MENG_3331-Charpy_Lab_Group_Technical_Report_resubmission

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MENG 3331 Materials Science Department of Mechanical Engineering Sept. 20, 2023, Statesboro, Georgia, USA Technical Report 4 CHARPY TEST Bryce Cone Georgia Southern Student Sparks, GA, United States Dylan Butler Georgia Southern University Albany, Georgia, United States Scott Rhodes Georgia Southern University Warner Robins, GA, United States Lawrence Almeter Georgia Southern University Dearing, GA, United States A BSTRACT Charpy testing is a test used to study the toughness of a material. In this test, a material is struck at different temperatures to see how it absorbs energy and deforms. In this test, the material is a mild steel kept at different temperatures, 71.4, -92.4, 209.5, -94.3, -0.6. All these measurements are taken in degrees Fahrenheit. Each of the materials had a slight notch made in them and were each placed in the Charpy testing machine with the grove facing outward. The Charpy testing machine consists of a giant swing hammer on a pendulum which swings down and strikes the material. Upon conducting the experiment, it was discovered that the boiled and the freezer material had a more ductile behavior while the room temp and dry ice material had a more brittle behavior. Ductile materials under certain conditions can display brittleness. N OMENCLATURE CVN Charpy V-Notch Test ft-lb Energy [foot pounds] INTRODUCTION The Charpy test is performed by machining a V-notch into a 10mm x 10mm x 55mm on one of the rectangular faces of the sample. Next the pendulum will be set, and the sample will be set center in the fixture with the notch facing away from the point of impact/ towards the wall opposite of the side of the hammer. Then the pendulum will be released causing the hammer to smash into the sample allowing the Charpy test machine to record the difference of the original height and the highest point reached after the collision, which gives a measured value of the energy absorbed due to the machine being built in such a way that the pendulum is set at a predetermined height and with a set weight [1]. The standardized Charpy test was developed in 1901 by Georges Charpy who standardized S.B. Russell’s idea of residual fracture energy [1]. These impact tests are carried out generally only on materials whose brittle/ductile properties are affected by temperature. Generally, the Charpy test is used to show a ductile-brittle transition in a material due to change of temperature. This ductile-brittle transition can be used to determine the ductile-brittle transition temperature, which is the temperature at which there is a large change in the energy needed to fracture a material [1]. EXPERIMENTAL METHODS To begin the Charpy test, pick out 5 soft steel samples with a square face of 10x10 mm and 55mm long. Each sample will need to be given a V-notch with the manual V-notch Charpy machine. To do this, place the metal sample into the slot and tighten up the pins to lock it in place. Now release the pin on the machine and slowly crank the wheel down until the blade has fully gone past the sample. Remove the sample and repeat for all samples. Next will be to prep each sample for what environment they are going into. One sample will be room temperature, one goes into the freezer, two go into dry ice, and 1 Copyright © 2023 by ASME

one goes into boiling water. Once each sample is undergoing a temperature change, it will be time to set up the Charpy hammer. To do this the hammer will be lifted until it latches onto the lever, once the hammer is latched, slide the safety onto the lever which locks the lever in place. Now that the hammer is set, take the room temperature sample and place it on the little platform with the V-notch facing the opposite wall of the hammer. Once the sample is set, release the safety and push the lever forward. Once the hammer is released it will strike the sample. Take the sample, examine it, and record the foot pounds from the dial on the Charpy machine. This process will be repeated for each sample after the desired temperature is reached. The sample in the boiling water will boil for 20 minutes, the sample in the freezer should freeze for 45 minutes, one dry ice sample stays in the box for 15 minutes and the other stays in the dry ice for 35 minutes. DATA AND R ESULTS Table 1 contains all measurements and results taken from each sample test. Figure 1 shows the visual results of the Charpy test. Figure 2 displays the trend of the data found in Table 1. The two dry ice samples performed as expected during the test. Both samples were brittle from the colder temperature and therefore had the lowest absorption energy. The dry ice sample prepared at 15 min had a higher absorbed energy of 34 ft-lb while the 35 min dry ice sample had a absorbed energy of 23 ft-lb. This was expected as the 35 min sample had longer to cool down and become more brittle. Both dry ice samples fully separated and broke in half during the collision. The room temperature and boiled samples also performed as expected. The room temperature sample had an absorption value of 63 ft- lb that was in between the dry ice and the boiled samples. The room temperature sample also broke completely in half. The boiled sample had a high absorption energy of 195 ft-lb and did not fully separate from the collision. The freezer sample performed differently than expected. It should have had a value somewhere between the dry ice samples and the room temperature sample or between 34 and 63 ft-lb. However, it had a higher absorbed energy than the boiled sample at 203 ft- lb and it did not break in half during the collision. Figure 3 shows the expected data trend including a theoretical freezer value of around 40 ft-lb. The lower shelf, transitional temperature, and upper shelf are more distinguishable in this figure. Table 1. Steel Sample Data Sample Time [min] Temperatur e [°F] Absorbed Energy [ft-lb] Dry Ice 35 -94.3 23 Dry Ice 15 -92.4 34 Freezer 45 -0.6 203 Room - 71.4 63 Temp Boiled 20 209.5 195 Figure 1. Fracture Surface of Samples at Different Temperatures Figure 2. Absorbed Energy vs Temperature Curve Figure 3. Theoretical Absorbed Energy vs Temperature Curve DISCUSSION The following experiment requires an individual to be quick when working with material because in order to get the 2 Copyright © 2023 by ASME

most accurate result the material must be tested quickly after the temperature has been taken. This experiment requires one trial for each of the 5 temperatures of material. The first piece of material tested was room temperature steel. Its temperature was recorded at 71.4° F and its absorbed energy is 63 ft-lb. Next was the first dry ice material which was recorded at - 92.4°F and it absorbed 34 ft-lb. This temperature is obtained by letting the steel bar sit in dry ice for 15 minutes. The boiled steel was 209.5° and withstood 195 ft-lb of force. This temperature was reached by allowing the steel bar to sit in boiling water for 20 minutes. The second dry ice material had a recorded temperature of -94.3°F and withstood 23 ft-lb of force. This temperature was achieved by letting the steel bar sit in dry ice for 35 minutes. The final piece of material tested was the freezer material. The recorded temperature was -.06° F and it withstood 203 ft-lb of force. The temperature was recorded after letting the bar sit in the freezer for 45 minutes. Before testing it was believed that the colder materials would handle more force but after testing the freezer sample, the hypothesis was incorrect. There are many reasons as to why the test for the freezer material could be invalid. It could have taken too long to transfer material from the freezer to the testing station, the notch could have been off center, and a tougher material could have been used since the given samples were unlabeled and could have been a variety of different steels. CONCLUSION The Charpy test is done by a big hammer on a pendulum and is released to strike a metal sample. After performing the test 5 times on metal subjects with each a different temperature. It was observed that the 71.4° Fahrenheit sample absorbed 63 ft/lb. The 209.5° Fahrenheit sample absorbed 195 ft/lb. The -94.3° Fahrenheit sample absorbed 23 ft/lb. The -92.4° Fahrenheit sample absorbed 34 ft/lb. The -0.6° Fahrenheit sample absorbed 203 ft/lb. Q UESTIONS 1. The notch is necessary for the notched-bar impact testing in order for the samples to perform similarly to each other and to give more accurate testing results. The notch gives a consistent striking target that is easily controllable by the depth of the notch. 2. The sharper the point in the notch the faster the crack will develop due to the smaller radius. The notch also needs to be centered as best as possible so that the tests have less variability. The faster the hammer swings, the more kinetic energy it will have. So the speed needs to be consistent in order to correctly find the energy absorbed by the material. 3. In general, the colder the temperature, the more brittle the mild steel should be resulting in lower toughness. Raising the temperature increases the ductility, which increases the amount of energy the material can absorb, therefore making the toughness of the material greater. 4. E = ΔPE + ΔKE ΔKE = 0 Since v 1 = v 2 = 0 E = mgh =( 60 lb / 32.2 ft / s 2 )( 32.2 ft / s 2 ) ¿ R EFERENCES [1] "Charpy Impact Test." Wikipedia , Wikimedia Foundation,22,Oct.,2022, en.wikipedia.org/wiki/Charpy_impact_test. Accessed 20 Sept. 2023. 3 Copyright © 2023 by ASME

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