WS2/SnS2 Impact Copper-Free Brake Pad Performance

Industrial Lubrication and Tribology
Influence of WS2/SnS2 on the tribological performance of copper-free brake pads
Justin Antonyraj I., Vijay R., Lenin Singaravelu D.,
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Influence of WS2/SnS2 on the tribological
performance of copper-free brake pads
Justin Antonyraj I., Vijay R. and Lenin Singaravelu D.
Department of Production Engineering, National Institute of Technology, Tiruchirappalli, India
Abstract
Purpose – The purpose of this study is to investigate the influence of solid lubricants (tungsten disulfide [WS2]/ Tin disulfide [SnS2]) on the
tribological performance of brake pads.
Design/methodology/approach – In this study, the brake pads were developed by varying the solid lubricants (WS2/SnS2) without varying the
other ingredients. The brake pads were developed as per the industrial procedure. Thermal stability was found for varying ingredients and developed
pads. The physical, mechanical and thermal properties of the developed brake pads were analyzed as per the industrial standards. The tribological
properties were analyzed using the Chase test. The worn surface analysis was done using scanning electron microscopy, elemental mapping and
three-dimensional profile analysis.
Findings – The experimental results indicate that the WS2-based brake pads possess good physical, chemical and mechanical properties with stable
friction and less wear rate due to its good lubrication film formation and thermal stability natures of WS2.
Originality/value – This paper explains the effect of solid lubricants in brake pads for enhancing the tribological performance by the shearing of
crystal structure, thermal stability and tribo film properties of the lubricants.
Keywords Friction, Solid lubricants
Paper type Research paper
1. Introduction
Solid lubricants play a crucial role in maintaining the friction
and wear in friction composites. Graphite is used commonly as
solid lubricants, but it has some disadvantages that it tends to
oxidize and losses its lubricity by evaporating the water
molecules at elevated temperatures. To provide the lubricity at
elevated temperature, metal sulfides are used with and without
the combination of graphite. Metal sulfides stabilizes friction,
reduces wear and sensitivity to both pressure & speed. Its effect
is also about their capacity to be transformed into oxide in the
atmosphere and deposited on the rotor surface, that alters
chemical-physical and tribological properties. Lee et al. (2013)
assessed the Sb2S3 effect on fade resistance by stimulating the
formation of smooth transfer film on the disc surface at an
elevated temperature and showed lower stick-slip than
graphite-based material. Cho et al. (2006) studied the three
different solid lubricants namely graphite, Sb2S3 and MoS2 on
various tribological aspects, and showed that friction material
containing Sb2S3 possess improved fade resistance and friction
stability. Although from the above literature, Sb2S3 was one of
the promising solid lubricants, due to health concerns, it was
banned globally. Many researchers used various other metal
sulfides, namely, MoS2, TiS2 and Cu2S (Österle and Dmitriev,
2016), in which WS2 and SnS2 are unique. Tungsten disulfide
(WS2) is one of the best lubricants that possesses nominal m
and excellent dry condition lubricity than others. Kachhap and
Satapathy (2014) studied the synergetic effect of WS2 with
cenosphere and proved that 10 Wt.% of WS2 with cenosphere
produced effective frictional stability. Tin disulfide (SnS2) is
another metal sulfide, stable up to 400°C and it as
experimentally proved that it could replace Sb2S3 in brake
applications by reducing the metal pickup. Yamamoto and
Hattori (2017) studied the metal pickup in non-asbestos
friction materials by using tin sulfide in combination with a
mixture of tin and tin compounds. It was shown that metal
pickup was reduced, the surface became hard by forming a
cutting edge that resulted in severe abrasion on both mating
surfaces. Although few literature focuses on the WS2 and SnS2
in friction materials, the effect of WS2 and SnS2 as the varying
ingredient is unexplored. Thus, the current study dealt with the
development of WS2/SnS2 based brake pads and to
characterize them as per the standard industrial practice.
2. Materials and methods
2.1 Materials
WS2 and SnS2 of purity 99.9 per cent and F.S.S.S. particle size
of 0.8-1.1 mm are used as varying solid lubricants in this work.
The scanning electron microscopy (SEM) images of the WS2
and SnS2 are shown in Figure 1. The density of WS2 is 7.5 g/cc
The current issue and full text archive of this journal is available on
Emerald Insight at: www.emeraldinsight.com/0036-8792.htm
© Emerald Publishing Limited [ISSN 0036-8792]
[DOI 10.1108/ILT-06-2018-0249]
Authors are thankful to Dr Vijay Subramanian (Alroko GmbH & Co KG)
for providing WS2/SnS2 samples for research purpose. Authors are also
thankful to the well-wisher(s) who have helped in manufacturing and
testing of the composites.
Received 5 July 2018
Revised 9 August 2018
Accepted 10 September 2018

with hexagonal crystal structure, while SnS2 has the density of
4.5 g/cc with rhombohedral crystal structure.
2.2 Formulation and designation of the friction
composites
The developed pads possessed 13 parental ingredients
(94 Wt.%), namely cellulose pulp, aramid pulp, hydrated
lime, straight phenolic resin, NBR, crumb rubber, SiO2,
artificial graphite, exfoliated vermiculite, CaO, tin powder,
synthetic barites, furfural modified friction dust and mica
with a varying ingredient of WS2/SnS2 (6 Wt.%) as
frictional modifier (lubricant). The broad categories of
ingredients in the developed brake pads is given in Table I.
The developed brake pads were designed to suit for Indian
vehicle scenario and are designated as C1 and C2.
2.3 Development of friction composites
The methodology involved in the development of brake pads
are given below in Table II. The sandblasted low carbon steel
back plate was prepared by applying the adhesive uniformly
and was then dried in hot air oven at 60°C for 45 min for
bonding with friction layer.
2.4 Characterizations
Thermal stability was found out using thermo gravimetric
analyis (TGA) in the air atmosphere. An alumina crucible was
used to place the samples, and they were heated from room
temperature to 800°C with 10°C/min heat rate having the gas
flow of 20 mL/min. The temperature vs weight loss per cent
was obtained and given in Figure 2. The density was measured
by Archimedes principle. Hardness was measured using
Rockwell hardness possessing K Scale. The uncured resins
were found out using acetone extraction test with Soxhlet
extraction apparatus. The loss on ignition (LOI) was found by
heating 5-10 g of developed samples in a silica crucible in a
muffle furnace maintained at 800°C for 2 h. Heat swell was
done by maintaining the sample at 200 6 3°C for about 40 min
in a hot air oven. The sample was soaked in water for 30 min at
room temperature conditions for water swell. The difference in
thickness was measured for both the swell tests and reported.
All the above-said tests were done as per the IS2742 Part-3.
The developed brake pads were heated to 200°C and
maintained at that temperature for 30 min to find out hot shear
strength, while cold shear strength was done at normal room
temperature. The above said shear tests were done as per the
ISO 6312. The porosity of the composites was measured for a
sample size of 25 Â 25 mm as per the JIS D 4418. The
specimen was placed inside the desiccator for 24 hours. After
that the specimen was soaked in a pre-heated oil bath at 90 6 1°
C for 8 h. SAE 90 grade oil was used. The heaters of the heating
mantle were turned off after the stipulated time and cooled in
the oil bath to ambient temperature with the specimen still
inside the oil bath. The excess oil adhering the specimen was
wiped using the filter paper and the final weight of the specimen
was noted. The porosity of the specimen was calculated using
the formula given by equation (1) (Thiyagarajan et al., 2016).
Figure 1 SEM images of (a) WS2 and (b) SnS2
Table I Broad categories of ingredients in the developed brake pads
S.No. Broad Categories Ingredients C1 (weight %) C2 (weight %)
1 Fibers inclusive of additives Aramid Pulp, Hydrated Lime, Cellulose Pulp 13 13
2 Binders (primary, secondary with
additives)
Straight Phenolic Resin, NBR, Crumb
rubber, Calcium Oxide
19 19
3 Friction Modifier (Abrasives and
Lubricants)
Silicon oxide, Artificial graphite, Metallic
Lubricant (inclusive of 6 Wt.%)Ã
22 (WS2)Ã
22 (SnS2)Ã
4 Fillers (Inert and Functional) Exfoliated vermiculite, Tin Powder,
Synthetic Barites, Furfural modified friction
dust, Mica
46 46
Note: Ã
Varying Ingredient
Tribological performance of copper-free brake pads

% Porosity ¼ W2 – W1ð Þ 100=d Â V (1)
where
W1 = Initial weight of specimen (grams);
W2 = Final weight of specimen (grams);
d = density of oil used for testing (g/cc); and
V = Volume of specimen (cc) computed by dividing the
weight of the specimen by the density of the specimen
measured.
The tribological characteristics namely fade, recovery and wear
were measured in Chase testing machine as per the IS2742
Part-4 for the developed brake pad specimen size of 25 Â 25
mm, that slides against cast iron drum of 280 mm diameter.
The drum was polished using 320 grit size abrasive paper before
the commencement of the test. Before the commencement of
cycles, burnish cycle was carried out with a load 440 N at 308
rpm for 20 min to establish 95 per cent contact with the mating
surface. The test possess two fade cycles, two recovery cycles,
one wear, initial and final baseline cycles. The parametric details
of the Chase test is given in the Table III (Manoharan et al.,
2017). The coefficient of friction (m) is the outcome which was
recorded for each brake applications in the interfaced computer.
The weight loss and thickness loss of the tested samples were
found out using digital weighing balance possessing 0.001 g
accuracy and digital micrometer possessing 0.01mm least count
respectively. The m normal, m hot, m fade, m recovery, m
performance, and m difference (dm), fade rate and recovery rate
(all in percentage) are calculated as per the literature
(Aranganathan and Bijwe, 2015) Three specimens were tested,
and the consistent values were reported. Five percent standard
error is allowed as per the industrial practice. The worn surface
characteristics were analyzed using the Tescan VEGA 3LMU
Scanning Electron Microscopy (SEM) machine of the Czech
Republic.
3. Results and discussions
3.1 Thermal stability of the varying ingredients and
developed brake pads
In the TGA curve (Figure 2), WS2 was stable up to 450°C, then
there is weight loss of 9 per cent, due to decomposition of disulfide
into tungsten and sulfur with subsequent oxidation to the WO3
formation and sulfur oxides loss as shown in equation (2) below
(Wong et al., 2008):
2WS2 1 7O2 ! 2WO3 1 4SO2 (2)
SnS2 is stable up to 400°C, then it starts oxidation and
completes at 547°C. SnS2 undergoes decomposition and forms
SnO2 and SO2 as shown equation (3). This SO2 gets liberated
into the atmosphere, thereby causing weight loss of about 17.9
per cent:
SnS2 1 2O2 ! SnO2 1 SO2 (3)
The degradation of individual ingredients takes place at
different temperatures plays a significant role in the thermal
stability of the developed brake pads. Phenolic resin
decomposition occurs with the evolution of CO2 between 140
and 175°C. The decomposition of NBR occurs at 200-220°C,
then by crumb rubber at 300°C. At 250°C, cellulose fiber
degradation occurs. Decomposition of friction dust takes place
during 300°C-450°C. The degradation of aramid fiber occurs
between 400-600°C. The rapid degradation of graphite occurs
after 700°C liberating CO and CO2. Rest of the ingredients
namely, CaO, mica, tin and vermiculite are highly stable, and
they do not undergo decomposition before 800°C. The
decomposition of the WS2 takes place around 450°C forming
WoO3 by liberating SO2 for C1, while SnS2 decomposition
takes place at 400°C forming SnO2 by liberating SO2 for C2.
The C1 showed more thermal stability due to the presence of
Table II Methodology involved in development of brake pads
Procedure Conditions
Sequential mixing in plow shear
mixer
Total duration 20 min, shovel and chopper speed: 140 and 2,800 rpm and 1 kg mixer was prepared. The mixer has
one shovel and three choppers
Mixing sequence has three stages: fibers with additives for 3 min followed by frictional modifiers and fillers for 13
min, at last by binders with additives for 4 min
Curing in hydraulic cure press Compression molding machine with six die cavities, Temperature 145°C; Compression Pressure 13 MPa; Each
cavity was filled with 70 g of mixture, Curing Time: 8 min
Seven intermittent breathings for removing volatile gases evolved during curing
Post curing 5.5 h at 160°C in a hot air oven
Finishing Grinding of the baked pad in belt grinder
Figure 2 TGA graphs for the varying ingredients and developed brake
pad

WS2 with char residue of 61 per cent, while the C2 showed char
residue of 56 per cent. The onset, end set, midpoint
temperatures are 450.85°C, 760.1°C and 524.53°C for C1 and
441.10°C, 752°C and 507.28°C for C2.
3.2 Physical, chemical and mechanical properties of the
developed brake pads
The test results of the brake pads are given in Table IV. The
density of C1 composite is higher than C2 because of the
presence of denser WS2 in its formulation. In general, higher
the density, higher will be the hardness. This postulate comes
true in the current study, where C1 composite showed higher
hardness. This is due to the close packing nature of the WS2
which increased the hardness. The acetone extraction value of
C1 is less compared to C2, this shows the better curing of the
composites (Thiyagarajan et al., 2016). LOI value of C1 is
higher than C2, which is due to the presence of heat resistant
WS2 in its formulation that prevents excessive weight loss. The
shear strength of C1 composite is higher in both cold and hot
conditions because of its better adhesion with the back plate
due to its better curing of the composite, it can be also inferred
from acetone extraction. Heat and water swell of the C1 is less
compared to C2 which is mainly due to its resistance to heat
and water because of dense WS2 that fills the composite
effectively. In case of porosity, C2 showed little higher porosity
than C1 because as stated above, lower the density, higher will
be porosity (Jaafar et al., 2012). As per the literature findings of
Jaafar et al. (2012) better physical and mechanical properties
don’t alter the brake performance. But in the current study
certain properties are influencing namely hardness were
influencing.
3.3 Tribological characteristics of the developed brake
pads
3.3.1 Fade and recovery characteristics of chase tested composites
The Chase test results shows m values is higher for C1
compared to C2 due to the following reasons. The existence
of lubrication film helps to prevent the pyrolysis of the
polymeric ingredients that decompose and deteriorate m.
Similarly, for C1 the WS2 present in the formulation smears
well over the braking interface which prevents the
degradation of ingredients. Oxidation rate is also important
as braking interface temperature is 400°C, and it is
mandatory for the lubricant to perform well without
compromising friction stability. WS2 is stable up to 450°C,
which is confirmed from the TGA curve shown in Figure 2,
while in case of SnS2, the degradation occurs at 400°C.
Upon oxidation, if the lubricant converts from sulfide to
oxide, then the effect of lubricant is reduced, thereby leading
to deteriorated results as in case of C2 (Österle and
Dmitriev, 2016). The friction stability is found out from the
difference in m (dm) in which lower the difference better the
stability in the current study C1 produced such behavior
compared to C2. Thus, the fade rate of C1 is 1.32 times
lesser compared to C2. The friction values of C2 is also
lower, that could be due to the presence of aramid fibers that
undergoes degradation and forms a film layer, upon contact
with the mating surface due to inadequate lubrication in C2
by SnS2. Another possible reason for the reduction in m for
both the composites during the fade cycle is due to the
overloading of load bearing elements both mechanically and
thermally, leading to a redistribution of input shear stress
generated. These stresses get dissipated through thermal
overloading of the contacting asperities leading to failure of
the same, thereby reducing to the desired m. The recovery
performance of the composites remained well above 100 per
cent. On cooling, the wear debris present on the surface gets
entrapped in the interface and also exposes the hard layer
underneath thereby restoring the m by rolling-abrasion
mechanism, which can be evident from the SEM studies 4
(a-d). Also, the increase in real contact eventually leads to
increased friction value as shown in C1. Thus mr is more
when compared to mf as shown in Figure 3(a). In this study,
the recovery rate for C1 is 1.05 times higher than C2 as
Table III Experimental procedure of the Chase test as per IS 2742 part-4 standards
Stages Speed (rpm)
Temp (°C)
Load (N)
On time Off time
No. of Applications Heatermin max min sec sec
Burnish 308 – 93 440 20 – – 1 Off
Baseline-I 411 82 104 660 – 10 – 20 Off
Fade-I 411 82 289 660 10 – – 1 On
Recovery-I 411 261 93 660 – 10 – 1 Off
Wear 411 193 204 660 – 20 10 100 Off
Fade-II 411 82 345 660 10 – – 1 On
Recovery-II 411 317 93 660 – 10 – 1 Off
Baseline-II 411 82 104 660 – 10 20 20 Off
Table IV Test results of physical, chemical and mechanical properties of
the developed brake pads
Sr. No. Properties Unit Test Standards C1 C2
1 Density g/cc IS 2742 PART 3 1.964 1.94
2 Hardness HRS 56.7 51.05
3 Acetone Extraction % 2.9 3.1
4 Loss of Ignition % 39.114 40.4885
5 Cold Shear Strength kg/cm2
ISO 6312 27.83 26.37
6 Hot Shear Strength/ kg/cm2
27.9 18.69
7 Heat Swell mm IS 2742 PART 3 0.18 0.2
8 Water Swell mm 0.05 0.09
9 Porosity % JIS D 4418 5.96 6.102

shown in Figure 3(b). The m values for all the cycles is
within the range of 0.3-0.4, the fade (0-30 per cent) and
recovery rate (90-140 per cent) also remained within the IS-
2742 standard (Kachhap and Satapathy, 2017).
3.3.2 Wear characteristics of the chase tested composites
In case of Chase test, the weight loss per cent of C1 is 1.35
times lesser than C2 while the thickness loss is 1.38 times
lesser than C2 as shown in Figure 3(c). The pad surface that
possesses effective lubrication prevents more wear by
forming a good lubrication film over the mating surface.
This type of effect is seen in C1, because of WS2 which
forms an effective film. This film is mainly formed as the
interplanar spacing of WS2 (3.052 A) is more than SnS2
(2.920 A). As a result of shorter interplanar spacing leads in
strong cohesion between the sulfides of the lamella. Due to
the weaker interlayer bonding of WS2, it is easier to be
sheared along the basal plane of the crystalline structure
than SnS2 (Chen et al., 2008). The sheared WS2 particles
become finer and finer than SnS2. This effectively fills the
interfaces by forming continuous tribofilms, which enhance
wear resistance. For higher hardness, the resistance to
penetration is exerted thereby reducing scars. While
composite with lower hardness is vulnerable to plastic
deformation causing more scratches and material removal
leading to more wear. This type of behavior lies in C2 which
has more scratches and fiber pullout as confirmed from SEM
Figure 4(c) and 4(d).
3.4 Worn surface characterizations of the chase tested
samples
The SEM images of C1 shows film formation on the surface of
the Chase tested sample. It shows less abrasion and scars on the
surface which is due to the presence of WS2 that neutralizes the
abrading/grooving mechanism of the counter disc over the
interface as shown in Figure 4(a). It also has some hard
materials which got attached to the surface upon debonding. In
Figure 4(b), the surface has some small cracks which are due to
the temperature effects during braking, and that crack is also
filled with some wear debris that acts as third body and boost
friction. C1 showed little smooth surface than C2 due to the
compaction of stable ingredients. Figure 4(b) shows more
contact plateau formations which is mainly due to
predomination of ironing mechanism (Manoharan et al.,
2017). Also there is no debonding of contact plateaus due to
better lubrication. The literature states that contact plateaus
surface layer consists of nanocrystalline materials which are
generated by mechanical alloying that helps to increase the
wear resistance (Sugozu et al., 2016). SEM Figure 4(c) shows
the presence of cracks, non-continuous films with plowing
action due to the counter surface mating caused by poor
lubrication of SnS2 in C2. This improper lubrication also
promotes the aggressive contact of the surfaces leading to
pullout of fibers and hard materials which are entrapped
between the interfaces leading to abrasive wear. Shear-induced
subsurface damages are seen in C2, which are due to the
removal of hard materials from the surface due to poor strength
Figure 3 (a) m Normal, m Hot, m Fade, m Recovery, m Performance, and m difference (dm); (b) fade rate and recovery rate (all in percentage);
(c) wear loss in percentage (weight and thickness) of the Chase tested composites

caused at that point or thermal fatigue failure softening locally.
These also cause the wear debris formation that further tears
the film exposing the underlayer, leading to more wear and
reducing friction levels at elevated temperatures. In Figure 4(c)
and 4(d), due to improper film formation, there are more
plateau nucleation and debonding with crack propulsion. The
detailed study of wear debris will be the scope of the future
work.
To study the distribution of ingredients present in the
composites elemental mapping for the worn surfaces of C1 and
C2 were done and given in Figures 5 and 6. In Figure 5(a), the
black color patches denote the contact plateaus (Denotation 1),
while the silvery color denotes the back transfer (Denotation 2).
In Figure 5(b), the mapping of W shows evenly distribution of
it throughout the surface. In Figure 5(c), the mapping of S
denotes sulfide, but this S can be from crumb rubber also. To
confirm this map is matched with W map to confirm the WS2.
The C map denotes the aramid fiber and cellulose pulp as it is
concentrated more in the contact plateaus (1) region as shown
in Figure 5(d), but to confirm the back transfer (Denotation 2)
of polymeric materials, O map is used as polymeric ingredients
possess O in its chemical formula, the regions of back transfer
are confirmed from Figure 5(f). The transfer of Fe from the
counter surface causes the Fe to adhere on the sample surface,
as confirmed from Fe mapping given in Figure 5(e). It is also
confirmed with the presence of O elemental map. It is inferred
that less concentration of Fe is seen on the contact plateaus,
while it has more concentration in the back transfer region,
both enabling to boost friction and reduces wear rate. It is also
seen from the Denotation 2 that there is less distribution of ‘C’
in that region denoting less back transfer of polymeric
ingredients.
In case of C2, the trend is different. It has more back transfer
rate than the contact plateaus as shown in Figure 6(a). The
mapping of Sn and S is done to confirm SnS2 as shown in
Figure 6(b) and (c). It was also evident that lubrication was
inadequate in SnS2, which could not protect the plateaus
effectively leading to a reduction in friction and wear resistance.
There exists more back transfer of polymeric ingredients due to
thermal changes occurring while braking as the lubrication was
Figure 4 SEM images of worn surfaces of (a, b) C1 and (c, d) C2
Figure 5 Worn surfaces of C1 composite

not so effective. Thus, the materials got exposed, and the
materials tend to thermal degradation. There is also more iron
debris as visualized from the elemental maps of Fe and O
denoted by 2, which is because of abrasive action caused at the
interface.
4. Conclusions
The brake pads were developed using WS2/SnS2 and tested for
various properties. Based on the test results the following
inferences were drawn:
Thermal stability of WS2 was higher compared to SnS2,
and the same was replicated in the developed brake pads.
WS2-based pads showed higher density, hardness, good
shear strength with fewer swells, LOI and porosity
compared to SnS2 one.
WS2-based pads showed enhanced fade resistance, good
recovery rate and wear resistance during Chase test due to
the shear of intercrystalline structure owing to uniform
lubrication film.
WS2 brake pads-based worn specimen showed good
contact plateau and film formation leading to less
abrasion. The drum debris back transfer was also less
compared to the other composite as confirmed by
Elemental mapping.
Thus, the C1 composite possessing WS2 could be a positive
solution for meeting out the present scenario trend in brake
friction applications.
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20-11-2017.
About the authors
Justin Antony I. is doing PhD (on campus) in the
Department of Production Engineering, National
Institute of Technology, Tiruchirappalli, Tamil Nadu,
India. He completed his BE in Mechanical Engineering
from Anjalai Ammal Mahalingam Engineering College,
Kovilvenni, Tamil Nadu, India, and MTech in
Manufacturing Technology from PRIST University,
Tamil Nadu, India. He is currently working as an
Figure 6 Worn surfaces of C2 composite

Assistant Professor in the Department of Mechanical
Engineering from Vandayar Engineering College,
Thanjavur, Tamil Nadu, India. His areas of expertise are
brake friction materials and welding.
Vijay R. is pursuing PhD in the field of brake friction
materials from the Department of Production Engineering,
National Institute of Technology, Tiruchirappalli, since
2015. He completed his UG in Mechanical Engineering in
2012 and PG in Computer Integrated Manufacturing in
2014 from Anna University, Chennai, India. His areas of
interest are brake friction materials, natural fiber
composites and tribology.
Dr Lenin Singaravelu D. is working as an Associate
Professor in the Department of Production Engineering,
National Institute of Technology Tiruchirappalli, Tamil
Nadu, India. He obtained his PhD in the field of brake friction
materials in Metallurgical and Materials Engineering
Department from IIT Roorkee. He holds an Indian Patent in
his name in the field of brake friction materials. He has
published many research papers in reputed international
journals. He has also presented papers in various conferences
at national and international levels, which took place in India
and abroad. He is currently working in the field of brake
friction materials with many researchers from industries and
academicians across the globe. He has 14 years of research
experience and 10 years of teaching experience. His areas of
expertise are brake friction materials, natural fiber composites,
powder metallurgy, processing of polymer products, non-
conventional machining and shape memory alloys. Lenin
Singaravelu D. is the corresponding author and can be
contacted at: dlenin@nitt.edu
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