Rail crack

[JHWC]

Hi Experts,

Would like to seek your opinion on the rail crack (see attached). Please advise.

1. Is that consider a beach mark around the circular patch? To me, it seem more like an oxidation rather than beach mark.

2. Consider thermite welding was performed to this rail 7 years ago, how will it affect the surrounding material? I noticed inclusion in the middle of the rail. Such failure could be due to the process but I am surprised it actually survived for 7 years w/o failing.

3. What are some of the possible defects that I have missed out? I saw ratchet marks.

Thanks all.

 

[JHWC]

Hi experts,

Is me again. Could you please advise whether the arrow pointed to the rail is crack origin or final fracture? Since the rail is consistently under compression, i would have expected it to be final fracture instead of crack origin. If it is crack origin, not sure why it appears there.

Thanks!

 

[kingnero]

Is it common that thermite welds add so much thickness?

Yes, that's like that due to the mould forms. Generous radii have been provided though, and the process is subject to severe fatigue testing, so that normally isn't a problem.

@ JHWC: impossible to tell just based on a photo, however it is common to have crack initiation in the compression zone of the rail, e.g. surface defects resulting in rail breaks. Based on the first photo you posted, I'd say yes, the web/head transition is the initiation point. However, don't believe an internet poster and conduct some serious analysis if you want to be sure!

 

[mrfailure]

Agree with kingnero that you would should do closer work such as looking under a microscope to really identify the origin. The head/web corner looks most likely from your photos because it is at the mid-point of the crack on that surface and fatigue generally grows in both directions about equally, so mid-points are usually a good first estimate.

 

[JHWC]

Hi all,

Thanks for the valuable input. Just to clarify, if the web/head is the crack initiation point, do you mean the surface defect is the cause of the rail break? I would assume the crack initation point could also come from inclusion? I a bit confused who is the cuplrit to the rail break. Haha.

 

[kingnero]

Both are possible, a third option as I said above is also a possibility (hardness too high).
In that case, you don't actually need an external material influence to have cracking (like inclusions of surface defects). Overloading or fatigue loading can also cause cracking. They'll find the weakest point to initiate, this could be the stress riser from the geometry change.
Any surface imperfection in that area will happily act as initiation point then.

 

[JHWC]

Thanks!

 

[kingnero]

In addition, the dips on the rolling surface generate impact loading, depending on the track conditions there should be periodical grinding/milling of the rail head to renew the rail profile in order to avoid this. Grinding/milling and improving rolling surface geometry (wheel/rail contact) will mitigate fatigue cracking on the surface (squats, head-checking ...) and impact loading due to joints and/or surface defects like these dips, and will generally largely prolong the lifetime of the rails. Also, under-sleeper stability (too much deformation under load) is an often overlooked cause of rail breaks. These steels are pearlitic, and thus brittle as f*.
What you'll find on the fracture surface is only part of the underlying cause.

 

[JHWC]

Hahaha! Thanks kingnero for the valuable input!! Is really a blessing to learn from so many experts over here.