Forces on a Checkrail

[charles]

Hi guys,

I'm new to the forums and was hoping someone here could help me out with a technical question.

Here it is:

What are the forces which result when a bogie traverses and impacts a checkrail around a curve assuming no cant deficiency?

I am tending towards believing the centrifugal force of the wheelset would be the main force which the checkrail would have to bear, and from a stationary point of reference the direction of this force would be the angle of attack of the wheelsets. but it is well documented that there are quasi-static lateral loads produced by the wheelsets. I don’t agree that these forces are relevant as they should be forces that act on the rail, but due to sliding friction, do these forces transfer to the checkrail?
Are there are other forces acting on this checkrail system that I have overlooked?

Also, since the centrifugal force is the tendency of the bogie to keep travelling in a straight line. If for the sake of simplicity around a curve, the direction of momentum (i.e. centrifugal force) is tangent to that point on the curve, it will impact the checkrail at an angle. So then, is the actual force perpendicular to the face of the checkrail actually only a component of the momentum?

It would be great if you could give me ideas that I could work forward on, or better yet if you know with good reason or documentation the actual forces relevant to the checkrail system.

Best Regards,
Charles.

 

[Old Timer]

Much depends upon the track geometry and the speed. Ideally the wheel flange should not make contact but with a wide range of speeds, it is inevitable that some will occur.

The angle of attack, and the lateral force should never equal or exceed the vertical force applied on each wheel otherwise the wheel will climb into derailment.

With no cant deficiency the wheel will run true provided that the speed and the wheel profile are appropriate. Even on curved track, there will be a tendency on the wheel to follow the railhead and we achieve this by means of a transition into the true curve. Even with cant deficiency the wheel will to a large degree run true but the degree will vary with speed and load, as well as a coule of other factors.

There is a calculation on this but it is not with me right now as we don't ever need to calculate this.

I will see what I can get hold of but it might be a day or two before I can go through my various reference manuals.

 

[charles]

Assume having all the variables such as axle loads, train speed, radius of the curve, etc. Would you any documents with reference to how you could calculate the forces acting on the checkrail? If it also makes it easier to solve, we can introduce a cant deficiency that will allow the train to traverse the curve at equilibrium speed. We can also assume the rail is canted 1:20 by means of the baseplates.

I know BS EN 13481-7:2003, British Standards specifies a lateral load between 5kN to 50kN for a cyclic load, but there is no mention of how this value was derived, so I can only assume it was derived empirically.

Would the lateral force exceeding the vertical force causing derailment still apply for a raised UIC33 checkrail?

 

[Wyvern]

May I suggest Fundamentals of Rail Vehicle Dynamics (Advances in Engineering Series) by A. H. Wickens

Mind you at £95 I'd get it from the library.

 

[LWB]

I know that I am going to regret posting this. However I type things in forums they come across curtly but here goes, in a spirit of tuition and not disparagement;

Before tackling tomes such as the one mentioned you really ought to get a grip of the basic physics involved. Your whole posting is flawed and woolly. Don't take offence though for it is exactly the same sort of thing I find in undergraduate theses from people who should know better. For example your statement "since the centrifugal force is the tendency of the bogie to keep travelling in a straight line" shows a complete failure to grasp Newton's first law which states that every body will continue in its state of rest or uniform motion in a straight line unless acted upon by a net external force. Your idea that centrifugal force is somehow involved in causing circular motion is also deepy wrong. Centripetal force is required to do this (as requred by Newton's law). Your statement the direction of momentum (i.e. centrifugal force) would be totally correct if you had said the direction of momentum change (and of course used centripeetal instead of centrifugal force). I would be happy to discuss this further by pm should you wish.

Sorry again

 

[charles]

Wyvern:
Thanks, I actually do own that text and am using it as a reference. I am not too sure of its relevance to checkrails though, it mainly details the interaction between the wheelsets and the rail. It is probably somewhat applicable, as the forces exerted on flange may be synonymous with those acting on the checkrail.

LWB:
You don't understand my post.

Read it again.
Centripetal force is the force exerted on the wheelset by the rail keeping it going along a circular path. Due to the mechanisms of sliding friction, and the dynamics of the interaction between the rail and wheel, the wheelset displaces outwards thus imparting a force onto the checkrail. This force is hence termed the "centrifugal force".

In the industry, the use of this term is common. Don't believe me? Go read up on texts by Mackenzie or Wickens, who are experts when it comes to railway vehicle dynamics. (The one suggested by Wyvern would be a good start).

You apply Newtons laws in a rotating frame of reference and you will get a centrifugal force.

if you want to discuss this further, go read a book.

 

[90019]

Your idea that centrifugal force is somehow involved in causing circular motion is also deepy wrong. Centripetal force is required to do this (as requred by Newton's law). Your statement the direction of momentum (i.e. centrifugal force) would be totally correct if you had said the direction of momentum change (and of course used centripeetal instead of centrifugal force).

Centrifugal force is involved in causing circular motion, as it is not an actual force, but a device. In this case the rail/check rail/camber causing the wheels to turn. It is what generates the centripetal force.

 

[Domeyhead]

I know that I am going to regret posting this.

You were right. You do regret posting it. <sadface thingy>