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#937390 - 01/29/10 09:53 AM Re: OR show - neat shit thread [Re: murraysovereign]
tomtom Offline
Pooh-Bah

Registered: 01/15/02
Posts: 2385
TRs: 0 Photos: 28
Loc: Russia With Love
Originally Posted By: murraysovereign


Wire gates have a shorter lifespan because each time you open the gate you're stressing it in such a way that, over time, weakens the spring effect until it loses much of its strength - how many times can you bend a paperclip back and forth before it stops being useful as a paperclip? At least, that's the rationale I got from the Petzl rep when I asked about it. The other advantages of wire gates (lighter weight, larger gate opening than the same size biner with solid gate, and reduced gate flutter under stress due to lower mass) are retained in this design, but with longer useful gate life due to a "conventional" spring mechanism.

I'll step back now and let the metallurgists and structural engineers tear the s#*t out of everything I just said. But for the record, at first glance I prefer the wire-gate design we're all accustomed to. It's intuitive and elegantly simple - the "Ocham's Razor" committee would approve. That's not to say there's anything wrong with this newfangled thing, I'm just not convinced it's solving a problem that really needed solving.


Bullshit. The Petzl rep is an idiot and should be publicly ridiculed.

For stainless steel, the endurance limit is something like 50% of the tensile strength. And the endurance limit (fatigue strength) is the cyclical loading for which the material can survive 10 million cycles. Even Raindawg hasn't clipped 10 million bolts in his lifetime. I seriously doubt normal loading of the wire when opening the gate on any biner is anywhere near 50% of the tensile strength.

And a shorter live span than what? Every carabiner uses some sort of metallic spring to close the gate. What is Petzl using for a spring? Something steel, I guess, which one could make the same arguments.

If this is Petzl's engineering expertise then they and their products should be avoided at all costs.
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#937453 - 01/29/10 12:46 PM Re: OR show - neat shit thread [Re: tomtom]
murraysovereign Offline
old hand

Registered: 07/06/03
Posts: 1131
TRs: 0 Photos: 0
Loc: In the Rainshadow of the Chief
Originally Posted By: tomtom
Bullshit. The Petzl rep is an idiot and should be publicly ridiculed...

...If this is Petzl's engineering expertise then they and their products should be avoided at all costs.


That's perhaps just a wee bit over the top. This wasn't one of Petzl's engineers talking: it was a sales rep. He's not a metallurgist, nor is he an engineer of any stripe. He was answering my question with whatever information had been passed on to him at a meeting who knows how long ago. He may or may not have been given a detailed engineering explanation for every aspect of every carabiner, every ice tool, every LED in every headlamp, but I rather doubt it. I suspect they'd been given brief summaries of a whole pile of different technical matters, all of which left them vaguely confused.

What he told me (or at least, what I have recalled from a 15-second portion of a 1/2-hour meeting that was one of more than a dozen similar meetings strung together one after another through the entire day) was by no means meant to be received with biblical certainty. He's not an idiot, he's not deserving of public ridicule, and his remark should in no way be interpreted as representing "Petzl's engineering expertise", or warranting a panicked boycotting of their products.

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#937485 - 01/29/10 03:09 PM Re: OR show - neat shit thread [Re: tomtom]
RuMR Offline
Spray Master

Registered: 04/26/02
Posts: 11711
TRs: 0 Photos: 75
Loc: Seattle
Originally Posted By: tomtom
Originally Posted By: murraysovereign


Wire gates have a shorter lifespan because each time you open the gate you're stressing it in such a way that, over time, weakens the spring effect until it loses much of its strength - how many times can you bend a paperclip back and forth before it stops being useful as a paperclip? At least, that's the rationale I got from the Petzl rep when I asked about it. The other advantages of wire gates (lighter weight, larger gate opening than the same size biner with solid gate, and reduced gate flutter under stress due to lower mass) are retained in this design, but with longer useful gate life due to a "conventional" spring mechanism.

I'll step back now and let the metallurgists and structural engineers tear the s#*t out of everything I just said. But for the record, at first glance I prefer the wire-gate design we're all accustomed to. It's intuitive and elegantly simple - the "Ocham's Razor" committee would approve. That's not to say there's anything wrong with this newfangled thing, I'm just not convinced it's solving a problem that really needed solving.


Bullshit. The Petzl rep is an idiot and should be publicly ridiculed.

For stainless steel, the endurance limit is something like 50% of the tensile strength. And the endurance limit (fatigue strength) is the cyclical loading for which the material can survive 10 million cycles. Even Raindawg hasn't clipped 10 million bolts in his lifetime. I seriously doubt normal loading of the wire when opening the gate on any biner is anywhere near 50% of the tensile strength.

And a shorter live span than what? Every carabiner uses some sort of metallic spring to close the gate. What is Petzl using for a spring? Something steel, I guess, which one could make the same arguments.

If this is Petzl's engineering expertise then they and their products should be avoided at all costs.

my thoughts exactly...either the spring is flexing or the wire...can't have it both ways...so, if you make a fatigue arguement (which really doesn't happen...seriously, anyone snap a gate from opening it??? ever??) for one system it applies to the other as well...
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#938076 - 02/01/10 10:43 AM Re: OR show - neat shit thread [Re: tomtom]
nhluhr Offline
member

Registered: 02/16/09
Posts: 105
TRs: 0 Photos: 0
Loc: Seattle, WA
Originally Posted By: tomtom
For stainless steel, the endurance limit is something like 50% of the tensile strength. And the endurance limit (fatigue strength) is the cyclical loading for which the material can survive 10 million cycles. Even Raindawg hasn't clipped 10 million bolts in his lifetime.
Thanks for pointing that out... it was what I was about to post. I just don't see the benefit of this. I call gimmick.

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#938095 - 02/01/10 11:18 AM Re: OR show - neat shit thread [Re: nhluhr]
G-spotter Offline
Elite Sprayforce Team

Registered: 12/20/01
Posts: 14800
TRs: 56 Photos: 397
Loc: free range
Originally Posted By: nhluhr
Originally Posted By: tomtom
For stainless steel, the endurance limit is something like 50% of the tensile strength. And the endurance limit (fatigue strength) is the cyclical loading for which the material can survive 10 million cycles. Even Raindawg hasn't clipped 10 million bolts in his lifetime.
Thanks for pointing that out... it was what I was about to post. I just don't see the benefit of this. I call gimmick.


What is it for aluminum?
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#938387 - 02/01/10 10:41 PM Re: OR show - neat shit thread [Re: G-spotter]
nhluhr Offline
member

Registered: 02/16/09
Posts: 105
TRs: 0 Photos: 0
Loc: Seattle, WA
Aluminum has no endurance limit.

Well, to be less brief... The "Endurance Limit" is really the maximum stress at which the material does not exhibit fatigue (at infinite cycles). Although aluminum does not have such a limit, engineering circles generally consider the stress to which it can survive 500million cycles to be adequate.

Obviously the exact composition and temper will have a significant effect.


Edited by nhluhr (02/01/10 10:46 PM)

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#938422 - 02/02/10 07:29 AM Re: OR show - neat shit thread [Re: nhluhr]
Autoxfil Offline
n00b

Registered: 01/25/10
Posts: 47
TRs: 0 Photos: 1
Loc: United States
I think you have that backwards:

Steel can undergo an infinite number of cylces at low stress without ever weakening or failing. Aluminum cannot - even at very low forces, it will fail if you stress it enough times.

The "fatigue limit" is that value for steel where if you stay under the limit, the lifetime is essentially infinite. For aluminum, there is no fatigue limit. That's a bad thing, and why aluminum springs don't work.

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#938429 - 02/02/10 08:23 AM Re: OR show - neat shit thread [Re: Autoxfil]
nhluhr Offline
member

Registered: 02/16/09
Posts: 105
TRs: 0 Photos: 0
Loc: Seattle, WA
What you said... is not different from what I said; except that I provided an additional engineering equivalency that is widely accepted.

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