Study which was treated for 24hrs. The flexure strength

Study
On Mechanical & Cryogenic Properties of Carbon Epoxy Composites

Sunil Kumar B.V *1,
Dr. Neelakantha V.Londe 2

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

1 Assistant Professor, Mechanical Engineering
Department, Canara Engineering College, Mangalore, VTU, Karnataka, India

2 Professor, Mechanical Engineering Department,
Mangalore Institute Of Technology and Engineering, Moodabidri, VTU, Karnataka,
India

(*Corresponding author E-mail:  [email protected])

 

Abstract.
Carbon-fiber-reinforced
polymers are composite materials. In this case the composite consists of two
parts: a matrix and reinforcement. In CFRP the reinforcement is carbon fiber
which provides the strength. The matrix is usually a polymer resin such as
epoxy to bind the reinforcements together. The material properties depend on
these two elements. The reinforcement will give the CFRP its strength and
rigidity measured by stress and elastic modulus respectively. Unlike isotropic
materials like steel and aluminium CFRP has directional strength properties.
The properties of CFRP depend on the layouts of the carbon fiber and the
proportion of the carbon fibers relative to the polymer. This paper deals with
the studies done on cryogenic treatment (Liquid Nitrogen) of composites having
different fiber and matrix composition. In this work studies are done to find
the effects caused by the liquid nitrogen on composites mechanical properties
and change in properties due to different fiber and matrix composition in composites.
It was observed that due to cryogenic treatment there was changes in the
physical properties of the specimens. The specimens had deformed in their
shape. The more deformation was seen in 60:40 specimen which was treated for 48
hrs and tensile strength of the composites at cryogenic temperature had higher
values than that normal temperature for 70:30 specimen which was treated for
24hrs. The flexure strength of the composites at cryogenic temperature had
higher values than the normal temperature for all the specimens. The flexure
strength is more for 70:30 specimen which was treated for 48hrs.

1. Introduction

In
the current quest for improved performance which may be specified by numerous
criteria comprising less weight, more strength and lower cost currently used
materials frequently reach the limit of their utility. Thus material
researchers, engineers and scientists are always determined to produce either
improved traditional materials or completely novel materials 12. Composites
have already proven their worth as weight-saving materials; the current
challenge is to make them cost effective. The hard work to produce economically
attractive composite components has resulted in several innovative
manufacturing techniques currently being used in the composites industry. The
composites industry has begun to recognize that the commercial applications of
composites promise to offer much larger business opportunities than the
aerospace sector due to the sheer size of transportation industry 13. The biggest
advantage of modern composite materials is that they are light as well as
strong. By choosing an appropriate combination of reinforcement material and
matrix, a novel material can be made that exactly meets the requirements of a
specific application. Composites also give design flexibility because many of
them can be moulded into complex shapes 17.

Carbon
fiber alternatively graphite fiber carbon graphite or CF is a material
consisting of fibers about 5–10 ?m in diameter and composed mostly of carbon atoms.
To produce carbon fiber the carbon atoms are bonded together in crystals that
are more or less aligned parallel to the long axis of the fiber as the crystal
alignment gives the fiber high strength-to-volume ratio (making it strong for
its size). Several thousand carbon fibers are bundled together to form a tow
which may be used by itself or woven into a fabric 15.Figure 1.1 shows a
carbon fiber fabric.

The
properties of carbon fibers such as high stiffness, high tensile strength, low
weight, high chemical resistance, high temperature tolerance and low thermal
expansion make them very popular in aerospace, civil engineering, military, and
motorsports, along with other competition sports. Composites made from carbon
fiber are five times stronger than grade 1020 steel for structural parts yet
are still five times lighter.

Figure
1.1. Carbon
Fiber

 

Cryogenics
is defined as the branches of physics and engineering that study very low temperatures.
How to produce them and how materials behave at those temperatures. Rather than
the familiar temperature scales of Fahrenheit and Celsius, cryogenicists use
the Kelvin and Rankine scales 8.

The
word cryogenics literally means “the production of icy cold”; however
the term is used today as a synonym for the low-temperature state. It is not
well-defined at what point on the temperature scale refrigeration ends and
cryogenics begins. Cryogenic temperatures are achieved either by the rapid
evaporation of volatile liquids or by the expansion of gases confined initially
at pressures of 150 to 200 atmospheres 10. Liquefied gases such as liquid
nitrogen and liquid helium are used in many cryogenic applications. Liquid
nitrogen is the most commonly used element in cryogenics and is legally
purchasable around the world. Liquid helium is also commonly used and allows
for the lowest attainable temperatures to be reached. These gases are held in
either special containers known as Dewar flasks which are generally about six
feet tall (1.8 m) and three feet (91.5 cm) in diameter or giant tanks in larger
commercial operations.

2. Experiment Details

2.1. Fabrication
of composites

Three different laminates with different carbon epoxy proportions are
fabricated using hand layup technique. Carbon fiber was selected as
reinforcement and epoxy as matrix material.

 

  

                     Figure 2.1. Preparing Mould                             Figure 2.2. Mould after curing 

 

Figure 2.3. Specimen Cutting                      Figure
2.4. Specimens after cutting

2.2. Cryogenic
Treatment (Liquid Nitrogen)

The
composite specimens prepared of three different composition were immersed in
liquid nitrogen tank. The specimens were inserted in liquid nitrogen tank for a
duration of 24 hrs and 48 hrs.

 

 

Figure
2.5. Specimens immersed in liquid
nitrogen tank for 24 hrs and 48 hrs

 

2.3. Testing
of Specimens

2.3.1. Tensile Test

 

 

Figure
2.6. Computerized Universal testing machine and
Dimensions of Tensile test specimen (mm)

 

Ø Specimen is cut according to ASTM D-638 dimensions shown in figure 2.6

Ø Specimen plate is enclosed between the grippers of universal testing
machine shown.

Ø Load is applied by deforming the specimen and corresponding to
deformation is noted down.

Ø Stress strain for corresponding load and corresponding deformation are
calculated and repeated for different trials.

2.3.2. Flexure Test

Ø Specimen is cut according to ASTM D-790 dimensions shown in figure 2.7

Ø Specimen plate is placed as simply supported beam of flexural testing
machine and a central load is applied as shown

Ø Load is slowly applied by deforming the specimen.

Ø Load at which maximum deformation is noted down and repeated for
different trials.

 

Figure
2.7. Flexure testing machine and Flexure testing specimen (mm)

 

3. Results and Discussion

The results and discussion consists of studying and
analyzing results of tensile strength and flexure strength of three different
composition of specimens at normal condition. It also consists of studying and
analyzing results of tensile strength and flexure strength of three different
composition of specimens when they are cryogenically treated for 24hrs and
48hrs respectively.

 

3.1. Tensile
Strength

The tensile strength obtained for all the different conditions and
different compositions discussed previously are as shown in table 3.1

 

Table
3.1: Results of tensile strength

Sl
No

Specimen
No / Composition

Tensile
Strength (Mpa)

Normal

24
Hrs Treated

48
Hrs Treated

1

S1  /
(70:30)

168

303

286

2

S2 / (60:40)

82.7

84.9

74.5

3

S3  /
(50:50)

80

82.4

78.2

 

Figure
3.1. Results of tensile strength

 

From the table 3.1 and figure 3.1 it is observed that the 70:30
specimen which was 24 hrs treated had more tensile strength when compared to
other specimens. It was also observed that the tensile strength had increased
for 24 hrs and then reduced for 48 hrs cryogenic treated specimens. For 60:40
and 50:50 specimens the values reduced for 48 hrs treated specimens than the
normal values.

3.2. Flexure
Strength

The flexure strength obtained for all the different conditions and
different compositions discussed previously are as shown in table 3.2

 

Table
3.2: Results of flexure strength

Sl
No

Specimen
No / Composition

Flexure
Strength (Mpa)

Normal

24
Hrs Treated

48
Hrs Treated

1

S1  /
(70:30)

568

573

589

2

S2 / (60:40)

146

334

375

3

S3  /
(50:50)

125

135

148

 

Figure
3.2. Results of flexure strength

 

From the table 3.2 and figure 3.2 it is observed that the 70:30
specimen which was 48 hrs treated had more flexure strength when compared to
other specimens. It was also observed that the flexure strength had increased
for 24 hrs and for 48 hrs cryogenic treated specimens. The flexure strength
gradually increased for 24 hrs and 48 hrs treated specimens.

 

3.3. SEM
Analysis

3.3.1. Normal Specimens

  

Figure
3.3. SEM images of 70:30 composition – Normal
specimens

 

Figure 3.3 shows the SEM analysis of normal specimens of 70:30
composition. From the figures we can see that the fiber layers are bonded
correctly and the fracture is of brittle fracture nature.

 

  

Figure
3.4. SEM images of 60:40 composition – Normal specimens

 

Figure 3.4 shows the SEM analysis of normal specimens of 60:40
composition. From the figures we can see that the fiber and epoxy bonding is
not as strong as the 70:30 composition and the fracture is of brittle fracture
nature.

3.3.2. Cryogenic Treated – 24
Hours

 

Figure
3.5. SEM images of 70:30 composition – Cryogenic
treated 24 hrs

 

Figure 3.5 shows the SEM analysis of 24 hrs treated specimens of 70:30
composition. From the figures we can see the adhesion between fiber and matrix
due to liquid nitrogen penetration and the fracture is of brittle fracture
nature.

 

 

Figure
3.6. SEM images of 60:40 composition – Cryogenic
treated 24 hrs

 

Figure 3.6 shows the SEM analysis of 24 hrs treated specimens of 60:40
composition. From the figures we can see the bonding between fiber and matrix
due to liquid nitrogen penetration and the fracture is of brittle fracture
nature. The bonding is less when compared to 70:30 composition

3.3.3. Cryogenic Treated – 48
Hours

Figure 3.7 shows the SEM analysis of 48 hrs treated specimens of 70:30
composition. From the figures we can see the bonding between fiber and matrix
due to liquid nitrogen penetration. The bonding or adhesion is more when
compared to 70:30 composition treated for 24 hrs.

 

 

 

  

Figure
3.7. SEM images of 70:30 composition – Cryogenic
treated 48 hrs

 

 

Figure
3.8. SEM images of 60:40 composition – Cryogenic
treated 48 hrs

 

Figure 3.8 shows the SEM analysis of 48 hrs treated specimens of 60:40
composition. From the figures we can see the bonding or adhesion between fiber
and matrix. The bonding is more when compared other specimens which were
treated for 24 hrs and 48 hrs. This is due to more liquid nitrogen penetration
and the fiber content is less in this composition.

4. Conclusions

From the results, discussion and analysis
the following conclusions are drawn.

Ø  Due to cryogenic treatment there was
changes in the physical properties of the specimens. The specimens had deformed
in their shape. The more deformation was seen in 60:40 specimen which was
treated for 48 hrs.

Ø  The tensile strength of the composites at
cryogenic temperature has higher values than that normal temperature for 70:30
specimen which was treated for 24hrs.The tensile strength for 60:40 and 50:50
specimens which were treateated for 48 hrs had lesser values than the normal
specimens. This may be due to the deformation which had occurred.

Ø  The flexure strength of the composites at
cryogenic temperature had higher values than the normal temperature for all the
specimens. The flexure strength is more for 70:30 specimen which was treated
for 48hrs.

Ø  The improvement in the strength value
after cryogenic conditioning is probably due to differential thermal
contraction of the matrix during sudden cooling which leads to the development
of greater cryogenic compressive stresses.

Ø  This may increase the resistance to
debonding and better adhesion by mechanical keying factor at the interface
between fiber and the matrix.

Ø  The SEM analysis showed that the liquid
nitrogen penetration along the fiber/matrix interfaces caused resistance to
debonding and better adhesion.

5. References

1 Prashanth Banakar and H.K. Shivananda,
“Preparation and Characterization of the Carbon Fiber Reinforced Epoxy Resin
Composites”, IOSR Journal of Mechanical and Civil Engineering (IOSRJMCE),
ISSN: 2278-1684 Volume 1, Issue 2 (May-June 2012), PP 15-18

2 T D Jagannatha and G Harish, “Mechanical
properties of carbon/glass Fiber reinforced epoxy hybrid polymer Composites”,
Int. J. Mech. Eng. & Rob. Res. 2015, Vol. 4, No. 2, April 2015

3 S.Pichi Reddy1, P.V.Chandra Sekhar
Rao, A.Chennakesava Reddy,

G.Parmeswari, “Tensile and flexural
strength of glass fiber epoxy composites” International Conference on
Advanced Materials and manufacturing Technologies (AMMT) December 18-20, 2014.

4 Amit Kumar Tanwer, “Mechanical
Properties Testing of Uni-directional and Bi-directional Glass Fibre Reinforced
Epoxy Based

Composites”, International Journal of Research in
Advent Technology, Vol.2, No.11, November 2014.

5 Jane Maria
Faulstich de Paiva, Sérgio Mayerc, Mirabel Cerqueira Rezende, “Comparison of Tensile Strength of
Different Carbon

Fabric Reinforced Epoxy Composites”, Materials Research, Vol. 9, No. 1,
83-89, 2006.

6 P. Baldissera and
C. Delprete, “Deep
Cryogenic Treatment: A Bibliographic Review”, The Open Mechanical Engineering
Journal, 2008, 2, 1-11.

7 Seyed Ebrahim Vahdat and Keyvan Seyedi
Niaki, “Design of metal matrix composite with particle reinforcement
produced by deep cryogenic treatment”, IOP Conf. Series: Materials Science
and Engineering 87 (2015) 012003.

8 Surendra Kumar M, Neeti Sharma and B.
C. Ray, “Mechanical Behavior of Glass/Epoxy Composites at Liquid Nitrogen
Temperature”

9 Blaise Solomon, Davis George, K.
Shunmugesh, and Akhil K.T., “The Effect
of Fibers Loading on the Mechanical Properties of Carbon Epoxy Composite” Polymers
& Polymer Composites, Vol. 25, No. 3, 2017.

10 Shangtan Liu, Xiaochun Wu, Lei Shi,
Yiwen Wu and Wei Qu, “Influence of
Cryogenic Treatment on Microstructure and Properties Improvement of Die Steel”,

Journal of Materials Science and Chemical Engineering,
2015, 3, 37-46.

11 Jatinder Singh, Arun Kumar and Dr.
Jagtar Singh, “Effect Of Cryogenic
Treatment On Metals & Alloys”.

12
COMPOSITE MATERIALS Web-based Course

13
Composite design Section 1 of 3: Composite design theory, AMTS standard workshop
practice

14
http://en.wikipedia.org/w/index.php?title=Carbon_ (fiber) &oldid=614269153

15
http://en.wikipedia.org/w/index.php?title=Epoxy&oldid=613169841

16
http://en.wikipedia.org/w/index.php?title=Carbon-fiberreinforced polymer &
oldid = 613198147

17
K.Chawla, “Composite Materials”. Second Edition.

18
https://en.wikipedia.org/wiki/Strength_of_materials

19
https://ocw.mit.edu/courses/materials-science-and-engineering/3-11-mechanics-of-materials-fall-1999/

20
https://www.coursera.org/learn/mechanics-1

 

x

Hi!
I'm Brent!

Would you like to get a custom essay? How about receiving a customized one?

Check it out