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Department of Building, Civil, & Environmental Engineering ENGR 244: Mechanics of Materials Experiment No.2: Tension Test on Metals Luis Alberto Alvarado Bravo 40193230 Group members: Erica Sciotto, Sofia Mendicino Section: CC-CM-X Summer 2022 July 11, 2022

1 OBJECTIVE The main purpose of this experiment is to test the tensile strength of an aluminum rod & a steel rod and see at what maximum load the rods reach their fracture points. INTRODUCTION Tensile strength is the ability of a material to resists and sustain uniaxial loads. The tensile strength of any material can be represented using a stress-strain curve. Figure 1- Stress-strain curve As shown in Figure 1, the stress-strain curve has three distinct points: yield strength, ultimate strength, and fracture point. The yield strength is the maximum stress a material can experience before permanent deformation is visible. When looking at figure, the yield strength can be identified as the point where the linear trend stops. This section of the curve is the elastic behavior of the material, meaning that no matter what the load was, the material will always return to its original state. The slope of the linear section of the curve is called the Young’s modulus , also called the modulus of elasticity, which means how easily a material can stretch. The second point on the curve, the ultimate strength, is the maximum

2 load a material can withstand. The trend at this point of curve is curved, and on the material, itself necking would begin to show. When the neck has reached its limit, it would break, which would be the fracture point of the material. The combined curved of the ultimate strength and the fracture point is called the plastic behavior, because the deformation at this point is permanent. The tension stress and subsequent use of the stress-strain curve have real-life applications in many fields. One use would be in selecting the material needed for beams used as bridge trusses. Static analysis of a bridge shows that many the majority of the truss’ members experience one of two loads, compression or tension. If engineers wanted to make bridge that would itself well for a long time, they would have to choose the material that would have a high ultimate strength value to avoid reaching the fracture point easily. For this lab however, the test materials are subjected to loads that would make it reach their fracture point. In a real scenario, like the bridges, the beams would most likely never experience loads close to their ultimate strength value.

3 PROCEDURE To perform the experiment, the following materials were used: • Tension test machine • Deformation measurement device • Vernier caliper • Steel and aluminum rods of length 100 mm • V-groove tray The tension machine has two latch-like spaces where the material can be attached. The machine itself is connected to a hydraulic pump that increases the load with every stroke. The deformation measurement device has two ends with set screws that hold the metal rods in place. A thin rod sticks out of the device that determines how much elongation the material experiences. Each device is connected to a reader. The experiment follows these next steps: 1. Measure the diameters of the material rods at the center using the caliper. 2. Place the metal rod in the deformation measurement device, securing it with the set screws 3. Using a couple screw-on caps, place the rod in the tension test machine. The number of exposed threads on the rod should be equal on each end to make sure that the load is being applied evenly. 4. Apply the load steadily and record the load and deformation every 500 N. After reaching 5000 N, record data every 200 N. The load reader will begin fluctuating at some point, when that happens data is taken every 0.5 mm for aluminum, and every 0.25 mm for steel. 5. When the rod snaps, record the maximum load stored on the reader’s memory. 6. While still keeping the rod in the deformation device, using the v-groove tray, measure the diameter of the rod at the fracture point. 7. Repeat the process for the other test material.

4 RESULTS As stated earlier, measurements were taken of the diameter and initial lengths of the rods. These measurements were later retaken after the rods snapped. Table 1 - Rod measurements Table 2 - Load and deformation values Having taken all the values of the load and corresponding deformation, a stress-strain table can be created. Stress can be determined using the following formula, 𝜎 = 𝑃 𝐴 where P is the load in Newtons and A is the cross-sectional area of the material. Since the rod is cylindrical, the cross-sectional area formula is 𝐴 = 𝜋𝑟 2 Sample Steel Li = 100 mm di = 4.01 mm Lf = 103.2 mm df = 3.03 mm Aluminum Li = 100 mm di = 4.99 mm Lf = 111.4 mm df = 3.50 mm Before fracture After fracture Load (N) Deformation (δ) Load (N) Deformation (δ) Load (N) Deformation (δ) Load (N) Deformation (δ) 0 0.00 5775 3.91 0 0.00 6800 0.25 491 0.01 5857 4.45 449 0.00 7010 0.30 1001 0.01 5882 4.84 976 0.00 7210 0.30 1502 0.07 5906 5.33 1524 0.00 7399 0.31 2000 0.13 5932 5.89 2008 0.01 7606 0.53 2499 0.19 5961 6.47 2593 0.02 7696 0.77 3001 0.26 5992 6.78 3004 0.05 7744 1.05 3502 0.30 5998 7.26 3504 0.05 7770 1.29 4011 0.31 6007 7.89 4005 0.10 7780 1.54 4491 0.38 6012 8.35 4507 0.16 7789 1.76 4990 0.45 6034 8.87 4998 0.16 7750 1.98 5216 0.50 6026 9.32 5201 0.16 7494 2.40 5402 0.57 5959 9.99 5404 0.18 7199 2.93 5544 0.87 5931 10.60 5606 0.19 6892 3.65 5584 1.36 5502 11.17 5824 0.19 6629 3.75 5649 1.81 4838 11.71 6002 0.21 6425 3.94 5671 2.33 6189 0.21 5712 2.86 6389 0.24 5750 3.38 6619 0.25 Maximum Load, P max = 6062 N Maximum Load, P max = 7838 N ALUMINUM STEEL

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