Effect of knots left tied in human rated rope

[agent_smith]

I have been looking for peer reviewed test data on the effects of knots left tied in human rated ropes.
Definition of 'human rated' means ropes which are certified against any of the following standards:
[ ] EN 892
[ ] EN 1891
[ ] EN 564
[ ] NFPA 2500 (1983)

Postulate: Leaving knots tied in a human rated rope causes no safety risks due to damage caused by the knot and/or significant reduction in MBS.

Background:
There is a belief held by some in the 'roping industry' that knots must never be left tied in a human rated rope. When an activity is concluded, all knots must be untied.
I am seeking test data to prove (or disprove) that leaving a knot tied in a human rated rope does not weaken it to the point where it is threat to safety.
Stated another way, my postulate is that leaving a knot tied in a rope causes no harm to the rope - and so if there is any measurable reduction in MBS, it should be insignificant (as opposed to significant).

I have been looking for existing test data to prove my postulate - but could find none.

So I post here - at the IGKT forum - to call for interested individuals to run some tests.

Test design:
[ ] Tie a #1047 F8 knot in a human rated rope - and load it to 5.0kN (approx 500kg).
[ ] Do not untie the knot for a period of 24 hours (ie, leave it tied in the rope for 24 hours).
[ ] After 24 hours, and without untying the knot - load test this sample and record its MBS yield point.

Control:
Tie the same knot (#1047) in the same rope material - and test it within a period of 10 minutes.
Load test the 'control' knot to determine its MBS yield point.

Compare the results.

...

If the results are not statistically different (within the uncertainty of the measuring device) - I propose increasing the wait period to 72 hours.
And if this also produces no statistically significant difference, I propose increasing the wait time to 30 days.

I plan to run some tests when I have time... but it would be good to gather data from other sources (not just my own).
Gathering data from other testers will help to obtain reliable results to prove or disprove my postulate.

NOTE: I chose 5.0kN because this is the upper limit of what a user could generate in the field (eg a vertical rescue team, a falling climber, prusik cord, a high line termination knot, etc).
I chose #1047 F8 because it is ubiquitous across the entire roping industry (everyone uses it in life critical applications).
One could also test #1415 Double Fishermans bend, or #1053 Butterfly (both are ubiquitous).

Edit note:
I did not include another test sample where a knot is tied in a rope - but not loaded beyond hand strength - and left for a period of time (eg 24 hours).
I have assumed that leaving an unloaded knot tied in a rope will cause no harm...
However, this could also be tested to prove this assumption.

[Dan_Lehman]

Unless you're willing to --and you're not--
expend a lot of samples per case,
IMO you should just check a control
and then go for a long period of this possibly
injurious state of hard-set knot left tied.
For "long",  I'd say a month-ish for that?

NOT reaching torwards it by baby steps of time
--go big, and then one can wonder about
where along-the-way differences accrued;
but small durations would likely at most
have small differences in values,
and the stats folks will say that such differences
fall well within expected differences neverminding
the difference in time.

--dl*
====

[DerekSmith]

Nice challenge Mark.

However, I would caution that you cannot prove a negative because absence of proof is not proof of absence.  It is good to see that you are falling back to stats to demonstrate any statistically insignificant differences - but remember this will demand a lot of samples and the result will only be as robust as the diversity of cases you include in the trial data.  Don't forget the importance of 'Black Swans'  it is better to try to prove that knots do weaken the rope over time, and fail.  The illusive prof defines the rarity of the event...

I would make one suggestion though based on the confounding factor that you can never predict in advance where the weak point / section in a cord will be and you can never know if you have tied the test knot on aweak or strong spot...  One way of reducing this confounding aspect would be to tie your test knot in a length of rope and 'store' it  for the defined duration, then prior to MBS testing, tie a second (identical) knot near the test knot,  then load both knots simultaneously to destruction.  If there is no degradation, then both knots should have the same frequency of failure.  If the stored knot is weaker, it should fail more often and if it is stronger , then it should have a lower failure rate.

Going back to first principles, knots with highly compressed zones may contain sufficient localised compression such as to cause the polymers to 'creep', much as an elastic band left under tension looses its elasticity while a non stretched band does not.  In the knot situation, this might be expected to cause weakening in the most highly stressed part of the knot, setting it up for advanced failure.  In this respect, the F8 is not the ideal knot to disprove your postulation as, by design , it distributes forces over wide parts of its structure to improve strength and reduce jamming.

A more challenging knot would be a knot that jams hard under 5kN and is therefore more likely to effect plastic deformation of the structural filaments.  I would like to offer you access to my 10,000kg comparative press, but finances prevent me from accessing the grades of rope you have stipulated.  However, I would like to do some work on lighter (cheaper) cordage to see in any degradation can be shown.

NB  You have stipulated a loading of 500kg which I presume you would apply slowly.  However, I believe an equivalent loading applied kinetically may prove to be more damaging (spot heating).  To this end, what mass and drop height would you be happy to see in setting the test knots?

Derek

[DerekSmith]

Localization of breakage points in knotted strings.
https://www.researchgate.net/publication/37449796_Localization_of_breakage_points_in_knotted_strings

Interesting paper, and yes, knots act as focal points for failure.  But I think the essence of this post is not the presence of the knot, but its age and the long term compression damage it might cause to bring about an early demise.

I think temporal aspects of knotting is a very interesting topic and I am glad Mark is sharing it with us.

Derek

[agent_smith]

Posting a 'call for testing' does not always bear fruit in the IGKT forum.
For me, the real fruit is how to move beyond theoretical posts to actual testing done by an individual.

To struktor: The written word is sometimes hard to understand and interpret.
Your post that points to a research paper is totally off=track, and has nothing to do with my stated aims.
I have seen and read this paper before - it is unhelpful (sorry).

To Derek: Summarizing the key points again:
1. Testing must be in human rated rope.
2. Testing must use knots that are commonly/routinely used in the 'roping industry'.
Examples of acceptable knots: #1047 F8; #1053 Butterfly; #1415 Double Fishermans
3. The construction of my words in my original post (in English language) are highly relevant and  necessary.
There is a strong perception in the 'roping industry' that it is dangerous and unacceptable to leave knots tied in human rated ropes.
People in the 'roping industry' only use specific types of knots (key examples of which I had already identified).

Points of clarification:
1. It seems that you are unaware that #1047 F8 does in fact jam?
The F8 has a 'threshold' - and when force exceeds that 'threshold' - jamming begins.
I have found that the threshold force needed to jam an F8 (in EN1891 11mm diameter rope) is around 4.0kN.
5.0kN should be sufficient to induce jamming in an F8.
NOTE: There are essentially 2 ways to dress and set an F8. One form is more vulnerable to jamming than the other.

2. #1415 Double Fishermans is vulnerable to irreversible jamming once the force exceeds 2.0kN (in 10-11mm diameter EN892 or EN1891 ropes).
In thinner diameter EN564 cord, irreversible jamming occurs once the force exceeds around 1.5kN.
The Double Fishermans is more vulnerable to jamming than an F8 (a well established and understood fact).

3. #1053 Butterfly is vulnerable to jamming when 'eye loaded'. I see evidence of jammed Butterfly knots frequently in my visits
to various indoor climbing gyms - where the #1053 Butterfly is employed as part of a dual clip-in system.
The load threshold to trigger jamming in a Butterfly is around 3.5kN-4.0kN (in EN892 single category ropes, 10.2-11.0mm diameter)
NOTE: Jamming only occurs when eye loaded.. the Butterfly appears to be resistant to jamming when through loaded.

Summary:
In my view, testing to prove or disprove my postulate should only be carried out with human rated ropes.
As far as I am aware, nobody has actually conducted any testing or written any papers on this subject.
I believe that I am the first person on Earth to advocate such testing in a public forum...
Furthermore, knots used in the tests should be confined to #1047 F8; #1053 Butterfly; and #1415 Double Fishermans.
These are the 'core group of knots' used by all user groups within the 'roping industry'.
5.0kN ought to be sufficient to induce jamming in these knots - and 5.0kN force is the upper limit of what any user group could achieve in the field.
I assume that most IGKT home brew testers could achieve a force of 5.0kN - without use of more expensive testing equipment?
As for Dan Lehman's advice with respect to "going hard and long" straight up - sure, why not? Pun intended
I had already mentioned 24 hours, 72 hours, and 30 days.
There is nothing to stop a tester going really BIG - eg 6 months or even a year...!

The Future:
How do we move from pure theory (and potentially endless posts) to actual testing?
I have no issues with a willing tester going straight for 30 days wait time.

[Kost_Greg]

The Future:
How do we move from pure theory (and potentially endless posts) to actual testing?

Dare i say, with respect to your noble intentions, that this "call for testing" sounds like a knotting trap to the unsuspecting casual reader.

Besides the fact that it is a quite challenging endeavour, posing some risk to the tester's physical integrity, it requires a lot of material resources, effort and plenty of free time, to set up and operate such a testing system.

Even if we pass all that and also assume that there is actually some serious, new, knotting content by an individual, with actual proof of testing with EN rated ropes, do you really think that this very content, is going to shake the whole knotting establishment and change everything?

Beyond a couple of potential positive comments, coming from the usual suspects, I think the very next day will find the majority of the knotting community tying another F8.

Let us not forget, that there were people, who really took most of their time and effort to delve deeply into the knot testing concept, although undoubtedly got wiser in a knotting way, they certainly didn't get as much appreciation as they would had expected.

So, what's the point of getting into all this trouble if there's no actual strong incentive for potential  tester's/'inventors?

In a best case scenario, the content would be uploaded to another platform, involving subscriptions, views and potential profit from sponsors, or at worst it will remain sealed within the boundaries of a closed group of knot aficionados.

This is just my interpretation of how things work in the knotting world, which is fine and explains why people do not get in the process of knot testing or sharing their results.

As far as i am concerned, if i believe i have some good knotting stuff that would be a bit more than a theory, i certainly would provide some hints for the interested readers within the realm of knowledge sharing. From that point on, it's up to them if they are willing to take a step further and conduct any tests and share or not their findings.

[agent_smith]

To 'Kost_Greg':
Wow, I didn't realize that performing knot tests involve risks of "knotting traps" for unsuspecting persons?
And I also didn't know that a knot test would pose risk to a testers "physical integrity".
I also assumed that most (of the active) IGKT members like to share their test results (or knowledge) freely - without expectation of a 'reward' (ie without expectation of appreciation, recognition, or dare I say it, payment).

There are lots of examples of knot tests and test results that have been openly shared in the public space without expectation of some form of reward for their effort.
We have a section right here in this forum - which is dedicated to knot test results (which is all shared in good faith to evolve our common knowledge base).
And there are quite a few knot tests that can be seen on the youtube platform - some have their own dedicated channel (eg Alan Lee, HowNot2, Hard-is-Easy, etc).
The ITRS website also have lots of published technical papers on knots - which are freely shared to the world.

...

Hmmm, your post seems a bit 'odd' (ie strange) to me.
I would hope that all IGKT members/visitors don't hold personal views that undertaking knot testing poses risks to their physical integrity, traps, lack of incentives, and other unspecified trouble - which act to create a negative space.

In terms of this topic and my original post, the intent is to answer a relatively simple question... What effect does leaving a knot tied in a human rated rope have on the MBS/integrity of that rope (if left tied for a lengthy period of time)?
Maybe it will turn out that I will be the only human being on planet Earth who is willing to run a test to answer the question?

It seems improbable that only one person out of the approximate 8 billion on Earth would be willing to risk it all to answer such a simple question?

[Dan_Lehman]

I'm remiss in not pointing out that there are (at least)
TWO cases to test, in general;

1) Does knotted rope lose strength
--knot left in continuously, and tested after some duration--
over time because of the knot (after being hard set)?

2) Does a hard-set knot left in rope
weaken the (later) UNknotted rope?

To my awareness, a general consensus is that the #1
case is NOT believed to be the case, at least to any
harmful degree;
or (at least) it is especially the #2 case that is of
concern --that a rope having held long-term
significant deformation will "never be the same"
and ... weaker.

--dl*
====

[Dan_Lehman]

... this will demand a lot of samples

Which is why I pointed to having larger
forces & duration and looking first to see
if there is a big weakening in such a case
vs. inching towards it, where small differences
if any are going to beg for large # of samples
as per that Slovak study on eye knots ca. 2019.
There will (likely) NOT be such number;
frankly, I think that it's not needed,
at least to get to get a first take on this.
I.e., I'm looking for such a difference as to
be a strong indicator of weakening.

highly compressed zones may contain sufficient localised compression
such as to cause the polymers to 'creep', ..., this might be expected to cause
weakening in the most highly stressed part of the knot, setting it up for advanced failure.

Or the knotted rope indeed has these adjustments,
but in a sense doing so *accommodates* the knot,
and the knotted rope is not much worse for wear
STAYING KNOTTED THUS.  BUT, untie the knot and
now this formerly knotted & so disturbed rope of
force-imbalanced fibres WILL be weaker --to quite
a degree-- than rope that is balanced.

NB  You have stipulated a loading of 500kg which I presume you would apply slowly.
However, I believe an equivalent loading applied kinetically may prove to be more
damaging (spot heating).

But such damage isn't the sort of thing we're looking
for testing --that's immediate, and another direction of interest.


--dl*
====

[KC]

To a certain sense, rope was made to relax between job assignments, especially dynamic properties?
.
Seeing with eyes and fingers, have noted rigidities set in that would make me question premise; especially in a more dynamic, even wind/water blowing instances of not just locked in 1 direction against constant load.  Then have environment as a variable compounded over time; need more towards lab enviro to filter that out(pristine vs. ravaging environments). 
.
Several times now in posts i think,
focus should be wider than human weighted (lessers and greaters)for biggest picture to show truest pattern logic;
then specialize to the powerband of human weights from the larger pattern.
Lest throw part of this baby out with the surrounding bathwater.
.