Composites Science and Technology 72 (2012) 1183–1190
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Composites Science and Technology
journal homepage: www.elsevier.com/locate/compscitech
Tensile and flexural properties of snake grass natural fiber reinforced
isophthallic polyester composites
T.P. Sathishkumar a,⇑, P. Navaneethakrishnan a, S. Shankar b
a
b
Department of Mechanical Engineering, Kongu Engineering College, Erode, Tamilnadu, India
Department of Mechatronics Engineering, Kongu Engineering College, Erode, Tamilnadu, India
a r t i c l e
i n f o
Article history:
Received 5 August 2011
Received in revised form 26 March 2012
Accepted 1 April 2012
Available online 6 April 2012
Keywords:
A. Fibers
A. Polymer–matrix composites
B. Mechanical properties
D. Scanning electron microscopy (SEM)
Snake grass fiber
a b s t r a c t
Natural fiber composite materials are one such capable material which replaces the conventional and
synthetic materials for the practical applications where we require less weight and energy conservation.
The present paper, which emphasis the importance of the newly identified snake grass fibers which are
extracted from snake grass plants by manual process. In this paper, the tensile properties of the snake
grass fiber are studied and compared with the traditionally available other natural fibers. The mixed
chopped snake grass fiber reinforced composite is prepared by using the isophthallic polyester resin
and the detailed preparation methodology is presented. Fiber pull-outs on the fractured specimen during
the physical testing of the composites are also investigated. The experimental evidence also shows that
the volume fraction increases the tensile, flexural strength and modulus of the snake grass fiber reinforce
composite.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Global market is promptly moving towards the energy conservation and energy reduction process. Generally the natural fibers
were frequently used to reduce the weight of the components
i.e. the fibers are reinforced with the suitable matrix. In the aspect
of cost, renewable and biodegradability, the natural plant fibers
have plenty of advantages when compare to the synthetic fibers.
Several authors carried out their research in the area of natural fibers. Athijayamania et al. [1] extracted the roselle and sisal fibers
by simple manual water treatment process. The experimental tensile and flexural strength results were compared with the hirsch
theoretical model. Later, Bakare et al. [2] studied the mechanical
properties of the sisal fiber rubber seed oil polyurethane composite, with and with-out water treatment process. Cao and Wu [3]
followed the weibull distribution to find out the optimum strength
of the bamboo fiber with the K–S test. Gonzalez and Ansell [4]
suggested that the mechanical properties of chemically treated
henequen fiber epoxy composite produces similar results as like
the untreated fiber composite. Silva et al. [5] investigated the
tensile properties of the sisal fiber for the different fiber gauge
length. Herrera-Franco and Valadez-Gonzalez [6] concluded that
the stress distribution between the fibers and matrix for a short
discontinuous fiber were better than the continuous fibers. The
importance of the short fiber composites was also discussed. Bos
⇑ Corresponding author.
E-mail address: [email protected] (T.P. Sathishkumar).
0266-3538/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.compscitech.2012.04.001
et al. [7] suggested that the tensile strength of flax fiber bundles
were strongly depends on the clamping length. The compressive
properties were obtained by the loop test with the decortication
process. Kuruvilla et al. [8] also worked on the natural fiber reinforced composite. The tensile strength and modulus of the longitudinal and random orientated fiber composite were studied and
compared. Igor et al. [9] investigated the importance of phormium
(flax fiber)/epoxy laminated composite with short fiber and long fiber. Various chemical compositions of the fibers were compared
with the other natural fibers. Jayabal and Natarajan [10] analyzed
the tensile, flexural and impact properties of the non woven coir fiber reinforced composites with various fiber lengths and fiber contents. The results were used to generate a nonlinear quadratic
regression model and optimized the fiber length and fiber content
using a commercially available statistical tool.
Mathur [11] prepared the sisal, jute and coir fiber reinforced
composites with unsaturated polyester/epoxy resin. Murali Mohan
Rao et al. [12] extracted and processed the newly identified
elephant grass fiber by manual and chemical methods. They observed that the chemically extracted fibers have higher tensile
strength than the raw fibers but the difference between those values was very less. Murali Mohan Rao and Mohan Rao [13] also
processed the vakka fibers from the foliage tree of sheath leaves
by simple manual method. The result shows that the percentage
of moisture absorption was higher in vakka fiber than the date
and bamboo fiber. Obi Reddy et al. [14] prepared the composites
by using the leaf sheath of the coconut tree and studied its
significance with and without chemical treatment process. Rakesh
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T.P. Sathishkumar et al. / Composites Science and Technology 72 (2012) 1183–1190
et al. [15] investigated the strength of the banana fiber reinforced
composites with the help of soy protein resin. They concluded that
the mechanical properties of the composites were strongly
depends on the fiber volume fraction. Rigoberto et al. [16] investigated the significance of the natural fiber composites by making it
as a housing panel. Random orientation technique was adopted to
archive the isotropic behavior of the nature fiber reinforced composites. Sergio et al. [17] suggested that the different interior and
exterior components of the automobiles can be replaced with the
help of natural fiber reinforced composites. Shinji et al. [18] also
investigated the mechanical properties of kenaf natural fibers.
Xue and Lope [19] observed that the structural stability and adhesion properties in the reinforced composite were improved by
adopting the various chemical treatment processes. Kiruthika and
Veluraja [20] analyzed the tensile strength of the various banana
plant fibers and compared the results with and with out chemical
treatment processes. Byoung-Ho et al. [21] briefly investigated the
Table 1
Comparison of the tensile properties of snake grass fiber with other natural fibers.
effects of the long and discontinuous fiber reinforced polypropylene bio-composites by utilizing the compressive mold. The theoretical model values for the kenaf and jute fiber composites were
also compared. Satyanarayana et al. [22] compared the physical
and chemical properties of the various natural fibers. These fibers
were reinforced with the polymer and epoxy resin composites.
The cotton/ polymer and jute/epoxy/polymer composites were
prepared and its significance was reported. Sreenivasan et al.
[23] investigated the tensile, flexural and impact properties of
randomly oriented short Sansevieria cylindrica fiber/polyester
(SCFP) composites.
Most of the previous literatures presented the significance of
newly developed fibers that have used to prepare the composites
and also optimized the fiber length, volume and weight fractions.
The fibers were randomly orientated during the composite preparation. In this paper, one such natural fiber is extracted from the
naturally available plants; the properties of the prepared materials
are tested and compared with the other existing natural fibers as
shown in Table 1. Snake grass fibers are the newly identified fiber
which is extracted from the snake grass plants (Sansevieria ehrenbergii) by simple manual and biodegradable treatment. The snake
grass is a new plant in fibrous form and it is abundantly available
in southern part of the INDIA. This work is also extended to fabricate the reinforced composite using the polyester resin to study its
mechanical properties.
Fiber name
Density
(kg/m3)
Diameter
(lm)
Tensile
strength
(MPa)
Tensile
modulus
(GPa)
% Elongation
Cotton
[19,22]
Ramie [19]
Flax [7,19]
1600
–
287–597
5.5–12.6
3–10
1500
1500
–
44–128
27.6–80
2–3
1.2–3.2
2. Experiments
Hemp [19]
Jute [19,12]
Sisal
[5,8,12]
Pineapple
leaf [22]
Kenaf [21]
Banana
[12,15]
Coir [12]
Root [22]
Palymyrah
[22]
Date [13]
Bamboo
[13]
Talipot [22]
Snake grass
Elephant
grass
[12]
Petiole bark
[22]
Spatha [22]
Rachilla
[22]
Rachis [22]
Coconut
tree leaf
sheath
[14]
Red banana
[20]
Nendran
banana
[20]
Rasthaly
banana
[20]
Morris
banana
[20]
Poovan
banana
[20]
1480
1460
1450
–
–
50–300
220–938
345–
1500
550–900
393–800
227–400
70
10–30
9–20
1.6
1.5–1.8
2–14
2.1. Fiber materials
1440
20–80
81
80–250
34.5–
82.5
4.3
8.20
0.8–1
1400
1350
413–
1627
250
529–759
1150
1150
1090
100–460
100–650
70–1300
108–252
157
180–215
4–6
6.2
7.4–604
15–40
3
7–15
309
503
11.32
35.91
2.73
1.4
990
910
–
1–3.5
The length of the snake grass plants that grown in the field
ranges from 30 cm to 120 cm. The actual processing of fibers from
the snake grass natural plants is shown in Fig. 1. Fig. 1 shows the
plucking of snake grass plant and the sand are removed by water.
The external green layers of the plants (stamp) are removed. After
which the plants are immersed in water for four consecutive days
to remove the primary and secondary walls of the plants by biodegradable process which will be useful to extract the fibers continuously from the plant without any damage. The untreated snake
grass fiber is then cut into different lengths for preparing the specimens of composites i.e. the length used for preparing the composite varies from 10 mm, 30 mm, 60 mm, 90 mm, 120 mm and
150 mm respectively.
890
887
817
200–700
45–250
70–400
143–294
278.82
185
9.3–13.3
9.71
7.4
2.7–5
2.87
2.5
690
250–650
185
15.
2.1
690
650
150–400
200–400
75.6
61
3.1
2.8
6
8.1
610
–
350–408
–
73
119.8
2.5
18
13.5
5.5
–
–
482–567
–
30.6
–
–
407–505
–
28.3
2.3. Preparation of the composite specimen
–
–
304–388
–
27.8
–
–
222–282
–
24.2
–
–
144–206
–
21.8
After 4 days, the extracted snake grass fibers is taken out from
the water, then the water content present inside of the fiber is removed by keeping it in natural air for 8 h. Then the fibers are kept
in the hot air oven for 60 min at 160 °C [18]. The dried fibers are
then chopped into various lengths as mentioned earlier to prepare
the composites. The simple hand lay-up technique is adapted to
prepare the composite specimen with various volume fractions
(Vf) like 10%, 15%, 20%, 25% and 30% respectively. One percent of
2.2. Polyester resin
Commercially available isophthallic unsaturated polyester resin
is used for the investigation. Accelerator (Methyl Ethyl Ketone
Peroxide) and the catalyst (Cobalt Naphthalene) are used to cure
the resin. Thermoset isiophthallic polyester resin is one of the
economical resins when compare to other resins due to its very
low water absorbing capability and excellent bonding tendency
as well as mechanical properties. The distinctive properties of the
isophthallic polyester resin are shown in Table 2.
T.P. Sathishkumar et al. / Composites Science and Technology 72 (2012) 1183–1190
1185
Fig. 1. (a) Snake grass fiber plants, (b) plucking of snake grass fiber plants, (c) removing the sand by water and (d) fiber collection.
Table 2
Properties of the isophthallic polyester resin.
S. No
Properties
Unit
Range
1
2
3
4
5
6
7
8
Specific gravity
Density
Tensile strength
Tensile modulus
Compressive strength
Flexural strength
Flexural modulus
Shrinkage
–
kg/m3
MPa
GPa
MPa
MPa
GPa
%
1.1–1.46
1125
18
0.8–1.1
90–250
30
1.2–1.5
0.004–0.008
catalyst and one percent of accelerator is used to cure the
isophthallic polyester resin. Steel dies are designed to prepare
the composite specimens. Initially the releasing agent is coated
over the male and female section of the die for easy removal of
the specimens after the solidification process. The surfaces are then
allowed to dry for 15 min, and the fibers are spread over the die.
Fiber orientation and uniformity in the composites are maintained
by the rolling process using steel rollers to achieve the maximum
isotropic material property and almost all the air bubbles are removed by the continuous rolling process. At the time of curing,
the closed mould is kept on the hydraulic press and a compressive
pressure is applied for 8 h at atmospheric temperature. Finally the
fibers are reinforced with the polyester resin within the mould cavity of dimensions 230 mm 200 mm 4 mm to prepare the required composite plate. After solidification process, the
composite plate is then post-cured for one hour in oven.
used through out the testing. Twenty-five samples were tested in
this work and the average value of the tensile strength; tensile
modulus and elongation at the failure/break were obtained. The
density of the fiber was evaluated using the meltbertoledoxsz05
balances method.
2.4.2. Tensile testing of the composite
Tensile tests were conducted for the composite specimen using
the electronic tensometer setup to obtain the tensile properties.
The dog-bone specimens of the composites were prepared according to the ASTM D 638 [10] standards. The specimens were
machined to a standard size of 165 mm 13 mm 4 mm for a
gauge length of 50 mm. For this testing, the load cell of 5 kN was
utilized in the tensometer with the same cross head speed of
1 mm/min [9,18]. Five identical test specimens were used for each
testing and numbered in series as T1, T2, T3, T4 and T5. Properties
such as tensile strength, tensile (elastic) modulus, tensile load and
elongation at break of the composites were measured from the
experimentation. During tensile testing, the specimens were broken in between the gauge length of the specimen and the corresponding image was shown in Fig. 2.
2.4. Analysis
2.4.1. Tensile testing of a single fiber
The tensile properties of the long continuous snake grass fiber
were measured by a single fiber tensile testing method according
to the ASTM D3379-75 [12] standards using the Instron Universal
Testing machine. The gauge length of each fiber was taken as
100 mm and a 1000 g load cell was used for the testing. The cross
head speed of the grippers was 5 mm/min and the same speed was
Fig. 2. Tensile tested specimens.
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3.2. Effect of tensile properties of the snake grass natural fiber
reinforced composites
2.4.3. Flexural testing of the composite
Three point flexural testing were conducted according to the
ASTM D 790 [10] standards using the spring mass testing machine.
The specimens were machined for the dimensions of 125 mm 12
mm 4 mm. The span to the depth ratio of the specimens was
considered as 16:1. For this testing, the load cell of 6 kN was utilized with the cross head speed of 2.5 mm/min [18]. Five identical
test specimens were prepared and numbered as F1, F2, F3, F4 and
F5 for each flexural testing. Deflections of the specimen were measured using the digital dial gauge and the flexural properties like
flexural strength, flexural modulus, flexural load and deflection at
break of the composites were evaluated. As similar to the tensile
testing, the five identical specimens were broken in between the
gauge length and the corresponding image was shown in Fig. 3.
2.4.4. Scanning Electron Microscope
The micro structural failures of the tensile and flexural fracture
composite were studied and analyzed using the cross section analyses method through the Scanning Electron Microscope (SEM) of
model JEOL JSM-6390. The following specifications were used for
scanning the image: (a) Resolution (3.0 nm (Acc V 30 kV, WD
8 mm, and SEI), (b) Magnification (5 (WD 48 mm or less) and
(c) Electron gun (Accelerating voltage: 0.5–30 kV and Filament:
Pre-Centered tungsten hairpin filament).
3. Results and discussion
3.1. Mechanical properties of the snake grass fiber
The raw single snake grass fibers of gauge length of 100 mm were
taken for the tensile testing. Multiple filaments in the fibers were removed and tested with out any surface modification process. The
tensile strength of the fiber was obtained by the ratio of average load
to the average area for the twenty-five identical samples. The tensile
properties of the snake grass fiber with the various available natural
fibers were compared and shown in Table 1. The diameter of the fiber was varied from 45 lm to 250 lm. Density is one of the important parameter for designing any light weighted materials. From the
table, it was very clear that the density of the snake grass fiber was
very less when compared to the other natural fibers but it was marginally higher than the elephant grass, petiole bark, spatha rachilla
and rachis fibers. The average tensile strength of snake grass fiber
was better than the elephant grass, kenaf, root, coir fibers, petiole
bark, spatha rachilla and rachis fibers and also equal to the sisal
and closer to the date and bamboo. The percentage elongation at
break was little higher than the elephant grass, petiole bark, pineapple leaf, date and bamboo and equal to the flex, banana, hemp and
jute. From the available properties, it is evident that the snake grass
fiber is one among the future alternative of any natural fibers.
40
Tensile Strength (MPa)
Fig. 3. Flexural tested specimens.
The tensile properties of the snake grass chopped fiber reinforced composites are compared with the various fiber volume
fractions for various fiber lengths. Fig. 4 shows the variation of tensile strength over the percentage increase in fiber volume fractions
for the various fiber lengths. The tensile strength decreases from
20.15 MPa to 17.25 MPa when the fiber length is increased from
10 mm to 150 mm for 10% Vf. For 10% Vf, the fiber accumulation
is very less in the composite, so the percentage increase between
the maximum and minimum tensile strength for the present case
is almost 16.8%. Similar decreasing trend in the tensile strength
is visible for other cases up to 25% Vf. The percentage increase
between the maximum and minimum tensile strength for 15% Vf
is 11.85%. This percentage was reduced when compare to 10%
Vf is due to the more accumulation of fiber in the composite. Similarly the improvement percentage between the maximum and
minimum tensile strength was further reduced to 10.37% for 20%
Vf. Maximum tensile strength of 35.89 MPa is obtained for
30 mm fiber length in the present work when the percentage volume fraction is 25. The percentage improvement between the
maximum and minimum tensile strength for 25% Vf is 11.49%. This
percentage is increased when compared to the previous 20% Vf. Because in the composite, the fiber accumulation is more and also
30 mm fibers having higher fiber ends than the 150 mm. The fiber
ends plays an important roll and it is one of the main factor which
affects the tensile strength. The tensile strength is suddenly
reduced to 14.02–11.85 MPa for various fiber lengths when the
percentage volume fraction is 30. From the results, it is inferred
that the load and stress transfer between the fiber and the matrix
is highly reduced due to the less matrix content in composite
which is also the main reason for the reduction in tensile strength.
The maximum tensile strength of the composite lies in between
30 mm and 60 mm of the fiber length. The percentage of improvement from 10% Vf to 25% Vf for 30 mm and 60 mm fiber lengths are
44.99% and 43.66% respectively. It is absorbed that the tensile
strength of the composite increases with the increase in fiber content. Hence a good load transfer is visible in between the fibers and
the matrix. Further increase in the fiber length and volume fraction
highly reduces the tensile strength and load transfers between the
fibers and matrix which cannot be a significant one for any
applications.
Fig. 5 shows the tensile stress–strain curves for the various fiber
volume fractions at 30 mm fiber length. The stress–strain curve for
the cure polyester resin is similar to the brittle materials [22,23].
Then the addition of fibers in the polyester resin which converts
35
30
25
1
20
10mm
60mm
120mm
15
10
10
15
20
30mm
90mm
150mm
25
30
Volume fraction of snake grass fiber (%)
Fig. 4. Effect of tensile strength verses volume fraction of snake grass fiber with
different fiber lengths.
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Flexural Strength (MPa)
85
10mm
60mm
120mm
75
30mm
90mm
150mm
65
55
45
35
25
10
15
20
25
30
Volume fraction of snake grass fiber (%)
Fig. 5. Tensile stress and tensile strain curve for various fiber volume fractions at
30 mm fiber length.
215.11 MPa when the fiber length is 60 mm. When the fiber length
is increased beyond a limit, then the tensile modulus value gets decreased. This shows that the fiber length has influential effect in
setting the tensile modulus value of any natural fiber composites.
500
Tensile Modulus (MPa)
Fig. 7. Effect of flexural strength verses volume fraction of snake grass fiber with
different fiber lengths.
450
400
350
3.3. Effect of flexural properties of snake grass natural fiber reinforced
composites
300
10mm
60mm
120mm
250
200
30mm
90mm
150mm
150
10
15
20
25
30
Volume fraction of fiber (%)
Fig. 6. Effect of tensile modulus verses volume fraction of snake grass fiber with
different fiber lengths.
the brittleness to the ductile nature as indicated in the stress–
strain curve. The elongation at break in the cure resin is lesser than
the composite specimens. The maximum stress is found at 25% Vf
with increase in strain values. When the volume fraction is
increased to 25% then the stress–strain curve is more or similar
in nature, so the optimum fiber volume fraction is accounted as
25%. Young’s modulus of the specimens is calculated with the corresponding machine compliances i.e. by considering the elastic
portion of the stress–strain curve. From Fig. 5, it is also clear that
for any given strain level, the stress is increased with the fiber
length up to 30 mm and then decreased indicating a critical fiber
length of 30 mm for short snake grass fiber reinforced composites.
The lowering of stress values at higher fiber lengths can be attributed to the fiber entanglements formed at higher lengths [23]. In
Fig. 6 shows the variation in the tensile modulus values over the
volume fraction for the various fiber lengths of snake grass fiber
composites. For 10% Vf, composites have maximum tensile modulus of 336.93 MPa when the fiber length is 10 mm and the minimum tensile modulus of 287.02 MPa for 150 mm fiber length.
Similarly, the tensile modulus value gradually increases when
the volume fraction increases up to 25%. For 15% Vf, composites
have maximum tensile modulus of 379.06 MPa and when Vf is
20% the maximum tensile modulus is increased to 421.81 MPa.
The maximum tensile modulus for the entire experimentation is
481.75 MPa for 25% Vf. It is clearly visible that there is a marginal
amount of change in tensile modulus value for any constant volume fraction when the fiber length gets altered. When the volume
fraction is 30%, the maximum tensile modulus is decreased to
The flexural property is one of the important parameter in composites mainly useful to quantify in structural applications. Fig. 7
shows the variations in the flexural strength values over% increase
in volume fractions. It is observed that the flexural strength values
are gradually increased up to 20% Vf. Beyond 20% Vf of fiber in composite, the flexural strength is suddenly increased. Then the
increasing trend suddenly changes and the flexural strength gets
drastically reduced when Vf of fiber in composite is 30%. During
the composite preparation, if the fiber content is more than 30%
Vf, it leads to insufficient filling of matrix into the surrounding
fibers and it is one of the main reason for the incomplete composite. 10% Vf composite have the maximum flexural strength of
33.45 MPa and it has significant change of 12.01% when the fiber
content is varied. The maximum flexural strength is increased to
38.14 MPa when the %Vf is 15 and the flexural strength is significantly varied by 6.87% depends on the fiber content present in
the composite. The increasing trend of the flexural strength value
continues as like in the previous cases up to the 25% Vf. 25% Vf composite has the maximum flexural strength of 75.29 MPa when the
fiber length is 150 mm. The increasing trend suddenly decreases as
like in previous cases to 49.64 MPa when the %Vf of the fiber in
composite is 30. The maximum flexural strength of the composite
depends upon the length of the fiber in the composite, in the present case it lie in between 120 mm and 150 mm for 25% Vf. It is also
noted that the flexural strength depends upon the fiber content
and the fiber length. From the extensive experimentation, it is evident that the maximum flexural load is carried by the long fiber
than the short fiber.
Fig. 8 shows the variation in the flexural modulus value over the
various volume fractions of snake grass fiber composites. As like in
previous cases, the values of the flexural modulus increases while
increasing the volume fraction. The increasing trend continues up
to 25% Vf of the composite, which have the maximum flexural
modulus of 15.99GPa when the fiber length is 150 mm. For a
constant volume fraction when the fiber content changes, the variations in the flexural modulus is clearly visible from the results.
Then the maximum flexural modulus value is suddenly decreased
to 6.72 GPa when% Vf of the composite is 30. The observation
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the performances and potentials of the corresponding composite
materials.
4. Scanning Electron Microscope analysis
The fractured specimen from the tensile and flexural testing of
the snake grass natural fiber reinforced polyester composite is considered for the cross section analysis using Scanning Electron
Microscope. One half of the fractured dog-bone shaped specimen
is utilized for performing the SEM analysis.
4.1. SEM micrograph analysis of tensile fractured specimen
The SEM micrograph of the tensile fractured specimen of 10% Vf
is shown in Fig. 9a. Fiber pull-out is visible from the micrograph
and in particular, snake grass fibers are found to be more broken
in that image. Also, the intra fiber delamination is found to be more
predominant in snake grass fibers. Fiber pull-out occurs mainly
due to the poor interfacial bonding at the interphase of the fiber
and matrix. Interphase specifies the intersectional plane of the
fiber and the matrix whose properties are studied by using
the SEM micrograph. It is found that the fibers at the vicinity of
the loading region are more prone to damage. Strain values of
the fiber at this region might have decreased and that leads to
the fiber pull-out at this region. Due to the improper interfacial
bonding, a smaller amount of the delamination at the interphase
is found. It is evident from the micrograph that the adhesion area
between the fiber and matrix is reasonably less, so the tensile
strength is also less in the composites.
Fig. 9b shows the SEM micrograph of tensile fractured 25% Vf
specimen. Interfacial delamination of the interphase is found to
be much higher than the 10% Vf specimen. Tensile strength values
have confirmed that the adhesion between the fiber and matrix is
good and the fiber pull-out is not so predominant. Strength at the
interphase of the fiber and matrix is found to be higher due to the
breakage of the individual fiber to the vicinity of the interphase at
the loading region. Due to the strong interphase, snake grass fibers
have undergone individual fiber breakage appreciably. At this volume fraction, intra fiber delamination is not as frequent as the fiber
breakage which is found to be dominant. Fiber wetting at this
volume fraction is higher when compare to the 10% Vf which leads
to the fiber breakage and also the intra fiber delamination. The
effective stress transfer between the fiber and matrix is proven
due to the higher stress values. Altogether, the optimized strength
values of the 25% volume fraction of the composites have very
good interfacial properties, higher wetting, lesser fiber pull-out
and poor intra fiber delamination. This is due to the very less splitting of single fiber in to fibrils. At 30% Vf, the interfacial bonding is
better due to the presence of more fibers, but percentage fiber and
matrix bonding is highly reduced and causes the reduction in the
Fig. 8. Effect of flexural modulus verses volume fraction of snake grass fiber with
different fiber lengths.
concludes that the maximum flexural modulus of the composite is
obtained at 25% Vf for the fiber length of 150 mm. Compiling all the
results (Figs. 4–8), it is evident that the tensile strength, tensile
modulus, flexural strength and flexural modulus of isophthallic
polyester resin reinforced composite is gradually increased with
the amalgamation of chopped snake grass fibers up to 25% Vf. At
25% volume fraction, fiber reinforcement effect is one of the competitive phenomena for the improvement of strength and modulus,
also the microcrack initiation is relatively high for the higher loading of chopped fibers. The tensile and flexural modulus values have
increased extensively with the increasing in fiber volume fraction.
It is observed that the strength of chopped fiber reinforced composite mainly depends on several factors like the fiber strength
and modulus, fiber length, density of fiber and matrix, fiber volume
fraction, fiber weight content and the fiber orientation. Among
these factors, the preparation of the composite should be considered into account with the fiber volume fraction and fiber orientation over the different fiber lengths. In general, the chopped fibers
have higher ends and aligned with higher degree of orientation in
the matrix resin. The applied load is directly observed by the fiber,
it transfers the load from one end to the other end so it leads to increase in the mechanical properties of the composite.
In general, natural fibers have variable diameter along with its
fiber length. Therefore it is a very difficult task to compare its
composite properties by any direct methods. Hence, the indirect
comparison used in this work is one of the simplest techniques
for the composite material preparation at corresponding volume
fraction with the similar type of reinforcement. It is one of the sufficient approach which gives useful information on understanding
a
Fig. 9. SEM micrograph of tensile fractured specimen (a) 10% Vf and (b) 25% Vf.
b
T.P. Sathishkumar et al. / Composites Science and Technology 72 (2012) 1183–1190
1189
Fig. 10. SEM micrograph of the flexural fractured specimen (a) 10% Vf and (b) 25% Vf.
mechanical properties. Hence plasticization of the primary wall of
fiber facilitates the bonding fiber and matrix.
4.2. SEM micrograph analysis of flexural fractured specimen
Fig. 10a shows that the SEM micrograph of flexural fractured
10% Vf specimen. Due to the flexural load, the interphase delamination is found at the cross section of the composite. Due to the uniform compressive force applied during the manufacturing of the
composite specimen, presence of voids in the specimen is found
to be very minimal. Fiber pull-out is very much evident in the
micrograph, as the bonding between the fiber and the matrix is
very weak. Due to the fiber pull-out at the interphase, holes are
created because of the poor interfacial wetting. More pull-out is
observed in the compression region due to the higher stress concentration whereas in the tensile region, it is found to be very less.
Fibers have undergone the minimal breakage due to the predominance of fiber pull-out. Individual fiber delamination is not found
as so frequently in the composite, but rarely seen. Flexural strength
values indicate that the elongation is very minimal due to the poor
stress transfer between the fiber and the matrix at the interphase
region of the composite.
Fig. 10b shows that the SEM micrograph of flexural fractured
25Vf specimen. Fiber pull-out behavior of the composite occurs
rarely when compared to 10% Vf. This indicates that there is a good
interaction between the fiber and matrix at the interphase. Stress
transfer between the reinforcement and the fiber is appreciable
which is also evident from the flexural strength values of 25% Vf
for 150 mm fiber length. Fiber breakage occurs very frequently in
both tensile and compressive region due to the less fiber pull-out
and higher fiber accumulation leads to better adhesion at the interphase region. Crater like structures in the image is found in the
micrograph of the specimen which is due to the curing of the matrix under the action of catalyst and accelerator. Due to the minimal fiber pull-out in the composite, the fiber breakage is high
and the individual fiber delamination is also predominant due to
the same reason.
Loading region consists of the concentration of the fibers which
is dominant for the fiber breakage and it have justified the higher
flexural strength and modulus values and less agglomeration of fiber in the composite. Traces of thin layer of resin are found to be
coated over the fiber surface which shows the better adhesion between the fiber and the matrix. Less impurities in the fiber surface,
smooth fiber walls are the most probable reasons for the less variation in the mechanical properties. Considering all the factors, that
the optimized strength values for 25% Vf of snake fiber composites
which have good interfacial properties, higher wetting, lesser fiber
pull-out and poor intra fiber delamination.
5. Conclusions
Convincingly, the present work clearly shows that the snake
grass fiber will become a future alternative for the conventional
materials due to its enhanced mechanical properties and availability. The following conclusions are made based on the extensive
experimental study
1. The tensile strength and tensile modulus of the snake grass
fiber is higher and equal to the other natural fibers. The density
of the snake grass fiber is very less compared to all other fibers.
2. The tensile and flexural properties of the snake grass fiber
isophthallic polyester composite are significantly improved
with the various fiber volume fraction and fiber length. It is
found that the increase in the fiber volume fraction increases
the tensile strengths and tensile modulus. The maximum tensile strength and modulus of the chopped fiber isophthallic
polyester composite is achieved at 25% Vf for the 30 mm fiber
length. In general, the short fibers have higher strength and
higher fiber ends which is accumulated in the composite.
3. The maximum flexural strength and modulus of the chopped
fiber isophthallic polyester composite is achieved at 25% Vf for
120 mm and 150 mm fiber lengths. But the values have significant improvement in 150 mm.
4. The SEM micrograph of tensile and flexural tested specimens
predicts the fiber failure, matrix crack and fibers pull out during
the loading condition at 10% Vf and 25% Vf of the composite. At
higher strength, the volume fraction composite has less fiber
pull out due to the more accumulation of fiber being wetted
in matrix and also it transfers higher load.
Overall, it can be concluded that the 25% volume fraction of the
snake grass fibers composite have the maximum mechanical properties. While manufacturing the composite specimens, the fiber
length plays an important role. The snake grass fibers can be
extracted with less cost and the composites can be made by simply
manual method.
Acknowledgements
Authors kindly acknowledge the Karunya University Coimbatore and SITRA Coimbatore for providing the necessary facilities
to carry out the research.
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