Author Topic: Knot breaking strengths and theories - again  (Read 38298 times)

agent_smith

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Knot breaking strengths and theories - again
« on: June 07, 2007, 01:34:43 AM »
Hello all IGKT knotting theorists,

As usual, after trawling the internet for more research articles on knot breaking tests and theories, I came across this site:

http://www.iop.org/EJ/article/1367-2630/9/3/065/njp7_3_065.html

It was published this year so it is quite recent research.

Have any IGKT members seen this research?

Would like to hear opinions and comments - particularly from Mr Dan Lehman.

I am still planning to conduct a definitive series of knot breaking tests in Australia - and have taken on board all the advice from Dan Lehman in his well thought out previous posts on this and other forums.

As a side note, I also came across this site (which most would no doubt already be aware of):  http://www.selah.k12.wa.us/soar/sciproj2005/BrittneyS.html

Although Ms Brittney S obviously put considerable effort into her work, it falls way short of being useful. For starters, she gives no high quality and detailed photos of the actual knots she tied. As Dan Lehman would probably say, 'there is no way for any IGKT member to verify the tying method'. Furthermore, as Dan Lehman has previously pointed out, nobody seems to try to tie two knots in a rope sling... ie form a rope sling (a circle) by tying 2 equal lengths of rope together. Apply a spreading/pulling force with a ram or similar - that way there is symmetry on both sides (in other words, two equally tied knots would be subject to the force simultaneously). I cant find any test reports anywhere where this has been done...

Another report here: http://www.caves.org/section/vertical/nh/50/knotrope.html from Dave Richards Cordage institute USA at least shows us a photo of the test rig - but no rope sling was created - it was a typical configuration of a straight line pull with one end wrapped and clamped in a 'tensionless hitch' around a large diameter bollard and the knot end attached to a 1 inch pin/bollard. Double fishermans bend was tested by pulling apart with each end termination wrapped around large diameter bollards and clamped (ie tensionless hitches again). Once again, we do not see how the knots were tied - although Mr Richards does state that the knots were always tied by the same person and in the same way... in fairness to Mr Richards, he does state that this is a 'work in progress'.

Another interesting report is here: http://72.14.253.104/search?q=cache:PDP95YBYuRAJ:www.bwrs.org.au/research/documents/2%2520Annex%2520A%25201-2.pdf+knot+breaking+strengths&hl=en&ct=clnk&cd=15&gl=au
This one is from the fatherland (Australia) - 'The Bushwalkers Wilderness Rescue Squad'

The report focuses on two knots - the 'Tape knot' (Ring knot/bend or water knot) ABoK #1412, and the 'Double Fishermans' ABoK #498 & #1415. Again, no photos of how the knots were tied or precisely how the test was configured. Oh well...

There are numerous other tests conducted throughout the world - but all seem to fall short of the mark in a few critical areas.

Perhaps this is a challenge for clever members of the IGKT - is there any reason in principle why the IGKT cant carried out THE definitive knot testing and publish the results here on this website?

I realise that knot breaking strengths and knot theory is but a small part of the scope of interests of IGKT members but it is nevertheless an important one.

Particularly for climbers, cavers, abseilers, vertical rescue teams, rope access workers and anyone else who places reliance upon knots for life support.

What do you think Dan Lehman?


agent smith

TheTreeSpyder

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Re: Knot breaking strengths and theories - again
« Reply #1 on: June 07, 2007, 06:41:09 PM »
Pretty cool; i might try that sometime.  Still theorizing conceptual models though

i keep a list i recently added to, at my lil'place: MTL; if'n ya like such things.

Dan_Lehman

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Re: Knot breaking strengths and theories - again
« Reply #2 on: June 08, 2007, 04:32:58 PM »
Hello all IGKT knotting theorists,

As usual, after trawling the internet for more research articles on knot breaking tests and theories, I came across this site:

http://www.iop.org/EJ/article/1367-2630/9/3/065/njp7_3_065.html

It was published this year so it is quite recent research.
Wow, that's a BINGO!  --great find.  No, I'd not been aware of that testing.
(Just sent a query to the PoC about how the test specimens were tied
and pre-loaded--if all done with one initial fixing to the device anchors,
then there is a capture of torsion in the specimen that would in practical
usage be lost to greater length of line.  But it's not clear what happened.)

I've wondered how torsion figures in knot behavior, as one can often
(usually?!) see in braided rope one direction of the sheath's strands
arcing severely, clearly bearing no tension, and the opposite direction's
strands taut--that's a 50% loss of material contribution, at least on the
surface.  (Were it laid rope, ALL of the material would be affected in
one or other way and so more equally share the load.)

Quote
As a side note, I also came across this site (which most would no doubt already be aware of):
  http://www.selah.k12.wa.us/soar/sciproj2005/BrittneyS.html
Yes, that I've seen, and indeed the information is limited.

Quote
Another interesting report is here: [...] This one is from the fatherland (Australia) - 'The Bushwalkers Wilderness Rescue Squad'
The report focuses on two knots - the 'Tape knot' (Ring knot/bend or water knot) ABoK #1412, and the 'Double Fishermans' ABoK #498 & #1415. Again, no photos of how the knots were tied or precisely how the test was configured. Oh well...
I find it very hard to understand how there can be 25%-points difference between the
strength of the Grapevine bend between 10mm & 12mm laid sisal ropes from the same
manufacturer, even!!?  I did a quick sanity check on the rated tensile strength--which
is always a notch shy of rigor (relying on rating, i.e., vs. testing that, too)--, and indeed
the relation between ratings makes sense in proportion to cross-section area for ropes
(if anything, the smaller rope should have the higher strengths given this).  But for the
12mm knotted rope to come out 50% stronger (90% vs. 60%, roughly) is baffling.  One
might suspect that the delivered "10mm" product was less than that.   (I also note in
some cases that the breaks occurred at values exceeding the tensile rating in other
materials--again, a point about TESTING for that base value and not relying on some
rating (maybe, e.g., one's test device is reading high or low)?)

Quote
There are numerous other tests conducted throughout the world
 - but all seem to fall short of the mark in a few critical areas.
Frankly, while we might sympathize a little with some lack of rigor and attention to
detail, I find it a bit beyond forgiveness that most of the testing is published almost
w/o  recognition of other testings, or any serious comment on them.  E.g., recently
it was reported that the AMGA (rockclimbing guides org, USA but maybe with int.
affiliations?) had tested many Fig.8 loopknots of various orientations and found
most of them to break OUTSIDE OF THE KNOT !!!  Now, there is a great deal of
testing of just such knots in just such or similar materials, NONE of which gives
such results (or apparently doesn't:  i.e., each reports rupture values of 80% or less,
which one presumes comes from a break within the knot--but maybe we shouldn't
deny the possibility that rope outside of the knot can be weakened?).  Yet the
AMGA seem only to want to present their testing as showing some surprising
truth, though w/o addressing how all the other testing could have missed this!

Quote
Perhaps this is a challenge for clever members of the IGKT
 - is there any reason in principle why the IGKT cant carried out THE definitive knot testing
 and publish the results here on this website?
Funding comes to mind, for starters.
But at least what could be done w/o funding is for some Wise Men to critique extant testing
and in so doing build test-method guidance, which could then be offered-to/urged-upon
those with the resources doing the testing.  And which might become sufficiently known
to be in the forefront of future testing consideration?
(Did I just hear something more hit my desk?   :-\  )

--dl*
====

squarerigger

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Re: Knot breaking strengths and theories - again
« Reply #3 on: June 08, 2007, 11:18:47 PM »
Hi Dan,

Well, this is all very intriguiing work!  Agent Smith appears to have a reasonable handle on things - is he a member of IGKT?  Maybe if you or he or, better still, both of you were to provide a proposal of work to be performed, the IGKT Council could consider the work and seek funding?  Normally in the US, as you probably know, there is an RFP or request for proposals that is published by a body wanting to know something.  Usually the body knows something about the funding and can set limits, but in this case I would be willing to wager that one may have to be putting the chicken before the egg (or the egg before the chicken, depending on your point of view) to determine what might be a suitable size of project for which to consider funding opportunities.  So how about your making an outline of some few important or pressing k/b/h in question and setting out a suitable schema for inquiry into the strengths of the k/b/h under different loading conditions (static Vs dynamic comes to mind) and using some selected types of line with some types of apparatus that would satisfy the eager and astute mind?  That way, one could start the eating of the elephant one bite at a time?  I am more than happy to take part with you in an enterprise trying to establish under scientific inquiry the strength of k/b/h for various types and conditions of load and resistance.

SR

agent_smith

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Re: Knot breaking strengths and theories - again
« Reply #4 on: June 10, 2007, 12:30:57 PM »
I consider myself subordinate to Dan Lehman.

But, I am a fast learner (a bold statement).

I have been trying to compile Mr Lehman's recommendations from this site and others together with my own theoretical knowledge.

One thing I remain unclear on is whether is whether Dan Lehman and/or IGKT require a certified testing facility to conduct the actual knot load tests (eg NATA - http://www.nata.asn.au/go/about-nata ). I am not sure about the USA - other than NFPA (but this is mainly concerned with fire protection standards).

In Australia, NATA represents the highest level of quality assurance and certainty about test results.


Other than that, here is a short list of recommendations I have gleaned from this and other sites: (hopefully to be added to, amended and/or expanded upon by IGKT members...)

Objective 1: To determine with a degree of certainty, the static MBL of certain knots (to be specified)
Objective 2: To determine with a degree of certainty, the dynamic MBL of certain knots (to be specified)
Objective 3: Determine - with a degree of precision - the location of the failure point of each particular knot (this could be achieved by video or by a series of still photos)

Notes:
1. My personal area of interest is knots used in a life supporting role - eg vertical rescue applications, climbing, abseiling, caving, etc
2. It is recommended that ABoK numbers be used as a means to verify the particular species of knot


To achieve the stated objectives:
[ ] need high quality photos of all knots that are subjected to load testing

[ ] method of tying each knot must be in accordance with rules established by authoritative (executive?) IGKT members

[ ] static and dynamic testing is ideal but, if the budget restricts, static load testing might be deemed first priority until further funding can be arranged

[ ] use braided rope for the testing (ie 'kernmantel' rope) - not sure if Mr Lehman or others also require hawser laid rope to tested as a control
     #2 types of braided rope in production i) EN 892 'dynamic' rope and; ii) EN 1891 low stretch 'static' rope (not sure which category is deemed to be higher priority - budget will force initial selection)
     # unclear as to what rope diameters Mr Lehman and other IGKT believe should be tested and why...

[ ] knots ought to be grouped into testing categories; eg
     #bends (joining knots - eg Double fishermans ABoK #1415)
     #loops (end line knots - eg Figure 8 loop ABoK #1047)

[ ] bends should be tested as follows:
     #test by forming a 'rope sling' - 2 knots would exist - one on each side & subject to simultaneous loading
     #the sling would be subjected to a spreading force in a suitable 'ram'
     #the pin/bollard diameter on the ram would need to be determined (eg 10mm to simulate a carabiner)

[ ] end line knots (eg figure 8 loop ABoK #1047) should be tested with the loop portion of the knot attached to a pin/bollard simulating a carabiner
     #the opposite (loose) end of the rope should be wrapped and clamped around a large diameter bollard (ie a 'tensionless hitch')

[ ] the rate of increase of force in the static load testing machine (eg ram) should be determined and agreed upon by IGKT

[ ] ? please add...

[ ] ? please add...

[ ] ? please add...

[ ] ? please add...

and so on...



agent smith

SS369

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Re: Knot breaking strengths and theories - again
« Reply #5 on: June 10, 2007, 03:06:52 PM »
This thread is getting interesting.
I wonder if any of the rope manufacturers would be willing to "donate" testing time on their facilities? In my town, Bluewater Ropes has the original mill still in production and the test facility works daily. Perhaps if the test procedures could be worked out and guesstimated as to time on facility, I could present to them a request for help (donation of time).
Maybe publicly thank them for their assistance in lieu of drawing out funds?
I think that many of the "utility" knots should be in the testing, not just the few beginners knots.
Maybe a membership poll of the knots to be included?
And what type of testing criterion could be dreamed up for testing multi- looped knots (my favorite types)?
Keep this going.
SS369 aka Scott
« Last Edit: January 12, 2014, 11:08:41 PM by SS369 »

DerekSmith

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Questions -- questions
« Reply #6 on: June 10, 2007, 04:57:06 PM »
I read a report on knot testing and it raises questions -- why did they use that type of cord?  What would have been the outcome if they had used  xxx cord?  How fast did they apply the load?  what diameter was the cord?  Was the twist taken out or the knot set correctly?  What would have happened to the strength if the knot had been set differently?  What happens when we change the cord construction or material? -- the list just goes on and on.

Then I read a proposal such as those by posed by SR or agent_smith and the questions start all over again -- why that cord......? etc. etc. and I begin to wonder if all these questions are telling me something.

When I was a schoolboy I was told a joke.

An American touring England became totally lost in Norfolk and stopped to ask directions of a hayseed who was leaning on a field gate.  "Which way to Norwich buddy?" asked the American.  The hayseed thought for a moment and then answered "Warl, if I werz a goin thar, then I woudn't be a startin from ere".  The joke is against the hayseed for being such a bumpkin.

As years went by and I came to know and understand the Norfolk mentality, I realised that this 'joke' actually reflects a deep philosophical analysis of the Norfolk perception of life.  This little schoolboy 'joke' has come to influence and direct my life and approach to problems.  The moral of this 'joke' is that the outcome of a situation will be heavily influenced by its starting point and that when considering how to achieve a goal, one should first consider the disadvantages of the present starting point and advantages to be gleaned by starting from a different point or perspective.  This is a great parallel with the wisdom of 'Not being able to see the wood for the trees'.  At the moment, we are in the wrong place and all we can see is 'bark and wood beetles' (aka too much detail).  Perhaps if we step away from the 'trees' and start from a better vantage point then we might be able to see more clearly where we are going and an optimum route to getting there.

My take on this problem is that we are trying to perform differential calculus when all we have is a khipu.  The problem is highly complex and yet we keep jumping in the middle and try to understand the rules by pulling a knot to pieces and the only for sure thing we manage to resolve is that --  it broke!  How a knot fails and the difference between knots are complex problems with many variables and I would suggest that the approach would be to find ways of decomposing the problem to its elemental parts, then see if our understanding of the components can be used to model and understand the whole knot.

I would suggest that forum members are ideally placed to start proposing aspects which could be seen as the fundamentals involved in fibre failure; like:-

   1. How does a radius influence the failure characteristics of a mono filament; or what is the 50% strength reduction radius for a monofilament and how does 'Bend Angle' influence this?
   2. How does monofilament diameter influence 1. or what is the filament diameter : 50% break radius diameter ratio and why?
   3. How does torsion influence 1. and 2.
   4. How does material nature and molecular structure influence 1. 2. and 3.
   5. As work is done on these systems, where is the energy deposited and what is its impact?
   6. If the load is applied as a kinetic shock wave, how does this influence filament response.
   7. What is the influence of radial compression of the filament on the above.

Debating the pros and cons of how this information might help us understand complex knot performance might just point us in the right direction for proposing experimental assessments and help us stop time wasting through pulling knots apart and wondering why the only reliable answer was -- it broke!

By going far enough away from the knot, we should be able to see the parts played by key components of the knot.  Questions 1-6 ask about how a fibre behaves when we bend it over some object (another part of the knot) and question 7 asks what happens when we squeeze the fibre.  The next question might be -- if I knew how a fibre responded in 1-7, then how could I extrapolate this to understanding the actions of fibres within  a knot and how would I verify my perception?

One major advantage of breaking down the problem in this way is that gathering the initial data becomes relatively easy.  A simple Instron Tensiometer would be more than adequate and most Universities boast this basic type of equipment, putting this type of experimentation easily within the grasp of a Graduate project.  When I was within industry, Universities were crying out for well structured 'Real World' projects.  We could break down our final bag of questions into a number of Projects and offer them to a number of Universities -- perhaps the IGKT could 'broker' the interface?

If we carry on pulling knots to bits and show that 'generally' - 'sometimes' knot x is half as strong as knot y, but that tends to depend on any number of factors - then have we really gone forward, have we progressed our Science?  If you feel, as I do, that we would not have progressed our Science, then where do you feel we should move to before we start to grope our way forward?

agent_smith

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Re: Knot breaking strengths and theories - again
« Reply #7 on: June 11, 2007, 03:38:12 PM »
My take on any proposed knot testing is grounded in practical application rather than pure theory.

By practical application I mean that the test results might have direct benefit to personnel who use the knots - vertical rescue teams, climbers, cavers, etc.

When I started this thread, I most definitely had as bias toward roped sports (eg climbing) and emergency applications (vertical rescue teams).

The ropes used by both these user groups are braided ropes (better known as 'kernmantel' rope). However, rock climbers and mountaineers primarily use EN 892 'dynamic' rope, while vertical rescue (VR) teams primarily use EN 1891 low stretch 'static' ropes. As stated, both categories of rope are 'braided'.

VR team personnel tie and apply knots under time pressure - that is, they will use knots and ropes to save lives. The business of saving lives often involves acting within a time-critical situation.

VR teams and climbers only use a limited range of knots. They certainly don't use all of the hundreds of knots described in Ashleys Book of Knots (ABoK) - yes, I know that ABoK has some 3600 knots illustrations - but a lot are repeated rather like 'isotopes' of a defined 'element'.

It might be argued that climbers and VR teams use in the vicinity of around 10-11 knots and hitches.

Certainly, the prevailing wisdom is to limit the total range of knots to learn because in dire emergencies (as might happen a high altitude with low atmospheric O2 levels) - you dont want confusion. Better to master a select few knots rather than attempt to learn or memorise hundreds of knots - some of which may be of no practical value.

It is my hope that any knot testing might take the needs of climbers and VR into consideration. For example, a member of a VR team might pick up a rope bag, pull some rope out of the bag and then tie a knot (Note: Many VR teams try to have knots pre-tied to save time and reduce human error). Climbers will also have to tie knots reasonably quickly - particularly if they need to retreat off a mountain/cliff in storm conditions.

From my experience, these are the typical thoughts running though a climbers/VR team members mind when tying knots:
[ ] have I tied this knot correctly?
[ ] is this the optimum tying method?
[ ] is this the best knot for the intended application?
[ ] should I have chosen a different knot
[ ] is this the right amount of 'tail' - should I have left more tail protruding from the knot?
[ ] will this knot hold the load?
[ ] etc, etc...

When these classes of people pick up a rope and tie a knot - they don't think about mathematics. Its more about shape recognition - that is, I tie a knot and then inspect its form and structure. This is where memory comes in. The climber will not have ABoK with him/her (they don't carry fat books in their pockets while climbing rocks and mountains). There will only be a limited number of ways a particular knot can be tied.

Take the figure 8 loop as an example (ABoK #1047). I found an old website where Dan Lehman illustrates a F8 loop in its 'strong form' (http://www.iland.net/~jbritton/KnotPhotoContributions.html ).
Updated Link > www.pssurvival.com/PS/Knots/Knot_Knowledge_Photo_Illustrations_2004.pdf

I know that many VR teams and even defence force instructors insist that their trainees tie the F8 loop in the 'strong form'.

I would envisage that any knot testing would attempt to prove by experiment the merit of the 'strong form' F8 loop Vs an F8 loop that has no symmetry (ie loosely & sloppily tied with no attempt to 'dress' the knot).

It may be that two (2) different brands of 'kernmantel' rope are used in the testing - eg Edelrid (German) and Bluewater (USA) come to mind.

I know that Mr Lehman has some issues with knot tests that report % strength reduction as compared to the same unknotted rope.

If a 'strong form' F8 loop is tied in 11mm diameter Edelrid EN 892 'dynamic rope' and then the test repeated with Bluewater rope - this should give an indication of variations. Note: Bluewater low stretch 'static' rope is probably the worlds most popular abseiling rope. Therefore, it makes sense to test knots using Bluewater rope. Edelrid is a company that has been around longer than Bluewater - and their ropes have heavy market penetration worldwide. I would be an advocate of testing ropes that have widespread community use worldwide (and no, I am not trying to give advertising kudos to either of these companies - nor do I work for them).

In my mind, it's a case of tying a 'strong form' F8 loop and photographing it. Make sure the knot is indeed a 'strong form' F8 loop and it also conforms to IGKT recommendations. Place said knot in test machine and pull to failure. As stated in previous posts, the test might need to be carried out by an accredited facility (eg NATA certified or similar). The 'cross-head speed' of the tensile test machine (eg ram), the ambient temp, the size of the pins/bollards on the machine, amount of pre-loading given to knot specimens before testing, etc would all have to be worked out and agreed upon.

Lets face it, bodies such as the NFPA, Standards Australia, CEN, etc all set standards for PPE (personal protective equipment). Harnesses, lanyards, energy absorbers, rope, connectors (eg carabiners), are all PPE. The PPE worn by a worker (which might have to catch a fall), all has to meet the various national standards for use in a workplace.

That PPE has to be attached to a solid and reliable anchor (which is usually 15kN for 1 person fall-arrest).

Nowhere have I seen any mention of knots in these standards. Wonder why? Hmmmmm... (sarcasm here).

Obviously, many industrial workplaces try to have all end terminations of PPE swaged with thimble eyes. The idea behind having pre-swaged (or stitched) end terminations is to eliminate the risk of human error in tying a knot.

But, try as they may, there are still situations where knots must be used.

So there it is... I am an advocate of knots used in life support applications - particularly by climbers and VR teams. Yes, and all you tree climbers and cavers are also included here! These user groups almost exclusively use 'kernmantel' (ie braided) ropes. As for diameters, its typically 11mm. In the USA, NFPA specify half inch (12.5mm) diameter for rescue ropes. Climbers and VR teams also use thinner cords to make 'prusik loops' - typically 6mm to 8mm diameter. A lot of canyoners and climbers also use 9mm diameter rope. If I had to specify some diameters, my preference would be:
[ ] 6mm
[ ] 9mm
[ ] 11mm

I'll sign off here as its getting past my bed time...


agent smith
« Last Edit: December 09, 2012, 08:32:45 PM by SS369 »

Dan_Lehman

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Re: Knot breaking strengths and theories - again
« Reply #8 on: June 15, 2007, 05:38:33 PM »
One can see the water of interest here thrown on this topic running off in many directions.
To be effective in getting substantial results of analysis & testing, there needs to be some
channeling of efforts to fewer directions.

As a start, we can try to find sources and compile a list; then, those referenced reports
can be critiqued, from which effort some vision of what improved testing/reporting will
look like can be gained, with the extant testing standing as illustrative example of its
absence.

Quote
Another interesting report is ... from the fatherland (Australia) - 'The Bushwalkers Wilderness Rescue Squad'
More recent than this is the updated Life on a Line e-book ($15 US download fee),
coming from the, ah, "fatherland" Down Under.  It makes some surprising, unusual assertions
of testing results, which suggest that traditional testing is far from adequate to practical needs.
(It also contains some obvious nonsense, raising questions itself!)

Quote
... whether Dan Lehman and/or IGKT require a certified testing facility ...
I'm not.  Good, repeatable methods are important; whether someone has (had the funding ...)
jumped through some hoops required for certification is less important (and conceivably could
even be seen as limiting--binding to methods of questionable relevance to practice).
Like the old joke about a person looking around a street lit sidewalk instead of back
in the alley where he likely lost whatever "because the light is better here", testing using
traditional slow-pull devices might be done because that's what's available (and given
in prescribed procedures) but maybe not all so relevant.
In short, methods need to be analyzed and given a rationale, citing relevance and limitations.

And there might be some clever ways of maximizing the use of materials & equipment.
E.g., suppose one used as a test bridle a future test specimen with loopknots in each
end, and this was wrapped to a bollard and the two eyes attached to a shackle that
connected to another test specimen.  The single exercise of the device would then both
pretension this bridle's knots as well as result in the break of whatever else; after some
use qua bridles, the loopknot-ended material itself could come under test.

Quote
Determine - with a degree of precision - the location of the failure point of each particular knot
 (this could be achieved by video or by a series of still photos)
It's asserted by the spaghetti testers that high-speed cameras can't do this (well enough)
--they might have been specifically focused on monofilament line, though (not sure).
By another tester (Kathrine Milne university/graduate? testing of yacht rope), it was asserted
that there was an upper limit on camera rate beyond which images were too blurred; that
they helped but weren't so clear as we'd like.

So, I think that one means to do this would be to sew marker threads through rope at every
centimeter (or half-centimeter), and to photograph the knot as it tightens.  (Early (lower tension, i.e.)
images won't be needed re break point but might be helpful to assess material movement
under increasing tension.  Even with uncertainty about the exact point of initial rupture,
this sort of information I think will mark a big step towards getting that knowledge (and we
might come to believe that further exactness is overly pedantic rather than edifying).

Quote
method of tying each knot must be in accordance with rules established by authoritative (executive?) IGKT members
We should step back and first get a basis for testing--what is it that we want to know & why?
One might point out that pulling new rope, esp. w/o pre-loading cycles, to failure doesn't model
much of practical behavior.  Maybe it's more relevant to climbing, where tie-in is manually set
and unloaded until a fall, and less so to other applications where loading is continual and maybe
some abnormal increase might be seen (or one might be concerned about the effects of a history
of loading on ultimate strength).

Quote
use braided rope for the testing (ie 'kernmantel' rope)
This goes back to an assessment of purposes.  If you want to know how such rope behaves,
then test that rope.  If you're more interested in knot mechanics in general, you'd better broaden
your knotted media.  (Btw, Google favors spelling 'kernmantle' almost 3:1, and English's difference
between "mantle" and "mantel" makes sense of the former; I'm trying to learn of German spelling.)

Quote
bends should be tested as follows:
     #test by forming a 'rope sling' - 2 knots would exist - one on each side & subject to simultaneous loading
     #the sling would be subjected to a spreading force in a suitable 'ram'
     #the pin/bollard diameter on the ram would need to be determined (eg 10mm to simulate a carabiner)
Well, a critique might show up a need for different testing--AS WELL--, and comparing results.
I suggested the knots-in-both-sides-of-sling/loop as a way to redress breaks that seemed to come
at the pins and not the knot, allegedly by friction from material fed out from the compressed knot;
one might fear that although knots on both sides allows feed on both sides, that the timing would
not match so well, and there'd be some effect of that imbalance.  But one would end up with a surviving knot.

If it's possible to test w/o forming a sling/loop, one might like to have still two knots in the specimen
so as to have a survivor (at presumed near-rupture load) for analysis--but this too raises questions
about effects of knots in proximity.
Quote
end line knots ... should be tested with the loop portion of the knot attached to a pin/bollard simulating a carabiner
     #the opposite (loose) end of the rope should be wrapped and clamped around a large diameter bollard (ie a 'tensionless hitch')
Here I see less of a reason for not using two knots.  And if one is insisting on using a 'biner, it shows an
interest beyond the knot, I'd say.

Quote
the rate of increase of force in the static load testing machine (eg ram) should be determined and agreed upon by IGKT
I think that a slow rate tends towards lower break points possibly because fatigue can work,
and fast rates high values.  But LoaL asserts that some knots fare poorly under "shock loads",
because of heat from friction on knot compression!?  And some folks assert that "shock load" is a myth!

Quote
yes, I know that ABoK has some 3600 knots illustrations
I don't; have you bothered to count?  --might be that fewer are of knots, and more of other things.
In any case, somewhere in this forums archives is my rant against the boneheaded assertions
that the book has nearly 4,000 knots--which, btw, LoaL echoes (the boneheaded...), alas.
If you e.g. go count loopknots, I think you come to around 150, with similar counts for other major
classes.  To that I can say that there are many knots not presented by Ashley or anyonElse.
(That so-called "bollard loop" discussed in Knotting Matters a couple years back is one
seldom seen, though apparently Samson Ropes(?) knew about it enough to photograph it.)

Quote
I found an old website where Dan Lehman illustrates a F8 loop in its 'strong form' http://www.iland.net/~jbritton/KnotPhotoContributions.html.
I know that many VR teams and even defence force instructors insist that their trainees tie the F8 loop in the 'strong form'.
Egads!  This points to a lack of rigor in forming rationales!  FYI, *my* basis for the name comes from
Rob Chisnall (et al.?) and the ca. 1985 Ontario Rock Climbing Assoc. Safety Manual and its
assertion of  this being stronger than if its ends were loaded.  Testing by Lyon Equipment of seemingly
just such "perfect" forms--my name, as the knot's symmetric--suggests otherwise; but one can question
now the setting of the knot--I'd guess that setting by loading the END is what forms the shape that makes
the best bending of the SPart re strength; and on this conjecture I devised the "Lehman8", also at
that site, which is hoped to have like strength but w/easier untying.
Meanwhile, LoaL contends that this form will result in a permanent knot, and they give a particular
and less easily dressed/set symmetric form in which they claim about a "10%" strength difference.
(And as usual there's the ambiguity of what "X%" means--likely a diff. of percentage POINTS, which
is an immediate, easily determined value (e.g., 66% is 10% more than 60%; 70% is 10%-pt.s greater).)
AND, in seeming direct response to the new book, OnRope1's site has Mythbuster #(?) asserting that
it's all bunk, and loading either end gets the same result--but it's clear by their image of the knot,
which is the Fig.8 in idiotic flat form (simplistic tracing of an 8 by 2nd rope), that they (or just Bruce)
aren't dealing with the same entity, except in name.

And any of these references might be seized by someone as Gospel beyond question.
--truly UNscientific, and quite unwise.

Quote
I would envisage that any knot testing would attempt to prove by experiment the merit of the 'strong form'
F8 loop Vs an F8 loop that has no symmetry (ie loosely & sloppily tied with no attempt to 'dress' the knot).
I would challenge you to prove that "sloppily tied" gets one the same entity time after time
such that one can make such assertions!  "Correctly tied" stands in need of just such a specification
of what it is, but once agreed it should give like results across different users; but that doesn't hold
for "not correctly tied" and derivatives.

--dl*
====

squarerigger

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Re: Knot breaking strengths and theories - again
« Reply #9 on: June 15, 2007, 09:02:56 PM »
To Agent Smith, Derek Smith, Dan Lehman and Scott aka ss369,

Having looked for the umpteenth time at the various messages, links and information/opinions expressed on this subject, I feel that a slightly different approach may be beneficial.  There are so many variables in the tying, testing, materials, conditions and methods for attempting to find this "holy grail" of knot strengths, that it appears to me that the "answer" may never be found.  Why?  The "answer" may never be found because the conditions keep shifting, from the testing perspective, the use and wear perspective, through the conditions of use perspective and the materials perspective as well as to the brilliance or otherwise of the tyer.  With all of those variables (and who knows how many more within each of those headings?) it seems to me that perhaps we could try to approach the problem not as something definitive (the "answer") but rather as a range of values (ROV).

The ROV for one material, at one size, under specific conditions of humidity, temperature, exposure and other climatic and environment may, however, be different for each knot when tied by a different tyer, used under different circumstances (shock, static, etc.), attached by different methods (shackle, thimble, seizing use, etc.).  However, the difference appears to me to be much smaller than the difference when we do not take all the above into account.  So using a ROV may help to provide some framework.

CAUTION!

Even if we cannot provide a specific and definitive "answer" for all known variables, even if we can only provide the ROV, we are still no further ahead than we are now, because the tyer may be inept or better qualified or able, the line may have been culled from a different batch with perhaps changing BS values, the user may change conditions part way through usage - I think you are getting the picture (if not please PM me and I'll give you a potted version).  So why do we struggle to provide an "answer" to this problem?  Perhaps because we feel that it should be solvable.  Technically, it should, given enough money and resources.  However, at the end of the day it is the user who really has to determine what the best knot/hitch/bend/splice is to be used.  What to do then?

Provide education & training to those who want to know what the strength of the knot is and you will have removed some of the uncontrolled variables down to a minimal few.  Provide experience in the form of exposure to many different k/h/b/s so that the person asking the question becomes more aware of the variables and their effects.  Then, and only then, let them loose to find how best they can tie what they want to tie.  Don't certify them, unless you have all the money in the world to pay out in lawsuits, but do provide people with information that says "We don't know what the strength of the k/h/b/s is, because there are too many variables for us to make that assessment.  We do know that with education, training, experience and skills like our own or better, you will be able to make that determination for yourself, so that you can pass it on to others." 

Dan, Derek or some other erudite soul has probably made this statement before, so this is nothing new.  I just felt it needed to be said or repeated - the "answer" is "I don't know" which is a perfectly good answer, particularly when coupled with the caveat that all the testing in the world will not determine definitively what the strength is, even in a relative sense.

Just my two cent's worth.... ???

SR

Dan_Lehman

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Re: Knot breaking strengths and theories - again
« Reply #10 on: June 16, 2007, 04:05:50 AM »
...I feel that a slightly different approach may be beneficial.  There are so many variables ... for attempting to find this "holy grail"
of knot strengths, that it appears to me that the "answer" may never be found.  ...
 we could try to approach the problem not as something definitive (the "answer") but rather as a range of values (ROV).

Yes, except for some academic contest of sorts, seeking some sort of ultimate value or definitive
ranking by strengths is not a good goal; but I see these deliberations as working to move the
popular thinking away from naive to enlightened views.  Most rope uses include safety factors
that preclude breaking strength from affecting the system.  Anglers maybe are those knot tyers
who most regularly approach/see knot failure where strength was a factor.

Quote
The ROV for one material, at one size, under specific conditions of humidity, temperature, exposure and other...
 may, however, be different for each knot when tied by a different tyer, used under different circumstances (shock, static, etc.),

But one point is that most testing reports are devoid of information that would inform us of the effects
of these various factors, or even state the conditions (w/o assessing effects) such that replication can
be made.  One can start with the variance in the knot dressing/setting, even!

Quote
Even if we cannot provide a specific and definitive "answer" for all known variables, ...
We should be able to recognize factors and specify what they are and maybe test a few changes here
and there and thus take some incremental steps to showing how they might influence knot behavior.
A hope is that with some early results indicating certain affects, that later testing might limit the sampling
on these factors provided that the fewer results fall within an expected range.  (My musing at least about
some envisioned "sparse multi-dimensional matrix" of test results, where, e.g., we start finding no effect
of changes in diameter, or of cycling to X% load vs. Y% load, or of some couple materials, and so reduce
future sampling of such variables as long as results are within expected ranges.)

Quote
However, at the end of the day it is the user who really has to determine what the best knot/hitch/bend/splice is to be used. 

I hear things like this and wonder How does this user come to make such a decision, but we cannot?!
I.e., the user must have a basis for judgement, and such bases as one can occasionally read about e.g.
in rockclimbing forums are just lame--"if you don't trust it, then ...":  begs the question of a basis for trust!

Quote
"We don't know what the strength of the k/h/b/s is, because there are too many variables ..."
Maybe we come at it from the other direction, and say only what we DO know--that changing this variable
in this way in this material (and perhaps it is found to be "in these materials") has this effect.  It can then
be pointed out that not all variables have been tested.

--dl*
====
« Last Edit: June 17, 2007, 01:46:39 AM by Dan_Lehman »

DerekSmith

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Re: Knot breaking strengths and theories - again
« Reply #11 on: June 17, 2007, 02:18:45 PM »
Before posting this reply I took time to re-read the topic and conclude that a number of posters have said directly or by paraphrase what I have aimed to say below.  To those I would add my comments as support for their prior comments.

Agent-smith,

You are interested in testing relative to the real world i.e. not theoretical understanding.

I am an Analyst and consequently I am used to measuring things very accurately to defined protocols.  It really starts to worry me when I read that folks are looking for a definitive answer to a generalistic question and they seek to find this accurate answer by tightly defining the conditions and controls of the test procedure.  Let me make a prediction based partly on experience and partly on common sense:-

"The results that you get will depend upon the conditions you set"

Whoopty do -- big surprise -- so what?  At least we will have some accurate, reliable, reproducible results to work with.  But will we?

My fear is that if we do indeed rely on those accurate and reproducible results, will we be heading for a fall?  A lesson that all analysts have to learn very early on is that you can measure something as precisely and carefully as possible and yet your result/conclusion can be  WRONG.  Analytical results and Statistical results can be accurate to the hundredth decimal place, but without reference to context, they can both be meaningless.  Don't believe me?  Well try this little hypothetical example.

Take two knots, similar in all respects -- memorability, ease of tying etc. -- except one, knot 'A', regularly returns a percent strength of 40% and the other, knot 'B' regularly returns a strength of 60% under the carefully laid down conditions of our testing environment.

Well, it's obvious isn't it?  We should move immediately to using only knot 'B' and train everyone to tie it the same way as used in the tested procedure-- job jobbed and pints of Wherry all round landlord please.

BUT -- what if.

What if, knot 'A' always dressed itself into only one possible form, no matter who tied it, where, when ,or under whatever conditions or duress and in all weathers it consistently returned a strength in the range of 35% to 45%.

And what if knot 'B' had three intrinsic nasty attributes i) it could easily be dressed into two similar looking forms, one of which was prone to capsize ii) it had a habit of taking a twist and keeping it inside the knot, unseen and iii) in new or wet rope it could slip open.  If we measured all the possible variant strengths we might find that knot 'B' returned a strength in the range of 0% to 65%.

Now which knot do you prefer?  A consistently reliable knot that always needs the rope strength to be regraded to one third, or a potentially much stronger knot that could fail if I do not take a multitude of variables into consideration?

And don't say "That could never happen, because we would ensure the correct level of professionalism and training"

I was at Bisley Nationals one year and the only gun related incident was when a highly trained professional Police Officer shot himself in the leg through a tiny slip in procedure under the pressure of time trials.  Then there was the time a climbing instructor watched as a novice tied a bowline in the end of their protection and checked it.  Then as we both watched the novice start his climb, the bowline simply fell open (for me, that is a strength of ZERO).

The point that I am trying to make is that, in any attempt to create some reproducible results, we can easily fool ourselves into believing that the results are representative of the knot in real world use.  However, when safety is an issue we should be doing the opposite i.e. looking to see just how variable results for a knot can be, and most importantly -- why?  Then we could choose quality knots or at least train users not to allow the knot to exhibit its bad habits.

So, I'll say it again :-

"The results that you get will depend upon the conditions you set"  and if you nail the conditions, you nail the results to those conditions and wipe out any chance of seeing a knot for what it really is.  Is that what you want?  A lovely tidy set of reproducible numbers that might be meaningless, even dangerous in the real world the knot will be used in.

And the next thing that gets me worried is the inevitable response  "Well, we have to start somewhere" -- I agree, but does this have a ring of a schoolboy joke about it, involving a Hayseed and a tourist?  If you insist on pulling knots to bits, then please at least do not confuse accuracy with significance and give some thought as to which 'Somewhere' might be the best 'Somewhere' that we agree to start from.

Dan_Lehman

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Re: Knot breaking strengths and theories - again
« Reply #12 on: June 17, 2007, 08:47:15 PM »
You are interested in testing relative to the real world i.e. not theoretical understanding.
I think that with some well designed & reported testing, one can derive information
that advances both.  Yes, I quite agree that in presenting information one should
be honest about its relevance, and of course at the outset be making a pursuit that
IS relevant.  At this stage of information, though, it could be seen as relevant to do
just the same (arguably IRrelevant) traditional slow-pull testing with newly given
specification & care just to inform people of how misleading some past results are!
(In some sense this is like making sure to do a good job erasing a blackboard.)

Oh, in some similar regard about testing efficiency/productivity (getting the most
from each exercise of equipment and effort of personel), it occurred to me that
were one to be employing a high-speed camera, it might be possible to film
simultaneously the rupture of more than one knot--which arrangement might
only come with the meaninglessness of strength data (because one is pulling
2 or more specimens), but that is just a one-case loss and getting the film of
2 or more ruptures (generated by some sure increase of force to ensure
simultaneity) at one cost would be worthwhile!
(Or so it seems, w/o good sense of details.)

Quote
My fear is that if we do indeed rely on those accurate and reproducible results, will we be heading for a fall?
...
The point that I am trying to make is that, in any attempt to create some reproducible results,
we can easily fool ourselves into believing that the results are representative of the knot in real world use.
However, when safety is an issue we should be doing the opposite i.e. looking to see just how variable results for a knot can be,
and most importantly -- why?
...
"The results that you get will depend upon the conditions you set"  and if you nail the conditions,
you nail the results to those conditions and wipe out any chance of seeing a knot for what it really is.
A lovely tidy set of reproducible numbers that might be meaningless, ... .
Firstly, if you cannot know how to reproduce the results, then arguably you don't have the basis
for understanding them.  If they aren't reproducible, then they clearly can't have much use, can they?
And only by good specification, verified by reproducing, can one pause and say, "Okay, so THAT
much is known", and then turn some factor and see what effect comes.  Currently, we see lots of
results and have no way of knowing if they are surprising in being different (or similar!), or what.

No one is saying--or we should be here fighting anyone thinking--that we will in some limited
testing arrive at solid recommendations for using one or another knot.

--dl*
====

TheTreeSpyder

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Re: Knot breaking strengths and theories - again
« Reply #13 on: June 17, 2007, 09:13:35 PM »
i think that Nascar challenges the proper people to advance the whole auto industry.  If we have a field day contest in the workplace to see who can address the most labels, lift the most weight, cook the best barbecue, climb the highest it will turn work into fun.  But also, show many things as the envelope expands even if not in a real workplace conditions.

i do think that more variables should be considered; and even them singled out and tested; changing nothing else.  One of these things might be the teepee of a basket or choke; and how this angle effects knot strength enough to perhaps throw other tests off.    Elastic and static rope types under varying conditions to define better patterns of more predictable loadings.

i think that breaking knots into groups is fine; but the groups should be by angle bend types/mechanics, not by categories of use, for we already know the uses; it is the mechanical whys that are in question.  Like something that bends it's own Standing Part with 1 Turn vs. the stacked Turns of a Double/Triple Noose, Scaffold etc.  different extremes in line diameter to bit/pin is also in order to i think.  Then all these things singled out, then assembled in combinations with/against each other, realizing which are stacked multipliers and their most dynamic ranges of response to adjustmeant(when the payoff for scrutinizing further is much more powerfull).

Of course static vs. dynamic loading would be good too(and how knot can expand or slip to help); as well as cycles to failure with a side of construction types evaluated to....for here or to go!

DerekSmith

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Re: Knot breaking strengths and theories - again
« Reply #14 on: June 18, 2007, 10:42:40 AM »
No one is saying--or we should be here fighting anyone thinking--that we will in some limited
testing arrive at solid recommendations for using one or another knot.
====

Well said Dan, and I am sure a number of us are saying similar in different ways.  However, as well as that, I am proposing that as safety is at the heart of this posters question, I feel that as well as trying to measure how strong a knot is, we should also be attempting to assess how prone to variability a knot is so that we can focus on only those intrinsically stable knots for use in safety related situations.

We should also not forget that no matter how adamant we are about our objectives, others will be tempted to take results in simplistic form and promote them.

"In tests, the IGKT have shown that when properly tied, knot 'A' was 50% weaker than knot 'B'"

Once babies like that take flight, there is no pulling them back to wrap the significant context around them.

There are many great knots, which dressed correctly exhibit all the properties we ask of a good knot, yet when dressed incorrectly are either poor or even lethal.

I Strongly urge that the first stage of any knot assessment programme be designed to evaluate the intrinsic stability of a knot and that this becomes the first published information and only secondary to this do we consider enhancing the 'Table of Intrinsic Stability' with relative strength data.

Knot safety is not about strength or procedure or training.  Safety is about not choosing a competition handgun that is so finely tuned that it goes off in a moment of pressure and it is about not choosing a knot that falls apart just before you need to rely on it.

There are a number of aspects of knot safety, strength being one of them.  But my case is that reliability is by far and a way the most fundamental aspect of safety.  We can always downgrade a rope strength to an arbitrarily 'safe' limit of say 30% and use thicker or more ropes if the load demands, but how do we know which knots to tie that are not going to be overly sensitive to the pressure of the moment and the environment?

If we publish 'Strength' data without 'Intrinsic Stability' data, then we could quite rightly be held to the accusation that we led people to believe that knot 'B'  was stronger and therefore the safest knot, making the guild potentially party to any accidents that lead from using knot 'B'.

Perhaps it has been the inability to protect the Guild from the risk of litigation that has prevented any such initiative in the past.  Perhaps it should prevent it today !!  After all, what should it matter to the Guild if a VR member falls to their death through a faulty knot , so long as the Guild is safe from the risk of litigation.

As the Hayseed might have advised, perhaps we have just arrived at the real place to start this journey.

How can we promote the assessment of knot safety attributes without putting the Guild at risk of litigation?

Derek