Weird bolt crack
Weird bolt crack
(OP)
Attached is one of 24 bolts that holds a motor upper bearing bracket to the stator (goes into a tapped hole).
It was found during motor disassembly... nothing else unusual, other bolts are fine.
The externally visible crack starts in the center of the flat face at the "bottom" of the bolt (i.e. the opposite end as the head)... goes almost straight along the threads, and stops just short of the head.
I forgot to check bolt material - will report that tomorrow.
What could cause this type of crack?
It was found during motor disassembly... nothing else unusual, other bolts are fine.
The externally visible crack starts in the center of the flat face at the "bottom" of the bolt (i.e. the opposite end as the head)... goes almost straight along the threads, and stops just short of the head.
I forgot to check bolt material - will report that tomorrow.
What could cause this type of crack?
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RE: Weird bolt crack
I would start by looking at differential cooling during the tooling of the bolt.
I do not know if you can this failure pattern from an overtorquing of the bolt. It seems like the head would fail first in shear, not this scenario.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Weird bolt crack
mfgenggear
RE: Weird bolt crack
Looks like bolt was made from seamed bar. The ends of the wire stock should have been cropped to remove any piping. (rolled in scale)
H
www.tynevalleyplastics.co.uk
RE: Weird bolt crack
Such an even crack, not disinterrupted or changed by the windings, indicate in my opinion a throughgoing material fault or weakness, pre-existing before mounting and caused under fabrication of the bolt.
if the bolt is fabricated by drawing out of larger barstock, cut, and then machine-forged to form head and stem, some fault or gliding within or between the two halves of the forging tools could possibly have caused this type of fault.
Other causes may be possible, but I doubdt difference in cooling.
RE: Weird bolt crack
RE: Weird bolt crack
RE: Weird bolt crack
RE: Weird bolt crack
RE: Weird bolt crack
RE: Weird bolt crack
We will go ahead and replace all the bolts in this motor and have this one evaluated further.
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RE: Weird bolt crack
I'm tempted to say HTSR, do a metallurgical and look for residue in the crack at various points. If there is an oxide layer, then the crack was done in the furnace at a high temperature. If there is oil or rust, then the crack was present at the time of usage or cracked during usage.
But it looks more metallurgical than mechanical. The line is perfectly straight, sulfide stringer in the iron matrix? Poor quality steel at the foundry? Water quench process during HTSR?
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Weird bolt crack
Thanks for sharing. A very unusual event.
rmw
RE: Weird bolt crack
I was under impression all in-service stresses are in axial direction therefore, there are no stresses to "grow" crack during use.
RE: Weird bolt crack
I believe the correct answer is "the purchase of third world originated goods"
Which country did they come from ?
Consider re-posting in the forum "welding, bonding and fastener Engineering"
My opinion only
RE: Weird bolt crack
depends on the application - for the one described here, it's probably fair to say it's axial only.
For long bolts in rapidly-moving structures, the bolt inertia can (by itself) induce significant bending loads.
RE: Weird bolt crack