Quote:
Originally Posted by Bavafa
I was looking at Spruce catalog and it listed the breaking point for the ends that gets attached to the 5/32" cable only at 2800 lb. Most climbing slings strength is about 4000 lb and I have taken many lead falls on those and have never broken...
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Mehrdad, I have pull-tested a bunch of climbing gear and also aircraft materials and hardware to tensile failure (search YouTube on "breakotron"). My take on this issue is that there are a couple of differences that makes comparing climbing slings to steel cables an apples-to-oranges kind of thing.
For one, climbing gear is generally rated to its breaking strength using three sigma (Aliens excepted, of course). That means that the actual breaking strength is usually very close to the rated strength, with little and sometimes negative margin. Aircraft hardware, on the other hand, is usually rated much more conservatively, with much wider margins to allow for manufacturing tolerances and wear and tear in service.
For another, the strength of a sling or runner is rated for the system consisting of a loop of material (two strands) plus the sewn or knotted joining that forms the loop. But the 5/32" cable is rated for a single piece.
If a single strand of 5/32" cable doesn't meet your needs, you can always go to 3/16" or 7/32". Have McFarlane swage on some nice terminals with their Kearney press and you'd be good to go.
One reason that I would not use nylon, aramid, Dyneema (tm), or Spectra (tm) for a seat belt anchor cable is that, as others have already observed, all those materials have much lower Youngs modulus than steel or aluminum. Of course, the seat belts themselves are nylon, that's unavoidable. But the more of those elastic materials you have in your restraint system, the more the system will stretch under load and the less margin you have between your body and the things you want to restrain it from.
Thanks, Bob K.