Interestingly, to stop crack propagation in aircraft they will often times drill out a hole at the propagating end of the crack. This reduces stress concentration and thus the crack propagation but don't do it with your gear.

3) Lots of people have cited personal experience to the affect that it is not a concern i.e. you should inspect incredibly carefully, but it's OK to use dropped gear.

So says this german dude I meet in yosemite, and this chick from the creek. I can't think of a reason to disagree, clearly fractures are real but so small they can't me seen?
What do you think paranoia or reality?

... the wing on a plane experiences more flex cycles in one flight through bumpy air than all of the climbing gear on your rack experiences in your lifetime. Quit worrying about it.

Seek out a school where the instructor's parents aren't also first cousins.

Curt

He's from West Virginy..... That might not be possible...

My school's outdoor program pretty much tells everyone here that micro-fractures occur in aluminum and if you drop something over 15 feet it should be retired. In fact a lot of people who go through the program here come out as "steel" guys, they don't trust it if its not steel...

... unless the gear manufacturers come right out and say "dropping carabiners does NOT weaken them," then they aren't going to put themselves in a position of possible legal action when or if a carabiner failure resulting in an injury happens. The courts aren't going to care if everyone on RC.com laughs at anyone who mentions microfractures. They are going to ask why you didn't follow the standards. We follow ACCT's standards, which state that if you drop an aluminum carabiner over 15 feet, it must be retired.

Wow, "to come up to par with the rest of rope access world," indeed!
While rockclimbers might prefer NOT to be thought of as rope access
--they climb rock, with rope sometimes not even used--,
it was in their activity that carabiners were developed.
And while rockclimbers have no exact use to throwing 'biners about,
the metal can be slammed hard into the rock on a fall as the ropes
snap taut.
Need I point out that rock is much, much harder than a tree
(anyone climbing ebony?)?

Recently, in another rope-access sort of endeavor, the old tired
myth of microfractures arose, and drew this authoritative response from
one who worked for over a decade in the gear side of climbing--to wit

--------quote:
Neither the steel used in carabiners nor the aluminum alloys is subject to micro-cracking. There may be over-heat treated steel or titanium alloys that exhibit it, but the theory of micro-cracking only came up when they started using fancy ceramics for jet engine turbines.

You can drop your carabiners thousands of feet onto granite, and if they still open and close smoothly, they are fine to use. If you feel uncomfortable with this advice, then go ahead and retire them, or send them to me.

Can I prove this? There is an engineering argument - aluminum alloys (might be exceptions, but 7075-T6 is not one of them) and ordinary steel alloys (as used in carabiners) are not the type of material that exhibits micro-cracking. There is an evidence argument - while working at Black Diamond for 12 years, we NEVER saw a carabiner that exhibited any form of micro-cracking or loss of strength from being dropped (while still functional), including quite a few dropped the full height of El Cap (3000 feet). But no, I cannot PROVE that all biners over all time will never exhibit loss of strength.

And just to cover all the bases, carabiners dropped from outer space, on re-entry, will heat up substantially which will screw up the heat treating. There will likely be ablation of material off the outside also, so I advise against using biners that are dropped from outer space. Those should definitely be retired.

Perhaps Brian knows of some examples of hidden micro-cracking in conventional alloys.
...
-------end quote.

So, should the old adage "trees don't grow to heaven" be proved false,
THEN one might be concerned about dropping a 'biner; but doing
so in more mortal ways won't cause you to get to heaven.

*knudeNoggin*

It seems to me that the microcrack supporters stand in need of some test
evidence for their side of the issue

You know, I've never actually met a practicing materials physicist. Plenty of materials engineers and quite a few chemists. But no physicists that actually study how materials respond to load.

Shear thickening viscoelastic polymers? Like when you mix water and cornstarch? Much more fun than analyzing aluminum, I'm sure.

http://onemansblog.com/...ow-to-walk-on-water/

Oh, we exist - we just study more interesting materials. Steel and aluminum are boring, but give me some glassy colloids or shear thickening viscoelastic polymers and I'll do rheology 'till the cows come home.

YES! EXACTLY!

For those who say that microfractures DO exist, please show us the proof.

It's like the Loch Ness monster, Big Foot, UFO/Aliens, and intelligent liberals: There is no proof of their existence, but everyone thinks it's true.

My background is in materials science as well, but is focused on compound semiconductor materials like gallium arsenide. I'm with you--who wants to study Al?

Curt

Actually, E (not F) = 1/2 * m * V^1/2. Your math is wrong. But let's pursue this line of analysis anyway to see if my empirical evidence measures up.

First, energy is not the right measure to apply. In a fall, kinetic energy is absorbed by the rope and its friction against 'biners in the system. The top piece doesn't move appreciably, so beyond friction not much energy is absorbed by the top piece.

The more appropriate measure when talking about microfractures is force or, perhaps even more appropriately, pressure. We can accept 8kN as reference for the force exerted on the top piece’s carabiner (while it seems high, I don’t have the necessary data to refute it), but what about a dropped carabiner? Consider a 100g carabiner which strikes talus at 10m/s (the speed incurred by a 15 foot drop).

E = ½ * m * V^2
= .5 * 0.1kg * (10m/s)^2
= 5 kgm^2/s^2

If this energy is absorbed within a millimeter (a rough estimation of the distance required to slow from 10m/s to a stop, and we’ll ignore elasticity), then

F = E / d
= (5 kgm^2/s^2) / 0.001m
= 5,000 kgm/s^2
= 5kN

Thus, the force applied to a carabiner dropped from 15 feet is about the same as the force experienced by the top carabiner in a fall. (To be more precise, a carabiner dropped from 20 feet will experience ~8kN of force.)

There is a major difference, however, in how the force is distributed. In a fall, the force is spread across the surface of the ‘biner that contacts the rope. I’d estimate that the effective surface area is at least 50mm^2. A dropped carabiner, in contrast, experiences all its force at a point, perhaps 1mm^2.

Thus, the pressure exerted at the point of contact – where deformation and, thus, microfractures would originate – is many times higher with a carabiner dropped from 20 feet. And a carabiner dropped from hundreds of feet would experience forces several orders of magnitude greater.

Wow.

I took a few shortcuts all right. But lets not over do this. My numbers are correct.

F=MA integrated to dt where t--->0
F=1/2 M V^2 if Vfinal=0

Assuming the rock didn't deflect, it would take a force equal to that of the biner.

Check your equations first. Energy has a time component. sky7high is right W=FD. No time constraint.

chris

...My numbers are correct.

F=MA integrated to dt where t--->0
F=1/2 M V^2 if Vfinal=0

...Back to high school phyisics - F does not equal 1/2mv^2,
...

I took a few shortcuts all right. But lets not over do this. My numbers are correct.

F=MA integrated to dt where t--->0
F=1/2 M V^2 if Vfinal=0