Nut failure- What do you think? 1

[strWennie1]

I grabbed this off an hot-rod website.

It was holding a cylinder head on .. running high boost. Failure mode looks strange to me for a nut. I expect shearout of either nut or stud threads.
Reading around my only viable scenerious are ..

1) just wasn't heattreated and residual forming stresses give a hoop stress failure
2) Heat-treated and then acid bath for cleanup. The part experienced hydrogen embrittlement.
3)Manufacture used too high a heat-treatment for the material and failure is fatigue related- still would have expected thread shear.



Michael

 

[rb1957]

it's failed thru the root of one of the 12pt grooves ... maybe overtorquing, maybe bogus h/ware ?

 

[MintJulep]

Can't see any detail of the fracture surface, so all we can do is speculated - which is fun enough.

Hydrogen embrittlement is a possibility, as is a glass-hard and brittle heat treatment, or too rapid a quench.

 

[jmw]

Possibly the bolt was the wrong size and the threads finished too soon so that when tightening up they ran out of thread?

JMW

http://www.ViscoAnalyser.com

 

[eromlignod]

I agree with most of you guys: it looks like a faulty nut. I'd guess either bad material or a bad heat treatment, or both. A good nut just shouldn't fail in that manner.

Don
Kansas City

 

[metengr]

A seam defect in the bar used to machine the nut.

 

[drawoh]

strWennie1,

Is it possible for something to fracture that straight? Is it possible it was cut with a hacksaw?

JHG

 

[CorBlimeyLimey]

Don't you just hate it when that happens to your nuts? [lookaroud]

Can you take close up shots of the fractured faces?

 

[unclesyd]

Is that cracking I see opposite the break?

What was the spec on the nut?

Are there any markings on the nut?

Do you have any more of similar nuts laying around that you can check?

First off this failure has the appearance of being busted by a chisel or nut buster, with the exception that the picture where the nut is on the stud it appears that there is some bright metal in a sea of black. There is apparent markings on the flanks if drive points from an ill fitting socket.

As stated above it would be nice to see the fracture surface. I would finish breaking the nut without damaging
any fracture surface.

 

[plasgears]

Bogus, made in China?

 

[strWennie1]

I wish I could fill in details...

I begged the guy for a defective nut. Vendor fedex him new hardware and he sent it all back. So, just speculation unless the manufacture admits to the problem.
If I do happen to get a nut- I'll take a close up pic at work with inspection equipment and get a Rc number of the material.
It didn't fail on intial preload.

Thanks for the speculation!

Michael

 

[MikeHalloran]

That's an incredibly thin nut. I mean, the distance between the spline root and the thread major diameter has to be real close to zero.

With geometry like that, even Unobtainium would crack...



Mike Halloran
Pembroke Pines, FL, USA

 

[RossABQ]

I agree with JMW, I'd be looking to see if there was supposed to be a washer under it to keep it on the threaded portion of the bolt. If a connecting rod bolt, perhaps the cap was machined and this allowed the cap to sit deeper over the bolt?

 

[HeviiGuy]

Ouch!

Initial gut feel is that the sizes were incompatible (and possibly exacerbated by conditions noted above). It'd be interesting to know whether the degree of resistance felt when turning the nut down was greater than expected.

"Made in China?" Maybe the heat was contaminated by melamine ;-)

Ciao,

HevïGuy

http://www.heviitech.com

 

[strWennie1]

These are nuts for head stud conversion. Fits a 6BT cummins engine aka Dodge diesel. 125 ft-lb torque, running 60 psi of boost.

 

[RossABQ]

Was the stud threaded completely into the block? Or more to the point, are the threads sticking up above the head completely cut?

 

[hacksaw]

Embrittlement can be caused by the solution used to blacken the parts. Having said that,
I agree with unclesyd a cracked nut failure especially one that is likely CrMo nut, is a bit unusual.

By the way the photo appears to be edited, two cracked nut images are shown and the washer is missing in both

 

[unclesyd]

Was this by chance a deformed nut?
I'm talking about a radial deformed barrel.

The type nut in the failure doesn't normally use a washer as the flange area on the nut acts as a washer and also carries the majority of the preload.

I have to go along with jmw as it looks like the nut ran out of threads and started to climb the thread runout.

 

[hydtools]

The way the nut break has remained open after failure would suggest retained stress as the result of production process. The break would relieve the stress and the nut would spring open. High strength nuts would crack but not remain open. There appears to be no yielding before failure. If the nut was radially forced open I would expect it to break on the opposite side, too. Break before yielding.
Maybe the nut was already hoop-stressed before being installed.

Ted

 

[CorBlimeyLimey]

Strangely though, the nut on the stud has split at the thick section of a 'point'.