The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015
DOI Number: 10.6567/IFToMM.14TH.WC.OS18.010
Static and Kinematic Friction Coefficients of Carbon Fiber Binded Brush
and improvement of its wear resistance
Noritsugu Umehara1
Nagoya University
Nagoya, Japan
Tsukasa Isogai
Nagoya University
Nagoya, Japan
Yuka Ohtsuka
Nagoya University
Nagoya, Japan
Takayuki Tokoroyama
Akita University
Akita, Japan
Abstract: Carbon fiber has not only high strength property but
also flexible under applied load. In order to develop a new
tribology material from carbon fibers, two types of carbon fiber
binded brushs as a straight type and a looped type are fabricated
and evaluated of friction and wear properties. After the
measurement of friction at the starting of sliding, static
friction coefficients of both type of carbon fiber binded
brushs are almost the same as kinematic friction
coefficient even if conventional metals show larger static
friction than kinematic one. From the results of friction
properties of the different overhang length and sliding
direction, it can be considered that elastic deformation is
important to show specific friction property. Also wear
resistance of carbon fiber binded brush is observed.
Straight type carbon fiber binded brush shows large
specific wear rate as 10-3 mm3/Nm. In order to overcome
this wear issue, looped type one is proposed. This new
looped type carbon fiber binded brush shows much
smaller specific wear rate as around 10-4 mm3/Nm than
straight type. Also this new looped type one shows the
same specific friction property as static friction coefficient
s is almost the same as the kinematic friction coefficient
k.
Fig. 1 Straight type
carbon fiber binded brush specimen
Gap
Round bar
8
Keywords: Carbon fiber, Static friction, Kinematic friction, Wear
I. Introduction
Carbon fiber is one of the special high strength materials
that would have low friction if the crystalline structure
changes to slippery material as a graphite.
The friction properties of side wall of carbon fiber
have already been measured and discussed [1, 2].
However if the carbon fibers were binded and made a
carbon fiber binded brush, the friction properties of the
end of the carbon fiber binded brush were not shown
clearly. The fiber binded brush should show special
friction properties especially for the friction stage at the
start of sliding because of the easy elastic deformation of
fibers. Also wear properties of the carbon fiber binded
brush was anticipated to show the large amount of wear of
counter material and itself. So we introduce the loopedtype carbon fiber binded brush to prevent from cutting
wear of counter material and itself.
II. Experimental Apparatus and Procedure
Figure 1 shows the straight type carbon fiber binded brush.
A carbon fiber tow consists of a large number of carbon
filaments. The large number of carbon fiber tows were
binded to make the straight brush by a heat shrink tube
and the tube was fixed with a metal jig as shown in Fig. 1.
1
[email protected]
Overhang length Overhang length Overhang length Hexagon head bolt
(l = 0 mm)
(l = 1mm)
(l = 3mm)
Fig. 2 Looped type carbon fiber binded
brush specimen
x
y
Leaf spring
z
Pin specimen
Block specimen
Z-stage
Strain gauge
Y-stage
X-stage
Fig. 3 Reciprocating type friction tester of
the carbon fiber binded brush that slid
against block specimen
Figure 2 shows the looped type carbon fiber binded brush.
Both ends of cut carbon fiber were fixed with plates by
screw bolts. In order to control the stiffness of brush,
overhang length of the brush were varied as 0 mm, 1mm
and 3mm as shown in Fig.2. Block specimens are Al alloy
and PTFE that surface roughness is 0.2 mRa.
Friction tests are conducted using the reciprocating
tribometer shown in Fig.3. Block specimen is clamped on
the X stage and cylinder specimen of 6 mm diameter fixed
on the end of leaf springs attached to the Z stage. Friction
test are conducted in the means arbitrary normal load is
applied by shifting the Z stage and moving X stage by a
stepping motor. Normal loads and friction forces are
measured by strain gauge load cells attached to leaf
springs. Normal load is 0.3, 0.5 and 0.7 N. The stroke of
reciprocating motion is 15 mm. Maximum sliding speed is
5.0 mm/s.
III. Experimental Results and Discussion
A. Static and kinematic friction coefficient of straight
type carbon fiber binded brush
Figure 4 shows the typical friction behavior of straight
type carbon fiber bided brush starting to slide against
PTFE block specimen with the reciprocating type
friction teste as shown in Fig.3. Also friction behavior
of brass and Al alloy pins are described. From this
figure, it can be seen that both metal pins show the
large static friction compared to the kinematic friction.
On the other hand, straight type carbon fiber brush
shows no large static friction compared to the
kinematic friction.
Figure 5 shows comparison of s/k ratio of
straight carbon fiber binded brush pin, Brass pin and
Al alloy pin against PTFE block specimen under
various normal loads. s and k shows static and
kinematic friction coefficients, respectively. It can be
seen that the straight type carbon fiber binded brush
shows that s/k ratio is about 1. Normally static
friction is larger than kinematic friction. However this
straight type carbon fiber binding brush showed that
static friction was the same as the kinematic friction.
Theses specific friction properties would be expected
for the application of no stick-slip slider.
B. Wear properties of straight type carbon fiber
binding brush
The wear property of straight type carbon fiber binded
brush and counter material were observed with pin-ondisk type tribotester as shown in Fig.6. Counter disk
materials are Al alloy, PTFE and glass. The hardness
of these materials is 130 MPa, 6.1 MPa and 447 MPa,
respectively. In wear test, normal load, sliding speed,
sliding distance and environmental condition is 2.6 N,
200 mm/s, 500 ma and air, respectively. After sliding
wear test under dry condition, specific wear rate of pin
and disk materials are calculated as shown in Fig.7.
From Fig.7, it can be seen that the wear rate of straight
type carbon fiber bided brush is quite large as the order
of 10-3 mm3/Nm. This order of wear rate is quite huge.
On the other hand, the wear rate of disk material is the
order of 10-4 mm3/Nm. From the observation results of
wear surface of straight type carbon fiber binded brush
as shown in Fig. 8, it can be seen that tip of carbon
fibers were broken and wear debris of counter
materials were filled in the space of carbon fibers that
means the strong abrasion ability of carbon fiber to
counter materials. So we should overcome the issue of
large wear of straight type carbon fiber binded brush.
Fig. 4 Variation of friction force during
sliding for the carbon fiber binded brush
that started to slide against PTFE block
specimen
Fig. 5 Comparison of s/k ratio of straight
carbon fiber binded brush pin, Brass pin
and Al alloy pin against PTFE block
specimen under various normal load
Fig. 6. Pin-od-Disk type tribotester for
straight type carbon fiber binded brush
against Al alloy, PTFE and glass disk
C. Introduction of looped type carbon fiber binding
brush for high wear resistance
In order to overcome the issue of large wear of straight
type carbon binded brush, looped type carbon fiber
binded brush was developed as shown in Fig. 2.
At first, specific wear rate of looped type and
straight type were compared as shown in Fig.9. These
wear tests were carried out for the different sliding
direction of looped one against carbon fiber direction
as 0o and 90o. It can be seen that from this figure that
looped one shows smaller specific wear rate than
straight one by 1/15 for both sliding direction as 0o and
90o. Also specific wear amount of counter material as
Al alloy was not increased a lot. So it was found that
looped type can reduce wear of carbon fiber brush and
counter material so well.
D. Static and kinematic friction coefficient of looped
type carbon fiber binded brush
Looped type one showed better wear resistance than
straight one. In the next, we should check the specific
friction property especially for the uniform friction
coefficient in static and kinematic friction coefficients.
Figure 10 (a)-(c) show the variation of friction
force of looped type carbon fiber binded brush sliding
against Al alloy block specimen when sliding is started
and transits to the stable sliding condition for different
normal load as 0.3 N, 0.5 N and 0.7 N, respectively. It
can be seen from this figure that there are no
distinguished peaks of static friction for various
normal load sliding condition.
Figure 11 shows static and kinematic friction
coefficients of looped type carbon fiber binded brush
under various normal load. It can be seen that static
friction coefficient s is slightly larger than kinematic
friction coefficient k ratio under various normal load.
However the difference of s and k was not so much.
It means that the specific friction property of carbon
fiber binded brush was kept for looped type one.
E. Effect of overhang length and sliding direction on
the ratio of static and kinematic friction coefficient
of looped type carbon fiber binded brush
Figure 12 shows the effect of overhand length of
carbon fiber on the ratio of static friction coefficient s
to kinematic friction coefficient k sliding against Al
alloy block with various overhang length of carbon
fiber as 0 mm, 1 mm and 3 mm under various normal
loads. It can be seen that enough overhang length is
necessary to have specific friction property as the s/k
ratio is about 1. When the overhang length is 0 mm, it
can be considered that the elastic deformation of
looped carbon fiber is not enough to keep friction
coefficient.
Figure 13 shows the effect of sliding direction of
looped type carbon fiber binded brush against fiber
direction on the ratio of static friction coefficient s to
kinematic friction coefficient k sliding against Al
alloy block under various normal loads. It can be seen
that 90 degree is better to keep the specific friction
Fig. 7. Specific wear rate of pin and disk
materials after pin-on-disk sliding wear test
in air
Fig. 8 SEM image of wear surface of
straight type carbon fiber binded brush after
sliding wear test
Fig. 9 Specific wear rates of looped and
straight types carbon fiber binding brush
and counter material of Al alloy
property of fiber brush as s/k ratio is about 1. This
tendency also shows the elastic deformation of looped
carbon fiber is in important to keep friction coefficient
at the stage of starting of sliding.
Fig. 11 Static and kinematic friction
coefficients of looped type carbon fiber
binded brush under various normal load
Fig. 12 The ratio of static friction
coefficient s to kinematic friction
coefficient k under different overhang
length of fiber as 0 mm, 1 mm and 3 mm.
Fig. 10 The friction test results of carbon
fiber brash (overhand length: l = 3 mm)
sliding against Al alloy block with normal
load at (a) 0.3 N, (b) 0.5 N and (c) 0.7 N
Fig. 13 The ratio of static friction
coefficient s to kinematic friction
coefficient k under different sliding
direction to fiber direction as 0o and 90o
IV. Conclusions
In order to develop a new tribology material from carbon
fibers, two types of carbon fiber binded brush as straight
and looped types are fabricated and evaluated of friction
and wear properties. Obtained main results are follows:
(1) After the measurement of friction at initial sliding
stage, static friction coefficients of both type of carbon
fiber binded brush is almost the same as kinematic friction
coefficient even if conventional metals show larger static
friction than kinematic one.
(2) Wear resistance of carbon fiber binded brush is
evaluated. Straight type carbon fiber binded brush shows
large specific wear rate as 10-3 mm3/Nm. In order to
overcome this wear issue, looped type one is proposed.
This new looped type carbon fiber binded brush shows
much smaller specific wear rate as around 10-4 mm3/Nm
than straight type. Also this new looped type one shows
the same specific friction property as static friction
coefficient s is almost the same as the kinematic friction
coefficient k.
Acknowledgment
The authors gratefully acknowledge the funding by the
Ministry of Education, Science, Sports and Culture as
Grant-in-Aid for Scientific Research (26630040) in Japan.
References
[1] Roselma I.C., Tabor D.. The Friction of Carbon Fiber, J. Phys. D:
Appl. Phys., 9, (1976) , pp.2517-2532.
[2] Cornelissen B, Warnet L, Akkerman, Frictional measurement on
carbon fibre tows: Friction experiments, Composites Part A: Applied
Science and Manufacturing, 44, (2013) p.95