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Re: [squamishdirtbag] Microfractures are a myth?:
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trenchdigger
Jul 13, 2007, 9:53 PM
Views: 15585
Registered: Mar 9, 2003
Posts: 1447
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squamishdirtbag wrote: 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?
Preface and disclaimer: I'm an engineer with a ME degree and have been working with structural repairs to aluminum and other metals in Navy fighter jets for the past 5 years or so. I'm not what I would consider an expert in the field of fatigue and fracture, but I would say I have a decent background in the subject. Keep in mind that some of my comments below are pure speculation based on my experience and background. Consider it a well-educated guess...
Fact: "Microfractures" (or more commonly "Microcracks") do exist and are known to engineers.
What is a Microcrack? Basically, a microcrack is a crack too small to see with the naked eye. Microcracks form due to fatigue.
What is Fatigue? Fatigue is the progressive, localized, cumulative damage to an object due to repeated loading and unloading at loads below the ultimate strength of the object.
If you want an example of Fatigue, take a metal paper clip and bend it back and forth at the same location. After a certain number of cycles, it will eventually fail.
The greater the amplitude of the load (stress) applied at each cycle, the less cycles the object will be able to endure before failure. Likewise, smaller loads will result in longer life. The relative amplitude and frequency of applied loads to climbing gear in normal use is so small that failure due to fatigue is not a concern.
Can a carabiner break due to fatigue? Sure, a carabiner could conceivably break due to fatigue, but standard use in rock climbing fails to generate the type of cyclic loading necessary propagate fatigue cracks at a fast enough rate to be a danger. A crack large enough to be a fatigue danger would be visible upon careful inspection with the naked eye.
Could dropping a carabiner cause Microcracks? No. Microcracks occur as a result of fatigue. Dropping a carabiner COULD damage it enough to make it unsafe for use. Such damage would be apparent under careful inspection. I would not hesitate to use a dropped carabiner that (a)still functions normally and (b)exhibits no visible signs of significant structural damage.
(This post was edited by trenchdigger on Jul 13, 2007, 10:01 PM)
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