Experiment 4 - Testing of Materials in Tension
Object: The object of this experiment is to measure the tensile properties of two polymeric
materials, steel and aluminum at a constant strain rate on the Tension testing machine.
Background: For structural applications of materials such as bridges, pressure vessels, ships,
and automobiles, the tensile properties of the metal material set the criteria for a safe design.
Polymeric materials are being used more and more in structural applications, particularly in
automobiles and pressure vessels. New applications emerge as designers become aware of
the differences in the properties of metals and polymers and take full advantage of them. The
analyses of structures using metals or plastics require that the data be available.
Stress-Strain: The tensile properties of a material are obtained by pulling a specimen of
known geometry apart at a fixed rate of straining until it breaks or stretches to the machines
limit. It is useful to define the load per unit area (stress) as a parameter rather than load to
avoid the confusion that would arise from the fact that the load and the change in length are
dependent on the cross-sectional area and original length of the specimen. The stress,
however, changes during the test for two reasons: the load increases and the cross-sectional
area decreases as the specimen gets longer.
Therefore, the stress can be calculated by two formulae which are distinguished as
engineering stress and true stress, respectively.
(1) = P/Ao= Engineering Stress (lbs/in
2 or psi)
P = load (lbs)
Ao= original cross-sectional area (in
2)
(2) T= P/Ai = True Stress
Ai = instantaneous cross-sectional area (in
2)
Likewise, the elongation is normalized per unit length of specimen and is called strain. The
strain may be based on the original length or the instantaneous length such that
(3) =(lf - lo)/ lo = l / lo = Engineering Strain, where
lf= final gage length (in)
lo= original gage length (in)
(4) T= ln ( li / lo ) = ln (1 +) = True Strain, where
li = instantaneous gage length (in)
ln = natural logarithm
For a small elongation the engineering strain is very close to the true strain when l=1.2 lo,
then = 0.2 and T= ln 1.2 = 0.182. The engineering stress is related to the true stress by
(5) T= (1 + )
The true stress would be 20% higher in the case above where the specimen is 20% longer
than the original length. As the relative elongation increases, the true strain will become
significantly less than the engineering strain while the true stress becomes much greater than
the engineering stress. When l= 4.0 lo then = 3.0 but the true strain =ln 4.0 = 1.39.
Therefore, the true strain is less than 1/2 of the engineering strain. The true stress (T) = (1+
3.0) = 4, or the true stress is 4 times the engineering stress.
Tensile Test Nom ...
Experiment 4 - Testing of Materials in Tension Object .docx
1. Experiment 4 - Testing of Materials in Tension
Object: The object of this experiment is to measure the tensile
properties of two polymeric
materials, steel and aluminum at a constant strain rate on the
Tension testing machine.
Background: For structural applications of materials such as
bridges, pressure vessels, ships,
and automobiles, the tensile properties of the metal material set
the criteria for a safe design.
Polymeric materials are being used more and more in structural
applications, particularly in
automobiles and pressure vessels. New applications emerge as
designers become aware of
the differences in the properties of metals and polymers and
take full advantage of them. The
analyses of structures using metals or plastics require that the
data be available.
Stress-Strain: The tensile properties of a material are obtained
by pulling a specimen of
2. known geometry apart at a fixed rate of straining until it breaks
or stretches to the machines
limit. It is useful to define the load per unit area (stress) as a
parameter rather than load to
avoid the confusion that would arise from the fact that the load
and the change in length are
dependent on the cross-sectional area and original length of the
specimen. The stress,
however, changes during the test for two reasons: the load
increases and the cross-sectional
area decreases as the specimen gets longer.
Therefore, the stress can be calculated by two formulae which
are distinguished as
engineering stress and true stress, respectively.
2 or psi)
P = load (lbs)
Ao= original cross-sectional area (in
2)
Ai = instantaneous cross-sectional area (in
2)
3. Likewise, the elongation is normalized per unit length of
specimen and is called strain. The
strain may be based on the original length or the instantaneous
length such that
-
lf= final gage length (in)
lo= original gage length (in)
li = instantaneous gage length (in)
ln = natural logarithm
For a small elongation the engineering strain is very close to the
true strain when l=1.2 lo,
related to the true stress by
The true stress would be 20% higher in the case above where
the specimen is 20% longer
than the original length. As the relative elongation increases,
4. the true strain will become
significantly less than the engineering strain while the true
stress becomes much greater than
strain =ln 4.0 = 1.39.
Therefore, the true strain is less than 1/2 of the engineering
Tensile Test Nomenclature: The tensile test data are
characterized by terminology shown in
Figure 4-1.
The material test curves have a region where the deformation
caused by the stress is elastic,
or not permanent. This means when the stress is removed the
specimen returns to its original
length. At stresses greater than a certain value, a portion of the
strain becomes permanent or
plastic. The stress required to cause a 0.2% plastic strain, or
off-set, is called the yield stress.
5. Ductility is measured as % elongation, representing the ability
to deform in the plastic range
(6)
100%
0
0
l
ll
elongation
f
6. Equipment
United Tensile Testing Machine: floor-mounted (20,000 lb.
capacity)
Calipers, Ruler
Procedure
You will receive 4 specimens (high density polyethylene, low
density polyethylene, steel and
aluminum.
Using calipers measure (in the reduced area):
1) the thickness of the specimen to +.002 inches.
2) the width of the specimen to + 0.02 inch.
Make sure to record the specific metal alloy, original specimen
width, thickness, gage length;
and after fracture load and percent elongation (total strain).
Place the specimen as instructed and tighten the clamps
securely. The original crosshead
distance (gage length) will be measured with a ruler after the
sample has been placed firmly
in the grips. The gage length is the distance from the top of the
7. lower clamp to the bottom of
the upper one. Measure the gage length to + 0.1 inch.
MSE 227 LAB – Tensile Machine Operation
Click on DATUM shortcut on the Desktop (wait for program to
finish loading)
Click on Template for:
- testing rate will be 0.2
inch/minute
- testing rate will be 2.0
inch/minute
Click on SAMPLE INFORMATION tab:
Enter
(Make sure to ENTER the information, so that it calculates the
Area correctly)
The CONTROL SEGMENT tab shows the testing rate for the
given set up.
8. Tighten the grips on the sample; you can see the force you are
applying on the computer screen.
You want to be sure the grips are secure (hopefully with no
more than 5lb force preload).
Click on TEST when ready to begin testing.
Make sure to record test number, so you can find your data.
Click on REPORT to Export your file.
To retrieve data go to:
Glossary of Terms
Understanding the following terms will help in understanding
this experiment:
Ductility - The ability of a material to be permanently deformed
without breaking when a force is
applied.
Elastic deformation - Deformation of the material that is
9. recovered when the applied load is
removed. This temporary deformation is associated with the
stretching of atomic bonds.
% Elongation - The total percent increase in the length of a
specimen during a tensile test.
Engineering strain - Increase in sample length at a given load
divided by the original (stress-free)
length.
Engineering stress - The applied load, or force, divided by the
original cross-sectional area of the
material.
Engineering stress-strain curve - A plot of the Engineering
stress versus the Engineering strain.
Hooke's law - the linear relationship between stress and strain
in the elastic portion of the stress-
strain curve.
Modulus of elasticity - Young's modulus, or the slope of the
stress-strain curve in the elastic region.
Necking - Local deformation of a tensile specimen. Necking
begins at the tensile point.
Offset yield strength - yield strength obtained graphically that
describes the stress that gives no more
than a specified amount of plastic deformation.
10. Plastic deformation - Permanent deformation of the material
when a load is applied, then removed.
% Reduction in area - The total percent decrease in the cross-
sectional area of a specimen during the
tensile test.
Tensile strength - The maximum engineering stress experienced
by a material during a tensile test
(ultimate tensile strength).
Tensile test - Measures the response of a material to a slowly
applied uniaxial force. The yield
strength, tensile strength, modulus of elasticity, and ductility
are obtained.
True strain - The actual strain produced when a load is applied
to a material.
True stress - The load divided by the actual area at that load in
a tensile test.
Yield strength - The stress applied to a material that just causes
permanent plastic deformation.
Write Up
Prepare a memo report on the results of the tests. The report
should contain 4 Figures
(graphs) that contain an overlay of engineering and true stress-
11. strain curves from the
tensile tests for each material. All graphs should be graphed
using Excel. Label engineering
curves to show Young's Modulus, Yield Stress, Ultimate Tensile
Strength, and Total
Strain (also label values; for example, Young’s modulus =
41000 psi). Discuss these values
in your report and compare them with published values for the
same alloys. Discuss your
4 graphs, the errors involved in this experiment and their
sources.
References
McClinock, Mechanical Behavior of Materials
Dieter, Mechanical Metallurgy
Nielsen, Mechanical Properties of Polymers
MSE 227L Name ________________________
Testing of Materials in Tension
Poor Fair Average Good Excellent
12. Memorandum Format Used 1 2 3 4 5
Spelling, grammar & punctuation correct 1 2 3 4 5
Report includes: Poor Fair Average Good Excellent
Compare graphs for engineering stress-
engineering strain, and true stress-true strain
using data from tensile tests for each material
(4 graphs total; 2 curves overlaid per graph).
4 8 12 16 20
Label Engineering Curves only
Young's Modulus labeled neatly using Excel
(Include values on graph). Show calculations.
1 2 3 4 5
Yield Stress labeled neatly using Excel
(Include values on graph).
1 2 3 4 5
Total Strain labeled neatly using Excel
(Include values on graph).
1 2 3 4 5
13. Ultimate Tensile Strength labeled neatly
using Excel (Include values on graph).
1 2 3 4 5
elongation compared to published values.
Include table with compared values and
measured data.
2 4 6 8 10
Discussion of errors in this experiment and
their sources.
1 2 3 4 5
Poor Fair Average Good Excellent
Overall level of effort apparent 1 2 3 4 5
Quality of graphs 1 2 3 4 5
Quality of Abstract 1 2 3 4 5
Quality of work description 1 2 3 4 5
Quality of conclusions 1 2 3 4 5
14. Laboratory Experiment No. 4
Testing of Materials in Tension Aldousari 1
Abstract
Engineers are eager to design safe structural applications. In
order to achieve that goal, they need to know the tensile
properties for the material used. In this experiment, we have
studied the tensile properties of four samples of materials. We
have given steel, aluminum and two polymeric materials (the
high-density polyethylene and low-density polyethylene. The
samples have been tested on the Tension testing machine with a
constant strain rate. Before doing the test, the length, width and
thickness were measured. The machine provides all the data
needed on a screen. From the stress-strain graph we were able
to see the result of the yield strength, ultimate tensile strength,
total strain and the extension for each material.
Introduction
The Tension Testing Machine helps us as engineering to choose
the best material for a certain application. The term tensile
strength refers to the amount of tensile (stretching) stress a
material can withstand before breaking or failing. Some
structure projects need a certain tensile properties in order to be
safe. We are able to predict the reaction of the material by
running it on the tension-testing machine. However, Structural
engineering depends on the knowledge of materials and their
properties, in order to understand how different materials
support and resist loads. Basically, The machine we were using
was pulling the specimen from the top by a fixed rate of
straining and fixed the lower part. It keeps pulling the specimen
15. to the top until it breaks. In some cases, the material does not
break but it stretch due to its low tensile strength. Therefore. It
can be calculated both the stress and the strain. Moreover, The
true and engineering stress or strain can be both calculated. To
calculate the engineering stress,
(lbs/in2 or psi). The load p in lbs. is divided by the original
cross-sectional area in in2.
For the true stress, we divide the load p by the instantaneous
cross-sectional area. For the engineering strain, It can be
calculated by taking the change in the gage length and dividing
it by the original gage length. The true strain is calculated by
taking the natural logarithm of one plus the engineering strain).
We can calculate the elongation percentage by Then, by using
excel we can get the graphs and measure the, Young’s Modulus,
yield strength, elongation percentage, ultimate tensile strength,
and total strain.
Procedure
· The first step was measuring the width and thickness of all the
materials by using the digital calipers with a +.002 inches.
· Place one sample at a time and make sure it is tight between
the clamps of the tension-testing machine.
· Measure the gage length before and after the test with a +1
inch by a ruler.
· Start the test and the result will appear on the computer
screen.
· Transfer the data into an excel file and save it on a hard disc.
· Covert the force into a stress by dividing the force by the area.
· Graph the stress-strain curves
· Measure Young’s Modulus by using the equation m =
· Repeat the test four times.
16. Discussion of Results
The results have been concluded in four Tables that show the
different between the measured values and the published values.
There are also a four graphs that represent the stress- strain
curves both the true and engineering curve. The units of
engineering stress are KSI, which stands for a thousand pounds
per square inch and one thousand PSI. First, the steel has to be
strong material in some instance. In general, brittle material by
nature will show effectively no plastic deformation prior to
rupture and their elongation and reduction of area values will be
small value. We can notice from Table 1 that the steel has
almost the same values as the published except the total strain.
The Young’s Modulus is equal to m= .The total strain was not
close as the other because of some initial measurement errors.
The Figure 2 shows that there is a plastic and elastic region for
the steel.
Table 1: Measured Values versus Published Values
Steel
Measured Values
Published Values
Ultimate Tensile Strength (PSI)
66985
63800
Yield Strength (PSI)
55161
53700
Young’s Modulus (PSI)
2325821.23
29700000
Total Strain
0.2286
0.15
17. Figure 1: Steel Stress-Strain graph
For the Aluminum, the graph shows that it has the higher
ultimate tensile strength and the higher yield strength among the
other samples. From Figure 2, it takes more time to transfer
from the elastic region to the plastic region. The engineering
and true curves increase uniformly till they reach the yield
point. They keep the same stress on the plastic region. The
Young’s Modulus value is inaccurate due to the error when
taking the slope of the curve. The Young’s Modulus is equal to
m=
Table 2: Measured Values versus Published Values
Aluminum
Measured Values
Published Values
Ultimate Tensile Strength (PSI)
82891
68000
Yield Strength (PSI)
74273
47000
Young’s Modulus (PSI)
2487432
10600000
Total Strain
0.16894
0.19
Figure 2: Aluminum Stress-Strain Graph
The High Density Polyethylene results for this test shows that
this material has very low properties compared to others. The
18. true stress and engineering stress increased at same proportion
for the same strain. They both decreased again, but after that,
the engineering curve had the same stress value but the true had
not. The measured values are close enough to the published
values. Again, the Young’s Modulus value is off the published
value due to the same reason mentioned before. The Young’s
Modulus is equal to m= this material did not break or fail when
it was tested. The opposite, it stretched until we stopped the
machine manually. The reason behind that is the yield strength
value not high.
Table 3: Measured Values versus Published Values
High Density Polyethylene
Measured Values
Published Values
Ultimate Tensile Strength (PSI)
45981
4423
Yield Strength (PSI)
4301
4279
Young’s Modulus (PSI)
39456.256
87022 to 203000
Total Strain
0.9182
1.3
Figure 3: High Density Polyethylene Stress-Strain Graph
The Low Density Polyethylene values are very small compared
to the other materials. The true and engineering curves
increased uniformly for a very short period of time. Then the
true curve kept increasing where the engineering curve was on
19. the same stress value. Also, the measured values are not close to
the published values except the total strain. The Young’s
Modulus is equal to m=. This material has the ability to stretch
for a long distance. The percentage elongation is high.
Table 4: Measured Values versus Published Values
Low Density Polyethylene
Measured Values
Published Values
Ultimate Tensile Strength (PSI)
7.015
1310 to 2600
Yield Strength (PSI)
4.974
1100 to 1740
Young’s Modulus (PSI)
42100
Total Strain
6.90012
2.2 to 6.5
Figure 4: Low Density Polyethylene Stress-Strain Graph
Conclusion
The values of the width and thickness for the metals are smaller
then the polymers where the percentage elongation of the
polymers is higher then the metals. The high-density polymer
does not fail at high strain. It is obvious that our measurement
20. method produces data consistently much lower than the
published values. The published values maybe using pure
elements where the samples that we were given are not that
pure. Moreover, the published sample used different
measurement and that might affect the values. Despite, the
inaccurate values tested for tension test property, the stress-
strain curves from which they were generated still conform to
the expected profile and mechanics of metals.
References
Work Cited
· Lab Manual
· W.F. Hosford, Overview of Tensile Testing, Tensile Testing,
P. Han, Ed., ASM International, 1992, p 1–24
· Johnson, Mark. "2024 Alloy." 2024 Alloy. California Metal
and Supply, 10 May 2013. Web. 22 Sept. 2015.
Aluminum Stress Vs Strain Diagram
0.0 0.0 0.000882352948846186 0.00136029413517784
0.00200735295520109 0.00292647054747624