1.0 Abstract

The elastic modulus, yield point, and ultimate strength of mild steel were determined in uniaxial tension. The "dogbone" specimen geometry was used with the region of minimum cross section having the dimensions: thickness =1.04 mm, width = 3.14 mm, and length section = 30 mm. This experiment was accomplished by first placing our specimens one at a time into a tensile testing machine (A G.U.N.T Hamburg Tensile Testing Machine (Max. load = 2kN)), which, under physical control, slowly increased the tension force on each specimen, stretching each until failure. We then analyzed the data output from the load and extension gauge. Referring from the resultant graph, we can see that the obtained graph line is straight until the one point it decrease gradually and be rupture. This shows that both variables on the graph are linearly related with each other. From the data obtained, we identify types of fracture surface of mild steel under tensile loading. The yield strength was determined to be 165.165MPa.The ultimate strength was determined to be 285.285MPa.Calculation for percentage elongation was determined to be 43 percent. After all, experimental result was compared with theoretical data.

Table of Contents1.0Abstract12.0Introduction43.0Objectives54.0Theory65.0Experimental Procedure85.1Apparatus/Experimental Setup85.2Procedure96.0Data107.0References168.0Appendices17

List of table:Table 1: Data13

List of Figures:Figure 1: Standard tensile test specimen4Figure 2: Sample mild steel shape6Figure 3: Stress-strain graph of mild steel7Figure 4: G.U.N.T Hamburg Tensile Testing Machine (Max. load = 2kN)8Figure 5: Specimen (aluminum)8Figure 6: Vernier calliper8Figure 7: Load(kN) vs Extension(mm) graph14Figure 8: Stress vs strain graph14

List of SymbolsA Area over which force (F) acts (m2)E Elastic modulus (GPa)F Force (N)Initial dimension in direction i (mm)T Specimen thickness (m)Rate of chart displacement (mm/min) Rate of sample displacement (mm/min)w Specimen width (m) Displacement of chart (mm) Displacement of sample (mm) Strain =0 Predicted strain at zero stress Normal strain in direction iE Error in the predicted elastic modulus (GPa)F Error in the force (N) Change in dimension in direction i (mm)t Error in the specimen thickness (m)w Error in the width (m) =0 Error in the predicted strain at zero stress Error in the predicted intercept of stress-stain data (MPa)Error in the stress (MPa) Predicted intercept of stress-strain data (MPa) Engineering stress (MPa)Yield point (MPa) Ultimate strength (MPa)

2.0 IntroductionOne material property that is widely used and recognized is the strength of a material. But what does the word strength mean? Strength can have many meanings, so let us take a closer look at what is meant by the strength of a material. We will look at a very easy experiment that provides lots of information about the strength or the mechanical behavior of a material, called the tensile test.The basic idea of a tensile test is to place a sample of a material between two fixtures called grips which clamp the material.The material has known dimensions, like length and cross-sectional area.We then begin to apply weight to the material gripped at one end while the other end is fixed.We keep increasing the weight often called the load or force while at the same time measuring the change in length of the sample.The result of this test is a graph of load amount of weight versus displacement amount it stretched.Since the amount of weight needed to stretch the material depends on the size of the material and of course the properties of the material, comparison between materials can be very challenging.The ability to make a proper comparison can be very important to someone designing for structural applications where the material must withstand certain forces.

Figure 1: Standard tensile test specimen

3.0 Objectives

The purpose of this experiment is to :1.0 determine the tensile properties subjected to tensile loading.2.0 Identify Types of fracture surface under tensile loading.3.0 Validate the data between experimental and theoretical values.

4.0 TheoryCertain materials which are linear, homogeneous, elastic, and isotropic can bedescribed by their material properties. These properties include the modulus of elasticity, ultimate tensile strength, modulus of toughness, modulus of resilience and yield strength. Assuming mild steel is homogenous material, tensile testing had been carried out. One of important fundamental material Science is tensile testing which is carried out by applying uniaxial stress on the subject until it fracture such below. Figure 2: Sample mild steel shape

When force are applied to materials, it deform in reaction to those forces. This uniaxial stress also known as tensile stress is given by a formula of:(1)

While normal strain is given by:(2)

In theory, properties of material include the modulus of elasticity, modulus of toughness, modulus of resilience, ultimate tensile strength, and yield strength applied to all instances of that material undergoing the same type of stress, allowing one to design structural elements whose behaviour can be predicted but in at early stage of tested material will elongate to show elastic behaviour as the apply stress is proportional to the strain and Hookes law is obeyed. Hence this formula came:(3)

Figure 3: Stress-strain graph of mild steel

Elastic modulus, E also can be determine from Stress-strain graph which act as the gradient from the initial to limit of proportionality. As stress increasing, elastic behaviour stop at their elastic limit and entering plastic deformation. (4)E = slope =

Since many metals lack a sharp yields points, i.e a sudden, observable transition between the elastic region and the plastic region, the yields points is often defined as the stress that gives rise to a 0.2% permanent plastic strain. By this convention, a line is drawn parallel to the elastic region of the materials, starting at a strain level of 0.2% strain. The point at which this line intersects the curve is called the yield point or yield stress. The ultimate tensile strength( stress), in contrast is found by determining the maximum stress, reached by the materials.The ductility of the material can be measured most accurately from the tensile test using this definition:Ductility = Change in x-sectional area Original x-sectional area

This measure of ductility is closely related to one based upon the change in gage length divided by the original gage length, but after fracture the gage length is difficult to measure Tensile testing is very important because the performance of materials are a matter of life or death. Cars and airplanes cannot fail, and buildings must stay standing or it will cost life.

5.0 Experimental Procedure5.1 Apparatus/Experimental Setup

A G.U.N.T Hamburg Tensile Testing Machine (Max. load = 2kN), Vernier Caliper and specimen.

Figure 4: G.U.N.T Hamburg Tensile Testing Machine (Max. load = 2kN)

Figure 5: Specimen (aluminum)Figure 6: Vernier calliper

5.2 Procedure1. Vernier caliper used to measure the initial gage length, width and thickness of the test specimen.2. The specimen was mounted to the gripping grip of the machine.3. The load anchor was turned slowly to counter clockwise rotation until the specimen fixed in gripping head.(Notes: The specimen must lays correctly to the ground of the gripping head groove)4. Both gauges were reset to zero (extension gauge and load gauge).5. The wheel rotated until the extension gauge reading reached 10 units.6. Take and record the load reading7. Step 5 and 6 repeated until the specimen fracture.

Note that: Counter clockwise turning for tension, clockwise turning for compressive. Ratio for load gage: 1cm = 0.05N, dial gage: 1cm = 0.01

6.0 Data

w

tLo

Lo = 30mm, L = 42.9 mm, w = 3.14 mm, t = 1.06 mm, A = 3.33 mmNo.Extension(mm)Load (Kn)StrainStress (kPa)

10.10.10.003330030.03003

20.20.250.006775075.07508

30.30.40.0100120120.1201

40.40.50.0133150150.1502

50.50.550.0167165165.1652

60.60.550.0200165165.1652

70.70.550.0233165165.1652

80.80.60.0267180180.1802

90.90.60.0300180180.1802

1010.650.0333195195.1952

111.10.650.0367195195.1952

121.20.70.0400210210.2102

131.30.70.0433210210.2102

141.40.70.0467210210.2102

151.50.70.0500210210.2102

161.60.750.0533225225.2252

171.70.750.0567225225.2252

181.80.750.0600225225.2252

191.90.750.0633225225.2252

2020.750.0667225225.2252

212.10.80.0700240240.2402

222.20.80.0733240240.2402

232.30.80.0767240240.2402

242.40.80.0800240240.2402

252.50.80.0833240240.2402

262.60.80.0867240240.2402

272.70.80.0900240240.2402

282.80.850.0933255255.2553

292.90.850.0967255255.2553

3030.850.1000255255.2553

313.10.850.1033255255.2553

323.20.850.1067255255.2553

333.30.850.1100255255.2553

343.40.850.1133255255.2553

353.50.850.1167255255.2553

363.60.850.1200255255.2553

373.70.850.1233255255.2553

383.80.850.1267255255.2553

393.90.850.1300255255.2553

4040.850.1333255255.2553

414.10.850.1367255255.2553

424.20.850.1400255255.2553

434.30.90.1433270270.2703

444.40.90.1467270270.2703

454.50.90.1500270270.2703

464.60.90.1533270270.2703

474.70.90.1567270270.2703

484.80.90.1600270270.2703

494.90.90.1633270270.2703

5050.90.1667270270.2703

515.10.90.1700270270.2703

525.20.90.1733270270.2703

535.30.90.1767270270.2703

545.40.90.1800270270.2703

555.50.90.1833270270.2703

565.60.90.1867270270.2703

575.70.90.1900270270.2703

585.80.90.1933270270.2703

595.90.90.1967270270.2703

6060.90.2000270270.2703

616.10.90.2033270270.2703

626.20.90.2067270270.2703

636.30.90.2100270270.2703

646.40.90.2133270270.2703

656.50.90.2167270270.2703

666.60.90.2200270270.2703

676.70.90.2233270270.2703

686.80.90.2267270270.2703

696.90.90.2300270270.2703

7070.90.2333270270.2703

717.10.90.2367270270.2703

727.20.90.2400270270.2703

737.30.90.2433270270.2703

747.40.90.2467270270.2703

757.50.90.2500270270.2703

767.60.90.2533270270.2703

777.70.90.2567270270.2703

787.80.90.2600270270.2703

797.90.90.2633270270.2703

8080.90.2667270270.2703

818.10.90.2700270270.2703

828.20.90.2733270270.2703

838.30.90.2767270270.2703

848.40.90.2800270270.2703

858.50.90.2833270270.2703

868.60.90.2867270270.2703

878.70.950.2900285285.2853

888.80.950.2933285285.2853

898.90.950.2967285285.2853

9090.950.3000285285.2853

919.10.950.3033285285.2853

929.20.950.3067285285.2853

939.30.950.3100285285.2853

949.40.950.3133285285.2853

959.50.950.3167285285.2853

969.60.950.3200285285.2853

979.70.950.3233285285.2853

989.80.950.3267285285.2853

999.90.950.3300285285.2853

100100.950.3333285285.2853

10110.10.950.3367285285.2853

10210.20.950.3400285285.2853

10310.30.950.3433285285.2853

10410.40.950.3467285285.2853

10510.50.950.3500285285.2853

10610.60.950.3533285285.2853

10710.70.950.3567285285.2853

10810.80.950.3600285285.2853

10910.90.950.3633285285.2853

110110.950.3667285285.2853

11111.10.950.3700285285.2853

11211.20.950.3733285285.2853

11311.30.950.3767285285.2853

11411.40.950.3800285285.2853

11511.50.950.3833285285.2853

11611.60.950.3867285285.2853

11711.70.950.3900285285.2853

11811.80.950.3933285285.2853

11911.90.950.3967285285.2853

120120.950.4000285285.2853

12112.10.950.4033285285.2853

12212.20.950.4067285285.2853

12312.30.90.4100270270.2703

12412.40.90.4133270270.2703

12512.50.850.4167255255.2553

12612.60.850.4200255255.2553

12712.70.750.4233225225.2252

12812.80.70.4267210210.2102

12912.900.43000

Table 1: Data

Figure 7: Load(kN) vs Extension(mm) graph

Figure 8: Stress vs strain graph

The actual characteristic of the materials sample:The specimen used for this experiment is mild steel. The actual characteristic of the Mild steel is the most common form of steel as its price is relatively low while it provides material properties that are acceptable for many applications. Low carbon steel contains approximately 0.050.15% carbon and mild steel contains 0.160.29% carbon, therefore it is neither brittle nor ductile. Mild steel has a relatively low tensile strength, but it is cheap and malleable surface hardness can be increased through carburizing. It is often used when large amounts of steel is needed, for example as structural steel. The density of mild steel is 7,861.093kg/m (0.284lb/in), the tensile strength is a maximum of 500MPa (73,000psi) and the Young's modulus is 210,000MPa (30,000,000psi). Calculation of stress and strain:Area = (width x thickness) = 3.14 x 1.06 = 3.33 x 10-6 m2

7.0 References

1. Ashby, M. (2006). Engineering Materials 1: An Introduction to Properties, Applications and Design. 3rd ed. Butterworth-Heinemann2. Hibbeler, R.C. (2004). Statics and Mechanics of Materials. Prentice Hall.3. Tarr, M. (no date). Stress and its effect on Materials [online]. Available from4. http://www.ami.ac.uk/courses/topics/0124_seom/index.html. [Accessed 29/03/14].5. Van Vlack, L.H., Introduction to Materials Science and Engineering - 6th Edition, Addison Wesley, 1989, p 8.6. Smith,W.F., Principles of Materials Science and Engineering - 2nd Edition, McGraw Hill, 1990, p 255.7. Van Vlack, L.H., Introduction to Materials Science and Engineering - 6th Edition, Addison Wesley, 1989, p 556.8. Dewey, B. R., Introduction to Engineering Computing - 2nd Edition, McGraw-Hill, 1995, p 69.

8.0 AppendicesPage | 4