Lab report engineering materials lab - tensile test
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The document presents a lab report on the tensile testing of two unknown steel specimens to determine their mechanical properties, including tensile strength, yield strength, and ductility. The results indicate that both specimens have yield strengths of 400 MPa and 350 MPa respectively, suggesting similarities to 304 stainless steel. The methodology, experimental setup, and data analysis are thoroughly detailed, demonstrating the importance of tensile tests in material selection.
Lab report engineering materials lab - tensile test
- 1. 0 Lab Report Engineering Materials Lab Module A: Tensile Test Name : Muhammad Yossi Hadiyoso Student Number : 2014 31 0003 Lab Date : Saturday, March 4th 2017 Report Handover Date : Friday, March 10th 2017 Materials Engineering Laboratory Applied Physics Study Program Faculty of Science and Technology Sampoerna University 2017
- 2. 1 Abstract The mechanical properties of material can be observed through tensile test. It gives the the characteristic of tensile strength, yield strength, modulus of elasticity, ductility, recilience, and toughness. These characteristics might useful for material testing reference. In this experiment, the two unknown steel are being tested using tensile test machine. The result are being computed. The similarity of mechanical properties of the specimens are being compared to the exist material on the data sheet.
- 3. 2 Table of Content Cover............................................................................................................................................. Abstract....................................................................................................................................... 1 Table of Content........................................................................................................................... 2 List of Figures and Tables.............................................................................................................. 3 Chapter 1: Introduction................................................................................................................. 4 1.1 Background......................................................................................................................... 5 1.2 Experiment Objective .......................................................................................................... 5 Chapter 2: Fundamental Theory.................................................................................................... 5 2.1 Tensile Test......................................................................................................................... 5 2.1.1 Specimen ..................................................................................................................... 5 2.2 Mechanical Propertiesfrom Tensile Test............................................................................... 5 2.2.1 Yield Strength............................................................................................................... 5 2.2.2 Tensile Strength............................................................................................................ 5 2.2.3 Modulus of Elasticity..................................................................................................... 6 2.2.4 Modulus of Resilience................................................................................................... 6 2.2.5 Modulus of Resilience................................................................................................... 6 Chapter 3: Experimental Method................................................................................................... 7 3.1 Apparatus ........................................................................................................................... 7 3.2 Procedure........................................................................................................................... 7 3.3 Experimental Data............................................................................................................... 7 Chapter 4: Discussion and Analysis ...............................................................................................10 Chapter 5: Conclusions and Recommendations .............................................................................19 References..................................................................................................................................20 Appendix.....................................................................................................................................21
- 4. 3 List of Figures and Tables Figure 1. Figure 1 Tensile test machine................................................................................................. 5 2. Figure 2 The standard specimen dimension of tensile test ....................................................... 5 3. Figure 3 Initial dimension of specimens used on the experiment.............................................. 7 4. Figure 4 Force vs time: Specimen A......................................................................................... 8 5. Figure 5 Force vs time: Specimen B......................................................................................... 8 6. Figure 6 Engineering stress-strain curve andits yield strength ................................................10 7. Figure 7 Force vs elongation curve of the specimens ..............................................................13 8. Figure 8 Engineering Stress-strain curve of the specimens ......................................................14 9. Figure 9 True stress-strain curve of the specimens..................................................................15 10. Figure 10 Logaritmic plot of true stress-strain curve .............................................................15 11. Figure 11 Engineering-True stress-strain plot........................................................................17 Tabel 1. Table 1 Data measurement.................................................................................................... 7 2. Table 2 DataCalculation from Specimen A .............................................................................. 9 3. Table 3 DataCalculation from Specimen B .............................................................................. 9
- 5. 4 Chapter 1: Introduction 1.1. Background Metals have its own properties including physical, mechanical, and thermal characteristic. The most important properties is the mechanical properties, which is including ductility, hardness, strength, and toughness. The mechanical properties is the measurements that used as a reference for material selection. To know the mechanical properies of metals, it needs material testing. One of the material testing is the tensile test. Tensile test is a measurement that examine the strength of material within giving loads in unaxial direction to the specimen. The tested specimen is exposed by the increasing unaxial force continuously while its change on elongation is being observed. The tensile test measures the resistant of a material to the given static load. The results that generated from the tensile test shows the mechanical properties of the specimen. The mechanical properties of material that can be known from tensile test including: - tensile strength - yield strength - modulus of elasticity - ductility - resilience - toughness Furthermore, the stress strain curve which is can be obtained from the measurement, which allows one to compute the mechanical properties above. The tensile test is very important because it tells the impact of load given to the material’s mechanical properties of a material. These mechanical properties parameters would provide the basic data if the strength of an material, in this experiment is metal. 1.2. Experiment Objectives - To evaluate the mechanical properties of the specimen through an understanding of curve result of tensile test.
- 6. 5 Chapter 2: Fundamental Theory 2.1. Tensile Test Tensile test is a method used to measure the strength of an material by giving a static load on unaxial direction of the specimen. The following is the scheme of tensile test: Figure 1 Tensile test machine The specimen that being tested is given some force in two directions, which is in unaxial direction. The specimen would experience a stretch and an elongation until it fracture or break. Moreover, the specimen size is standardized by some standard. For example, the Indonesian tensile test specimen standard SNI 07-0371-1998, the standard American Society for Testing and Materials (ASTM) E8 & E8M. 2.1.1. Specimen The standard specimen by ASTM is the following: Figure 2 The standard specimen dimension of tensile test From the ASTM standard, the dimensions of the specimen of tensile test is looks like above. The reduction section A, 2.25 inch, the diameter D, 0.505 inch, the gauge length G, 2 inch, and the radius R, 0.375 inch. Or diameter D : gauge length G is 1:4. 2.2. Mechanical Properties from Tensile Test 2.2.1. Yield Strength Yield strength determine the stress of the material due to elastic limit. It is the maximum load that obtained by the material when it is in between of elastic deformation and plastic deformation. 2.2.2.Tensile Strength
- 7. 6 It is the maximum load that can be hold by the specimen before it experiencing necking phenomenon. Necking happens when the gage of the specimen is starting to decrease. The tensile strength happens in the plastic regime. 2.2.3. Modulus of Elasticity Modulus of elasticity of young modulus is a measurement of resistant of the material due to elastic deformation. It shows the stiffness of a material. 2.2.4. Modulus of Resilience It is the properties that shows maximum energy that can be absorbed by the material until the elastic limit. It is the area below the elastic deformation of stress-strain curve. 2.2.5. Toughness Toughness measures the energy that is needed for material to fracture.
- 8. 7 Chapter 3: Experimental Method 3.1. Apparatus The apparatus that is used in the experiment are: - Tensile Machine (TEST RESOURCES 313 Q:1) - Vernier Caliper - Stopwatch - 2 unknown steel specimens with the same initial dimensions: Figure 3 Initial dimension of specimens used on the experiment 3.2. Procedure The procedure of the tensile test experiment: - Prepare tensile test specimen - Determine the initial dimension of the specimen (diameter, gage length) - Prepare tensile test machine - Record the testing parameters - Put the specimen into the machine - Test the material - Measure the time until the specimen is break - Take the specimen from the machine - Measure the final diameter and gage length - Repeat the test for the other specimen 3.3. Experiment Data - Machine Type : TEST RESOURCES 313 Q:1 Maximum load capacity : 50,000 N Test rate : 3 mm/min 0.05 mm/s - Data measurement: Specimen A Specimen B Maximum load capacity 17,426.8 N 14,660.2 N Initial length, Lo 35 mm 35 mm Initial diameter, do 6.1 mm 6.1 mm Final length, Lf 44.9 mm 46.5 mm Final diameter, df 4.0 mm 3.6 mm Total testing duration 225 seconds 220 seconds Table 1 Data measurement
- 9. 8 - Data from machine: Figure 4 Force vs time: Specimen A Figure 5 Force vs time: Specimen B
- 10. 9 Data for plottingrandompoints: Table 2 DataCalculation from Specimen A Table 3 DataCalculation from Specimen B Force (N) Time (s) Elongation (t*0.05mm/s) Engineering Stress (MPa) Engineering Strain True Stress (Mpa) True Strain 0 0 0 0.00E+00 0 0 0 1500 5 0.25 5.13E+07 0.007142857 51692533.3 0.007117468 5000 10 0.5 1.71E+08 0.014285714 173530490 0.014184635 9250 20 1 3.17E+08 0.028571429 325552975.7 0.028170877 11250 25 1.25 3.85E+08 0.035714286 398692411.1 0.03509132 11750 30 1.5 4.02E+08 0.042857143 419283881.2 0.041964199 11500 32.5 1.625 3.93E+08 0.046428571 411768300.1 0.045383006 12000 35 1.75 4.11E+08 0.05 431137724.6 0.048790164 14250 50 2.5 4.88E+08 0.071428571 522424538.7 0.068992871 15250 60 3 5.22E+08 0.085714286 566540388.6 0.082238098 16000 70 3.5 5.47E+08 0.1 602224123.2 0.09531018 16750 85 4.25 5.73E+08 0.121428571 642734938.3 0.114603383 17250 100 5 5.90E+08 0.142857143 674569228.9 0.133531393 17500 132.5 6.625 5.99E+08 0.189285714 712147134.3 0.173352887 17250 170 8.5 5.90E+08 0.242857143 590248075.3 0.217412877 17000 180 9 5.82E+08 0.257142857 581693755.3 0.228841572 16500 190 9.5 5.65E+08 0.271428571 564585115.5 0.240141128 16250 195 9.75 5.56E+08 0.278571429 556030795.6 0.245743383 16000 200 10 5.47E+08 0.285714286 547476475.6 0.251314428 15000 210 10.5 5.13E+08 0.3 513259195.9 0.262364264 13250 220 11 4.53E+08 0.314285714 453378956.4 0.273293335 12697.1 222.5 11.125 4.34E+08 0.317857143 1010432914 0.844029753 Steel A Force (N) TIME Elongation (t*0.05mm/s) Engineering Stress (MPa) Engineering Strain True Stress (Mpa) True Strain 0 0 0 0 0 0 0 2250 5 0.25 76988879.38 0.007142857 77538799.95 0.007117468 7500 15 0.75 256629597.9 0.021428571 262128803.6 0.021202208 9375 20 1 320786997.4 0.028571429 329952340.2 0.028170877 10125 22.5 1.125 346449957.2 0.032142857 357585848.7 0.031637085 9750 25 1.25 333618477.3 0.035714286 345533423 0.03509132 10312.5 30 1.5 352865697.2 0.042857143 367988512.8 0.041964199 9937.5 32.5 1.625 340034217.3 0.046428571 355821520.2 0.045383006 11250 40 2 384944396.9 0.057142857 406941219.6 0.055569851 12187.5 50 2.5 417023096.7 0.071428571 446810460.7 0.068992871 12937.5 60 3 442686056.5 0.085714286 480630575.6 0.082238098 13687.5 75 3.75 468349016.3 0.107142857 518529268 0.101782694 14062.5 85 4.25 481180496.2 0.121428571 539609556.4 0.114603383 14437.5 100 5 494011976 0.142857143 564585115.5 0.133531393 14625 117.5 5.875 500427716 0.167857143 584428082.6 0.155170568 14660.2 142.5 7.125 501632164.2 0.203571429 603750140.5 0.185293327 14625 167.5 8.375 500427716 0.239285714 500427716 0.214535177 14437.5 175 8.75 494011976 0.25 494011976 0.223143551 14062.5 185 9.25 481180496.2 0.264285714 481180496.2 0.23450731 13312.5 195 9.75 455517536.4 0.278571429 455517536.4 0.245743383 12375 205 10.25 423438836.6 0.292857143 423438836.6 0.256854609 11062.5 215 10.75 378528657 0.307142857 378528657 0.26784373 10312.5 220 11 352865697.2 0.314285714 1013214777 1.054795979 Steel B
- 11. 10 Chapter 4: Discussion and Analysis From the tensile test result, the two unknown steel specimens gives its own mechanical properties measurement value. Figure 6 Engineering stress-strain curve and its yield strength By approximation plot from the engineering stress-strain plot of each specimen, the yield strength σy of steel A is 400 Mpa and σy of steel B us 350 Mpa. It is quite lower than the data sheet of steel, which is exactly 301, 304, and 310 stainless steels. However, the nearest value of yield strength of those specimens is close to the 304 stainless steel. The 304 stainless steel has a yield strength about 470-1000 Mpa (Rowlands, David P., n.d.). And the specimens has the value around 400 Mpa, for the largest. The different value perhaps comes from the approximation data plotting when it is convert from the force-time curve to the engineering stress-strain curve. Such that, the reading of plotting might contributes error. For the tensile strength σu of the specimens, steel A has the engineering tensile strength about 599 Mpa, and steel B about 501 Mpa. However, its true stress value gives the closer value to the 304 stainless steel’s tensile strength. The true tensile strength of steel A is about 712 Mpa, and steel B about 603 Mpa, where the 304 stainless steel has 685- 1100 Mpa of tensile strength (Rowlands, David P., n.d.). From these experimental data (value of true stress of tensile strength), steel A and steel B maybe have similar composition to the 304 stainless steel, because the value of yield strength and tensile strength are close. But the yield strength and tensile strength are not enough to evaluate these specimens to what kind of steel is. Then, for the elongation of the specimen, steel A has elongate about 11.125 mm and steel B about 11 mm, where both steel A and steel B experienced 31% elongation at break. According to the ASM Aerospace Specification Metal Inc. (n.d.), the elongation of 304 stainless steel is about 70% at break. Perhaps, the difference comes from the size of the specimen from this experiment to the ASM. The ASM states that its elongate about 70% at break in 50 mm. The ASM does not mention what is the meaning of 55 mm. It is unclear,
- 12. 11 evenmore the percent elongation is very far. However, according to American Metals Co., the 304 stainless steel has 40% elongation minimum, where the specimen dimension is using the standard ASTM. These value is not too far to this experiment. In addition, during the tensile test, the specimen is being strecthed and it is elongate. While the length is getting longer, the area of speciment is being narrower. The percent reduction of the area, q, then given by: 𝑞 = 𝐴 𝑜 − 𝐴𝑓 𝐴 𝑜 where Ao is the initial cross section area, and Af is the final cross section area. Both steel A and B has an Ao about 29.225 mm2. The Af of steel A is 12.566 mm2 and steel B is 10.178 mm2. Therefore, 𝑞 𝑠𝑡𝑒𝑒𝑙 𝐴 = 29.225 − 12.566 29.225 = 0.57 → 57% 𝑜𝑓 𝑎𝑟𝑒𝑎 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑞 𝑠𝑡𝑒𝑒𝑙 𝐵 = 29.225 − 10.178 29.225 = 0.65 → 65% 𝑜𝑓 𝑎𝑟𝑒𝑎 𝑟𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛 Steel A experienced the lower reduction of area than steel B, but steel A got more elongation than steel B. The (engineering) strain of steel A is about 0.317 while steel B is 0.314. It shows that the composition of these two steel probably are same. The Young Modulus, E, of the specimen, the elasticity of the steel specimens, are described from the ratio of stress and strain before its yield strength. Therefore, taking engineering value before yield strength: 𝐸𝑠𝑡𝑒𝑒𝑙 𝐴 = σ 𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 ε 𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 = 4.02𝐸 + 08 𝑁 0.042857143 𝑚2 = 9.38 × 109 𝑃𝑎 𝐸𝑠𝑡𝑒𝑒𝑙 𝐵 = σ 𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 ε 𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 = 352865697.2 𝑁 0.042857143 𝑚2 = 8.23 × 109 𝑃𝑎 Steel A has 9.38 GPa of elastic modulus, while steel B has 8.23 GPa. However, modulus of elasticity of steel generally is aroud 200 GPa. This is a big different with general steel’s elastic modulus. This big difference perhaps because of the reading when converting the force-time curve to the stress-strain curve. Futhermore, when the specimen is stretched until its yield strength, it means it starting to began transform to the plastic deformation, thereby, achieving the limit of elastic deformation. When it achieved the limit, the modulus of resilience is being determined. The modulus of resilience tells the maximum energy that can be absorbed until the elastic limit. The modulus of resilience, Ur, is given by: 𝑈𝑟 = 1 2 σy εy where the specimen yield strength and yield strain are:
- 13. 12 Hence, the modulus of resilience: 𝑈𝑟−𝑠𝑡𝑒𝑒𝑙 𝐴 = 1 2 (4.00 × 𝑒8)(0.048) = 9.6 × 106 𝐽𝑚−3 𝑈𝑟−𝑠𝑡𝑒𝑒𝑙 𝐵 = 1 2 (3.5 × 𝑒8)(0.035) = 6.125 × 106 𝐽𝑚−3 It shows how much the energy per surface of the elastical deformation of the specimen. In other hand, when it is come to fracture, the toughness is measured. Toughness describes the energy of mechanical deformation per unit volume until it is fracture, or it measures the required energy for fracture. Therefore, it described as: 𝑈𝑡 = σy + σu 2 × εf where εy is the strain when it is fracture. Then, the specimen toughness are: 𝑈𝑡− 𝑠𝑡𝑒𝑒𝑙 𝐴 = 4.00 × 𝑒8 + 599 × 106 2 × 0.317 = 1.58 × 108 𝐽𝑚−3 𝑈𝑡− 𝑠𝑡𝑒𝑒𝑙 𝐵 = 3.5 × 𝑒8 + 501 × 106 2 × 0.314 = 1.34 × 108 𝐽𝑚−3 The toughness of steel A is greater than steel B. It means the specimen A could absorb more energy to do mechanical deformation until its fracture. The steel B is more fracture perhaps because the composition that build up this specimen is more brittle. It is shown from the plot of stress-strain curve that the stress and strain of steel B is lower than steel A. The plot of the force vs elongation curves of the specimen that can be obtained through experiment are the following:
- 14. 13 Figure 7 Force vs elongation curve of the specimens This curve is obtained by converting the time axis from the experimental data to its elongation. The plots are the appoximation plot, which is by random picking of 21 points for steel A, and 23 points for steel B. The previous data of x-axis is in the form of time interval of testing duration until it fracture was recorded on the experiment. To make this axis as elongation, it needs to be converted. Besides, the speed of the tensile test’s strecthing is been determined from the first, where the test duration for steel A is 225 seconds, while for steel B is 220 seconds. The speed of the test machine is 0.05 mm/s. Hence, the final elongation can be obtained by calculating the following: 𝑒𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝑠𝑡𝑒𝑒𝑙 𝐴 = 𝑟𝑎𝑡𝑒 𝑥 𝑡𝑖𝑚𝑒 = 0.05 × 225 = 11.25 𝑚𝑚 𝑒𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝑠𝑡𝑒𝑒𝑙 𝐵 = 𝑟𝑎𝑡𝑒 𝑥 𝑡𝑖𝑚𝑒 = 0.05 × 220 = 11 𝑚𝑚 That is the elongation based on the data obtained from the machine. However, the measured final elongation using vernier caliper is the following: 𝑒𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙𝑙𝑦− 𝑠𝑡𝑒𝑒𝑙 𝐴 = 𝐿 𝑓 − 𝐿 𝑖 = 44. 9 − 35 = 9.9 𝑚𝑚 𝑒𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙𝑙𝑦− 𝑠𝑡𝑒𝑒𝑙 𝐵 = 𝐿 𝑓 − 𝐿 𝑖 = 46. 5 − 35 = 11.5 𝑚𝑚 The different of elongation is quite far for steel A, which is about 1.35 mm length difference. The measurement of test duration might be not very accurate and it deviate just a little bit second. Moreover, the fracture is happen sunddenly. Perhaps the one that record the final time test duration is too late a little bit. Thereby, affecting the convertion from time axis to elongation axis. The plot of the engineering stress vs engineering strain curves of the specimen that can be obtained through experiment are the following:
- 15. 14 Figure 8 Engineering Stress-strain curve of the specimens This curve is obtained by converting the force to the engineering stress and the elongation to the engineering strain. By previous force vs elongation curve, the data then is able to be converted to the engineering stress-strain by the following: 𝜎𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 = 𝐹 𝐴0 𝑒 𝑒𝑛𝑔𝑖𝑛𝑒𝑒𝑟𝑖𝑛𝑔 = ∆𝐿 𝐿 𝑜 where the A0 is the initial area, ∆L is the elongation, and Lo is the initial length of the specimen. Both steel A and steel B shows almost similar curve. The curve is similar to tensile test curve for metal, yes, because they are steel. In addition, the curve shows the the leaning line when it pass the yield strength position. The curve is getting lean beyond its yield strength. This line is showing the strain hardening phenomena. It happens when elastic limit is passed. The material is begin to experience plastic deformation by strengthening it. It is strengthened because the dislocation is moving. It makes the material is more stronger, but the ductility is decrease. The material would continue to deform plastically through the movement of dislocation, stretching the bonds of its atoms until the fracture is happen. On the other hand, there is a jumping back line on the curve, increase-and-decrease, upper and lower yielding, when it is across the yield strength position. Here, the material has finished its elastic deformation. However, the dislocation is still continue as the given force is still going. The dislocation is actually meet the resistant that hold up the moving of dislocation. The resistant is might be the impurities that present on that material which is spread on the grain. Let say the impurities of these steel specimen is carbon. When the dislocation meets carbon impurities, then the higher stress is needed to pass the impurities. After the carbon impurities is passed, the energy that needed to move the dislocation is getting low. Then, it makes the stress curve is going down. When the dislocation is meet the carbon impurities again, the same thing would happen until all the impurities is passed, and
- 16. 15 the dislocation keep happen until its plastic deformation. The number of carbon atom inside these steel not large, hence it can bee observed through the upper and lower yielding of the stress. This phenomenon is called cottrell phenomenon. Another plot that can be obtained is the true stress-strain curve, which is the following: Figure 9 True stress-strain curve of the specimens From this curve, the true stress at maximum load can be obtained. For steel A, the true stress at maximum load is 712 MPa, while the steel B is 603 MPa. The specimen A has higher true stress than specimen B. It means, the energy required to fracture for steel A is higher than steel B. From the true stress-strain curve, the strength coefficient can be obtained by taking a linear regression of logaritmic plot of these curve: Figure 10 Logaritmic plot of true stress-strain curve The strength coefficient can be generated from the formula: 𝜎𝑡𝑟𝑢𝑒 = 𝐾𝜀 𝑛
- 17. 16 where σtrue is the true stress, ε is the true strain, n is the strain hardening exponent, ε is the true strain, and K is the strength coefficient. The value of n is lies between 0 to 1. 0 means the material is a prefectly plastic solid, 1 means it prefectly elastic solid. Most metal have an n between 0.1 until 0.5. Then, the logaritmic form of the above simple power equation: log (𝜎𝑡𝑟𝑢𝑒) = log(𝐾. 𝜀 𝑛 ) or it can be written as: log(𝜎𝑡𝑟𝑢𝑒 ) = 𝑛 log ( 𝜀)+ log 𝐾 It is same as the: 𝑦 = 𝑚𝑥 + 𝑐 Which is similar to the linear regression equation from the curve above. Hence we can compute the value of n and K of the specimen. Specimen A: 𝑦 = 0.6003𝑥 + 9.3535 𝑦 = log(𝜎𝑡𝑟𝑢𝑒) = log(712 𝑥 106 𝑃𝑎) = 8.85 0.6003𝑥 = 𝑛 log (0.173) = −0.76𝑛 Then, 8.85 = −0.76𝑛 + 9.3535 𝑛 = 0.659 log 𝑘 = 9.3535 109.3535 = 𝑘 𝑘 = 2.256 GPa Specimen B: 𝑦 = 0.4489𝑥 + 9.1376 𝑦 = log(𝜎𝑡𝑟𝑢𝑒) = log(603 𝑥 106 𝑃𝑎) = 8.78 0.4489𝑥 = 𝑛 log (0.185) = −0.73𝑛
- 18. 17 Then, 8.78 = −0.73𝑛 + 9.1376 𝑛 = 0.48 log 𝑘 = 9.1376 109.1376 = 𝑘 𝑘 = 1.373 GPa From the calculation of both specimen, the value of its strain hardening n exponent is close to the 304 stainless steel material, which has an n about 0.43. However, the value of K of both specimen are different. Steel A has 2.256 GPa of K, which is quite same with 4340 steel alloy with the K about 2.650 GPa. While steel B has K about 1.373 GPa, which is very close to the value of K of 304 stainless steel with 1.400 GPa of K. From here, steel A could be catagorized to have a same composition with the 4340 steel alloy because of this strength coefficient. While steel B is almost similar with the strength coefficient of the 304 stainless steel. Comparison of Engineering Stress-strain and True Stress-strain Figure 11 Engineering-True stress-strain plot The above curve shown the comparison of true and engineering stress-strain curves. The engineering stress-strain curve shows the deformation characteristic of the specimen, where it is based on the original known dimensions. Hence, the plot is based on the initial value, while actually the dimensions is changing over the given tensile load. Contrary, the true stress-strain curve shows a true value of the deformation changing. It consider the changing of the dimension. That is why the true stress-strain plot is important. Why the difference composition of steel has almost similar young modulus, E?
- 19. 18 The young modulus or modulus of elasticity is a measurement of resistant to the separation adjacent of atoms in the material, in this case is iron atoms, Fe – Fe bonding. In the steel, the addition of carbon solid solution is very small, which is less than 2%. It is spread out in the interstitial of steel as the impurities. The present of carbon impurities affecting the bonding of Fe – Fe atoms. So that, the bonding beetween Fe in the steel is determine its young modulus. The Fracture Shape The specimen’s fracture are in the form of cup-cone with the fracture angle around 45o. It shows that the specimens experience rupture or ductile rupture.
- 20. 19 Chapter 5: Conclusions and Recommendations Conclusions From the tensile test experiment using tensile test machine, the mechanical properties of a material can be obtained. When the material is being streched, it experiencing elastic and plastic deformation. The strain hardening phenomenon is occur when the material is getting strengthened until it goes to fracture. For this experiment, the specimen steel A and steel B gives two different mechanical properties. Eventhough both’s characteristic are almost same, steel A and steel B have a different strength coefficient. Steel A is almost similar to the 4340 steel alloy, while steel B is behave like 304 stainless steel. The value that obtain that from this experiment is actually not accurate. It is because of the approximation of plot from the raw data that generated by the machine. Recommendations For further experiment, it is better to obtain the data of stress-strain directly from the machine. It is for increasing the accuracy of the analysis.
- 21. 20 References 304 Stainless Steel TechnicalData Sheet. (t.thn.). Diambil kembali dari https://www.metalshims.com/t-304-Stainless-Steel-technical-data- sheet.aspx ASMMaterial Data Sheet. (t.thn.). Diambil kembali dari http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MQ304 A Batang Uji Tarik untuk Bahan Logam. (1998). Standar NasionalIndonesia. Indonesia. Callister, W. D. (2009). MaterialScience and Engineering.USA: John Wuley & Sons, Inc. Dieter, G. E. (1988). MechanicalMetallurgy. British Library.
- 22. 21 Appendix Specimen A fracture Specimen B fracture