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MIME 1650 Laboratory 5

By Eddie Andrews,2014-01-20 02:14
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MIME 1650 Laboratory 5

    MIME 1650 Laboratory 5

     Tensile and Compression Tests

Objective

The student should learn to use Universal Testing Machine to perform tensile and

    compression test of materials. A deeper understanding of stress-strain diagram is

    expected as well.

Agenda

-Introduction to Universal Testing Machine

    -Review of stress-strain curves

    -Laboratory procedure

Instron Universal Testing Machine

    Fig. 1 Instron universal testing machine [1]

Stress-Strain Curve (see text book pp. 132 pp. 150)

Proportional Limit

     In Figs 2 and 3 it will be noted that, up to a certain stress, the strain is directly

    proportional to the stress. The stress at which this proportionality ceases to exist is

    known as the proportional limit.

Young’s Modulus (or Modulus or Elasticity)

    ?? E???

    Up to the proportional limit, the material obeys Hooke’s law, which states that stress is directly proportional to strain. The proportionality constant, or ratio of stress to strain in

    this region, is known as Young’s modulus or the modulus of elasticity.

    Fig. 2 The Stress-strain curve for an aluminum alloy

    Fig. 3 The Stress-strain curve for carbon steel

Elastic Limit

    The maximum stress for which truly elastic behavior exists is called the elastic limit.

Permanent Set (or Plastic Deformation)

    Elongation beyond the elastic limit becomes unrecoverable and is known as permanent set or plastic deformation.

Yield Point

Beyond the elastic limit, increases in strain do not require proportionate increases in

    stress. In some materials, a point may be reached where additional strain occurs without

    any increase in stress, this point being known as the yield point or yield-point stress.

Ultimate Strength (or Tensile Strength)

In the tensile test, however, a point is reached where the drop in the area with increased

    strain dominates the increase in strength and the overall load-bearing capacity peaks and

    begins to diminish, as in Figure 2 and Figure 3. The value of this point on the stress-train

    curve is known as the ultimate strength or tensile strength of the material.

Breaking Strength (or Fracture Strength)

If straining is continued far enough, the tensile specimen will ultimately fracture. The

    stress at which this occurs is called the breaking strength or fracture strength.

Safety Precautions

    ? Wear safety glasses all times

    ? Close the glass lid after mounting the specimen.

    ? Do not stand behind the test machine.

    ? If something goes wrong, there are three different ways to stop the test.

    ? The emergency stop button.

    ? Control panel stop button.

    ? Software stop button shown as in the small icon respectively.

Experimental Procedure:

A. Initial Measurements

    1. (Tensile Test) Measure the diameter and gauge length of the Al-Alloy

    sample and the width and thickness of the steel sheet tensile sample and the

    nylon (non-transparent plastic) and acrylic (transparent plastic) samples.

    Mark lines to show the gauge length on the samples.

2. (Compression Test) Measure the width and length of the compression

    sample Wood Block.

    B. Tensile Test ( Al bar, Steel sheet, Plastics)

    1. Turn on the power to the computer first and then Instron Machine.

    2. Open the Bluehill 2 software using the shortcut on the desktop. The Home

    Screen of Bluehill interface will be showing. The Home Screen is going to

    be your main access point for all the features of Bluehill software.

    3. Before running a test the load transducer must be calibrated. Once the

    Bluehill2 software appears on the screen, there are couple transducers

    shown on the right hand corner of the screen. Click on the Load Cell icon

    shown on the right. Transducer Setup dialog box pops up. Hit on

    Calibrate button. When warning dialog box pops up click on OK. Then

    load must be balanced by hitting on Balance button in same dialog box.

    After balancing the load press Done button to exit the dialog box. 4. To mount the sample in between the grips of the test machine grips can be

    controlled by the up and down button on the control panel. Tighten the

    jaws no more than necessary. Lose jaws might cause slippage and very

    tight jaws might also yield wrong results.

    5. On Home Screen just click on Test button. 6. The Create a New Sample screen will be displayed. In this screen

    methods already saved in the computer will be selected for specific test

    samples. There are four Tension Tests that are going to be performed in

    this lab.

    7. In the New Sample view there is a list of methods have recently been used.

    For aluminum bar sample tests select the method file called

    aluminum.im_tens, for the rectangular steel specimen select the method file

    called rectangular_steel.im_tens, for acrylic (transparent plastic) select the

    method file called transparent_plastic.im_tens, and similarly for nylon

    (non-transparent plastic) select the method file called non-

    transparent_plastic.im_tens. The method file at the top of the list is

    highlighted. On the right, the preview pane shows the important

    parameters of the highlighted method.

    8. Choose a method and click Next button to proceed. 9. Second step of Create a Sample screen asks you to type a file name for

    your sample. Type your group number and the name of the specimen that

    you are testing, for example group1_rectangular_steel click Browse to

    find your section folder and hit Save. There are going to be fourteen

    folders for each section and sections are going to be split up according to

    availability of the test specimens. Then click Next to continue.

    10. The first screen of the prompted test is the reminder of calibration. If

    calibration is not done, the specimen must be unmounted and Step: 3 must

    be followed for calibration. If calibration has already been done click

    Next to continue. (If you are not sure whether the calibration has been

    done, ask your TA.)

11. The second screen of the prompted test is the Before Specimen section.

    Here the prompt and input controls require you to enter some information

    about the specimen. Default values for the specimen will show in the

    inputs. This data is not required to be changed. Click Next to continue.

    12. Before the Test prompt screen will appear. Please make sure the specimen

    is properly installed in the test machine. Keep clear of the machine and

    make sure no student is close by. Everybody MUST wear safety glasses.

    The softkeys at the top of the screen is set to be Reset Gauge Length and

    Balance Load button, respectively. First reset the gauge length pressing on

    Reset Gauge Length key, and then hit the Load Balance. At this screen

    the Next button is grayed out. On the other hand Start button is enabled. If

    everything is ready click the Start button to start the test. 13. The workspace screen displays. Progress of test can be viewed here. The

    stress vs. strain curve can be observed growing and autosizing as the test

    progresses. Once the test is complete, the workspace will still be showing

    for students to examine it. After examined the graph and results click on

    Next to proceed.

    14. Finishing screen will be displayed. In this screen click on the Finish

    Sample button. The software will save your file in selected directory.

    Then a dialog box appears asking if another sample is going to be tested

    using same test parameters. Click on No in that dialog box. Once again

    Create a Sample screen will display.

    15. Then let the next group of students run the same test starting from Step: 4.

    16. Last lab section of the day should close to software; turn off Instron

    Machine and computer.

    C. Compression Test (Wood). You will be performing compression tests on two

    wood samples. First with the load applied parallel to the grain and then with

    the load perpendicular to the grain.

    1. Turn on power computer first and then Instron Machine.

    2. Open the Bluehill 2 software which has a shortcut on desktop. Home Screen

    of Bluehill interface will be showing. Home Screen is going to be your main

    access point for all the features of Bluehill software.

    3. Before running a test the load transducer must be calibrated. Once the

    Bluehill2 software appears on the screen, there are couple transducers shown

    on the right hand corner of the screen. Click on the Load Cell icon shown on

    the right. Transducer Setup dialog box pops up. Hit on Calibrate button.

    When warning dialog box pops up click on OK. Then load must be balanced

    by hitting on Balance button in same dialog box. After balancing the load

    press Done button to exit the dialog box.

    4. To mount the sample in between the grips of the test machine grips can be

    controlled by the up and down button on the control panel. Tighten the jaws

    no more than necessary. Lose jaws might cause slippage and very tight jaws

    might cause initial bending both of which yield wrong results.

    5. On Home Screen just click on Test button.

6. The Create a New Sample screen will be displayed. In this screen methods

    already saved in the computer will be selected for specific test samples. There

    are four Tension Tests that are going to be held in the lab.

    7. In the New Sample view there is a list of methods have recently been used.

    For wood prism sample tests select the method file called wood.im_com. The

    method file at the top of the list is highlighted. On the right, Preview pane

    shows the important parameters of the highlighted method.

    8. Prompt in this screen requests you to choose a method and click Next button

    to proceed.

    9. Second step of Create a Sample screen asks you to type a file name for your

    sample. Type your group number and the name of the specimen that you are

    testing, like group1_wood click Browse to find your section folder and hit

    Save. There is going to be fourteen folders for each section and sections are

    going to be split up according to availability of the test specimens. Then click

    Next to continue.

    10. The first screen of the prompted test is the reminder of calibration. If

    calibration is not done, the specimen must be dismounted and Step: 3 must be

    followed for calibration. If calibration has already been done click Next to

    continue.

    11. The second screen of the prompted test is the Before Specimen section. Here

    the prompt and input controls require you to enter some information about the

    specimen. Default values for the specimen will show in the inputs. This data

    is not required to be changed. Then click Next to continue. 12. Before the Test prompt screen will appear. Please make sure the specimen is

    properly installed in the test machine. Keep clear of the machine and make

    sure no student is close by. Everybody MUST wear safety glasses. The

    softkeys at the top of the screen is set to be Reset Gauge Length and Balance

    Load button, respectively. First reset the gauge length pressing on Reset

    Gauge Length key, and then hit the Load Balance. At this screen the Next

    button is grayed out. On the other hand Start button is enabled. If everything is

    ready click the Start button to start the test.

    13. The workspace screen displays. Progress of test can be viewed here. The

    stress vs. strain curve can be observed growing and autosizing as the test

    progress. Once the test is complete, the workspace will still be showing for

    students to examine it. After examined the graph and results click on Next to

    proceed.

    14. Finishing screen comes out. In this screen click on the Finish Sample button.

    The software will save your file in selected directory. Then a dialog box

    appears asking if another sample is going to be tested using same test

    parameters. Click on No in that dialog box. Once again Create a Sample

    screen will display.

    15. Then let next group of students run the same test starting from Step: 4.

    16. Last lab section of the day should close to software; turn off Instron Machine

    and computer.

D. Draw Stress-strain curve for each sample

    1. Open data file in ‘MS Excel’. The data will be in two columns: Displacement

    (Extension) and Load.

    2. In Excel, use the extension and load data to compute strain and stress using

    the initial sample dimensions you measured.

Report Requirements

    1. Can you determine whether the testing material is ductile or brittle from observing

    the shape of the cross section after tensile test? How?

    2. Describe the shape and surface of the cross section after tensile test.

    3. What is stress? How does it differ from load or force?

    4. What is strain? How it is normally expressed?

    5. Is strain proportional to stress at all stress levels?

    6. What is the significance of the modulus of elasticity of a material to a designer? 7. What is the yield point? Do all materials exhibit the yield point phenomenon? For

    those cases in which the material changes from elastic to plastic behavior is not

    easily detected, how is the yield point determined?

    8. What factors should be considered to determine whether a tension or compression

    test is used to evaluate a material property?

    9. Describe the morphology of the fractured specimens.

    10. Draw the load displacement and stress-strain curves obtained in each experiment.

    11. What is the percentage elongation at fracture for the aluminum and steel samples?

Data Sheet

Tensile Test for aluminum tensile specimen

    Material of Specimen Diameter Before D (in.)

    After d (in.)

    2Cross-Sectional Area Before A (in.) 0

    2After A’ (in.) Length Before L (in.) 0

    After L’ (in.) Upper Yield Point Load P (lb.) y

    2Yield Strength = P/ A (lb./in.) y 0

    Max.(Ultimate) Load Load P (lb.) u2Point Tensile Strength = P/ A(lb./in.) u 0

    Elongation = L’ L (in.) 0

    % of Elongation = (L’ L) / L × 100 (%) 0 0

    % of Area Reduction = (A A’) / A × 100 (%) 0 0

    Breaking (Fracture) Load P (lb.) z

    2Point Breaking Strength = P/ A(lb./in.) z 0

Tensile Test for Sheet tensile specimen

    Material of Specimen Width Before W (in.) 0

    After W’ (in.) Thickness Before T (in.) 0

    After T’ (in.)

    2Cross-Sectional Area Before A (in.) 0

    2After A’ (in.) Length Before L (in.) 0

    After L’ (in.) Upper Yield Point Load P (lb.) y2Yield Strength = P/ A (lb./in.) y 0

    Max.(Ultimate) Load Load P (lb.) u2Point Tensile Strength = P/ A(lb./in.) u 0

    Elongation = L’ L (in.) 0

    % of Elongation = (L’ L) / L × 100 (%) 0 0

    % of Area Reduction = (A A’) / A × 100 (%) 0 0

    Breaking (Fracture) Load P (lb.) z

    2Point Breaking Strength = P/ A(lb./in.) z 0

Tensile Test for nylon specimen

    Material of Specimen Diameter Before D (in.)

    After d (in.)

    2Cross-Sectional Area Before A (in.) 02After A’ (in.) Length Before L (in.) 0

    After L’ (in.) Upper Yield Point Load P (lb.) y

    2Yield Strength = P/ A (lb./in.) y 0

    Max.(Ultimate) Load Load P (lb.) u2Point Tensile Strength = P/ A(lb./in.) u 0

    Elongation = L’ L (in.) 0

    % of Elongation = (L’ L) / L × 100 (%) 0 0

    % of Area Reduction = (A A’) / A × 100 (%) 0 0

    Breaking (Fracture) Load P (lb.) z

    2Point Breaking Strength = P/ A(lb./in.) z 0

Tensile Test for acrylic specimen

    Material of Specimen Width Before W (in.) 0

    After W’ (in.) Thickness Before T (in.) 0

    After T’ (in.)

    2Cross-Sectional Area Before A (in.) 02After A’ (in.) Length Before L (in.) 0

    After L’ (in.) Upper Yield Point Load P (lb.) y

    2Yield Strength = P/ A (lb./in.) y 0

    Max.(Ultimate) Load Load P (lb.) u2Point Tensile Strength = P/ A(lb./in.) u 0

    Elongation = L’ L (in.) 0

    % of Elongation = (L’ L) / L × 100 (%) 0 0

    % of Area Reduction = (A A’) / A × 100 (%) 0 0

    Breaking (Fracture) Load P (lb.) z

    2Point Breaking Strength = P/ A(lb./in.) z 0

Material of Specimen Compression Test

    Before Width (W) (in.) 0

    Length (L) (in.) 0

    2Cross-sectional Area (A) (in.) 0

    After Width (W’) (in.)

    Length (L’) (in.)

    2Cross-sectional Area (A’) (in.) Max.(Ultimate) Load P (lb.) m

    2Compression Strength = P/ A(lb./in.) m 0

    % of Compression (Length) = (L’ L) / L × 100 (%) 0 0

References

    [1] http://www.instron.us/wa/products/universal_material/5560.aspx [2] All small iconic pictures are taken from documentations supplied by Instron at

    purchase.

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