cfrp surface coatings in bridge design
TRANSCRIPT
Carbon Fiber Reinforced Polymer Surface
Coatings in Bridge Design
Texas A&M University
MEEN 404 - Section 505
May 2, 2014
Team 05
Jordan Ellington
__________________________________
Garin Gaalema
__________________________________
Michael Wampler
__________________________________
"On my honor, as an Aggie, I have neither given nor received
unauthorized aid on this academic work."
i
Abstract
This experiment determined how thickness, temperature, and corrosion affect the specific flexural
strength of a composite, consisting of outer plies of carbon fiber reinforced polymer (CFRP) and an inner
sample of steel, in order to optimize bridge design with respect to strength and cost. Steel is the most
common structural member used in bridge design due to its high specific strength, low cost, and
durability. A significant problem with the use of steel is it is highly susceptible to corrosion. The Golden
Gate Bridge has to be repainted every year to prevent corrosion and ensure the structural integrity. The
cost of that maintenance between 2012 and 2013 was $37.74 million [1]. The goal of this experiment was
to determine if a carbon fiber reinforced polymer and steel composite could serve as a replacement to
paint coatings any many other retrofitting processes in order to mitigate the cost of today’s bridges and
increase structural integrity. This was accomplished by using an Instron 5567 to bend test the carbon fiber
reinforced polymer and steel composite specimen and determine the flexural strength of each sample. The
CFRP and steel composite specimens were cured using Cycom’s manufacturing specifications. This
consisted of preparing the CFRP and steel composite, a lay-up process, and use of an autoclave for the
curing process. The first variable was the thickness of the CFRP, the number of plies wrapped around the
steel. The second variable to be tested was the operating temperature, and the third variable was
corrosion. It should be noted that the corrosion was also done at the corresponding operating temperature
for each sample in order to determine the interaction between temperature and corrosion. Finally, with the
samples prepped, they were tested using a three point blend. The samples were divided into three testing
temperatures: 22°C (room), 60°F (oven), and 7.5°C (ice bath). After the data was reduced from the bend
testing, the results were analyzed to determine the specific flexural strength. The specific flexural strength
ranged from 280 to 640 ksi/(lbm/in3), with the highest value associated with the lowest temperature. The
number of plies affected the strength the most with 8 plies doubling the strength with approximately 2.3
times the strength of steel for the corrosion samples and approximately 2.1 times the strength of steel for
the non-corrosion samples. Corrosion had an effect on the specific flexural strength, because a porous
film peel-ply allowed the epoxy resin to flow to the outer faces of the samples, and depleted the resin
from the edges of the samples. A three way ANOVA was performed, and all seven interactions were
statistically significant, thus all null hypotheses were rejected. A cost analysis was conducted, and in the
first year carbon fiber was predicted to save $22 million when compared to the maintenance cost of
painting steel. The two greatest discrepancies found in this experiment were the nitrogen purge gas
running out during manufacturing, and the use of porous release film. Despite the discrepancies, the
uncertainty only ranged between 3-6%. Further testing should be done with the discrepancies corrected in
order to increase the accuracy of the cost analysis. Overall, 8 plies of carbon fiber would increase the
structural integrity of a seawater bridge, prevent corrosion, and decrease the overall cost.
ii
Table of Contents
Abstract .................................................................................................................................................... i
Table of Contents .................................................................................................................................... ii
Table of Figures ..................................................................................................................................... iv
Table of Tables....................................................................................................................................... iv
Introduction ............................................................................................................................................. 1
Objective ............................................................................................................................................. 1
Background ......................................................................................................................................... 1
Assumptions and Constraints ............................................................................................................... 2
Theory..................................................................................................................................................... 2
Materials ............................................................................................................................................. 2
Bend Testing ....................................................................................................................................... 3
Specific Flexural Strength .................................................................................................................... 4
Composite Strength Prediction ............................................................................................................. 5
Corrosion ............................................................................................................................................ 6
Operating Temperature ........................................................................................................................ 7
Apparatus and Experimentation ............................................................................................................... 8
Design and Instrumentation ................................................................................................................. 8
Uncertainty Analysis ......................................................................................................................... 13
Design of Experimental Procedures ....................................................................................................... 15
Equipment and Material List .............................................................................................................. 15
Procedures ......................................................................................................................................... 15
Results .................................................................................................................................................. 16
Discussion ............................................................................................................................................. 20
Discrepancies .................................................................................................................................... 23
Summary ............................................................................................................................................... 24
Conclusions ........................................................................................................................................... 24
Appendix A. Reference Figures ............................................................................................................. 26
iii
Appendix B. Function Structure and Requirements ................................................................................ 27
Functional and Performance Requirements ........................................................................................ 27
Appendix C. Data Reduction ................................................................................................................. 28
Appendix D. Results of Failure Modes and Effects Analysis .................................................................. 29
Appendix E. Safety and Hazard Analysis ............................................................................................... 31
Safety and Hazard Analysis ............................................................................................................... 31
Appendix F. Specimen Data .................................................................................................................. 32
Appendix G. Experimental Results ........................................................................................................ 32
Expected Data ................................................................................................................................... 32
Raw Data........................................................................................................................................... 34
Sample Calculations .......................................................................................................................... 36
Uncertainty .................................................................................................................................... 36
Experimental Data ......................................................................................................................... 36
Cost Analysis................................................................................................................................. 37
References............................................................................................................................................. 37
iv
Table of Figures
Figure 1. Three-Point Bend Tester ........................................................................................................... 3
Figure 2. Bending Stress Distribution for a Specimen in Pure Bending..................................................... 4
Figure 3. Tensile Toughness Example...................................................................................................... 7
Figure 4. Stored Roll of Carbon Fiber Reinforced Polymer Pre-preg ........................................................ 8
Figure 5. Depiction of Pre-preg Lay-Up Process ...................................................................................... 9
Figure 6. Experimental Lay-Up of CFRP Samples ................................................................................. 10
Figure 7. Schematic of Autoclave Process ............................................................................................. 10
Figure 8. CFRP/Steel composite with 1/16” CFRP thickness on top and bottom of steel specimen ......... 11
Figure 9. Instron 5567 Bend Test Apparatus .......................................................................................... 13
Figure 10. Comparison of Expected Results to Experimental Results at Room Temperature ................... 17
Figure 11. Mean Specific Strength as a function of Temperature, Number of Plies, and Corrosion (0 = No
Corrosion, 1 = Corrosion) ...................................................................................................................... 18
Figure 12. Normalized Specific Strength as a function of Temperature, Number of Plies, and Corrosion (0
= No Corrosion, 1 = Corrosion) ............................................................................................................. 19
Figure 13. Normalized Specific Strength as a function of Number of Plies, Temperature, and Corrosion (0
= No Corrosion, 1 = Corrosion) ............................................................................................................. 19
Figure 14. Specific Strength [ksi/(lbm/in3)] as a function of Temperature (C) and Number of Plies [dim]
.............................................................................................................................................................. 20
Figure 15. 4 Ply (Left) With Visible Corrosion and 8 Ply (Right) With No Visible Corrosion ................ 22
Figure 16. Plain Weave Carbon Fiber Fabric.......................................................................................... 26
Figure 17. Curing Process for Plain Weave Fabric [12] .......................................................................... 26
Figure 18. Schematic of Function Structure ........................................................................................... 27
Table of Tables
Table 1. Bend Test Results for Samples not Subject to Corrosion ........................................................... 16
Table 2. Bend Test Results for Samples Subject to Corrosion ................................................................ 17
Table 3. ANOVA for Temperature, Number of Plies, and Corrosion ...................................................... 20
Table 4. Summary of Specific Strength Relative to Steel for the Three Thickness Ratios........................ 22
Table 5. Estimated Cost Analysis for Bridge Design .............................................................................. 23
Table 6. Material Properties of CFRP and Steel [6] [12] ........................................................................ 26
Table 7. Failure Mode and Effects Analysis chart including mitigation of possible failures .................... 30
Table 8. Test Matrix for SFC Specimens with Varying Thicknesses ....................................................... 32
Table 9. Expected Temperature Effect on Flexural Strength ................................................................... 33
v
Table 10. Predicted vs. Actual Flexural Strengths with Uncertainty at Room Temperature ..................... 33
Table 11. Predicted vs. Actual Specific Flexural Strengths with Uncertainty at Room Temperature........ 33
Table 12. Corrosion Samples Raw Data ................................................................................................. 34
Table 13. Non Corrosion Samples Raw Data ......................................................................................... 35
1
Introduction
Objective
Determine how corrosion, operating temperature, and carbon-fiber reinforced polymer coating thickness
affects flexural strength of structural steel.
Background
The Golden Gate Bridge is constructed of steel and concrete and suspends 8980 [ft] across the Golden
Gate Strait to connect San Francisco to Marin County [1]. Steel is used in bridges because of its high
strength to weight ratio, or specific strength, high quality at low cost, constructability, and durability [2].
The major limitations of steel in bridge design are its susceptibility to corrosion and its weight. Corrosion
of metals costs the U.S. economy on average $300 billion per year in maintenance, repair and
replacement [3]. The Golden Gate Bridge is suspended across seawater, which corrodes the steel structure
at a high rate. The rate at which corrosion deteriorated the integrity of the bridge was severely
underestimated at the time of erection, 1939, and resulted in an expedited implementation of painting
program to protect the steelwork. The primary maintenance cost of the steel bridge today is painting the
bridge to protect from corrosion. In the Comprehensive Annual Financial Report for the Fiscal Year,
which ended June 30, 2013 for 2012, the maintenance cost alone was $37.74 million [1]. To solve these
problems, carbon fiber reinforced polymers’ (CFRP) high strength to weight ratio and corrosion resistant
material properties have the potential to reduce the lifetime cost and improve the structural integrity of
bridges.
Advancements in composite materials have been a focus in materials science over the last forty years [4].
Fibrous composites are materials that have fibers reinforce a matrix. The matrix orients the fibers to take
the load in the fiber direction.
We are on the verge of an explosion in the use of these fibrous materials for structural
applications. More recently we are seeing applications in the infrastructure, including
plans for an all-composite bridge over an interstate highway. These advancements will be
seen because the polymer or ceramic matrix that reinforces the fibrous material in the
composite can often be made to be essentially maintenance free compared with
traditional engineering materials. Reduced maintenance can represent substantial savings,
and is a major driver in overall cost evaluations [5].
A carbon fiber composite material pre-impregnated with epoxy resin (pre-preg) could reduce the costs
associated with construction and maintenance of a bridge in corrosive environments.
2
To determine the effectiveness of pre-preg, it is valuable to understand the physical and environmental
effects on the composites material properties. In this experiment, the composite was combined with steel
to find the flexural strength. The combined steel and fibrous composite (SFC) was tested under the
following three performance parameters: thickness, operating temperature, and corrosive resistance. The
results were related to the Golden Gate Bridge as a possible replacement for paint. The goal of this
experiment was to determine the effects of these parameters on the flexural strength of steel samples
coated in fiber-reinforced polymers in order to generate recommendations on methods to increase the
structural integrity. These recommendations could predict the necessary lifetime of the composite in order
to reduce the costs associated with overall lifetime cost of current bridge design.
Assumptions and Constraints
The assumed conditions of the materials and test setup to simplify calculations and are given below [4].
1. Experimental woven fiber (Figure 16, in Appendix A) has perfect �� and ��� directions.
2. The bond between the CFRP and steel is free of voids, and the CFRP is free of voids.
3. There are no residual stresses in the SFC.
4. The steel and CFRP act as linearly elastic materials.
5. Corrosion occurs at the same rate for each specimen during corrosion testing.
6. The SFC is sealed on its ends during corrosion testing.
7. Corrosion induced on the boundary layer between the CFRP and steel is negligible.
8. Thermal expansion on the cross sectional area of the test specimens is negligible.
Theory
Materials
CFRP composites have high strength in the fiber direction. Carbon fibers are lightweight, chemically
resistant, and are created to have the atoms oriented with the highest strength in the fiber direction. The
polymer matrix binds and orients the fibers. Most of the load is transmitted to the fibers through the
matrix. Specifically, epoxy resins display properties of high mechanical strength, high corrosion
resistance, versatility, resistance to water and heat (over other polymers), simple cure process, little
shrinkage when curing, soldering, caulking, and sealant abilities for buildings and highway construction
[4]. CFRP will experience brittle failure, which can be a problem for bridge design. Failure occurs at the
maximum load where the tensile strength and breaking strength are the same [11]. Preventions for bridge
failure would be more difficult with an all-composite brittle bridge [8]. For this reason, a steel core will be
used to mitigate brittle failure.
3
A36 steel is the most common structural steel used in the United States, but does not have atmospheric
corrosion resistance [6] [7]. The corrosion resistant property of epoxy resin has the potential of blocking
corrosion on the surface of steel by combining the two materials. The ductility of A36 steel can be used to
reduce the effects of brittle CFRP failure in bridge design. Ductile behavior is preferred over brittle
behavior, because ductile materials exhibit yield before failure. Brittle materials do not exhibit this yield
point, which can lead to sudden, catastrophic failure. Bridge inspectors can determine where a bridge is
weakened when ductile failure has occurred, and can fix the problem.
Bridge girders are designed to carry the load of the bridge, which causes it to bend. Bending strength, or
flexural strength, is therefore an important property of a bridges’ structural integrity. Bend testing is
commonly used for brittle materials that cannot withstand the grips used for a traditional axial tensile
tester [11]. Thus a bend test was utilized to test the SFC materials.
Bend Testing
A three-point bend tester applies three loads along the test specimen as seen in Figure 1. Two stationary
supports pins are maintained a set distance apart, and a third loading pin compresses the specimen in the
center between the support pins to induce bending. During the test, the force and distance deflected by the
loading pins are recorded. To calculate the maximum stress in the specimen, an understanding of bending
theory must be explained. The bending stress can be seen in Equation 1
Figure 1. Three-Point Bend Tester
����� � ��� Equation 1
M is the bending moment in the specimen, y is the distance from the neutral axis Figure 2, and I is the
moment of inertia of a rectangular beam [15]. The maximum bending moment occurs when the load is in
the center of the specimen, as can be seen in Equation 2.
4
Figure 2. Bending Stress Distribution for a Specimen in Pure Bending
�� � � � Equation 2
F is the force applied during the test, and L is the set distance between the stationary support pins. The
moment of inertia, I, for a rectangular cross sectional specimen can be seen in Equation 3.
� � �����
Equation 3
The width of the specimen is w and the height, or thickness, is h. The neutral axis for symmetrical
specimens is in the center. The maximum distance from the neutral axis is therefore can be seen in
Equation 4.
�� � �� Equation 4
The flexural strength is the highest bending stress the specimen’s experience. The flexural strength is
calculated by combining Equation 2, Equation 3, and Equation 4, as seen in Equation 5.
����� � �� ���� Equation 5
Specific Flexural Strength
Density changes as the CFRP thickness increases on the SFC. The rule of mixtures was used to find the
density of the SFC specimens. To use the rule of mixtures, the volume fractions of the SFC were
determined using the cross sectional areas of the steel and CFRP. The volume fractions of CFRP and steel
are given in Equation 6 and Equation 7, respectively.
����� � ���� Equation 6
5
�� ��� � �!�� Equation 7
��, �����, �� ��� are the cross sectional areas of the composite, CFRP, and steel, respectively. To find
density, the rule of mixtures was used as seen in Equation 8.
" � ����� # "���� $ �� ��� # "� ��� Equation 8
The CFRP density is "���� and steel density is "� ���. To normalize the flexural strengths found during
testing, the specific flexural strength is calculated using Equation 9.
%&'()*)(+�,'-./0,+%1/'231� � �����" Equation 9
Comparisons can be made between the thickness of the CFRP and the flexural strength of the SFC when
the density of the samples is accounted for. The specific flexural strength trend was analyzed to
understand the properties of the SFC as the thickness of the CFRP was increased.
Composite Strength Prediction
The predicted specific flexural strength of the SFC was determined for comparison to the actual results.
The predicted results for the specific bending strength were generated using the rule of mixtures [4]. The
equivalent specific flexural strength of the SFC can then be used to predict how thick the CFRP needs to
be to restore and maintain the structural integrity of a bridge.
To use the rule of mixtures, the tensile strength and flexural strength properties of the SFC are assumed to
be the same. This simplification is useful because the flexural strength of CFRP is not given, but the
tensile strength is. The equivalent tensile strength properties of the SFC were calculated using the below
equations. An equal strain assumption is used first. Strain is the change in length of the specimen over the
original length, as seen in Equation 10.
4 � 5,,6 Equation 10
The equal strain assumption can be seen in Equation 11.
4� ��� � 4���� � 4� Equation 11
Where 4� ��� is the steel strain, 4���� is the CFRP strain, and 4� is the composite strain. Total resultant
force on the composite in static equilibrium is equal to the sum of the forces on the steel and the CFRP.
The force is equal to stress times the cross sectional area of the specimen, as can be seen in Equation 12.
� � � # � Equation 12
The equivalent tensile strength is then calculated with the rule of mixtures in Equation 13.
6
�� �+����� # ����� $+�� ��� # �� ��� Equation 13
Where ����� and �� ��� are the tensile strengths of the CFRP and steel. The predicted specific strength is
shown in Equation 14.
%&'()*)(+%1/'231� � ��" Equation 14
Corrosion
Corrosion damage is a major problem in bridge design. Steels are primarily composed of iron. Rust, or
iron oxide (�'�7�8, is the reaction between iron and oxygen. When water comes into contact with iron, a
reaction begins. The electrolytic water combines with carbon dioxide on the iron and creates an acid,
which is a better electrolyte than pure water. When the acid is formed, the iron (anode) dissolves as the
water breaks into hydrogen and oxygen. The freed oxygen and freed iron combine into iron oxide. During
this part of the process, electrons are emitted. The electrons move through the water to another section of
iron (cathode). Seawater is a better electrolyte than pure water, which increases the corrosion process. The
steel structure can withstand a smaller load because the cross sectional area of the steel structure
decreases during rusting [9]. Polymers do not corrode as fast as steels because they are resistant to
oxidation. Polymers can degrade through absorbed solvents, UV radiation, thermal degradation, and
oxidation that disrupt the chemical composition of the polymer, but occur over a much longer period of
time [4]. For this experiment, the CFRP was tested to understand its ability to block corrosion.
Corrosion is measured by the weight loss of the test specimen when exposed in corrosive environments.
The corrosion rate of low carbon steel in a marine environment ranges from .5 mils/year to 20 mils/year,
depending on the circumstances [10]. To find the theoretical amount of corrosion, the following equations
were used. The first step is to calculate the volume of the steel bar, Equation 15.
9:,.;' � � # � # 1 Equation 15
Where w is the width, h is the height, and t is the thickness of the bar. The rate of corrosion was found by
converting mils/year into inches/day. The number of days was multiplied by the rate of corrosion to find
how many inches of corrosion should come off of the steel in that time. Next, the new volume of the bar
is calculated using Equation 15 by subtracting the corrosion depth from the original bar. The mass
;<�< <�+of the original bar was calculated using the volume from Equation 15, and the density of the
steel+"!, as seen in Table 6. The new mass of the corroded bar ;�<�� was calculated the same way. The
amount of mass lost can be calculated using Equation 16.
7
;�6! � ;<�< <� =;�<�� Equation 16
To find the level of corrosion in the experiment, each specimen was weighed before and after exposure.
After the bend testing, the CFRP coating was broken off to see surface of the steel. A visual inspection of
the surface was done to confirm whether CFRP is able to block corrosion. To maintain similarities
between tests, the thickness of the SFC specimens was the same as the non-corrosion specimens.
Operating Temperature
Toughness is defined as the energy absorbed by the material during deformation, or the area under the
true stress – strain curve. In Figure 3, material B has a lower yield and ultimate strength than A, but
absorbs more energy than material A. This indicates that material B is more ductile than material A. The
strength of material A is notably higher because it takes more stress to strain the material, due to its brittle
properties.
Figure 3. Tensile Toughness Example
The ductile to brittle transition temperature (DBTT) gives an indication of the properties a material will
display when exposed to different temperatures. The DBTT is determined from the Charpy Impact Test.
In the test, the energy absorbed by the test material during failure is found. A36 steel has a body centered
cubic atomic structure, which is known to have a DBTT. As the temperature decreases, A36 steel
becomes more brittle, causing the tensile strength to increase like material A in Figure 3 [11].
The glass transition temperature characterizes temperature effects on polymers. Thermoset polymers, like
the one used in this experiment, have an amorphous structure and show a distinct glass transition
temperature. The glass transition temperature for Cycom E773 resin is 155�C [12]. Weather conditions do
not generate a temperature as high as 155�C, so the resin in bridge applications should not reach the glass
transition temperature. The Cycom E773 Epoxy Pre-preg Technical Data Sheet shows that the composite
displays high strength at room temperature and at high temperatures [12].
8
NASA created a technical paper titled Low Temperature Mechanical Testing of Carbon-Fiber/Epoxy-
Resin Composite Materials [13]. Quasi-isotropic laminate test samples were made at room temperature
(25�C), in a dry ice or carbon dioxide bath (-56.6�C), and a liquid nitrogen bath (-195.8�C). The average
tensile strength of the samples at room temperature, carbon dioxide bath, and liquid nitrogen bath were
110.5 ksi, 117.2 ksi, and 100,7 ksi, respectively. The average tensile modulus remained close to each
other, and exhibited values of 8.9 msi, 8.8 msi, and 9.3 msi for the three temperatures. This indicates that
the carbon fiber was insensitive to temperature. The matrix resin is dependent on temperature. If the
epoxy is below its glass transition temperature, it will fail before it plastically deforms. There is a
possibility for the epoxy resin to have micro cracks propagate during the test. This is a concern for the
corrosion mitigation abilities of the resin. Micro cracks could allow corrosion to reach the metal specimen
underneath, and therefore weaken the bridge structure. The expected result for temperature effects on the
SFC is a higher strength at low temperatures from the DBTT of the steel and no effect from the thickness
of the CFRP. The expected results for temperature effects on flexural strength of the steel samples are
given in Table 9.
Apparatus and Experimentation
Design and Instrumentation
The first step of the design of this experiment was the manufacturing process of the samples. This was
done by laying and curing the Cycom E773 Epoxy Pre-preg fabric and A36 Carbon steel to make the
samples. First the pre-preg had to be wrapped around the steel. The pre-preg was unrolled and a strip was
cut strip with the width 1 inch greater than width of the steel sample. The rolled pre-preg can be seen in
Figure 4.
Figure 4. Stored Roll of Carbon Fiber Reinforced Polymer Pre-preg
9
Starting in the middle of a steel sample, one team member rolled the steel sample while another team
member held the pre-preg in tension. Once desired number of wraps was reached, the pre-preg was cut
with the extra rolled to the middle of the next side of sample. The SFCs need to be symmetric to create
uniform specimens ideal for bend testing, and to utilize the equations in the theory portion [4]. All the
samples were marked and placed inside a freezer till curing process.
The curing process consisted of a steel plate (tool), solid release film, porous release film, surface bleeder,
solid release film, a surface breather, a cork dam with double sided tape, and a vacuum bag. The order of
these layers can be seen in Figure 5.
Figure 5. Depiction of Pre-preg Lay-Up Process
The steel plate served as the tool, which consisted of a non-galvanized steel plate. A solid release film, or
non-porous, moderate temperature bagging was used to prevent the pre-preg specimen from curing to the
tool. This bagging was taped using high-temperature glass-fiber tape. A polyester fabric cloth peel ply
was used for the porous release film. This film allows resin to flow through the matrix, allowing for
uniform material properties. To prevent the resin from being sucked out of the vacuum bagging, a surface
bleeder breather is folded over the samples to absorb excess resin. A high-temperature polymer tacky tape
was surrounding the edges of the tooling to create an effective seal around the samples. This tacky tape
was used as a replacement to the cork dam with double-sided tape. Moderate temperature bagging was
then used to create the vacuum seal. A seal was connected to the bagging to connect to a copper vacuum
tube that would create the pressure differential. This can be seen via Figure 6.
10
Figure 6. Experimental Lay-Up of CFRP Samples
The plate from Figure 6 was inserted inside the autoclave, and a pump was used to verify the vacuum’s
bag functionality. An autoclave is a hyperbaric chamber that allows for heat and pressure to be applied to
the specimen, which is necessary to cure fiber reinforced polymers. The autoclave was shut and properly
torqued with a torque wrench, and nitrogen gas was hooked up for added pressure to purge the autoclave.
This purge is necessary to prevent the exothermic process of curing from combusting in the autoclave.
Heat was added to the autoclave at a controlled rate, according to curing procedure, with a member
recording and timing changes in temperature. When the heat process was finished, the heaters within the
autoclave were turned off and the samples were cooled and removed. A schematic of the set-up can be
seen via Figure 7.
Figure 7. Schematic of Autoclave Process
Nitrogen
Autoclave
Control
System
Vacuum
Pump
11
For the specific flexural strength test, plain steel bar and CFRP only samples were tested separately to
determine their individual properties. This was done to validate the results of our experiment. Specimens
with four varying thicknesses were prepared for curing to create a sandwich composite, consisting of
CFRP on the outside and steel on the inside. The dimensions for the samples were 1”x5”, with respect to
width and length in order to match the dimensions of the steel samples. A model for the composite
specimen can be seen via Figure 8. Each of the four variations needed three samples, resulting in three
samples with 0 ply thickness, three samples with 1 ply thickness on each side, three samples with 1/64”
thickness on each side, and three samples 1/32” thickness on each side. Since the steel thickness was
1/16”, three more samples of CFRP only were prepared to determine and validate the results of our
experiment to the manufacturer specifications. The steel only samples were not subjected to the curing
cycle. The resulting total number of specimens thus far, is 9 CFRP/steel composite specimens, 3 steel
only specimens, and 3 CFRP only samples.
Figure 8. CFRP/Steel composite with 1/16” CFRP thickness on top and bottom of steel specimen
Each of these twelve different samples were subjected to various temperature in order determine the
relationship between temperature and specific strength. The samples were tested at a relatively low
temperature (7.5˚C), room temperature (22.5˚C), and a relatively high temperature (60˚C), resulting in
three different temperatures for this test. This increased the total number from 12 to 36, or 27 CFRP/steel
composite specimens, 9 steel only specimens, and 9 CFRP only specimens.
For the corrosion test, since no chemical reaction occurs between carbon and salt water, only SFC needed
to be tested. Also, given the short amount of time the samples were be subjected to corrosion, only two
variations were used for corrosion testing. The two variations were either the specimens were subject to
corrosion, or they were not subject to corrosion. The corrosion specimens were subject to a 5% NaCl-
water solution for one week’s time. In order to determine the interaction between corrosion and
temperature, three corrosion baths were prepared. One corrosion bath was submersed in an ice bath, one
left at room temperature, and one subject to a hot plate. The salinity was measured twice a day to ensure
the salinity remained within 1% of the aforementioned salinity. This increased the total number of
samples from 36 to 72, or 54 CFRP/steel composite specimens, 18 steel only specimens, and 18 CFRP
only samples. To reiterate there were a total of four different thicknesses. A sample from each of these
four thicknesses was subject to 3 different operating temperatures. Finally for each operating temperature
there was a set subject to corrosion at that temperature and a set not subject to corrosion at that
Steel Specimen – 1/16”
CFRP Specimen – 1/32”
CFRP Specimen – 1/32”
12
temperature. A summary of the test specimens can be seen in Table 8. For statistical purposes there were
3 samples per each of the four thicknesses.
After the aforementioned manufacturer’s specification for the curing process was followed, the next step
was to create the salt-water bath to simulate a corrosive environment. Three salt-water baths with 5%
solution of NaCl and water were prepared in a pyrex glass container. Each bath would have three
specimens for each varying thickness for a total of 12 CFRP/steel samples and 3 CFRP only samples.
These baths were then subjected to the operating temperature, i.e. ice bath, room temperature, and hot
plate. After one week the samples were removed from their corrosion bath.
After the corrosion bath was complete the samples subjected to corrosion were mixed in with their non-
corrosion, same operating temperature counter-parts, and 24 samples per operating temperature. A
Coleman cooler filled with 20 [lbs] of ice was used to bring the corrosion (12 samples) and non-corrosion
(12 samples) samples to 0˚C, total of 24 samples at 0˚C. An oven was used to heat the corrosion and non-
corrosion samples to 60˚C, total of 24 samples at 60˚C. The corrosion and non-corrosion samples
remained at ambient room temperature, total of 24 samples at 22.5˚C.
With the samples at their desired initial conditions, they were then tested on the Instron 5567 tensile
testing apparatus. In accordance with ASTM standards for testing of composite materials, the dimensions
of each sample were determined before testing in order to determine the span the support beams [16]. To
meet ASTM standards the recommended span length, rate of crosshead speed, and the max deflection
assuming a maximum 5% strain is needed should be calculated based off the specimen’s dimensions. The
span, rate of crosshead speed, and max deflection can be determined using Equation 17, Equation 18, and
Equation 19.
%&02 > �? @ 1 Equation 17
A � B �?C Equation 18
D � 4� �?C Equation 19
In Equation 17, t is the thickness of the sample. For the purpose of our experiment, the max span needed
was determined to be 2 [in]. In Equation 18, Z is the rate of strain for the outermost fiber, which
according to ASTM standards should be 0.01 [(in/in)/min], L is the support span, and d is the thickness of
the specimen. In Equation 19, 4�, is the max strain in the outer most fiber, assumed to be 5%, L is the
support span, and d is the thickness of the specimen.
As seen in Figure 9, the samples were placed evenly on the supports. Once the sample was securely
placed on the supports, the testing machine applied a constant increasing load to the specimen. Using the
13
rate at which the load increases in conjunction with the displacement, a stress-strain plot can be produced
in order to predict the flexural strength.
Figure 9. Instron 5567 Bend Test Apparatus
With the flexural strength known for all the specimens, plots were generated for each testing parameter.
From these findings, conclusions were made about the performance of the SFC, and recommendations for
using the SFC for bridge design are given. It should be noted due to autoclave dimension limitations, all
specimens could not be completed in one cure process. Upon analysis of the data this turned out to be a
confounding variable and the second batch of specimens were disregarded, thus instead of three samples
for each thickness, only two were used for statistical analysis.
Uncertainty Analysis
Each device needed to calculate the strength of the samples in the experiment adds uncertainty. The
uncertainty for each device can be quantified and added using Kline McClintock uncertainty analysis.
Control
System DAQ
Oven Ice
Bath
Room
Temp
Oven Ice
Bath
Room
Temp
Corrosion
Non-
corrosion
14
This is the ideal method to account for these variables as it is the root sum squared of the ratio each
variable contributes to the overall equation as seen in Equation 20.
��� � EFG���� +H� $ FG���� +H� $I$+FG���� +H�) Equation 20
In this equation, ��� is the overall relative uncertainty, with xn being the variable in question, and x being
the uncertainty for that variable. The uncertainties for each variable are based on the precision of each
measurement taken and how relatively off the measurement could be. Using Equation 20, the
uncertainties for the strength of the samples can be found. The flexural strength is found using Equation 5
on page 4, and the relative uncertainty is calculated using Equation 21.
JKL�� � MFN�O H� $ FNP H� $ FNQ� H� $ FNR��H�
Equation 21
The relative uncertainty of the specific flexural strength from found from Equation 9 on page 5 and is
given in Equation 22.
JKSL�!� � MTJKL�� U� $ VJWXYZ"��� [�
Equation 22
The relative uncertainty for the density of the steel and CFRP are given in Equation 23.
JWS&! � MFNR� H� $ FNQ� H� $ VNPS ! [� $ FN; H�
Equation 23
The relative uncertainty of the density of the SFC, or ��XYZWXYZ , is given in Equation 24.
JWXYZ"��� � MVJ\S�� [� $ VJ\ZY]^����� [� $ VJWS&! [� $ VJWZY]^"���� [�
Equation 24
The relative uncertainty of the volume fraction of the steel and CFRP from Equation 6 and Equation 7 on
page 5 are given in Equation 25.
J\S�! � MVNRS�! [� $ VNQS�! [� $ FNR� H� $ FNQ� H�
Equation 25
These relative uncertainty equations give an indication of the validity of the recorded values.
15
Design of Experimental Procedures
Equipment and Material List
Pre-preg carbon-fiber material
Resin and epoxy
50 1/16” A36 carbon steel samples (5”x1”)
Ice and Ice Reservoir
Hot plate to heat corrosion bath
Oven capable of heating specimen to 60˚C
Pyrometer
Salt-Water bath
Hydrometer
Instron 5567 Bend Testing Machine
Measuring Calipers
Procedures
1. Obtain safety glasses, protective gloves, and any other protective equipment suggested by
professional
2. Obtain pre-preg material, 72 steel samples, and all the materials listed in the experiment list.
3. Lay 18, 1/16” thick fiber reinforced polymer only samples.
4. Lay 18-1-ply thick, 18-1/64” thick, and 18-1/32” thick pre-preg fiber samples on top and bottom
of a steel sample. (Summary of samples can be seen in Table 8.
5. Lay the solid release film on the tooling (non-galvanized steel plate)
6. Lay pre-preg samples on solid release film (leave room for vacuum connection at top right
portion of the tooling)
7. Cover the pre-preg with, porous release film and bleeder breather
8. Use high temperature tacky tape on edges of tooling to create seal
9. Place solid release film on the tacky tape to apply seal
10. Place vacuum connection at top right by connecting to solid release film
11. Connect to vacuum to ensure bagging is properly sealed
12. Cure the pre-preg fiber only and pre-preg fiber/steel composite samples in autoclave according to
Figure 17.
13. Record the thickness of the sample on the data sheet.
14. Visually inspect bond integrity
15. Draw a 5% NaCl, Salt-water bath.
16. Put 12 varying thickness samples in each of the three salt-water baths
17. Place the 0˚C corrosion bath in ice bath
18. Place the 60˚C corrosion bath on hot plate
19. Place the 22.5˚C corrosion bath in ambient room temperature
20. Leave samples in corrosion bath for 1 weeks’ time
16
21. Place corrosion and non-corrosion samples into corresponding temperature bath for testing (ice-
bath, room temperature, and hot oven)
22. Calibrate the Instron 5567.
23. Load steel test specimen in Instron 5567
24. Close insulating door to keep temperature constant and perform the bend test.
25. Record the test data and maximum load from test apparatus, and denote test specimen on data.
26. Repeat Step 23 and Step 24, for all 24 ice-bath samples with varying thicknesses, all 24 samples
at room temperature, and all 24 high temperature samples
27. Remove CFRP coating from steel to visually inspect for signs of corrosion
Results
Using the procedure detailed in data reduction procedures, Appendix C, the following data were
developed, shown in Table 1 and Table 2. Sample calculations can be seen in Appendix G. It is important
to note after analysis of our data, the specimens cured in the second batch were marked as outliers due to
their significant differences in strength, thus for statistical purposes only two data points were included.
Table 1. Bend Test Results for Samples not Subject to Corrosion
Temperature
Bath
Number of
Plys (Total)Average
Standard
Deviation
Relative
UncertaintyAverage
Standard
Deviation
Relative
Uncertainty
8 75.05 0.20 3.37% 565.82 0.49 4.95%
4 61.80 1.06 3.42% 382.51 2.62 5.06%
2 62.42 1.94 3.46% 355.91 10.06 5.17%
0 77.48 0.97 3.72% 278.33 3.48 5.62%
8 78.65 1.48 3.37% 578.41 15.01 4.96%
4 60.15 2.32 3.42% 374.01 15.13 5.07%
2 62.46 1.19 3.48% 334.60 16.87 5.19%
0 75.69 0.83 3.71% 271.92 2.99 5.61%
8 64.23 0.75 3.37% 478.76 8.13 4.95%
4 61.77 0.54 3.43% 372.14 4.59 5.11%
2 50.88 1.58 3.46% 280.91 2.62 5.12%
0 75.36 2.03 3.73% 270.72 7.29 5.65%
Specific Strength [ksi/(lbm/in^3)]
Cold
Room
Hot
Flexural Strength [ksi]
17
Table 2. Bend Test Results for Samples Subject to Corrosion
With the acquired results the experimental results were compared to the expected data points at room
temperature in order to determine the validity of the results. Figure 10 shows the experimental data was in
accordance with the expected parameters, with a few variations in actual data points. The data used for
this plot can be seen in Table 10 and Table 11 This is likely due to the complex mechanics intertwined in
composites.
Figure 10. Comparison of Expected Results to Experimental Results at Room Temperature
Temperature
Bath
Number of
Plys (Total)Average
Standard
Deviation
Relative
UncertaintyAverage
Standard
Deviation
Relative
Uncertainty
8 84.94 0.56 3.37% 631.49 9.77 4.96%
4 63.92 1.44 3.42% 388.08 10.32 5.07%
2 56.87 1.39 3.47% 315.48 16.20 5.18%
0 78.48 0.97 3.72% 281.92 3.48 5.63%
8 70.14 2.29 3.37% 532.00 21.07 4.97%
4 65.75 1.21 3.43% 388.86 3.39 5.05%
2 54.16 1.21 3.47% 301.06 5.87 5.18%
0 75.36 1.07 3.72% 270.72 3.86 5.61%
8 58.83 1.77 3.37% 441.90 13.60 4.93%
4 58.77 0.58 3.42% 365.39 8.09 5.07%
2 48.57 1.75 3.45% 275.00 10.12 5.14%
0 73.36 1.38 3.72% 263.54 4.94 5.63%
Specific Strength [ksi/(lbm/in^3)]
Cold
Room
Hot
Flexural Strength [ksi]
18
In order to determine the how each parameter affected the specific strength of the specimens, a main
effects plot was generated that highlights the main trends for each independent variable, as seen in Figure
11. It should be noted that a zero indicates the subject was not subjected to corrosion, whereas a one
indicates the specimen was subjected to corrosion. It can be seen with increasing temperature, the average
value of specific strength is reduced. Also with increasing number of plies or increasing the ratio of CFRP
to steel, the specific strength of the specimens also increased. Finally, subjecting the specimens to
corrosion decreased the specific strength of the specimen.
Figure 11. Mean Specific Strength as a function of Temperature, Number of Plies, and Corrosion
(0 = No Corrosion, 1 = Corrosion)
Since the main purpose of the experiment is to determine the performance of CFRP relative to steel, the
results for specific strength were then normalized relative to the specfic strength of steel at room
temperature. Interval plots were generatred to compare the individual parameters and their respective
standard deviations. Figure 12 groups the specimens according to temperature, followed by number of
plies, and finally whether or not the specimen was subject to corrosion. The grouping of this plot
highlights the decreasing trend in specific strength relative to operating temperature. Figure 13, groups the
specimens according to number of plies, followed by temperature, and finally whether or not the
specimen was subject to corrosion. The grouping of this plot highlights the increasing trend in specific
strength relative to number of plies.
60.022.07.5
550
500
450
400
350
300
8420 10
Temp (C)
Mean
Sp
eci
fic
Str
en
gth
[ksi
/(lb
m/i
n^
3)] Number of Plys (Total) Corrosion
19
Figure 12. Normalized Specific Strength as a function of Temperature, Number of Plies, and
Corrosion (0 = No Corrosion, 1 = Corrosion)
Figure 13. Normalized Specific Strength as a function of Number of Plies, Temperature, and
Corrosion (0 = No Corrosion, 1 = Corrosion)
Finally, because CFRP is assumed to be corrosion resistant, it is useful to understand the interaction
between temperature and the number of plies, and how they collectively affect the specific strength of the
specimens. Figure 14 shows the maximum specific strength occurs at a low temperature and with a high
Temp (C)
Number of Plys (Total)
Corrosion
60.022.07.5
842084208420
101010101010101010101010
2.5
2.0
1.5
1.0
0.5
Norm
. S
treng
th
Individual standard deviations were used to calculate the intervals.
Number of Plys (Total)
Temp (C)
Corrosion
8420
60.022.07.560.022.07.560.022.07.560.022.07.5
101010101010101010101010
2.5
2.0
1.5
1.0
0.5
Norm
. S
tre
ng
th
Individual standard deviations were used to calculate the intervals.
20
number of plies. The figure also confirms the strength of steel is increased at lower temperatures, as
expected from the ductile to brittle transition temperature theory. It should be noted, that the temperature
variations were not significant enough to see this ductile to brittle transition temperature effect.
Figure 14. Specific Strength [ksi/(lbm/in3)] as a function of Temperature (C) and Number of Plies
[dim]
Table 3 displays the results of the ANOVA analysis for the independent variables: temperature, number
of plies, and corrosion.
Table 3. ANOVA for Temperature, Number of Plies, and Corrosion
The null hypotheses states that carbon fiber thickness, operating temperature, and corrosion, or any
interaction between the three, have no significant correlation to specific flexural strength. From the
analysis of the ANOVA results we can reject the null hypotheses with 95% confidence.
Discussion
After analysis of the results, the relative uncertainty for our experimental data was between 4-6% for the
specific strength. This low relative uncertainty can be attributed to the high precision of the Instron testing
apparatus. The first step in before drawing conclusions and findings from our data was to verify the
0
0240
3 00
04 0
005
00
60
52.
0.0
7
0.5
52.
7 5.7
006
ec StrengthpS
P fo rebmuN l )latoT(ys
(C)empT
21
results with the expected data. Knowing that the two curing processes could possibly constitute as a
confounding variable this data was analyzed before the results were presented. Upon analysis a significant
difference in strength of these samples was observed. Due to this difference the data points from the
second cure were excluded from further analysis, decreasing the data point from three samples to two
samples for statistical purposes. As previously stated, the experimental data collected was confirmed to
show similar trends to what was expected.
After verifying the results, the main trends were then highlighted in order to make extrapolations from the
data. It can be seen at lower temperatures SFCs exhibit higher specific strengths; however, this can be
problematic from an engineering standpoint as the materials modulus of elasticity will also increase
causing higher strain at smaller deflections. Depending on where the bridge design is to be utilized, type
of climate, a higher factor of safety should be utilized if the modulus of elasticity is increased. Also noted
in the main effects plot is the exponential increase in strength as number of plies increase. This increase
would allow for the structural integrity of the bridge to significantly increase; however, this comes with
the tradeoff of stiffness, that is with increased strength comes increased stiffness. Finally the major
important trend is the effect of corrosion.
Because, the main goal of this experiment is to increase the structural integrity and prevent corrosion, the
data was normalized to determine the strength of each specimen with respect to a plain steel sample. The
first major finding from the experimental data was the corrosive samples decreased the strength for steel
and carbon fiber samples. This was not expected, as CFRP should serve as a barrier to the saltwater. Upon
further analysis of our samples, we noticed the SFC samples showed signs of corrosion on the steel
member, as shown via the sample on the left side of Figure 15. After examination of the specimen this
reduction in strength was attributed to the porous fabric peel-ply. This peel ply allows the resin epoxy to
flow through the fibers to create uniform material properties. The flow of the resin allowed the resin
epoxy to flow to the top and bottom surfaces of the SFC samples, which depleted the resin from the sides
of the samples. In order to create a uniform barrier to corrosion either a non-perforated peel ply should be
used or a separate manufacturing method must be utilized. Another important finding was the 8 ply
samples subjected to corrosion actually prevented corrosion on the steel bar. This is likely due to the
number of layers of the sample. These layers, in conjunction with trapped resin between the layers, were
able to deter the salt-water from penetrating the CFRP. This is shown in Figure 15 in the sample on the
right.
22
Figure 15. 4 Ply (Left) With Visible Corrosion and 8 Ply (Right) With No Visible Corrosion
Although the CFRP was unable to deter corrosion due to the manufacturing process recommended from
the supplier, useful data regarding temperature and number of plies was still obtained. As shown in Figure
13, the number of plies significantly increases the strength of the specimen. For the maximum number of
plies, eight, the strength was approximately 2.3 times stronger than the steel specimen alone. It is also
important to note this would require a 1:1 ratio for amount of steel to the amount of CFRP. This may not
always be feasible, thus it is important for an engineer to determine how much material should be utilized.
A summary of the specific strength relative to steel for the various ratios of CFRP to steel can be seen in
Table 4. The samples with a 1:1 ratio or 8 ply thickness are highlighted because they showed no visible
signs of corrosion.
Table 4. Summary of Specific Strength Relative to Steel for the All Three Thickness Ratios
CFRP/Steel Plies Temp Strength Relative to
Steel
Ratio # (°C) Non-Corr. Corr.
1:1 8 7.5 2.05 2.30 22 2.15 2.00 60 1.80 1.70
1:2 4 7.5 1.35 1.40 22 1.40 1.45 60 1.35 1.40
1:4 2 7.5 1.30 1.15 22 1.25 1.10 60 1.05 1.05
Figure 14 shows the relationship between temperature and thickness of the sample. This figure should
serve as a useful tool that could enhance an engineer’s ability to choose the amount of reinforcement he
23
might need based on environmental considerations. This would be beneficial for economic analysis when
utilizing CFRP to reinforce steel.
Before the cost analysis was performed, the assumption that CFRP prevents corrosion was used because it
is a material property when manufactured properly. Also, it is assumed only the steel girders were
wrapped by the CFRP, and all the steel were wrapped 8 times in order to provide a worst case scenario.
The cost analysis compared the maintenance cost for steel to the added cost of CFRP which includes:
material, manufacturing cost, and manual labor. The annual maintenance cost for the Golden Gate Bridge
is $37.74 million [1], so this cost was used. The length of the bridge is 2,737 meters, and the surface area
associated with that length was 47,462 m2 using the largest I-beam data from Statewide Steel [16]. The
data from this experiment was used to come up with the weight to area ratio for CFRP by calculating the
weight difference between 8 plies SCF and a steel sample. According to the Rocky Mountain Institute,
carbon fiber costs approximately $16 a pound, so the material cost was around $300,000.
The next costs considered were manual labor and manufacturing. In order to determine the time it would
take to manufacture the CFRP and steel, this experiment’s data was used. The time it took to wrap and
cure the 8 ply samples were totaled along with the total surface area to determine the time to surface area
ratio. Because the wrapping of these samples is a bit simpler than steel girders, a conversion factor of 10
was used to better reflect the time it would take for manufacturing. This factor indicates it would take ten
times as long to lay-up a girder than it would for a plain steel beam of equal surface area. Finally a wage
of $15 dollars an hour was used to pay for the labor, this is made under the assumption that trained
employers would be manufacturing this material, rather than a composites expert or professional in the
field. This cost amounted to $10.7 million.
The addition of CFRP to a steel bridge girder, according to the analysis, was around $11.1 million.
Therefore in the first year of the bridge, the CFRP addition would save $22 million, but to receive better
estimates, further studies should be developed. Such studies should include: epoxy-resin that provides UV
protection for the polymer, scaled manufacturing information, and operating life for CFRP seal. A
summary of this data is displayed in Table 5.
Table 5. Estimated Cost Analysis for Bridge Design
Material Length
(m)
Area
(m^2)
Weight
(kg)
Material
Cost ($)
Maint. Cost
($)
Install Time
(man hrs)
Install Cost
($)
Total Addition
Cost ($)
Steel 2737 5720 342125 1,697,075 37,740,000 - - -
CFRP 2737 45762 8497 299,725 - 71,836 10,775,296 11,075,200
Discrepancies
Experiments in general have discrepancies. A few major discrepancies from this experiment are listed
below. The first major discrepancy was the CFRP did not act as a barrier to corrosion. This is likely due
24
to the manufacturing process incorporated in the experiment. The manufacturer recommended this
manufacturing process; however, after further research it was determined that using a non-perforated film
peel-ply could mitigate this effect, and create a uniform barrier for the specimens. Another pseudo-
discrepancy is the large confidence intervals presented in Figure 12 and Figure 13. This is likely due to
the complexity of ply-mechanics. It is recommended that further analysis incorporating ply-mechanics be
incorporated before predicting the actual flexural strength of the specimen.
Other discrepancies:
The experimental woven fiber did not have perfect �� and ��� fiber angle directions.
The bond between the CFRP and steel was not completely free of voids as corrosion was able to
permeate through CFRP.
CFRP does not exhibit completely linear elastic behavior, but actually linear orthotropic behavior.
Complex modeling should be developed for more accurate expected results.
To mitigate these discrepancies it is recommended that non-perforated film peel-ply be utilized to not
allow the epoxy resin to flow out of the matrix during the autoclave process. The functionality of the
matrix bond should also be analyzed thoroughly before applications in which CFRP can be utilized.
Further manufacturing techniques should be analyzed and implemented during testing to determine
differences between methods. Any one of these recommendations will increase the validity of this
experiment and result in a more efficient cost-analysis for use of CFRP as a deterrent to corrosion, while
increasing the structural integrity of steel bridge girders.
Summary
• Nitrogen pressure resulted in a better curing process.
• As temperature increased, specific flexural strength decreased.
• As CFRP plies increased, specific flexural strength increased.
• Corrosion decreases specific flexural strength.
• CFRP did not serve as a barrier to corrosion for samples with 4 or less plies.
• CFRP plies reduced the amount of corrosion on the steel.
Conclusions
• As CFRP thickness increases, specific flexural strength of the SCF will increase
• CFRP did not deter corrosion due to the manufacturing process.
• Non-perforated peel-ply should be used to create a uniform barrier to corrosion.
25
• Further analysis is needed to determine the optimal thickness with respect to elasticity and
flexural strength.
• Further analysis on ply mechanics is necessary to predict failure loads.
• Interactions between all of the independent variables would require further experimentation.
• It would cost approximately 11.1 million dollars for the addition of CFRP on a bridge similar in
size to the Golden Gate Bridge, resulting in an initial cost savings of approximately 26 million
dollars.
26
Appendix A. Reference Figures
The plain weave carbon fiber composite fabric has carbon in the �� and ��� direction, as seen in Figure
16.
Figure 16. Plain Weave Carbon Fiber Fabric
Table 6. Material Properties of CFRP and Steel [6] [12]
Figure 17. Curing Process for Plain Weave Fabric [12]
27
Appendix B. Function Structure and Requirements
The function structure and performance requirements shown were used to satisfy the required needs for
the experiment.
Figure 18. Schematic of Function Structure
Functional and Performance Requirements
1. There is a need for an experimental design that can measure the mechanical properties of a
Cycom E773 Epoxy Prepreg woven fabric carbon fiber composite.
o FR 1. PMT: Obtain prepreg composite
FR 1.1. PMT: Cut prepreg into desired dimension
PR 1.1. Determine dimensions with precision 0.1 in.
FR 1.2. PMT: Cure prepreg carbon-fiber reinforced polymer
PR 1.2. Cure at recommended temperature with a precision of +/- 5˚F
o FR 2. PMT: Vary thickness of the composite sample
FR 2.1. PMT: Layer correct number of ply’s of carbon-fiber only composite
samplse for desired thickness
PR 2.1. Determine thickness with precision of 0.1 in.
Need
FR 2. PMT: Vary thickness of the composite sample
FR 2.1. PMT: Layer correct number of ply’s of carbon-fiber only composite samplse for desired thickness
FR 2.2. PMT: Layer correct number of ply’s for carbon-fiber and
steel composite samples for desired thickness
FR 3. PMT: Test Samples
FR 3.1. PMT: Apply a force
FR 3.1.1. PMT: Secure specimen
FR 3.1.2. PMT: Pull specimen in a tensile
test
FR 4. PMT: Regulate specimen
temperature
FR 4.1. PMT: Measure Specimen
Temperature
FR 4.2. PMT: Adjust Specimen
Temperature
FR 5. PMT: Simulate corrosive atmosphere
for samples
FR 5.1. PMT: Generate corrosive
bath
FR 5.2. PMT: Determine corrosive
effects
FR 1. PMT: Obtain pre-preg composite
FR 1.1. PMT: Cut pre-preg into desired
dimension
FR 1.2. PMT: Cure pre-preg carbon-fiber reinforced polymer
28
FR 2.2. PMT: Layer correct number of ply’s for carbon-fiber and steel composite
samples for desired thickness
PR 2.2. Determine thickness with precision of 0.1 in.
o FR 3. PMT: Test Samples
FR 3.1. PMT: Apply a force
FR 3.1.1. PMT: Secure specimen
FR 3.1.2. PMT: Pull specimen in a tensile test
o PR 3.1.2. PMT: Determine force applied within 0.1 N
o FR 4. PMT: Regulate specimen temperature
FR 4.1. PMT: Measure Specimen Temperature
PR 4.1. Determine desired temperature within +/- 1˚C
FR 4.2. PMT: Adjust Specimen Temperature
PR 4.2. Must be able to reach temperature as low as -40˚C and as high as
+40˚C
o FR 5. PMT: Simulate corrosive atmosphere for samples
FR 5.1. PMT: Generate corrosive bath
PR 5.1. Measure salinity with precision of +/- 0.1%
FR 5.2. PMT: Determine corrosive effects
PR 5.2. Measure corrosive effects with precision of 0.01 in.
Appendix C. Data Reduction
The data will be analyzed with the following approach:
1. Calculate the density of the SFC using Equation 8 on page 5 and the values of the mass of the test
specimens.
2. Analysis data from three point bend test.
a. Calculate the flexural strength using Equation 5 on page 4 from the load data taken from
the test.
b. Calculate the specific flexural strength using Equation 9 on page 5 with the densities
found in part 1.
3. Calculate the average and standard deviation for density, steel width, steel thickness, overall
thickness, overall width, overall length, flexural strength, and specific flexural strength from each
run.
4. Repeat steps 1 and 2 for all combinations.
5. Perform Kline-Mclintock Uncertainty Analysis using Equation 20 to Equation 25.
6. Plot the specific flexural strength vs. CFRP coating thickness for the specific strength samples.
29
7. Plot the specific flexural strength and verses temperature for the temperature samples.
8. Perform ANOVA analysis to test the null-hypothesis that there is no relation between CFRP
thickness and specific flexural strength.
9. Perform ANOVA analysis to test the null-hypothesis that there is no relation between temperature
and specific flexural strength.
10. Perform ANOVA analysis to test the null-hypothesis that there is no relation between corrosion
and non-corrosion on specific flexural strength.
11. Perform three way ANOVA to compare all variables to find if they are statically significant.
12. Using the data, predict the cost savings of using CFRP as a coating for steel structures.
13. Make recommendations for CFRP use.
Appendix D. Results of Failure Modes and Effects Analysis
In Table 7 the failure mode and effects analysis used in to prevent detrimental failure in the experiment.
Using the FMEA, possible failures were mitigated for the experiment. Due to limitations of the autoclave,
the cure process was split into two batches, which upon analysis of the data proved to be a confounding
variable. The samples manufactured in the second cure process were not utilized in the analysis of the
data. Outside of this failure all other failures were successfully mitigated, and minimal setbacks were
encountered.
30
Table 7. Failure Mode and Effects Analysis chart including mitigation of possible failures
Item Function Potential Failure
Mode
Potential Cause
of Failure
Potential Effect
of Failure
Probability
of Failure
Severity
of Failure
Preventative
Measures
Prepreg
Raw material
for composite
sample
Not cured
properly
Curing
specification not
followed in
detail
Non-uniform
material
properties
Mid Mid
Caution when
performing caution,
and allotting extra
time for curing
process
Carbon-
Fiber/Steel
Composite
Raw material
for composite
sample
Inadequate bond
between carbon-
fiber and steel
specimen
Curing
specification not
followed in
detail
Inconsistent
material
properties
Mid High
Check integrity of
bond visually and
provide extra
samples.
Carbon-
Fiber/Steel
Composite
Raw material
for composite
sample
Improper
prepreg lay-up
Prepreg lay-up
not equal and
symmetric
Induced
bending during
tensile test
Mid High
Caution when laying
prepreg samples, and
laying prepreg equal
and symmetric
Instron Test
Apparatus
Apply tensile
force
Specimen slips
out of the grips
of the apparatus
Insufficient force
applied to
specimen from
grips
Integrity of test
sample
diminished
Low Mid
Ensure sample is
secure before testing
and provide extra
samples
Instron Test
Apparatus
Measure
corresponding
force
Inaccurate
readings
Test apparatus
not properly
calibrated
Inadequate and
sporadic results Low High
Ensure appartus is
calibrated and
perform test trials
prior to testing
Pyrometer
Measure
temperature
of the sample
Inaccurate
temperature
reading
Reading
temperature of
surrounding
parts
Inadequate and
sporadic results Low Low
Take multiple
readings from
different positions
before test.
Salt Water
Bath
Corrosive
Environment
for samples
No effects of
corrosion
Insufficient time
to allow
chemical
reaction to occur
Inconclusive
results
regarding
corrosion
protection
Low High
Perform calculations
to ensure adequate
time in corrosive
bath is provided.
Carbon-
Fiber/Steel
Composite
Determine
effects of
corrosion
No measureable
effects of
corrosion
Insufficient
measuring
device
Inconclusive
results
regarding
corrosion
protection
Low Low
Allot time for
alternative corrosive
measurement testing
to be performed
Safety
Equipment
Protection
from hazards
in the
experiment
Inadequate
Clothing and
Eyewear
Unaware of
potential risks Personal Injury Medium High
Read MSDS of
materials being used
31
Appendix E. Safety and Hazard Analysis
The greatest safety concerns in this experiment were the handling and manufacturing of the carbon fiber
reinforced polymer. Following proper personal protective equipment mitigated these hazards.
Safety and Hazard Analysis
1. When curing and handling the pre-preg samples, care should be taken to prevent epoxies and
resins from coming in contact with skin. To prevent possible skin irritation or chemical burns
closed toed shoes, long pants, long sleeves, and protective gloves will be worn.
2. Safety is required when handling dry ice and any sample in the dry ice reservoir. To prevent
severe frostbite when handling dry ice or sub-cooled specimens, closed toed shoes, long pants,
long sleeves, and thermal gloves, are required.
3. Caution should be heeded when dealing with oven used to heat samples, and when dealing with
heat samples. To prevent burning of the skin, the heated sampled will be handled with tongs and
closed toed shoes, long pants, long sleeves, and thermal gloves will be worn.
4. Care should be taken when producing corrosive bath, and when handling material subject to
corrosive bath. To prevent skin irritation tongs should be used to prevent direct contact with salt-
water bath, and closed toed shoes, long pants, long sleeves, and protective gloves will be worn.
5. Testing the samples on the Instron tensile testing machine could result in personal injury or
degradation of sample and machinery. To prevent any damage, use of the testing apparatus will
be done under professional supervision and closed toed shoes, long pants, long sleeves, and
protective glasses will be worn.
6. Handling of broken samples of CFRP can result in puncturing of skin. To prevent personal injury,
care should be taken when handling all broken samples and protective gloves should be worn.
32
Appendix F. Specimen Data
Table 8. Test Matrix for SFC Specimens with Varying Thicknesses
Appendix G. Experimental Results
Expected Data
The expected temperature effect on the data can be seen in Table 6.
1”
1/16”
1”
5/64”
1”
3/32”
1/8”
33
Table 9. Expected Temperature Effect on Flexural Strength
Table 10. Predicted vs. Actual Flexural Strengths with Uncertainty at Room Temperature
Table 11. Predicted vs. Actual Specific Flexural Strengths with Uncertainty at Room Temperature
TemperatureEquivalent Flexural
Strength [ksi]
Icewater (0 C) 78.02
Room Temp (25
C)78.02
Oven (60 C) 74.14
SFC (1/64"
CFRP Coating)
Material Dimensions
Number
Of Plys
(Total)
Predicted SFC
Flexural Strength
Actual SFC
Flexural
Strength
Flexural Strength
Relative Uncertainty
Flexural Strength
Uncertainty
[ksi] [ksi] (±) [ksi]
A 36 Steel 1/16" Thick 0 66 76 3.71% 1.4
One Wrap Coating 2 73 62 3.48% 1.1
1/64" Coating 4 78 60 3.42% 1.0
1/32" Coating 8 84 79 3.37% 1.3
CFRP 1/16" Thick 8 100 106 3.65% 1.9
SFC
Material Dimensions
Number
Of Plys
(Total)
Predicted Specific
Flexural Strength
Actual
Specific
Flexural
Strength
Specific Flexural
Strength Relative
Uncertainty
Specific Flexural
Strength
Uncertainty
[ksi/(lb/in^3)] [ksi/(lb/in^3)] (±) [ksi/(lb/in^3)]
A 36 Steel 1/16" Thick 0 234 272 5.61% 7.6
One Wrap Coating 2 313 335 5.19% 8.7
1/64" Coating 4 386 374 5.07% 9.5
1/32" Coating 8 517 578 4.96% 14.3
CFRP 1/16" Thick 8 1776 2252 5.40% 60.9
SFC
34
Raw Data
Table 12. Corrosion Samples Raw Data
35
Table 13. Non Corrosion Samples Raw Data
Specimen
#
Number
of
Ply
s
(Total)
Steel
Thic
kne
ss
[in]
Steel
Width
[in]
Overall
Thic
kne
ss
[in]
Overall
Width
[in]
Volume
Fraction
Steel
Volume
Fraction
CFR
P
SFC
Den
sity
[g/in^
3]
Flexural
Strength
[ksi]
Specific
Strength
[ksi
/(lbm
/in^
3)]
Relative
Flexural
Strength
Uncertainty
Relative
Volume
Fraction
Uncertainty
Relative
SFC
Den
sity
Uncertainty
Relative
Specific
Strength
Uncertainty
38
0.0
56
00
.98
45
0.1
32
51
.13
05
0.3
70
.63
60
.02
74
.91
56
6.1
73
.37
%1
.94
%3
.63
%4
.95
%
68
0.0
56
00
.98
45
0.1
32
1.1
26
0.3
70
.63
60
.32
75
.19
56
5.4
83
.37
%1
.94
%3
.63
%4
.95
%
18
40
.05
70
0.9
84
00
.10
55
1.0
64
0.5
00
.50
73
.81
62
.55
38
4.3
63
.42
%2
.00
%3
.69
%5
.02
%
21
40
.05
45
0.9
82
00
.10
31
.06
15
0.4
90
.51
72
.75
61
.05
38
0.6
63
.42
%2
.08
%3
.77
%5
.09
%
33
20
.05
45
0.9
80
50
.09
11
.05
65
0.5
60
.44
79
.70
63
.79
36
3.0
23
.46
%2
.14
%3
.84
%5
.17
%
36
20
.05
45
0.9
82
50
.09
15
1.0
58
50
.55
0.4
57
9.3
96
1.0
53
48
.79
3.4
6%
2.1
4%
3.8
4%
5.1
7%
G 1
70
0.0
57
50
.98
80
0.0
57
50
.98
80
10
12
6.2
77
6.8
72
76
.13
3.7
1%
2.4
6%
4.2
1%
5.6
1%
G 1
80
0.0
57
00
.98
45
0.0
57
00
.98
45
10
12
6.2
77
8.5
92
82
.34
3.7
2%
2.4
9%
4.2
4%
5.6
4%
G 1
90
0.0
57
50
.98
95
0.0
57
50
.98
95
10
12
6.2
77
6.9
72
76
.51
3.7
1%
2.4
6%
4.2
1%
5.6
1%
1CFR
P
0.0
62
51
.15
90
0.0
62
51
.15
90
01
21
.43
11
6.3
32
46
2.3
03
.65
%2
.27
%3
.98
%5
.40
%
2CFR
P0
.06
20
1.1
53
00
.06
20
1.1
53
00
12
1.4
31
06
.16
22
47
.02
3.6
6%
2.2
8%
4.0
0%
5.4
2%
3CFR
P0
.06
65
1.2
47
00
.06
65
1.2
47
00
12
1.4
39
7.3
12
05
9.7
13
.61
%2
.13
%3
.83
%5
.26
%
98
0.0
56
50
.98
60
0.1
29
51
.12
90
.38
0.6
26
1.3
87
9.7
05
89
.02
3.3
7%
1.9
4%
3.6
2%
4.9
4%
10
80
.05
60
0.9
83
00
.12
51
.13
80
.39
0.6
16
2.0
07
7.6
15
67
.79
3.3
8%
1.9
6%
3.6
4%
4.9
7%
24
40
.05
50
0.9
85
00
.10
35
1.0
63
0.4
90
.51
73
.05
58
.51
36
3.3
13
.42
%2
.06
%3
.76
%5
.08
%
25
40
.05
55
0.9
86
00
.10
55
1.0
57
50
.49
0.5
17
2.8
56
1.7
93
84
.71
3.4
2%
2.0
4%
3.7
3%
5.0
6%
37
20
.05
60
0.9
86
00
.08
21
.04
50
.64
0.3
68
8.9
86
3.3
03
22
.68
3.5
0%
2.1
7%
3.8
7%
5.2
2%
40
20
.05
50
0.9
82
50
.09
15
1.0
45
50
.56
0.4
48
0.6
56
1.6
13
46
.53
3.4
6%
2.1
3%
3.8
2%
5.1
6%
G 1
40
0.0
57
00
.98
35
0.0
57
00
.98
35
10
12
6.2
77
5.7
42
72
.10
3.7
2%
2.4
9%
4.2
4%
5.6
4%
G 1
50
0.0
58
50
.98
45
0.0
58
50
.98
45
10
12
6.2
77
4.8
42
68
.85
3.7
0%
2.4
2%
4.1
6%
5.5
7%
G 1
60
0.0
57
00
.98
50
0.0
57
00
.98
50
10
12
6.2
77
6.5
02
74
.82
3.7
2%
2.4
9%
4.2
4%
5.6
4%
4CFR
P
0.0
62
51
.15
90
0.0
62
51
.15
90
01
21
.43
10
2.2
32
16
3.9
03
.65
%2
.27
%3
.98
%5
.40
%
5CFR
P0
.06
40
1.2
44
50
.06
40
1.2
44
50
12
1.4
31
06
.05
22
44
.72
3.6
3%
2.2
1%
3.9
2%
5.3
5%
6CFR
P0
.06
10
1.1
18
00
.06
10
1.1
18
00
12
1.4
31
10
.97
23
48
.82
3.6
7%
2.3
2%
4.0
5%
5.4
6%
11
80
.05
65
0.9
85
00
.13
25
1.1
10
50
.38
0.6
26
1.0
86
3.7
04
73
.02
3.3
7%
1.9
3%
3.6
1%
4.9
4%
12
80
.05
55
0.9
86
00
.13
15
1.1
13
0.3
70
.63
60
.63
64
.76
48
4.5
13
.37
%1
.96
%3
.64
%4
.96
%
26
40
.05
45
0.9
83
50
.09
91
.05
75
0.5
10
.49
75
.10
62
.15
37
5.3
83
.43
%2
.10
%3
.79
%5
.12
%
27
40
.05
55
0.9
85
50
.09
91
.07
15
0.5
20
.48
75
.49
61
.39
36
8.8
93
.43
%2
.07
%3
.76
%5
.09
%
41
20
.05
65
0.9
88
00
.09
05
1.0
43
50
.59
0.4
18
3.4
05
1.9
92
82
.77
3.4
6%
2.0
9%
3.7
9%
5.1
3%
42
20
.05
65
0.9
86
00
.09
25
1.0
62
0.5
70
.43
80
.88
49
.76
27
9.0
63
.45
%2
.08
%3
.77
%5
.12
%
G 1
00
0.0
56
50
.98
35
0.0
56
50
.98
35
10
12
6.2
77
7.3
62
77
.90
3.7
3%
2.5
1%
4.2
6%
5.6
6%
G 1
10
0.0
57
00
.98
50
0.0
57
00
.98
50
10
12
6.2
77
5.4
22
70
.94
3.7
2%
2.4
9%
4.2
4%
5.6
4%
G 1
20
0.0
56
50
.98
45
0.0
56
50
.98
45
10
12
6.2
77
3.3
02
63
.33
3.7
3%
2.5
1%
4.2
6%
5.6
6%
7CFR
P
0.0
64
01
.07
70
0.0
64
01
.07
70
01
21
.43
87
.98
18
62
.20
3.6
3%
2.2
1%
3.9
2%
5.3
5%
8CFR
P0
.06
20
1.1
42
50
.06
20
1.1
42
50
12
1.4
38
5.6
61
81
3.0
83
.66
%2
.28
%4
.00
%5
.42
%
9CFR
P0
.06
30
1.2
13
00
.06
30
1.2
13
00
12
1.4
39
8.3
72
08
2.2
33
.65
%2
.25
%3
.96
%5
.38
%
Cold
Room
Hot
Non
Corro
sion
Sample
s
36
Sample Calculations
Uncertainty JKL�� � MFN�O H� $ FNP H� $ FNQ� H� $ FNR��H�
JKL�� � M_`��8� $ V`�?�a� [� $ V `����`���a[� $ V `����_`���a8[
� � b` bcd
J\S�! � MVNRS�! [� $ VNQS�! [� $ FNR� H� $ FNQ� H�
J\S�! � MV`���`�a?[� $ V `���`���a[
� $ V `���` ���a[� $ V `����`���a[
� � e` fgd
JWS&! � MFNR� H� $ FNQ� H� $ VNPS ! [� $ FN; H�
JWS&! � MV`���`�a�[� $ V`���`���[
� $ V `����`�?�[� $ _�8� � e`cbd
JWZY]^"���� � MV`���� [� $ V`���� [� $ V`��� ! [� $ FN; H� � e`hfd
JWXYZ"��� � MVJ\S�� [� $ VJ\ZY]^����� [� $ VJWS&! [� $ VJWZY]^"���� [�
JWXYZ"��� � i_`����8� $ _`����8� $ _`����8� $ _`��a�8� � g`fhd
Experimental Data
����� � �� ����
�!� � �����"���
Assuming the force has a value of, F = 455.9 [lbf], the length has a value of, L = 2 [in], the width has a
value of w = .1325 [in], the height has a value of h = 1.1305 [in], and the density of the steel, CFRP
composite has a value of "��� = 60.6 [g/in^3] the flexural strength and specific flexural strength were
calculated as follows:
37
����� � �_�aa`�8_�8�_`��8_�`��8� � jh`b+klm �!� � �a`�_?�`?8_`����8 � nbj`g klmopqmrb
Cost Analysis
;01'/)0,+(:s1 � �')3�1 # (:s1�')3�1 �����`��+t3 # �`���?�+ ,ut3 # �? v,u � vwff�cwh
)2s10,,01):2+(:s1 � �:./s # (:s1�:./
�����a`��+�/ # �a+ v�/ � vex�cch�wfh`fg
1:10,+s./*0('+0/'0+:*+y�AO � ,'231� # s./*0('+0/'0,'231� # &,)'s
�����+; # �`��+ ;�; # �+&,)'s � gh�cnw`ng+;�
1:10,+0CC)1):2+(:s1 � ;01'/)0,+(:s1 $ )2s10,,01):2+(:s1 v������a+ $ +v�����a���a � +vee�xch�wxx
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