Lab 2 Tension Test PDF

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ME 307 - Mechanics of Materials Laboratory University of Wisconsin - Madison, Summer 2018 Engineering Hall – June 26, 2018 Laboratory 2: Tension Test Jacob WonBin Im, Tim Mayeshiba, Trevor Powell, Ryne Wang, Anson Liow - Section 001

Abstract Aluminum, steel, and acrylic are known to be strong and robust materials that can withstand thousands of pounds of force, but few people can test their limits and be able to describe quantitatively their mechanical properties. When someone would wish to use a material to perform an arduous task, it would be useful to know how much of the material to use to perform the task successfully. Clearly, a test to determine the tensile strength of materials such as steel would require the utilization of specialized machinery. Luckily, an MTS Sintech 10GL with a load capacity of 10,000 pounds was available. It is a machine that is specifically designed to test tensile and compressive strengths of many different types of materials, but in this case we limited ourselves to A-36 steel, aluminum, and cast acrylic. To carry out the test, we procured material specimens of a uniform diameter and gage length so we could easily measure the deformities that appeared under large amounts of stress. By recording the initial diameter of the specimens and the length prior to applying the load and after the material fractured, we were able to calculate the yield stress, ultimate stress, fracture stress and strain, and the toughness of the materials. In addition to being able to describe those properties quantitatively, we were also able to determine their ductility, or their ability to stretch, and conversely, how brittle they were. We found that A-36 steel to be particularly ductile in relation to the other materials, cast acrylic to be brittle, and aluminum to be in between.

1. In one table, provide the following geometrical information for each test specimen: 1. Initial diameter [in] 2. Initial gage length [in] 3. Final diameter [in] 4. Final gage length [in] 5. Percent reduction in area [-] 6. Percent ductility [-]

A 36 Steel

Aluminum

Acrylic

Initial diameter [in]

0.335

0.335

0.359

Initial gage length [in]

3.500

3.546

2.148

Final diameter [in]

0.208

0.258

0.357

Final gage length [in]

4.350

4.025

2.199

Percent reduction in area [-]

61.449

40.687

1.111

Percent ductility [-]

24.286

13.508

2.374

Initial cross-section area [in2 ]

0.088

0.088

0.101

Final cross-section area [in2 ]

0.034

0.052

0.100

Table 1. Geometrical information for steel, aluminum, and acrylic specimen

(a) The percent reduction in area is a function of the difference in initial and final cross-section area and division of initial cross-section area, as given by Equation 1.

(b) The percent ductility is a function of the difference in final and initial gage length and division of initial gage length, as given by Equation 2.

2. In another table, provide the following load information for each test specimen: 1. Yield Load [lbf] 2. Ultimate Load [lbf] 3. Fracture Load [lbf]

Yield Load [lbf]

A 36 steel

Aluminum

Acrylic

5566.0

4221.1

1214.7

Ultimate Load [lbf]

7201.3

4496.8

1214.7

Fracture Load [lbf]

5146.2

3427.1

1214.7

Table 2. Load information for steel, aluminum, and acrylic specimen

(a) The experiment of acrylic specimen is failed because there is a gap between specimen and top grip. Therefore the yield and the ultimate loads have the same values. The yield load also has the same value because the .2% offset never intercepts the data plot.

3. In a third table, provide the following data derived from the engineering stresses and strains, for each test specimen: 1. Yield strength [psi] 2. Ultimate strength [psi] 3. Fracture strength [psi] 4. Fracture strain [-] 5. Toughness [psi] (formula) 6. Toughness [psi] (integrated)

A36 Steel

Aluminum

Acrylic

Yield Strength [psi]

63250

47967.0

12026.7

Ultimate strength [psi]

81833.0

51100

12026.7

Fracture strength [psi]

58479.5

38944.3

12026.7

Fracture strain [-]

0.2429

0.1351

0.0237

Toughness [psi] (formula)

17620.0

6692.0

285.0

Toughness [psi] (integrated)

16217.2

4852.9

808.7

Table 3. Strength, Strain and toughness of each tested specimen

4. Using the information from Table 3, make a fourth table with the percent differences of each value (3.1, 3.2, and 3.4), for each test specimen. Theoretical values can be found by searching for "mechanical properties of _______" in google. Trusted sources include azom.com, matweb.com and textbooks. Provide a critique of these differences. The percent difference for each value can be found through equation (3):

%Dif f erence =

theoretical value − experimental value theoretical + experimental 2

(3)

The percentage difference between the data obtained and the expected outputs is demonstrated in table 4. % Difference of

Steel

Aluminum

Acrylic

Yield Strength [%]

54.14

18.11

24.52

Ultimate Strength [%]

2.52 (used 79800 for theoretical value)

12.69

0.61

Fracture Strain [%]

5.46

22.88

23.46

Table 4. Comparison between theoretical and experimental values for Yield Strength, Ultimate Strength, and Fracture Strain.

According to matweb.com, Steel has a yield strength of 36300 psi, ultimate strength of 58000-79800 psi, and fracture strain of 23%. Aluminum has a yield strength, ultimate strength, and fracture strain of 40000 psi, 45000 psi, and 17% respectively. Finally, acrylic has a yield strength, ultimate strength, and fracture strain of 9400 psi, 12100 psi, and 3% respectively.

5.) In this test we had attached an extensometer to obtain data from a more localized area on the specimen. However, the data differed from that obtained through the testing software for the machine as shown in Figure 5:

Figure 1: A graph showing the data from the machine software compared to data obtained using the extensometer.

In a professional setting, I would use the data from the machine since it shows the material having a less ductile response to stress in the elastic region. Data obtained from the extensometer seems to show that the material has a much higher tolerance to deformation in the elastic region.

6) Figure 2 shows the intersection of the measured data and the offset data of the steel specimen, which is at the stress of approximately 54.55 ksi.The value of stress corresponding to this intersection is determined to be the yield strength of the steel specimen.

Figure 2. Local details of intersection between stress-strain data and 0.2% offset line....