youth of a belay device

I really am tired of micro fractures being brought up as if they are actually a thing despite the fact that it's been debunked over and over again, the only micro fractures that exist are theoretical. They have never been observed and have yet to be created even under laboratory conditions.

that guy named seb wrote:I really am tired of micro fractures being brought up as if they are actually a thing despite the fact that it's been debunked over and over again, the only micro fractures that exist are theoretical. They have never been observed and have yet to be created even under laboratory conditions.

No, micro-fractures do exist, they just don't cause a significant loss in strength and are therefore not a concern

You guys are going to be held responsible for destroying my micro-fractured gear disposer business if you keep carrying on like this.

eli poss wrote: No, micro-fractures do exist, they just don't cause a significant loss in strength and are therefore not a concern

From the first link I posted up-thread:
"...aluminum just isn't a material prone to the kind of microfractures that would be invisible to the naked eye. It's too ductile of a metal..."

IMO a blog written by some climber whose been doing it 8 years isn't exactly the most credible source of information. I recall reading something written on here by either a metallurgist or an engineer (I can't remember, honestly) explaining how a significant impact could potentially create micro-fractures, but due to some property of aluminum (I think it was ductility but I'm not 100% sure), these fractures do not result in any noticeable loss in strength.

I think I have also read a more formal report either by DAV, or some caving organization that came to the same conclusion.

eli poss wrote:IMO ... something ... I can't remember ... I'm not 100% sure ... I think.

Man - that wasn't very convincing.

... you're starting to sound like me. ;-)

Bill Lawry wrote: Man - that wasn't very convincing. ... you're starting to sound like me. ;-)

I figured somebody else (probably bearbreeder) would dig it up eventually. I'm too lazy...

So work hardening and microfractures do go hand-in-hand: if you repeatedly load a piece above the elastic limit, you induce work hardening, such that microstructural defects can be enlarged via repeated loading, becoming micro (and later macro) fractures.

Have any of you *ever* loaded a carabiner past the elastic limit without breaking it? That is, is the carabiner still sort-of intact, but the gate either doesn't close or doesn't open? If not, then you have not really entered, in any meaningful capacity, the region in which microfractures can occur, let alone grow.

Mike13 wrote: This really depends on your definition of fatigue. I've had some metallurgical and materials engineers that I've worked with make a very strong case for considering one cycle fatigue (aka overload) as extremely low cycle fatigue. It can make for fun arguments among engineers. Of course there's the argument that there has to be at least two loads for it to be cyclic. But when viewed under an SEM after the transition into the low cycle fatigue zone you can typically go to a high enough mag to only show details that look like overload.

Just found this gem so...

eli poss wrote: Just found this gem so...

Sorry I'm an engineer and I'm bored. I used to spend a lot of time doing failure analysis so thinking about how things break is one of my favorite pass times. I have no other excuse for my rambling.

Don't worry about it, I'm the kind of nerd who'd probably be interested if I understood. Just out of curiosity, since you appear to know a decent amount about metallurgy, how do steel carabiners hold up to fatigue?

Well, steel carabiners are much stronger than an aluminum one of the same dimensions by comparison so that gives them a huge edge up front. But in truth you're going to have to replace your carabiners for wear long before you need to worry about fatigue. Steel does have the advantage that it has a structure which allows for a true fatigue threshold, meaning if you don't achieve a certain stress you will never even start a crack. Aluminum on the other hand can initiate a crack at any load. It is however usually best fit by a logarithm shape so at very low loads, it's a lot of cycles. The bicycle industry found this out the hard way as some people ride their marginally strong enough super light aluminum bikes a very long time and over a lot of bumps. If you have a more specific question I would be happy to answer.

http://www.outdoorsafetyinstitute.com/index.php/news/single/should_you_retire_a_dropped_carabiner/

interesting. Do you know the equation for the logarithmic shape that I could make a spreadsheet out of? I think it would be interesting to look at ~ how many cycles at "x" load it would take to fatigue a biner.

If your worried enough about it to post a thread buy a new one. Climbing accidents rarely occur from gear breaking they happen from human error.

eli poss wrote:IMO a blog written by some climber whose been doing it 8 years isn't exactly the most credible source of information. I recall reading something written on here by either a metallurgist or an engineer (I can't remember, honestly) explaining how a significant impact could potentially create micro-fractures, but due to some property of aluminum (I think it was ductility but I'm not 100% sure), these fractures do not result in any noticeable loss in strength. I think I have also read a more formal report either by DAV, or some caving organization that came to the same conclusion.

I'm not sure if this really answers anything, but ductility essentially the
stretchability of a material.

Ductility is when a solid material stretches under tensile stress. If ductile, a material may be stretched into a wire. Malleability, a similar property, is a material's ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.

See mountainproject.com/v/quest…. We probably shouldn't hijack the thread with the discussion of (micro)fracturing under (repeated) load.