Author Topic: A 2020 paper on loop 'efficiency' testing  (Read 2683 times)

mcjtom

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A 2020 paper on loop 'efficiency' testing
« on: May 30, 2022, 07:40:30 AM »
A paper on loop testing.  Thermal scans in the end are especially interesting.

https://www.researchgate.net/publication/344689340_Revision_of_Commonly_Used_Loop_Knots_Efficiencies/figures?lo=1

mcjtom

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Re: A 2020 paper on loop 'efficiency' testing
« Reply #1 on: May 31, 2022, 04:55:01 PM »
Just a comment on the part of the paper that presents high-speed thermal images of the knots near the breaking point. 

While the authors admit that it is inconclusive if the momentary rise of temperature near the breaking moment is the cause of the breaking, or perhaps the result of the fibers breaking, the unique part seems to be that they conclusively show that the temperature rises beyond the glass point (making the material rubbery and much weaker) and up to the melting point of the nylon polymer fibers as they strain and break, and that the process is very fast (even their high-speed thermal camera seems to have a too slow frame rate - slightly less than 1 ms apart - to make more solid conclusions). 

Mark may like this, as he has speculated that this may occur in the tie-in knots subjected to falls (in the paper they use the stretching rate of 3 mm/s, while during the fall this would be significantly faster, possibly exacerbating the thermal effects).
« Last Edit: May 31, 2022, 05:34:54 PM by mcjtom »

Dan_Lehman

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Re: A 2020 paper on loop 'efficiency' testing
« Reply #2 on: June 18, 2022, 07:50:27 PM »
Just a comment on the part of the paper that presents high-speed thermal images of the knots near the breaking point.
Which are really neat!  --and from which one can also
get an idea --irrespective of temperature-- of GEOMETRY
of the loaded knot (which might be surprisingly changed
from what one saw upon mere setting of the knot). 

Quote
While the authors admit that it is inconclusive
if the momentary rise of temperature near the breaking moment
is the cause of the breaking ...
... it must do well to show were forces concentrate.
I.p., nb the Fig.9 (interior ("O") loading) being so MUCH
a-glow, not concentrating feeling the burn in one spot.
I'll conjecture that the Fig.9 "I" ("exterior", in my terms;
"on top" in some others')-loaded eased the load of the
SPart straight(er) through to nip eye legs and thereby
impede them from reciprocating around the SPart
--enough so for the 5%pt.s difference (which still saw
the knot stronger than others but for the "O" loading).

Mark & I have mused that the diameter (we put in terms
of # of enclosed strands) of the SPart's main U-turn will
affect strength; but here we must acknowledge that the
bunny ears ("double") Fig.8 though doing well in "O"
loading (by reasoning I give above, IMO), was not at
the top of the heap strongest!  --and in other testing
we can see only close results to single-eye Fig.8s
(both > & <, I think).

Thanks for re-bringing up this interesting report!

--dl*
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anything