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Metro-North engineer saw broken rail before accident
That was a great explanation of occurred and perhaps what the cause was, all the technical info on broken rails!
Thanks!
thanks for the “Thomas and friends” explanation
I thought of Hatfield as well. But part of the deal with Hatfield was problems in inspection which was the reason the Brit’s are now doing much more ultrasonic inspection of rail for flaws. Is that part of the process over here? I thought it was.
If this is not just a freak one-off but really down to bad maintenance it is a huge deal. Could happen anywhere on the network, even at high speeds. Something similar happened at Hatfield, England in 2000, killing 4, resulting in widespread speed restrictions throughout the country and the demise of Railtrack.
From my Mechanical Engineering classes many years ago, the failure is not from steel becoming brittle, but a classic case of fatigue failure. Failure as a result of fatigue occurs after millions of repeated load cycles. This occurs at stress levels substantially less than what would cause a yield failure.
The failure usually starts at an imperfection or a sharp corner. A micro crack forms, which slowly grows, with more cycles, following the grain boundaries. As this crack grows the portion of steel carrying the load decreases with a resulting increase in local stress. This stage takes a long time. Eventually, the local stress exceeds the yield limit, and the remaining portion fails suddenly.
The crack growth phase follows the boundaries of the steel grains ( all steel has grains ), so this portion has a rough appearance. Since it appears the same as the failure of a brittle material, such as cast iron, the incorrect assumption is made that the steel has become brittle.
The portion which fails by yielding does not have this rough appearance.
Such a failure would not be detectable by an electrical signal until after the final sudden failure. Even then it might not be detectable if the two ends were still in contact.
Defects will occur, unfortunately. Another good reason to use common sense when railfanning and keep a safe distance from the tracks, off the property.
No daily track inspection?
I appreciate the Thomas version, things like rail wear need to be dumbed down for the non technical. My kids’ favorite book years ago was Thomas’ “A Crack in the Track”, where you can’t go forward and you can’t go back. How prescient.
I would like to know a lot more about how the engineer that claims to have seen a broken rail actually saw it. Unless it was an absolutely major break, something like this would be really hard to see at 70 mph. Not disputing his or her veracity; would simply like to know more as it would be virtually impossible to see something like a hairline crack or the like - and a major break would likely have been seen or felt by other engineers - so I’m kind of skeptical without more evidence or explanation.
While the NTSB and all parties review the details…if some form of rail failure is the end result, not doubt there will be many inspection trains roaming the entire property seraching for other such potential failures. That said- let’s not overlook the value of untested crash worthiness (collision) of the M-8 cars. Given the dynamics of speed, weight etc. it’s amazing more were not injured. The crews of both trains acted totally professionally, thus eliminating further injury detraining in an area that’s difficult at best.
Heck of a way to see how those cars stand up though…
What the author of the article is describing is checking, which, if left untreated for a VERY long time can destroy the rail. If this is Continuous Welded Rail CWR, manufacturing or welding defects can cause a failure. Failures can also be caused by not nuteralizing rail that has been repaired.
All of these have distinct tell-tale marks which I’m confident the NTSB folks will evaluate. Will be interesting to see what they conclude.