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Characterization of Mechanical Properties of Materials Composed of Epoxy Resin Reinforced with Carbon Fiber and Polyurethane Foam, Epoxy Resin Reinforced with Carbon Fiber and Aluminum Honey-Comb and Polyester Resin Reinforced with Glass Fiber with Polyurethane Foam for an Electric Sports Vehicle for Academic Purposes

Abstract and Figures

In the present work, the main objective is to characterize the mechanical properties of composites materials such as epoxy resin reinforced with carbon fiber and polyurethane foam (ER-CP), epoxy resin reinforced with carbon fiber and aluminum honeycomb (ER-CA), and polyester resin reinforced with glass fiber and polyurethane foam (PR-GP), that will allow selecting the most accurate material for the future construction of parts for a prototype electric vehicle for academic competitions, taking into account the impact resistance, deformation for flexure charges and the cost. To obtain the variables, identification is required by the performance of mechanic tests like flexion and impact. The investigation begins with the manufacture of all test tubes for mechanical flexural and impact tests according to ASTM C393 and ASTM D6110 respectively. Finally, the analysis of each test is carried out according to the criteria of resistance, weight, and cost to select the most precise material. The experimental evaluation found that the composite material with the best performance as a proposal for use in applications of an electric sports vehicle in academic competitions is PR-GP.
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Characterization of mechanical properties of materials
composed of epoxy resin reinforced with carbon fiber and
polyurethane foam, epoxy resin reinforced with carbon
fiber and aluminum honey-comb and polyester resin rein-
forced with glass fiber with polyurethane foam for an
electric sports vehicle for academic purposes.
D C Dulcey-Diaz 1[0000-0002-1771-7628], O Lengerke-Pérez 1[0000-0001-9360-7319], A D Rincón-
Quintero 1,2[0000-0002-4479-5613], C L Sandoval-Rodriguez 1,2[0000-0001-8584-0137], C G Car-
denas-Arias 1,2[0000-0003-4447-5828] and C A Castañeda-Flórez 1[0000-0002-4877-9426]
1 Unidades Tecnológicas de Santander UTS, Bucaramanga Santander 680005, Colombia
2 University of the Basque Country UPV/EHU, Bizkaia 48013, Spain
ddulcey@correo.uts.edu.co, olengerke@correo.uts.edu.co,
arincon@correo.uts.edu.co,csandoval@correo.uts.edu.co,ccardenas@
correo.uts.edu.co,cjosecastaneda@uts.edu.co
Abstract. In the present work, the main objective is to characterize the mechan-
ical properties of composites materials such as epoxy resin reinforced with car-
bon fiber and polyurethane foam (ER-CP), epoxy resin reinforced with carbon
fiber and aluminum honeycomb (ER-CA), and polyester resin reinforced with
glass fiber and polyurethane foam (PR-GP), that will allow selecting the most
accurate material for the future construction of parts for a prototype electric ve-
hicle for academic competitions, taking into account the impact resistance, de-
formation for flexure charges and the cost. To obtain the variables, identification
is required by the performance of mechanic tests like flexion and impact. The
investigation begins with the manufacture of all test tubes for mechanical flexural
and impact tests according to ASTM C393 and ASTM D6110 respectively. Fi-
nally, the analysis of each test is carried out according to the criteria of resistance,
weight, and cost to select the most precise material. The experimental evaluation
found that the composite material with the best performance as a proposal for use
in applications of an electric sports vehicle in academic competitions is PR-GP.
Keywords: Bodywork, Composite, Electric Vehicle, Flexure, Impact.
1 Introduction
Composite materials for automotive applications overview
In the present, the composite materials are born by the need to bond two or more mate-
rials to obtain a combination of properties not found individually in the materials. In
the fabrication of bodyworks is common to find metallic materials like steel and alumi-
num alloys. In the manufacture of chassis, aluminum is the second most used material,
due to its advantages of low weight and good resistance to fluctuating loads, torsion,
and impact loads, and it is not corrosive in atmospheric condition[1][2]. These materials
make the vehicles heavier and consume more fuel because of that; in the last decades,
the automotive industry has been set in composite materials since they can preserve
mechanical properties and reduce the weight of the vehicle, saving fuel consumption.
Greenhouse gases continue to increase, to reverse it is necessary to replace high-
strength steel, aluminum, and CFRP with new materials of lower density that allow to
improve fuel efficiency and increase the life-long drive distance[3]. Composite materi-
als reinforced with fiberglass and carbon fiber have an excellent performance to impact
loads; due to their high levels of specific energy absorption, especially those whose
thermoplastic matrix provides benefits in terms of toughness[4][5]. Wang et al. [6] use
composite materials of Carbon Fiber-Reinforced Composite Sandwich Structures with
Aluminum Honeycomb Cores through the effects of core thickness and density on the
laminate material properties studying the three-point bending and panel peeling tests.
The challenges to design a composite material are often part of the process. One of
the main characteristics of a composite material is its ability to be lighten without losing
good mechanical properties but also the performance and productions costs are im-
portant too, the methodology that couples weight-optimization and technical cost mod-
eling through an application-bound cost. Lightweight designs and implementation of
electric motors are strategies of the automotive industry to avoid high demand for fuel
and reduce emissions, respectively, both strategies could be combined to reduce envi-
ronmental impacts even more[7][8]. The material systems method and application-
bound comparative value of weight have led to a solid discussion for future design
recommendations; the sandwich structures are weight and cost efficient, the recycled
carbon fiber prepeg provide up to a 50% on cost reductions[9], but this structures are
susceptible to failures like de-bonding of skin and core, core shear failure, buck-
ling[10][11].
The carbon fiber reinforced polymer composites are used in many industries such as
the vehicle industry because can reduce the weight of structures and increase the
strength, durability, and stiffness due to its good mechanical properties. It is well known
that the aerospace industry has used composite materials for many decades and in con-
sequence, its prices have risen, but now thanks to the new materials the inclusion on
the market can be easier[12].
In these changing times, the need to improve and be more efficiently has led to the
automobile transportation and industry to grow fast in the past few decades especially,
in the urban area, considering composites materials to be the new alternative due to its
good performance in such good mechanical properties like fatigue resistance and im-
pact. Customer demands and global warning for carbon saving and green mobility have
been the principal motive in this investigation and how the new composite materials
will provide a very important approaching a new era for the automotive indus-
try[13][14].
Before using a composite material for a racing propose or an efficiently competition
it is important to know how will the vehicle react on a collision situation, the energy
|
absorption is an important test to implement when designing a prototype. Based on the
energy absorption characteristics of composites, the competitions rules and the overall
vehicle arrangement, the most accurate material for the components have to be selected,
in order to protect the driver. The fiber reinforced epoxy resin composite is used for its
good mechanical properties[15].
Carlstedt, D., & Asp, L. E. [16] presents an approach in the use of composite mate-
rials to analyze the performance for a framework on a structural battery on an electric
vehicle (EV). The mechanical and electrical properties are known from the material.
The framework is to evaluate the estimation of the electric vehicle drive range for ex-
isting batteries in EV. The study shows that weight saving potential doesn’t affect the
drive range performance and also increases by up to 70%. The application of CFRP
unidirectional plies on batteries for EV presented good results, due to the high specific
mechanical and electrical performance; the mass reduce especially in this area helps to
increase the vehicle drive range and provides the battery for a better life span. This
investigation provides a better understanding of the use of CFRP on battery systems
and the environmental impact.
There are many international academic competitions focused on the development of
prototype vehicles such as the Shell Eco-Marathon and The Solar Challenge that seek
energy efficiency through the use of composite materials but most of their resistance
providing a high increase compared to traditional materials in their mechanical proper-
ties. The University of Lisbon Formula Student Team developed a crash absorber for
their vehicle prototype to replace the aluminum one using composite materi-
als[17][18].The World Solar Challenge is a competition of solar vehicles; the Univer-
sity of Bologna designed a strategy based on changing the prototype vehicle form metal
to a fiber-reinforced composite, the new prototype with CFRP lightening the roof as a
whole. This integration between structural and non-structural parts in the composite
roof prototype also allowed other elements to be lightening, in particular, those locally
supporting the solar cells, reducing the overall weight by roughly 15kg[19]. The Shell
Eco-Marathon competition is about energetic efficiency more than a velocity competi-
tion, for that, the materials used in the tests named above are composites materials ER-
CP, ER-CA, and PR-GP, resulting in the selection of the most suitable material for the
future construction of the bodywork for the prototype vehicle.
Among the activities to justify the use of composite materials in the automotive
industry is to achieve an analysis of the fuel consumption induced by the weight of the
automobile to determine the fuel reduction coefficient, seeking the lowest process ben-
efit amount of fuel and reduce the cost of its operation[7]. For this reason, this investi-
gation is focused on the characterization of composites sandwich materials by perform-
ing mechanical tests of flexion and impact for the future use of bodywork for a vehicle
in an academic energy efficiency competition.
2 Methods and materials selection
In this research, analyzed three materials were worked, ER-CP, ER-CA, and PR-GP,
the volumetric fractions for the work are: 80% matrix and 20% reinforcement, and the
density of the composite material was determined by the mix rule for reinforced fiber
materials [19].
The sandwich-structured composite is chosen on the bases of material properties.
The reinforcement and core materials acquired for the construction of the specimens
are the carbon fiber Fig.1(a) hat is made up of fine carbon composite filaments, the
glass fiber Fig. 1(b) consists of numerous polymeric filaments based on silicon dioxide
are used as reinforcement and the aluminum honeycomb Fig. 1(c) is constructed by
honeycomb aluminum panels used as the core. Other materials such as isocyanate and
polyol are chemical compounds used to make polyurethane foam, the 856 polyester
resin is the main compound of the polyester matrix, the Mek (methyl ethyl ketone) is
the catalyst for polyester resin and the styrene is used that serves to dissolve the poly-
ester resin and acts in the catalyzing time, the rigid epoxy resin (A) is the main com-
pound of the matrix of the ER-CP and ER-CA materials, together with the epoxy resin
is used as the catalyst (B).
Fig. 1. Reinforcement materials
2.1 Test tubes for flexure testing
The manual stratification method was used to elaborate the test tubes for the flexure
testing, due to its simple application. But before starting the PU core for the material
has to be made.
a) Elaborations of the molds for PU foam for the flexure test tubes.
Two wooden-molds are considered for the elaboration for the PU foam core
used on test tubes for the flexure testing, each mold is up to 4 test tubes,
due to the ASTM C393 norm. The molds have a tolerance in its dimensions.
b) Elaboration of the PU foam core for the flexure testing.
Wooden was the chosen material due to the low cost and easy way to han-
dle. The specifications of the mold are listed on the Table 1.
(a)
(b)
(c)
|
Table 1. Flex Test Mold Specifications.
Specification
Dimensions (cm)
Long
41
Width
16
Depth
2.1
Volume
1337.6 cm3
c) PU foam elaboration.
The PU foam has two components, an A part called Isocyanate and a B part
called polyol. It is necessary to know the mold volume, because the PU
foam grows up to 40 times its original volume, on the Table 2 there are the
quantities for the A and B parts.
Table 2. Proportions for polyurethane foam for bending specimens
Proportion (cm3)
34,4
34,4
d) Measurements and work volume for the flexure test tubes.
For the flexure test tubes, the ASTM C393 norm was used, which says the
specific measurements for the testing, also says the is recommended to test
5 specimens for the material. In Table 3., it can be found the measurements
for the specimens and detailed the new work volume for the epoxy resin
and polyester resin.
Table 3. Measurements plane and work volume for the flexion test.
Specification
Dimensions
Measurements
and plane
Work volume
epoxy and polyes-
ter resin
Large (cm)
20
41
Width(cm)
7
16
Thickness(cm)
1.5
0.2
Volume (cm3)
210
131.2
When the volumetric fractions are established and the work volume, on the
Table 4 the volume and weight for the matrix needed.
Table 4. Necessary amounts of matrix and reinforcement for polyurethane foam
for bending specimens.
Matrix
Reinforcement
Volume
(cm3)
Weight(g)
Volume
(cm3)
Weight(g)
104,96
114,4
26,24
49,85
2.2 Test tubes for impact testing
The manual stratification method was used to elaborate the test tubes for the flexure
testing, due to its simple application. But before starting the PU core for the material
has to be made.
a) Elaborations of the molds for PU foam for the impact test tubes.
A wooden-mold is considered for the elaboration for the PU foam core for
test tubes for the impact testing, the mold is up to 7 test tubes, due to the
ASTM D6110 norm. The molds have a tolerance in its dimensions.
b) Elaboration of the PU foam core for the impact testing.
Wooden was the chosen material due to the low cost and easy way to han-
dle. The specifications of the mold are listed on the Table 5.
Table 5. Impact Test Mold Specifications.
Specification
Dimensions (cm)
Long
18
Width
13
Depth
2.1
Volume
491.4 cm3
3 Experimental set up
3.1 Three-point flexure Testing developing.
For the three-point flexure testing, the Universal MTS Bionix 515 machine is used,
located on the mechanical engineering building at Universidad Industrial de Santander
in Bucaramanga, Santander. In conformity whit, ASTM C393 specification, Fig.2,
Fig.3, and Fig.4 shows before test samples.
|
Fig. 2. Test sample ER-CP for flexure testing
Fig. 3. Test sample ER-CA for flexure testing
Fig. 4. Test sample PR-GP for flexure testing
3.2 Charpy Impact Testing Developing.
For the Charpy Impact Testing, the Treble Charpy Impact Machine is used, located on
the materials characterization building of the civil engineering faculty at Universidad
Industrial de Santander in Bucaramanga. In conformity with ASTM D6110 specifica-
tion, Fig.5, Fig.6 and Fig.7 show before the samples.
Fig. 5. Test sample ER-CP for impact testing
Fig. 6. Test sample ER-CA for impact testing
Fig. 7. Test sample PR-GP for impact testing
Before starting the impact testing, a rub test should be performed in which the pendu-
lum free falls without placing any specimen on the support beam; the energy, angle,
and stress for rubbing readings are taken.
4 Results and discussions
4.1 Flexure testing results
The core shear ultimate stress (Fs), was calculated from eq (1), with respect to the fac-
ing stress is needed to know the core shear ultimate stress(σr), and eq (3) use in the
calculation of ultimate flexion (σf), the flexion module (E) takin into account the max-
imum deflection (δ) and the spacing between supports calculated from the thickness of
the specimen, all of the above items using the values of the maximum load (Pm), the
sandwich thickness (d), the core thickness (tn),the width of the specimen(b), the length
of support span (s), and the reinforce thickness (t).
 
 (1)
  
 (2)
  
 (3)
 
 (4)
On Fig.8 (a) it is observed that the core shear ultimate stress average by each group
mate-rial, the ER-CA core has the higher core shear ultimate stress resistance of all
materials, similarly on Fig.8 (b) is indicating the facing stress (average), the ER-CA
has the high up facing stress resistance of all materials. The contrast in the ultimate
flexion stress average shown in Fig.8 (c) the ER-CA core has the higher ultimate flexion
stress resistance of all materials. And Fig.8(d) provides adequate information for the
study flexion module average by each group material, the ER-CA core has the higher
flex-ion module resistance of all materials with 492 MPa.
|
The unitary deformation (ε) is needed to know δ were used to calculate the relation
shown in the eq (5), the ER-CA has ε maximum of 9%, that is superior to ER-CP with
8.2% and PR-GP with 4.1% of unitary deformation.
  
 (5)
The failure mode of 5 specimens under flexural test of the composite sandwich for
the ER-CA, ER-CP and PR-GP shown in the Fig.9.The results of the experiments
shown the relation of the flexion stress vs unitary deformation is observed in the Fig.
10, Fig.11 and Fig. 12. The ER-CA has more stress than deformation on the elastic
zone, the PR-GP has the intermediate value on the deformation stress. Lastly, the
material with the lowest results respecting stress and deformation is the ER-CP.
1.2
0.2 0.3
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
ER-CA ER-CP PR-GP
Strenght [MPa]
83.0
5.8 9.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
ER-CA ER-CP PR-GP
Strenght [MPa]
33.7
4.0 6.1
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
ER-CA ER-CP PR-GP
Strenght [MPa]
492.4
30.4 42.8
0.0
100.0
200.0
300.0
400.0
500.0
600.0
ER-CA ER-CP PR-GP
Strenght [MPa]
(a)
(b)
(c)
(d)
Fig. 8. Comparison maximum core shear strength (a), maximum facing stress average (b),
ultimate flexion stress average (c) and the flexion module (d).
Fig. 9. Failure mode of specimen the flexure test; A, B, C, D, E specimen test ER-CA; F, G, H,
I, J specimen test ER-CP, K, L, M, N, O specimen test PR-GP.
Fig. 10. The stress versus strain curve A, B, C, D, E specimen test ER-CA.
ER-CP
PR-GP
ER-CA
|
Fig. 11. The stress versus strain curve F, G, H, I, J specimen test ER-CP.
Fig. 12. The stress versus strain curve K, L, M, N, O specimen test PR-GP.
4.2 Impact testing results
The results obtained from the Charpy impact test are used to determine the energy
absorbed by the specimens when it is impacted, must know the energy impact and
friction energy. To calculate it, eq.(6) was used where impact energy absorption is Ei,
test energy is Ee, and friction energy is Ef. For determination of the impact resistance
(Is) the Ei and the specimen width (t) has to be known were use it eq(7).
   (6)
 
 (7)
Fig. 13 (a) shows the comparison of typical average absorbed energy by group of
materials, the PR-GP is the material that most absorbed energy of all. From Fig. 13 (b)
explains the comparison of the average impact resistance by group of materials is ob-
served, PR-GP is the material with the highest resistance to impact among the other
materials. There is a perceptual increasing in both properties of 28.6% regarding the
ER-CA and a perceptual increasing of 41.5% regarding the ER-CP.
Fig. 13. Comparison of average absorbed energy(a); comparison of the average impact resistance
(b).
4.3 Results of the application of selection criteria according to performance
Production costs and the properties of the materials according to the behavior of the
three-point flexure test and the Charpy impact test are used to apply the selection
methodology for materials and processes by Ph.D. Michael Ashby[21].
In this methodology the selection of materials and the elaboration processes work
together to bring an organized scheme in order to identify all the variables that interfere
with a selection process when a material is a design, using a taxonomy to classify the
different materials and processes. To support this method, materials properties charts
are used to graphically select the accurate materials for the product according to its
properties, another important aspect to take into account is the elaboration costs.
On the Fig. 14 (a) it is observable that ER-CA is the material with the best properties
according to the three-point flexure test and the PR-GP presents the best relation
between impact energy absorbed, the impact resistance, and elaboration besides, and
the Fig. 14 (b) the costs for minimum quantities of raw material that are available in the
market are U$D 21.17, making this material the cheapest material to elaborate, thus the
most suitable composite material for use in an electric sports vehicle in academic
competitions is PR-GP.
|
Fig. 14. Material map with properties
The selection methodology for materials elaboration and processes by Ph.D. Michael
Ashby related many mechanical properties such: the flexion module, the ultimate
flexion stress, the weight, the impact energy absorbed, the impact resistance, and the
elaboration cost; these properties allowed to construct graphics that show the relations
between them and finally select the best material for use in an electric sports vehicle in
academic competition.
5 Conclusion
The inclusion of lightweight materials in the manufacturing vehicle process can present
good results in terms of high-efficiency fuel consumption, some parts like bumpers,
seats, dashboards, car roofs, seatbelts, and some electronic components such as sensors.
Other applications can be on the brake system and suspension system, however more
investigation and tests have to be developed to validate the mechanical properties and
compare the results to traditional materials, properties such as thermoelectrically be-
havior, magnetism behavior, and fatigue behavior have to be tested as well. One im-
portant aspect that has to be considered on future investigations is the energy efficiency
and how the lightweight materials not also increase the autonomy and life span of the
battery but also the reduction for environmental impact due to low greenhouse gases
emission, composite materials has the advantage to reduce considerately the weight-
maintaining the mechanical properties.
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Article
Full-text available
The study of materials corrosion effect is a great importance topic for the manufacturing industry and also for the customer that requires this. That is why a research study was conducted that aimed to determine the elasticity modulus variation of AISI SAE 1045 steel subjected to corrosion. To achieve this, thirty-five specimens were used, which were exposed to chlorides by immersion processes and salt spray chamber in three periods of time and then subjected to stress test destructive, following the guidelines established under ASTM G-1 standards, ASTM G-31 and ASTM E-8. Variation was found in the elastic behavior of steel and curves that differ from the theoretical ones raised in the documents.
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