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Florida Institute of Technology College of Engineering Department of chemical Engineering CHE 3265 – Materials Laboratory Tensile Test for Aluminum 6061 Alloy (Untreated) Experiment Performed on: February 8, 2016

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Page 1: my.fit.edumy.fit.edu/~akurdi2012/Materials Lab/Tensile Test/Tensile... · Web viewFlorida Institute of Technology College of Engineering Department of chemical Engineering CHE 3265

Florida Institute of Technology

College of Engineering

Department of chemical Engineering

CHE 3265 – Materials Laboratory

Tensile Testfor

Aluminum 6061 Alloy(Untreated)

Experiment Performed on: February 8, 2016Report Submitted: February 15, 2016

Instructor: Prof. Vipuil KishoreGSA: Thuy-Uyen Nguyen

Performed By: Abdullah Kurdi

Page 2: my.fit.edumy.fit.edu/~akurdi2012/Materials Lab/Tensile Test/Tensile... · Web viewFlorida Institute of Technology College of Engineering Department of chemical Engineering CHE 3265

Introduction:

The tensile test is one of the fundamental mechanical tests that can be performed on a material to learn about its characteristics. The test involves pulling on a material from two ends and applying tension on it. As tension increases, the material expands until it breaks. The two variables that are being recorded are the applied force “Stress” and the change in length “Strain.”

Using the stress and strain data a curve can be generated to show the relationship between them; from the stress vs. strain curve, several properties about the material can be determined; these properties are the Modulus of Elasticity, MOE, the Yield Stress, YS, the Ultimate Tensile Stress, UTS, and the Rupture Stress, RS.

The modulus of elasticity, MOE, is the slope of the linear part of the stress vs. strain curve, which is the elastic region, the slope measures the stiffness of the material. The yield stress, YS, is the point at which the material starts to undertake plastic deformation after undergoing elastic deformation. The ultimate tensile stress, UTS, is the maximum stress that a material can withstand in the plastic region before it starts to fail. Finally, the rupture stress, RS, is the point at which a material fails or breaks.

Materials in this test exhibit one of two behaviors, ductile or brittle. A ductile material is a material that undergoes plastic deformation for a significant amount of strain before it breaks; a brittle material is a material that does not undergo plastic deformation for a significant amount of strain and breaks fast. In this experiment, an aluminum alloy, Al 6061 (Aluminum with Magnesium impurities), undergoes the tensile test to determine its properties against external forces.

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Experimental Procedure:

The experiment began with measuring the radius of the cylindrical aluminum sample using a caliper, and recording the error of the measurement. The cylindrical aluminum sample, as shown in Figure 1 below, was then placed in the Universal Tensile Tester, as shown in Figure 2 below. The sample was locked in the machine using the upper and lower clamps, and finally an extensometer was placed on the sample to record the strain values using the computer, as shown in Figure 3 below.

Both the Universal Tensile Tester and the Extensometer are connected to the computer were the values of stress and strain are recorded.

XS Area=π D2

4; Stress (σ )= Force

Area;Strain (ϵ )=Change∈length

Initial length

The machine was turned on, and the test was started; values of stress and strain were recorded with respect to time. As time passed, it was noticed that the sample was stretching, and after a period of time, the sample started necking, soon after that it broke.

Figure 1: Cylindrical Aluminum 6061 Alloy Sample (1)

Figure 2: Universal Tensile Tester (2) Figure 3: Extensometer placed on the sample(1)

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Clamps

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Results:

From the collected stress and strain data, a plot of stress versus strain can be generated as shown in Figure 4:

Figure 4: Stress vs. Strain for Aluminum 6061 Alloy (1)

It can be noticed that the sample undergoes elastic deformation in the initial linear part of the graph; then the sample undergoes plastic deformation beyond the yield stress point. The sample continues to experience plastic deformation until it reaches a maximum point, where the Ultimate Tensile Stress is, and then it starts to approach the Rupture Stress point, where the sample fails.

The Modules of Elasticity was found to be (940 ± 2)*104 psi; the Yield Stress was found to be 42700 ± 400 psi; and the Ultimate Tensile Stress was found to be 46400 ± 400 psi.

The following Figures 5, 6, and 7 show the sample after the test was done, the necking part of the sample, and a before and after the test image of the sample.

Figure 5: The Aluminum Sample after the Tensile Test (1)

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Figure 6: The Necking in the Sample (1)

Figure 7: The Sample Before and After the Tensile Test (1)

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Discussion:

Table 1: Experimental Results versus Literature Values

Property Experimental Literature 1(3) Literature 2(4)

MOE (940 ± 2)×104 psi (10 ± 1)×106 psi (10 ± 1)×106 psiYS 42700 ± 400 psi 40000 ± 1000 psi 35000 ± 1000 psi

UTS 46400 ± 400 psi 45000 ± 1000 psi 38000 ± 1000 psi

In Table 1, the experimental values are compared to two different literature values. It can be noticed that the experimental MOE value is less than the both literature value, yet it is within the error boundary. The experimental YS value is greater than both literature values, and is not within the error boundary. Finally, the experimental UTS value is also greater than both literature values, yet it is partly within the error boundary of Literature 1, but not Literature 2.

The error in the MOE value could be due to omitting some points that were in the elastic region; the error in the YS value could be due to estimating it using the 0.2% Strain offset method, which could have overestimated the value. As for the error related to the UTS value, it could be due to shape and or the size of the sample.

The mechanical properties of Al 6061 can change depending on the temper or heat treatment. The value of the MOE does not change regardless of the temper and is (10 ± 1) ×106 psi. Annealed Al 6061 has a UTS value of 18,000 psi, a YS value of 8,000 psi, and exhibits 25-30% higher elongation(5). Aluminum 2024 alloy has a UTS value of 70000 psi, a YS value of 50000 psi, and an 18 % elongation (6).

Materials in the tensile test exhibit one of two behaviors, ductile or brittle fracture. A ductile material is a material that undergoes extensive plastic deformation before it cracks; on the other hand, a brittle material is a material that has a relatively small plastic deformation for a significant amount of strain and breaks fast. Figure 8, below, shows the difference between both behaviors.

Figure 8: Brittle material versus Ductile material with respect to stress and strain

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From Figure 8, it can be concluded that the Aluminum 6061 Alloy is a ductile material.

It is important to note that the area under the curve at any point corresponds to the strain energy density, strain energy per unit volume, which is required to stress the material to that point in the curve. The area under the curve up to the yield stress is the modulus of resilience; i.e. it is the strain energy density required to stress the material to its yield stress (8).

From Figure 6, it can be noticed that the material started necking as stress was being applied; the material exhibited a cup and cone fracture type of failure mechanism.

Several sources of error in the experiment were encountered that could have affected the results. First the systematic error in the tensile test machine, which could be due to the machine not being calibrated after a previous experiment. The error in the extensometer, also could be due to it not being calibrated.

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References:

1) Dr. Kishore, Canvas.fit.edu, Materials Laboratory CHE 3265-012) Jinan Kehui Testing Instrument CO.,LTD3) Callister Textbook4) Askeland Textbook5) Aluminum Standards and Data 2006 Metric SI, by the Aluminum Association Inc.6) http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA2024T37) https://www.nde-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/

Tensile.htm8) http://materion.com/~/media/Files/PDFs/Alloy/Newsletters/Technical%20Tidbits/Issue

%20No%2022-%20Elastic%20Resilience.pdf

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Appendix A: Sample Calculation

Area of the Cylindrical Sample

XS Area= π D2

4=

π (0.25)2

4=0.049 1 in2

Error in Area of the Cylindrical Sample

d ( XS Area )=|( ∂ A∂ D )× dD|=|2 πD

4×dD|=0.0004 i n2

Stress

σ= FXS Area

= Fπ D2

4

=100.31344π (0.25)2

4

=2044 psi

Error in Stress

d σ=|( ∂σ∂ F )× d F|+|( ∂ σ

∂ D )× dD|=|4 D−2

π×dF|+|4 F

π(−2 ) D−3 × dD|

d σ=|4 (0.25)−2

π×1|+|4(100.31344)

π(−2 )(0.25)−3× 0.001|=37 psi

Strain

ϵ=lf −lo

lo=0.00000562−0

2=0.000003∈¿∈¿

Error in Strain

dϵ=|( ∂ϵ∂ lf )× d lf|+|( ∂ ϵ

∂lo )× dlo|=|lo−1 × d lf|+|lf

l o2 (−1)×d lo|=0.0 0 005∈¿∈¿

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Appendix B: Datasheet (Part of the Excel Sheet)

Initial Length (in) 2.00000 Error in load (lb) 1.0000 Calibration Correction 1.0000

Error in length (in) 0.00001 Modulus of Elasticity (psi) 9403025.00 .2% Strain Intercept -

18806.05Diameter (in) 0.2500 Error in diameter (in) 0.0010

Load (lb) Extensometer reading (in) Stress (psi) Strain (in/in) Error in Stress (psi) .2% Strain

Line100.313 0 2044 0.000000 0 -18806.05101.453 0 2067 0.000000 37 -18806.05103.733 5.62E-06 2113 0.000003 37 -18779.64106.013 1.69E-05 2160 0.000008 38 -18726.83106.013 1.69E-05 2160 0.00001 38 -18726.83108.293 3.37E-05 2206 0.00002 38 -18647.61110.573 2.81E-05 2253 0.00001 38 -18674.01111.713 3.93E-05 2276 0.00002 39 -18621.20112.853 4.49E-05 2299 0.00002 39 -18594.79113.993 5.06E-05 2322 0.00003 39 -18568.39116.272 5.62E-05 2369 0.00003 39 -18541.98118.552 6.18E-05 2415 0.00003 40 -18515.57120.832 7.30E-05 2462 0.00004 40 -18462.76121.972 8.43E-05 2485 0.00004 40 -18409.94124.252 8.43E-05 2531 0.00004 41 -18409.94126.532 8.99E-05 2578 0.00004 41 -18383.54128.812 9.55E-05 2624 0.00005 41 -18357.13129.951 1.01E-04 2647 0.00005 42 -18330.72132.231 1.12E-04 2694 0.00006 42 -18277.91133.371 1.12E-04 2717 0.00006 42 -18277.91135.651 1.24E-04 2763 0.00006 42 -18225.09139.071 1.35E-04 2833 0.00007 43 -18172.28141.351 1.40E-04 2880 0.00007 43 -18145.87144.771 1.52E-04 2949 0.00008 44 -18093.06148.190 1.63E-04 3019 0.00008 45 -18040.25149.330 1.74E-04 3042 0.00009 45 -17987.43152.750 1.85E-04 3112 0.00009 45 -17934.62155.030 1.97E-04 3158 0.00010 46 -17881.80158.450 2.13E-04 3228 0.00011 46 -17802.58163.009 2.25E-04 3321 0.00011 47 -17749.77165.289 2.36E-04 3367 0.00012 47 -17696.95169.849 2.47E-04 3460 0.00012 48 -17644.14173.269 2.58E-04 3530 0.00013 49 -17591.33175.549 2.75E-04 3576 0.00014 49 -17512.10180.108 2.86E-04 3669 0.00014 50 -17459.29182.388 2.98E-04 3716 0.00015 50 -17406.48185.808 3.09E-04 3785 0.00015 51 -17353.66189.228 3.26E-04 3855 0.00016 51 -17274.44192.647 3.43E-04 3925 0.00017 52 -17195.22

Appendix C: DataFit Results

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DataFit version 6.1.10Results from project "Untitled1"Equation ID: a*x+bNumber of observations = 282Number of missing observations = 0Solver type: LinearSum of Residuals = 1.89902493730187E-09Average Residual = 6.73413098333998E-12Residual Sum of Squares (Absolute) = 15426820.1294233Residual Sum of Squares (Relative) = 15426820.1294233Standard Error of the Estimate = 234.724915968697Coefficient of Multiple Determination (R^2) = 0.9995865096Proportion of Variance Explained = 99.95865096%Adjusted coefficient of multiple determination (Ra^2) = 0.9995850329Durbin-Watson statistic = 5.12011324934008E-02Regression Variable ResultsVariable Value Standard Errort-ratio Prob(t)a 9403025.269 11429.07546 822.7284267 0.0b 2475.672409 22.72390582 108.9457256 0.068% Confidence IntervalsVariable Value 68% (+/-) Lower Limit Upper Limita 9403025.269 11385.64497 9391639.624 9414410.914b 2475.672409 22.63755498 2453.034854 2498.30996490% Confidence IntervalsVariable Value 90% (+/-) Lower Limit Upper Limita 9403025.269 18861.40323 9384163.866 9421886.672b 2475.672409 37.50126177 2438.171147 2513.17367195% Confidence IntervalsVariable Value 95% (+/-) Lower Limit Upper Limita 9403025.269 22498.13504 9380527.134 9425523.404b 2475.672409 44.7320086 2430.9404 2520.40441799% Confidence IntervalsVariable Value 99% (+/-) Lower Limit Upper Limita 9403025.269 29641.3072 9373383.962 9432666.576b 2475.672409 58.93444974 2416.737959 2534.606859Variance AnalysisSource DF Sum of Squares Mean Square F Ratio Prob(F)Regression 1 3.729334947E+010 3.729334947E+010 676882.0641 0Error 280 15426820.13 55095.78618Total 281 3.730877629E+010

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