Tensile Test

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Tensile Test Florida International University Seyed Alavi (Groupe 1) Panther Id: 2630064 03/02/2010 Section 1

Transcript of Tensile Test

Page 1: Tensile Test

Tensile Test

Florida International University

Seyed Alavi (Groupe 1)

Panther Id: 2630064

03/02/2010

Section 1

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Introduction

A tensile test, also known as a tension test, tests a material's strength. It's a mechanical test where a pulling force is applied to a material from both sides until the sample changes its shape or breaks. It's is a common and important test that provides a variety of information about the material being tested, including the elongation, yield point, tensile strength, and ultimate strength of the material. Tensile tests are commonly performed on substances such as metals, plastics, wood, and ceramics.

By performing the tensile test the substance from tensile testing can be learned. As the materials continue being pulled out until it breaks, a good, complete tensile profile can be obtained. A curve will result showing how it reacted to the forces being applied. The point of failure is of much interest and is typically called its "Ultimate Strength" or UTS on the chart.

For most tensile testing of materials, it can be noticed that in the initial portion of the test, the relationship between the applied force, or load, and the elongation the specimen exhibits is linear. In this linear region, the line obeys the relationship defined as "Hooke's Law" where the ratio of stress to strain is a constant, or E is the slope of the line in this region where stress ( ) is proportional to strain ( ) and isσ ε called the "Modulus of Elasticity" or "Young's Modulus".

The modulus of elasticity is a measure of the stiffness of the material, but it only applies in the linear region of the curve. If a specimen is loaded within this linear region, the material will return to its exact

Figure 1-stress vs strain

Figure 2-stress vs strain

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same condition if the load is removed. At the point that the curve is no longer linear and deviates from the straight-line relationship, Hooke's Law no longer applies and some permanent deformation occurs in the specimen. This point is called the "elastic, or proportional, limit". From this point on in the tensile test, the material reacts plastically to any further increase in load or stress. It will not return to its original, unstressed condition if the load were removed.

Procedure

The width and thickness of the specimens which is steel # 28 model D25668 was Measured and recorded. The software will request these values later on. Also, for the specimen, the length of the segment with a reduced cross sectional area was measured. The steel specimen was installed into the jaws of the Test machine, as shown in figure. The position of the jaws can be adjusted with the buttons on the lower right side of the Test base.

The computer software was used to calculate the elongation and also to illustrate the graph of the tensile test. The data also can be imported to Microsoft Excel. The proportional limit point and the yield strength and the ultimate strength and the fracture strength points were obtained and recorded.

Data and Analysis

The specimen that was used in this experiment was D23689, which had 8-inch length and 0.0571 inch thickness and 0.5028 inch width. Table 1 shows the value of most important points in the Stress versus strain graph. It was obtained that the specimen deforms completely when the stress pass 35.3 KSI. This result was obtained form plotting the original data to excel sheet and graph them. The linear straight line to the cross section of the graph indicates the magnitude of the points.

Figure 3 -The tensile machines

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Table 2

Point Strength (KSI)Proportional Limit 34.926

Elastic Limit 35.108Yield Strength 35.291

Ultimate Strength 52.200Fracture Strength 37.559

Figure 1 shows the stress versus strain graph. It was obtained that when the stress increases the strain increases too. Thus, the specimen deforms too. At some certain points of strain, the deformation is in elastic range. But when the strain pass point 0.05, it goes to plastic range which wont come back to the original shape. As it shown, at 0.4 inch, the specimen brakes and the experiment end. The 0.2 % parallel shift line is shown to calculate the yield point at stress axis.

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

10000

20000

30000

40000

50000

60000

Stress vs. Strain Graph

Series2Parallel LineLinear (Parallel Line)

Strain (in/in)

Stre

ss (

psi

)

Figure 4-Stress vs strain

Table 1-Specimen specification

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Figure 2 also shows the Load versus deformation. The load has a direct relationship to stress. When load increase, the stress increases too and as a result the spice men deforms. The critical point for load is 1050 Ib which the specimen change its phase from elastic to plastic.

0 0.2 0.4 0.6 0.8 1 1.20

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400

600

800

1000

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1600

Load vs. Deformation 0.02% shif lineLinear ( 0.02% shif line)

Deformation (in)

Forc

e (l

b)

Figure 5- load vs deformation curve of the specimen

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Figure 6- load vs deformation curve of the specimen obtain from the sofrware

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Table 2 shows the calculation of module of elasticity based on stress and strain. The average value of stress and strain for all the steps was used to determine the value of module if elasticity.

Table 3- Force, Stress, Strain and modulus chart

FORCE (lbs) EXT MOD (in)STRAIN (in/in) STRESS (psi)

596.6829224 0.081004453 0.027001484 21107.62197613.4852905 0.081306749 0.02710225 21702.00472631.0200806 0.081683903 0.027227968 22322.29684648.5405884 0.081986199 0.027328733 22942.08374666.7503052 0.082289937 0.027429979 23586.25136684.7302246 0.082593673 0.027531224 24222.28991701.3745117 0.082891649 0.02763055 24811.08055717.6956787 0.083130609 0.027710203 25388.44084735.0004272 0.083421393 0.027807131 26000.59526751.3862305 0.083654596 0.027884865 26580.24205768.5402222 0.083969846 0.027989949 27187.06346785.7946167 0.084275026 0.028091675 27797.43662803.1998291 0.08457588 0.02819196 28413.14494

E 6136642.864 psi

Area 0.0282686 in^2

Figure 14 was illustrated to show the value of E, which is the Modulus of Elasticity fir specimen. It is quite understandable that the Stress versus strain graph has the linear relationship. Thus, the slope of the graph gives us the magnitude of the module of elasticity. Because the module of elasticity is equal to Stress over strain. For the specimen that was used, the modulus of elasticity was determine 6E+06 Psi

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0.0268 0.027 0.0272 0.0274 0.0276 0.0278 0.028 0.0282 0.02840

5000

10000

15000

20000

25000

30000

f(x) = 6231812.1696831 x − 147285.472806773

Modulus of Elasticity Calculation (E)

Series2Linear (Series2)

Strain (in/in)

Stre

ss (

psi

)

Figure 5

From the graph above, the Modulus of elasticity (E) was determined to be 6E6 psi.

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Table 3 shows the original data, which was obtained from computer software that was used in this experiment. All the data was exported to excel sheet.

Table 4- original data obtained from software

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Discussion

In the tensile test experiment our main goal was to find the elongation and the stress, which was applied to our sample. The stress of a material can be compute by dividing force over Areal. The cross section of our sample was 0.0282686 in^2 and force start from 22.62 up to1061.76. Our sample will deform totally in that force and will fail.

Base on the graph of stress versus strain, the stress of the material at proportional limit, Elastic limit, Yield strength, Ultimate strength and Fracture strength points were recorded and shown in table 1. Before Yield strength point, our sample is in elastic range. But once the force increases and pass this point, our material will go to plastic phase which means it will deform totally and never come back to its original shape.

In order to find the value of each point from graph, a straight parallel line with the 0.002 shifts and same slop of the original graph was drawn. This line is shown in figure 2. The cross section of this line and the graph will give us our Yield point and the Elastic point is the average value of our Yield point and Proportional limit point.

Figure 3 was plotted base on the original number, which was taken from our software. But it was shifted to the center of X and Y-axis in order to find the exact value of module of elasticity. The module of elasticity is the slop of our graph. In another word, the module of elasticity was calculated from diving stress our strain. The table 2 shows the value of the stress and strain related to the forces that were applied to our sample. The graph 2 shows the just the straight portion of our stress versus strain graph.

The original graph, which was recorded from computer software, was illustrated in figure 3. In addition, the excel sheet that was received from the software is included in this report. The last column of the excel sheet is the stress which was computed from the force over our cross section area.

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Conclusion and Recommendation

In this experiment we found the deformation steel # 28 model D25668. The deformation was computed by computer software. Also, the stress related to the force was computed. The stress of five important points, which are; proportional limit, elastic limit, yield point, strength point and the fracture point were computed. The graph of stress versus strain was plotted to find the modulus of elasticity. This procedure of calculation is very important because we can design our material base on the elongation and the total stress, which our material can tolerate.

As a recommendation, the accuracy of the software should be checked before doing the experience, because if we get a wrong value for elongation, all of the calculation will have a significant error.

References:

1. Beer, Ferdinand P. (2009). Mechanics of Materials. McGraw-Hill.

2. Dr. Bao (2009). Mechanics and Materials Science Lab Experiment 5 Handouts.