Fracture Mechanics

  • #1
Summary:
Fracture in a switch rail
Hello everybody
We saw a fracture in a switch rail, now we're trying to find the reason, may be you can help us.
This rail is made of R260 steel.
Let me know if any other information is needed.
I have attached pictures of this rail.
Thanks in advance
 

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Answers and Replies

  • #2
494
197
From the cracked surface, it looks like stress corrosion cracking, not a fatigue cracking. Nearly whole cross-section is rusted, and rust forms an irregular stripes, while for fatigue cracking you do expect at least 1/3 of cross section to be fresh, and fresh area to be continuous.
 
  • #3
Thanks for your answer.
Yesterday I captured some clear photos of cracks.
Actually it is obvious that there was a crack at the location of the fracture.
I have to add that the rail is at the outdoor environment for about a month and the rust can be from this.
Now, we should discuss 1-What caused the crack?
2- What caused the crack to grow and finally the fracture?
 

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  • #4
Tom.G
Science Advisor
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Now, we should discuss 1-What caused the crack?
2- What caused the crack to grow and finally the fracture?
I hazard a guess that the original material was nonhomogeneous (either alloy-wise or crystallographic-wise) before it was even formed into a rail.
 
  • #5
This is a switch point rail and was used for about ten years without any problem. Now it is transferred to our company for repairment but after a month being at the outdoor, before repairing the fracture occurred.
 
  • #6
Tom.G
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but after a month being at the outdoor, before repairing the fracture occurred.
Ahh! Very high internal stresses. Sounds like its proper place is the scrap heap... cheaper than a derailment. :eek:
 
  • #7
494
197
Ahh! Very high internal stresses. Sounds like its proper place is the scrap heap... cheaper than a derailment. :eek:
Seems the stress at defective section was compressive while rail was used, therefore stress corrosion cracking did not develop. After the ties were removed, the conditions became favorable for accelerated cracking.
 
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  • #8
Seems the stress at defective section was compressive while rail was used, therefore stress corrosion cracking did not develop. After the ties were removed, the conditions became favorable for accelerated cracking.

May you explain more :wink:
 
  • #9
Ahh! Very high internal stresses. Sounds like its proper place is the scrap heap... cheaper than a derailment. :eek:
Okay what do you guess about the reason of cracking?
 
  • #10
494
197
May you explain more :wink:
This type of crack require both corrosive environment and tensile stress. While tied down on switch, tensile stress caused by metalurgical inclusion was likely counteracted by fasteners connecting rail to ties. After fasteners were removed, the cracking have accelerated.
 
Last edited:
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  • #11
Tom.G
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What He Said.png
 
  • #12
This type of crack require both corrosive environment and tensile stress. While tied down on switch, tensile stress caused by metalurgical inclusion was likely counteracted by fasteners connecting rail to ties. After fasteners were removed, the cracking have accelerated.
Our environment is somehow humid and the part that fracture occurred there was on a slide chair
 

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