Brian Grimley wrote:

First, what is holding a knot together?
I would suggest that the answer is friction.

Duck tape--the universal answer.

To have friction there must be some forces or loads in the knot
and the material must have some coefficient of friction.

Actually, one can form, e.g., a SquaREef Knot with stoppers in the ends
(and SParts anchored) such that the knot itself is l o o s e but won't
come undone, the stoppers preventing the ends from working through (so,
only SO loose). Incorporating Overhand stoppers into some surgical
knots might be an answer (OH stoppers can sometimes be worked tight
snug against something--not so with e.g. a Fig.8 stopper).

Doug Turner wrote:

We repeated the experiment 7 times for each of 11 different suture materials.
The final 2 throws were tied with a standardised tension of 500gms.


And what was the knot that had a "final 2 throws"?
--sounds ominously large & repetitive! (Maybe there is a better structure.)

I would try to obtain the "stretch" ....

This might be a factor. Some of the materials (particularly the
monofilaments) stretch but don't seem to recover. Ductile might be the
term I think. We did not "prestretch" to remove this ductility. Maybe that
? would make a difference.

As for "stretch" being much help in knotting, consider ropes of high-modulus
materials (such as Vectran or HMPE, with elasticities 4% at rupture): one
often will have scant or nil stretch by manual tying. (And, in the case esp.
of HMPE, not much help in coef. of friction.)
Absent much stretch, the slightest loss of binding tension can lead to a loose
knot.

.... range of tensions with a specific knot and specific material, one
could repeat the "knot-in-a-sponge - warm rinse cycle" and see if
there is a threshold. Similarily, different materials may have a
requirement for a much higher tension when setting a knot to obtain
resistance to unravelling than other materials.

I think this might be a fruitfull avenue to explore.


Although to me it sounds bothersomely complex for pratical circumstances.
(Esp. when occasionally we learn of operations to e.g. the wrong leg or with
wrong blood type--now, for doctors to mind matching tensions & fibers?)

Intuitively I think that with failure under load the tension when tying


In what might be one of the few scientific investigations of knotting,
Stanley Barnes found that maximum strength for angling knots was achieved
with about a 50-60% tensile load on setting (which equates to maybe 80+%
of knotted break point). Simply, the shape of knot can be affected (and
maybe this partly explains lower breaks in some common knots in rope,
where getting 50% load isn't achievable w/o some leveraging device.

the knot might not matter all that much, whereas for unravelling when
not loaded (I still think there needs to be a generally accepted term
for this) it might be a more important factor.


"passive loosening"?
Certainly, the tighter one sets a knot, often the harder it is to untie.
(And perhaps a jammed overhand knot is the ultimate challenge.)

--dl*
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