Titanium Bolt Failure

[ModulustheMighty]

I have a climber with two broken feet.
He was clipped into a Ti bolt that was installed in a rock ceiling.

I need to know how to calculate the stresses on this part for a failure analysis report, but the math is a little fuzzy.

Here is the bolt in question:

Here is one end of the bolt that failed.
The shaft is still in the rock.

Here is a Free Body Diagram I drew of what is happening:

I believe that the eye should be aligned with the shaft so as not to introduce a sheer component.

How do I calculate the sheer pressure of the guy weighs 210 lbs and the Ti bolt is 3/8 shaft, with a 1 inch offset.

Also, does it matter if the shaft is hanging out of the rock?
I say it is better, the shaft can flex and distribute the sideways component, where as a coleague says that any additional length will facilitate failure, as more leverage is present.

I think, depending on the Modulus of Elasticity, that it would be easier to snap he bolt if it were installed flush, as there is a small bend radius at the glue in point?

Thank you for any help in analizing this mathematically.

How would I compute the stress for differen lengths of shaft hanging out of the rock?

The bolt was made by USHBA.
It is bent from round stock Ti alloy, I do not know the mix.
It is also welded, another question mark.
Ti is tough to weld.

Thanks!

 

[GregLocock]

Sorry mate, you aren't even asking the right questions.

If you are going to court with this get a professional.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[berkshire]

modulus,
Did by any chance, that bolt fail at the last thread, before the plain shank started?
B.E.

 

[mechengdude]

I agree with Greg. Get a professional to do this. The plaintiff probably will.

You need a proper failure investigation done (ie) metallurgical analysis, etc.

 

[ModulustheMighty]

Berkshire, Thanks for the reply!
Yes it appears that the shaft was broken at the last thread.

This bolt had been installed four years ago.
In order to test it, many falls were taken, which would have introduced a dynamic load, as opposed to just hanging there.
I am thinking that since the rod was bent one way, and the load bent the rod the other way agfter installed, that thisa is the equivalent of bending a coat hanger back and forth.

Also, 210 lbs is not a heavy load, these things are supposed to take 25 Kn.

A German Lab did some tests and three out of five failed due to shaft breakage at 9 Kn.

I have a pic of the cross section, it just looks like shiny fine crystals with an outer oxide, no cracks or anomalies present.

There is no CE cert for bolts, unfortunately, so any old Joe can get into this bussiness.

As fa as Liability, I really doubt that the victim is going to go forward with a suit.

He has medical, and is healing fine.

And most insurance companies do not cove climbing, as it is considered an Extreme sport.

Just want to explain to some of the climbers that this thing is not safe!

M<any are blaming the installation.

I feel that a Personal Safety device should have some anti-murphy nuilt into it, just in case somebody does not install it perfectly.

Thanks Again!

Modulus

 

[hydtools]

Start with stress due to bending load caused by moment due to climber load eccentric to the bolt shaft. Add tensile load due to climber load. Consider reduced section at thread root as area carrying the load, not the full dimension unthreaded shaft. Then pick some multiplier to account for dynamic load due to climber stopping climber free fall. Suddenly applied loads are 2x the static loads. Dynamic loads will be higher. Or calculate load due to stopping a free fall. This will give you some idea of applied loads/stresses.

Ted

 

[GBor]

Don't forget the stress concentration for the thread root shape.

 

[IFRs]

A few thoughts: Titanium is very light but is not a very ductile material and will break rather than bend. I don't think these devices are meant for long term repeated loads, especialy loads that are reversed. Many safety devices say "replace me when I am used" (ropes, helmets, etc). I always wondered who was doing the maintenance on these climbin aids, especially since few know when they were installed, if they were overtorqued or hammered in and how many times they have been stressed, re-torqued or re-pounded in. I'm glad the climber is relatively unhurt.

 

[ModulustheMighty]

Thank you.