×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

fatigue failure anomaly
3

fatigue failure anomaly

fatigue failure anomaly

(OP)
I have a 3/4-10 UNC threaded rod, conforming to IEEE standard C135.1-1999, IEEE standard for zinc-coated steel bolts and nuts for overhead line construction.

The failed section of the bolt has striation marks indicative of fatigue failure, and a small zone with typical brittile failure charateristics.

The anomaly:
parallel to the fatigue striations is a zone of discoloration. The zone is approximatly .08" wide, with "clean" normal fatigue striations on either side.  The discoloration is blueish rain-bow, similare in apearance to when heat-treated steel is overheated by grinding.  The depth of the discoloration appears to be very shallow, i.e. less than .005" into the fatigue fracture face.

Anyone have some thoughts as to what might have caused this anomaly?

Thanks  

RE: fatigue failure anomaly

2
Temperature is the cause of color changes on steel.  In order to produce a bluish-type color, a temperature of greater than ~ 250 C is necessary.  Time at temperature is also a factor.  ASM Volume 4, Heat Treating, has some data on SAE 1035 steel:

Deep Blue: exposed to ~ 310 C for 10 minutes, or ~ 250 C for 1000 minutes.

Blue, purple tinge: ~ 340 C for 10 minutes, or ~ 265 C for 1000 minutes.

Deep grey-blue: ~ 370 C for 10 minutes, or ~ 280 C for 1000 minutes.

RE: fatigue failure anomaly

Thorangle
From your decription it sounds like fatigue cracks propagated from the discolouration.  The discolouration could be caused by a material defect ie inclusion or segregation introduced during casting.  Alternatively mechanical damage during bolt manufacture.
Suggest you examine the fracture surface using a low power microscope and look for changes in surface morphology at the discoloured surface and or zinc deposition on the discoloured surface.  If present you can trace when the crack occured.
If the bolt was heat treated during processing, crack discolouration could have been caused by oxidation in the furnace atmosphere.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources