The document summarizes an experiment investigating the ductile-to-brittle transition in steel and aluminum samples under varying temperatures. Steel samples exhibited increasing impact energy and more brittle fractures as temperature increased, while aluminum impact energy and ductile fractures remained constant regardless of temperature. Data tables and figures show the relationships between impact energy, lateral expansion, shear percentage, and temperature for each material. There was some variability in the fracture energy calculations between the samples.

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Memo Report No. I College of Engineering and Computer Science at California State
University, Northridge
Group # 4, Tuesday, Metallographic Observations
To: Lisa R. Reiner
From: Stephanie Ha
Date: September 30, 2008
ABSTRACT
The purpose of this experiment was to investigate the ductile-to-brittle transition in five
samples of 1018-steel and 2024-Aluminum as a function of temperature. The specimens were
placed in different temperature baths ranging from -110˚F (-79˚C) to 212˚F (100˚C) for ten
minutes to reach thermal equilibrium. Specimens were then transferred to a Charpy testing
machine to measure the impact energy (in ft-lbs). After impacting, fracture surfaces were
examined for evidence of shear or cleavage failure and lateral expansion at the breaking point of
the notch. Three curves were obtained to measure fracture energy as a function of temperature
for the steel and aluminum samples. As the temperature increased for steel, its impact energy
increased. However, for aluminum, it remained the same meaning that temperature did not
influence its fracture energy.
DESCRIPTION OF WORK
Initial width of each notch for aluminum and steel samples were measured with vernier
calipers before labeling and placement in different temperature baths. Specimens were taken out
of their temperature baths and impacted with the Charpy testing machine to measure its impact
energy. After this, fracture surfaces were examined using a booklet to estimate the %shear. Final
width was then measured at the root of each notch with vernier calipers.
RESULTS AND DISCUSSION
Data comparing impact energies vs. temperature is illustrated in Table (1) and Figure 1.
As the temperature increased, impact energies for steel varied. Its impact energy rose from 17 ft-
lbs at -75°C to 34 ft-lbs at 100°C. As the table 1 and figure 1 indicates: impact energy for steel
was greatest at -40°C and 1°C with 44.5 ft-lbs. However, aluminum remained consistent at 10 ft-
lbs and on occasion, 10.5 ft-lbs.
From Table 2 and Figure 2, our findings indicated that temperature varied the lateral
expansion of each specimen. In other words, temperature did influence the lateral expansion in
the root of the notch but the components of each temperature bath should be considered.
Table 3 and Figure 3 illustrates the ductile-to-brittle transitions in the aluminum and steel
samples based on their shear%. Based on these estimates, Aluminum has more shear than

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cleavage because its fracture surface after impacting was smooth. Steel, on the other hand, is
more brittle as temperature decreases. This is defined as cleavage.
As the impact energy increased with steel, it was found to have a cleavage type fracture while
Aluminum was shear. Despite the increase in temperature, its impact energy remained the same.
Because of this, Aluminum’s fracture was rather smooth and thus, consistent.
Consequently, the test temperatures slightly deviated from the recommended setting.
While temperature does affect the type of fractures observed (shear or cleavage) with respect to
temperature, material properties should also be considered. Aluminum, by itself, is malleable,
rather soft, and can be easily fractured. Steel, on the other hand, is nearly the opposite. It is more
brittle (less shear). Whenever there is an increase in temperature, steel tends to become more
brittle and display further signs of cleavage. Aluminum, on the other hand, shows the reverse.
To sum it all up, the more energy a material is able to absorb, the more suspectible it is to
fracture and become brittle.
Tables 4 and 5 and Figures 4 and 5 shows the upper and lower values of fracture energy
values for steel and aluminum. This data indicates that there is some amount of error involved if
the majority of these calculated values (from calculating σ, standard deviation) were variable
from each other by various factors. To illustrate this point, steel has average fracture energy of
45 ft-lbs while its HIGH value is 48.461538 ft-lbs and its LOW value is 41.538462 ft-lbs.
APPENDIX
Table 1. Impact Energies vs. Temperature (T)
Sample Label Temp (˚C) Impact Energy (ft-
lbs)
Al-4 N -75 10.5
Al-2 L -40 10
Al-1 K 1 10
Al-5 V 20 10
Al-3 M 100 10
Steel-4 E -75 17
Steel-2 C -40 44.5
Steel-1 B 1 44.5
Steel-5 F 20 39
Steel-3 D 100 34
*Note: Al abbreviates to Aluminum.
Table 3. Shear% vs. Temperature
Sample Label Temp (˚C) Shear%
Al-4 N -75 10
Al-2 L -40 10
Al-1 K 1 20
Al-5 V 20 10
Al-3 M 100 20
Steel-4 E -75 80
Steel-2 C -40 90
Steel-1 B 1 60
Steel-5 F 20 70
Steel-3 D 100 40
*Note: Al abbreviates to Aluminum.
Table 4. Steel - Average Fracture Energy vs. T
Steel
Table 2. Change in width (Δw) vs. T
Sample Label Temp (˚C) Δw (inches)
Al-4 N -75 0.003
Al-2 L -40 0.01
Al-1 K 1 0.004
Al-5 V 20 0
Al-3 M 100 0.02
Steel-4 E -75 0.008
Steel-2 C -40 0.02
Steel-1 B 1 0.004
Steel-5 F 20 0.002
Steel-3 D 100 0.02
*Note: Al abbreviates to Aluminum.

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Temp (°C) -70 -44 0 25 100
Average (ft-lbs) 5.3846154 16.57692308 10 26 45
HIGH (ft-lbs) 5.7988166 17.85207101 22.98816568 28 48.461538
LOW (ft-lbs) 4.1094675 15.30177515 19.70414201 24 41.538462
*Note: Average values based on students’ data from previous semester. HIGH/LOW = Average ± σ
Table 5. Aluminum – Average Fracture Energy vs. T
Aluminum
Temp (Celsius) -70 -44 0 25 100
Average (ft-lbs) 8.6538462 8.384615385 8.538461538 8.6923077 8.6923077
HIGH (ft-lbs) 9.3195266 9.029585799 9.195266272 9.3609467 9.3609467
LOW (ft-lbs) 7.9881657 7.73964497 7.881656805 8.0236686 8.0236686
*Note: Average values based on students’ data from previous semester. HIGH/LOW = Average
± σ
Figure 4. Steel - Average Fracture Energies as a Function of Temperature
*Note: Middle line represents average, Top line is HIGH, and Bottom line is LOW
Figure 1. Impact Energies vs. Temperature
*Note: Top line represents steel, Bottom line represents aluminum
Figure 3. Shear% vs. Temperature
*Note: Top line represents steel, Bottom line represents aluminum
Figure 2. Δw vs. Temperature
*Note: Top line represents steel, Bottom line represents aluminum

4. Steel - Average Fracture Energy Vs. Temp (Celsius)
0
10
20
30
40
50
60
-100 -80 -60 -40 -20 0 20 40 60 80 100 120
Temp (Celsius)
AverageFractureEnergy(ft-
lbs)
4
Figure 4. Steel – Average Fracture Energy vs. Temperature (°C)
*Note: Middle line represents Average. Bottom is LOW. Top is HIGH.
Figure 5. Aluminium – Average Fracture Energy vs. Temperature (°C)
*Note: Middle line represents Average. Bottom is LOW. Top is HIGH.
REFERENCES
1. R.A and P.K Trojan, “Engineering Materials and Their Applications,” Houghton Mifflin Co.,
1975.
2. A.G Guy, “Introduction to Materials Science,” McGraw Hill Book Co., 1972.
3. Metals Handbook, ASM, edited by T. Lyman, 1948.
Al - Average Fracture Energy Vs. Temp (Celsius)
7
7.5
8
8.5
9
9.5
10
-80 -60 -40 -20 0 20 40 60 80 100 120
Temp (Celsius)
FractureEnergy(ft-lbs)

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