CE335_PRM_LAB4

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Dec 6, 2023

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Peter Martin Lab #4 Hardness and Impact Test CE 335 – Section 01 9/27/2022

Synopsis The main purpose of this lab is to be able to use non-destructive means to obtain a rough estimate of a material’s strength. By using different materials, we can familiarize ourselves with analyzing data. From that analysis, we could identify which material is what specimen. The first part was the hardness test experiment which was run with three different material specimens including 1018, 1045, and 1095 steel. Our goal was to identify which is which from looking at the data. We were able to figure this out from two different testing method. We first used the Brinell method and then the Rockwell method. The softer the material, the smaller the hardness number. From this number were checked the table provided that showed the tensile strength applied on the material according to the number. By comparing those values, we could identify the specimen values. While each test may not have provided accurate results, the experiment ended up being successful since our objectives were fulfilled. In the second part of the experiment, the objective was to familiarize ourselves with the methods for toughness measurement with impact tests, and to observe the effects on temperature on the energy absorption capability of materials. To complete this objective, the operation procedure of the Charpy V-notch impact testing machine. Four samples of Cast Steel, 18/8 Steel, 1020 HR Steel, and Aluminum were tested between the Izod test and the Charpy Impact test. These specimens were tested at different temperatures to measure the impact force of each material. The impact load always produces a peak stress higher than that produced by a load of the same magnitude if it is applied slowly. Introduction Non distractive means are commonly used in the engineering field since they have many advantages of quick control, no or very little damage of the specimen and fast result

output. There are two main tests which we will conduct during the experiment including the Brinell and Rockwell hardness test. During the Brinell test the steel ball is pressed on a metal surface to provide an impression as demonstrated in Figure 1. This impression should not be distorted and must not be too deep since this might cause too much of plastic deformation, leading to errors of the hardness values. Different levels of material hardness result in impression of various diameters and depths. Therefore, different loads are used for hardness testing of different materials. Hard metals such as steels require a 3,000 kgf load while brass and aluminum involve the loads of 2,000 and 1,000 or 500 kgf, respectively. For materials with very high hardness, a tungsten carbide ball is utilized to avoid the distortion of the ball. In practice, pressing of the steel ball on to the metal surface is carried out for 30 second, followed by measuring two values of impression diameters normal to each other using a low magnification macroscope. An average value is used for the calculation according to equation on Figure 2. Figure 1. Brinell indentation. Figure 2. Calculations for obtaining hardness results.

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Impact testing can be applied in order to study the behavior of a given material over a range of temperature. In addition, the result of the test which is a qualitative index of a material’s ability to resist extreme conditions can be used to compare the behavior of different materials or different alloys of a metal. Impact testing is used in the real world to determine how much impact load a material can take without failing. For impact testing, calculations of the energy required for fracture is the primary importance. This is because that shows how much energy a material can take before the material fails or fractures. For example, the stronger the steel, the more bitter is it, therefore it requires less energy to fail. For the material to handle dynamic loads such as vibrations, it must have toughness to absorb the energy. Toughness is associated with high strength and good ductility. Impact testing is done using the Charpy test. This test employs a swinging pendulum that falls and strikes the sample on a small V-notch in the sample as a horizontal simple beam. The toughness of a material is dependent on the temperature. At high temperatures, the energy that is required to fracture that sample is much higher than samples at low temperatures. The impact tests show the transition from ductile fracture that absorbs more energy to brittle fracture that absorbs little energy. Objectives The objectives of the hardness test include the following:  Use non-distractive means to obtain a rough estimate of material’s strength  Learn how to use the Nomograph to obtain the corresponding tensile strength from the hardness numbers  Identify the steel samples with different carbon contents The objectives of the impact test include the following:

 Discuss the behavior of different materials (nylon, polyethylene, and aluminum) under impact loading  Discuss the effect of temperature on the impact resistance of metals Experimental Procedure For the hardness test, put each of the three rods on the HRB machine. Set the force, run the machine, wait 15 seconds, and then check the gage. From the gage, we can check the HB number from the given table to find the tensile strength applied on the material. The smaller the hardness number, the softer the material is. This process is then repeated for the other machines, using both methods of the experiment. Make sure to pick a flat surface on each of the rods to avoid a disturbance in the results from the machine. While, the machines may not be very accurate, we did the best we could with what we were given to decide on the strength of each of the red, blue, and black rods. Results Color of the Specimen Brinell Test Rockwe ll Test Specimen Indentation Diameter [mm] HB # Tensile Strength [ksi] HRB HR # Tensile Strength Red 4.16 211 101 60.5 104 1095 (0.95%) Blue 4.47 183 88 74.75 85 1018 (0.15%) Black 4.432 184 88 66.5 96.25 1045 (0.45%) Table 1 – Summary of the Hardness Test results These results from Table 1 suggest that the red specimen has a higher carbon content while the blue specimen has the least carbon content. It was expected that the steel with higher carbon content has the higher tensile strength that the one with less. In tables 2-4, shows each of the steel

bar’s data analysis with the averages and standard deviations between the Rockwell and Brinell tests. 1018 Steel Rockwell Brinell 1st. Average 78.4375 133.25 Std. Dev. 5.864796 6.159004 Average+ Dev 84.3023 139.409 Average - Dev 72.5727 127.091 New Average 79 135.7692 Tensile Strength 81 77 Table 2 – 1018 Steel Data Analysis 1045 Steel Rockwell Brinell 1st. Average 92 172.0625 Std. Dev. 2.5819889 34.15547 Average + Dev 94.581989 206.218 Average - Dev 89.418011 137.907 New Average 91.166667 175.17 Tensile Strength 112 68 Table 3 – 1045 Steel Data Analysis 1095 Steel Rockwell Brinell 1st. Average 96.6875 206.125 Std. Dev. 3.553754 8.94334 Average +Dev 100.2413 215.0683 Average - Dev 93.13375 197.1817

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Table 4 – 1095 Steel Data Analysis It can be noticed from these tables that often the Brinell and Rockwell give out a different number for tensile strength. This shows how many errors and uncertainties go into these experiments. Plot 1 – Brinell Hardness # vs. Carbon Content % New Average 97.78571 203.29 TensileStrength 116 88

Plot 2 - Rockwell Hardness # vs. Carbon Content % Plot 3 - Tensile Strength vs Carbon Content Shown in these graphs, there is a trend with the amount of carbon in the specimen and the tensile strength. As carbon content increases, so does the tensile strength of the specimen.

Plot 4 – Impact Energy vs. Temperature This table and plot represent the obtained results with Charpy Test. The graph indicates that the aluminum remains ductile at all temperatures in the range covered by this experiment. In contrast, nylon remains brittle, as seen from low impact energies. The polyethylene becomes more ductile at temperatures above 25 degrees Celsius.

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Plot 5 – Energy vs Temperature for Cast Steel and 18/8 Steel Plot 6 – Energy vs Temperature for 1020 HR Steel and Aluminum In plot 5, it represents the relationship between the two sets of metals. The transition

temperature is from -175C to 25C. In plot 6, the transition temperature range is from -78C to 100C. Discussion The smaller the hardness number, the softer the material is. We could identify the materials by using the hardness tent machines. The steel specimens (1018, 1045, and 1095) had different percent of carbon inside of the material. The more carbon contained in the material, the harder the material is. Since the blue specimen had the lowest value in tensile strength, it is expected that the material has the least % carbon content in it. Both red and black specimen have indicated higher tensile strength, however, the red specimen showed 101-109 ksi. in strength, while black specimen has showed only 88-98 ksi, which indicates that the red specimen is harder. This contradicts our expectations, however, there are several possible errors behind the results. The data analysis indicated that strength does vary from different tests. That is because we use different properties of the material when analyzing the data. For Brinell hardness test, we measure the diameter of impression, while using Rockwell tests we analyze the height of the impression. Some possible errors behind the results could be uncalibrated machines. During the experiment we had some problems adjusting the machines, and that could result in potential error in outcomes. The rapid tests also provide us strength properties of the surface region of the materials, as the indention is not deep. Some advantages of the Impact Test might include the following: it is easy to perform, cost and time effective, provides fast measurement results. We have also shown that the test is useful for evaluating mechanical properties of the different materials and assessing the quality of

the material. Some disadvantages of the Impact Test. The test can also be applied in many industrialareas and engineering fields. However, the Impact Test has some limitations due to its small sizeand total energy measurement. As seen from the results obtained from the experiment, some materials when exposed to higher temperatures change their properties. Polyethylene, for example, become more ductile as the temperature increases. However, some materials, such as aluminum stays relatively ductile or nylon remain brittle. Some possible errors might come from machinery errors. Faulty adjustments of the impact machine, or faulty thermometer can cause an error in calculations. Some of the errors also might come from the Loss Energy, such as Mechanical or Air friction. Conclusion From the hardness experiment, we have learnt how to read the nomograph, use 2 different hardness machines, analyze data, which enabled us to convey several non-destructive tests. We have also determined how strength properties on the surface of the materials and hardness properties are related to Carbon components of steel. The impact experiment was successful since we have been able to obtain general information on the behavior of different materials. We have also learnt to identify ductile-brittle transitions and use the impact testing machine. Other objectives of the experiment were also achieve.

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