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ja1484
Nov 26, 2008, 12:21 AM
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<3 Metolius.
Never have to wonder if it's bomber. Ever.
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j_ung
Nov 26, 2008, 5:31 PM
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ja1484 wrote: <3 Metolius. Never have to wonder if it's bomber. Ever.
Word.
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granite_grrl
Nov 26, 2008, 6:38 PM
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Rad! Though I do feel bad for the cam. 
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jamatt
Nov 26, 2008, 8:30 PM
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I'm wondering if pull tests results really represent the strength of a piece of gear.
Assume that the line on your graph represents about a minute. Would the gear fail sooner if the same force was applied in 5 seconds? 1 second?
EMWTK
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adatesman
Nov 26, 2008, 8:59 PM
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carbonrx8
Nov 26, 2008, 9:14 PM
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I think what he is wanting to know, qualitativly, is what amount of hysteresis is inherent to the system.
For instance, if you took a banana and tied a loop around it, then put the banana over a gap about 1 inch wide, then very slowly pulled the free end of the loop, you would expect the banana to be smooshed into the gap, whereas if you yanked the free end of the loop very very quickly the loop would slice cleanly through the banana leaving two halves. THe peak forces generated, measured disregarding dynamics or hysteresis in your equipment, may be different in the two cases.
Now, would this be the case here (again disregarding dynamics, which is, i think, the major reason to pull reasonablly slowly)? If you applied 12kN within 100 microseconds, would the cam break? I.e., would forces within the cam not be able to reach a dynamic equilibrium (steady-state) such that some other part of the cam experiences very high forces allowing some other failure mode to occur at a lower rating?
Another question might be, if you pulled a piton very slowly vs with a funkness device, would the piton dislodge at a higher peak force when pulled slowly than when funked?
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rightarmbad
Nov 27, 2008, 8:08 AM
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Which brings up the most important topic of frictional losses within the cam.
More friction, as in lobe to axel and the like, the less outward force applied to the lobes.
I am sure that a very quickly applied load, as in a drop test, would show up such losses, under the conditions that it will experience in the field, much better.
I have a couple of booty cams that I would love to see measured during a drop test, but alas, postage from Australia would be prohibitive.
(This post was edited by rightarmbad on Nov 27, 2008, 8:10 AM)
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josephgdawson
Nov 27, 2008, 6:55 PM
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Interesting to watch and good to know the cams holds up well past 3000. Thanks for posting.
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adatesman
Nov 28, 2008, 12:45 AM
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ja1484
Nov 28, 2008, 2:35 AM
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I'm compelled, for some reason, to again state that I doubt the gear is *ever* the weak link (i.e. first item to reach catastrophic failure) in a real world climbing system.
I would love - positively adore - someone to go out to several different choss piles and take a look at deformation loads in various rock types.
We already know sandstone deserves some pucker. We already know clean granite is almost always "hard enough". What about the stuff in the middle ground?
(not that I'm not grateful for the testing, but I'm struggling to apply it. I usually retire cams when they're looking haggard, so the relative holding power of a retire-worthy cam vs. new @ retail doesn't change my climbing practices much)
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rocknice2
Nov 28, 2008, 2:40 AM
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jamatt wrote: I'm wondering if pull tests results really represent the strength of a piece of gear. Assume that the line on your graph represents about a minute. Would the gear fail sooner if the same force was applied in 5 seconds? 1 second? EMWTK
My opinion is just the opposite. A short duration using the same force would cause LESS damage.
A comparison would be tests done on the human body where very high G-forces for very short periods of time were survived but much lower G-forces for longer periods of time caused severe injury.
For example 40 G's @ 100 milliseconds might cause less injury than 12 G's @ 100 seconds.
I made up these numbers but you get the drift.
It must have something to do with the elastic nature of the material. Yes aluminum has elasticity, hell even steel cable has some.
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patmay81
Nov 28, 2008, 4:46 AM
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adatesman wrote: beat up, rusty and hacked apart it still held above rating.
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rightarmbad
Nov 28, 2008, 10:39 AM
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The stiction issue is not a strength one, but a loss of holding power.
A fast applied load may very well resist movement in the cam long enough for the cam to not have a chance to apply any significant outward force before it is loaded heavily, and may therefore slip out.
Probably the reason behind mystery cam slippage reported by Metolius.
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atlnq9
Dec 2, 2008, 10:28 PM
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My guess is higher if fast pull, but not sure on the mechanics of the camming action or friction.
But I'll say this when your material (metals at least) isn't meeting the customers tensile specs, just pull it faster. But then you never take it to the extreme of shock loading. But we might just see failure move to a different part, ie. impact energy on the axle possibly? but that is my quick thought.
I am almost positive the failure is from bending stress on the lobes missing the chunks. That axle deformed enough to make those cam lobes open up quite a bit more. But the material looks to be pretty clean from the fracture surface (inclusion free relative to the alloy). (thats why you see the 45 degree surface then the flat section. Real pure materials won't see that flat surface but it's not like this was a perfect tension on the lobe... and it is the alloy too...)
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