CUA THE CATHOLIC UNIVERSITY OF AMERICA School of Engineering Washington, DC 20064 Lab Report TITLE OF A SPECIFIC EXPERIMENT for Fall 2017 ENGR 395-0X Engineering Materials Laboratory Prepared by YOUR NAME HERE of Team A/B Submitted on Month Day, 2017 (Page Number) Abstract This is a single paragraph (with no references or equations) that summarizes the key background information of the experiment and major findings you will get from the experiment. This paragraph must be concise as possible while containing the necessary information. When preparing this paragraph, try to answer the following questions: • What is the objective of this experiment (What are the material properties you measured or the structural behavior you explored)? • Why are such properties/behavior so important in your field (What are the significant engineering applications)? • What experimental approaches/tools you used? What are the specific specimens you tested? How did you analyze the data (by curve plotting, side-by-side comparison, etc.)? • What are your major findings? (Do they agree with theories you learned from previous coursework or information you obtained from the library/internet?) • What are the implications of such findings (Can you make any recommendations or warnings for potential engineering applications in your fields)? Keywords: Pick the several words/phrases that best describe the key components/features of the experiment. 1. Introduction This section describes the background of the subject that is to be tested/observed in the present experiment. Please note the information provided in the handout for each experiment is intentionally kept to a minimum. You are expected to search in textbooks or internet to obtain more comprehensive knowledge of the subject in your own field. In the "Introduction" section, you can write multiple paragraphs, each having an individual focus. For example, you may want to discuss: • Why is this subject so important for engineering applications in general and/or in your own field? • Any real-world engineering failures due to lack of relevant knowledge on this subject? 2. Materials and Method Describe what engineering materials you tested in the experiment. List the key steps for conducting the experiment in our lab. Try to use your own words instead of simply copying those from the lab handouts. 3. Results and Discussion Plot the data (connecting the dots, curve fitting, histograms...) and/or put data in a table. Please note all figures/graphs/flowcharts should be numbered, have captions, and be referenced in the main text (otherwise, the figure should be removed). Same rules apply to tables. Discussion of the experimental data is the most important component of a lab report. You should take time to carefully examine the data, and try to find any trend suggested by the data. Ask (Page Number) yourself the following question: Does the trend make sense based on what you have learned from other classes or information you have found from the literature/internet? Another important portion is to discuss the possible experimental errors in the data or mistakes your team made during the experiment. Use your best judgment to explain why the data are different from theoretical values. You will still be able to get most of the grade for a lab report, provided you successfully identify the key sources of errors/mistakes and discuss in detail what you can do to avoid such mistakes or reduce the errors if you could conduct the experiment all over again. 4. Conclusions Use only a few sentences to summarize your major findings from the present experiment. Acknowledgements This part is optional. You may want to take this opportunity to thank your team members, who have made this experiment a success and/or a great learning experience. References A scientific writing requires that all referenced sources be listed and numbered at the end of the main text and referenced by their respective numbers in the main text. You may want to follow this practice. --------------------------- This is the end of the lab report template. -----------------------------------Special notes: • • Write what you did in past tense and the general knowledge and your discussion in present tense. Write your report as neat as possible (you are what you write). Make the font size and style consistent throughout the whole report. • Try to avoid drawing a graph/flowchart by hand. But if you have to, make sure it is neat and legible. • Proofread your writing before submission! • Plagiarism is strictly prohibited. - You are expected to write your own report. Copying other’s reports, in part or as a whole, will be a clear violation of the University rules and never be accepted. - When you find a useful source of information, you should put the name of that source in the "References" section and refer to it by a number in the main text. It is suggested that you rephrase the original text of the referenced source. If you find it difficult to rephrase it, you are allowed to include the original sentences in your report, provided double quotation marks are properly used and the original source is identified. (Page Number) Fall 2017 - ENGR 395 Engineering Materials Laboratory Instructor: Dr. Max Liu | (202) 319-5165 | lium@cua.edu | http://faculty.cua.edu/lium/ Tension Testing of Metals Objective: To experimentally obtain important mechanical properties (e.g., yield strength, Young's modulus, maximum tensile stress, and ductility) of different metal materials. Specimens: Two flat “dog-bone” specimens made of Aluminum, Brass, Copper, or Steel. Equipment: Instron Universal Testing Machine Model 5566, with a load capacity of 10 kN (2250 lbf) Overview: Each specimen is slowly pulled by the testing machine until the specimen fractures. The extension (i.e., elongation) of the gauge segment is recorded against the increaing force. Make sure lower limit bar @ 19 inches (48.5 cm) and upper limit bar @ 30 inches (76 cm). Control Panel Emergency Stop Button Specimen Hazard Warnings: • Materials testing involves inherent hazards from high forces, rapid motions, stored energy, and electricity. • You should not touch any part of the machine while the testing is in progress. • Press the Emergency Stop Button whenever you consider that an unsafe condition exists. • Avoid flying debris hazard by observing at least 2 meters away and wearing eye protection if necessary. Figure 1. Hardware for the tension testing. Page 1 of 5 Prior to the Experiment: • • Be aware of the potential hazards. Measure the gauge length, width, and thickness of each metal specimen. Calibration icon (Step 3). Experimental Procedure: 1. Turn on the power of the testing machine. Wait about one minute to let it warm up. “Test” tab (Step 4). 2. On the lab computer, double click the "Bluehill" icon on desktop to start the testing software. Wait until the screen in Figure 2 appears. 3. Click the middle icon in the upper right corner of the software screen to calibrate the machine (Once calibrated, the icon color turns from grey to green.) Figure 2. The start screen (Step 2). 4. Click the "Test" tab. Then “Browse” to choose the "Tension Test Method – ENGR 395.im_flex". Click “Open”. Wait while the computer communicates with the testing machine. 5. In the new screen, type a name (e.g., ENGR 3950x) in the "Sample filename" box. Click “Next”. 6. In the new screen (Figure 3), revise the Thickness, Width, and Length for the gauge portion of the current specimen. Click “Next”. 7. On the new screen, enter the current metal type in the "Specimen label" box. Change the Thickness, Width, and Length if needed. Click “Next”. 8. When the screen in Figure 4 appears, place the upper grip section of the specimen inside the slot of the upper gripper. Then fasten the screw on the left side. Make sure that the specimen is placed Figure 3. Screen to enter the dimensions of a metal specimen (Step 6). vertically. If there is not enough vertical space for the specimen to fit in, press the "JOG UP" button on the Control Panel to lift the upper gripper. 9. On the Control Panel, press "JOG DOWN" button to lower down the upper gripper such that the lower grip section of the specimen just slides inside the slot of the lower gripper. Rotate clockwise the screw on the left side of the lower gripper to tightly grip the specimen. Make sure there is no distortion of the specimen. Page 2 of 5 Figure 4. Now place the metal specimen (Step 8). 10. Turn the "FINE POSITION" thumbwheel up/down to fine tune the position of upper gripper, until the reading of "Load" on the computer screen is quite small (less than 50 N). NOTE: such reading must be set to a positive value. 11. On the Control Panel, press "RESET GL” button to zero the "Extension" reading on the screen. 12. On the computer screen, click "Start" to begin the tension testing. You will observe the progression of the load vs. extension curve as time elapses. As the metal specimen finally fractures, you will hear a sudden sound and observe a deep drop in the curve. 13. Each test lasts a maximum of 10 minutes during which the maximum upward movement of the upper gripper is set to be 30 mm (so the maximum possible "Extension" reading on the screen is 30 mm). If the specimen has already fractured, there is no need to continue the test. In this case, click “Stop” on the screen, then click “OK” in the dialog box of “Remove specimen then click OK to return to the gauge length”. 14. After the completion of the current test, loosen the screws on the left hand side of both upper and lower grippers to remove the fractured pieces of the specimen. 15. Click the "Finish” button in the lower right corner of the screen to save the raw test data of the just completed specimen (in the "Tension Output" folder on the computer desktop). If a box “Results Export File Already Exists. Do you want to overwrite it?” appears, click “No”. Then in dialog box “Some Raw Data Export Files Already Exist”, click “Yes” to export all raw data. Figure 5. Finish or continue? (Step 16). 16. If you have another specimen to test, click "Continue Testing" (Fig. 5), then enter new Thickness, Width, and Length, and specimen label on the screen. Click “Next” and repeat steps 8 to 15. If the testing for all specimens has been done, click "Finish Sample" then click “No” in “Start another New Sample”. Data Processing for Lab Report Team A and Team B will each perform the tension testing using one different metal specimen. Both sets of data will be emailed to all students and used for analysis and report writing. Each data file has three columns: time (sec), extension Δ (mm) (i.e., axial elongation), and Tensile force P (N). Note that both extension and force are recorded as positive values, meaning both the displacement and load of the upper gripper are upward. For each specimen, you are required to perform the following calculations: • • • • • Convert the raw data of P- Δ curve to a stress-strain curve. Compute the stress using the unit of “MPa” and strain in “%”. Plot both curves. Use the initial elastic portion of the stress-strain curve (i.e., where the curve has not yet started to significantly flatten out) to compute the modulus of elasticity E1 (i.e., Young's modulus). Find the stress σy and strain εy at yield, using the “offset method” (see the next page). Find the tensile strength σmax (i.e., maximum stress) and ultimate strain εu (i.e., strain at fracture). Calculate the ductility µ = εu /εy. After you have calculated the mechanical properties of the metal specimens, compare and discuss the relative strength, stiffness, and ductility as well as different applications of these metal materials. Page 3 of 5 Background Information Converting the load-extension curve to stress-strain curve Stress σ = Load P Cross Sectional Area Strain ε = [MPa]; Extension Gauge Length [%] Figure 6 illustrates a typical stress vs. strain curve for a metal material. Plastic deformation Engineering Stress Elastic deformation σmax X E2 σy 1 Tensile Strength Offset Yield Strength Fracture Strength E1 1 εy εu Engineering Strain Modulus of elasticity E1 indicates how stiff a metal material is (that is, how difficult it deforms elastically) under applied loads. In our experiment, E is the slope of the initial straight (linear) portion of the stress-strain curve. Yield strength σy is the maximum stress beyond which the metal material exhibits significant plastic (i.e., permanent) deformation. σy will be determined by the “offset method.” Strain-hardening ratio is the ratio of the post-yield modulus E2 to the initial modulus of elasticity E1. It is the strengthening by plastic deformation, due to dislocation movement and generation within the metal crystal structure. Ductility is the ratio of εu (strain at fracture) to the εy (strain at yield). It demonstrates the deformation capability of a metal material after yielding but before the total failure. Figure 6. A typical stress-strain diagram for a metal specimen in tension showing a ductile behavior. Determine the yield strength by “offset method” • • On the stress-strain diagram (Fig. 7) lay off Om equal to the specified value of the offset (use ε = 0.2% for your lab report.) Draw mn parallel to OA, and thus locate r, the intersection of mn with the stress-strain diagram. The stress associated with point r is considered the yield strength. To report the yield strength value obtained by this method, the specified value of offset should be stated in parentheses after the term yield strength. That is: Yield strength (offset = 0.2%) = xxx MPa Yield strength (offset = 0.2%) = xx MPa xx MPa Figure 7. Stress-strain diagram for determining the yield strength by the ASTM E8 offset method. Reference: ASTM E8 “Standard Test Methods for Tension Testing of Metallic Materials.” Page 4 of 5 Specimen Type Gauge Thickness t (mm) Page 5 of 5 Table 1. Measurements and calculation of metal specimens. Gauge Gauge Initial Yield Yield Maximum Modulus of strength strain stress Width Length Elasticity (MPa) εy (MPa) b L E1 (MPa) σ σmax y (mm) (mm) DATA SHEET Tension Testing of Metals Fracture strain εu Ductility µ= εu / εy A G = 2 E Lg Extension=A DATA SHEET Tension Testing of Metals Specimen Type Gauge Thickness t Table 1. Measurements and calculation of metal specimens. Gauge Gauge Initial Yield Yield Maximum Width Length Modulus of strength strain stress b Elasticity L (MPa) Ey (MPa) (mm) E: (MPa) (mm) Fracture Ductility strain u (mm) Eu Oy Eulky Omar Copper brittle 1.6 Steel ductile 16 6.3/2375 6.024.35 Page 5 of 5
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