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Comment by salty_biscuits | Hacker News Reader

Buckling at high temperature is better than fracture at low temperatures. I used to do research in this area. The "holy grail" technology would be a non destructive way to infer the "neutral stress temperature" of continuously welded rail that has been already installed in a quick and non destructive way. Saw lots of weird hopeful technology prototypes based of measuring the hysteresis curves of induced magnetism in the rail, idea being that the stress would have some effect on the magnetic domains. Never worked in the field AFAIK. Here in Australia they will get hoses out on hot days desperately trying to cool the rail down to stop it buckling.

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My weird idea would be if sound waves would travel differently down the rail dependent on temperature. Although, the rail is likely not uniform enough to detect the differences?

I found a device that is in use - Verse[1]. It claims to be able to measure the neutral? Although my read says the rail must be below neutral, and therefore under tension, to determine what the neutral is?

They unclip the rail and then lift it with a known force? I guess that lets them measure the tension and lateral forces on the rail?

[1] https://www.pandrol.com/us/product/verse-rail-stress-managem...

https://www.youtube.com/watch?v=Qg9vn50ZOdo

https://www.youtube.com/watch?v=WbNzhMsUOwA

Railway buckling video: https://www.youtube.com/watch?v=jJeiYaSFCf0

Verse PDF: https://railway-news.com/wp-content/uploads/2020/02/VERSE-Te...

That's interesting. Unclipping the rail is a bit of an exercise though. Makes sense that it must be in tension, otherwise it would move on unclipping. I guess they just measure it in the morning. All these types of devices are less practical as soon as you have to disrupt services to do the measurement. Your idea of the measuring the dynamic response is something that has been investigated. Modal testing is very common (using accelerometers on the rail and a force measuring hammer). The effect would depend on the boundary conditions of the rail (so basically something that varies from site to site) so you would need to track how it changes over time. The engineering problem is how to collect this data easily.

> Here in Australia they will get hoses out on hot days desperately trying to cool the rail down to stop it buckling.

Have you got anything to show that?

Never seen or heard of that in NSW, and not heard of any track buckling issues during summer, either.

I've only found mentions online about spraying post buckling during repairs, but pre-emptive spraying does (did) occur. You will hear about speed restrictions on hot days to avoid buckling.

https://www.researchgate.net/figure/Buckling-of-a-railway-tr...

Yeah I have never seen anything like that in NSW either - anyway on 38°+ days one would have to spray continually anyway, and there’s no way you could do that along a whole rail line in a country that routinely experiences droughts and water restrictions in the summer.

It wouldn't help for rail already installed, but I wonder if you could insert two corrosion-resistant pins in the rail at some standard distance apart. The pins would be installed when the rail is at its "neutral stress temperature". Then you could use some Go/No Go gauges to quickly check if the rail has expanded or contracted. By measuring the distance you could get a more accurate assessment of the stress state. The accuracy required might be too much, though.

It's an interesting problem. It's simple in theory, but may not have a perfect solution.

Part of the problem is that even the state of stress at installation isn't known very precisely. I basically did some pre work on a similar idea. Working through if you could track the displacement of sleepers could you figure it out. Problem is the extension in nominal range is linear and there isn't a simple way to work out where zero is.

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