Effect of tilting trains on track

[RAGNARØKR]

A few months ago I noticed that the head of the outer rail on the down track was cracked, and shortly afterwards it was replaced. The outer rail on the up track is now about to be replaced, as the new rail has been laid alongside in preparation for the work.

Could this be an effect of the tilting trains that use the line? It is a known phenomenon?

 

[LNW-GW Joint]

A few months ago I noticed that the head of the outer rail on the down track was cracked, and shortly afterwards it was replaced. The outer rail on the up track is now about to be replaced, as the new rail has been laid alongside in preparation for the work.
Could this be an effect of the tilting trains that use the line? It is a known phenomenon?

Where are you talking about?

 

[Ships]

When you say cracked, do you mean like RCF? where the rail has been ground it can look like cracks perpendicular to the rail. If its on a high cant curve on a mixed traffic line then the rail could be being replaced due to side wear caused by heavy freight running well under line speed around the curves.

 

[222001]

Surely tilting trains would even weight distribution on both rails?

 

[edwin_m]

A tilting train can go round a curve faster, and at greater "cant deficiency". This is likely to mean more wear on the outer rail, but also more grinding because of the increased risk of rolling contact fatigue. I think the wear from heavy freights would be more on the inner rail.

 

[MarkyT]

Surely tilting trains would even weight distribution on both rails?

Cant or super-elevation distributes the weight at a design speed, but cannot be increased beyond a certain limit because of the weight transfer to the inner rail of a stopped or slowly moving train. To go any faster, car-body tilting may be employed but this does not distribute weight in any meaningful way. On sharper curves the speed limit of non tilting trains is more constrained by passenger comfort than by the ability of the train to stay on the rails. Tilting merely allows a trains to go faster around a given curve, closer to the absolute limit, whilst not throwing passenger or other loads violently from side to side. The increase in weight transfer to the outer rail from the higher speed thus allowed cannot be avoided and increases rail wear and perhaps RCF crack formation. That results in increased inspection and rail replacement costs.

 

[snowball]

On a Pendolino and on APT, how high is the tilt axis in relation to the centre of gravity of the tilting coach body?

 

[edwin_m]

On a Pendolino and on APT, how high is the tilt axis in relation to the centre of gravity of the tilting coach body?

I believe the APT and current Pendolino were designed to rotate about the centre of gravity, tilt being applied and removed by powered actuators ("active tilt").

However some train designs have/had "passive tilt" systems where the lateral acceleration on the curve swings the bodies outwards - so the axis of rotation must be well above the centre of gravity.

 

[DaveNewcastle]

. . .

so the axis of rotation must be well above the centre of gravity.

You're right, I'd guess it's about a meter above, at the least.

Surely tilting trains would even weight distribution on both rails?

Eh? Weight distribution?
The instantaneous moving mass would be expressed through vertical, lateral and forward vectors. Tilt isn't going to have any bearing on the lateral or forward forces, and not much bearing on the differential vertical forces between the two rails.
Is it?

 

[edwin_m]

Eh? Weight distribution?
The instantaneous moving mass would be expressed through vertical, lateral and forward vectors. Tilt isn't going to have any bearing on the lateral or forward forces, and not much bearing on the differential vertical forces between the two rails.
Is it?

The increase in lateral forces is not directly related to the tilt itself, but arises because the tilting train is allowed to go faster round the curves.

 

[ac6000cw]

However some train designs have/had "passive tilt" systems where the lateral acceleration on the curve swings the bodies outwards - so the axis of rotation must be well above the centre of gravity.

The 'Talgo Pendular' is probably the commonest passive system - http://en.wikipedia.org/wiki/Talgo#Talgo_Pendular and http://www.talgo.com/index.php/en/pendulacion.php (although the diagrams are difficult to read in detail)

 

[RAGNARØKR]

Where are you talking about?

One of my local stations about 10 miles from Gothenburg. It is traversed by X2000 tilting trains, also a lot of other traffic. The tilting trains go through in tilt mode and would be running slower if they did not have the tilt facility.
--- old post above --- --- new post below ---

When you say cracked, do you mean like RCF? where the rail has been ground it can look like cracks perpendicular to the rail. If its on a high cant curve on a mixed traffic line then the rail could be being replaced due to side wear caused by heavy freight running well under line speed around the curves.

What could be seen were a few cracks across the head of the rail, irregularly spaced but roughly 20 cm apart over stretches a metre or two.

They were obviously considered sufficiently serious to be worth replacing the rail rather than grinding them out.

 

[edwin_m]

That sounds very much like rolling contact fatigue. You are probably aware of our Hatfield accident where due to management failures this was allowed to deteriorate until the rail disintegrated into many pieces underneath a passing train. This was also on a high speed curve though not one used by tilting trains.

 

[RAGNARØKR]

That sounds very much like rolling contact fatigue. You are probably aware of our Hatfield accident where due to management failures this was allowed to deteriorate until the rail disintegrated into many pieces underneath a passing train. This was also on a high speed curve though not one used by tilting trains.

I have looked for pictures of something similar and cannot find them. If it was RCF why would not both rails have been similarly affected? If you Google "rolling contact fatigue" you get a lot of pictures showing damage to the edge of the rail head. These were cracks, or apparent cracks, since it was impossible to determine how deep they were just by looking, across the shiny head of the rail.

Something is going on which affects just the outer rail.

 

[rebmcr]

Where are you talking about?

One of my local stations about 10 miles from Gothenburg.

This should be in International Rail then?

 

[MarkyT]

I have looked for pictures of something similar and cannot find them. If it was RCF why would not both rails have been similarly affected? If you Google "rolling contact fatigue" you get a lot of pictures showing damage to the edge of the rail head. These were cracks, or apparent cracks, since it was impossible to determine how deep they were just by looking, across the shiny head of the rail.

Something is going on which affects just the outer rail.

Tilt or no tilt, on most sharper curves with a cant deficiency, the outer rail carries a greater proportion of the load than the inner one. Even though there were no tilting trains on the route, the UK Hatfield derailment occurred when the outer rail of a curve shattered under a fast moving express, and investigation revealed the many micro-fractures caused by rolling contact fatigue

I think the additional speed that tilting allows is very significant for wear and tear to the outer rail's running surface. The likelyhood and severity of RCF definitely increases with rising load at any given speed. Following Hatfield all rail administrations today are very aware of the phenomenon and implement enhanced inspection, rail grinding and rail changing regimes at sites known to be at risk. RCF has changed the economics of tilting operation. At one time tilting trains were seen as a universal solution to raising speeds on twisty old routes. That extra speed costs serious money in track maintenance however, so today there's a broad consensus that high speed is best accomplished on dedicated straighter tracks without the complexities of tilt. That's not to say there can't be some niche operations where tilt still makes sense.
--- old post above --- --- new post below ---

This should be in International Rail then?

RCF is a railway technical issue common to all parts of the world including the UK. It just so happens the original observation was made in Sweden.

 

[edwin_m]

The various reports into the Hatfield accident are available here:

http://www.railwaysarchive.co.uk/eventsummary.php?eventID=143

The final 2006 one is probably most interesting. Pages 199 onwards include photos of the rail after the accident and the text commentary on rail condition starts on p60. Obviously it had shattered by then but the reconstructions do show cracks across the rail though further than 20cm apart.

I've already suggested a reason why the outer rail was more affected - fast trains will put more stress on the outer rail, as at Hatfield, and this will be particularly true with tilting trains.

 

[RAGNARØKR]

The various reports into the Hatfield accident are available here:

http://www.railwaysarchive.co.uk/eventsummary.php?eventID=143

The final 2006 one is probably most interesting. Pages 199 onwards include photos of the rail after the accident and the text commentary on rail condition starts on p60. Obviously it had shattered by then but the reconstructions do show cracks across the rail though further than 20cm apart.

I've already suggested a reason why the outer rail was more affected - fast trains will put more stress on the outer rail, as at Hatfield, and this will be particularly true with tilting trains.

Thanks for the clarifications.

 

[Daniel Pyke]

It is also worth noting that rolling contact fatigue is often called "Head checks" or "head checking" in some countries on the continent.

The spacing of cracks is usually a lot less than 20cm though in my experience. Typically they are regular spaced cracks nearer 20mm than 20cm (sometimes a lot closer spaced too).

When a curve is laid it is laid with a certain cant, i.e. the outer rail is higher than the lower one. The level of cant depends on the traffic types and speeds. If you have a mix of slow freight and higher speed passenger traffic than a compromise is needed. In this case the cant is usually excessive for freight trains, i.e. more load is taken by the low rail, and for passenger traffic the cant is deficient as the high rail takes more load on the fast trains.

RCF can (and does) happen on both the low and the high rails, but it is usually most prevalent on the high rail.

The type of traffic passing over the track has a huge effect on the degradation of the track. There has been numerous cases where a new vehicle type has been introduced and suddenly there is a large increase in the appearance of certain types of track defects.