influence of aramid fibers on tribological behavior …
TRANSCRIPT
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
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PAPER REF: 5540
INFLUENCE OF ARAMID FIBERS ON TRIBOLOGICAL
BEHAVIOR OF PBT
Mihail Botan1, Constantin Georgescu
1, George Catalin Cristea
1, Lorena Deleanu
1(*)
1Faculty of Engineering, “Dunarea de Jos” University of Galati, Galati, Romania
(*)Email: [email protected]
ABSTRACT
This work presents the tribological behavior of PBT (polybuthylene terephthalate) + 10%
aramid fibbers and PBT, when sliding against steel in dry regime in order to point out the
influence of adding fibers. Tests were done on a block-on-ring tribotester, for normal loads of
5 ... 30 N and sliding speeds 0.25 ... 0.75 m/s, for a sliding distance of 5000 m. Based on the
experimental data, the authors recommend the composite for functioning in the tested ranges
for speed and force, as its wear and temperature in contact and friction coefficient are reduced
as compared to polymer.
The wear maps plotted based on the experimental results help to rank the tested materials and
to emphasis several advantages of the composite PBT and 10% wt short aramid fibers: it
allows for decreasing the temperature in contact (as measured at a lateral point of the contact)
with 5...10º C for the highest values of the testing parameters, but for low speed and load the
difference in temperature is almost insensible to the block made of neat polymer; for the
composite, wear is reduced almost twice for F = 15-30 N and all tested speed range; wear of
the composite is less dependent on speed, recommending it for applications with variable
regimes; the friction coefficient is only several percentages higher as compared to that
obtained for the block made of PBT, except for high load and speed (v = 0.75 m/s and F = 30
N), when the friction coefficient increases to 0.32-0.36). The SEM images pointed out a very
particular lumpy transfer, both for polymer and composite, meaning the leading factor is the
matrix material (PBT).
Keywords: PBT, short aramid fibers, block-on-ring test, wear map, friction coefficient.
INTRODUCTION
Researches on polymers and polymeric composites are focused on improving their properties
related to particular applications, including the tribological ones (Stachowiack, 2001),
(Bahadur, 2009), (Samyn, 2009), (Briscoe, 1981), (Thorpe, 1986), (Wardle, 2000), (Besnea,
2014) (Bang, 2004), sensors and aerospace materials (Meguid, 2005).
Polymeric composites with short aramid fibers have become of interest in the research field in
the last decade, both as friction and antifriction materials. For tribological applications,
length/diameter ratio characterizing the aramid fibers introduced in polymeric composites
varies from 20 to 550 µm (Dorigato, 2013). Composites with thermoplastic matrix are
especially used for their low friction coefficient and higher wear resistance as compared to the
neat polymer (Akbarian, 2008), (Arroyo, 2002), (Bijwe, 2006) (Zhu, 2010), (Tang, 2011).
Materials with rigid resins as matrix were tested for applications like brakes (Kim, 2001),
(Larsen, 2007), (Singh, 2015), (Xian, 2006). Shibulal added coated short aramid fibers in a
thermoplastic elastomer (Shibulal, 2011) and Kashani added aramid fibers in an elastomer for
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tires (Kashani, 2009). There are several restrictions in using aramid fibers as reinforcement in
tribological applications: a technological one, caused by the difficulty of molding / processing
mixture with relevant concentration of aramid fibers, the quality of the fiber dispersion, even
under laboratory conditions, and the aramid fiber sensitivity in fluids containing water.
Thermoplastics polymers used as matrix in composites with short aramid fibers included PA
(Botan, 2014), (Gordon, 2009), PP (Maity, 2008), (Arroyo, 2002), PTFE (Qiu, 2015), (Fung,
2005), PS (Mukherjee, 2006), PI (Li, 2009), (Zhao, 2013). Reports on tribology of PBT
composites are few (Kim, 2001), (Larsen, 2007) (Georgescu, 2012) and further investigation
on a mixture like PBT and fibers is necessary for better exploitation its unique set of
properties.
Several studies make comparison among composites with same matrix but different fibers,
including mixture of fibers. Zhao et al. [Zhao, 2013] evaluated friction and wear of
polyimides reinforced with carbon, glass and aramid fibers, under dry sliding against
sandpaper and steel, under three-body abrasive conditions. The best performance was
exhibited by inorganic fiber composites due to the load sharing. Brittle glass fibers have not
contributed to improve wear resistance under abrasive conditions, due to insufficient support
from polyimide matrix.
Short aramid fibers in a polymeric matrix could improve wear of polymeric composites but
tests are required in order to evaluate the particular mix of wear mechanisms and the contact
durability under conditions of the future application. Dorigato and Fambri (Dorigato, 2013)
used regenerated aramid fibers in PA12, pointing out the effect of fiber concentration in the
range of 10...30%, after a synthetic review of mechanical and tribological bahavior of
composites with short aramid fibers, the conclusion being that wear could be improved when
using these materials and their application could include either antifriction or friction
tribosystems, depending on the matrix characteristics. Results with composites with PBT
matrix are promising as concern wear and temperature in contact as compared, for instance, to
PA (Botan, 2014), (Maftei, 2011), (Yu, 1994) (Tang, 2011), (Ioffe, 2011). Other fillers, like
carbon fibers, clay (Hwang, 2010) were added in PBT for improving wear behavior.
Polybuthylene terephthalate is a polymer only recently used as matrix because of
technological reasons in molding parts made of this material, including properties’ control
with the help of thermal treatment. Thus, researches on composites with PBT matrix are few
and the future studies will help to introduce it (as neat polymer or composites) in tribological
and mechanical applications.
MATERIALS AND TESTING METHODOLOGY
The block-on-ring tribotester is often used for characterizing the tribological behavior of a
pair of materials, especially when dealing with polymeric materials sliding against steel
because of block simplicity and high accuracy of the rolling bearing external ring,
characterized by a high quality of surface texture and steel structure. The variables could be
the sliding distance (L), the block material, the specific load (W), the speed (v) and, if the
tribometer has a controlled enclosure, temperature and composition of the environment. Also,
it is easy to compare dry and lubricated regimes.
This study deals with a composite with matrix made of PBT (grade Crastin 6130 NC010 –
DuPont) and 10% wt short aramid fibers (Twaron D1088, 250 µm average length, supplied by
Teijin). The material code is PBX in all figures. For technological reason, the composite
contains 1% wt polyamide 6 (grade Relamid, produced by ICEFS) and 1% wt black carbon.
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
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Samples were obtained by molding at Research Institute for Synthetic Fibers Savinesti
(ICEFS) Romania and they were heat treated.
Table 5 - Studies on block-on-ring tribotester
Authors, year Block material,
Matrix/ fillers
Test parameters (dry regime)
L [m] W [N/mm] v [m/s]
(Li, 2007) PTFE and PI 7.14 ...40 0.424
(Georgescu, 2012) PBT/ glass bead, PTFE 5000, 7500, 1000 1.25 ...7.50 0.25 ... 0.75
(Wannasri, 2009) UHMWPE/ carbon nanotubes 3840 22.85 0.32
(Qiao, 2007) PEEK/ Al2O3 3000 28 0.42
(Jia, 2005) PI, PEEK /carbon fibers 3000 28.5 0.43
(Cong, 2008) PA 3000 7 0.42
(Zheng, 2007) PA6/ braided carbon fiber 1500 8.3...41.6 0.42
Experimental results are difficult to be compared, but qualitative evaluation was taken into
consideration for this work (Table 1). The authors, based on (Maftei, 2011),
(Georgescu, 2012), considered that 5000 m was reliable for pointing out a stable friction and
wear rate, for the tested materials and the test parameter ranges (v = 0.25 m/s, 0.5 m/s and
0.75 m/s, W = 1.25 N/mm, 2.5 N/mm, 3.75 N/mm and 7.5 N/mm).
The geometry of the tribotester is given in Fig. 1. The blocks (16.5 mm × 10 mm × 4 mm)
were cut with the help of a water jet machine, from the mold plates. Figure 2 presents the way
of cutting the blocks from a mold plate; the molding nozzle is positioned in the centre of the
plate. Selected zone have a good dispertion of fibers and central and peripheral zone are
excluded because of high probablity of having a non-uniform dispersion of aramid fibers.
The blocks were dried in an oven immediately after being cut. The other triboelement was the
external ring of the tapered rolling bearing KBS 30202, made of steel grade DIN 100Cr6 (see
Table 2), with 60-62 HRC and Ra = 0.8 µm on the exterior surface.
Fig. 1 - Geometry of the block-on-ring tester Fig. 2 - Cutting of the block from a mold plate
Taking into account that an average stress on the contact is not relevant for evaluating such a
contact between two materials with very different mechanical properties, the maximum
pressure depending on the elasto-plastic behavior of the polymeric block. In order to compare
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some results from literature for block
linear load, this type of contact better characterizing by the linear load:
b
FW = [N/mm]
where F is the normal load, in N,
Table 6 - Chemical composition of steel grade 100Cr6 (DIN 17230) (wt%)
C Si Mn
0.90-1.05 0.15-0.35 0.25-0.45
RESULTS AND CONCLUSIONS
The values for the friction coefficient are good f
4), with lower values for the polymer as compared to the composite
N, but at F=30 N, this parameter is in a close range for both materials.
Fig. 3 - Evolution of friction coefficient in time, for different loads and sliding speeds
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some results from literature for block-on-ring tests (see Table 1), the authors calculated a
linear load, this type of contact better characterizing by the linear load:
[N/mm]
is the normal load, in N, b – the theoretical length of the contact, in [mm]
Chemical composition of steel grade 100Cr6 (DIN 17230) (wt%)
Mn P S Cr
0.45 ≤0.030 ≤0.025 1.35-1.65 ≤0.30
RESULTS AND CONCLUSIONS
The values for the friction coefficient are good for both tested materials (see Fig. 3 and Fig.
), with lower values for the polymer as compared to the composite, for normal load
ameter is in a close range for both materials.
Evolution of friction coefficient in time, for different loads and sliding speeds
, the authors calculated a
[N/mm] (1)
the theoretical length of the contact, in [mm].
Chemical composition of steel grade 100Cr6 (DIN 17230) (wt%)
Ni Cu
≤0.30 ≤0.30
or both tested materials (see Fig. 3 and Fig.
normal loads of 5–15
Evolution of friction coefficient in time, for different loads and sliding speeds
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26
The temperature on the lateral side was monitored with the help of a thermographic camera
and the maximum recorded values
interested in having materials with low temperature in functioning and low influence of load
and speed on this temperature.
Fig. 4 - The influence of normal load and sliding
PROCESSES IN THE SUPERFICIAL LAYERS
Transfer processes are very important in selecting the pair of materials
tribological applications, especially when dealing with polymers
(Stachowiak, 2001), (Czicosh, 2009). Their generation and evolution influence friction and
wear. Transfer processes have to be studied on both triboelements. PBT and its composites
(Georgescu, 2012) have a very particular transfer pro
tribological behavior, as compared to other polymeric composites on steel. SEM images
reveal several aspects due to the combination
and f), abrasive wear (Fig. 5), transfer film
8f), wear debris generation and evolution (Fig. 8b and d).
SEM investigations proved that
polymer or composite: for instance
morphology: belt-like and spiral rod
against steel were adhesive wear and melting flow. The melting flow was not visible on PBT
block due to its better thermal character
a) v = 0.25 m/s
Fig. 5
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
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The temperature on the lateral side was monitored with the help of a thermographic camera
aximum recorded values are points on the maps in Fig. 9. An engineer will be
interested in having materials with low temperature in functioning and low influence of load
.
The influence of normal load and sliding speed on the average and the spead range of
PROCESSES IN THE SUPERFICIAL LAYERS
Transfer processes are very important in selecting the pair of materials
tribological applications, especially when dealing with polymers and their composites
(Czicosh, 2009). Their generation and evolution influence friction and
wear. Transfer processes have to be studied on both triboelements. PBT and its composites
have a very particular transfer process, which differenciate their
tribological behavior, as compared to other polymeric composites on steel. SEM images
aspects due to the combination PBT – aramid fibers: adhesion wear (Fig. 8a, c
and f), abrasive wear (Fig. 5), transfer film (Fig. 8a, b, c and e), fiber degradation (Fig. 7, Fig.
8f), wear debris generation and evolution (Fig. 8b and d).
that (Cong, 2008) wear debris shapes are strongly dependent
instance, PA46 formed two kinds of wear debris with different
like and spiral rod-like wear debris. The main wear mechanisms of PA46
wear and melting flow. The melting flow was not visible on PBT
block due to its better thermal characteristics (Figures 5 and 7).
b) v = 0.5 m/s c) v
- SEM images for blocks made of PBX, F = 15 N
The temperature on the lateral side was monitored with the help of a thermographic camera
. An engineer will be
interested in having materials with low temperature in functioning and low influence of load
average and the spead range of friction coefficient
Transfer processes are very important in selecting the pair of materials involved in a
and their composites
(Czicosh, 2009). Their generation and evolution influence friction and
wear. Transfer processes have to be studied on both triboelements. PBT and its composites
cess, which differenciate their
tribological behavior, as compared to other polymeric composites on steel. SEM images
aramid fibers: adhesion wear (Fig. 8a, c
(Fig. 8a, b, c and e), fiber degradation (Fig. 7, Fig.
ear debris shapes are strongly dependent on
kinds of wear debris with different
The main wear mechanisms of PA46
wear and melting flow. The melting flow was not visible on PBT
c) v = 0.75 m/s
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a) v = 0.5 m/s
Fig. 6
a) v = 0.25 m/s
Fig. 7 - Aramid fibers within the PBT matrix,
Because of their visco-elastic nature, the fibers almost perpendicular to the friction surface do
not remain up the surface, being defo
(Fig. 6b and c), even if the test condition differ from slow speed (v = 0.25 m/s) to high one (v
= 0.75 m/s) (Fig. 7). And the surface of aramid fiber is deformed, printed, but not scrached,
the wear debris have few and small fiber fragments (see Fig. 8c).
Comparing these SEM images to those presented by Chang and Friedrich (Chang, 2013), due
to the elasticity of fibers and to a good adherence of their adherence to the matrix, the fibers
do not remain outside the surface of the matrix and the load distribution would be better. The
fiber detaching from the matrix is taking place especially for fibers that are positioned along
or inclined to the surface (Fig. 6a and Fig. 8d). The surface of the fibers underg
seems to be less influenced by the sliding speed increase (Fig. 7), the fibers being deformed
and not fragmented or scratch by the asperities of the metalic surface. Even if the load
increases from 15 N to 30 N, this does not evidently change
matrix seems to be soften, but it has a good adherence to the fibers, even after testing at F =
30 N.
Few polymers exhibit a contin
(Myshkin, 2005) and high den
polyethylene (UHMWPE). Their similar behavior
profile’ or the absence of side groups in the
have a continuous transfer film on a steel pin (
difficult to investigate this aspect. The majority of polymers and polymer composites exhibit a
‘lumpy transfer’ when sliding against a hard counterface (Wieleba, 2007)
not too “smooth” and this could explain
sliding against. The size of these lumps depends on friction pair of materials, test conditions
and could vary in a large dimensional range (from microns to
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b) v = 0.5 m/s c) v
Fig. 6 - SEM images for blocks made of PBX, F = 15 N
b) v = 0.5 m/s c) v
Aramid fibers within the PBT matrix, F = 30 N, block made of PBX
elastic nature, the fibers almost perpendicular to the friction surface do
not remain up the surface, being deformed when the matrix is torn off from the tribolayer
(Fig. 6b and c), even if the test condition differ from slow speed (v = 0.25 m/s) to high one (v
= 0.75 m/s) (Fig. 7). And the surface of aramid fiber is deformed, printed, but not scrached,
ris have few and small fiber fragments (see Fig. 8c).
Comparing these SEM images to those presented by Chang and Friedrich (Chang, 2013), due
to the elasticity of fibers and to a good adherence of their adherence to the matrix, the fibers
side the surface of the matrix and the load distribution would be better. The
fiber detaching from the matrix is taking place especially for fibers that are positioned along
or inclined to the surface (Fig. 6a and Fig. 8d). The surface of the fibers underg
seems to be less influenced by the sliding speed increase (Fig. 7), the fibers being deformed
and not fragmented or scratch by the asperities of the metalic surface. Even if the load
increases from 15 N to 30 N, this does not evidently change the fibbers behavior. Only the
matrix seems to be soften, but it has a good adherence to the fibers, even after testing at F =
Few polymers exhibit a continuous film transfer, similar to that of PTFE (Stachowiack, 2001),
and high density polyethylene (HDPE) and ultra-high
. Their similar behavior would be caused by a ‘smooth molecular
profile’ or the absence of side groups in the molecular chain. Yet, polyamide was proved to
sfer film on a steel pin (Maftei, 2010), but in actual tribosystems
this aspect. The majority of polymers and polymer composites exhibit a
ing against a hard counterface (Wieleba, 2007). PBT molecule
not too “smooth” and this could explain its tendency not to creep when a metallic surface is
The size of these lumps depends on friction pair of materials, test conditions
and could vary in a large dimensional range (from microns to millimeters) (Fig.
c) v = 0.75 m/s
c) v = 0.75 m/s
PBX
elastic nature, the fibers almost perpendicular to the friction surface do
rmed when the matrix is torn off from the tribolayer
(Fig. 6b and c), even if the test condition differ from slow speed (v = 0.25 m/s) to high one (v
= 0.75 m/s) (Fig. 7). And the surface of aramid fiber is deformed, printed, but not scrached,
Comparing these SEM images to those presented by Chang and Friedrich (Chang, 2013), due
to the elasticity of fibers and to a good adherence of their adherence to the matrix, the fibers
side the surface of the matrix and the load distribution would be better. The
fiber detaching from the matrix is taking place especially for fibers that are positioned along
or inclined to the surface (Fig. 6a and Fig. 8d). The surface of the fibers undergoing the load
seems to be less influenced by the sliding speed increase (Fig. 7), the fibers being deformed
and not fragmented or scratch by the asperities of the metalic surface. Even if the load
the fibbers behavior. Only the
matrix seems to be soften, but it has a good adherence to the fibers, even after testing at F =
(Stachowiack, 2001),
high-molecular weight
be caused by a ‘smooth molecular
Yet, polyamide was proved to
, but in actual tribosystems it is
this aspect. The majority of polymers and polymer composites exhibit a
. PBT molecules are
not to creep when a metallic surface is
The size of these lumps depends on friction pair of materials, test conditions
millimeters) (Fig. 8a). Some
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26
polymer materials have better lubricating properties than others (i.e. PTFE), however,
exhibit low mechanical properties and
polymer matrix, like PEEK (Greco, 2011)
a) lump transfer on the steel ring,
having a variable thickness (block
made of PBX)
d) F = 15 N, v = 0.25 m/s
(block made of PBT)
Due to wear debris generation and fragmentation of the already transferred islands, the dry
regime of a friction couple polymeric material
tribosystem (Myshkin, 2005).
In this study, on both PBT materials, fatigues crac
cracks appear on transferred lumps (see Fig. 8c) and possible detaching of a wear particle will
worsen the surface quality of the ring. Load and speed variation does not appear to give a
strong correlation between film transfer covering area on the steel ring and its thickness, the
islands of polymer adhesion on steel being similar for both polymer and composite (compare
Fig. 8b and Fig. 7a), this conclusion being also pointed out by Laux and Schwartz (Laux,
2013), for different grades of PEEK. A strong correlation does not appear to exist between
film thickness and volumetric wear.
Aramid fibers are not crushed and fragmented as the glass fibers and glass beads do under the
load (Georgescu, 2012), (Maftei, 2010). SEM
aramid fibers from the tribolayer and even the way they are fixed on the steel texture imply a
“drag” of these worn fibers (but not fragmented) along the contact (Fig. 8d and
the friction coefficient to oscillate (see Fig. 3, for load F
individual lands meet, merge and detach, forming a discontinuous transfer film. Analyzing
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
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polymer materials have better lubricating properties than others (i.e. PTFE), however,
mechanical properties and, therefore, they are used as fillers to other more robust
, like PEEK (Greco, 2011), (Li, 2009), (Ye, 2014).
b) wear debris, laminated and
rolled (block made of PBX)
c) detail from a
e) transfer of neat PBT on the steel
ring, F = 15 N, v = 0.25 m/s
f) Aramid fibber, torn off from the
matrix, bent because of the uneven
fixing on the metallic texture,
made PBX,
Fig. 8 - Wear mechanisms
ear debris generation and fragmentation of the already transferred islands, the dry
regime of a friction couple polymeric material – steel should be analyzed as a ‘third body’
In this study, on both PBT materials, fatigues cracks were not noticed, but fatigue micro
cracks appear on transferred lumps (see Fig. 8c) and possible detaching of a wear particle will
worsen the surface quality of the ring. Load and speed variation does not appear to give a
m transfer covering area on the steel ring and its thickness, the
islands of polymer adhesion on steel being similar for both polymer and composite (compare
Fig. 8b and Fig. 7a), this conclusion being also pointed out by Laux and Schwartz (Laux,
different grades of PEEK. A strong correlation does not appear to exist between
film thickness and volumetric wear.
Aramid fibers are not crushed and fragmented as the glass fibers and glass beads do under the
load (Georgescu, 2012), (Maftei, 2010). SEM images reveal the detaching mechanisms of
aramid fibers from the tribolayer and even the way they are fixed on the steel texture imply a
“drag” of these worn fibers (but not fragmented) along the contact (Fig. 8d and
oscillate (see Fig. 3, for load F = 5 N and 30 N). During sliding,
individual lands meet, merge and detach, forming a discontinuous transfer film. Analyzing
polymer materials have better lubricating properties than others (i.e. PTFE), however, they
are used as fillers to other more robust
c) detail from a) (block made of
PBX)
Aramid fibber, torn off from the
bent because of the uneven
fixing on the metallic texture, block
F = 15 N, v = 0.75 m/s
ear debris generation and fragmentation of the already transferred islands, the dry
steel should be analyzed as a ‘third body’
ks were not noticed, but fatigue micro-
cracks appear on transferred lumps (see Fig. 8c) and possible detaching of a wear particle will
worsen the surface quality of the ring. Load and speed variation does not appear to give a
m transfer covering area on the steel ring and its thickness, the
islands of polymer adhesion on steel being similar for both polymer and composite (compare
Fig. 8b and Fig. 7a), this conclusion being also pointed out by Laux and Schwartz (Laux,
different grades of PEEK. A strong correlation does not appear to exist between
Aramid fibers are not crushed and fragmented as the glass fibers and glass beads do under the
images reveal the detaching mechanisms of
aramid fibers from the tribolayer and even the way they are fixed on the steel texture imply a
“drag” of these worn fibers (but not fragmented) along the contact (Fig. 8d and 8f), making
5 N and 30 N). During sliding,
individual lands meet, merge and detach, forming a discontinuous transfer film. Analyzing
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Fig. 8a, 8b and 8c, one may notice a high dynamics of generating, adhering and detaching,
partially or entirely, of the wear debris; big debris are rare but make the friction coefficient to
oscillate.
Wear maps are very useful in comparing tendencies of wear evolution for different materials
sliding on the same surface (here, hardened steel). Figure 9 evidences a lower temperature for
the friction couple with the block made of composite with aramid fibers, for higher speed (0.5
m/s...0.75 m/s) and higher loads (15 N... 30 N). For low values of speed and load, it seems
that the neat polymer also keeps the contact temperature close to that of the composite. Other
parameters will make the selection between the two materials.
The wear maps were plotted using MATLAB R2009b, the wear parameter (mass loss) being
represented for each material as a function of sliding speed and normal force, with the help of
a cubic interpolation.
Fig. 9 - Temperature maps (maximum values on the lateral side of the contact) at the end of the test
Fig. 10 - Wear maps generated with the help of experimental data (sliding distance of 5000 m)
Mass loss of the block is lower for the composite, especially at low speed v = 0.25 m/s (Fig.
10). This could assume that abrasive wear under F = 30 N is more intense for the polymer and
thus, it may be assumed that fibers avoid the polymer to be plough and tear off from the
tribolayers. The composite is sensitive to low load (F = 5 N) and have higher values for the
mass loss because the fibber are easier to be detached from the matrix when normal load is
low.
Proceedings of the 6th International Conference on Mechanics and Materials in Design,
Editors: J.F. Silva Gomes & S.A. Meguid, P.Delgada/Azores, 26-30 July 2015
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CONCLUSIONS
Based on the experimental data, the authors recommend the composite for functioning in the
tested ranges for speed and force, as its wear (see Fig. 10) and temperature in contact (see Fig.
9) are reduced and the friction coefficient is higher only with less 20% as compared to that
exhibits by neat polymer, under the same test conditions.
The wear maps plotted based on the experimental results help to rank the tested materials and
to point out several advantages of a block made of PBX:
• it allows for decreasing the temperature in contact (as measured at the lateral point of the
contact) with 5...10º C for the highest values of the testing parameters (F = 20...30 N and
v = 0.5...0.75 m/s); but, for low speed and load, the difference in temperature is almost
insensible to the block material;
• wear is reduced almost twice for F = 15...30 N and all tested speed range;
• wear is less dependent on speed, recommending the composite for applications with
variable parameter regimes;
• the friction coefficient is only several percentage higher as compared to that obtained for
the block made of PBT, except the higher speed (v = 0.75 m/s).
The SEM images pointed out a very particular lumpy transfer, both for polymer and
composite, meaning the leading factor is the matrix material (PBT).
ACKNOWLEDGMENTS
The work of MIHAIL BOTAN, CONSTANTIN GEORGESCU and LORENA DELEANU
was supported by Project SOP HRD /159/1.5/S/138963 - PERFORM.
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