Knots weakening high strength cords by greater margin

[mcjtom]

Knots reduce the nominal strength of ropes, but I didn't realise that the difference is much more pronounced in a low-stretch, high-strength cords with cores made of 'exotic' fibers, even when sheathed with nylon or polyester.

There is an old-ish test paper on it and a new video showing a similar pattern.

https://user.xmission.com/~tmoyer/testing/High_Strength_Cord.pdf

https://youtu.be/yA4gcc2ExsQ

p.s. Figure 6 in this paper suggest similar phenomenon

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

[KC]

This is also aggravated in dynamic hits maintained more rigidly against the greater weakened node deformities.
Where more normal 'less savant' materials would pass softened hit to less compromised efficiency at knot/ node deformity.
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Rope is about usability to me, that tho super strong, these materials lose in trade.
To me kinda born for water with low heat tolerance; but also helped out of water with low friction; that in turn gives knotting problems.
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As with bungee, normal usage strategies fight against the Nature, not with, of these materials.
i think the usability/re-usability of flexibles class/ropes as key to our evolution of engineering.
All other (rigid) materials (wood, bone and stone) took much more work to form and not quite as repetitively reusable to learn as tune.  But perhaps more importantly gave power to connect devices and properties.
i kinda stay with quick re-usability heritage shown , and require ropes chosen to lend to and keep a DBY and seat to self well enough for adjustable Friction Hitch eye as 2 tests, along with strength and visibility to be usable in own quick, confident field strategies.

[Dan_Lehman]

HMPE (Dyneema / Spectra) is hard to figure.
I recall one angling advice for use of "gel-spun" line
--their code name for HMPE-- claiming low strength for
bare material in OH knot, then good strength if that
knotted line were in a PES sheath !?!?

*I* had a urethane-coated 12-strand cord knotted
with like eye knots at each end --so that I'd have
one survivor to analyze, some colored threads stitched
to mark positions--, and all my knots held to rupture
at/in knot, with seemingly little slippage (even for a
Tucked Quick8 !).
But then EStar found that a #1452 with full turn of
S.Part --i.e., each collared the opposite one-- and
then TWO tuckings through center . . .  SLIPPED !?!?

Now,re heat, the Kevlar & Technora aramid fibres go long
into heat w/o trouble, opposite of the HMPE stuff;
Vectran, too, better w/heat.  Flexing is their issue.

--dl*
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[KC]

Sailor's ??
with the fantastic doubled and stabilizing Xnipper (like constrictor has on less premium side nip position that works great even there).
Then greater CoF host mating for this stabilized tension?
Round host only, super especially top half circle on opposing side of load pull input.
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BE used as handle to push nipping X framework directly to the opposing side of host's face(12o'clock from an input at 6o'clock pull position) as greatest radial nip position from the linear input.
i think of true noon TDC nip on that opposing side as potential nip force of 2 xTension; and the region of from 11o'clock to 1o'clock almost as favorable for most knot purposes of top nip form downward pull, i think of as target 'polar cap' region.  The draw of the SPart if not set firm or in more elastic may try to move the Xnipper some towards load, so may seek to nip at 11o'clock or a bit earlier against 6o'clock pull applied counter clockwise to host, so any drift tries to pull from a bit less Xnipper position to even greater, as better than if creep from TDC noon greatest tension to more relief of lesser as like uphill vs downhill options against creep.
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Frictions as tension reducers pre final nip help; but his might be a most non friction reliant build? 
>>just prefers friction to make job easier
>>but gives least SPart distortion and most intense nip position x2
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Pile close relative, just sneak BE under SPart side of X and pull BE out of finish position inside Turn around SPart (next to SPart), and position the X to top and IMMEDIATELY some side/Samson Angle pressure comes off  from across SPart column.
>>less SPart distortion always with Sailor's is all ever seen vs. Pile that is another excellent Crossed Turn UNDER form on it's own, but Sailor's takes a step further.
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Such a great knot, Sailor's great name for it's excellence, but not called that in great book;
kinda always reflective to me of what Mr. Ashley lent concept of that of course in surgeon's circles, the Surgeon's knot would not be called a Surgeon's, almost seems why Sailor's was un-named..but so appropriately now.
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