Bolts Failing Due To Fatigue

https://www.accessfund.org/educate-yourself/for-advocates/managing-fixed-anchors/bolt-basics-what-every-climber-should-know#trust

This article listed bolts failing due to fatigue as a concern.

Are there any confirmed, suspected, or even "urban myths" about a bolt failing primarily due to fatigue?  If yes, could you link please?  

The failure mode I think is most likely is that of a rusty wedge bolt on slightly overhanging terrain. I have read cases where rusty wedges were wiggled out by hand, and I have removed wedges that slipped out under very little force. Bolt hangers usually do a good job of converting the force of a fall to shearing force, but an axial pull can happen. I don't think that normal climbing falls generate enough force to shear a 3/8" bolt, even if it is quite rusty. 

I was climbing on bolted terrain a couple of weeks ago and there were a number of loose bolts, no big, but specifically minded a partner to not lean back with his weight in a stance, the pull out direction, and he was looking at me like I was a ridiculous nag and finally moved to sit instead.  Mechanical awareness is a sorely diminshed asset of late.  Thinking at the margin and learning about how things respond to changes, in this case direction, is a skill we need to encourage.

Tyler Metheney wrote:

I've only read 1 case where a climber fell an a bolt failed causing a ground fall. Climber survived though. I can't find where I read it at.  I too would be interested to know if there's more incidences. 

There was the death at ORG from a bolt that apparently failed at body weight. http://www.rockandice.com/climbing-accidents/bolt-breaks-climber-falls-to-death

There have been other incidences of bolt failures causing fatal accidents as well.

The 5/16" split shaft that failed at Owens River Gorge looks like it cracked when it was installed based on how the broken end was rusty:

Mike Slavens wrote:

https://www.accessfund.org/educate-yourself/for-advocates/managing-fixed-anchors/bolt-basics-what-every-climber-should-know#trust

This article listed bolts failing due to fatigue as a concern.

Are there any confirmed, suspected, or even "urban myths" about a bolt failing primarily due to fatigue?  If yes, could you link please?  

I read that article yesterday and was astounded by the amount of incorrect information it had.  Climbing bolts do not fail due to fatigue.  When you are talking about fatigue you are talking about millions of cycles.  In climbing, the only time you really put enough stress on a bolt to be considered a cycle would be during a lead fall, and even the most popular sport routes in the world are not seeing millions of falls over the life of the bolt.  

Bolts can fail due to many different things, but fatigue isn't one of them.

Ken Noyce wrote:

I read that article yesterday and was astounded by the amount of incorrect information it had.  

I agree; but to be fair there was a lot of good information as well, IMO a lot more good info than incorrect.  

Ken Noyce wrote:

When you are talking about fatigue you are talking about millions of cycles.  In climbing, the only time you really put enough stress on a bolt to be considered a cycle would be during a lead fall, and even the most popular sport routes in the world are not seeing millions of falls over the life of the bolt.  

Bolts can fail due to many different things, but fatigue isn't one of them.

Much more commonly yes fatigue is associated with million+ cycles.  However there is still low cycle-high stress fatigue where steel will fail in the range of 1,000's of cycles, particularly if there is significant plastic deformation from each cycle.  This seems like the more relevant failure mode for climbing bolts.  Still 1,000's of cycles seems a lot even for the crux bolt on a trade route that is typically projected.  I agree failure from fatigue sounds improbable if not impossible but I wanted to see if there is info out there that I'm not aware of.

The only climbing gear would ever fail for top fatigue is if you mixed your climbing gear with slacklining gear

I´m not going to offer an opinion on steel bolts as we never use them but stainless glue-ins we have tested for fatigue. I installed a 6mm rod twisted leg bolt in a granite block and pulled it straight out at 25kN for 1,000 cycles (the load/unload speed is 0.2 sec so represents the typical speed the peak load is achieved in a fall) then raised the force 5kN at a time for 100 cycles until failure. The granite block cracked from fatigue at 1382 cycles and 44,8kN.

The 10mm wedge bolt I tested failed after 172 cycles of 25kN when the test block also cracked (it already had a few other holes in it from other tests).

To test for high-frequency fatigue (someone said they vibrated in the wind and would eventually fail) we installed a glue-in in the concrete wall in our generator room and used it as an anchor for the head steady for one of the generators. These are 480hp six cylinder diesel engines running at 1600rpm, pre-loaded at 25kN the bolt is still doing it´s job nine years later and has outlived one engine already.

Mike Slavens wrote:

I agree; but to be fair there was a lot of good information as well, IMO a lot more good info than incorrect.  

Much more commonly yes fatigue is associated with million+ cycles.  However there is still low cycle-high stress fatigue where steel will fail in the range of 1,000's of cycles, particularly if there is significant plastic deformation from each cycle.  This seems like the more relevant failure mode for climbing bolts.  Still 1,000's of cycles seems a lot even for the crux bolt on a trade route that is typically projected.  I agree failure from fatigue sounds improbable if not impossible but I wanted to see if there is info out there that I'm not aware of.

True, there was good information there, but it really should have been reviewed prior to publication.  The problem with fatigue is the fact that steel has an endurance limit which is around 50% of the ultimate strength of the material.  The stresses on a typical bolt during a fall (I'm excluding Titt bolts and Wave bolts in this) are going to be well below the endurance limit of the metal which means that there will be no fatigue.  The only type of fall that could possibly exceed the endurance limit of the material would be a factor 2 fall, and I can guarantee you that we aren't seeing enough factor 2 falls on any bolts to cause low cycle fatigue. 

Ken Noyce wrote:

True, there was good information there, but it really should have been reviewed prior to publication.  The problem with fatigue is the fact that steel has an endurance limit which is around 50% of the ultimate strength of the material.  The stresses on a typical bolt during a fall (I'm excluding Titt bolts and Wave bolts in this) are going to be well below the endurance limit of the metal which means that there will be no fatigue.  The only type of fall that could possibly exceed the endurance limit of the material would be a factor 2 fall, and I can guarantee you that we aren't seeing enough factor 2 falls on any bolts to cause low cycle fatigue. 

Just put off curiosity, why do you exclude the wave and Titt bolts in your statement? Do they have different material properties with regards to fatigue? 

eli poss wrote:

Just put off curiosity, why do you exclude the wave and Titt bolts in your statement? Do they have different material properties with regards to fatigue? 

The Wave and Titt bolts are both made of very thin bar stock which means that although they are plenty strong, they will see higher stresses, possibly above the endurance limit of the material.  I haven't ever seen it, but I believe I've heard of Titt bolts that have been permanently deformed due to big falls which means that the material has yielded, and that would definitely be above the endurance limit of the material.  

Bolt hangers also get loaded above their endurance limit, but they are easy to inspect and will look like they are in bad shape long before you would ever come close to having one fail due to fatigue. 

Ken Noyce wrote:

The Wave and Titt bolts are both made of very thin bar stock which means that although they are plenty strong, they will see higher stresses, possibly above the endurance limit of the material.  I haven't ever seen it, but I believe I've heard of Titt bolts that have been permanently deformed due to big falls which means that the material has yielded, and that would definitely be above the endurance limit of the material.  

Bolt hangers also get loaded above their endurance limit, but they are easy to inspect and will look like they are in bad shape long before you would ever come close to having one fail due to fatigue. 

That is confused to put it gently! All bolts are permanently deformed in manufacturing and all of them deform under high loads as well. However to exceed the endurance limit you need to bend the bolt back and forward exceeding the yield repeatedly, the standard test is 10.000.000 times. As gravity works in a constant direction and considering the normal climbing scenarios it is unlikely a bolt could be repeatedly bent in different directions for this number of cycles.

Like most forum posts, the science is mostly correct but a little off and/or confusingly stated.  However, I think we all agree that 1) No known cases, or even speculation, of a bolt at the crag failing primarily due to fatigue, 2) There isn't a plausible situation where a climbing bolt could fail primarily due to fatigue.

Jim Titt wrote:

That is confused to put it gently! All bolts are permanently deformed in manufacturing and all of them deform under high loads as well. However to exceed the endurance limit you need to bend the bolt back and forward exceeding the yield repeatedly, the standard test is 10.000.000 times. As gravity works in a constant direction and considering the normal climbing scenarios it is unlikely a bolt could be repeatedly bent in different directions for this number of cycles.

Sorry Jim, normally you're spot on, but in this case, you seem a bit confused.  My career is in fatigue of metal aircraft parts, so I think I have a pretty good understanding of the mechanisms involved, and I can assure you that you don't need reverse loading to have fatigue, nor do you need to exceed the yield strength of the material to have fatigue.  I do agree that there is no way that you would ever have fatigue on a climbing bolt (including on your bolts), but fatigue certainly does happen due to unidirectional cyclical loading, and well below the materials yield strength.

Ken Noyce wrote:

I read that article yesterday and was astounded by the amount of incorrect information it had.  Climbing bolts do not fail due to fatigue.  When you are talking about fatigue you are talking about millions of cycles.

Bolts can fail due to many different things, but fatigue isn't one of them.

Fatigue life is dependent of design, and highly dependent on materials. Saying that fatigue life for every bolt hangar is in the millions of cycles is at least misleading. 

As others have said, this problem is not a problem at all. Fatigue in modern steel climbing anchors simply is not an issue with our application. While any bolt can fail from fatigue given enough load cycles, the required cycles and load values are well outside even the most extreme climbing scenario. Aluminum is far more susceptible to fatigue than steel on an order of several times and yet fatigue in aluminum carabiners caused from taking too many whips is basically unheard of. 

eli poss wrote:

The only climbing gear would ever fail for top fatigue is if you mixed your climbing gear with slacklining gear

Does gear take that much extra abuse from a slacking setup?

Mike T wrote:

Does gear take that much extra abuse from a slacking setup?

Yes, especially high lining.  Fatigue is certainly possible when using climbing gear for high lining (especially with aluminum gear).

Does anybody know of a confirmed case of the Jim Titt Bolts bolts or Wave bolts conforming or bending from ONLY a climbing fall ?  That would require a huge force