1. Abstract—In this lab, students learned how to use the Instron
Universal Testing Machine to create stress vs. strain plots. Using
the data obtainedin lab, students were responsible forfinding the
values of unknown material properties for four different
materials. These materials include: An unknown metal, carbon-
fiber, nylon and plaster of paris. The students had to determine
the unknown metal by finding the appropriate material properties
and comparing the found properties to those obtained by a
reputable source for a given material. In the second part of this
lab, students had to test a copper wire specimen in tension to
failure using a fixture provided in lab. Based on data obtained in
LabVIEW during this testing, students createda stress-strain-plot
and found other material properties based on the specimen’s
behavior.
Index Terms—Instron Universal Testing Machine, carbon-
fiber, nylon, stress, strain
I. INTRODUCTION
HIS lab demonstrates how to use the Instron Universal
Testing Machine to perform tensile/compressive testing.
From the data obtained through the tensile/compressive testing,
stress-strain plots were generated. Other material properties
found from this data include: Young’s modulus (the slope of the
stress-strain curve in the linear region), yield strength (the point
during testing that plastic deformation begins to occur),
ultimate strength (The greatest amount of stress the specimen
experiences during testing), breaking strength (the amount of
stress the specimen experiences at fracture), toughness (the total
amount of energy the specimen can absorb before fracture),
percent elongation (percentage of how much the specimen
strained during testing), specific strength (the specimen’s
strength to weight ratio) and specific stiffness (the specimen’s
stiffness to weight ratio). Also,the uncertainties associated with
the values of stress and strain were calculated.
Three different materials were tensile tested including: An
unknown metal, carbon-fiber and nylon. The first three test
performed were tensile test.During this type of testing,the test
specimen is clamped into the machine on both ends. After the
specimen is clamped, the machine applies equal and opposite
forces to the piece in directions away from the center of mass
of the material. During the testing, force versus displacement is
recorded until the specimen fractures. Displacement is measure
using either an extensometer (a sensor that is connected to the
test piece that measures the elongation of the test piece) or by
using cross head displacement (a method where strain is
measured using the displacement of the machine’s grips).
The last material tested, plaster of paris, was placed in a
compressive test. Like in tensile testing, the piece was first
clamped into the machine. After properly clamping the
material, the machine applies equal and opposite forces to the
piece in directions towards the materials center of mass. Unlike
in tensile testing,an extensometer is not used to measure strain.
In the second part of this lab, a copper wire specimen was
tested using a fixture provided in lab. Strain during testing was
measured using a LVDT (linear variable differential
transformer). Using LabVIEW, students tested the copperwire
specimen to failure using brass weights and created stress-strain
plots based on the materials behavior as well as other material
properties.
II. PROCEDURE
Lab 3a
A. Specimen Measurements
The first part of this required students to take turns measuring
the various specimens. For the first specimen (unknown metal)
ten measurements of width and thickness were performed and
recorded as well as the specimen’s mass. For the second/third
specimens (carbon-fiber/nylon respectively) width and
thickness were measured and recorded. Finally, for the fourth
specimen (plaster of paris) diameter and height were measured
and recorded.
B. Specimen Testing
After all the necessary measurements were found and
recorded, the specimens were tested.The first step in testing
is to clamp the specimen to the machine’s grips. This
provides proper security of the specimen during testing.The
second step of testing (for tensile test)is to attach the
extensometer and measure the initial length between the
grips. Lastly, the Instron software is opened to provide an
interface to the machine for testing. After all these steps are
performed, testing can begin. The test last until the specimen
fractures (except for the compressive test of plaster of paris).
Lab 3: Determining Unknown Materials Based
on Stress vs. Strain Plots
Ballingham, Ryland
Section 3236 3/1/2016
T

2. <Section####_Lab#> Double Click to Edit 2
2
C. Post Testing
After the test were performed, the method of failure for each
specimen was noted and a photograph was taken (except for
carbon-fiber due to its method of failure). The data and
photographs for test was placed into a zip file on canvas for
analysis.
Lab 3b
A. LabVIEW VI
In this part of the lab, a LabVIEW VI is required to properly
obtain the data during the testing of the copper wire specimen.
This VI logs the strain based on readings from the LDVT and
allows the input of a loading weight value. Based on this data,
the VI calculates the stress that the wire undergoes during
testing. This is all done within a while loop and the data is
written to a spreadsheet.
B. Setting up fixture
The students were required to properly assemble the
fixture to obtain proper data readings. The first step to
assembly is to wrap one end of the wire around the top of the
tensile loading fixture and anchor it. After this, the students
wrapped the other end of the wire around the weight carrier
and anchored it. Finally, the students measured the initial
length of the wire.
C. Data collection
After the fixture is setup,data collection can begin.
Weight is incrementally added to the weight carrier and
using the LabVIEW VI, data is collected. This is done until
the wire fails.
III. RESULTS
Fig. 1. Stress vs. strain plot for unknown metal.
Fig. 2. Stress vs. strain plot for carbon-fiber.
Fig. 3. Stress vs. strain plot for nylon.
Fig. 1. Stress vs. strain plot for plaster of paris.
TABLE I
MATERIAL RESULTS
Carbon-fiber Nylon
Unknown
Metal
Young’s
Modulus (GPa)
35.486 0.785 54.38
0.2% Offset
Yield Strength
(MPa)
- 25 500
Ultimate
Strength (MPa)
1349.3 28.21
521.8
Breaking
Strength (MPa)
1349.3 13.83 503.3
0
100
200
300
400
500
600
0 0.01 0.02 0.03 0.04 0.05 0.06
Stress(MPa)
Strain
-200
0
200
400
600
800
1000
1200
1400
1600
0 0.01 0.02 0.03 0.04
Stress(MPa)
Strain
0
5
10
15
20
25
30
0 0.5 1 1.5
Stress(MPa)
Strain
-5
0
5
10
15
20
0 0.005 0.01 0.015 0.02
Stress(MPa)
Strain

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3
Percent
Elongation (%)
3.702 136.62 5.342
Toughness
(mJ*m-3
)
115.6 150.89 122.692
IV. DISCUSSION
Unknown Metal
The material properties found in Table I are very similar
to SAE J2340 grade 340 X steel. According to [5], this type of
steelhas a range ofyield strength ofabout from340 MPa to 440
MPa, a minimum ultimate strength of 410 MPa and a Young’s
modulus of 40 GPa.
TABLE II
MECHANICAL PROPERTIES OF SAE J2340 GRADE
340 X STEEL
Tensile
Strength (MPa)
Yield Strength
(MPa)
Elastic
Modulus (GPa)
410 340-440 40
Failure analysis
A. Unknown metal
The metal appears to have been ductile due to the fact that the
specimen showed signs of failure before failure occurred.
Failure seems to have occurred at approximately 45 degrees
with respect to the horizontal (plane of maximum shear
stress).
B. Carbon-fiber
The carbon-fiber method of failure was sudden and
catastrophic.The material showed no signs of impending
failure suggesting that carbon-fiber is a brittle material. Once
it failed, it was a very violent and quick failure with strings
of carbon-fiber scattered around the testing machine.
C. Nylon
The nylon shows characteristics of a ductile material due to
the fact that a large amount of strain occurs before the
specimen fractures. Anothercharacteristic to note is the fact
that during testing,pitting occurs in the material. These pits
represent microscopic tears in the material due to the
induced strain of the testing machine.
D. Plaster of paris
The plaster of paris was the only material tested in
compression. This material exhibits cracking in the vertical
direction before failure occurs. This is due to the fact that
micro-cracks begin to form in the specimen under
compressive loading and propagate in the direction of the
maximum normal stress. Plaster of paris is a brittle material
due to catastrophic mode of failure.
Extensometer vs. Cross head displacement
An extensometer is best used when failure occurs within
the range of the extensometer. If the material failures out of
this range, then this data should be discarded as it is no
longer accurate. The advantages ofan extensometer is higher
accuracy in measurements (due to potential “slipping” of the
specimen in the grips when using cross head displacement).
Cross head displacement should only be used when fitting an
extensometer isn’t practical or possible.
Specific Strength/Specific Stiffness values
TABLE III
SPECIFIC STRENGTH/ SPECIFIC STIFFNESS VALUES
Material
Density
(kg/m3
)
Breaking
Strength
(MPa)
Young’s
Modulus
(GPa)
Specific
Strength
(N*m/Pa)
Specific
Stiffness
(N*m/Pa)
Metal 17,000 503.3 54.38 184359 3,198,889
Carbon-
fiber
1,600 1349 35.49 843,313 2.218*107
Nylon 1,140 13.83 0.785 12,135 687,719
The density of the unknown metal was found by dividing
the mass that was calculated in lab by the volume of the
specimen. The density values for carbon-fiber and nylon were
found from reputable sources online. From the table, it appears
that carbon-fiber has the highest specific strength and specific
stiffness.
V. CONCLUSION
In this lab, students were taught how to use the Instron
Universal Testing Machine to test materials in tension and
compression. Students also learned how to create stress-strain
diagrams from the data collected in these test and how to find
other material properties based on the stress-strain plots. By
analyzing the data for the unknown metal, students were able to
figure out what the unknown metal was simply based on the
stress-strain plots generated fromthe data.
APPENDIX
Uncertainty values for the stress, strain and cross head
displacement are located in [1]. The uncertainty values of
Young’s modulus were calculated using the Monte Carlo
simulation method. The formulas used for this method are
located in [1].
TABLE IV
UNCERTAINTY CALCULATIONS
Parameter Uncertainty
width ±0.00005 in.
thickness ±0.00005 in.
height ±0.00005 in.
diameter ±0.00005 in.
AM ±0.20 mm2
AN ±0.54 mm2
ACF ±0.16 mm2
APOP ±0.20 mm2
𝜖 ±0.6%
𝜎 𝑀 ±240 MPa

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4
𝜎𝑁 ±38 MPa
𝜎𝐶𝐹 ±56 MPa
𝜎𝑃𝑂𝑃 ±0.100 MPa
EM ±800 MPa
EN ±10 GPa
ECF ±150 MPa
EPOP ±0.125 MPa
Cross head displacement ±0.5%
0.2% offset equations
TABLE V
EQUATION OF 0.2% OFFSET LINE
Material Equation
Unknown Metal y=33804x-1.715
Carbon-fiber y=35486x+122.534
Nylon y=784.69x-3.50098
Uncertainty equations used
𝑈𝐴 = √(
𝑑𝐴
𝑑𝑤
)
2
( 𝑈 𝑤)2
+ (
𝑑𝐴
𝑑𝑏
)
2
( 𝑈 𝑏)2 (1)
𝑈 𝜎 = √(
𝑑𝜎
𝑑𝑃
)
2
( 𝑈 𝑃)2
+ (
𝑑𝜎
𝑑𝐴
)
2
( 𝑈𝐴)2 (2)
𝑈𝜖 = √(
𝑑𝜖
𝑑𝐿
)
2
( 𝑈 𝐿)2
+ (
𝑑𝜖
𝑑𝐿𝑜
)
2
( 𝑈 𝐿𝑜)2 (3)
𝑈𝐸 = √(
𝑑𝐸
𝑑𝜎
)
2
( 𝑈 𝜎)2
+ (
𝑑𝐸
𝑑𝜖
)
2
( 𝑈 𝜖)2
(4)
REFERENCES
[1] Pandkar, A. “Lab3 Monte Carlo Spring2016 Students,” EML3301C-
Mechanics of Materials Laboratory - Spring2016
[2] Pandkar, A. “Lab3 Lecture Slides,” EML3301C- Mechanics of
Materials Laboratory- Spring2016
[3] "Toughness." Wikipedia.Wikimedia Foundation,05 Mar. 2015. Web.
02 July 2015.
[4] Beer, FerdinandP., andE. Russell Johnston. Mechanics of Materials.
New York: McGraw-Hill, 2015. Print.
[5] High Strength Steel StampingDesign Manual. (2014, July 25).
RetrievedMarch6, 2016.<http://www.a-
sp.org/~/media/Files/ASP/Enabling%20Programs/High_Strength_Steel_
Stamping_Design_Manual.pdf