The investigation is just beginning
The investigation is just beginning
(OP)
The investigation is just beginning. I only have 2 pictures for now, and almost no details.
One brand new M36 "bolt" out of a litter of 26 snapped at installation.
The thread runout detail may not be the best. That will be part of the investigation.
The material nominally is hot rolled 1045, about Grade 8.8, but with yield strength more like 50% of UTS, not 80%.
The full diameter body bolts I've broken by tightening to maximum Moosage generally show some some necking as I recall.
One brand new M36 "bolt" out of a litter of 26 snapped at installation.
The thread runout detail may not be the best. That will be part of the investigation.
The material nominally is hot rolled 1045, about Grade 8.8, but with yield strength more like 50% of UTS, not 80%.
The full diameter body bolts I've broken by tightening to maximum Moosage generally show some some necking as I recall.





RE: The investigation is just beginning
were the bolts made in a far eastern country by any chance ?
B.E.
You are judged not by what you know, but by what you can do.
RE: The investigation is just beginning
Seems like a thorough investigation of materials, annealing, etc. is in order, particularly if another one does the same thing
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: The investigation is just beginning
RE: The investigation is just beginning
RE: The investigation is just beginning
RE: The investigation is just beginning
After machining about a year ago, and sitting in our warehouse the parts moved around by truck up to Canada where they were being installed Tuesday.
I learned that 6 bolts were installed fine, but the 7th the nutted stump snapped and flew away at high velocity awhile being tightened, allegedly to 1900 lb-ft.
I'm hoping to get lots more info over the next day or 2, and even the broken parts.
Wouldn't intergranular corrosion require a sophisticated nasty atmosphere to affect an unstressed HR carbon steel part?
RE: The investigation is just beginning
Mike Halloran
Pembroke Pines, FL, USA
RE: The investigation is just beginning
I'd look for hydrogen as well. We had some steel belleville washers that were embrittled and could be snapped like a potato chip with finger pressure.
I don't see much runout on the thread - maybe it's the angle the photo is taken, but if it is short, then that would have been a stress concentration that would push it over the edge.
Did they just stop advancing and cut a ring groove rather than spiraling out? Sometimes the body is relieved after the threads to make the stress transition smoother.
It also looks like a really sharp root, also a nasty stress concentrator. Maybe this was the first one and the cutter was duller for the rest.
I would not trust any of them without inspecting them.
RE: The investigation is just beginning
Additional questions
- Have these bolts been hardened or tempered?
- What was the lubricant when nuts were tightened?
- Is there a washer under the nut?
For metric threads, to smoothen the notch at the end of the thread by a defined thread runout there's DIN standard 76. However, the bolt would need to be checked for the smaller diameter in the runout's root. dg would be 30.7 mm, pls. refer att. pic.
Another direction for improvement might be the bolts material. The tightening torque being approx. adequate to a 8.8 quality M36 slightly oiled at assembly, then is the 1045 in the chosen state adequate to this? Perhaps you could contact a bolt manufacturer for advice?
Regards
Roland Heilmann
Lpz FRG
RE: The investigation is just beginning
Folks, read the original post this is a brand new bolt. It snapped on installation. Either improper heat treatment or hydrogen embrittlement. Corrosion????
RE: The investigation is just beginning
Dik
RE: The investigation is just beginning
The "bolt" is machined from a bar of this stuff.
Here are the material certs provided.
RE: The investigation is just beginning
RE: The investigation is just beginning
RE: The investigation is just beginning
I believe the "continually cast" refers to the billet that was then patty-caked/hot rolled to an 8-1 reduction ratio.
I think Pretty much All us puny earthlings' steel forgings start their lives as castings.
https://www.youtube.com/watch?v=9AMbKpeJRoU
RE: The investigation is just beginning
I'm Not very far into this, but I'm finding hot rolled materials often have similar Yield/UTS ratios close to 50%.
Here is good old A36.
RE: The investigation is just beginning
RE: The investigation is just beginning
Best regards - Al
RE: The investigation is just beginning
Cut threads (I guess from the very sharp pictures) or rolled?
Were they even stress relieved after forming?
Not bad looking steel.
I sure didn't see 18% elong in the failure pictures.
Something doesn't add up.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: The investigation is just beginning
I did a quick calculation based on the 1900lbf-ft and the 55100 psi figure from the specification and it appears the tension in the bolts after tightening should be around 95% of the yield, now given that torqueing of bolts is subject to huge errors, I just wonder whether that particular bolt got overloaded because of some change in friction value or thread geometry etc.
I also note that the bolt failed during tightening and that is when the bolt see's the most stress because its subject to both tensile and shear stress until the wrench is removed.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: The investigation is just beginning
The attached image shows XRF test results for the broken bolt, and an old bolt.
It includes the material certs for the new bolts.
One thing that has me scratching my head is the different results for two locations on the broken new bolt.
Maybe the surface prep needed to be more severe.
The fact XRF does not measure carbon content makes me (an XRF ignoramus) wonder how useful it really can be.
More news at 11.
thanks
Dan T
RE: The investigation is just beginning
The other thing is that most people are not careful enough with surface prep, and they don't know how to turn on the 'high precision' mode.
Is your cert chem from the melt or a product check?
I will assume melt, so given the variation in a portable XRF and the allowances for check chem, it looks like a match to me.
I usually re-test the same spot 5 times and record each time. That gives a good idea of how precise the readings are.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: The investigation is just beginning
Should I take that to mean the new, broken bolt //could be// 1045?
thanks
Dan T
RE: The investigation is just beginning
I would be more concerned with mechanical properties and microstructure.
Though at some point a detailed analysis would be good to have.
Mix-ups have been known to happen.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: The investigation is just beginning
RE: The investigation is just beginning
RE: The investigation is just beginning
RE: The investigation is just beginning