International Journal of Mechanical and Materials Engineering (IJMME), Vol. 7 (2012), No. 2, 166-170.
NEW NATURAL FIBRE REINFORCED ALUMINIUM COMPOSITE FOR
AUTOMOTIVE BRAKE PAD
M.A. Maleque1*, A. Atiqah1, R.J. Talib2 and H. Zahurin1
1
Department of Manufacturing and Materials Engineering, International Islamic University Malaysia, Jalan Gombak,
53100 Kuala Lumpur, Malaysia
2
Advanced Materials Centre, SIRIM Berhad, 09000 Kulim, Kedah, Malaysia
*Corresponding author’s E-mail: [email protected]
Received 07 June 2012, Accepted 05 September 2012
brake materials as to fulfill the requirement such as, a
stable friction coefficient and a lower wear rate at various
operating speeds, pressures, temperatures, and
environmental conditions in the automotive sectors
(Wannik et al., 2012; Adebisi et al., 2011). This is
important of having appropriate combination of materials
in order to have those requirements with reasonable cost
of materials. Selection of the material is not an easy task
rather a complex process (Maleque and Dyuti, 2010).
The constituents are often based on experience or a trial
and error method to develop a new formulation in any
application including brake pad material.
ABSTRACT
The aim of this paper is to develop new natural fibre
reinforced aluminium composite for automotive brake
pad application. Four different laboratory formulations
were prepared with varying coconut fibre contents from
0, 5, 10 and 15 volume fraction along with binder,
friction modifiers, abrasive material and solid lubricant
using powder metallurgy technique for the development
of new natural fibre reinforced aluminium composites.
The properties examined are density, porosity,
microstructural analysis, hardness and mechanical
properties using densometer, SEM, hardness tester and
universal testing machine. The better properties in terms
of higher density, lower porosity and higher compressive
strength were obtained from 5 and 10% coconut fiber
composites. The microstructure reveals uniform
distribution of resin and coconut fibre in the matrix. It
can be concluded that 5 and 10% showed better physicomechanical properties compared to other formulations.
Hence, natural coconut fibre is a potential candidate fiber
or filler material for the automotive brake pad material.
Recently, more research has been focused on the
potential of warm compaction method to manufacture
cost-effective and highly-dense brake pad materials
through powder metallurgy (PM) technique (Jones et al.,
1997; Asif et al., 2011). The prime reason for using the
PM process is the possibility of obtaining uniform parts
and reducing tedious and expensive machining processes.
The use of asbestos fiber is decreasing day by day due to
its carcinogenic nature (Rinek and Cowen, 1995). In
order to avoid this carcinogenic asbestos, efforts are
ongoing for the replacement of material. However, no
information is available in literature on the use of
coconut fiber for the formulation of new brake pad
materials. Therefore, new natural fibre brake pad
materials have been formulated with the aim of using
natural coconut fibre as reinforcement filler material in
aluminium matrix for the automotive application.
Keywords: natural fibre, composite material, density,
hardness, compressive strength and microstructures.
1. INTRODUCTION
The braking system is composed of many parts,
including brake pads on each wheel, a master cylinder,
wheel cylinders, and a hydraulic control system.
Different types of brake materials are used in different
braking systems. They are often categorized into four
classes of ingredients: binders, fillers, friction modifiers,
and reinforcements. The brake pads generally consist of
asbestos fibers embedded in polymeric matrix along with
several other ingredients. Over the few years, several
research works have been carried out in the area of
development of asbestos-free brake pads. The use of
bagasse (Aigbodian et al., 2010), palm kernel shell
(Dagwa and Ibhadode, 2006) and palm oil clinker (Zamri
et al., 2011) have been investigated in order to replace
the asbestos-free brake pad material. Current trend in the
research field is to utilization of industrial or agricultural
wastes as a source of raw materials for composite
development (Leman et al., 2008). This will provide
more economical benefit and also environmental
preservation by utilize the waste of natural fibre.
Moreover, many factors should be considered to develop
2. EXPERIMENTAL PROCEDURES
2.1 Raw Materials and Formulations
The main raw materials used in the research were filler,
abrasive, solid lubricant, binder, friction modifier and
additives. The current natural fibre brake pad material
was developed through the process beginning with the
selection of raw materials, weighing, mixing, compacting
and sintering. There are four formulations with different
composition of coconut fibre content. Grouping was
made based on the variation of the coconut fibre material
in the formulation and aluminum used as a matrix
material. However, abrasive, solid lubricant, binder,
friction modifier and lubricants were kept same for all
formulations. Table 1 shows the detail formulation of
four different types of new materials.
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Table 1 Formulation of coconut fibre reinforced
aluminium brake pad materials
Raw Materials
Aluminium
Silicon carbide
Coconut fibre
Graphite
Alumina oxide
Zirconia oxide
Phenolic resin
Total
BP1
0
45
20
0
10
13
2
10
100
2.3 Characterization of Brake Pad Material
Specific gravity measures density which depends upon
the ingredient of the brake material formulation (Talib,
2007; Nirmal et al., 2011). The true density of the
specimen was determined by weighing the specimen on a
digital weighing machine and measuring their volume by
liquid displacement method. The specific gravity formula
is [as Eq. (1)]:
Percentage (%)
BP2
BP3
BP4
5
10
15
40
35
30
20
20
20
5
10
15
10
10
10
13
13
13
2
2
2
10
10
10
100
100
100
(1)
Porosity test was performed in accordance with Japanese
Standard JIS D 4418: 1996. The specimen was cut to a
dimension of 25 mm x 25 mm x 7 mm, then left in a
desiccator for 24 hours at room temperature and cooled
to room temperature in desiccator. The sample was
weighed to the nearest 1 mg before test sample placed in
the test oil in the container and keeps at 90±10 °C for 8
hours. The test sample was left in the oil container for 12
hours until the oil cools to the room temperature and then
withdrawn from the oil container, finally the sample was
rolled on a piece of cloth for 4 to 5 times to remove oil
from the test sample. The sample was weighed again to
the nearest 1 mg.
2.2 Preparation of Material
Four different combinations (such as BP1, BP2, BP3 and
BP4) were prepared with varying coconut fibre contents
from 0, 5, 10 and 15 volume fraction along with binder,
friction modifiers, abrasive material and solid lubricant
using powder metallurgy technique for the development
of natural fibre reinforced aluminium automotive brake
pad materials. The coconut fibre was used as a filler
material in this investigation which is shown in Figure 1.
The Rockwell hardness measurements were conducted
under test load of 980.7 N and steel ball diameter of 12.7
mm using Scale S as stipulated in Malaysian Standard
MS 474 PART 2: 2003. The measurements were
performed at a distance of at least 12 mm from any edge
and uniformly spaced on the surface of the specimen.
The hardness of the sample is the arithmetic mean of the
readings from ten indentations.
The compressive strength test was done using a universal
tensile testing machine. The sample of 25mm x 25mm x
7mm was subjected to compressive force, loaded
continuously until failure occurred. The load at which
failure occurred was then recorded.
For morphology study scanning electron microscopy
(SEM) with EDX was used in order to observe and
investigate the distribution of microstructural features
along with elemental constituents of new natural fibre
reinforced aluminium automotive brake pad materials.
Figure 1 Coconut fibre from waste
This was collected from waste coconut fruit and cleaned
thoroughly using ethanol to remove impurities. It was
crushed and ground to a fine powder (with a range of
100-200 µm), and sieved using crusher machine.
3. RESULTS AND DISCUSSION
3.1 Density and Porosity of Brake Pad Materials
A density measurement test has been carried out on a
laboratory scale to examine the density of the material
after sintering. Density is depends upon the ingredients in
the pad material. A metallic element will have a higher
density than an organic element. Friction elements often
exist in combination of various elements. The results
shown in Figure 2 are the average density of three
readings for each formulation.
Raw materials were blended together in mini mixer to get
evenly distributed ingredients. The mixing process
proposes to get the uniform and homogeneous of
metallurgy powder. All materials were prepared in
powder form. The method for fabrication of brake pad
material was powder metallurgy technique. Graphite4071 was added to minimize fracture in the mixing
process. Then, the pre-form samples were heated to
170°C and at the same time and compacted using 20 kg
load 60 seconds holding time in a hot compaction die.
The compaction was performed using a hydraulic press
machine under a predetermined temperature and
pressure. After removing from compaction, the material
was sintered in an oven at a temperature of 200°C for 5
hours.
It is seen from Figure 2 that the density of the 15 %
coconut fibre composite shows lower than 0% coconut
fibre which have more coconut fibre. However,
formulation BP1 has better properties because of having
higher density with the value of 2.176 g/cm³. This
167
formulation has no coconut fibre in its constituents,
hence, shows higher density of this composite material.
The formulation, BP2 shows the second highest density
with the value of 2.099 g/cm³.
Graph of Hardness Rockwell
Average Hardness
Value(HRS)
Graph of Density
2.176
2.2
Density(g/cm³)
Density
2.099
2.1
1.974
2
25.91
30
20
10
Figure 4 Hardness-Rockwell (HRS) of materials
It can be seen from Figure 4 that the hardness value of 5
% of coconut fibre is higher while S4 (with 15 % coconut
fibre) show lower hardness value. This is because of too
ductile nature of the material as more coconut fibre
content in the composition. Formulation BP2 has the
highest hardness value of 63.92 HRS because of having
more aluminium content used as a matrix. Too hard
results may indicate brittleness while too soft may
indicate higher wear and porosity with lower density.
Varying content of aluminium and coconut fibre will
exhibit different hardness value of the material.
Figure 2 Density of materials
Figure 3 shows the porosity test results for all
formulations of brake pad materials. Porosity plays an
important role in automotive brake pad materials (Sasaki,
1995). The function of porosity is to absorb energy and
heat. This is a very important for the effectiveness of the
brake system. Theoretically, lower porosity will result in
higher friction coefficient and wear rate due to higher
contact areas between the mating surfaces. Brake pad
should have a certain amount of porosity to minimize the
effect of water and oil on the friction coefficient. Sasaki
(1995) found that increasing porosity by more than 10%
could reduce the brake noise.
Graph of Porosity
Porosity (%)
40
1.7
BP1
BP2
BP3
BP4
Brake pad materials formulation
3.3 Mechanical Properties of Brake Pad Materials
Table 2 shows the compressive mechanical properties for
BP2 and BP3 (with 5 and 10 of coconut fibre)
formulations only as other combinations showed very
low strength during testing. The speed used for this
testing is 0.5 mm/sec.
Porosity
22.26
20.25
20
15
43.52
BP1
BP2
BP3
BP4
Brake pad materials formulation
1.8
1.6
25
60
50
Average Hardness
52.18
0
1.821
1.9
63.92
70
13.77
Table 2 Mechanical strength for BP2 and BP3
15.32
Properties
10
Compressive strength (MPa)
Compressive strain (%)
Compressive load (N)
5
0
BP1
BP2
BP3
BP4
Brake pad materials formulation
BP2
5%
414.75
9.11
76742.7
BP3
10%
393.11
11.61
75961.41
The compressive strength value in Table 2 for 5 % of
coconut fibre shows higher with the lower compressive
strain and able to withstand higher compressive load
compared 10% of coconutt fibre composite.The ultimate
strength of the formulation BP2 is corresponds to the
stress of 414.75 MPa. The sample starts to break at stress
of 408.74 MPa. The breaking strength of the sample is
0.66 MPa.
Figure 3 Porosity of materials
Porosity, a gross measure of the pore structure, gives the
fraction of total volume which is void. The pore structure
should be preserved during specimen grinding and
polishing. Distortion by excess working will smear
material over the pores, giving the appearance of a low
porosity (German, 1997). From the porosity results as
shown in Figure 3 it can be seen that two brake pad
formulations such as, 5 and 10 % of coconut fibre
composite shows lower percentage of porosity compared
to other two.
3.4 Surface Morphology
The surface morphology of the new pad materials was
analyzed using SEM followed by elemental analysis of
the materials using EDX. Figures 5 to 7 showed the SEM
micrographs for BP1, BP2 and BP3 specimens while
Table 3 showed the EDX analysis results.
3.2 Hardness of the Brake Pad Materials
Figure 4 shows the hardness values of the four
formulations brake pad materials.
Formulation BP1 (as in Figure 5) showed that the
aluminium clumps with graphite and zirconium oxide
168
and corresponding EDX analysis (in Table 3) showed
that this formulation content more aluminium element.
size and weight of particles or elements are also
contributed to heterogeneous distribution. Besides, it is
evident that there is no such thing as a typical brake
friction composition because a composition that can
represent the majority of the brake pad in existence will
not be accurate. Morphology of the structure also might
change due to sintering of material at different
temperatures.
On the other hand, formulation BP2 (as in Figure 6)
showed that the resin binder is in dark region together
with alumina oxide and the EDX analysis showed that
this formulation content less aluminium element
compared to formulation S1.
Clumps Aluminum
with Graphite
Graphite
element
(Carbon)
Resin binder
(dark region)
Alumina Oxide
Zirconium
Oxide
Figure 5 SEM microstructure for 0% of coconut fibre
(Magnification 500x)
Figure 7 SEM microstructure for 10% of coconut fibre
(Magnification 500x)
Table 3 Elemental composition based on EDX analysis
Resin binder
(dark region)
Alumina Oxide
Elements
BP1
BP2
BP3
BP4
C K
38.29
40.69
48.36
44.30
Si K
10.79
11.61
16.92
20.34
O K
23.59
19.84
9.08
10.79
Al K
24.83
25.57
23.02
22.00
Zr L
2.50
2.29
2.61
2.56
Total
100
100
100
100
From Table 3, it can be seen that, the amounts of C, Si,
O, Al and Zr are comparable with the amount present for
each constituent before formulation. The atomic
composition had been changed after the samples were
thermally treated through sintering process. Less amount
of aluminium is present in BP4 due to more coconut fibre
in the formulation. Higher amount of aluminum can be
seen in the formulation BP2 followed by BP1.
Figure 6 SEM microstructure for 5% of coconut fibre
(Magnification 500x)
The resin binder in dark region can be seen in Figure 7
along with alumina distribution in white region. The
graphite and coconut fibre content in BP3 formulation
also can be visualized in Figure 7.
From the SEM study it can be postulated in generally
that microstructures of 0 to 10 % of coconut fibre
composites showed the homogeneous distribution of
abrasive, solid lubricant, binder and friction modifier in
the aluminium matrix. This might be only confirmed by
either EDX or XRD. The EDX analysis results of the
present investigation are shown in Table 3 and again
showed very good combination of the elemental
distribution which reflect to the heterogeneous
distribution. Finally, it can be said that the structures
showed the heterogeneously distribution of elements
where they contributed to inconsistent result. Different
4. CONCLUSIONS
From the results and discussion of this work the
following conclusions can be made:
Formulation with 5 and 10 volume fractions of coconut
fibres (BP2 and BP3) have higher density and lower
porosity compared to other formulations.
The compressive strength showed the formulation BP3
(with 10 % coconut fibre) exhibited higher strength to
withstand the load application and higher ability to hold
169
the compressive force. From the morphological study of
the materials, it was found that the coconut fibre well
distributed to the matrix and acts as filler in the friction
materials.
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Leman Z., Sapuan, S.M. Saifol, A.M. Maleque M.A. and
Ahmad, M.M. 2008. Moisture absorption behaviour
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Malaysian Standard.
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It can be concluded that BP2 and BP3 showed almost
similar properties from the four formulations, hence coir
could be a candidate fibre or filler material for the massscale fabrication of asbestos-free brake pad without any
harmful effect.
ACKNOWLEDGEMENT
This work was supported by FRGS research grants
scheme No. FRGS10-027-0146 from Ministry of Higher
Education, Malaysia. Authors are grateful to the
International Islamic University (IIUM) and AMREC,
SIRIM which made this study possible.
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