Procedia Engineering 144 ( 2016 ) 1119 – 1128

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1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of ICOVP 2015doi: 10.1016/j.proeng.2016.05.076

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12th International Conference on Vibration Problems, ICOVP 2015

Dynamics Analysis of Wheel Rail Contact Using FEA

Sunil Kumar Sharmaa,*, Anil Kumarb aCentre for Transportation Systems, IIT Roorkee, Uttarakhand, 247667 India,.

bDepartment of Mechanical and Industrial Engineering, IIT Roorkee, Uttarakhand, 247667 India

Abstract

A rail wheel contact mechanism has been a keen interest area for railway engineers. The present study focuses on the influence of interacting wheel and rail profile topology. A standard rail UIC 60 and standard wheel profile, as per the standards of Indian railways, were taken for different rail profile radii, wheel profile radii and wheel profile tapers. The mathematical and numerical studies were done by using Quasi–Hertz and FE analysis to analyze the impact of the interacting wheel and rail profiles on the distribution of contact zones and stresses. Moreover, the effect of contact forces and contact stresses on the deformation of rolling wheels and rails were also evaluated. The effect of lateral movement in the evaluation of frictional forces was found using Kalker theory. © 2016 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of ICOVP 2015.

Keywords:wheel-rail contact; wheel profile; rail profile; elastic-plastic model.

Nomenclature

a, b semi axes of contact patch A12, B12 coefficients are local curvature for wheel and rail P0 vertical load of wheel and rail σ1, σ2, σ3 Principles stress in x, y, z direction Fx, Fy, Fz tangential forces in x, y, z direction Δy lateral displacement of the wheelset relative to the track YCW, YCR lateral coordinate of the contact point in wheel and rail coordinate

* Corresponding author. Tel.: +918265800900.

E-mail address:sks24dce@iitr.ac.in

© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the organizing committee of ICOVP 2015

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1. Introduction

Indian Railways (IR) is one of the largest railway systems in the World. According to the Vision 2020, the significant focus will be on track enhancement, environmental sustainability, network expansion of railway, capacity creation, train safety, carbon footprint reduction, high-speed train introduction and technological excellence. There are enormous challenges before Indian railways [1]. The wheel-rail contact has been of crucial interest to the railway engineers. Without having an appropriate understanding of the wheel-rail interaction, the essential safety analysis of stability and derailment or the ride comfort analysis are incomplete [2]. Hence, the primary step investigates such mechanisms to clearly know the shape and size of the contact patch, and the distribution of the stresses within it.

Generally, the treatment of wheel-rail contact can be divided into two parts: a geometric (kinematic) part, which aims at the detection of the contact points and an elastic (Elasto-plastic) part, which solves the contact problems from a solid mechanics point of view. The geometric part requires the geometrical data for track and wheel set together with the kinematics data for evaluating the tangential force [3]. Fig 1 illustrates how this contact module is coupled to the system dynamics.

Fig 1: The contact module for calculating contact forces and moments.

In this Paper, a fait bogie was considered which was used in some of the major trains in Indian railways, such as Rajdhani express, Shatabdi express etc. Hence, the focus was merely on the elastic part of the wheel-rail contact. The numerical approach of the rail and wheel contact was based on the Hertz theory of contact and Kalker linear theory [4]. Then, a finite element analysis was carried out for the contact zone to study the effect of variation of wheel-rail profile parameters on the contact dimension, contact stress and contact pressure.

2. Numerical Formulation

A hypothetical rectangular contact area denoted Ah is built on the common tangent plane, around the initial contact point. The hypothetical area is large enough to fully contain the unknown real contact area, Ah ≥ Aras is shown in Fig 2. At uniformly spaced rectangular array is built on the hypothetical rectangular contact area with the grid sides parallel to the x- and y-axes in Fig 2. The nodes of the grid are denoted by (i, j), where indices i and j refer to the grid columns and rows, respectively [5]. The real pressure distribution is approximated by a virtual pressure distribution, a piecewise-constant approximation between grid nodes is being typically used.

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Fig. 2. Real and hypothetical contact areas

The numerical formulation is given by the following set of discrete equations [6]: a) The equations for radius of the curvature rail and wheel:

2 2 2 21 1 1 2 2 2

2 2 21 1 2

1 1 22 2 2

1 1 12 ; 2 ; 2

1 1 1 1

;

2 2

wx n rx

n wx rx

z A x B y z A x B y

d z d z d zB A B

R r Rdy dx dy

A and Br R R

(1)

b) The geometric equation for the dimensions of elliptic boundary of the surface of contact patch:

1/32

1/32

3 1 1

2

3 1 1

2

va m N

E A B

vb n N

E A B

(2)

c) The equations for the hertz coefficient:

4 3 2

4 3 2

cos

(5.9309 007* ) (0.00014928* ) (0.013817* ) 0.57829*

11.095;norm of residuals=0.31292

(1.7133 008* ) (3.3677 006* ) (0.00023584* ) (0.0014623* )

norm of residuals0.28878 ; = 0.03

B A

B Am e

n e e

8332

(3)

d) The load balance equation: On the tread, with a low conicity, the vertical load on the wheel, calculated for a cone angle of 1:20 [7] 0 * 1/ 20p N cos atan (4)

e) The equation for the stresses in the wheel and rail head.

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1 0 0

2 0 0

3 0

2 1 2

2 1 2

bp p

a ba

p pa b

p

(5)

f) The equations for the tangential force in x, y and z-direction: [7]

11

22 23

2

23 33

0 0

0

0

x x

y y

CF v

F abG C abC v

M abC ab C

(6)

Fig 3: Relationship between the m and n with respect to 0

as given in Eqs. (3)

3. Contact Geometry

The wheelset and track gauges are shown schematically in Fig 4. The track gauge is measured between the points on the rail profile located inside the track at a distance of 14 mm from the common tangent to the profiles of both rails. The wheel radius is measured at the mean wheel circle, usually at 70 mm from the back of the wheel. Considering here a S1002 wheel profile and a UIC60 rail inclined at 1/20, the wheel has a radius of 458 mm in the rolling direction as per Indian railway[8]. The material model of wheel and rail is assumed to be linear-elastic and the friction is taken as 0.78 between the contacting surfaces for the analysis of contact pressure. The contact load is considered as 16.25 ton of wheelset. Material data is considered as Ewheel=210 GPa, Erail=200 GPa, Poisson ratio μwheel =0.27 &μrail=0.29, σut rail =680 MPa, σut wheel = 883 MPa, σy = 0.5 σut for the both. When the wheelset is in perfect alignment with the track, the above dimensions would result in a lateral displacement between the mean wheel circle of the left wheel and rail centerline (Δyr) of 3 mm. of course, during the train movement the wheelset changes its relative position to the rail. The rail profile and wheel profile using the mathematical definition of the UIC60 rail profile and the S1002 wheel profile are shown in Fig 5 and 6, respectively. In addition, to the analytical model, a FE model is also made in Ansys for the wheel set and rail setup considering the hexa-dominating meshing for sleepers, rail and wheel as shown in Fig 4. For the numerical analysis, the varying wheel curvature, conicity and rail curvature are considered respectively. Afterward, a comparison is shown between the analytical and FE results of the behavior of the contact patch and the contact pressure. Moreover, the frictional force is calculated by varying the lateral displacement.

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Fig 4: Rail wheel interaction model in Ansys for FEA analysis

Fig. 5: Rail Profile of UIC60 as per Indian railway standard.

Fig. 6: Wheel left and right profile as per Indian railway standard used in Fiat bogie.

Fig 7: Rail wheel Interaction with lateral displacement

4. Results and Discussion

In Fig 8, the 3D pressure distribution for the wheel profile / UIC60 rail profile with inclination 1/20 and zero initial lateral displacements. This pattern is based on wheel radius of 458 mm and the wheel profile curvature radius

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of 330 mm and rail wheel profile curvature 300 mm.

(a)

(b)

Fig 8: (a) 3D Pressure distribution on Rail (b) Pressure distribution in rail FEA model (elastic model, lateral displacement 0 mm)

Fig 9 -10 shows that the conicity of the wheel had a strong influence on both the maximum value of the pressure distribution and the shape of the real contact area.

(a)

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(b)

Fig 9: (a) The effect of conicity on the dimensions a, b and (b) area of the contact patch

Therefore, wheel/rail configurations examined are for the geometrical parameters like conicity, which varies

from 1:5 to 1:40. Moreover, a comparison is also shown for the variation in the contact area, pressure and stress using finite element analysis.

Fig 10: The effect of conicity on the contact pressure and Von mises stress

Fig 11 - 14 shows that the wheel and rail profile varies from 300 to 360 mm and 270 to 330 mm, respectively. For the calculation of contact dimension, contact pressure and contact stress, Eqs. (1) - Eqs. (5) are used for wheel-rail contact pair by varying the contact geometry.

(a) (b)

Fig 11: (a) The effect of wheel profile radius (R12) on the dimension of contact patch a, b and (b) area of contact patch

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Rail inclination also acts to be a major factor which affect the dimension of the real contact area and consequently the entire elastic pressure distribution. It can be noticed that a higher rail inclination provides a higher maximum pressure and it is also validated from the FE analysis.

Fig 12: The effect of wheel profile radius (R12) on the contact pressure and Von mises stress

(a) (b)

Fig13: (a) The effect of Rail profile radius (R22) on the dimension a, b and (b) area of he of contact patch

Fig14: The effect of Rail profile radius (R22) on the contact pressure and Von mises stress

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Fig 15 shows the tangential forces for the rail profile inclination 1/20 for different lateral creepages. It can be observed that the frictional force is higher in the absence of creepages, but as the lateral creepages increase the frictional force gets reduced. The lateral creepage were taken from 0 to 0.1 and its effects on friction force is explained by varying the lateral creepages.

Fig 15: Tangential forces in terms of creepages in x and y directions.

Rail wheel contact problem was investigated by varying contact profile geometries to estimate the contact pressure and contact stress. For a given configuration, i.e. R12 = 330 mm, R22=300 and conicity=20, a contact pressure found as 679.6 MPa (numerically) and 681.5 MPa (FE simulation) on rail surface. A comparison of Hertzian calculation and FE-simulation shows a close agreement in contact pressure and contact stress for different contact patches as shown in Fig 9-14.Therefore, the present model indicates that the contact stress decreases with an increment of rail profile radii as well as the effect of increasing wheel profile radii increases the width and decreases the length of the contact area ellipse causes higher sliding friction. Moreover, Influence of wheel taper increases the length and reduces width of contact area causes reduction in sliding friction. The stress-ellipsoids indicate the dependence of stress state on the contact pair topology. Moreover, the normal maximum pressure in left wheel has a trend toward the centre of contact patches itch and the normal maximum pressure in right wheel have a trend toward the other centre of contact patches with incensement of displacement. The maximum creepage force was found out when ξy=0.1.

5. Conclusions

The functioning of a train is affected by the wheel profiles and the rail inclination. The lateral displacement of the wheel considerably alters both, the shape of the real contact area and the maximum value of the pressure distribution. The major factor which affects the pressure distribution and the shape of the real contact area is the shape of a wheel. The numerical simulation showed that the pressure distribution is affected by the rolling radius curvature. Moreover, the wheel lateral movement changes on: the contact location and area, as well as, the pressure distribution and its maximum value. The effects of lateral movement on frictional forces were founded using Kalker theory.

References

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Dyn. 44 (2006) 921–931. doi:10.1080/00423110600907667. [8] K. Chandra, Maintenance manual for BG coaches of LHB design, Gwalior, 2002.