Abstract
The Charpy test is an impact test designated to measure the impact energy of
different materials. The Charpy test is often used because it is very easy and cheap to
conduct. Different material shave different impact energy based on DBTT, composition,
and ductility. Ductile materials tend to have a higher impact energy than brittle materials.
However when materials are placed in different conditions, the materials respond
differently in a Charpy test.
Introduction
Often, an impact test is used to test the brittleness of a material [1]. An example of this
kind of test is the Charpy test. The Charpy test was invented by Monsieur G. Charpy and has
been widely standardized by the several international organizations including the ASTM [2]. The
Charpy test is used to measure the impact energy of certain materials. In the Charpy test, a heavy
pendulum is positioned at a certain height. The sample is placed in a chamber below the
pendulum within the pendulum’s swinging arc. The pendulum is swung and breaks the sample
(Fig.1) resulting in certain impact energy [1]. Another term associated with the Charpy test is
impact toughness which is the ability of the material to withstand the impact of the pendulum
during a Charpy test [1]. Many choose to use the Charpy test because the test is very easy and
inexpensive to conduct.
However, there are many factors that could affect the
results of the Charpy test. Some of those include the
the condition of the material, composition, ductility,
factors. Some of these factors can increase and
energy from the Charpy test.
temperature,
and other
decrease the impact
Procedure
For this procedure, around 7-8 Charpy samples of three plain carbon steels (1018, 1045,
and 1095), polyvinyl, stainless steel (304), and an aluminum alloy (6061-T651) were used.
Approximately 3-4 of the plain carbon steels were used to be normalized. For the 1018 Charpy
samples, the samples were normalized at 915 C and then placed in a stainless steel bag. The
1045 and 1095 samples were done together and normalized at 860 C. Those samples were also
placed into the stainless steel bag and then placed in a furnace. The furnace was returned to
temperature and held for an hour. The samples were removed from the furnace and allowed to air
cool. After cooling, the samples were separated and ready for testing.
Before testing, one of each material, normalized and cold-finished, was placed in
different environments. The temperatures of those environments were 250 C, 100 C, 22 C, 0 C,
and -196 C. The materials were left in each environment until the material required the same
temperature of the environment. The samples were transferred from their specific temperature
environment into the Charpy tester within 5 seconds from the ASTM standards for testing.
Results
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Table 1 is a summary of the materials in the different conditions and the results from the
Charpy test in each condition. The 1018 material showed similar properties in the lower
temperatures in how the material broke. However, the material changed from brittle to ductile in
the cold-finished sample around 100°C. Fig. 2 shows how the impact energy changed in how the
material. The impact energy was higher in the normalized sample than the cold finished sample.
Fig. 3 compares the data for the 1045 sample. In contrast, the 1045 sample was opposite of the
1018 sample. The cold finished sample had higher impact energy than the normalized sample.
Fig. 4 compares the 1095 cold finished and normalized sample. This data did not have a normal
comparison with one set of data being higher than the others. The data intertwine at a certain
point and the graph switch positions. Originally, the normalized sample had the higher impact
energy, and then later in the graph the cold-finished sample had the higher impact energy. Fig.5
shows how the compositions of different samples affect the impact energy. Stainless steel had the
overall highest impact energy followed by the aluminum alloy and the polyvinyl chloride being
last.
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Table 1. Summary results of the Charpy test
Material
Temperature (°C)
Impact Energy (J)
-196
3.1
0
7.8
1018 CF
22
24.7
100
84.5
250
93.2
1018 N
-196
0
22
100
250
2
150
60
150
150
1045 CF
-196
0
22
100
250
2.1
5.9
11.7
15.1
18.4
-196
0
22
100
250
-196
0
22
100
250
-196
0
22
100
250
-196
0
22
100
-196
0
22
100
-196
0
22
100
2.6
43.2
52.7
88.3
90.3
1.4
8.3
7.1
7.5
28.2
1.2
3.2
3.6
13.8
28.1
33.9
34.6
39.7
35.2
99
100
105.2
102.2
3.3
4.3
4
12.2
1045 N
1095 CF
1095 N
6061 Al
304 SS
PVC
Quantitative
As the temperature increased, the
material became more ductile. The
samples placed in the 100°C and 250°C
environments formed sheer lips. The
samples in lower temperature had very
clean breaks making them brittle.
This sample was hard to distinguish
whether or not it was ductile or brittle.
The two samples placed in the higher
temperatures did not completely break.
The samples at the temperatures lower
than 100°C did not do a clean break but
did break with a somewhat flat surface
so those materials were brittle.
The material broke in half. The material
appeared to be brittle break was a clean
break for most of the samples except for
one. The sample placed in the 250°C
became ductile because the sample
formed sheer lips instead of the clean
break like the other samples.
The sample placed in the -196 °C
environment became ductile. This
sample did not have a clean break and
formed sheer lips the other samples were
very brittle and had very clean breaks.
This material was very brittle. Each
sample had a clean break.
This material was very brittle
throughout. Each sample had clean
breaks.
Aluminum is a very ductile material.
None of the samples had a clean break
and some of the samples formed sheer
lips.
Overall, this material was very ductile.
Each sample had sheer lips. None of the
samples had a clean break as seen with
the brittle materials.
This material was different from the
others. The sample in the -196°C did
break but the other half of the sample
completely shattered. However the
sample in the 100°C did not break.
Figure 2 shows the difference in the impact energy between the cold-finished and normalized 1018 sample.
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Figure 3 shows the difference in the impact energy between the cold finished and normalized 1045 sample.
Figure 4 shows the difference in impact energy between the normalized and cold finished 1095 sample.
Figure 5 is to show how the different material affects the impact energy. The samples included are 6061 Al, 304 Stainless
Steel, and Polyvinyl Chloride.
Discussion
Fig 1. shows how whether the material was cold-finished or normalized affected the
different material at different temperatures. As stated in Table 1, the cold finished material began
to become ductile around 100°C. The material began to reach its Ductile to Brittle Transition
Temperature (DBTT) [1]. The DBTT is the temperature where the material changes from brittle
to ductile failure [1]. Before reaching that temperature, the 1018 sample was brittle. However,
the normalized 1018 sample did not follow the same trend. Instead, the impact energy reached
the maximum amount of energy that could be recorded on the Charpy tester. The graph however
does not properly display this data. The points located at the 0°C and 22°C are very strange. The
point at 0°C was is very high compared to the 22°C. Reasons for this error could include the
sample being mislabeled and the right sample was not used, the test was not completed with the
5 second rule standardized by ASTM, or the machine was not calibrated properly before
experimentation. The graph should have shown a gradually increase to the sample not breaking.
The 1045 sample did not have the properties as the 1018 sample although they are both
plain carbons. The cold-finished sample started to become ductile at a higher temperature than
the 1018. The 1045 sample has more carbon in the sample than the 1018. The more carbon in the
sample causes the sample to become stronger and more brittle. The DBTT is moved to a higher
position than the 1018 sample. However when comparing the normalized to the cold-finished
sample, the opposite happens. When the material was normalized, the material was ductile at a
lower temperature and then became brittle. The normalized material had a lower impact energy
than the cold-finished sample.
When comparing the 1095 sample to the other plain carbon samples, the impact energy
became less than the plain carbon sample with the least amount of carbon. The sample became
very brittle and easy to break. However when the samples are normalized, the more carbon
present does not cause a change in whether or not the material is ductile or brittle. The more
carbon in a material causes the material to remain brittle and normalizing the material does not
change that property.
In comparison to the aluminum alloy, the polyvinyl chloride, and stainless steel, the plain
carbon cold finished sample with the least amount of carbon had the second highest impact
energy. The stainless steel had the highest. Data found in Table 1. The stainless steel composition
of the stainless steel shows that it has quite a bit of chromium and less than 0.12% carbon.
Chromium is a very ductile metal which helps to explain why its impact energy was higher than
the other materials.
Conclusion
The stainless steel had the highest impact energy as temperature increases. The stainless
steel has Chromium which is a very ductile metal. The very ductile materials tended to have the
higher impact energy. For the plain carbons, the lower amount of carbon caused the material to
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have higher impact energy. As more carbon is added to a material, the material becomes very
brittle and has lower impact energy. Temperature affects each material different based on its
composition of the material and whether or not the material is ductile or not. The temperature is
used to determine the DBTT of the material.
References
Askeland, Donald R., Pradeep P. Fulay, and Wendelin Wright. The Science and
Materials. 6th ed. Stamford: Cengage Learning, 2011. Print.
Engineering of
Kobayashi, T., S. Morita, and H. J. Kim. "Progress and Development in the Instrumented Charpy
Impact Test." Materialwissenschaft Und Werkstofftechnik 32.6 (2001): 525-31. Print.
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