1、MIME 1650 Laboratory 5Tensile and Compression TestsObjectiveThe 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 s
2、tress-strain curves-Laboratory procedureInstron Universal Testing MachineFig. 1 Instron universal testing machine 1Stress-Strain Curve (see text book pp. 132 pp. 150)Proportional LimitIn Figs 2 and 3 it will be noted that, up to a certain stress, the strain is directly proportional to the stress. Th
3、e stress at which this proportionality ceases to exist is known as the proportional limit.Youngs Modulus (or Modulus or Elasticity)EUp to the proportional limit, the material obeys Hookes law, which states that stress is directly proportional to strain. The proportionality constant, or ratio of stre
4、ss to strain in this region, is known as Youngs modulus or the modulus of elasticity. Fig. 2 The Stress-strain curve for an aluminum alloyFig. 3 The Stress-strain curve for carbon steelElastic LimitThe maximum stress for which truly elastic behavior exists is called the elastic limit.Permanent Set (
5、or Plastic Deformation)Elongation beyond the elastic limit becomes unrecoverable and is known as permanent set or plastic deformation.Yield PointBeyond the elastic limit, increases in strain do not require proportionate increases in stress. In some materials, a point may be reached where additional
6、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 lo
7、ad-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 wi
8、ll 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 way
9、s 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 Measurements1. (Tensile Test) Measure the diameter and gauge length of the Al-Alloy sample and the width and thickness of the steel
10、 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
11、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 te
12、st 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 b
13、ox 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 pane
14、l. 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 sp
15、ecific 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 meth
16、od 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 highlighte
17、d. 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 tes
18、ting, 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 pro
19、mpted 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 scr
20、een 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 s
21、creen 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.
22、 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 te
23、st 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 disp
24、layed. 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. Th
25、en 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
26、 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 feat
27、ures 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
28、. 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 controll
29、ed 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 displaye
30、d. 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 call
31、ed 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
32、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 o
33、f 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 se
34、cond 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
35、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,
36、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. P
37、rogress 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 c
38、omes 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.
39、 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 sample1. Open data file in MS Excel. The data will be in two columns: Displacement (Extension
40、) and Load.2. In Excel, use the extension and load data to compute strain and stress using the initial sample dimensions you measured.Report Requirements1. Can you determine whether the testing material is ductile or brittle from observing the shape of the cross section after tensile test? How?2. De
41、scribe 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 materia
42、l 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 tensio
43、n 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 SheetTensi
44、le Test for aluminum tensile specimenMaterial of SpecimenBefore D (in.)DiameterAfter d (in.)Before A0 (in2.)Cross-Sectional AreaAfter A (in2.)Before L0 (in.)LengthAfter L (in.)Load Py (lb.)Upper Yield PointYield Strength = Py / A0 (lb./in2.) Load Pu (lb.)Max.(Ultimate) Load Point Tensile Strength =
45、Pu / A0 (lb./in2.) Elongation = L L0 (in.)% of Elongation = (L L0 ) / L0 100 (%) % of Area Reduction = (A0 A ) / A0 100 (%) Load Pz (lb.)Breaking (Fracture) Point Breaking Strength = Pz / A0 (lb./in2.) Tensile Test for Sheet tensile specimenMaterial of SpecimenBefore W0 (in.)WidthAfter W (in.)Before
46、 T0 (in.)ThicknessAfter T (in.)Before A0 (in2.)Cross-Sectional AreaAfter A (in2.)Before L0 (in.)LengthAfter L (in.)Load Py (lb.)Upper Yield PointYield Strength = Py / A0 (lb./in2.) Load Pu (lb.)Max.(Ultimate) Load Point Tensile Strength = Pu / A0 (lb./in2.) Elongation = L L0 (in.)% of Elongation = (
47、L L0 ) / L0 100 (%) % of Area Reduction = (A0 A ) / A0 100 (%) Load Pz (lb.)Breaking (Fracture) Point Breaking Strength = Pz / A0 (lb./in2.) Tensile Test for nylon specimenMaterial of SpecimenBefore D (in.)DiameterAfter d (in.)Before A0 (in2.)Cross-Sectional AreaAfter A (in2.)Before L0 (in.)LengthAfter L (in.)Load Py (lb.)Upper Yield PointYield Strength = Py / A0 (lb./in2.) Load Pu (lb.)Max.(Ultimate) Load Point Tensile
