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                                I.                
INTRODUCTION

Rail defects lead up to having not comfortable and noise
journey conditions, accidents, enhance in maintenance and operation costs,
negative influence to environment. Rail corrugation is one of the most
important rail defects. Rail corrugation means planar irregularity occurring periodically at rolling surface
of rail caused by interaction between rails steel and wheels. It has generally
certain between each other. The corrugations have specific wavelengths and
frequency. Reasons and damaging mechanism of the corrugations can be changed
from each other. 

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In this report, information about types of rail
corrugation, how rail corrugation occurs, effects of rail corrugation and
solutions to rail corrugation are given respectively.

                            
II.                
TYPES
OF RAIL CORRUGATION

Rail corrugation are classified
according to their wave lengths and wearing types. International Union of
Railways (UIC) defines 3-8 cm wavelength corrugation as short pitch rail
corrugation while 8-30 cm as long pitch corrugation. However, Alias classifies
rail corrugation into 3 different class as 3-8 cm for short pitch, 15-30 cm for
medium pitch and 50-200 cm for long pitch.

The second type of
classification is performed according to their wavelength fixing mechanism and
damage mechanism. These are Heavy haul, light rail, pinned–pinned resonance,
rutting, other P2 resonance, and track-form specific. 

Heavy
Haul Corrugation

Heavy haul corrugation is
occurred on heavy haul railways. It is caused by heavy wheel loads which is
over 15 tons per wheel. Wavelengths of this type of corrugation is longer than
other types which is between 20 and 30 cm. Frequency of this type of
corrugation is 30 Hz at low speed at loaded trains.  Irregularities on the rail such as welds and
joints trigger heavy haul rail corrugation. In addition, it can be seen on the
curves. It cause the mushrooming on the rail head.

Light
Rail corrugation   

The corrugation that occurred
at light railway such as 50g/m or less. Weld points of rails are more suitable
to have light rail corrugation. The wavelength of light rail corrugation are at
the range of 50 and 150cm. Gross plastic flow which is one of the damage
mechanism type is not usual in light rail corrugation. 

Other
P2 Resonance Corrugation

It is the most frequently seen
corrugation and wavelength is between 30-40 cm. It occurs where the wheelsets’
torsional resonance triggers at the same frequency. It is the most common
reason of corrugation in tram systems. Wavelength fixing mechanism is P2
resonance while damage mechanism is wear.

Rutting

Corrugation where arise at the
inside rail of curved sections are called rutting corrugation. Furthermore, it
can be take place at the straight rails that traction or breaking are harsh.

Rutting might be so quick and wavelength appear uniform.  Furthermore, the damage mechanism of rutting
is wearing.

Roaring
Rails

When the trains have light axle
loads and go with high speeds causes to that rail corrugation. Furthermore, it
occurs at non-sharp curves where there is no interaction between rail lateral
side and wheel flange. It is commonly seen nearby sleeper head. Its frequency
is higher relatively than other corrugation types. Damaging mechanism is
wearing and wavelength fixing mechanism is pinned to pinned resonance.

Trackform-specific
Corrugation 

This kind of corrugations depend on the track form
type of the railways. It occurs at low rails of the curved section that have
less than 400m radius. Its wavelength is approximately 5 cm and it develops
very quickly after it is formed.

                          
III.                
HOW
RAIL CORRUGATION OCCURS

Rail corrugation starts with
wavelength–fixing mechanism due to friction between rail and wheel. This micro
wears cause to dynamic force when rail vehicle pass through rail. Consequently,
this dynamic forces become input for damage mechanism which results change in
initial longitudinal rail profiles. Finally, enhance in changes for rail
profiles due to damage mechanism that contains wear, plastic bending and
plastic flow are called rail corrugation.

Heavy
Haul Rail Corrugation

High dynamic loads that
triggered by rail head irregularities cause the rail corrugation. In addition,
tangential loads on curves and excessing of cant can propagate the corrugation.

Light
Rail Corrugation

The light rail corrugation
reasons are similar with those for heavy haul corrugation. Steel used in light
rail had less yield strength therefore, less amount of load causes to plastic
bending even if that load does not cause to plastic deformation.

Other
P2 Resonance Corrugation

Direct fixation and not have a
resilience element in the rail sleeper connections cause to have this kind of
rail corrugation. 

 

Rutting

The proportion of tangential
force to normal force (T/N) which is called traction ratio is close to friction
ratio. Therefore, it causes to stick slip oscillation where one wheel slips
while other wheel is driven. Applied traction enhance the tangential force on
the outer wheel while it decrease the tangential force on the inner rail. Thus,
difference between tangential forces increases for wheelset and it enhances the
stick slip oscillation that causes to rutting. 
    

Roaring
Rails

Main reason of roaring rail
corrugation is high vertical dynamic loads. In addition, high lateral and
longitudinal creeps and not aligning bogies correctly can cause the
corrugation.

Trackform-specific
Corrugation 

If the track forms have maximum
in the vertical dynamic contact force, it causes to this kind of corrugation.

Moreover, the curves due to tangential forces cause to trackform-specific
corrugation. 

                          
IV.                
EFFECTS
OF RAIL CORRUGATION

Rail corrugation causes the
deformation on the head of the rail such as wear, plastic bending and plastic
flow. These deformations enhance maintenance cost of track and vehicle, needed
energy to start the movement of vehicle and noise that cause environmental
pollution. Moreover, thinness in fasteners are observed. Furthermore,
corrugation reduces the fatigue strength of rails and ?nduces vibration that
causes ballast degradation

 

 

 

 

 

                            
V.                
SOLUTIONS
TO RAIL CORRUGATION

Heavy
Haul Rail Corrugation

The basic treatment
method for this type of corrugation is choosing adequately hard steel for
rails. Moreover, grinding the rail irregularities periodically, designing cant
properly and smoothing the welds are alternative solution of corrugation
problem. 

Light
Rail Corrugation

In order to solve corrugation
in light rail, railhead irregularities should be minimized particularly at the
weld zones. Unsprung mass of rail vehicles should be decreased as possible as
because heavy load is one of the main factor that cause rail corrugation.

Furthermore, steel used for rails should have higher flexural strength and
yield strength.

Other
P2 Resonance Corrugation

Using resilience elements
between rail and sleeper is one of the treatment. Using timber sleeper in a
ballastless railway system in order to supply resilience elements is an
alternative solution for that kind of corrugation. Using harder steel and
reducing irregularities on the rail head are available for the corrugation.

Rutting

In order to decrease rutting,
friction modifier might be used. It can be performed to either wheel or rail as
water based fluid.  Other solution that
can be used are application of grinding process, using harder rails and
lubrication gauge corner and making profiles asymmetrical.

Roaring
Rails

Grinding existing corrugation
and other irregularities at rail head and aligning the bogies correctly are
main solutions for roaring rails. Moreover, using proper friction modifier is
another type of treatment

Trackform-specific
Corrugation 

Using resilience rail path to
absorb the dynamic forces is one of the treatment for corrugation. To make the
wheels as higher degreed of conical shape is alternative solution. Using proper
friction modifier and grinding the existed corrugation and other irregularities
on the rail head is treatment for that corrugation.

                          
VI.                
CONCLUSION

As a result, corrugation that
causes bad journey, accidents, environment pollution and loss of money is
separated into six group by formation cause. These are heavy haul, light rail,
Pinned–pinned resonance, rutting, P2 resonance, and track-form specific. Their
definitions, causes and treatment methods have been explained respectively.

Friction between rail and wheel is the starting point of corrugation.

Consequently, irregularities at rail and weld zones are main propagator of
corrugation and grinding is the usual way to solve this problem. If the
damaging mechanism of corrugation is wear, using harder steel for rail is
common type of solution. Alternative solutions of corrugation are lubrication
of track, increasing radius of curves, using resilience element, avoid from
using single engine bogie, reduction of unsprung mass of vehicle, designing
cant properly.  

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