MTL300 - Lab 1

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Toronto Metropolitan University *

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300

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Mechanical Engineering

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Oct 30, 2023

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Department of Mechanical and Industrial Engineering Please select your current program below: Mechanical Engineering Industrial Engineering Course Number MTL300 Course Title Materials Science II Semester/Year F2023 Instructor Dr. Muhammad Hasibul Hasan Section Number 02 Lab/Tutorial Report No. 1 Report Title Hardness and Charpy Impact Testing Group Number 03 Submission Date 28/09/2023 Due Date 28/09/2023 Student Name Student ID (xxxx1234) Signature * Eugene Kim xxxx13519 James Mohrhardt xxxx97151 Andrew Kaseb xxxx88974 Rajbir Gill xxxx28940 (Note: Remove the first 4 digits from your student ID) *By signing above you attest that you have contributed to this submission and confirm that all work you have contributed to this submission is your own work. Any suspicion of copying or plagiarism in this work will result in an investigation of Academic Misconduct and may result in a “0” on the work, an “F” in the course, or possibly more severe penalties, as well as a Disciplinary Notice on your academic record under the Student Code of Academic Conduct, which can be found online at: http://www.ryerson.ca/senate/policies/pol60.pdf.

Objectives The primary objective of this lab was to find the absorbed impact energy versus temperature data using the Charpy impact test to observe the ductile to brittle transition temperature of a steel sample. A secondary objective was to collect and study the hardness measurements of various metallic materials. Using the hardness data it is possible to estimate the tensile strength of different materials which can be very useful for various engineering purposes. Introduction In this experiment conducted on September 14th 2023, we were given 4 blocks of metal all cooled and heated to different specific temperatures. With each temperature having a different effect on each of them in the strength of the materials and at the same time penetration and absorption. Starting off, there are many ways to test the hardness of a material such as the shore scleroscope or the Brinell hardness tester. They all differ due to some needing specific tips and weight to be added to get accurate readings and gathering sufficient data to refer to the charts from what material they might be. All machines are not perfect, they have pros and cons due to there being uncertainty in readings and some being more precise than others. The next test is the Charpy test which consists of just a sudden impact to a piece of metal to see what type of damage or deformation can be done and where the weak fracture points could have been. The height to which the anvil rises after impacting the sample is a measure of its toughness under the conditions of the experiment. This is automatically recorded by the machine and is measured in foot pounds (ft-lb). It will give a reading based on how the energy was absorbed after impact and result in high toughness. On the contrary a brittle material would break easily and will have little absorption of energy and not show up on the reading scale. (a) Comparing low and high strength metals (b) Impact energy versus temperature Figure 1: Curves that relate the impact energy absorbed by Charpy V-notch samples and temperature [3].

Here we have a clear image of high strength vs low strength steels acting against the impact of the test. Not only does the metal have a huge impact on the outcome but so does temperature and any deformations. Since the metal pieces are all notched at a certain point in the middle this severely gets rid of the integrity of the metal which we can guess where it will fracture. The machine will record how much resistance was caused and give a number along the scale of what was measured. Procedure Part A: Charpy Impact Test 1. Obtain the five steel samples prepared by the instructor to be used in the Charpy Impact Test. Samples will have a V-shaped notch in one of the sides, without the notch the Charpy Impact Test cannot be conducted. 2. Place one of the five steel samples in each of the following places, one in a deep freezer cabinet set at -40°C, one in another freezer set at 20°C, one in the prepared ice bath for an hour (0°C) and one a beaker of boiling water for 10 minutes (100°C), while the last one on the counter so that it may reach room temperature. 3. Measure the Rockwell C hardness of the room temperature sample with the measurement device after it is calibrated to Rc (by Instructor or Teaching Assistant) by putting an indent with the tip. a. Push the probe of the measurement device into the steel till the red bar turns green, if the bar turns red again it means that the indent is too deep and another spot must be chosen 4. Begin the Charpy Test by lifting the hammer/anvil of the device to the locked position at the top and set the indicator for the test on the far left. 5. Start the test by placing the room temperature steel sample in the device with the V-shaped notch facing away from where the anvil will fall and once everyone is clear pull the lever allowing the anvil to fall. 6. Let the anvil stop swinging to collect the sample to take a photo of the sample for the subsequent report and record the result of the Charpy Test. 7. Repeat steps 4 to 6 for the four other samples of steel. Part B: 1. Wait for the Teaching Assistant to demonstrate the Rockwell hardness tester. 2. Place the sample on the Rockwell hardness tester and take 2 readings for each of the 5 samples and record the results for the lab report. Part C: 1. Wait for the Teaching Assistant to demonstrate the Brinell hardness tester. 2. Place the sample on the Brinell hardness tester and make an indent away from other previously made indents. 3. Remove the sample from the Brinell hardness tester and put a magnifying scope over the indent to take an x & y in order to determine the average diameter. 4. Repeat steps 2 and 3 for all 3 samples and record the results for the lab report.

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Fracture Photos: (a) Room temperature specimen (b) -40°C temperature specimen (c) 100°C temperature specimen (d) -20°C temperature specimen (e) 0°C temperature specimen Figure 2: Fracture surfaces for various Charpy V-notch specimens after the impact test.

Analysis/Data CHARPY TEST Deg C Room Temp 0 -20 -40 100 lb-ft 4 2 1 1 5 Table 1: Charpy test for specimens at different temperature Room temp Hardness (HRC) Trial 1 1.2 Trial 2 3 Trail 3 1.8 Table 2: Rockwell C hardness for room temperature specimen ROCKWELL TEST 81/91 steel (HRC) 82/92 steel (HRC) Al alloy (HRE) Mg alloy (HRE) Iron (HRC) Trial 1 26 61 100 76 49 Trial 2 25 60 100 75 47 Table 3: Rockwell C hardness for room temperature specimen BRINELL TEST Sample 1 "skinny" Sample 2 "medium" Sample 3 "chunky" x y x y x y mm 3.95 3.70 4.85 4.80 4.00 4.00 Load of kg 39.1 44.9 25.4 25.9 38.1 38.1 Table 4: Brinell test for different sized specimens HARDNESS TEST Steel Samples 600 800 900 1000 1100 1200 HRC 42.6 38.4 34 30.2 28.8 23.3 Table 5: Rockwell hardness test for different sized specimens

2. Construct a graph of the energy absorbed (ft-lb) versus temperature and estimate the transition temperature for the steel supplied. Indicate the brittle and ductile zones. Figure 3: Measured impact energy absorbed by materially identical specimens at varying temperatures. We can see that the transition temperature is approximately 0 degree celsius. 3. Comment on the relative ductility of the impact test pieces based on the fracture at the notch as a function of temperature. From the graph above, it is clear that when specimens are at a lower temperature, they are brittle and when specimens are at a higher temperature, they are ductile. Due to this, brittle materials require less energy than ductile materials to cause them to fracture. As shown in the figure above, as you increase the specimen temperature, the energy absorbed increases, meaning that higher temperature materials require more energy to cause them to fracture. In addition, brittle materials experience less deformation (the surface is flat when it fractures) and provide no warning before fracturing. Oppositely, ductile materials experience deformation (edges on the surface when it fractures) and provide a warning before fracturing as shown by the figure in the procedure section. Overall, the higher the temperature is, the more ductile the material is, meaning that it will require more energy to fracture the material.

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4. Estimate from the hardness data the tensile strength in lb/in 2 of all the samples tested. Use either the chart in the laboratory or the appropriate formula. In the course textbook, there is a relationship between hardness and tensile strength at least for most steels, cast iron, and brass. Since both tensile strength and hardness indicate a metal's resistance to plastic deformation, the two qualities are shown to be roughly proportional. The textbook only describes this relationship between tensile strength and HB or Brinell hardness with the following equation for steel alloys and the graph [1]: ?? (𝑃𝑠𝑖) = 500 · 𝐻? Figure 4: Correlation between Brinell hardness and tensile strength of various materials [1]. Therefore we can estimate the tensile strength of the tested steel specimens to be roughly 500 times that of the measured hardness. However, in the experiments we only measured the HRC values of steel samples. In order to estimate the strength we can convert HRC units into HB units using the conversion table [2].

ROCKWELL TEST 81/91 steel 82/92 steel Iron Trial 1 (HRC) 26 61 49 Trial 2 (HRC) 25 60 47 Trial 1 (HB) 255 642 468 Trial 1 (HB) 250 627 445 HB Avg (HB) 252.5 634.5 456.5 TS (Psi) 126250 317250 228250 Table 6: HRC, HB, and tensile yield strength for room temperature steels. Room temp Hardness Trial 1 (HRC) 1.2 Trial 2 (HRC) 3.0 Trial 3 (HRC) 1.8 Trial 1 (HB) 154.4 Trial 2 (HB) 160 Trial 3 (HB) 155.6 HB Avg 156.7 TS (Psi) 78350 Table 7: HRC, HB, and tensile yield strength for a single room temperature Charpy test steel sample. HARDNESS TEST Steel Samples 600 800 900 1000 1100 1200 HRC 42.6 38.4 34 30.2 28.8 23.3 HB 396.4 352.8 314 279.6 269.6 241.5 TS (Psi) 198200 176400 157000 139800 134800 120750 Table 8: HRC, HB, and tensile yield strength for different test steel samples. Sample Calculations: 𝐻? ?𝑣𝑔 = 255−250 ( ) 𝐻? 2 = 252. 5 𝐻? ?? (𝑃𝑠𝑖) = 500 · 𝐻? = 500 · 252. 5 = 126250 𝑃𝑠𝑖

𝐻? 2 −154 ( ) 𝐻? 1.2−1 ( ) 𝐻?? = 156−154 ( ) 𝐻? 2−1 ( )𝐻?? ⇒ 𝐻? 2 = 154. 4 𝐻? The Brinell tester used a 500 or 300 kg load but usually a 3000 kg load is used to estimate the tensile strength using the equation shown earlier. Therefore, data for table 4 was not converted to tensile yield strength [3]. 5. Comment on the relative strengths of the materials tested based on the hardness tests. Compare to published data. Looking at the previous results, we can see that when a steel material increases in hardness, it also features a linearly increasing and proportional increase in tensile yield strength. Between the different tested steels we can see that there is a significant variation in the hardness and tensile strength values. There was an estimated tensile strength range for steel samples roughly between 78,000 and 320,000 psi. While it is difficult to find exact published data for each specific specimen's hardness and tensile strength, it can be determined that the measured values appear plausible. This is because we can estimate different steels to have a tensile strength between 50,000 and 250,000 psi as seen in the figure 4 which is where most of the experimental values fall [1]. The excessive 320,000 psi measurement could be from measurements taken too close to each other or the specimen edge which can introduce errors. When comparing steel to iron we can see that iron has a relatively high hardness and tensile strength exceeding the upper values indicated by figure 4 [1]. This is possibly because it was measured with the HRC scale instead of the softer HRE scale more appropriate for irons which might have caused this error. 6. Why is it necessary to use different hardness scales? Different scales have varying ranges that are specific to hardness values for different materials based on their relative hardness. For example, softer materials like soft-steels and non-ferrous alloys tend to use the HRE scale whereas harder steels use a different HRC scale. It is not ideal to use the same scale as much as possible because when values approach the upper and lower bounds of each scale, they lose accuracy. Fortunately, because of overlap between scales it is easy to switch between the next harder or softer hardness scales for better data [1]. 7. Discuss the significance of the above tests to engineering applications. Common hardness tests are in general considered one of the easier tests for determining mechanical properties. They are also performed more frequently than other mechanical tests because they are usually inexpensive to perform and the specimen is not excessively damaged by the test. While the hardness itself might not be the most valuable information by itself, it was established that hardness values correspond to other mechanical properties like ultimate tensile yield strength which is a very important quality [1]. In essence, a fairly simple test for hardness can estimate very important information for engineers who do not want to spend much money, time, or destroy samples. Using this information engineers can quickly and cheaply estimate the strength of unknown steel alloys that they may want to study further for various engineering projects.

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Conclusion In this experiment the main objective to see the ductile to brittle transition temperature for a steel material was successfully accomplished by setting 5 notched steel samples at varying temperatures and measuring the absorbed impact energy. Through this, we learned that the transition temperature is approximately 0°C for the steel as seen in figure 3. Also, we saw that at lower temperatures it appeared significantly more brittle and absorbed less energy while at higher temperatures it absorbed more energy and was more ductile. Additionally the fracture surface gave supporting indications of ductile or brittle material behavior. In the other part of the experiment, measurements of different metal samples yielded a large range of hardness values for the materials. Using the hardness values we could estimate the tensile strength of the metals after converting the hardness units to HB. We noticed for steel alloys that the hardness values roughly ranged from 1 to 60 HRC which corresponds to 78,000 and 320,000 psi of tensile strength. Although they do not closely match the range indicated by figure 4 which shows a range of 50,000 to 250,000 psi, it can easily be explained by errors in measurement technique. This could include accidentally measuring hardness too close to other measurements or too close to the edge of a sample’s face which could affect the experimental values. While the overall lab was successful, it is possible that with better attention to detail for hardness measurements there could be more consistent results. Also the Charpy test did not feature many graduations in energy values making precise measurements difficult and could have affected the results of the lab.

References [1] Callister, W.D., Materials Science and Engineering an Introduction 10th Edition, John Wiley & Sons, USA, 2018. [2] “Steel Hardness Conversion Table,” STEELEXPRESS, https://www.steelexpress.co.uk/steel-hardness-conversion.html (accessed Sep. 20, 2023). [3] Department of Mechanical Engineering and Industrial Engineering Materials Laboratory MTL 300 Manual, Toronto Metropolitan University. Page. 11-14