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Lab 5: Variability of Material Properties
CEE 3684-Civil Engineering Materials Laboratory
Wednesday Section: C
Group (4)
Ashish Sharma
Jack Knapp
Yong Uh
Zack Jezovit
Date: 11/28/2011
Any questions pertaining to this lab can be sent to sharms26@vt.edu
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Introduction:
Polymers are very important in the engineering field due to their low cost, ease of
processing, and their wide array of mechanical properties.
Objective:
The objective of this lab was for one to get used to variability in strength of different
polymers, and use descriptive statistics to analyze these calculated strengths. The percent
elongation, percent reduction of area, and fracture mode are used as a basis for finding
strength and the descriptive statistics.
Procedure:
The procedure was straightforward once the computer program was modified for
testing. First, preliminary measurements of gage length and diameter were measured. Then,
each polymer was placed in a loading fixture and once it was securely fastened, the test was
started. The test was completed when the polymer failed, and the final gage lengths/diameters
were measured along with the load at rupture. The data obtained, was then used with different
calculations to make an analytical observation of the polymer.
Results:
The following is the raw data taken with the polymers within our own lab section.
Table 1 Polymer Test Raw Data
Polyethylene
Polyvinyl
Chloride
Acrylic
Nylon
Initial Gage Length,
in.
1.978
1.96
1.965
1.795
Final Gage Length, in.
12.43
4.735
1.98
5.405
Initial Diameter, in.
0.504
0.5
0.355
0.505
Final Diameter, in.
0.18
0.31
0.325
0.265
Failure Load, kips
0.63348
1.50269
0.99588
2.069
Fracture Mode
Ductile
Ductile
Brittle
Ductile
Any questions pertaining to this lab can be sent to sharms26@vt.edu
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1.) The raw data obtained was used to calculate the percent elongation, percent reduction
in area, and the tensile strength:
Table 2 Polymer Test Results From Given Lab Section
Polyethylene
% Elongation
% Reduction in Area
Tensile Strength, ksi
Fracture Mode
Polyvinyl Chloride
528.4
87.2
3.18
Ductile
141.6
61.6
7.65
Ductile
Acrylic
Nylon
0.8
201.1
16.2
72.5
10.06
10.33
Brittle
Ductile
2.) The next step was to calculate the percent elongation, percent reduction in area and
tensile strength for each polymer in every lab section. This was obtained through data
given by the instructor. Once the calculations were complete, the descriptive statistics
of each polymer can be found:
Polymer Type
Table 3 Tensile Strength Summary of all 7 lab sections
Tensile Strength, ksi
B
C
D
E
F
G
A
Polyethylene
2.81
3.18
3.43
3.38
3.46
Polyvinyl Chloride
7.41
11.21
7.65
7.82
8.14
6.82
6.97
Acrylic
10.85
7.26
10.06
11.51
7.21
9.94
10.33
Nylon
10.58
18.69
10.33
10.84
10.45
10.41
10.64
Polymer Type
A
B
622.0%
Polyvinyl Chloride
40.5%
2.3%
141.6%
69.3%
77.1%
84.1%
Acrylic
1.0%
44.3%
0.8%
0.5%
1.0%
0.2%
0.0%
Nylon
61.1%
98.5%
64.7%
80.1%
82.6%
A
528.4% 592.3% 437.5%
104.7% 201.1%
88.1%
Polyvinyl Chloride
53.8%
Acrylic
9.7%
Nylon
67.7%
680.3%
572.1%
64.7%
6.8%
99.0%
σ
C.V.
0.930611 16.2662
0.440628 68.11136
0.165462 242.242
0.477856 48.2861
38.0%
86.4%
54.8%
13.2%
67.8%
σ
C.V.
0.013625 1.577219
0.069816 12.73197
0.197652 150.1405
0.034024 5.014955
Table 5 Reduction of Area Summary
Reduction of Area, %
C
D
E
F
G
B
Polyethylene
σ
C.V.
0.271362 8.346884
1.485018 18.55108
1.694309 17.66096
3.084428 26.35309
Table 4 Elongation Summary for all 7 lab sections
Elongation, %
C
D
E
F
G
Polyethylene
Polymer Type
3.25
8.01
9.59
11.70
87.2%
84.8%
86.6%
85.3%
42.5%
61.6%
54.3%
57.4%
63.4%
55.6%
16.2%
0.0%
10.7%
0.0%
0.0%
70.8%
72.5%
66.4%
68.6%
67.1%
61.9%
Any questions pertaining to this lab can be sent to sharms26@vt.edu
51.0%
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Discussion:
1. Discuss the variation in the results using the descriptive statistics to support your conclusions.
From the results of the test, Polyethylene, Polyvinyl Chloride, and Nylon were each observed to be
ductile materials, while the Acrylic was observed as a brittle material. The ductile materials tend to
stretch when under tensile loads while the brittle materials do not. As seen in table 4, Polyethylene
had an average elongation of 572.1% while Acrylic only had an average of 6.8%. When the material
is stretched, the cross section of the sample also decreases due to the material being compressed.
Again, the brittle material had a much lower reduction of area at 13.2% than Polyethylene, Polyvinyl
Chloride, and Nylon at 86.4, 54.8 and 67.8% respectively.
2. Research the chemical composition of each polymer tested and briefly discuss.
Polyethylene is made from the polymerization of ethylene which is composed of two carbon atoms
and four hydrogen atoms with a double bond between the carbons (C₂H₄).
Polyvinyl Chloride or PVC is produced by the polymerization of the vinyl chloride monomer. It is
composed of two carbon atoms, three hydrogen atoms, and one chlorine atom.
Acrylic is a rigid material which is composed of five carbon atoms, eight hydrogen atoms and two
oxygen atoms.
Nylon is produced by reacting adipic acid and hexamethylene diamene. This reaction creates nylon
that contains six carbon, thirteen hydrogen, one nitrogen and one oxygen atom.
3. Discuss how the chemical composition of the polymer influences the mechanical properties of the
polymers. Specifically, discuss the impact on the following, supporting your conclusions with the
data: tensile strength, elongation, reduction of area, and failure mode.
The chemical composition of a polymer determines the chain structure of that polymer, which
affects its mechanical responses. The stronger the attractive forces between chains, the stronger
and less flexible the polymer will be. Acrylic, which has eight hydrogen and two oxygen atoms,
which makes it very strong, is ductile and has a very low percent elongation and reduction of area.
Having a very strong chain also gives it a high tensile strength. Nylon, which has 13 hydrogen atoms,
has a very high tensile strength, but because of the chain that it forms with the nitrogen and oxygen
it is able to retain some of its flexibility which gives it a higher percent elongation and reduction of
area. Polyethylene and Polyvinyl Chloride have a relatively weak chain structure which gives them a
lower tensile strength but gives them higher percent elongation and reduction of area.
4. Can relationships be drawn between any of the following: tensile strength, elongation, reduction
of area, and failure mode. If so, discuss any relationships present.
Yes, each one of these properties affects each other. If a polymer has a low tensile strength, it will
tend to have a greater percent elongation and a greater reduction of area. The failure mode will also
tend to be more ductile, as it will stretch more. If the tensile strength of a polymer is higher it tends
to be more rigid and would have a brittle failure mode. This causes the percent elongation and the
reduction of area to be lower as well. From this lab, nylon seems to be an exception as it is able to
stretch and retain a very high tensile strength. This is due to its chain structure which allows it to
remain flexible but still keep its strength.
Any questions pertaining to this lab can be sent to sharms26@vt.edu
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Conclusion:
It is important to note the many reasons for error in this lab. First, the scratch marks used for
measuring the initial and final gage lengths may have weakened the polymer. Second, there
could have been factory errors that could have generated sample weaknesses. The last
important point to make is with human error. Human errors could have formed when taking
the gage length measurements, and there was a human error for polyethylene data because it
was not given for Groups B and F. It is crucial to prevent errors in the field of engineering, and
the polymer material is no reason to stray away from this goal. Polymers are used in a wide
array of materials/structures from helicopter rotors to the fuselages in Boeing 757’s. It is
important to understand how different polymers react to stress and strain in order to prevent
any failures (especially in a Boeing 757/helicopter during mid-flight).
Any questions pertaining to this lab can be sent to sharms26@vt.edu
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Appendix: Sample Calculations
% elongation of Nylon=
𝐹𝑖𝑛𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ−𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ
𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑔𝑎𝑔𝑒 𝑙𝑒𝑛𝑔𝑡ℎ
𝜋
Original Area of nylon = 4 ∗ 𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 2 =
Final Area of nylon =
𝜋
4
% Reduction of Area =
∗ 𝐹𝑖𝑛𝑎𝑙 𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟 2 =
𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎−𝐹𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎
𝑂𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝐴𝑟𝑒𝑎
𝑆𝑢𝑚 𝑜𝑓 𝑡ℎ𝑒 𝑑𝑎𝑡𝑎
𝜋
4
𝜋
4
* 100 =
5.405−1.795
∗ 100
1.795
= 201.1 %
∗ 0.5052 = 0.2003 in2
∗ 0.2652 = 0.0552 in2
∗ 100 =
Average of Tensile Strength = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑎𝑡𝑎 𝑠𝑒𝑡 =
0.2003−0.0552
∗ 100
0.2003
= 72.5 %
10.58+18.69+10.33+10.84+10.45+10.41+10.64
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= 11.7 ksi
̅ 2
∑(𝑋𝑖 −𝑋)
σ=√ 𝑛−1
=
(10.58−11.7)2 +(18.69−11.7)2 +(10.33−11.7)2 +(10.84−11.7)2 +(10.45−11.7)2 +(10.41−11.7)2 +(10.64−11.7)2
7−1
√
σ
C.V. = 𝑋̅ ∗ 100 =
3.0844
∗
11.7
100 = 26.35
Any questions pertaining to this lab can be sent to sharms26@vt.edu
= 3.0844