Improving Mechanical Properties by KENAF Natural Long Fiber

Journal of Applied Science and Engineering, Vol. 15, No. 3, pp. 275-280 (2012)
275
Improving Mechanical Properties by KENAF
Natural Long Fiber Reinforced Composite for
Automotive Structures
S. Jeyanthi* and J. Janci Rani
Department of Automobile Engineering, MIT, Anna University,
Chennai, India
Abstract
Natural fibers have recently become attractive to automotive industry as an alternative
reinforcement for glass fiber reinforced thermoplastics. The best way to increase the fuel efficiency
without sacrificing safety is to employ fiber reinforced composite materials in the body of the cars so
that weight reduction can be achieved. Designing the structures with the focus on improvement aspects
is very important in the automotive industry. The goals are to increase the performance of the beams
and also to find the solution to reduce the cost of beams hence able to reduce the production cost. The
latest thermo plastic developments have resulted in higher material properties and more possibilities in
the design of bumper beams. However the use of steel, Aluminum, Glass mat thermoplastics (GMT),
sheet metal components (SMC) Bumpers becomes at higher cost than long fiber reinforced
thermoplastics. This research is focused on partially eco-friendly hybrid long fiber reinforced thermo
plastics with natural kenaf fiber to enhance the desired mechanical properties for car bumper beams as
automotive structural components. A specimen without any modifier is tested and compared with a
typical bumper beam material called LFRT. the results indicate that some mechanical properties such
as tensile strength, young’s modulus, flexural strength an flexural modulus are more advantages to
LFRT, the new material also must improve the ability to absorb more impact load and increase the
protection of the front car component.
Key Words: Bumper Beam, LFRT, GMT, SMC, Kenaf Fiber, Hybrid
1. Introduction
The natural fiber-reinforced composites is growing
rapidly due to their mechanical properties, low cost, processing advantages and low density. The availability of
natural fibers such as kenaf in Asia is more and also has
some advantages over traditional reinforcement materials in terms of cost, density, renewability, recyclability, abrasiveness and biodegradability. The performance of the fiber reinforced composites mainly depends on the fiber matrix and the ability to transfer the
load from the matrix to the fiber [1].
*Corresponding author. E-mail: [email protected]
Bumpers are one of the key structures in automobiles
to protect the passengers which careful design and proper materials should be considered in order to achieve
good energy absorbing behavior [2,3].
To achieve the fuel efficiency the weight reduction
plays vital role in automobiles. Considering the safety
the reduction of weight should be achieved without compensating the mechanical properties of the traditional
materials. With the introduction of the automotive safety
legislation, crash worthy ness and safety should be considered as pre conditions in light weighting the bumper
beam [4,5]. Thermo plastics composites are being used
in a variety of application such as mass transit, automotive and military structures. They have an edge over
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S. Jeyanthi and J. Janci Rani
traditional materials such as steel and aluminum.
In these bumper beams long fiber thermoplastics
were widely used due to their high specific strength,
good damping capacity and corrosion resistance. The
matrix in thermo plastic composites is generally comprised of poly propylene (PP), poly ethylene (PE), nylon
or other inexpensive polymers. E glass fiber is a commonly used reinforced material [6]. Long fiber thermoplastic composites have seen one of the highest growth
rates approximately 30% per year in the plastic industry
during recent times [7]. The fiber length in long glass
fiber decides the mechanical properties of the long glass
fiber thermo plastics.hybridization of natural fiber with
glass fiber provides a method to improve the mechanical
properties of natural fiber composites [8].
The availability of kenaf fibers in India and also in
Asian countries are extended towards usage in automotives. In this research we developed a hybrid material
using natural kenaf and synthetic glass fiber as reinforcements. The hybrid of synthetic glass fibers and kenaf
fibers were used to enhance the mechanical properties.
Kenaf fiber is extracted from the bast of the annual fast
growing plant named Hibiscus cannabinus. The main
constituents of kenaf are cellulose (45-57 wt.%), hemicelluloses (21.5 wt.%), lignin (8-13 wt.%), and pectin
(3-5 wt.%) [9]. Kenaf fibers having good mechanical
properties and thermal properties compare to the other
types of natural fibers when it’s Blend with PP [10].
Amongst eco-compatible polymer composites, special
attention has been given to PP. PP could not be classified
as a biodegradable thermoplastics, but PP takes an important place in eco-composites materials to improve the
matrix with natural fibers [11].
duce impregnated kenaf/glass fiber. For this research
processed kenaf fiber were used, kenaf fiber was heated
up to 140 °C. In LFRT the reinforcement was the synthetic glass fiber; to increase the mechanical and recyclablity the natural fibers were used along with the
glass fibers.
In this process two fiber roving were used one is synthetic glass fiber and another is processed kenaf fiber.
The natural kenaf fiber was sent along with the synthetic
glass fiber to increase the mechanical properties.
Tows were protruded with kenaf fiber, ordinary kenaf
fiber and glass fiber sent through a heated die during
which the individual filaments are impregnated with matrix PP as shown in Figure 1.
In Figure 2 the twisted kenaf fiber and in Figure 3 the
ordinary kenaf fibers were shown. The pultruded tow
impregnated with the PP matrix was cooled and then
chopped in to kenaf/LFRT pallets approximately 11 mm
in length and 3 mm diameter. The glass fiber content by
weight 40% and kenaf fiber 25%. Hybrid Glass fiber/PP
LFRT pallets were used as a starting material for injection molding process. The specimens were molded according to the ASTM standard using injection molding
process. The orientation of fibers is anis tropic and the
flow axis is longitudinal.
In another process for increasing the mechanical
properties of LFRT the Kenaf fibers were twisted manu-
Figure 2. Twisted kenaf fiber.
2. Materials and Methods
A hot melt impregnation process was used to pro-
Figure 1. Manufacturing of hybrid LFRT.
Figure 3. Kenaf fiber.
Improving Mechanical Properties by KENAF Natural Long Fiber Reinforced Composite for Automotive Structures
ally to increase the strength. The twisted fiber had bundle
of kenaf fibers twisted by hand the twisted roving were
winded as a tows.
In this study two types of specimens were taken for
analysis. First one is ordinary kenaf hybrid LFRT (KLFRT)
another is twisted kenaf hybrid LFRT (TKLFRT). All the
properties were compared with LFRT Bumper materials.
The material properties were tabulated in Table 1.
3. Results and Discussions
3.1 Tensile Test
The tensile test were performed according to the
ASTM D3039 standard five set of specimens with recommended dimensions are created and tested by a calibrated AUTOGRAPH-AGS-2003 testing machine with
speed 5 mm/min. Five set of specimens with three different reinforcements were used for testing and the
readings were plotted in Figure 5. The tensile strength
and the Young’s modulus of the TKLFRT specimens
were higher than common bumper beam materials such
as LFRT [6]. The typical yield strength and Young’s
modulus of the LFRT is 101.3 MPa and 5.5 GPa, respectively [6]. The KLFRT material is also higher than the
LFRT. The tested specimens and the test machine were
shown in Figure 4.
Tensile modules of TKLFRT show dramatic property improvement with LFRT. Under a tensile load, this
is likely due to the improved adhesion at fiber/matrix interface also the reinforcement of the kenaf fiber results in
a more efficient stress transfer from the matrix to the
reinforced fibers.
3.2 Impact Test
Isod impact test methods were conducted according
to the ASTMD256-04 standard [12]. Six samples with
specified dimensions and defined notches were prepared
and the results were compared with LFRT material in Figure 6. The density of the hybrid is slightly higher than
LFRT materials. While comparing the izod test results it’s
proven that KLFRT having challenging strength to LFRT.
Impact strength of the KLFRT has to be improved considerably to compete with LFRT. Though the poor impact
strength of KLFRT restricts their use in structural applications were high impact strength is required, they can replace engineering plastics in applications where tensile and
flexural properties are important than the impact strength.
Table 1. Material properties of hybrid materials
Material Density
Kenaf
Glass
1.4
2.5
Strength
284-800
2000-3000
Modulus Elongation at
(GPa)
Break (%)
21-60
70
1.6
2.5
277
Figure 5. (a) Tensile modulus; (b) Tensile strength.
Figure 4. (a) Tested specimens; (b) Three-point bending machine.
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S. Jeyanthi and J. Janci Rani
3.3 Flexural Strength Analysis
The specimens were tested by a calibrated AUTOGRAPH-AGS-2003 testing machine. The flexural strength
was conducted according to the ASTM D790 (3 point
bending) [13] standard as shown in Figure 7. The five
specimens with desired dimensions and velocity of 10
mm/min were tested.
The testing was conducted for various span length
like 100 mm, 80 mm and 60 mm.
The sbh flexural strength, namely the maximum
stress at break, is calculated using the formula
(1)
where sbh the flexural strength, M is the maximum
bending moment in the specimen, K is the cross-sectional coefficient. Taking the moment and the crosssectional coefficient:
Figure 6. (a) Impact property; (b) Density.
(2)
(3)
After simplifying the equations (2) and (3) above formula of the flexural modulus becomes
(4)
where sbh in MPa, F is the breaking force in Newton, L
is the support distance in mm, b is the width of specimen in mm, h is the thickness of specimen in mm. By
substituting the values in equation (4) the flexural modulas values were obtained and the graphs were plotted.
The average flexural modulus and strength of five specimens are calculated and plotted in Figure 8. This graph
shows the flexural modulus of the LFRT is 5.6 GPa [6].
It is essential for the bumper materials to have the flexural modulus more than 2.1 GPa [14]. Due to the matrix
and fibre orientation of the Long Kenaf fiber the flexural strength and the flexural modulus of the TKLFRT
material were higher than the LFRT and KLFRT.
The results for flexural modulus are reasonably consistent for the three different span length in Figure 9
shows the flexural analysis of the specimens for 60 mm
span length, Figures 10 and 11 shows the graph of the
span length 80 mm and 100 mm. from the above graphs
the TKLFRT shows challenging strength compare to
LFRT and KLFRT. Hence its clearly proven that the
twisted kenaf fiber can help to increase the flexural
modulus and strength of LFRT by hybridation with natural fibers.
4. Conclusion
Figure 7. Three-point bending. 1: load probe, 2: support, 3:
specimen, h: thickness of specimen, L: support distance.
This study focused on the mechanical properties of a
hybrid kenaf/glass reinforced composites for utilization
in passenger car bumper beam. A twisted kenaf hybrid
material, which is fabricated by hot impregnation method present a good mechanical properties. The comparison charts shows some mechanical advantages compare
to LFRT bumper beam material. This implies that a hybrid kenaf/glass reinforced material could be utilized in
Improving Mechanical Properties by KENAF Natural Long Fiber Reinforced Composite for Automotive Structures
279
Figure 8. (a) Flexural modulus; (b) Flexural strength.
Figure 10. Flexural analysis for 80 mm span.
Figure 9. Flexural analysis for 60 mm span.
automotive structural components such as bumper beams
and front end modules. More over impact properties could
be improved by optimizing the structural parameters like
thickness, beam curvature, and strengthening ribs.
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Manuscript Received: Sep. 14, 2011
Accepted: Dec. 2, 2011