Lab 4 Tensile Test

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California State University, Long Beach *

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361

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Mechanical Engineering

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Dec 6, 2023

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California State University, Long Beach Department of Mechanical and Aerospace Engineering Fall 2023 Lab Report By Group Partners: Experiment Number: 4 Date Performed: October 11, 2023 Title: Tensile Test of Metals and Polymers Course Number: MAE 361 Section Number: 1 Class Number: EN 4 Room 125 Instructor: Dr. Shamim Mirza Objective: The goal of this experiment is to ascertain the mechanical characteristics of Aluminum 2024-T351, SAE-1018 Hot Rolled, and Brass through the utilization of a uniaxial tensile test apparatus. The outcomes of this experiment were subsequently compared to established reference values. Apparatus: 1

Figure 1: Tensile Testing Machine 2

Figure 2: Extensometer Samples: Figure 3: Brass, aluminum, and steel metal pieces 3

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Figure 4: Metal pieces after being tested Procedure: In this lab, we conducted a tensile test. This test is performed in an SFM-120 tensile machine. The software on this machine will be used to calculate the samples' tensile strength. To test the tensile strength of samples made of brass, steel, and aluminum, the machine was used. The cross-section of the standard 0.5-inch diameter is often shaped like a circle, with the distance between the shoulders being four times the diameter. The device will be used to insert a specimen with the shape depicted in Figure 1 and grasp it from both ends. Afterward, during the preloading phase, an extensometer—which measures its initial length—will be left on. After that, the machine moves on to the loading phase, where a tensile load is applied to the shoulder distance. The software tool then records our data. 4

Figure 5: Tensile Sample Test Results: Aluminum Brass Steel 1 Original Diameter 0.515 in 0.506 in 0.495 in 2 Original Area 0.208 in 0.201 in 0.193 in 3 Yield Load 9,700 lbs 9,750 lbs 15,100 lbs 4 Yield Stress 46,565.84 psi 48,485.70 psi 78,462.12 psi 5 Maximum Load 10,000 lbs 11,500 lbs 18,500 lbs 6 Tensile Strength 94018.75 psi 145710.03 psi 191191.07 psi 7 Rupture Load 7800 lbs 9000 lbs 15000 lbs 8 Rupture Strength (Final Area) 73,334.63 psi 114033.93 psi 155019.79 psi 9 Original Gage Length 2.00 in 2.00 in 2.00 in 10 Final Gage Length 2.368 in 2.469 in 2.445 in 11 Percent Elongation 18.4% 23.45% 22.25% 12 Final Diameter 0.368 in 0.317 in 0.351 in 13 Final Area 0.106 in 0.079 in 0.097 in 14 Percent Reduction In Area 48.94% 60.75% 43.02% 15 Modulus of Elasticity 16,002,005.15 psi 19,062,755.19 psi 32,044,256.13 psi 16 Modulus of Resilience 3.7257* psi 10 11 4.6213* psi 10 11 1.2572* psi 10 11 5

Calculations: Area & Cross Section: π𝑅 2 = π( ? 2 ) 2 Original—> Aluminum: = 0.208 π 0.515 2 ( ) 2 𝑖? 2 Final—> Aluminum: = 0.1064 π 0.368 2 ( ) 2 𝑖? 2 % Elongation: ∆? ? 0 (100) = ? ? −? 0 ? 0 (100) Aluminum: = 18.4% 2.368−2.00 2.00 (100) % Reduction in Area: ∆𝐴 𝐴 0 (100) = 𝐴 0 −𝐴 ? 𝐴 0 (100) 0.208−0.106 0.208 (100) = 48. 94% Modulus of Elasticity: σ 𝑃? ε 𝑃? psi 10000 0.208 (2·( 0.3 100 ))/2 = 48006.015 0.003 = 16, 002, 005. 15 Yield stress: σ ? = ? ? 𝐴 0 psi 9700 0.208 = 46, 565. 84 Tensile Stress: σ ? = ? ? 𝐴 ? psi 10000 0.106 = 94018. 75 Engineering Rupture Stress: σ ?𝑅 = ? ?𝑅 𝐴 ? psi 7800 0.106 = 73, 334. 63 % Difference between Tensile and Rupture: σ ? −σ ?𝑅 σ ? (100) 94018.75−73334.63 94018.75 (100) = 22% Modulus of Resilience: → —> = 3.7257* psi ?ℎ 2 σ ? ? ??𝑝 2 (46,565.84 𝑝?𝑖 * 16002005.15 𝑝?𝑖) 2 10 11 6

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Result and Discussion: The findings of the uniaxial loading test showed that the steel, brass, and aluminum specimens extension rates varied noticeably. When the same stresses were placed on each of the three specimens, aluminum showed significantly more extension than either steel or brass. These discrepancies were ascribed to differences in their individual microstructures. In particular, the rupture strength of stainless steel was 155019.79 psi, the yield point of brass was 48,485.70 psi, and the yield point of aluminum was 46,565.84 psi. The experiment also showed that steel, when compared to brass and aluminum, had the best tensile strength, mostly because of its crystalline structure. Because of this structural feature, steel can withstand significant axial stresses before cracking. It's crucial to remember that inaccurate measurement results and resource constraints were two possible sources of mistake that could have contributed to these disparities. Students marked each item with a pen before the experiment to assess changes in their lengths, but these markings were made obliquely and subjectively. It's possible that using more exact marking techniques will produce different outcomes. Additionally, because of the variances in these materials, the experiment's results were further clouded by the lack of published values for direct comparison, such as comparing SAE 1018 to SAE 1020. Answers to Questions: 1. Compare and contrast the set of graphs. Discuss the differences in: a) Modulus of elasticity (Young’s Modulus): The ratio of stress to strain for a material when the deformation is elastic. Aluminum is the softest material and therefore going to have the lowest modulus of elasticity. Aluminum would be the least likely to return to its original position after a heavy load is removed. Brass is a material with a moderate hardness and Young's Modulus. It shows a willingness to return to its original position and seems less prone to permanent deformation. Steel is the hardest material we tested and as seen on the graphs below it requires a strong force to cause permanent deformation (18,500 lbs). This high modulus of elasticity proves that after force is removed, Steel returns to its original size and shape. b) Proportional limit: The limit in which a material experiences the maximum stress in the elastic deformation values before transitioning to plastic deformation. Aluminums proportional limit is approximately 30-40% of its ultimate tensile strength. Lower than the other two materials, Aluminum can withstand less stress within its elastic deformation range before plastic deformation takes place. You can see this in the graph for aluminum where the blue line takes a sharp turn. Brass has a proportional limit of about 40-60% of its ultimate tensile strength. This is comparable to Steel which has a proportional limit of 50%-60% of its tensile strength. These two metals undergo significant stress in the elastic region before transitioning to plastic deformation. c) Yield point or yield strength: The point of stress on the graph, in which the material transforms from elastic to plastic deformation. 7

The Aluminum and Brass are very very comparable when it comes to yield strength, both exhibiting a value of 200-300 Mpa. The steel in this case can exhibit a yield strength as seen on the graph of about 15,000 pounds. d) Ultimate Strength: The maximum amount of stress a material can undergo before fracturing or breaking. The aluminum was the weakest in this case, completely splitting at 10,000 pounds. However, the brass didn’t do much better at only 11,500 pounds of force before it fractured. The steel had a notable higher ultimate strength than the brass and aluminum at a strength of 18,500 pounds e) Modulus of Resilience: The amount of force a material can withstand in the elastic region before plastic deformation. The energy absorption and resistance of Aluminum pales in comparison to both Brass and Steel. Brass and Steel both absorb force and energy at a much higher rate than of Aluminum. Figure 6: Tensile Properties of Aluminum 8

Figure 7: Tensile Properties of Brass Figure 8: Tensile Properties of Steel 9

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2. What properties, if any, of the material, are altered in this test? How and why does this occur? Properties such as strength, hardness, and ductility are altered. Through tensional force, alterations occur resulting in tension strain hardening; the material thereby becoming stronger and less ductile. Furthermore, it can be said that during the tensile test, length is a property that is effectively altered as a result of elongation under tension. 3. Discuss the type of fractures that occurred in the different materials. Discuss the variation of the load with deformation, yield point, and type of fracture in each specimen. A material can undergo ductile and brittle fractures. A ductile fracture experiences plastic deformation until the moment of fracture takes place. A Brittle fracture of a material endures the break in the structure. Aluminum saw a yield point of 9,700 lbs of force and experienced a ductile fracture. Brass experienced a yield strength of 9,750 lbs of force and underwent a ductile fracture. Additionally, Steel has a yield point of 15,100 lbs of force and sustained a brittle fracture. 4. What additional measurements in the experiment would have been necessary to calculate Poisson’s Ratio? State a suitable value for steel. In order to calculate Poisson’s Ratio additional measurements of axial and lateral strains would need to be conducted. Essentially, a general range of values for steel consists of 0.25 to 0.30-- therefore a suitable value for steel could be suggested as 0.27. 5. What is understood by the terms “elastic” and “inelastic” behavior? Give examples from the experiment. Elastic behavior points to the material’s ability to recover to its original shape after a tensile test. Additionally, factors of stress and strain correspond in a constant ratio. Inelastic behavior, on the other hand, can be described as non-recoverable-- as in this case, the material is not proportional to the applied force and cannot recover to its original shape. At the beginning of the tensile test, the materials experience elastic behavior, deforming proportionally to the load given; at yield point, the material will retain its deformation therefore behaving inelastically. 6. Compare the stress in the bar at rupture as computed from the area at the break with the ultimate strength obtained for the material. Explain your results. At the time of rupture, the stress in the bar is lower than the ultimate strength of the material. This can be proven because if the bar was to continue to elongate, the force necessary to create the deformation would be lower. 7. A member whose diameter is 15mm elongates 0.39mm in a gage length of 100mm under a load of 30kN. Find the modulus of elasticity and the strain energy per unit volume at this load. σ = ? 𝐴 = 30×10 3 π 4 ×15 2 = 169. 77 ?𝑃? ε = ∆? ? = 0.39 100 = 3. 9 × 10 −3 10

? = σ ε = 169.77 3.9×10 −3 = 43. 53 ?𝑝? ? = σ 2 2ε = 169.77 2 ×10 6 2 2×43.53×10 9 ≈ 331. 4 𝑘𝐽 ? 3 8. Why is an extensometer required for the tensile test of metals and alloys? Why did we not use an extensometer for the tensile test of plastics? Typically the extensometer is required for the tensile test of metals and alloys because of its ability to detect change in length. Additionally, the extensometer can detect small strain percentages as accuracy is increased. In plastics, on the other hand, we do not use an extensometer for tensile tests because of the corresponding high deformity that occurs. Conclusion: Tension is used for one of the most popular mechanical stress-strain tests. Engineering stress and engineering strain are two mechanical properties of materials that may be determined using the tension test and are crucial in design. Because it possesses the maximum modulus of elasticity, the SAE-1018 Hotrolled has the steepest slope in the elastic area. Because aluminum has a higher modulus of elasticity than brass, its The slope was slightly steeper. Because of how quickly the curve decreased at the end of the linear component of the curve, the SAE-1018 Hot Rolled was the easiest to identify as the proportional limit. Because of the rounded curve, it was a little harder to identify the proportionate limit for brass and aluminum 2024-T351. It may be concluded that SAE-1018 Hot Rolled and Brass are more ductile than Aluminum 2024-T351. There was a cup and cone fracture in the brass and SAE-1018HotRolled. There was a lot of plastic deformation in both specimens. Based on the yield strength and tensile strength, it is evident from the test results that Aluminum 2024-T351 was the strongest and least brittle material. Brass had the lowest modulus of elasticity and aluminum 2024-T351 the greatest, with SAE-1018 having the maximum. This indicates that while SAE-1018 was the stiffest material tested, it will have the greatest deformation before breaking once it leaves the elastic zone. One recommendation for this experiment is for students to wear goggles. Metal has to bend for this experiment to work. The metal fractures as a result of this deformation. The risks posed by flying debris could be avoided by donning safety goggles. It is also advised that participants use earplugs. When the accumulated strain energy was released during the experiment, all three specimens produced an audible emission. References: Materials Science and Engineering, Introduction, William D. Callister Jr. and David G. Rethwisch. 9th edition, Wiley 2014. 11