Rna Waheb Rameen HassanzadehRyan Oh Pavan Kumar NanneDhaval Prajapati Siddhesh SawantLab Time: Wednesday 8 pmLab Group #2MSE 527 Lab # 1 – Impact Test Lab

AbstractThe Charpy Impact Test was used to measure the impact energy of 1018 Carbon Steel and 6061

Aluminum at varying temperatures. Between 50ºF to -25 ºF, the impact of energy of aluminum was found to sharply decrease from 33 ft-lbs to 15 ft-lbs whereas the impact energy of steel was relatively unaffected by temperature. The amount of impact energy aluminum can absorb was evidenced through the % shear lip, which was observed from the fracture surfaces. The fracture toughness of both materials was also found to be unaffected by temperature. Graphs showing the effect of temperature on impact energy, fracture toughness, % shear lip, and changes in width were obtained.

ProcedureThe purpose of the Charpy Impact Test was to characterize the toughness of materials as a function of

temperature under impact loading and multi-axial stress state1. A pendulum impact testing machine with a heavy weight was used to perform the tests. It was accurately adjusted by performing a test without a sample and with the drag indicator to the left. The drag indicator stopped at position zero proving that the machine is correctly calibrated.

The experiment was performed on 5 samples of 6061 Aluminum and 5 samples of Carbon steel at 5 different temperatures.  Samples were marked for orientation and their widths were measured. Afterwards, 5 sets of aluminum and steel were placed in their respective dry ice/acetone, antifreeze/water mix with dry ice, ice/pure water, room temperature, or boiling water bath for 10 minutes to ensure thermal equilibrium.  The samples were then quickly transferred to the Charpy Impact Test, fractured, and had their impact energy measured. Their fracture surfaces were then examined measured and compared to standards to determine % shear lip.  

Results and Discussion

Table 1 shows the impact energy absorbed by the samples at their respective temperatures. The impact energy of Aluminum 2, the sample that was submerged in ice water, was not found due to a mechanical error. After the sample was placed, the pendulum was set and released, however the drag indicator did not move. Table 1 also shows their % shear lip, an indication of a sample's brittleness, which was determined by examining their fracture surfaces and comparing them with standards. Table 2 shows the change in width for each sample. There was general trend for both samples showing that higher temperatures contributed to a larger change in width. Table 3 shows the calculated fracture toughness, Kc. Figure 1 shows the plot of impact energy as a function of temperature. Between 50ºF to -25 ºF, the impact of energy of steel was found to sharply decrease from 33 ft-lbs to 15 ft-lbs. This displays a textbook ductile-brittle transition temperature, DBTT, in the steel samples. However this phenomena is absent in the aluminum samples. Figure 2 supports the DBTT in steel because starting from 50ºF, the % shear lip, decreases from 40% to 20%. The amount of % shear lip in carbon steel decreased sharply around the DBTT zone. Figure 3 displays the data from table 3 in graphical form. Figure 4 shows the relationship between the fracture toughness and temperature. Steel has higher fracture toughness values compared to aluminum, however both alloys were unaffected by temperature.

Table 1. Impact energies measured through Charpy test for the aluminum and steel samples at different temperatures. Shear lip % estimated from broken samples post Charpy test.

Sample Temperature (ºF) Impact Energy (ft-lb) Shear Lip %Aluminum 0 71 11.2 40Aluminum 1 194 13 40Aluminum 2 35 N/A 40Aluminum 3 -98 13 20Aluminum 4 -9 12.5 35

Steel 0 71 32 90Steel 1 196 29 85Steel 2 35 29 70Steel 3 -98 3.5 80Steel 4 -9 17.5 65

Table 2. Change of width of samples calculated from initial measurements and measurements post Charpy test.

Initial Width (mm)

Final widths of two pieces

(mm)

Average final width(mm)

Change in width (mm)

(Δw = wf - wi)Aluminum 0 9.46 9.74 & 9.68 9.71 0.25Aluminum 1 9.46 9.93 & 10.2 10.07 0.61Aluminum 2 9.46 9.90 & 9.88 9.89 0.43Aluminum 3 9.47 10.1 & 9.8 9.95 0.48Aluminum 4 9.46 9.72 & 9.96 9.84 0.38

Steel 0 9.50 9.78 & 9.84 9.81 0.31Steel 1 9.49 10.46 & 10.0 10.23 0.74Steel 2 9.50 9.91 & 9.8 9.86 0.36Steel 3 9.47 9.50 & 9.70 9.60 0.13Steel 4 9.48 9.80 & 9.95 9.875 0.395

Table 3. Calculated fracture toughness from the thickness of the samples.

Thickness(mm)

Kc

(MPa*m0.5)Aluminum 0 9.46 67.23Aluminum 1 9.46 67.23Aluminum 2 9.46 67.23Aluminum 3 9.47 67.26Aluminum 4 9.46 67.23

Steel 0 9.50 101.05Steel 1 9.49 101.00Steel 2 9.50 101.05Steel 3 9.47 100.90Steel 4 9.48 100.95

-150 -100 -50 0 50 100 150 200 2500

5

10

15

20

25

30

35Impact Energy vs. Temperature

AluminumSteel

Temperature (ºF)

Impa

ct E

nerg

y (ft

-lbs)

Figure 1. Relationship between the measured impact energy and temperature.

-150 -100 -50 0 50 100 150 200 2500

10

20

30

40

50

60

70

80

90

100Shear Lip % vs. Temperature

AluminumSteel

Temperature (ºF)

Shea

r Lip

%

Figure 2. Relationship between estimated shear lip % and temperature

-150 -100 -50 0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Change in Width vs Temperature

AluminumSteel

Temperature (ºF)

Cha

nge

in W

idth

(mm

)

Figure 3. Relationship between average change of width and temperature

-150 -100 -50 0 50 100 150 200 2500

20

40

60

80

100

120Fracture Toughness vs. Temperature

AluminumSteel

Temperature (ºF)

Frac

ture

Tou

ghne

ss (

MPa

m0.

5)

Figure 4. Relationship between fracture toughness and temperature

Figure 5. Charpy Impact Energy vs. Temperature for various metals and alloys.

Sample Calculations

D= 1(2 π )

∗( KC

σYS)

2

Eqn 1. Fracture Toughness Formula

D is the sample width, and σYS is the material tensile yield strength (40ksi for 6061 Al, 60ksi for 1018 Steel).

9.46= 12 π

∗( KC

40∗6.894 )2

K c=67.23 MPa∗m0.5

Conclusion

The Charpy impact test was used to determine the mechanical properties of 6061 Aluminum and 1018 Carbon Steel. By testing for impact energy with regards to sample temperature and through measurement and visual inspection of the samples, it was possible to surmise information about the ductility/brittleness of the samples. It was also possible to include an estimation of the Ductile-Brittle Transition Temperature (DBTT) for the steel sample.

The steel samples show very low impact energy while at low temperatures. It increases dramatically until ~50°F before leveling out, similar to the error function. This behavior is similar to the published DBTT curves.

However, even when assuming that the steel sample would follow the trend of leveling out at low temperature, its exact location of the DBTT is unknown. The data shows a strong point of interest when nearing 0°F; however, it is important to note that this estimate would be largely improved by increasing the temperature resolution near this area in order to best see where the point of inflection occurs.

The aluminum shows nominal change in impact energy in relation to temperature. This agrees with the existing literature, and it is safe to assume that the aluminum samples have this behavior due to its FCC structure (FCC structures will remain ductile at low temperatures3). Elongation vs. temperature data supports the notion that aluminum sample do not to have a correlation between elongation and temperature.

The samples were visually inspected to determine shear lip %, which was used to calculate the fracture toughness, KC. However, human error has to be accounted for when calculating fracture toughness because shear lip% was determined by visual inspection. The fracture toughness of both materials were unaffected by temperature.

References

1. Rainer Schwab. "Charpy Impact Test." YouTube. Karlsruhe University of Applied Sciences, 26 Jan. 2013. Web. 14 Sept. 2015.

2. TT, H., "THE IMPORTANCE OF THE IMPACT TEST," SAE Technical Paper 150018, 1915, doi:10.4271/150018. H.A. ELLIOTT.   

3. Richard W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials 4th ed. 1996. p378 

4. “Ductile-to-brittle transition.” University of Cambridge. http://www.doitpoms.ac.uk/tlplib/BD6/ductile-to-brittle.php