Optimum Lateral Railway Wheel Flange Radius WithMinimum Wear Rate: Twin Disc Simulation.
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JAYAKUMAR, Subash Chandra CHETAL
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FEM Stress Analysis and the Sealing Performance Prediction of Pipe Flange
pp.486-495
Connections under External Bending Moments and Internal Pressure
Vol.7(2013)
No.4 p.473-
Yoshio TAKAGI, Hiroyasu TORII, Yuya OMIYA, Takashi KOBAYASH,
No.3 p.340-
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Optimum Lateral Railway Wheel Flange Radius WithMinimum Wear Rate: Twin
Disc Simulation
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Bagus BUDIWANTORO, I. Made PARWATA, Wiratmaja PUJA, Satryo
Year 2013
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Released: July 31, 2013
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Journal of Solid Mechanics
and Materials
Engineering
Vol. 7, No. 4, 2013
Optimum Lateral Railway Wheel Flange
Radius WithMinimum Wear Rate: Twin Disc
Simulation*
Bagus BUDIWANTORO**, I. Made PARWATA***, Wiratmaja PUJA**
and Satryo SOEMANTRI**
**Faculty of Mechanical and Aeronautical Engineering, Institute of Technology-Bandung
JalanGanesha 10, Bandung 40132, Indonesia
E-mail: budiwan@edc.ms.itb.ac.id
***Department of Mechanical Engineering,
Faculty of Engineering, Udayana University
Kampus Bukit Jimbaran, Bali–80364, Indonesia
Abstract
An experimental model has been developed to characterize the effect of lateral
radius of curvature to the wear rate of a disc. This is to simulate the wheel-rail
contact wear phenomenon in railway transportation where excessive rail wear
commonly occurs at the curve, and eventually this will cause accidents such as
derailment, etc. The experiment was conducted using two stainless steel discs,
ST37 (0.132% C) and ST60 (0.458% C), with different lateral radius of curvature.
One disc has the radius of 13 mm while the other disc has several variations of the
radius i.e. 16 mm, 18 mm, 20 mm, 22 mm, and 24 mm. The lowest wear rate was
observed for the disc with 22 mm radius while the highest wear rate was observed
for the disc with 16 mm radius.
Key words: Wheel-Rail Contact, Hertzian Contact, Wear Rate, Twin-Disc Test
1. Introduction
*Received 25 Feb., 2013 (No. 13-0096)
[DOI: 10.1299/jmmp.7.x]
An attempt has been made to identify the major factor causing excessive wear in
railway track, and one of the possibilities is the occurrence of non-conformal contact
between the rail gage surface and the wheel flange surface when the train passes the tight
curve. Parwata et.al(1) succeeded in determining the contact pressure and the contact point
during rail-wheel surface contact. The point of contact occurs at the 20 mm radius of
curvature for the wheel and at 13 mm radius of curvature for the rail. The cross sectional
profile of the rail as well as of the wheel consists for several lateral radius of curvature.
Hernandez(2) has predicted that there will be a 30% error if the specimens are both cylinder.
Several twin disc experiments have been performed by some researchers. Fegredo and
Pritchard(3) observed wear rate as a function of contact pressure at 3%, 6%, and 9% creep,
using twin disc (cylinder type) experiment, the specimen dimensions are 35-40 mm
diameter and 10 mm width, one of the cylinder is rotating at 200 rpm while the other is
1.104 times faster. Subsurface crack was observed before and beyond the mild-severe wear
transition zone, and the observed crack is deeper and wider as the creep and contact
pressure is increasing.
Copyright © 2013 by JSME
1
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
Hernandez and Joyce(4) observed the surface contact temperature of both discs with
respect to slip change, and it showed that the temperature is increasing with the increase in
slip. Moreover they conducted a twin disc experiment to simulate the influence of
contaminants to surface adhesion, and the result shows that dry surface will provide strong
adhesion while water and oil will weaken the surface adhesion. Addition of leaves will
provide weaker surface adhesion than of oiled surface. Leaves will also damage the disc
surface, sands will damage wheel and rail surfaces(5). Takikawa and Iriya(6) observed the
occurrence of head check at high rail using twin disc test where 3 materials were used
namely HH340, standard, bainitic and hypereutectoid. The result showed that head check
occurred at the track with radius of curvature smaller than 800 m. Tassini also conducted a
twin disc test to obtain a formula to evaluate the existing railway wear models namely BRR
(British Rail Research), Royal Institute of Technology–Stockholm (KTH), and Sheffield
University (USFD)(7). Parwataet.al.(8) observed the wear model of TanjungEnim – Tarahan
railway track segment, it was excessive wear and therefore an effort is badly needed to
reduce wear rate.
Observation of wear phenomena has also been performed using pin on disc experiment.
Hung-KukOh(9) conducted a pin on disc test with unlubricated specimen loaded constantly
at a certain speed. The results showed that carbon concentration will influence the transition
zone from mild wear to severe wear. Goto and Amamoto(10) observed the wear rate and wear
depth with respect to varied step load using pin on disc test with unlubricated specimen.
Severe wear was observed for high load and mild wear was observed for low load.
Bahrami(11) conducted experiment on AISI H13 steel to obtain wear mechanism, wear track,
and wear debris. The results showed that at a load of 29.4 N the quenched specimen has the
highest wear resistance and the debris consists of a mixture of oxides and plate like metallic
powder. At a load of 98 N the 30-60 minute tempered specimen at T = 600 oC has high wear
resistance and the debris consists of oxides. Viafara and Sinatora(12) conducted a pin on disc
test to observe wear regime transition with respect to material hardness. The wear regime
transition depends on microstructure changes, surface oxidation, and workhardening. Lee(13)
conducted a pin on disc test to observe that wear performance of bainitic steel is worse than
of pearlit steel although the hardness is higher. Langueh(14) developed a numerical approach
to include material inelastic property so that the influence of steel grade difference to rolling
contact fatigue could be observed. Goto(15) observed the wear behaviour of a 0.35% C steel
under unlubricated condition at moist air environment. The loading is stepped, mild wear
was observed for increasing loading while severe wear was observed for decreasing
loading.
In this paper, a twin disc experiment was conducted using the discs as shown in Figure
1. With this type of disc a more accurate wear prediction could be obtained. The material of
disc 1 is medium carbon steel, ST 60 (0.458 % C) and of disc 2 is low carbon steel, ST 37
(0.132 % C). The lateral radius of curvature of disc 1 (lower disc) is fixed at 13 mm while
of disc 2 (upper disc) varies from 16, 18, 20, 22, 24 mm.
2. Experimental set up
Test Specimen
The experiment was conducted using 2 discs with 42 mm diameter, 20 mm width, and
10 mm width of contact surface. The shape and dimension of the disc is shown in Figure
1.Lateral radius of disc 1 (lower disc) is 13 mm while the lateral radius of disc 2 (upper
disc) is varied from 16, 18, 20, 22, and 24 mm. The material of disc 1 is ST60 carbon steel
and for disc 2 is ST37 carbon steel, the material properties are shown in Table 1.
2
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
Table 1.Chemical compositions and mechanical properties of test specimen
Material
Chemical composition (% weight)
C
Mn
Si
P
S
Cr
Mechanical properties
Tensile strength (kg/mm2)
Yield strength (kg/mm2)
Elongation (%)
Average hardness (HV)
ST37
ST60
0.132
0.42
0.209
0.036
0.021
0.059
0.458
0.684
0.251
0.036
0.023
0.034
31.5
22.84
28.9
113.4
67.74
49.12
12.38
165
Figure 1. Test specimen
Apparatus
The experimental set up is shown in Figure 2. Disc 1 (lower disc) is driven at fixed
speed of 149.7 rpm, while disc 2 (upper disc) is driven at several different speed depending
on the amount of slip needed. Contact pressure is delivered through the lower disc by screw
jack equipped with load cells. This apparatus is using 2 electric motors to drive the two
discs independently. Disc 1 is driven at a constant speed of 149.7 rpm while disc 2 is driven
at variable speeds depending on the needed amount of slip. The motors can be driven at any
speed using constant torque inverter. The tangential force of the motor is measured using
load cell. This force is needed to determine the motor torque so that the tangential force
acting on the surface contact can be determined. Contact pressure on the disc is provided by
a spring-jack equipped with a load cell, and the pressure is made constant manually. The
load cells are connected to strain amplifier and then to analog digital converter (ADC). The
ADC signal is transferred to computer to display the measurement results.
3
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
Figure 2. Twin disc experimental set up
3. Experimental Analysis
The formula for determining the maximum contact pressure p0 is taken from Hertz(16),
contact area elliptical half axis can be determined using the following formula:
Longitudinal half axis a:
⁄
(1)
Lateral half axis b:
⁄
(2)
with N is total normal force, while Y1, Y2, and Y3 are defined as the following
(3)
(4)
′
′
(5)
If both of disc materials are the same then the elastic modulus Ew=ER=E and the poisson ratio
vw=vR=v so that Y1=Y2=Y, and then equations (1) and (2) become
⁄
⁄
(6)
(7)
m and n are non-dimensional coefficients based on θ which is defined as
4
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
cos
(8)
where
′
′
2
′
(9)
′
γ is the angle between the normal surfaces containing R1and R2,then the maximum
contact pressure can be determined as
(10)
The values of m and n can be obtained from the table available on reference (16).
Using equation (10), a force of 200 N is needed to obtain a contact pressure of 2000 MPa.
Slip is defined as
(11)
The rotational speed of disc 1 is 149.7 rpm, in order to obtain a slip of 0.2% then the
rotational speed of disc 2 should be 150 rpm.
All tests were performed continuously until upper disc reached 10,000 rotational cycles,
and the tests were conducted under dry condition (unlubricated).
4. Experimental results
The results are shown in the following Figures 3 to 11. Figure 3 shows that the highest
mass loss occurs at the disc with a lateral radius of curvature of 16 mm, then it decreases at
radius of 18, 20, 22 mm and it increases again at radius of 24 mm. The minimum mass loss
is observed at radius of 22 mm.
140
Mass loss (mg)
120
0.2% Slip
10,000 cycles
Dry
100
80
60
40
20
0
14
16
18
20
22
24
26
Radius (mm)
Figure 3. Mass loss with respect of lateral radius of curvature
If mass loss is formulated as wear rate, Figure 4 shows the wear rate with respect to
lateral radius of curvature. Wear rate is defined as mass volume loss per unit sliding path
and per unit contact area(17). The minimum wear rate is observed at lateral radius of 22 mm
and therefore the combination of lateral radius of 13 and 22 mm provides the best sliding
contact performance.
5
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
600
Wear rate (µg/m/mm 2 )
500
0.2% Slip
10,000 cycles
Dry
400
300
200
100
0
14
16
18
20
22
24
26
Radius (mm)
Figure 4. Wear rate with respect to lateral radius of curvature.
The influence of contact force to wear rate is shown in Figure 5, where contact force is
formulated in wear index which is the product of traction force (T) multiplied by slip (γ)
and divided by contact area (A)(18, 19). Contact pressure (MPa) is shown in Figure 5
described as dots. There are two forces acting during disc contact, normal force and
tangential force. Normal force creates contact pressure while tangential force influences
wear index. Figure 5 shows that the combination of lateral radius of 13 and 22 mm provides
the lowest contact pressure and the minimum wear rate.
Figure 5. Wear rate with respect to wear index.
6
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
Observation of surface topology is shown in Figure 6 where the contact surface is rough
with cracks in the vicinity. In the center where high pressure occurs the roughness is much
severe than in the vicinity.
Figure 6.SEM of contact surface of disc 2 with lateral radius of 16 mm.
Figure 7 shows that the subsurface deformation is small while the surface deformation is
large.
Figure 7.Subsurface deformation of disc 2 with lateral radius of 16 mm.
Observation of surface topology of disc 2 with lateral radius of 22 mm is shown in
Figure 8 and it can be seen that the contact surface is smoother than of disc 2 with lateral
radius of 16 mm. The subsurface deformation of the 22 mm radius disc 2 is shown in Figure
9 and it can be seen that the deformation is larger than of 16 mm radius disc 2.
7
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
Figure 8.SEM of contact surface of disc 2 with laateral radius of 22 mm.
Figure 9.Subsurface deformation of disc 2 with laateral radius of 22 mm.
O
Observation
of surface topology and subsurface defoormation for both 22 mm radius
disc 2 and 16 mm radius disc 2 shows the correlation between
b
the intensity of contact
pressuure and the surface damage level. The contact pressurre of 22 mm radius disc 2 (1883
MPa) is lower than of 16 mm radius disc 2 (1986 MPa), seee Figure 5, therefore the surface
damagge of 16 mm radius disc 2 is much severe.
Thhe wear index of 22 mm radius disc 2 (4.08 N/mm2) is higher than of 16 mm radius
disc 2 (1.9 N/mm2), see Figure 5, therefore the subsurface deformation
d
of 22 mm radius disc
2 is laarger due to the contribution of higher tangential force in the wear index formula.
Thheoretical contact pressure for each lateral radius of
o curvature can be determined
using Hertz equation and it is shown in Figure 10. It can be seen that the minimum contact
pressuure occurs for 22 mm radius disc 2.
8
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
1950
Contact Pressure (MPa)
1940
1930
1920
1910
1900
1890
1880
1870
1860
1850
15
17
19
21
23
25
Lateral radius (mm)
Figure 10.Theoretical contact pressure with respect to lateral radius of curvature.
Figure 11 shows wear rate with respect to contact pressure and it can be seen that wear rate
increases with increasing contact pressure, and the minimum wear rate occurs for 22 mm
radius disc 2.
Figure 11. Wear rate with respect to contact pressure.
5. Analysis
In some research on rolling contact phenomena it is common to observe that wear rate
is increased if the contact pressure increases, in some cases the increase is linear and in
other cases it is non-linear. Clayton(20) showed that for pearlitic steel rail the effect is
non-linear while for bainitic steel rail the effect is linear.
Bolton and Clayton(18) showed the influence of contact pressure to wear rate for 4 types
of rails i.e. BS11 (0.53%C), UICA (0.73%C), UICB (0.62%C), and 1% chrome (0.7%C) in
contact with D type wheel (0.65% C). They showed that wear rate increases with the
increase of contact pressure at the same slip condition. Beagley(21) observed the same
phenomena.
Braghinet.al(22) showed that there is an inaccuracy in predicting wear rate at the flange
surface of the wheel, the difference between the predicted wear and the experimental result
9
Journal of Solid Mechanics
and Materials Engineering
Vol. 7, No. 4, 2013
is 30%. The experiment was performed using twin disc (cylindrical) apparatus.
In this research work, it can be seen from Figure 5 and Figure 10 that the observed
contact pressures are very close to the theoretical contact pressure, for example in the case
of 22 mm lateral radius the observed contact pressures are 1890 MPa, 1903 MPa, and 1883
MPa while the theoretical contact pressure is 1855 MPa. The difference is between 1.5 to
2.6 % which is much more accurate than the previous similar research works using twin
disc (cylindrical).
Figure 4 and Figure 11 show the consistency of the research results which describe that
at 22 mm lateral radius the wear rate is minimum and the contact pressure is also minimum,
and this confirms the proportionality between wear rate and contact pressure.
In the previous research work(1) it was shown that during rail-wheel surface contact, the
point of contact occurs at the 20 mm radius of curvature for the wheel and at 13 mm radius
of curvature for the rail. The cross sectional profile of the rail as well as of the wheel
consists for several lateral radius of curvature, commonly ranging from 13 to 24 mm.
6. Conclusion
This research work shows that, within the existing range of variation of lateral radius
i.e. 13 – 24 mm, the lateral radius of curvature of the wheel flange surface influences the
wear behaviour of wheel-rail contact. The research result shows that there is a configuration
of wheel – rail contact which causes least wear as compared to other configuration within
the 13 – 24 mm range of variation. The twin disc test with curved surfaces
(non-cylindrical) shows a more accurate simulation of the real wheel-rail contact
phenomena, since the test can simulate the non-conformal contact between two surfaces
with different radius of curvature.
Acknowledgement
The authors would like to convey their appreciation to the Directorate General of
Higher Education, Ministry of Education & Culture, Indonesia for the provision of research
grant No. 445/SP2H/PP/DP2M/VI/2010 and No. 508/SP2H/PL/Dit.Lintabmas/VII/2011.
References
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
Parwata I. M. et al.Effect of curving speed and mass of railway vehicle to the contact
characteristic on curve track.Int. J. Vehicle Systems Modelling and Testing, vol. 6, pp.
250-267, 2011.
Hernández F. C. R. et al.Mechanical properties and wear performance of premium rail
steels.Wear, vol. 263, pp. 766-772, 2007.
Fegredo C. P. D. M.A Metallographic Examination of Rollers Subjected to Wear
Under Rolling Sliding Conditions.Wear,vol. 49, pp. 67 - 78, 1978.
Gallardo-Hernandez R. L. E.A and Dwyer-Joyce R.S.Temperature in a twin-disc
wheel/rail contact simulation.Tribology International, vol. 39, pp. 1653–1663, 2006.
Gallardo Hernandez R. L. E.A.Twin disc assessment of wheel/rail adhesion.Wear, vol.
265, pp. 1309–1316, 2008.
Takikawa Y. I. M.Laboratory simulations with twin-disc machine on head check.Wear,
vol. 265, pp. 1300–1308, 2008.
Tassini X. Q. N., LewisR., Dwyer-Joyce R., Ariaudo C., Kuka N.A numerical model
of twin disc test arrangement for the evaluation of railway wheel wear prediction
methods.Wear, vol. 268, pp. 660-667, 2010.
Parwata I. M., et al.Keausan Excessive Roda Rel Kereta Api Babaranjang Jalur
Tajungenim ke Tarahan, 2012.
Hung-Kuk Oh K.-H. Y. and, Hak Yun Kim. The in¯uence of atmospheric humidity on
the friction and wear of carbon steels.Journal of Materials Processing Technology,
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and Materials Engineering
Vol. 7, No. 4, 2013
vol. 95, p. 10-16, 1999.
(10) Hozumi GotoY. A.Effect of varying load on wear resistance of carbon steel under
unlubricated conditions. Wear,vol. 254, pp. 1256–1266, 2003.
(11) Bahramia S. H. M. A. A., Golozarb M.A., Shamanianb M., Varahrama N.Effects of
conventional heat treatment on wear resistance of AISI H13 tool steel.Wear,vol. 258,
pp. 846–851, 2005.
(12) Viáfara A. S. C.C.Influence of hardness of the harder body on wear regime transition
in a sliding pair of steels.Wear, vol. 267, pp. 425–432, 2009.
(13) Ki Myung Lee A. A. P.Microscale experimental and modeling wear studies of rail
steels.Wear, vol. 271, pp. 1174– 1180, 2011.
(14) Langueha J.-F. B. A., Charkaluka E., Dufrénoya P., Demillye F.Influence of the steel
grades on rolling contact fatigue of railway wheels.Procedia Engineering vol. 10, pp.
2627–2632, 2011.
(15) Goto Y. A. H.Improvement of wear resistance for carbon steel under unlubricated
sliding and variable loading conditions.Wear, vol. 270, pp. 725–736, 2011.
(16) Garg V. K. and Dukkipati R. V.Dynamics of Railway Vehicle Systems. Orlando:
Academic Press, 1984.
(17) Lewis R. and Olofsson U.Mapping rail wear regimes and transitions.Wear, vol. 257,
pp. 721–729, 2004.
(18) Bolton P. J. and Clayton P.Rolling—sliding wear damage in rail and tyre steels.Wear,
vol. 93, pp. 145-165, 1984.
(19) Lewis R. and Dwyer-JoyceR. S.Wear mechanisms and transitions in railway wheel
steels.Journal of Engineering Tribology, vol. 218, pp. 467-478, 2004.
(20) Clayton P.Predicting the wear of rails on curves from laboratory data. Wear, vol.
181-183, pp. 11-19, 1995.
(21) Beagley T. M.Severe Wear of Rolling/Sliding Contacts. Wear, vol. 36, pp. 317-335,
1976.
(22) Braghin F., et al.A mathematical model to predict railway wheel profile evolution due
to wear.Wear, vol. 261, pp. 1253-1264, 2006.
11
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Sardari Lal MANNAN, Mannarathu Devasia MATHEW, Tammana
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JAYAKUMAR, Subash Chandra CHETAL
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Journal of Solid Mechanics and
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FEM Stress Analysis and the Sealing Performance Prediction of Pipe Flange
pp.486-495
Connections under External Bending Moments and Internal Pressure
Vol.7(2013)
No.4 p.473-
Yoshio TAKAGI, Hiroyasu TORII, Yuya OMIYA, Takashi KOBAYASH,
No.3 p.340-
Toshiyuki SAWA
No.2 p.124-
Released: July 31, 2013
Abstract
No.1 p.1-
Recommend by email
Full Text PDF[596K]
Vol.6(2012)
Vol.5(2011)
Operational Info
・J-STAGE will undergo
Vol.3(2009)
Optimum Lateral Railway Wheel Flange Radius WithMinimum Wear Rate: Twin
Disc Simulation
Vol.2(2008)
Bagus BUDIWANTORO, I. Made PARWATA, Wiratmaja PUJA, Satryo
Year 2013
Vol.1(2007)
SOEMANTRI
Sep 28(Sat) 10:00 -
Vol.4(2010)
pp.496-506
scheduled maintenance as
follows.
15:30(JST) (Sep 28(Sat) 01:00
Released: July 31, 2013
Abstract
Full Text PDF[972K]
- 06:30(GMT))
Details
Joint Strength and Their Improvement of Type 5052 Aluminum Alloy
pp.507-519
Autocompleting Friction Welded Joint
Masaaki KIMURA, Masahiro KUSAKA, Koichi KAIZU
Released: July 31, 2013
Abstract
Full Text PDF[3410K]
1 - 4 / 4 Articles.
1
Top of this Page
Edited and published by : The Japan Society of Mechanical Engineers Produced and listed by : Sanbi Printing Co., Ltd.
1 of 1
9/20/2013 9:57 PM
Journal of Solid Mechanics
and Materials
Engineering
Vol. 7, No. 4, 2013
Optimum Lateral Railway Wheel Flange
Radius WithMinimum Wear Rate: Twin Disc
Simulation*
Bagus BUDIWANTORO**, I. Made PARWATA***, Wiratmaja PUJA**
and Satryo SOEMANTRI**
**Faculty of Mechanical and Aeronautical Engineering, Institute of Technology-Bandung
JalanGanesha 10, Bandung 40132, Indonesia
E-mail: budiwan@edc.ms.itb.ac.id
***Department of Mechanical Engineering,
Faculty of Engineering, Udayana University
Kampus Bukit Jimbaran, Bali–80364, Indonesia
Abstract
An experimental model has been developed to characterize the effect of lateral
radius of curvature to the wear rate of a disc. This is to simulate the wheel-rail
contact wear phenomenon in railway transportation where excessive rail wear
commonly occurs at the curve, and eventually this will cause accidents such as
derailment, etc. The experiment was conducted using two stainless steel discs,
ST37 (0.132% C) and ST60 (0.458% C), with different lateral radius of curvature.
One disc has the radius of 13 mm while the other disc has several variations of the
radius i.e. 16 mm, 18 mm, 20 mm, 22 mm, and 24 mm. The lowest wear rate was
observed for the disc with 22 mm radius while the highest wear rate was observed
for the disc with 16 mm radius.
Key words: Wheel-Rail Contact, Hertzian Contact, Wear Rate, Twin-Disc Test
1. Introduction
*Received 25 Feb., 2013 (No. 13-0096)
[DOI: 10.1299/jmmp.7.x]
An attempt has been made to identify the major factor causing excessive wear in
railway track, and one of the possibilities is the occurrence of non-conformal contact
between the rail gage surface and the wheel flange surface when the train passes the tight
curve. Parwata et.al(1) succeeded in determining the contact pressure and the contact point
during rail-wheel surface contact. The point of contact occurs at the 20 mm radius of
curvature for the wheel and at 13 mm radius of curvature for the rail. The cross sectional
profile of the rail as well as of the wheel consists for several lateral radius of curvature.
Hernandez(2) has predicted that there will be a 30% error if the specimens are both cylinder.
Several twin disc experiments have been performed by some researchers. Fegredo and
Pritchard(3) observed wear rate as a function of contact pressure at 3%, 6%, and 9% creep,
using twin disc (cylinder type) experiment, the specimen dimensions are 35-40 mm
diameter and 10 mm width, one of the cylinder is rotating at 200 rpm while the other is
1.104 times faster. Subsurface crack was observed before and beyond the mild-severe wear
transition zone, and the observed crack is deeper and wider as the creep and contact
pressure is increasing.
Copyright © 2013 by JSME
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Hernandez and Joyce(4) observed the surface contact temperature of both discs with
respect to slip change, and it showed that the temperature is increasing with the increase in
slip. Moreover they conducted a twin disc experiment to simulate the influence of
contaminants to surface adhesion, and the result shows that dry surface will provide strong
adhesion while water and oil will weaken the surface adhesion. Addition of leaves will
provide weaker surface adhesion than of oiled surface. Leaves will also damage the disc
surface, sands will damage wheel and rail surfaces(5). Takikawa and Iriya(6) observed the
occurrence of head check at high rail using twin disc test where 3 materials were used
namely HH340, standard, bainitic and hypereutectoid. The result showed that head check
occurred at the track with radius of curvature smaller than 800 m. Tassini also conducted a
twin disc test to obtain a formula to evaluate the existing railway wear models namely BRR
(British Rail Research), Royal Institute of Technology–Stockholm (KTH), and Sheffield
University (USFD)(7). Parwataet.al.(8) observed the wear model of TanjungEnim – Tarahan
railway track segment, it was excessive wear and therefore an effort is badly needed to
reduce wear rate.
Observation of wear phenomena has also been performed using pin on disc experiment.
Hung-KukOh(9) conducted a pin on disc test with unlubricated specimen loaded constantly
at a certain speed. The results showed that carbon concentration will influence the transition
zone from mild wear to severe wear. Goto and Amamoto(10) observed the wear rate and wear
depth with respect to varied step load using pin on disc test with unlubricated specimen.
Severe wear was observed for high load and mild wear was observed for low load.
Bahrami(11) conducted experiment on AISI H13 steel to obtain wear mechanism, wear track,
and wear debris. The results showed that at a load of 29.4 N the quenched specimen has the
highest wear resistance and the debris consists of a mixture of oxides and plate like metallic
powder. At a load of 98 N the 30-60 minute tempered specimen at T = 600 oC has high wear
resistance and the debris consists of oxides. Viafara and Sinatora(12) conducted a pin on disc
test to observe wear regime transition with respect to material hardness. The wear regime
transition depends on microstructure changes, surface oxidation, and workhardening. Lee(13)
conducted a pin on disc test to observe that wear performance of bainitic steel is worse than
of pearlit steel although the hardness is higher. Langueh(14) developed a numerical approach
to include material inelastic property so that the influence of steel grade difference to rolling
contact fatigue could be observed. Goto(15) observed the wear behaviour of a 0.35% C steel
under unlubricated condition at moist air environment. The loading is stepped, mild wear
was observed for increasing loading while severe wear was observed for decreasing
loading.
In this paper, a twin disc experiment was conducted using the discs as shown in Figure
1. With this type of disc a more accurate wear prediction could be obtained. The material of
disc 1 is medium carbon steel, ST 60 (0.458 % C) and of disc 2 is low carbon steel, ST 37
(0.132 % C). The lateral radius of curvature of disc 1 (lower disc) is fixed at 13 mm while
of disc 2 (upper disc) varies from 16, 18, 20, 22, 24 mm.
2. Experimental set up
Test Specimen
The experiment was conducted using 2 discs with 42 mm diameter, 20 mm width, and
10 mm width of contact surface. The shape and dimension of the disc is shown in Figure
1.Lateral radius of disc 1 (lower disc) is 13 mm while the lateral radius of disc 2 (upper
disc) is varied from 16, 18, 20, 22, and 24 mm. The material of disc 1 is ST60 carbon steel
and for disc 2 is ST37 carbon steel, the material properties are shown in Table 1.
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Table 1.Chemical compositions and mechanical properties of test specimen
Material
Chemical composition (% weight)
C
Mn
Si
P
S
Cr
Mechanical properties
Tensile strength (kg/mm2)
Yield strength (kg/mm2)
Elongation (%)
Average hardness (HV)
ST37
ST60
0.132
0.42
0.209
0.036
0.021
0.059
0.458
0.684
0.251
0.036
0.023
0.034
31.5
22.84
28.9
113.4
67.74
49.12
12.38
165
Figure 1. Test specimen
Apparatus
The experimental set up is shown in Figure 2. Disc 1 (lower disc) is driven at fixed
speed of 149.7 rpm, while disc 2 (upper disc) is driven at several different speed depending
on the amount of slip needed. Contact pressure is delivered through the lower disc by screw
jack equipped with load cells. This apparatus is using 2 electric motors to drive the two
discs independently. Disc 1 is driven at a constant speed of 149.7 rpm while disc 2 is driven
at variable speeds depending on the needed amount of slip. The motors can be driven at any
speed using constant torque inverter. The tangential force of the motor is measured using
load cell. This force is needed to determine the motor torque so that the tangential force
acting on the surface contact can be determined. Contact pressure on the disc is provided by
a spring-jack equipped with a load cell, and the pressure is made constant manually. The
load cells are connected to strain amplifier and then to analog digital converter (ADC). The
ADC signal is transferred to computer to display the measurement results.
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Figure 2. Twin disc experimental set up
3. Experimental Analysis
The formula for determining the maximum contact pressure p0 is taken from Hertz(16),
contact area elliptical half axis can be determined using the following formula:
Longitudinal half axis a:
⁄
(1)
Lateral half axis b:
⁄
(2)
with N is total normal force, while Y1, Y2, and Y3 are defined as the following
(3)
(4)
′
′
(5)
If both of disc materials are the same then the elastic modulus Ew=ER=E and the poisson ratio
vw=vR=v so that Y1=Y2=Y, and then equations (1) and (2) become
⁄
⁄
(6)
(7)
m and n are non-dimensional coefficients based on θ which is defined as
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cos
(8)
where
′
′
2
′
(9)
′
γ is the angle between the normal surfaces containing R1and R2,then the maximum
contact pressure can be determined as
(10)
The values of m and n can be obtained from the table available on reference (16).
Using equation (10), a force of 200 N is needed to obtain a contact pressure of 2000 MPa.
Slip is defined as
(11)
The rotational speed of disc 1 is 149.7 rpm, in order to obtain a slip of 0.2% then the
rotational speed of disc 2 should be 150 rpm.
All tests were performed continuously until upper disc reached 10,000 rotational cycles,
and the tests were conducted under dry condition (unlubricated).
4. Experimental results
The results are shown in the following Figures 3 to 11. Figure 3 shows that the highest
mass loss occurs at the disc with a lateral radius of curvature of 16 mm, then it decreases at
radius of 18, 20, 22 mm and it increases again at radius of 24 mm. The minimum mass loss
is observed at radius of 22 mm.
140
Mass loss (mg)
120
0.2% Slip
10,000 cycles
Dry
100
80
60
40
20
0
14
16
18
20
22
24
26
Radius (mm)
Figure 3. Mass loss with respect of lateral radius of curvature
If mass loss is formulated as wear rate, Figure 4 shows the wear rate with respect to
lateral radius of curvature. Wear rate is defined as mass volume loss per unit sliding path
and per unit contact area(17). The minimum wear rate is observed at lateral radius of 22 mm
and therefore the combination of lateral radius of 13 and 22 mm provides the best sliding
contact performance.
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600
Wear rate (µg/m/mm 2 )
500
0.2% Slip
10,000 cycles
Dry
400
300
200
100
0
14
16
18
20
22
24
26
Radius (mm)
Figure 4. Wear rate with respect to lateral radius of curvature.
The influence of contact force to wear rate is shown in Figure 5, where contact force is
formulated in wear index which is the product of traction force (T) multiplied by slip (γ)
and divided by contact area (A)(18, 19). Contact pressure (MPa) is shown in Figure 5
described as dots. There are two forces acting during disc contact, normal force and
tangential force. Normal force creates contact pressure while tangential force influences
wear index. Figure 5 shows that the combination of lateral radius of 13 and 22 mm provides
the lowest contact pressure and the minimum wear rate.
Figure 5. Wear rate with respect to wear index.
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Observation of surface topology is shown in Figure 6 where the contact surface is rough
with cracks in the vicinity. In the center where high pressure occurs the roughness is much
severe than in the vicinity.
Figure 6.SEM of contact surface of disc 2 with lateral radius of 16 mm.
Figure 7 shows that the subsurface deformation is small while the surface deformation is
large.
Figure 7.Subsurface deformation of disc 2 with lateral radius of 16 mm.
Observation of surface topology of disc 2 with lateral radius of 22 mm is shown in
Figure 8 and it can be seen that the contact surface is smoother than of disc 2 with lateral
radius of 16 mm. The subsurface deformation of the 22 mm radius disc 2 is shown in Figure
9 and it can be seen that the deformation is larger than of 16 mm radius disc 2.
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Figure 8.SEM of contact surface of disc 2 with laateral radius of 22 mm.
Figure 9.Subsurface deformation of disc 2 with laateral radius of 22 mm.
O
Observation
of surface topology and subsurface defoormation for both 22 mm radius
disc 2 and 16 mm radius disc 2 shows the correlation between
b
the intensity of contact
pressuure and the surface damage level. The contact pressurre of 22 mm radius disc 2 (1883
MPa) is lower than of 16 mm radius disc 2 (1986 MPa), seee Figure 5, therefore the surface
damagge of 16 mm radius disc 2 is much severe.
Thhe wear index of 22 mm radius disc 2 (4.08 N/mm2) is higher than of 16 mm radius
disc 2 (1.9 N/mm2), see Figure 5, therefore the subsurface deformation
d
of 22 mm radius disc
2 is laarger due to the contribution of higher tangential force in the wear index formula.
Thheoretical contact pressure for each lateral radius of
o curvature can be determined
using Hertz equation and it is shown in Figure 10. It can be seen that the minimum contact
pressuure occurs for 22 mm radius disc 2.
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1950
Contact Pressure (MPa)
1940
1930
1920
1910
1900
1890
1880
1870
1860
1850
15
17
19
21
23
25
Lateral radius (mm)
Figure 10.Theoretical contact pressure with respect to lateral radius of curvature.
Figure 11 shows wear rate with respect to contact pressure and it can be seen that wear rate
increases with increasing contact pressure, and the minimum wear rate occurs for 22 mm
radius disc 2.
Figure 11. Wear rate with respect to contact pressure.
5. Analysis
In some research on rolling contact phenomena it is common to observe that wear rate
is increased if the contact pressure increases, in some cases the increase is linear and in
other cases it is non-linear. Clayton(20) showed that for pearlitic steel rail the effect is
non-linear while for bainitic steel rail the effect is linear.
Bolton and Clayton(18) showed the influence of contact pressure to wear rate for 4 types
of rails i.e. BS11 (0.53%C), UICA (0.73%C), UICB (0.62%C), and 1% chrome (0.7%C) in
contact with D type wheel (0.65% C). They showed that wear rate increases with the
increase of contact pressure at the same slip condition. Beagley(21) observed the same
phenomena.
Braghinet.al(22) showed that there is an inaccuracy in predicting wear rate at the flange
surface of the wheel, the difference between the predicted wear and the experimental result
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is 30%. The experiment was performed using twin disc (cylindrical) apparatus.
In this research work, it can be seen from Figure 5 and Figure 10 that the observed
contact pressures are very close to the theoretical contact pressure, for example in the case
of 22 mm lateral radius the observed contact pressures are 1890 MPa, 1903 MPa, and 1883
MPa while the theoretical contact pressure is 1855 MPa. The difference is between 1.5 to
2.6 % which is much more accurate than the previous similar research works using twin
disc (cylindrical).
Figure 4 and Figure 11 show the consistency of the research results which describe that
at 22 mm lateral radius the wear rate is minimum and the contact pressure is also minimum,
and this confirms the proportionality between wear rate and contact pressure.
In the previous research work(1) it was shown that during rail-wheel surface contact, the
point of contact occurs at the 20 mm radius of curvature for the wheel and at 13 mm radius
of curvature for the rail. The cross sectional profile of the rail as well as of the wheel
consists for several lateral radius of curvature, commonly ranging from 13 to 24 mm.
6. Conclusion
This research work shows that, within the existing range of variation of lateral radius
i.e. 13 – 24 mm, the lateral radius of curvature of the wheel flange surface influences the
wear behaviour of wheel-rail contact. The research result shows that there is a configuration
of wheel – rail contact which causes least wear as compared to other configuration within
the 13 – 24 mm range of variation. The twin disc test with curved surfaces
(non-cylindrical) shows a more accurate simulation of the real wheel-rail contact
phenomena, since the test can simulate the non-conformal contact between two surfaces
with different radius of curvature.
Acknowledgement
The authors would like to convey their appreciation to the Directorate General of
Higher Education, Ministry of Education & Culture, Indonesia for the provision of research
grant No. 445/SP2H/PP/DP2M/VI/2010 and No. 508/SP2H/PL/Dit.Lintabmas/VII/2011.
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