Data Sheet .................................................................. 21

Appendix A2 – Material Properties of Steel ................................................................. 22

Appendix A3 – Material Properties of Aluminum ....................................................... 23

TABLE OF FIGURES FIGURE 1 - BRINELL HARDNESS TESTER MODEL HB3000B ......................................................................................... 7 FIGURE 2 - ROCKWELL HARDNESS TESTER MODEL C504 ............................................................................................ 7 FIGURE 3 - RELATIONSHIP BETWEEN BRINELL EXPERIMENTAL HARDNESS AND REFERENCE HARDNESS ................................ 13 FIGURE 4 - RELATIONSHIP BETWEEN ROCKWELL EXPERIMENTAL HARDNESS AND REFERENCE HARDNESS ............................ 14 FIGURE 5 - COMPARISON OF TENSILE STRENGTH BASED ON BRINELL, ROCKWELL, AND REFERENCE DATA ............................ 15

TABLE 1- BRINELL STANDARDS FOR LOAD, TIME, AND HARDNESS ................................................................................. 4 TABLE 2 - RELATIONSHIP BETWEEN HARDNESS NUMBERS AND TENSILE STRENGTH ........................................................... 6 TABLE 3 - BRINELL HARDNESS TEST DATA AND RESULTS ............................................................................................ 11 TABLE 4 - ROCKWELL HARDNESS TEST DATA AND RESULTS ......................................................................................... 12

Purpose:

The purpose of this laboratory is to determine the hardness and the tensile

strength of three metal samples: 1020 Steel, 6061 Aluminum and 2024 Aluminum. The

Brinell and Rockwell Hardness Tests are used to determine this. With the results obtained

from each sample, the engineer will be able to determine how the samples relate to each

other. Both the Brinell and Rockwell Hardness Test are considered to be non-destructive.

Introduction:

Hardness is the resistance of a material to penetration or abrasion under a locally

applied load (Ref. 1). We use the concept of hardness almost every day. Any time we file

our nails with a nail file or scratch a CD with our finger nails, hardness is involved.

Hardness is used to measure a variety of resistances including: scratching, cutting, and

indenting (Ref. 2). Also, Hardness may be used for grading similar materials, checking or

controlling quality level and controlling uniformity of tensile strength (Ref. 2).

As engineers, we find hardness tests useful for estimating the tensile strength of

materials. The Brinell and Rockwell Tests are the most common experiments to

determine the hardness of metals. Both Tests measure the resistance to indentation of a

metal under a static load. However, as the technology has increased the usage of very

hard steels, very thin materials, very small sized parts, etc, a number of other hardness

tests have developed, and not just for metals but for wood, rubber, plastic, and paving

materials (Ref. 2).

The Brinell Test procedures and specifications can be found in ASTM E10. The

test consists of applying a load through a steel ball with a 10-millimeter diameter for a

specific period of time. The standard for load amount, time period and hardness is shown

below in Table I.

Table 1- Brinell Standards for Load, Time, and Hardness

If the sample is expected to have a Brinell Hardness Number (BHN) greater than 450, an

indenter made of a harder material should be used (Ref. 2). After removing the load, an

indentation is left on the metal sample. By measuring the diameter of the indentation and

using the known diameter of the steel ball that applies the load, the spherical area is

calculated. The Brinell Hardness Number (BHN) is the ratio of the applied load in

kilograms to the spherical area of the indentation in mm2 (Ref. 1). In order to find the

BHN, the following equation is used:

Equation (1)

Where:

D = diameter of the steel ball, mm

d = diameter of the indentation

P = load, kg

The Brinell Hardness Number is used to give an estimation of the tensile strength of the

metal using the following equation:

T.S. = 500 x BHN Equation (2)

Where:

T.S. = tensile strength, psi

BHN = Brinell Hardness Number

The Rockwell Test procedures and specifications can be found in ASTM E18.

This test uses the depth of indentation to determine the hardness number (Ref. 1). A

minor load is applied to hold the sample in place then a major load is applied to indent

the sample. The Rockwell Test is similar to the Brinell Test because both use indentation

of a samples surface to determine hardness; however, the Rockwell Test measures depth

of indentation not diameter as in the Brinell Test. The Rockwell Test uses smaller loads

and creates smaller indentations on the sample as well (Ref.2). Also the Rockwell

Hardness Tester has a gauge on the machine that will display the Rockwell Hardness

Number, RHN, after the load is removed.

For this test, a variety of indenters are used including: steel balls ranging from

1/16-inch to ½-inch and spheroconical diamond tips (Ref.1). There are three standard

loads of 60, 100, and 150 kilograms that can be applied to a sample. Diamond tips along

with a load of 150 kg are used for hard steel, while steel balls and a load of 100 kg is used

for softer steel and aluminum. The gauge on the machine has two sets of numbers, a red

and a black. 30 hardness numbers offset the scales with the black scale being the lower of

the two (Ref.2). Each scale also provides a different pre-fix to be recorded with the

hardness number, B for red and C for black. The combination of indenter and applied

load leads to what set of numbers, red or black, are used to measure the Rockwell

Hardness Number. A diamond tip with applied load of 150 kg corresponds to the black

scale and a steel ball with 100 kg corresponds to the red scale.

The Rockwell Test is used for materials that are beyond the capabilities of the

Brinell Test and because the Rockwell Hardness Number is shown on the machine if

returns faster and more accurate hardness numbers (Ref. 2). However, the Rockwell test

does not have such an easy way to calculated tensile strength as was afforded to us by the

Brinell Test. In order to determine tensile strength, a standardized table showing the

relationship between Rockwell Hardness Numbers, tensile strength and other properties

has been developed and is provided below in Table II.

Table 2 - Relationship between Hardness Numbers and Tensile Strength

Apparatus and Test Procedures:

Figure 1 - Brinell Hardness Tester Model HB3000B

Figure 2 - Rockwell Hardness Tester Model C504

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The Apparatus used for the Brinell Hardness Test is Model HB-3000B, shown in

Figure 1. The apparatus used for the Rockwell Hardness Test is Model C504, shown in

Figure 2.

The Brinell Hardness Test requires the use of the following:

1- Brinell Hardness Tester Model HB-3000B (shown in Figure 1)

1- Testing Block with known BHN

3- Metal test samples

1- Microscope of low power

1- Ten millimeter diameter steel ball

The Rockwell Hardness Test required the use of the following:

1- Rockwell Hardness Tester Model C504 (shown in Figure 2)

1- Testing Block with known RHN

3- Metal test samples

1- 1/16 inch diameter steel ball

Both the Brinell and Rockwell Hardness Tests require three metal cubes with 1-inch sides

to be the test samples. The samples to be tested are 1020 Steel, 6061 Aluminum and 2024

Aluminum. Before the test, each sample is inspected for any defects to the surface that

could affect the results. All three samples were clean and passed inspection.

The Brinell Test consists of pressing a steel ball of 10-millimeter diameter into

the test sample for a standard amount of time, which will be 12 seconds for our

laboratory. The 10-mm steel ball will impose a load of 3000 kg for steel samples and

1500 kg for aluminum samples. This load will cause a depression to remain on the

surface of the sample after the load is removed. The spherical area of the indentation can

be calculated from the diameter of the indenter and the diameter of the depression on the

surface of the sample. For the Brinell Test, the steel ball must not deviate in diameter

more than 0.01 mm and balls of harder material are to be used if the sample has a known

BHN greater than 450 (Ref. 1). Before starting either test, a test block was used on both

the Brinell and Rockwell testers in order to verify accurate results. Tests should not be

made too close together or too close to the edge of the sample.

Procedure for Brinell Hardness Test:

1. Verify using the test block that the machine is accurate.

2. Determine the proper load to apply to the sample: 3000 kg for steel

and 1500 kg for aluminum.

3. Set the amount of time for the test. In this lab we will use 12 seconds

as our test time.

4. Select a test area on the sample, being sure to stay away for the edges

and other indentions made on the sample.

5. Turn the screw until the sample and the steel ball contact each other

and continue to turn the screw until the screw slips.

6. Push “Start” to begin the test and create an indentation on the sample.

7. Repeat step (4)-(6) two times so that a total of 3 indentations are on the

sample.

8. Measure the diameter of each indentation with a low power

microscope.

9. Determine the Brinell Hardness Number using Equation (1).

The Rockwell Hardness Test uses a steel ball 1/16-inch in diameter to indent the

surface of a sample. This test uses a smaller load and indenter therefore the indentation is

smaller and shallower. Similar to the Brinell test, the hardness number found by the

Rockwell Test is a function of the indentation on the surface of the sample caused by the

indenter under a static load (Ref. 2). However, the Rockwell Test is faster because the

Rockwell Hardness Number is read straight from the machine. The Rockwell Hardness

Number, RHN, is inversely related to the depth of indentation.

Procedure for Rockwell Hardness Test:

1. Verify using the test block that the machine is accurate.

2. Determine the indenter to use. In this lab we will use a steel ball 1/16-

inch in diameter.

3. Select a test area on the sample, being sure to stay away for the edges

and other indentions made on the sample.

4. Raise the sample against the indenter by turning the large screw until

the center gauge is vertical.

5. Use the small screw to set the dial reading to zero.

6. Press the lever down to start the test.

7. Read the RHN from the red scale on the dial and include the prefix

“B”.

8. Repeat steps (3)-(7) four times so that a total of five indentations are

on the sample.

Results:

The Table III below shows the data from the Brinell Hardness Test. Three

diameter readings were recorded for each sample. The mean of the results for each

individual sample is calculated and used as the diameter of the indentation. Knowing the

applied load, the diameter of the indenter and the diameter of the indentation, equation

(1) is used to find the Brinell Hardness Number for each sample. Using Equation (2), the

tensile strength is determined.

Table 3 - Brinell Hardness Test data and results

1020 Steel 2024 Aluminum 6061 Aluminum

Test No.

1 4.30 3.90 4.30

2 4.40 3.80 4.30

3 4.40 3.80 4.25

Mean 4.37 3.83 4.28

BHN 190 125 99.2

Tensile Strength (psi) 95000 62500 49600

Reference BHN* 179 120 95

Reference Tensile

Strength (psi)* 87000 70000 45000

Brinell Hardness Test Data and Results

Diameter (mm)

Type of Material

Table IV below shows the results of the Rockwell Hardness Test. Five tests were

completed on each sample and the mean of each sample is calculated. The mean is

recorded and used as the Rockwell Hardness Number, RHN, for each sample. Using

Table II, the tensile strength of each sample is interpolated.

Table 4 - Rockwell Hardness Test data and results

1020 Steel 2024 Aluminum 6061 Aluminum

Test No.

1 91.7 77.7 58.9

2 93.0 78.2 58.6

3 93.0 79.0 58.1

4 93.2 78.9 59.1

5 93.0 78.0 59.0

Mean 92.8 78.4 58.7

Tensile Strength (psi) 96071 71750 51360

Reference RHN** 88 75 60

Reference Tensile

Strength (psi)** 87000 70000 45000

Type of Material

Rockwell Hardness Test Data and Results

Diameter (mm)

Discussion:

Figure 3 below shows a graph of the relationship between the experimental BHN

and the reference BHN obtained from MatWeb (Ref. 3), for both the steel and aluminum

samples. The results show only a small deviation from the reference data and it should be

noted that 1020 steel showed the most deviation at 5%. Also, each sample out preformed

the reference hardness number recording higher values for hardness.

0

20

40

60

80

100

120

140

160

180

200

1020 Steel 2024 Aluminum 6061 Aluminum

Bri

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ard

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be

r

BHN

Ref. BHN

Figure 3 - Relationship between Brinell Experimental Hardness and Reference Hardness

Figure 4, shown below, contains a graph of the experimental RHN and the

reference hardness numbers given on MatWeb (Ref. 3). Both steel and aluminum samples

remained close to the reference hardness with steel once again being 5% off of reference,

but it is interesting to point out that 6061 Aluminum has fallen below the reference data

provided by MatWeb (Ref. 3). In all other cases the hardness of the samples has exceeded

that of the reference hardness. After comparing the data, both the Brinell and Rockwell

test are producing accurate numbers and a maximum deviation of 5% over all further

backs up both tests accuracy.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

1020 Steel 2024 Aluminum 6061 Aluminum

Ro

ckw

ell

Har

dn

ess

Nu

mb

er

RHN

Ref. RHN

Figure 4 - Relationship between Rockwell Experimental Hardness and Reference Hardness

0

20000

40000

60000

80000

100000

120000

1020 Steel 2024 Aluminum 6061 Aluminum

Ten

sile

Str

en

gth

(p

si)

Brinell Tensile Strength (psi)

Rockwell Tensile Strength (psi)

Figure 5 - Comparison of Tensile Strength based on Brinell, Rockwell, and Reference data

Figure 5 above shows a comparison of the tensile strength recorded for each

sample based on the Brinell and Rockwell tests. The graphs show that the Rockwell test

recorded higher tensile strength for each of the samples but both 1020 steel and 6061

aluminum were determined to have values that were similar. The sample of 2024

Aluminum recorded interesting results as the greatest difference between the Brinell

strength and Rockwell strength was found here. The Brinell test is more accurate for

finding tensile strength, based on Equation (2)’s simplicity, where the Rockwell test has

more room for error when interpolating Table II. For both tests, steel was determined to

be the sample that exceeded the reference values for tensile strength by the most. 6061

Aluminum was found by both tests to be harder than the reference values. For 2024

Aluminum, the Rockwell test showed expected results, however the Brinell test

determined that the 2024 Aluminum was not as strong as the reference tensile strength.

Looking through the formulas, it seems that the Brinell Hardness Tests was able to create

too large of an indentation in the surface of the 2024 Aluminum, recording a diameter of

3.83 mm. An indentation closer to 3.63 mm would have given the correct tensile strength

according to the reference data.

From the results shown it Figures 4, 5 and 6, it is clear that some errors have

occurred. The Brinell Test required the reading of the diameter through a scope which

could have lead to inaccuracies due to human error. Also it is possible that the load was

prematurely removed from the sample before the 12 seconds had expired. For the

Rockwell test it is possible that the numbers on the gauge were incorrectly read.

However, there are other sources of error that can be pointed to in this lab. During the set

up of the experiment it was noticed that the last inspection of the equipment was in 1999

and the label stated that both machines need to be inspected yearly.

Sample Calculations:

Brinell Hardness Test

(1020 Steel) Brinell Hardness Number, BHN

D = 10-mm

P = 3000 kg

d = 4.37-mm

BHN = 190

Tensile Strength = BHN x 500

= 190 x 500

= 95000 psi

Rockwell Hardness Test

(1020 Steel) Rockwell Hardness Number, RHN

RHN = 92.8

(Read for gauge on Rockwell Tester)

Tensile Strength = 96071

(Found using Table II)

Conclusion:

The Brinell and Rockwell experiments are two tests that are both designed to test

the hardness of a metal sample. The Brinell test measures the diameter of an indentation

in order to obtain a hardness number and the Rockwell test measures the depth of

penetration and returns a hardness number. Both tests are similar in this way but each

offered its own individual advantages: Brinell with its ease of calculating tensile strength

and Rockwell with its direct readings of hardness number for the machine. Both

experiments are also considered non-destructive.

Looking at the results it seems that both tests found our samples for the most part

to be harder than the reference numbers indicated. The most likely source of error

however seems to be the decade between inspections for both machines leading to

uncertainty in the numbers they are providing. In future tests, more experience with the

machine and metal samples along with better maintenance of the equipment would help

to reduce errors. The recorded error for the hardness numbers was less than 5% for both

the Brinell and Rockwell Hardness Tests and therefore each test can be considered

reasonably accurate in terms of the tensile strength of a sample.

References

1. Mechanics of Materials Laboratory Manual CE 3410, Department of Civil and

Environmental Engineering, Spring 2007, pT1-1 – T1-10.

2. Jacobs, C., CE 3410 Notes – “Hardness Testing”, received in class on January 13, 2009.

3. www.MatWeb.com

4. ASTM E 10 Standard Test Method for Brinell Hardness of Metallic Materials, ASTM

International, April 2001.

5. ASTM E 18 Standard Test Method for Rockwell Hardness and Rockwell Superficial

Hardness of Metallic Materials, ASTM International, April 2001.

Appendix

Appendices A1 – Original Test Data Sheet

Brinell Hardness Test

(Diameter, mm)

Rockwell Hardness Test

(RHN)

1020 Steel 4.37 91.7

93.0

93.0

93.2

93.0

6061 Aluminum 4.28 58.9

58.6

58.1

59.1

59.0

2024 Aluminum 3.88 77.7

78.2

79.0

78.9

78.0

Appendix A2 – Material Properties of Steel

Mechanical Properties Metric English Comments

Hardness, Brinell 179 179

Hardness, Knoop 200 200 Converted from Brinell hardness.

Hardness, Rockwell B 88 88 Converted from Brinell hardness.

Hardness, Vickers 188 188 Converted from Brinell hardness.

Tensile Strength, Ultimate 600 MPa 87000 psiTensile Strength, Yield 370 MPa 53700 psiElongation at Break 23.00% 23.00% in 50 mm

Reduction of Area 64.20% 64.20%

Modulus of Elasticity 200 GPa 29000 ksi Typical for steel

Bulk Modulus 140 GPa 20300 ksi Typical for steel

Poissons Ratio 0.29 0.29

Appendix A3 – Material Properties of Aluminum

Mechanical Properties Metric English Comments

Hardness, Brinell 120 120 AA; Typical; 500 g load; 10 mm ball

Hardness, Knoop 150 150 Converted from Brinell Hardness Value

Hardness, Rockwell A 46.8 46.8 Converted from Brinell Hardness Value

Hardness, Rockwell B 75 75 Converted from Brinell Hardness Value

Hardness, Vickers 137 137 Converted from Brinell Hardness Value

Ultimate Tensile Strength 483 MPa 70.0 ksi AA; Typical

Tensile Yield Strength 345 MPa 50.0 ksi AA; Typical

Elongation at Break 18.00% 18.00% AA; Typical; 1/16 in. (1.6 mm) Thickness

Modulus of Elasticity 73.1 GPa 10600 ksiAA; Typical; Average of tension and compression. Compression modulus is about 2% greater than tensile modulus.

Notched Tensile Strength 379 MPa 55000 psi 2.5 cm width x 0.16 cm thick side-notched specimen, K t = 17.

Ultimate Bearing Strength 855 MPa 124000 psi Edge distance/pin diameter = 2.0

Bearing Yield Strength 524 MPa 76000 psi Edge distance/pin diameter = 2.0

Poissons Ratio 0.33 0.33

138 MPa 20000 psi

@# of Cycles 5.00e+8 @# of Cycles 5.00e+8

Machinability 70.00% 70.00% 0-100 Scale of Aluminum Alloys

Shear Modulus 28.0 GPa 4060 ksiShear Strength 283 MPa 41000 psi AA; Typical

Fatigue Strength completely reversed stress; RR Moore machine/specimen