Frame bolt failure

[FJmonkey]

Anyone ever see this kind of failure on a frame bolt?





This might make sense for broken/missing frame bolts...

[Pat Conlon]

Looks like, judging  by the rust, that bolt head was holding on by just a hair.
I've not seen a failure like that. Looks like a crack developed then rust and time did the rest.
All of the failures I've seen have been a shear failure at the thread line. I've never seen a cap twist off like that. I believe those oem chrome shoulder bolts are a grade 6.
The (4) button head M8 bolts at the lower frame attachment points need to be at least a grade 8 or 10...or drill and tap for some M10's or both M10 grade 8...belt and suspenders...

[Horse]

Jeeeees mate, been playin wiff nuts & bolts for over 45 years now & have never seen a fail like that one    should frame that one for sure 

[ken65]

I had a similar experience with an  81 xj650 maxim, a single caliper front end with a long bolt holding it onto the lower..
I was simply riding along about 40kph just changing into second and my brake caliper just fell off.  After some investigation
you could see the rusty bit where the bolt had initially  failed so many moons ago. It stays with you those experiences... 

[Troyskie]

Anyone ever see this kind of failure on a frame bolt?





This might make sense for broken/missing frame bolts...

This is a fault during manufacture. There is a clear delamination & Pat is right, the bolt was holding on by a hair. The crack would have been present since manufacture and use, then corrosion did the rest. It was likely not detected as the delamination looks like it began internally & when the crack reached the surface, corrosion accelerated the failure. Once coated some surface cracks are more obvious, but X-ray is the only way to be sure & not even all aviation bolts are X-rayed.

[The General]

Do we have a pic of the mating surface? (Not got much of an engineering brain, but I do find Mr google interesting.)...after this research I`ll be more respectfull to bolts & torque wrenches!

Apparently that failure can be caused by something caused by 1. Hydrogen Embrittlement (if the tensile strength is over 160000psi) 2. Sharp edges on the bolt hole. 3. Over Tightening combined with 2. (The torque exceeding the plastic deformation point). Item 4 here:- http://www.boltscience.com/pages/Failure%20Modes.swf

According to http://greensladeandcompany.com/wp-content/themes/greenslade-theme/pdf/articles/testing/Testing-Head%20to%20Shank%20%20Failures%20Are%20Prohibited.pdf :-
There are two applications problems that can cause otherwise good bolts or screws to fail where the head of the fastener joins its shank:
1. If the clearance hole is too small where the fastener goes through in the component that is immediately under the head of the bolt or screw the head-to-shank radius on the fastener can be cut when the part is seated. This cut can cause the bolt or screw to brake when the assembly is put into service.
2. If the edge around the hole in the component that the screw or bolt is seated on is not chamfered that sharp edge can cut the under-head radius of the fastener causing it to fail at the head-to-shank juncture when the assemble goes into use.

This one has a photomicrograph pic of a fatigue crack at the Head to Shank radius: http://www.bakerrisk.com/wp-content/uploads/2013/01/MEE_avoiding_bolt_failures.pdf

But I found this article the most enlightening (4.3.3 - p32) :  https://www.kimballmidwest.com/catalog/MarketingText/Avoiding%20Cap%20Screw%20Failure.pdf