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Hardness Testing Experiment

ME 3228: Materials and Mechanics Lab

Section: 519

Tyler Myers Patrick Scott Johnny Mckay Grant Goodwin Camron Claborn

Due: March 27th, 2014

Turn in to: Cargi M, Bakirci

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Summary

This experiment was tested in order to see how different types of materials would resist

plastic deformation or permanent indentation. The materials used were: Aluminum

7075-T24, Aluminum 6061-T6, AISI 1045, and AISI 1018. By using an indenter, which is

generally just a harder type of material, made of steel or diamond the machine pressed

down on the previously set up specimen until a hardness measurement was read out on

the front panel of the machine. For the Rockwell Hardness testing the results had came

out as a: 0% error for the Alum. 7075, 15.2% error for the Alum. 6061, 90% error for the

AISI 1045, and 39.4% error for the AISI 1018. The Brinell Hardness results were: 14.7%

error for the Alum. 7075, 13.7% error for the Alum. 6061, 60.1% error for the AISI 1045,

and 54.8% error for the AISI 1018. And lastly, the results of the tensile strength

measurements were: 3.7% for the Alum. 7075, 20.3% for the Alum. 6061, 59.5% for the

AISI 1045, and 53% for the AISI 1018. From all the results collected and compiled

together, there are several factors that come into play when determining the stronger

material. Factors like, geometry, such as between round or flat testing surface. Also

heat treatment, when looking at the Aluminum specimens there seems to be a

determining factor of which of the two samples handled the hardness testing better.

All of the information will be explained in detail now.

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Table of Contents

List of Figures ________________________________________________________4

List of Tables ________________________________________________________5

List of Equations ________________________________________________________6

Summary ________________________________________________________2

Introduction ________________________________________________________7

Theory ________________________________________________________7

Test Description ________________________________________________________10

Results ________________________________________________________11

Discussion ________________________________________________________15

Conclusion ________________________________________________________16

References ________________________________________________________17

Appendix ________________________________________________________18

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List of Figures Page

Figure 1: Classic Rockwell Testing Device 8

Figure 2: Various indenters 8

Figure 3: Minor-load and Major-load 8

Figure 4: Rockwell/Brinell Conversion Chart 9

Figure 5: Testing Setup with the Buehler Macromet 5100T 10

Figure 6: Aluminum and Steel Testing Specimens 11

Figure 7: Experimental vs Reference Values for Rockwell Hardness 12

Figure 8: Experimental vs Reference Values for Brinell Hardness 13

Figure 9: Experimental vs Reference Values for Tensile Strength 14

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List of Tables Page

Table 1 - Rockwell Hardness for Four Samples 10

Table 2 - Brinell Hardness for Four Samples 11

Table 3 - Tensile Strength for Four Samples 12

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List of Equations Page

Equation 1: Tensile Strength 13

𝑇𝑆 (𝑀𝑃𝑎) = 3.45 ∗ 𝐵𝐻𝑁

Equation 2: The Deviation Equation 11

𝑑𝑖 = 𝑥𝑖 − 𝑥𝑎𝑣𝑒

Equation 3: The Mean Deviation Equation 11

𝐷𝑚𝑒𝑎𝑛 = ∑𝑑𝑖

𝑛

𝑛

𝑖=1

Equation 4: The Standard Deviation Equation 11

𝑆 = √∑(𝑥𝑖 − 𝑥𝑎𝑣𝑒)2

(𝑛 − 1)

𝑛

𝑖=1

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Introduction

Hardness can be defined as how resistant solid matter is to permanent shape change when a

force is applied. A material’s hardness is a useful property to know since it allows us to predict

how that material will react when a load is applied, which can save lives as well as costs when

designing machines and structures.

There are three types of hardness that can be determined for a material; scratch hardness,

indentation hardness, and rebound hardness. In this lab we will be determining the indentation

hardness of four different metals, Aluminum 7075 T-24, Aluminum 6061 T-6, AISI Steel 1045,

and AISI Steel 1018. There are various scales used to define indentation hardness, out of these

there are two that this experiment is concerned with, the Rockwell Scale and the Brinell Scale.

After determining each metal’s hardness, their tensile strength can be calculated. With these

results, comparisons can be made about how each metal’s chemical composition,

manufacturing methods, and heat treatments affect the material’s resistance to deformation.

Since the specimen’s used in this experiment have been tested numerous times before, the

results obtained in this experiment can be compared to those acquired previously. The

expectations are that the results obtained in this experiment will be fairly similar to the

standards used for each metallic alloy with some slight errors.

Theory

Hugh M Rockwell and Stanley P Rockwell patented the original Rockwell hardness-testing device

on July 15, 1914 [Fig. 1]. This testing setup uses an indenter made of material harder than the

test specimen (in this case either steel or diamond (Fig. 2)) that is pressed into the test

specimen to produce an indention, which can be measured to determine the material’s

hardness.

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An important component of the Rockwell test is the Minor-load that is applied before the Major-

load, which causes the measurable indention. The Minor-loading of the specimen helps with the

accuracy of the test by slightly going through the material’s outer surface. This allows the test

to be conducted without the interference of surface imperfections. (Fig. 3)

Figure 1 – Classic Rockwell Testing

Device

Figure 3 – Minor-load (left) and Major-load (right)

Figure 2 – Various indenters

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The Rockwell scale and the Brinell scale are related and can be converted to each other by

using charts (Fig. 4), which are easily accessed either online or in our lab.

Using the Brinell Hardness Number (BHN) it is possible to calculate a materials tensile strength

using the following equations…

𝑇𝑆(𝑀𝑃𝐴) = 3.45 ∗ 𝐵𝐻𝑁

or

𝑇𝑆(𝑝𝑠𝑖) = 500 ∗ 𝐵𝐻𝑁

Figure 4 – Rockwell/Brinell Conversion Chart

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Test Description

This experiment is was up to test the hardness of four different materials: Aluminum

7075 -T24, Aluminum 6061-T6, AISI 1045 Steel, and AISI 1018 Steel. Steel specimens

used were the round gripping section of the same dog-bones that are used in tensile

tests. The Aluminum specimens were flat extrusion samples provided by Texas Tech.

The machine used in these tests was the Buehler Macromet 5100 Rockwell Type

Hardness Tester, manufactured by the Mitutoyo Corporation. To apply the load to the

samples, a 1/16 in. steel ball indenter was used in the Macromet. Below is a picture of

the testing setup.

Figure 5 - Testing Setup with the Buehler Macromet 5100T

The next figure shows the specimens used in this experiment.

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Figure 6 - Aluminum and Steel Testing Specimens

The testing procedure is as follows:

1. Turn on the Marcromet Rockwell Tester.

2. Fix the appropriate indenter and anvil in the machine.

3. Select the appropriate indenter type on the control panel.

4. Select the appropriate load.

5. Place specimen on the anvil.

6. Raise the anvil by rotating handle to apply preload. Slowly raise it further

until the display reads at least 360.0, but do not exceed 360.8.

7. Press start on the tester, wait for it to complete, then record the hardness

value.

8. Repeat the test three times on different surfaces on the specimen.

9. Lower the anvil, replace the specimen then repeat the procedure for the

rest of the testing specimens.

Results

Equations 2, 3, and 4 are used to calculate the standard deviation for the Rockwell

hardness values obtained in the experiment. These values are shown in the following

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table and displayed in Figure 7. All HR values are derived on the HRB scale unless noted

otherwise. Note that the steel specimens are round thus needed to be corrected for.

This is done by using the Cylindrical Correction Chart from the Wilson Instruments

Conversion Chart, found in the Appendix.

Table 1 - Rockwell Hardness for Four Samples

Specimen Composition Ave. HR EXP. Std. Dev. HR REF. Percentage of

Error

Aluminum 7075 (flat)

T24 87.0 1.83 87.0[5] 0.0%

Aluminum 6061 (flat)

T6 50.9 2.44 60.0[2] 15.2%

AISI 1045 (round) - 26.61 1.22 14.01[1] 90.0%

AISI 1018 (round) - 99.0 0.46 71.0[4] 39.4%

Note 1. HRC scale

Figure 7 -Experimental vs Reference Values for Rockwell Hardness

0.0

20.0

40.0

60.0

80.0

100.0

120.0

Aluminum7075

Aluminum6061

AISI 1045 AISI 1018

HRB HRB HRC 1 HRB

Rockwell Hardness Exp.

Rockwell Hardness Ref.

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Brinell hardness was tabulated using the Wilson Instruments Conversion Chart. Table 2

shows the experimental and reference Brinell hardness values along with a percentage

of error. Figure 8 represents the data in the table.

Table 2 - Brinell Hardness for Four Samples

Specimen BHN EXP. BHN REF. Percentage of

Error

Aluminum 7075

172 150[5] 14.7%

Aluminum 6061

108 95[2] 13.7%

AISI 1045 261 163[1] 60.1%

AISI 1018 195 126[4] 54.8%

Figure 8 - Experimental vs Reference Values for Brinell Hardness

Equation 1 was used to calculate the tensile strength from the Brinell hardness for each

specimen. Table 3 and Figure 9 both compare the experimental values and reference

values of the tensile strengths.

0

50

100

150

200

250

300

Aluminum7075

Aluminum6061

AISI 1045 AISI 1018

Brinell Hardness Exp.

Brinell Hardness Ref.

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Table 3 - Tensile Strength for Four Samples

Specimen Tensile

Strength EXP. (MPa)

Tensile Strength REF.

(MPa)

Percentage of Error

Aluminum 7075

593 572[5] 3.7%

Aluminum 6061

373 310[2] 20.3%

AISI 1045 901 565[1] 59.5%

AISI 1018 673 440[4] 53.0%

Figure 9 - Experimental vs Reference Values for Tensile Strength

0

100

200

300

400

500

600

700

800

900

1000

Aluminum7075

Aluminum6061

AISI 1045 AISI 1018

(MP

a)

Tensile Strength Exp.

Tensile Strength Ref.

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Discussion

The results received from the data and graphs above shows the different material

properties of each material tested. Now from the results obtained, it is evident that

steel is a stronger material than aluminum. The strength of steel and aluminum also

depends on the heat treatment such as the difference between 1045 steel and 1018

steel or 7075-T24 aluminum and 6061-T6 aluminum, along with the geometry such as

round steel and flat aluminum. From the data above, the 1045 steel is stronger and has

more elasticity than the 1018 steel. Also when comparing the aluminum it is clear that

the 6061 treatment is stronger than the 7075. Looking at Table 1, shows the

experimental Rockwell hardness to theoretical which presents that 7075-T24 aluminum

and 1018 steel are pretty close to each other’s values and the experimental data is

incorrect compared to the theoretical data. The data shows that the 7075 aluminum is

smaller than the 1018 steel but in reality the 7075 aluminum is a bigger value than 1018

which shows that flat 7075 aluminum is harder than round 1018 steel and 1045 round

steel. Along with that, the 6061 flat aluminum is harder than the 1045 round steel. In

this part of the experiment there were a few discrepancies from the experimental data

being too low or too high compared to the theoretical values of the Rockwell hardness

test. Now when looking at the Brinell hardness results, the experimental values are too

high compared the theoretical results. In the theoretical Brinell hardness it shows that

both steels are harder than both aluminum specimens tested. Even in the experimental

data collected, the steel in harder than the aluminum, but the experimental values for

the Brinell hardness was a lot higher than it was supposed to. With this in mind, the

round steel is harder than the flat aluminum so the geometry plays a role in the Brinell

hardness of the material. Table 3 of the results shows the tensile strength of each of

the four materials tested. It is clear that the steel is harder than the aluminum but

when comparing the 1045 steel to the 7075 aluminum it shows that the flat aluminum

is slightly harder than the steel, but the 6061 is weaker than the 1018 steel. When

comparing all of these materials together from the data calculated, the heat treatment

of the material plays a vital role in the ductility and or brittleness of the material. Heat

treatment can change strength and ductility of a material along with the geometry of

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the material such as round steel compared to flat aluminum. The heat treatment and

shape determines the strength of the material, and the strength of the material

determines the application in which that material can be used.

Conclusion

So in conclusion the Hardness testing experiment was a great way to see how the heat

treatment and the geometry of the material affect the material properties and the

hardness of the material. This experiment proved that the aluminum Rockwell hardness

is greater than steels but aluminums Brinell hardness is smaller than steel. Also that

the tensile strength of round steel is greater than flat aluminum which helps us

understand that the shape of a material can determine how much stress can affect it.

The goal of this experiment was satisfied in the fact that steel is harder than aluminum

and that rolling increases hardness compared to flat material. With experiments like

this it is easier to see what materials to use in different applications and know how

there geometry makes them harder or weaker and how it will react under stress. The

downside of this experiment is that when testing the material it can be structurally

flawed or defected in any way which will end in inaccurate results. Or the material can

be already used and the strength of it is weakened. Overall this experiment proved how

heat treatment and geometry of the material such as rolled or flat can change strength

and ductility of a material. To improve this experiment I would recommend using un-

used material to get a more accurate result and decrease the percent of error.

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References

[1] "1045 Medium Tensile Carbon Steel Bar." Interlloy Engineering Steels + Alloys 1045

Medium Tensile Carbon Steel Bar Comments. N.p., 2011. Web. 04 Mar. 2014,

http://www.interlloy.com.au/our-products/carbon-steels/1045-medium-

tensile-carbon-steel-bar/.

[2] "6061-T6 Aluminum." - Material Properties Data. N.p., 2013. Web. 04 Mar. 2014,

http://www.makeitfrom.com/material-data/?for=6061-T6-Aluminum.

[3] Chaudhuri, Jharna, 2014. Material and Mechanics Laboratory Experiments, Texas

Tech University, Cognella, INC., United States of America.

[4] "AISI 1018 Mild/Low Carbon Steel." AISI 1018 Mild/Low Carbon Steel. N.p., n.d.

Web. 02 Mar. 2014, http://www.azom.com/article.aspx?ArticleID=6115.

[5] "ASM Material Data Sheet." ASM Material Data Sheet. N.p., n.d. Web. 02 Mar. 2014,

http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA7075T6.

[6] Rockwell, H.M. Rockwell, S.P., (1919). Patent No.1,294,171. Washington, DC: US

Patent and Trademark Office.

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Appendix

Hardness Test Data Sheet

Table 5.1 from pg. 47 in Material and Mechanics Laboratory Experiments [3]

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The conversion chart used: