Lab 5: Tensile Testing of a Metal and a Polymer

Oliver Bashan

10/6/2014

MatSci Section 3

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Table of Contents

Abstract Pg. 2

Introduction.. Pg. 2

Procedure Pg. 2

Results and Observations. Pg. 3

Discussion Pg. 6

Conclusion.. Pg. 6

References.. Pg. 6

Tables and Charts.. Pg. 6

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Abstract:

The importance of this lab is to show how tensile strength and other properties of a given

material are determined and compared to literature using lab testing techniques. The elongation and

change in cross sectional area are the two main measurements that are required to produce the data to

be compared.

Introduction:

Mechanical testing is one if not the most important way to test materials and to determine what

the best material for any given job is. Nothing is better than putting a material in a machine that will

simulate the conditions that the material will face in the real world. On top of production similar

conditions, the machine can exceed the every day to day forces that the material will face to test its

ultimate limit. Formulas can only get one so far and because formulas are based off of theories that are

usually very accurate, mechanical testing is the only way to either confirm or deny the mathematical

calculations. Since hardly any given material is perfectly made due to large quantities, quality control

and just pure luck, not all parts of the same given material will have exactly the same strength

properties. There are many examples where materials including aluminum and polymers are used;

airplanes, boats, bridgesetc.

Procedure:

Open up the TESTVIEW2 software, then click RUN and then HOLD to pause the program. Click

on the SYSTEM button and set the units to N for Newtons, stroke to cm and STROKE RANGE to 4%. The

LOAD is the force being applied and the STROKE is the change in length of the test specimen. Next click

X-AXIS to set the stroke. Click HOLD and the POSITION 0 to set the machine back to its original position.

A few dimensions were needed before the samples could be placed into the machines. The width,

thickness, and test section length was measured using calipers. The test section length is the section

of the material that is under the highest stress. Once the polymer was put in place, centered between

the jaws, the 8 allen screws could be tightened to secure the test piece. For the aluminum, the two pins

needed to be pushed though the holes in the machine jaws and in the test piece.

For polymer sample:

Once the sample is mounted, press RAMP to set CONTROL to STROKE, enter 1.4 for

FINAL. This is used to set the total maximum stroke distance and then .2 for RATE, this is the rate of

movement. Next press SET to close the ramp window. Set the DATA POINTS to 10,000, the press CLEAR

DATA and then HOLD. The test will now begin and the jaws of the machine will start moving. The

computer will now record the data and sketch a graph of the force vs. stroke in the TESTVIEW2 window.

Once the sample fails or breaks, or once the stroke limit is reached, press HOLD. Click POSITION 0 then

SAVE YOUR DATA.

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For aluminum sample:

Once the sample is mounted, press HOLD then in the LOAD ENTRY box, enter 40N and

press SET LOAD. Next, press HOLD again to engage the command. The gage length of the extensometer

needs to be measured with the supplied calipers to have a starting value. Once the measurement is

made and recorded, the extensometer can be put onto the sample by pulling back the clips and sliding

onto the aluminum. Now, press OFFSET, and once the windows pops up, press ZERO STRAIN then OK.

This sets the strain to 0. Press RAMP and set CONTROL to STROKE, then enter .5 for FINAL, and .1 for

RATE. Press SET to close the ramp window. After this is completed, the TA came to check the setup and

to confirm that everything was done properly to ensure safe operation. Press CLEAR DATA and then

HOLD to start the test. Once the sample failed, POSITION 0 was pressed followed by SAVE YOUR DATA.

The ending extensometer gage length will be recorded by the TESTVIEW2 software so there was no

need to measure it by hand.

Results:

Figure 1: Stress Vs. Strain curve for the Polymer test sample

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Figure 2: Slope of Polymer sample producing Youngs Modulus

y = 17294x + 134.09 R = 0.9889

0

100

200

300

400

500

600

700

800

900

1000

-0.01 0 0.01 0.02 0.03 0.04 0.05

Series1

Linear (Series1)

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Figure 3: Stress Vs. Strain curve for the Aluminum test sample

Figure 4: Slope of Aluminum sample producing Youngs Modulus

0

5000

10000

15000

20000

25000

30000

0 0.1 0.2 0.3 0.4 0.5

Stre

ss

Strain

Stress vs. Strain Aluminum

Crosshead

Extensometer

y = 806908x - 16441 R = 0.9721

0

5000

10000

15000

20000

25000

0 0.01 0.02 0.03 0.04 0.05

Series1

Linear (Series1)

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Discussion:

On an atomic level, the samples cubic structure is being pulled out of its original shape. The

crystal structures must be able to re-arrange themselves in the correct orientation or the material will

fail and break. No new bonds are formed which renders the material useless. Aluminum is far less

elastic and isnt as able to reform new bonds as well as the Polymer which is why it cant stretch as far

and breaks earlier. The Polymer is a lot more elastic, allowing it to stretch and get skinnier before failing

and breaking. The extensometer is a lot more accurate as it is measuring the beginning and end gage

length, strain. Measurements were done accurately, at very small intervals, every time the computer

logged the data. The crosshead displacement data is based on no-precise measurements made by hand

estimating precise beginning gage length and no accurate ending gage length was obtained.

Literature Experimental

Aluminum 70.3 GPa 80.6 GPa

Polycarbonate 2.6 GPa 1.729 GPa Figure 5: Comparison of Young's Modulus between Literature and Experimental values

Conclusion:

This lab went to show how a weaker material, Polycarbonate, can stretch farther than a stronger

material, Aluminum. The difference between the two materials was measured and compared producing

a strong indication that Aluminum does in fact have a higher Youngs Modulus. This lab also shows how

off the Literature and Experimental values may be due to user error and machine error. It is possible

that these machines were not as accurate as the ones used by the authors of the book or just that

human error including caliper measurements has a larger part in it than previously thought.

References:

No references were used for this lab.

Tables, Charts:

Polymer Aluminum

Youngs Modulus 1.7293 GPa 80.6909 GPa

Yield Stress .1396 GPa 1.6340 GPa

Ultimate Strength .1450 GPa 2.4001 GPa

Fracture Stress .1450 GPa 1.8803 GPa

Strain to Failure .0192 GPa .0366 GPa