microfractures...are they real?

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Messages 1 - 15 of total 15 in this topic
Buju

Trad climber
the range of light
Topic Author's Original Post - Nov 1, 2009 - 08:05pm PT
This weekend, for the second time, I have had an engineer tell me that microfractures do not actually exist. He just completed his masters in metallurgy and he insisted that microfractures cannot occur in alluminum. Both of these guys have told me that any piece of gear is safe to use as long as it is not visably deformed....

Any of you gear geeks have anyting to say on the matter? ....before I start whipping on to all of those cams ive found below el cap!!

thanks
-rog
WBraun

climber
Nov 1, 2009 - 08:07pm PT
You have "faith" in the engineer?
Alex Baker

climber
Portland
Nov 1, 2009 - 08:13pm PT
Brohammed, don't listen to that drunken drivel.



Buju

Trad climber
the range of light
Topic Author's Reply - Nov 1, 2009 - 08:22pm PT
thanks a-bomb! but of course back in the old country, you would sling pieces of soviet tanks, and wedge 'em in for pro eh?

alex, by the way, i just found a par of shoes of yours and have some pics from tangerine trip to send you. e mail me your adress! rogerotter@hotmail.com
Domingo

Trad climber
El Portal, CA
Nov 1, 2009 - 08:26pm PT
Rog!

I've had this talk with a lot of people, including some profs in engineering. Aluminum is a highly ductile metal, so it shouldn't develop micro-fractures. This is compared to, say, most types of cast iron, which are considered very brittle and very very prone to micro-fracture. In general, metals that have to be cast are prone to these fractures - aluminum doesn't have to be cast and I'm pretty sure carabiners aren't cast most of the time anyway.

So I think you're fine on biners. That said, cams have a lot of inner sodering/connected working parts that can get f*#ked up in a fall. I don't think microfractures would be as much of a concern as other things (in fact, soder is a combination of several ductile materials), and I don't know enough about the inside of a cam to be say that things wouldn't separate or deform somewhere inside.







"You have "faith" in the engineer?"

Who made the sh#t in the first place? Unless you're free-soloing without shoes or chalk, you've got faith in someone...

noshoesnoshirt

climber
Arkansas, I suppose
Nov 1, 2009 - 08:32pm PT
As a mechanical engineer who worked with several materials engineers and did some background studying on my own, I gotta say no.

If you can't see visible damage, it's probably OK.

That being said, use your best judgment.
Blinky

Trad climber
Nov 1, 2009 - 11:10pm PT
This is a little off but worth adding.

First, I'm an arborist. Some of us use aluminum rings on our harnesses (almost identical to rap rings), to clip the rope into. Recently, two of those rings failed completely in separate instances under moderately low stress. These specific rings were aluminum and imported by Kong-Bonatti.

I think the conclusion was that a large batch of those rings made it to the US and Europe from the Pacific Rim without being heat treated. Micro-fractures were considered though.
The first failed during a bounce test (testing a high tie-in point with body weight) and the second failed at a competition during a rapid swinging descent, the climber fell about 15'... young tree guys are fairly resilient, he wasn't badly hurt.

Anyway, with the discussion about ductility and all, I thought that was a good example of brittle failure in aluminum. In that last case, the rings were visually inspected prior to the competition by an experienced judge. He said there were no visible sign of damage.

It's a good case for 100% proof testing of aluminum gear.
aguacaliente

climber
Nov 2, 2009 - 02:24am PT
There are a couple of different ways that metal objects can fail. Probably the most important distinction to make here is between impact damage (small number of sharp blows) and fatigue failure (crack propagation from repeated small loads). Fatigue failure happens when an object is stressed for many cycles, a stress concentration (or corrosion, etc) leads to the formation of a small hairline crack, and the repeated load cycles cause the crack to propagate. Eventually the piece is cracked halfway through, takes a load that is the straw that breaks its back, and suddenly cracks the rest of the way through. Although it may look like the last load suddenly cracked it, in reality the piece was already halfway gone. Bike parts sometimes break this way (I've broken bike rear axles, not by hucking off jumps, but from the repeated strain of pedaling).

For something like a biner, most of the time it isn't under much load at all. The locking biner you use on rappel takes repeated cycles of body weight, but it is much stronger than needed to take body weight and it doesn't have any sharp corners where cracks would start. However maybe it's possible that the arborists' rap rings described above could fail from fatigue if they were understrength to begin with, or had a weakness such as a bad weld. Another scary object could be an old hanger that had repeatedly been loaded or fallen on. When you hear about something that snaps under body weight, it's possible that it was already cracked partway through from fatigue.

So I think it may be more important to inspect gear for hairline fractures or visible damage than to worry about invisible microfractures. Sounds great, but hairline fractures can be pretty difficult to see. Fortunately, most gear is built strong enough that it won't develop fatigue failure in normal use, which is why you don't hear about biners cracking in half unless they were loaded over an edge or something. As usual, the bottom line is that if you don't have confidence in it, don't use it.


Disclaimer: I am not a metallurgist, but this is correct to the best of my knowledge.
aguacaliente

climber
Nov 2, 2009 - 02:51am PT
Rokjox, yes some aluminum alloys are heat treated for strength. This is especially important for aluminum that is welded and then heat treated to regain strength in the heat affected zone near the weld. When you see an aluminum alloy name like "6061-T6," the T6 part designates the type of heat treatment.
lostparrot

Trad climber
rockford,il
Nov 2, 2009 - 03:08am PT
aluminum that is used in car engines is heat treated. pistons, cylinder heads, blocks.
Brendan

Trad climber
Yosemite, CA
Nov 2, 2009 - 09:33am PT
Rog-

I'll build a bro-bot we can both wear like a diaper that will deploy air bag style when either of us falls into ledges or trees. haha.

Also, im pretty sure you dont have to worry about biners breaking unless you generate enough velocity to have the laws or relativity apply to you through time dialation... like myself.

P.S. New hampshire smells funny. I miss the west coast.
Buju

Trad climber
the range of light
Topic Author's Reply - Nov 2, 2009 - 09:34am PT
thanks...mr whipper of the year '09...
Domingo

Trad climber
El Portal, CA
Nov 2, 2009 - 04:56pm PT
"Anyway, with the discussion about ductility and all, I thought that was a good example of brittle failure in aluminum."

Those were KONG rings and they issued this statement:

"KONG Bonatti of Italy has confirmed the issuance of polished aluminum rings that were sourced elsewhere and distributed without individual testing. A quantity of these rings were mixed into KONG boxes without having been individually tested and laser marked."

.....so that says pretty sh#t quality control on an outsourced batch to me, and not standard typical aluminum. They weren't even marked with a strength rating. On top of that there seems to be a good chance the alloy in the batch was contaminated.

Beautiful work KONG, as always.
backwaays

Trad climber
north logan, Utah
Nov 2, 2009 - 06:45pm PT
I am an engineer and have been climbing for 12 year. As far as micro cracks are concerned. I do agree with rog in the fact that aluminum is a softer material. Harder material and tempered material tend to crack easier because of there brittle nature more than softer material. It is like ice vs playdough, will playdough crack if hit by a hammer. no it will deform though. but you hit ice with a hammer it will. if you have ever seen a dogbone test steel test when they pull apart metal it elongates but not cracks until it reaches a ultamate strength when the material reaches a hardened state from strain hardening in which caase it does crack at failure. when a peice falls to the ground and hits a rock below it is like taking a hammer and hitting that peice with the same impact. and if the material behaves more like playdough it it dent on impact if it is brittle it will crack depending on the magnitude of the load, on impact. the question is what are the material properties of the aluminum. however if you are concerned there are tests to see if cracks are present. like x rays and such. however, if you feel iffy about it and you don't want to use it and you don't want to run tests well don't use it. inner gut feelings tend to save your life.
scuffy b

climber
Whuttiz that Monstrosicos Inferno?
Nov 2, 2009 - 07:21pm PT
"Ardito Gersen" posted this on rec.climbing a few years back:

You know I have discovered the truth about dropped gear. It is not
microfractures or any other such crap that can cause it to fail.
Actually when the gear is dropped the universe has , for a
microsecond, to face an incongruent situation. IT expected you to
drop, not the gear. During that microsecond it takes for IT to adjust
some of the common laws of Physics get suspended in a small area
around the gear. The gear then does not "exist" anymore. Instead it
enters a Schrodingen Kitten state of probable/improbable existence.

It is during that period with the gear quickly fluctuating among
dimensions that it becomes possessed by demons. Yes, you have read
that correctly. DEMONS!!. They intertwine with the gear and it is
those demons trying to get out that cause the so called
"microfractures".Man you gotta be really careful because your rack may
now be a demon nest. All you can do now is:


A) Destroy the gear, to prevent the demons from causing any harm.
Dropping it into a volcano seems to be fashionable again due to the
influence of major Hollywood productions but I suggest an easier
solution just dig a hole in the ground, put the gear in, cover with an
adequate amount of thermite. Ignite a magnesium initiator on top of
the pile. Watch the demons burn!


B) Exorcise the demons. Contact the local representative of the Roman
Catholic Church, make sure that the Exorcist , if they send one, is
properly authorized by the local bishop,. There is only one authorized
Exorcist by dioceses and he has to be appointed by the bishop. Wannabe
exorcists are likely to compound the problem. If they are unavailable
or too busy you can try the Shamanic method described below:


Take off your clothes.


-Use a Sharpie to mark the middle of your belly. But do it a few
inches above or below true center , this is to avoid Demons to focus
on your center. You will appear to them as a blur and if they try to
posses you they are likely to come to the end of you and slip off.
Unless they knot your ends first.


-Cover the rest of your body with mysterious signs and inscriptions.
They may read things like CE, EN 7306, 22KN, T, DMM, 9 etc... those
are there to protect you against the demons entering your body, the
more you have the better.


-Cover yourself with lubricant oil, lest you get stuck in a different
dimension.


-Using a rope make a circle in the ground around the gear. Drive five
expansion bolts into the ground at regular intervals. now the demons
are contained. They have also took some of the qualities of the gear
and they now hate fixed stuff.


-Light fires around the circle. Attach headlamps to the top of ski
poles and direct their beams towards the gear.


-Put a tape of "Macarena" into a tape and play in a loop as loud as
you can!


-Get drunk and stoned ( you do not need instructions for this)


-Run around the circle dancing with a bottle in one hand and an old
issue of Rock and Ice on the other chanting the following formula:
"Get the f*#k outta my gear you as#@&%es!!" or any other ranting of
your liking, to the rhythm of the music.


-Remember to fart as much as you can . That is to prove to the demons
that you are a Tue Climber (tm). For an explanation of this do a
Google search for "farts climber". If possible ignite a few of the
farts (you do not need instructions for this either).


-Keep on drinking!!


-Sh#t into plastic bags and toss them at the gear while crying "MUD
BAT!! MUD BAAAAAT!! INCOMING!!"


-Read excerpts from the Rock and Ice mag (this is truly unbearable
for the demons)


-Collapse, be taken to the ER. Wake up. Stay in a mental institution
for a while. Be released (hopefully)


You can now use your gear without any fear, the demons have been now
expelled to the nether regions where they lived before.


I hope you find this helpful, let us know how it all went!


Ardito.


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