Karabiners becoming stronger with age ?

F

Frank1

Just a quick one.

In the ‘extra prussik lanyard?’ thread: a few persons mentioned Karabiners becoming stronger with age (choked or not!).

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I disagree with you and Norm, every time an aluminium alloy karabiner is loaded or chinked against metal it becomes stronger as the microscopic molecules that make up the aluminium alloy settle into to place creating a stronger bond than when the karabiner was first formed.


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My understanding (which may well be incorrect) is that this is an urban myth. ( I’ve been to Karabiner manufacturers factories a few times, and I’m sure they told me the same: unfortunately I was too busy watching them testing to destruction to pay full attention to basic information).

Any thoughts or definitive opinion would be appreciated (and possibly save me some money on the alloy wheel replacement for the truck!).
 
Hi Frank,
As far as i understand,It is steel that has a theoretical fatigue limit.So long as this is not exceeded it will never fatigue. Aluminium alloys on the other hand do not have this limit so are bound by cycles
This research paper is of no real use to us,except for the fact the topic demonstrates that aluminium does suffer fatigue.
didj
 

Attachments

didjon, thanks for the reply. I’m still digesting the bigger words in the fascinating article that you attached. However, it looks as though my alloys (on truck and on harness) are not going to improve with age!

On a serious note, I had not previously considered the question of properties of alloy Karabiners – However, several people have told me that steel Karabiners get stronger with use.

In either event, the definition of ‘cycles ‘ must have to be carefully defined: presumably if you repeatedly push any kit designed to withstand a load / force just over its safe operational range – this will ultimately lead to premature failure. Is this the same as ‘cycles to failure’? ….. So linking with this getting stronger business- does this mean that it is possible for the karabiner to become stronger whilst operating within its designed parameters ? will it eventually need up-rating from 22kN to account for the increased strength (only kidding)? presumably any increases would be marginal?

I understand the principal of this ‘cyclic’ approach to the alloy karabiners (I think): but still not sure about this karabiners getting stronger business.
 
This is the first time that I have ever heard about aluminum biners getting stronger with use. That makes me a bit skeptical. Over the years I've found many work/recreational rope use forums where there are plenty of engineers, gearheads and serious tech weenies. If this were an issue I am certain it would have surfaced somewhere along the line.

Of course, I am sure open to seeing new things. Please backtrack the source for this idea and see if you can provide some documentation.
 
[ QUOTE ]
Hi Frank,
As far as i understand,It is steel that has a theoretical fatigue limit.So long as this is not exceeded it will never fatigue. Aluminium alloys on the other hand do not have this limit so are bound by cycles
This research paper is of no real use to us,except for the fact the topic demonstrates that aluminium does suffer fatigue.
didj

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Tom you should to read the article.... it backs up your doubt



Frank1, I think that whoever posted that alum. gained strength with age/use(on the prussik page) was mistaken. there are cycles to failure on all of our gear metel parts included...

the concept that metel could gain strength i find easy to believe... if that metel is in a controlled inviorment... But think about our attachment points on our saddles... they are cycled many times and while the molocules(misspelled im sure) might align themselves in a more efficient pattern, there is another process taking place at the same time. they are interfacing with other gear... which causes metel fatuge


I could be wrong about this, but hey, it's my opinion
pokinit.gif
 
Hey removal wizard,
I hope no one is misinterpreting my last post.The point I was trying to make is that AL alloys DO NOT get stronger with use.I think the source of this thread is a spin off from the choked carabina thread where someone stated that aluminium gets stronger with use.I agree with you removal wizard.I would go further as to say that nearly everything has a certain amount of cycles to failure Whether its a tree or your hips.In the end everything that resists a force continuously or repetitively will in the end fail given a long enough time line.If this statement was true I think everyone would by now be moving there 5 year old climbing binas into their rigging kit.
In the 1700 or there abouts the Swedish were one of the first europeans to make wrought iron from pig iron which was much stronger and less brittle.This was achieved by removing the carbon from the smelting process.>The final process was to bash the iron with a very heavy hammer.This was align the molocules and more importantly to remove as much of the carbon as possible.Maybe this myth has origins going back as far as that..who knows....

Didj
 
I don't mean to be the nay sayer, but carbon in iron is what makes steel. The carbon atoms fill in the iron crystal structure, which stabilizes and strengthens iron and makes it steel. I also don't think it has anything to do with aluminum carabiners. And all metals have crystal structures which break over time due to repeated heat and vibrations. Otherwise known as "loads" or fatigue."
 
wwc,

what you say is true to an extent..... The Bessemer process converts Pig Iron into steel by removing all of the impurities including carbon..... some carbon is not removed depending on how hard/brittle you wish the steel to be (.02 - 1.7% carbon)

jawdrop.gif
no i didnt have to look that up!
 
i think that anything pushed near it's limits has a dramatic drop in cycles of useful life. Also, that though deformation in metals may make some points stronger; by thickening them; that thickness must come from some other of their parts. A chain is only as strong as it's weakest link; so the new strength should be assessed by the strength of the displaced thin piece, not the strength of the displaced thicker. Displacement parts from another device; only matter when they are properly bonded to the previous device.

If you bend a wire back and forth; part does become thicker; part becomes thinner.
 
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If you bend a wire back and forth; part does become thicker; part becomes thinner.

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then it breaks....

I have never heard of a carabiner getting stronger with use...
 
Hi,

I’ve done some further research into this subject and formulated the following conclusions (with no technical / metallurgical qualification to back it up-just my opinion).

In principal:-

Steel can become ‘stronger’ – check out links relating to ‘Dislocations and structure’

eg. www.llnl.gov/pao/news/news_releases/2006/NR-06-04-08.htmlge

(Providing we are clear about definitions of stress /fatigue/ distortion/ cycles to failure) –Alloys have cycles to failure – steel does not

How or if, this relates to karabiners in any meaningful way (given the differing manufacturing processes, metal ingredients mixtures and the other variables when we use them in the climbing system) – I still do not know.

I found a thread on another forum that makes for interesting reading ref Karabiners, its mainly relating to redundancy: but there is an interesting bit about alloy v steel. One of the chaps appears to actually know what he’s talking about.


www.sarinfo.bc.ca/Library/Equipment/binerlif.eqpage

That’s it for me on this one -I’ve used up all my cycles to failure
 
Well, that thread also recommends throwing away a biner if you drop it, so sounds like academic hot air losing sight of practicalities or an actual understanding of karabiner manufacture. They aren't rods of steel and alu just bent into shape. It all starts with the best quality stock (at least the manufacturers products that I use). Any cracks in krabs comes from the stock pre manufacture, not any drop.

I'd stick with your experiences of the tests Frank. I have sent many 20-30 yr old alu biners to the test machine under the gaze of a guy who has made 10 million of the bloody things, and not one of them failed below the MBS stamped on the side.

The cycles to failure are too many to worry about in all practicality.

It is interesting discussing the academic absolutes, but they have little bearing on practical daily forces.

Anyone reading that article would be inclined to think alloy should never be used in life support for very long or if it has been dropped, which is utter rubbish IMHO.

Its the same as anything alse - apply an appropriate margin of safety and don't overload the system.

Like you say, there is no point in planning a system for absolute strength when the forces aren't survivable. As for rigging, its one reason to use only steel krabs (higher repetitive forces)

I think the confusion of increasing strength with age comes from tempered metals - our karabiners have been through the high heat forge and bent and /or stamped into shape before cooling. This process agitates the molecules that slowly settle over time. So, as the karabiner ages, these molecules settle more. Krabs don't get stronger as such, just as they don't get weaker with the low loads we apply in climbing - hence the test results we have both experienced.

Have a good weekend!
cool.gif
 
I retired an aluminum biner after I dropped it 60 feet onto some big rocks. The biner looks like it's seen no more than normal wear but I know that it took that fall.

I sold it to an unsuspecting chap on ebay for 6 bucks.

No not really....
 
Zac, Both Black Diamond and Denny Morehouse say that their testing indicates that th ewhole dropped gear thing is a red herring. If it isn't visibly, significantly damaged a 'biner ISN'T significantly damaged.
 
And that is cool.
I had a support 'biner that was visibly worn from riding on a saddle D So I gave it to an eight year old boy. A Tri acting 'biner is super way cool for him and he A. Won't climb on it and B. If he were to climb on it it would be okay.
 
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