International Guild of Knot Tyers Forum

General => Practical Knots => Topic started by: agent_smith on January 02, 2009, 01:26:03 PM

Title: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 02, 2009, 01:26:03 PM
Thought I'd start a thread to set the scene for some testing that I plan to undertake soon.

I have the following equipment/materials:

[ ] 5 ton Dynafor digital load cell (can be set to output kN or kg and can remember highest load achieved - 50ms sampling rate - will check this) - check
[ ] concrete driveway with screw-in eye bolts (love that word 'eye') - check
[ ] 5.0mm diameter kernmantel construction accessory cord - check
[ ] Safety glasses (check)
[ ] Hearing protection (check)
[ ] Winch (yet to purchase - currently looking at a Tirfor or a chain/lever hoist - 2 ton capacity ought to be sufficient)

I have opted for 5.0mm diameter accessory cord (kernmantel construction) because 5.0mm cord conforms to an EN standard (cords less than 5.0mm in diameter do not conform to any EN standard). Also, by using 5.0mm cord, the force required to trigger failure is not excessive...I estimate most breaks will occur in the vicinity of 4kN give or take a bit - which gives me a margin of safety to operate in. This diameter also enables me to tie a knot with some recognisable shape and form and it will be easier to distinguish features in a photograph.

The specs on the cord is as follows:

[ ] Manufacturer: Sterling rope company USA
[ ] Construction: Kernmantel / accessory cord
[ ] Material: Nylon
[ ] Diameter: 5.0mm
[ ] MBS: 5.2kN (1169 LBS)
[ ] Certification: EN 564
[ ] Batch coding: A050AS0100  Lot #R6-092507KT
[ ] Condition: New
[ ] Purchase date: 02 Jan 2009


Test conditions:
1. I'll test the ultimate breaking strength of the 5.0mm kernmantel cord first - maybe 3 breaks to obtain a mean value - MBL (will be interesting to compare it to manufacturers claims)
2. Care must be taken in tying and dressing the knot specimens
3. Need to take care to isolate the forces with respect to the knot - will need to use large D shackles to obtain reasonable diameters at end termination anchor points
4. Results obtained will be compared to unknotted MBL of accessory cord
5. Will need to perform 3 tests on each knot to obtain at least some form of statistically valid sample (bearing in mind cost factors involved for each length of cord I break which eats into budget).
6. Will pause test at various loads to photograph the progressive knot geometry - eg pause at 1kN, 2kN, 3kN, 4kN and maybe at a point momentarily before failure (without risking personal injury)
7. Will weave small lengths of white cotton thread into sheath to act as 'markers'.
8. Will use a 'tensionless hitch' wrapped around a large diameter pin of a D shackle which will ensure stress and strain is at the knot specimen as not the end termination anchorage.

EDITS:

9. Will tie two (2) identical knots on each specimen - one each end - so both knots are simultaneously subjected to the force (as per Dan Lehman's recommendation).
10. Will use restraints to 'catch' the explosive recoil at instant of failure.
11. Load cell will be protected with bubble wrap, foam underlay and the recoil restraints.
12. Photography of knots under load (and moment before failure) - It will be difficult to photograph the knots from all all sides - the knot will lie close ground level, so I will typically only be able to observe one full side. I would like to hear comment on which side is best to observe and photograph (ie front or rear aspects as per my Bowlines paper).
13. As per Roo's comment, yes I will only be testing a select range of knots. This is dictated by budget as I can't break and endless range of knots. I will come back and put a list up for review. One thing I can tell you with absolute certainty is that the following knots will be on the test list:

[ ] Right hand Bowline - ABoK #1010
[ ] Yosemite Bowline - (ABoK #1010 variant with tail wrapped around eye leg and then through collar)
[ ] EBDB - (ABoK 1013 variant with 3 rope diameters encircled by the nipping loops)
[ ] EBSB (agent smith varient to DL's EBDB)
[ ] Rosendahl bend (Zeppelin bend)
[ ] Figure 8 eye knot (ABoK #1047)
[ ] Butterfly knot - ABoK #1053 (with specific attention to loading profiles)




It is beyond my means and budget to test larger cord diameters (eg 10-11mm diameter range). EDIT: Larger diameters will require larger forces and hence higher risk. Also, I can't afford to purchase EN 891 dynamic rope for destructive testing (there is no opportunity for me to ask around for older samples either... and in any case, I want to test new cordage with known batch coding).

I am of the view that thinner cords will still yield a useful relationship between knotted to unknotted % ratio. Provided the same accessory cord is used with the same end terminations and same ambient temp/humidity conditions, the results gathered should provide a good baseline of data to compare knots.

At this stage, the only thing holding me up is the mechanical winch - which I'll purchase tomorrow or the next day...


agent smith

Title: Re: Knot testing - Life support knots - procedures and results
Post by: TheTreeSpyder on January 02, 2009, 05:10:11 PM
Safety overlay or framework for catching 'exploding' rope recoil forces might be in order, along with specific protection for mea$uring device.
Title: Re: Knot testing - Life support knots - procedures and results
Post by: roo on January 02, 2009, 06:17:44 PM
Thought I'd start a thread to set the scene for some testing that I plan to undertake soon.


If this is related to your earlier questions, you can cut your costs dramatically if you only test the knots that pass your security requirements and ease-of-tying or ease-of-remembering requirements.

In other words, it may be best to start with the low-cost tests.  ;)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: SS369 on January 02, 2009, 06:45:39 PM
And if this goes well, maybe the Guild and members would like to connive some time for well tested knot testing and explorations.

SS
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 02, 2009, 10:26:17 PM

1. I'll test the ultimate breaking strength of the 5.0mm kernmantel cord first - maybe 3 breaks
to obtain a mean value - MBL (will be interesting to compare it to manufacturers claims)

It's interesting to see in Richards's tests for rope strength that in each of the thicker ropes
there was greater variance/Std.Dev. than in some of the knots' data!?  The two really low
figures are for the 12.5mm low-elongation & Grapevine and the 7mm unknotted.

Quote
2. Care must be taken in tying and dressing the knot specimens
Maybe not so much, in that you should have photos of each specimen; given that,
some variance in structure might be seen to correlate w/strength--though, yes, that
begs the question of reliability of the data given the implicit 1-case-only sampling.
OTOH, if all cases are identical (magic wand set, say), then one can question the
significance of the reliable data for other-tied/-dressed like knots.  (You can't win!)

Quote
5. Will need to perform 3 tests on each knot to obtain at least some form of statistically valid sample
(bearing in mind cost factors involved for each length of cord I break which eats into budget).
Dan Lehman suggested 2 tests should be adequate

???  I said no such thing, unless you do some implicit logic.  What I DID say was
that you should have TWO specimen knots per material sample--one at each end,
in the case if eyeknots--; in this way, the break at say 1,000# force will show that
BOTH knots held 999# force (and the survivor might be regarded to some small
measure >1000# strong (this I dubbed "Speculative Statistics")).
Conceivably, with adequate material length, you might be able to run say your
3 rope-piece tests, break 3 of 3x2 knots, and then re-test with the 3 surviving knots
(to see how strength was affected by such severe loading--pretty much academic,
I think, since such material should be retired).

Quote
6. Will pause test at various loads to photograph the progressive knot geometry
- eg pause at 1kN, 2kN, 3kN, 4kN and maybe at a point momentarily before failure

While this stands in contrast to standard continuous slow-pull loading, it should
be okay for the purposes of testing variance between knots (and slow-pull isn't
all so assuredly like what practice might throw at a knot).


Quote
7. Will weave small lengths of white cotton thread into sheath to act as 'markers'.
Having some different color in the middle of set could help you quickly count/pinpoint
the break ("ah, 2nd mark away from red thread going away from Spart").  The camera will
show us where the marks lay in the loaded knot.  This is REALLY intriguing!!

Quote
It is beyond my means and budget to test larger cord diameters (eg 10-11mm diameter range).

Not so:  it is ... if trying to do the full, multiple-repetitions set, agreed; but you might care
to break some bona fide DYNAMIC rope (get some donated old ends chopped from a long
length, which some climbers do as a way to extend the usable life of a rope (since it is at
the ends that the most degradation occurs), or a complete old rope--you should have some
contacts who can pitch in!).  The idea would be to show, via camera, what likeness, what
differences obtain in the actual target material--such as a tendency to deform more in some
way.  We might be able to project some results to be checked by sampling.  ("Hmmm, since
it seems that dynamic rope will do <this>, ... , then THIS variation of the Bowline should
improve strength by <...>.")
So, you might not give up the idea of doing SOME breaking of actual climbing rope,
which should occur with range of your set-up, yes (around 3,500# judging by Richards's
results for 10.5mm rope; less for used & thinner rope).

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 02, 2009, 10:40:02 PM
The comparative test rig I set up, used a hydraulic jack as the force source.  The advantage (apart from low cost) was that there was virtually no elasticity in the jack, so when the sample broke, there was virtually no jack reaction.

My test cord was 3mm polyester - 1kN MBL, yet even at this low level of breaking strain, the energy stored in the sample was huge and the stronger knots would literally explode off the rig with a puff of smoke.  I ended up working with a long camera lens and a long jack handle to keep me at a safe distance.  I was also at right angles to the trajectory of the fragments.

If you plan to use a chain hoist, how do you plan to stay out of the path of reaction?

Advice gleaned from my experience...

Keep the sample as short as possible, this will reduce the energy stored in the sample.
Make the loop fixing point as realistic a diameter as possible commensurate with intended use.
Make the SP fixing at least 5 turns onto a large diameter non rotating bar and clamp the free end to the bar, not to the specimen
Use two tells, 1cm apart and photograph the knot under pre break tension (you will hear the cord start to ping and crackle as it nears rupture), this will allow reasonably accurate measurement of failure point.
Photograph the fragments including tells to allow determination of rupture point.

Take great care to document the exact dressing of each knot tested, your photography is excellent, so take several perspective shots including end on.

I doubt it will be much use to you, but here is the protocol developed for comparative testing (unfortunately funding for the test cord fell through)
http://igktworkshop.pbwiki.com/Testing+Protocol (http://igktworkshop.pbwiki.com/Testing+Protocol)

It is probable that you have never been up close to a modern rope failure - please be exceptionally careful, the energies released at rupture are frightening.
(you can easily store 1kJ in the cord, that's enough energy to sling a 10g 'magnum' bullet at 450 m/s - faster than the speed of sound !!).

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 02, 2009, 10:49:00 PM
Having obtained a static loading failure value, you might consider exposing the same knot to a dynamic load of a similar magnitude (or say the 50% failure value)

500kg load dropped 1m onto the test sample would simulate 5kN loading dynamically.

Be prepared for the samples to fail at a far lower loading though.

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: roo on January 02, 2009, 11:59:01 PM

500kg load dropped 1m onto the test sample would simulate 5kN loading dynamically.


Maybe I'm missing something, but without knowing the elasticity of the system, how do you know 500 kg dropped 1m yields 5000 N?
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 03, 2009, 01:42:02 AM
Yes, what you are missing is a brain in gear - mine, not in gear that is.

Of course, you are right roo.  Dropping 500kg by 1m gives us an energy of 4,900 Joules (not Newtons force) and without knowing the dynamic elasticity, we cannot know the forces involved.  For that we would have to integrate the area under the Force/elongation curve for the system (which of course would be available from the testing carried out by AS if he records extension along with force.

Mea culpa - what a way to start 2009 - 0/10, must try harder...

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 03, 2009, 10:54:01 PM
Keep the sample as short as possible, this will reduce the energy stored in the sample.
Strictly speaking, I think that there is some potential bias from this, in terms of
how much material there is to allow some fibres to elongate and distribute load,
but otherwise I imagine that circumstances of the device & cost will so dictate shortness.

Quote
Make the loop fixing point as realistic a diameter as possible commensurate with intended use.
Not sure about this, as the break will come at the knot, and is unlikely altered by
other than unusually wide pins (or one so sharp as to cut).  I'm going to guess that
'biners might serve, or the like.  --but not harness tie-in loops.

Quote
Make the SP fixing at least 5 turns onto a large diameter
For the tensile check?
For per-specimen-knots, they are to be knotted at both ends (which maybe saves some
material, and otherwise yields behavior on TWO knot-tokens per exercise of device).

Quote
Use two tells, 1cm apart and photograph the knot under pre break tension
(you will hear the cord start to ping and crackle as it nears rupture),
this will allow reasonably accurate measurement of failure point.
Photograph the fragments including tells to allow determination of rupture point.

Not sure of what's asked, here.  But coming to photograph material so near rupture
that it's sounding--and I've read accounts of there being no such warning (a difference
betwee the Offset Ring Bend & (regular) Ring ("Water") Bend in tape, I recall)--seems
like tempting fate.  And I suspect that beyond a certain highly loaded (say, 45% tensile?)
point, the change to geometry is both minimal and well indicated by the recent change
to that point--so the report might remark "and it continued to ... very slightly up to break".

AND, with TWO knots per test, one won't know which one is going to burst first
--so (1) won't know where to train a camera, and (2) must protect against the
burst from both knots.

Quote
Take great care to document the exact dressing of each knot tested,
your photography is excellent, so take several perspective shots including end on.

One efficient way to do this is to tie several specimens, label them, and have them all in
the pictures together--perhaps even with some bearing of a load/weight so as to have them
in tension.   Saves on photography effort (your doing, & later reviewing, printing).
It might be worthwhile to deliberately vary the dressing on each 3rd specimen set,
leaving the collar a little looser (which can be seen to model tying in firmer or more
dynamic rope or more quickly/carelessly or ... ).

And you might budget in saving some material for special re-testing if something
strikes you as odd/interesting and you want to have a further look, or to try to alter
some result by making a particular change, as suggested by ... <whatever>.

Quote
It is probable that you have never been up close to a modern rope failure -
please be exceptionally careful, the energies released at rupture are frightening.
(you can easily store 1kJ in the cord, that's enough energy to sling a 10g 'magnum' bullet at 450 m/s - faster than the speed of sound !!).

Worth simply reiterating in bold.  (I have also not been ... .)

Thanks,
--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Bob Thrun on January 04, 2009, 09:55:40 AM
02 Jan 2009

1. I'll test the ultimate breaking strength of the 5.0mm kernmantel cord first - maybe 3 breaks to obtain a mean value - MBL (will be interesting to compare it to manufacturers claims)
Since the ultimate breaking strength of the unknotted cord is the baseline for all the other tests, it should be determined to more accuracy with more breaks than the other tests.

I once read an Alcoa aluminum handbook.  It said that engineers might not be concerned about the average strength of an alloy.  Instead, they might be interested in the minimum strength of an alloy.  The minimum strength of a knot should be reported.
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 04, 2009, 04:36:10 PM
02 Jan 2009

1. I'll test the ultimate breaking strength of the 5.0mm kernmantel cord first - maybe 3 breaks to obtain a mean value - MBL (will be interesting to compare it to manufacturers claims)
Since the ultimate breaking strength of the unknotted cord is the baseline for all the other tests, it should be determined to more accuracy with more breaks than the other tests.

I once read an Alcoa aluminum handbook.  It said that engineers might not be concerned about the average strength of an alloy.  Instead, they might be interested in the minimum strength of an alloy.  The minimum strength of a knot should be reported.

Could I also suggest that you test the cord failure periodically throughout the knot testing phase.  This will show any drift in the testing system and even potentially allow you to compensate if it is shown to be present.

As you will be comparing your results against manufacturers claims, could I ask how you intend to calibrate your system.  If you do not calibrate, then you will not be able to make a comparison with the manufacturers data and your results will have to be declared as % of MBL(measured).

As this is your own project, rope, equipment and work, could I ask if you intend to share the results with the Forum?

--------------------------

The minimum strength issue is an important one and although I believe comparison should be made on mean performance, the presence of low individual values are important and deserve much greater attention than simply being reported,  or as in some statistical approaches - deleted.

 A low figure will mean either the knot was tied happen stance on a weaker portion of the rope, or more likely, the construction of the knot created an adverse set of forces, causing an earlier failure.  It is these lows that have to potential to direct us to specifics in dressing which magnify the weakening effect of the knots structure.  If you find 'spurious' lows, they deserve hyper attention in the hope we might find the cause of the early failure, especially attention to the point and structure of the failure (that is structure of the debris, not the knot).

If we can identify the causes of critical weakness, then we can advise instructors to specifically include training to check to ensure the absence of these weaknesses.

I would have hoped that the Guild might have helped by funding the test cord to be used, but if the response to such a request is as forthcoming as the request for help to fund the 3mm cord for the trials I proposed, you will be a long time waiting.

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 04, 2009, 06:15:18 PM
02 Jan 2009

1. I'll test the ultimate breaking strength of the 5.0mm kernmantel cord first - maybe 3 breaks to obtain a mean value - MBL (will be interesting to compare it to manufacturers claims)
Since the ultimate breaking strength of the unknotted cord is the baseline for all the other tests, it should be determined to more accuracy with more breaks than the other tests.

I once read an Alcoa aluminum handbook.  It said that engineers might not be concerned about the average strength of an alloy.  Instead, they might be interested in the minimum strength of an alloy.  The minimum strength of a knot should be reported.

and

Quote
Could I also suggest that you test the cord failure periodically throughout the knot testing phase.
This will show any drift in the testing system and even potentially allow you to compensate if it is shown to be present.

As you will be comparing your results against manufacturers claims, could I ask how you intend to calibrate your system.

imply a measure of confidence/significance to this home-brew testing that strikes me
as way beyond the pale in having any value.
For one, how do you know that the data from elsewhere that you presume to make
comparisons with has any of this rigor and exactitude!?  The UIAA had an big issue
with differing results from different test labs in its certifying tests; I suspect that those
places had more resources in expertise & equipment, but still ended up with challenged
results, requiring official redress.

Take a look at Dave Richards's results:  I'd think that the least variation (he did 5 tests per item)
would occur for the material (tensile strength) --one might reason that by logic anything that
depends on the material could be no better(!)--, and yet his smallest standard deviations
are for the Grapevine in low-elongation 12.5mm rope, for tensile in the 7mm cord, and
nothing so small in the dynamic rope, but (single)Fisherman's knot & and ONE tying
--but not, should be identical(!!!) --the other tying (TIB vs. "rethreaded") Fig.8 eyeknot !?

.:.  Asking for some great precision of the tensile begs the question in any case as to
how valuable that is if specimen tests are less demanding, and comparisons to other
date again to their rigor, and in any case, their different material.
Agent_Smith isn't about to build a lawsuit case to claim fraud against Sterling, is he!?

Oddly, I was thinking just the opposite:  that, given the hoped-for consistency of the cord,
and the (we hope) smooth, uniform, terminal securing of the line for this test,
that a SINGLE test of it should suffice.
Frankly, the real comparisons of interest are of Knot-A to Knot-B to ... ,
and --irrespective of actual value/strength(!)-- the information about how/where knots
break!  Indeed, if this were ALL that he reported, along with the images for us to understand
what the *knot* was--in terms of exact geometry--that would go much further in advancing
the "science of knotting, its study and practice" than yet one more set of not-really-possible
-to-understand batch of strength figures.

Really, the comparisons of prime interest of knots to each other, and one could even
just assume  some out-of-the-air value to use as a baseline for producing %-of-X
values to compare.  Think about this comparison, Bob:  you have the material tested
for three days and 100 individual tests, and a MBL ... etc.; then for each knot you have
but ONE break; contrasted with the opposite scenario, rigor per knot, and one test of
the material.  I think that the choice is obvoiusly for the latter; very easy to take the
given results and adjust them by reason or later data on the material.  Especially when
dealing with a material that should be pretty uniform in strength.


If you're going for the original THREE breaks, I like Derek's suggestion to distribute
the testing--for evrything, actually.  Perhaps best is to set up a trio of full tests, and
within each test set, vary the ordering of specimens tested, which includes the
break of pure cord (and, if drift is much a risk, and you want an arguable surer
value for it, make the pure-cord tests all towards the center of your sets.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 04, 2009, 06:59:45 PM
One thing I can tell you with absolute certainty is that the following knots will be on the test list:

[A ] Right hand Bowline - ABoK #1010
[B ] Yosemite Bowline - (ABoK #1010 variant with tail wrapped around eye leg and then through collar)
[C ] EBDB - (ABoK 1013 variant with 3 rope diameters encircled by the nipping loops)
[D ] EBSB (agent smith varient to DL's EBDB)
[E ] Rosendahl bend (Zeppelin bend)
[F ] Figure 8 eye knot (ABoK #1047)
[G ] Butterfly knot - ABoK #1053 (with specific attention to loading profiles)

On A, you should have a specimen pair in which the end is dressed-set to cross UNDER
itself on exit re the Front perspective--a position the draw of the SPart will then bring,
under load, more into the position that is typically shown for the end to start (from which
an end is brought up & a little to the side).
B, you see, positions the end (to the opposite direction) and holds it there.

On E, you might have on specimen pair in which you deliberately leave the knot
a little looser than the what you might expect setting in good practice to do--this
can case can be seen to model stiff rope or careless/quick tying, and should give
a geometry tending towards that of the Bowline.
However, I find the inclusion of this dubious in light of any advocacy for use in
the kernmantle [sic] worlds, as for joining slings, the Grapevine will rule, and
for joining abseil ropes, an offset bend is wanted; what does this leave?  This
symmetric knot will work with dissimilar ropes pretty well, but I just don't see
much market for it in your presumed target audience.  (Still, at least a carefully
reported break test & photos will advance understanding ... !)

On F, there are two prime ways of loading the knot.  To my mind, if one is going
to load the strand that runs nearer around the eye, and that will press INTO its
shadow/parallel/twin partner, you should set the knot firmly by loading the end,
and by loading the eye in opposition to the nub (i.e., grasp knot, pull eye)
--the idea is to put more of a curved path for the SPart to take en route to
its tight turn around the eye legs--;
if loading the other strand (which will pull away from its twin, naturally), the
best setting might be to tension SPart against nub, to try to ease the force
that the eye legs will deliver to the SPart, which in this position seems to
have a broader curve around the body.

On G, well, there are two potential SParts here, too--although they depart
not in parallel/tandem but in opposite directions.  You should see that W&Magowan
give specific orientation instructions, having the eye legs crossing in the nub,
which is in contrast to most of the images of it that I've seen modern books
give (having not appreciated the variety of orientations possible).  So, here
you have an orientation of knot body/eye-legs, and THEN the question of
which end to load--already there are 4-6 distinct cases (two crossings & none,
times two ends).  For this reason, I do not like the choice of this.  We have now
no idea how the knot was tested elsewhere, which makes any comparison
impossible.  (Well, yeah, this is somewhat true for everything, alas.)

And of course I'm very disappointed to not see the Janus Cowboy bowline
in the set, as it's the simplest and best-looking of the bowline variations so far.
And it's a knot that I've examined carefully, and so advanced, especially on
account of how the curvature of the SPart looks GOOD/strong.

Quote
It is beyond my means and budget to test larger cord diameters (eg 10-11mm diameter range).
 EDIT: Larger diameters will require larger forces and hence higher risk.
Again, I will remark:  the "test" of such a rope need not be to destruction,
but only to a known, significant force, at which photo documentation can be used
to compare the target rope (dynamic) with like-loaded (%-of-tensile) 7mm rope,
and with that information, maybe some projections can be made.  --same bit of
rope (11mm) can be used repeatedly, thus; and just one test per knot, if ... .
Again, it's a matter of gaugeing how the greater elasticity enables greater distortion
and so affects effective knot geometry.  Loading climbing rope to 500-1000# say
will produce meaningful results; in terms of knot security on "cyclic" loading by sport
falls, this is the sort of loads you'll see, and you can see if anything changes re security.
.:.  so, no greater system loads; no cost of rope, other than having ONE to use (at
forces you are likely putting on it or are willing for it to endure anyway, in use).

Quote
(there is no opportunity for me to ask around for older samples either...
and in any case, I want to test new cordage with known batch coding).

A simple ping to a climbing forum could bring ONE rope fairly quickly, I think.
--or just a worn end of one, adequate.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 05, 2009, 04:47:30 PM

Quote
Could I also suggest that you test the cord failure periodically throughout the knot testing phase.
This will show any drift in the testing system and even potentially allow you to compensate if it is shown to be present.

As you will be comparing your results against manufacturers claims, could I ask how you intend to calibrate your system.

imply a measure of confidence/significance to this home-brew testing that strikes me
as way beyond the pale in having any value.
For one, how do you know that the data from elsewhere that you presume to make
comparisons with has any of this rigor and exactitude!?  The UIAA had an big issue
with differing results from different test labs in its certifying tests; I suspect that those
places had more resources in expertise & equipment, but still ended up with challenged
results, requiring official redress.


If I have understood your comments correctly Dan, would I be correct with paraphrasing them as --  'Home Brew is not professional so don't bother with attempting to achieve anything of value', and, 'If you publish anything of value, it is likely to end you up in court contesting the results'.

If that is what you meant, then I would have to disagree.

The level of professionalism present in many hobby organisations is generally well in advance of any commercial organisation because hobbyists do not have to turn a profit or report to a Board of Directors, consequently, profit does not get in the way of progress.  Just because something is 'Home Brew', does not automatically mean it is shoddy or worthless.  A job may be being performed on an extremely tight budget, but the use of intelligence and ingenuity can yield breakthroughs that commercial organisations would never dare set their sights at.

From a different perspective, many people have run strength testing studies, and how many times have members of the IGKT (or at least this Forum) criticised the reports for failing to cover, identify or document issues critical to a knots performance.  Probably the greatest gathering of knotting expertise is contained within the IGKT and is accessible through the IGKT and this Forum.  There is therefore a strong argument that better trials will be run where there is a large proportion of knotting expertise being put into the project rather than a high level of lab technician expertise.  I would consider my Analytical skills at knowing HOW to measure something as being far less important than knowing WHAT I should be measuring.

Finally the issue of having results contested in court.  The better structured a trial is and the more detail that goes into both the setup and the interpretation, then the less chance there is of someone misunderstanding or disagreeing with your findings, and even less chance of them winning.  Equally, rule 101 - never sue and empty pocket, tends to make it a non starter to take out an action against amateurs scattered around the world.   

If these tests are not approached with the attitude of making the results meaningful, then what is the point is doing them?  I can't see Agent Smith going to all this work and then not publishing them ??

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 06, 2009, 07:07:18 AM
If I have understood your comments correctly Dan, would I be correct with paraphrasing them as
 --  'Home Brew is not professional so don't bother with attempting to achieve anything of value',
 and, 'If you publish anything of value, it is likely to end you up in court contesting the results'.

That is a misreading.  I pointed to exactly the "at least" considerable value,
if documentation (images & marker threads) enable us to narrow down the
region of breakage; and I also believe that comparative strength values
will be informative (though we should remind ourselves that such values
can vary per situation).  I have no fear that there will be a legal issue.

My reaction was to those bits of urging for exactitude I think is out of proportion
in effort and even practicability for this home-brew situation.  Especially as I
read the protocol of there being interruptions to some hand-cranked? winching
for the sake of photography, I think that there will be siginficant deviations from
the industry standard (but perhaps not so entirely valuable/worthwhile) test
protocol of steady pull.

How does the measure (dynomometer) get calibrated?  Well, okay, let's see
about that (although if it understates forces uniformly, won't the results be
pretty much useful, in terms of percentages?).  But going to some extra effort
on figuring tensile strength, but doing less per knot specimen, strikes me as
backwards--as I stated (and gave a choice of extreme cases, for illustration).

(E.g., suppose some tests were later done at Sterling itself, on some of the knots
tested by Agent_Smith, and the results were comparable; but Sterling challenged
the A_S-measured tensile, and could suggest why those values differed.  We
might come to accept the different 100% figure, and then it would be a simple
matter to re-figure the % breaks per knot, trusting that at least they had been
rightly recorded.  (E.g., if A_S used a too-narrow anchor point for tensile or
something, and so had a lower value.))

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 09, 2009, 01:26:28 PM
Am back on the case...

I have purchased a suitable hand operated winch and installed a pair of eye bolts into the concrete floor of my garage.

I completed 4 shake-out tests today to confirm the following:
1. That the test rig as a whole system actually works
2. That I can avoid personal injury
3. That one (1) meter will be a practical length of cord to work with
4. That I can observe and measure events as they occur

Anyhow, during the shake-out tests, I was able to confirm the following observations (Knot tested was ABoK #1010 - Right hand Bowline):

Note: The specs on the cord is as follows:

[ ] Manufacturer: Sterling rope company USA
[ ] Construction: Kernmantel / accessory cord
[ ] Material: Nylon
[ ] Diameter: 5.0mm
[ ] MBS: 5.2kN (1169 LBS)
[ ] Certification: EN 564
[ ] Batch coding: A050AS0100  Lot #R6-092507KT
[ ] Condition: New
[ ] Purchase date: 02 Jan 2009

Procedure:
I tied two identical #1010 Bowline knots within the one (1) meter length of Stirling accessory cord. I gave due attention to shape/form/dressing of both knots. The knots were cinched tight by hand. 100mm tails were left on each knot. The eye of one bowline was attached directly to an end termination eye bolt (5mm radius - simulating a carabiner). The eye of the other Bowline was attached to the load cell via a D shackle with 5mm radius. Once all connection were confirmed, a suppression system was attached to prevent violent recoil at the instant of knot failure.

1. The Stirling accessory cord internal core failed at approximately 3.90kN - leaving the sheath intact (there was a very distinct 'popping' sound when the core yielded).
2. Final failure occurred when the external sheath yielded at approximately 4.12kN (for the initial core: 3.90/5.20 = 75% and for the final yield point: 4.12/5.20 = 79%)
3. For reasons I do not fully understand, failure always occurred at the Bowline attached to the end termination eye bolt (and not the other Bowline attached to the load cell).
4. The precise failure point was not determined - as I was not specifically examining this phenomena. To more accurately determine the local region of knot failure, it will be necessary to use small tracer threads woven through the sheath at strategic positions within the knot structure. This became obvious when observing the amount of stretch occurring with increasing load. Dan Lehman already advised that this would be necessary earlier and in many posts over the past few years. I can confirm that he is 100% correct in stipulating this requirement. It may even be necessary to video the process!
5. The recoil effect at the instant of failure was not as violent as I anticipated - I believe that this was due to the fact that the internal core yielded first, followed shortly thereafter by the outer sheath.
6. I had some trouble with the load cell - it uses 3 x AA batteries (1.5v) - and the recoil effect after the initial 'pop' of the internal core induces enough of a 'jolt' to dislodge the batteries from their cradle position! This happened on 2 occasions - so I'll need to tape the battery lid in position using gray tape. As soon as the batteries were dislodged, it interrupted power supply...and hence loss of digital output.

At this point in time, I am somewhat concerned by the mode of failure in the 5.0mm diameter accessory cord. With the core yielding first, it will be very difficult to determine the precise region of failure. I may need to use thicker cord - eg 6.0mm diameter cord...

I am open to suggestions/comments/advice...


agent smith

EDIT: I just completed a tensile strength test to determine the ultimate breaking strength of the 5.0mm diameter cord. I reached a peak force of 4.98kN when the internal core failed (with a distinct 'pop') followed shortly thereafter by the external sheath - also at 4.98kN. The load cell sampling rate is 40hz (the LCD screen updates 40 times per second when the load cell is set to read the peak force achieved). The end termination pin diameter used was 15.0mm.

Observations: The 4.98kN result is unreliable.
Reason: The end termination anchor pin diameter needs to be at least 20.0mm (15.0mm is too small). Cord failure occurred at a region where the cord immediately exited from the anchor pin. A tensionless hitch was used to secure the cord to the pin - 5 wraps were used and then the cord was terminated away from the 'tensionless wraps' to a shackle using ABoK #1047. Since the cord failed at a region close to, or at the pin itself, I conclude that the 7.5mm radius of the pin (ie 15mm diameter) caused undue stress and strain on the cord resulting in premature failure.

However, 4.98kN is not too far off Stirlings reported 5.2kN MBS (a difference of only about 20kg) - so I think a move to a 20mm diameter anchor pin ought to be sufficient.

This means I will have to go out and purchase bigger D shackles with larger pins of 20mm diameter - bugger, more money!
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 11, 2009, 07:18:08 AM
 :D  I can only imagine that your misspelling has the rope manufacturer shaken at being 'Stir''d!

I'll also add that all "cores" are "internal" (redundancy alert).

Now, about why "failure always occurred at the Bowline attached to the end termination eye bolt
(and not the other Bowline attached to the load cell),"
  I'll toss out a conjecture:  that there is a
difference in friction of the metal terminal points, and so the exact load on the eye legs differs
between the two knots--note that I'm not positing that an imbalance (at the more frictive end)
is weaker:  maybe it's what adds some strength!?  Again, this is a seeming possible  reason!?

Btw, what IS the core/kern, structure-wise:  a braid, or a collection of (mixed-lay) laid strands?

Quote
A tensionless hitch was used to secure the cord to the pin - 5 wraps were used
and then the cord was terminated away from the 'tensionless wraps' to a shackle using ABoK #1047

1) I think that the T.Hitch should have FEWER wraps--to limit the amount of (potential) movement
of material around the pin--it STILL should be quite effective at reducing force transmitted to the
ultimate termination point such that rupture occurs where you want it.  --even ONE turn!?

2) In what condition did you fine the Fig.8 eyeknot used as ultimate termination?
--could you untie it?  (seeing how much load it got through 5 tightish wraps)

3) Rather than involving the necessarily significant amount of material consumed by
an eye-knot, can you use something brief, such as a noose-hitch w/#1821form of the
Overhand (looking at #1821, connect the SPart to the RIGHT side of the ring, if you
will--as though the ring is in fact the SPart coming to turn around the anchor ping
from the left, clockwise around and flowing into 1821 around itself.  (This appeals
to me for the draw on the wrapped SPart into the knot of this noose hitch
will pull the end ever tighter, and somewhat pad the noose-SPart from the
tight squeeze of the tightening knot.  (Some tests of the "barrel hitch", where it's
a Strangle knot (Dbl.Oh.) noose, showed the noose-SPart breaking at entry into
the knot (and not, e.g., at the 10mm turn around the 'biner), so I'm looking for a
diminution of compression at this point.)

4) "I am somewhat concerned by the mode of failure in the 5.0mm diameter accessory cord."

You indeed might acquire some other cord.  But I think that if you have rigorous
test results from 5mm, and then do some sampling with say 6mm (and, as I
urged, at least l00k at the effective geometry of actual dynamic rope at loads
we can map into the 5mm results/images),
you'll have provided a good basis for understanding what's going on.

Perhaps the failure mode is attributable to peculiarities with the construction
of the 5mm cord, different from 6 or 7mm even though its roughly of the same
sort (in terms of braid in the mantle, and make-up (which is ... ?) of the kern),
and not noticeably different as braid is from twisted -- something that might
result from percentage of mantle to kern, or particular tightness of weave!?
(speculations, these)

------
I'm having similar doubts about my thought to use beached conch-pot warp,
worrying that its well-weathered, highly frictive mantle will be weakened much
by friction which will skew results.  (Although also noting that IF one is in fact
working with just such cord, it is THAT behavior that matters, and not that from
pristine cordage.)  Indeed, I recently BROKE A BOWLINE in aged CoExOlefin
("CEO" I'll coin! ("coextruded", btw)) 8/16-strand rope, with rather moderate
force from a (crummy) pulley:  it broke at initial entry point (as per Chisholm),
which I think is HIGHLY improbable for decent cordage; one can at times see
how much friction the surface fibres are fighting at such bend points through
a bight of surrounding material; but new/slick rope, will pull through and by
enduring greater force change the geometry favorably at that point.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 11, 2009, 10:18:53 AM
Suggestion - don't increase the diameter of the MBS test pin from 15mm, DECREASE it to the same value (i.e. 10mm) that you will be using to test the knots.  If it breaks at the shackles, then so be it, it is after all the weakest point in the system.  Then you will be comparing unknotted cord with knotted cord with everything else equal, so you will be comparing apples with apples.

POI, what makes you state "Observations: The 4.98kN result is unreliable."?

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 11, 2009, 02:38:09 PM
Reporting in here with some early test results for the IGKT forum...

This post will be updated on a regular basis as test results become available.


Cord specifications:
[ ] Manufacturer: Sterling rope company USA
[ ] Website: http://www.sterlingrope.com/supportingdocs/2008_climbing_cat_technicalspecs.pdf (look under 'Accessory & Prusik cord')
[ ] Construction: Kernmantel / accessory cord
[ ] Material: Nylon
[ ] Diameter: 5.0mm
[ ] MBS: 5.2kN (1169 LBS)
[ ] Certification: EN 564
[ ] Batch coding: A050AS0100  Lot #R6-092507KT
[ ] Condition: New
[ ] Purchase date: 02 Jan 2009

Load cell:
[ ] Model: Dynafor LLX5
[ ] Capacity: 5 ton
[ ] Sampling rate: Forty (40) times per second when set to record and display peak force achieved. Four (4) times per second when set to read current force.
[ ] Serial No. E04073
[ ] Calibrated by: Tractel S.A.S. (Calibration certificate No. 0414607)
[ ] Last calibration date: 25 April 2004


Accessory cord ultimate strength calibration test series:

MBS TEST #1
[ ] Test date: 10 Jan 2009
[ ] Knot: None
[ ] Cord length: 1.5m
[ ] Method of fixing: Each end of the cord was secured with a 5 wrap tensionless hitch around a 20mm pin on a bow shackle. The tail ends were then fed through a hole in the pin of another adjoining shackle using ABoK #515 as a stopper knot.
[ ] Peak force recorded at failure: 5.1 kN (a discrepancy of only 0.1kN from Sterling's reported MBS of 5.2kN)

Comment: The #515 stopper knots had cinched very tight after the test. I could not undo these knots by hand alone. They were easily untied with the aid of pointy nose pliers.

MBS TEST #2
[ ] Test date: 12 Jan 2009
[ ] Knot: None
[ ] Cord length: 1.5m
[ ] Method of fixing: Each end of the cord was secured with a 6 wrap tensionless hitch around a 20mm pin on a bow shackle. The tail ends were then fed through a hole in the pin of another adjoining shackle using ABoK #515 as a stopper knot.
[ ] Peak force recorded at failure: 5.0 kN (a discrepancy of 0.2kN from Sterling's reported MBS of 5.2kN)

Comment: I managed to fit 6 wraps around the 20mm pin of the bow shackle.
Note: The #515 stopper knots were able to be untied by hand with a small amount of effort.

MBS TEST #3
[ ] Test date: 12 Jan 2009
[ ] Knot: None
[ ] Cord length: 1.5m
[ ] Method of fixing: Each end of the cord was secured with a 6 wrap tensionless hitch around a 20mm pin on a bow shackle. The tail ends were then fed through a hole in the pin of another adjoining shackle using ABoK #515 as a stopper knot.
[ ] Peak force recorded at failure: 4.98 kN (a discrepancy of 0.22kN from Sterling's reported MBS of 5.2kN)

Comment: I managed to fit 6 wraps around the 20mm pin of the bow shackle.
Note: The #515 stopper knots were able to be untied by hand with a small amount of effort.



BOWLINE ABoK #1010 TEST SERIES:

TEST #1:
[ ] Test date: 10 Jan 2009
[ ] Knot: ABoK #1010 (Right hand Bowline)
[ ] Cord length: 1.0m
[ ] 2 x identical #1010 Bowlines were tied - to form an eye at each end of the cord
[ ] Tails: 100mm on each knot
[ ] Dressing: Attention given to shape and form - pulled tight by hand only
[ ] Peak force recorded at failure: 3.98 kN
[ ] End termination anchor pin diameters: 20mm

Observations:
The knot was cinched tight using hand force only. A single 'tracer' thread of white cotton was weaved through the sheath to mark the exact mid point of the collar on each knot. Under load, it was observed that the collar position did not move. The collar remained in a fixed position relative to the other parts of the knot. Examination of the specimen after failure indicated that the break/rupture did not occur at the collar. The precise break position could not be determined - more tracer threads need to be woven into the thread to determine the region of failure/rupture.

TEST #2:
[ ] Test date: 10 Jan 2009
[ ] Knot: ABoK #1010 (Right hand Bowline)
[ ] Cord length: 1.0m
[ ] 2 x identical #1010 Bowlines were tied - to form an eye at each end of the cord
[ ] Tails: 100mm on each knot
[ ] Dressing: Attention given to shape and form - pulled tight by hand initially, then loaded to 1kN before tracer threads were inserted.
[ ] Peak force recorded at failure: 3.78 kN
[ ] End termination anchor pin diameters: 20mm

Observations:

Only one of the #1010 knots failed. On this occasion, the knot that failed was closest to the end termination anchor point (and not the knot immediately adjacent to the load cell).
The test specimen was loaded to 1.0kN then removed from the test bed. Three tracer threads were woven through the sheath in strategic positions in order to more accurately determine the point of failure/rupture.
*White tracer thread was woven at the collar
*Red tracer thread was woven at the crossing point (G spot - DerekSmith)
*Blue tracer thread was woven at a position on the loop where it passes over the bight (when viewed from the 'front' side)

Examination of the specimen after failure indicated that the BLUE tracer thread was missing. I could locate the white and red tracer threads, but NOT the blue. This indicated that failure/rupture was occurring at a region on and/or around the blue tracer thread. A further test with a fourth tracer thread will be required to more accurately home in on the region of failure/rupture.

The fact that the other #1010 knot remained intact enabled location and comparison of the tracer thread positions.

TEST #3:
[ ] Test date: 10 Jan 2009
[ ] Knot: ABoK #1010 (Right hand Bowline)
[ ] Cord length: 1.0m
[ ] 2 x identical #1010 Bowlines were tied - to form an eye at each end of the cord
[ ] Tails: 100mm on each knot
[ ] Dressing: Attention given to shape and form - pulled tight by hand initially, then loaded to 1kN before tracer threads were inserted.
[ ] Peak force recorded at failure: 3.76 kN
[ ] End termination anchor pin diameters: 20mm

Observations:
Only one of the #1010 knots failed. On this occasion, the knot that failed was closer to the load cell. The test specimen was loaded to 1.0kN then removed from the test bed. Four tracer threads were woven through the sheath in strategic positions in order to more accurately determine the point of failure/rupture.
*White tracer thread was woven at the collar
*Red tracer thread was woven at the crossing point (G spot - DerekSmith)
*Blue tracer thread was woven at a position on the loop where it passes over the bight (when viewed from the 'front' side)

*Gray thread was woven at a position half-way between the blue and red thread.

Examination of the specimen after failure indicated that the BLUE tracer thread was again missing. I could locate the white , red and gray tracer threads, but NOT the blue. This indicated that failure/rupture was occurring at a region at, or immediately around the blue tracer thread.

The fact that the other #1010 knot remained intact enabled location and comparison of the tracer thread positions.

Further tests will be carried out to gather more data.

Thanks to Dan Lehman in particular for insisting that tracer threads be used and that 2 identical knots should be tied in each test specimen. Also thanks to DerekSmith for his suggestions.

I will post photos soon.


agent smith

EDIT: I would like to add the comment that this whole testing procedure is very time consuming and labor intensive. In particular, weaving the tracer threads through the sheath in strategic positions is tedious and testing both my eye sight and patience... I hope its worth the effort Dan!
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 11, 2009, 11:02:47 PM
Only one comment so far AS. these knots are never likely to see use around a 20mm fixing, so this poses the question of - what effect does the 'bina' diameter have?

Looking forward to the photos.

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 12, 2009, 07:43:20 AM
Quote
Suggestion - don't increase the diameter of the MBS test pin from 15mm,
DECREASE it to the same value (i.e. 10mm) that you will be using to test the knots.
If it breaks at the shackles, then so be it, it is after all the weakest point in the system.
Then you will be comparing unknotted cord with knotted cord with everything else equal,
so you will be comparing apples with apples.

1) This shows abandonment of the purpose of the testing:  which is to determine the
relative breaking strengths (under standard, slow-pull loading) of various knots, i.p.
several variations of the bowline.

2) It's highly unlikely that an eye will break:  the knot's SPart bears 100% tension
into turns of cordage around cordage (relatively frictive material compared with
cordage & metal); whereas an eye bears 50% tension around metal.  --mixed fruits.

Reporting in here with some early test results for the IGKT forum...

[ ] Manufacturer: Sterling rope company USA
[ ] MBS: 5.2kN (1169 LBS)
...
The result of 5.1kN was sufficiently close to Sterlings given MBS to enable me to move forward with actual knot testing.
I will purchase more 5.0mm cord to conduct 2 more tests to establish a mean force.

What does Sterling  mean by "MBS"?  ("M" unfortunately the initial of "Min"/"Max"/"Mean".)
SOMEwhere, I just saw some report referring to the ***minumum breaking strength*** which
was defined as 2 (3?) standard deviations below the mean.  And--I'll hope statistics-smart others
set this straight/confirm--if you were to get, say, 5.4 & 5.0 on next tests, you might have enough
variance to enlarge your Stnd.Dev. to give an *MBS* of this sort of, what, 4.8?
--just a remark to make sure these are all apples, and not that Sterling has a mean of say
5.4 or greater, and so ... .

AGAIN:  THE PRECISE FIXING OF MATERIAL STRENGTH, WHILE NICE,
IS LESS IMPORTANT than putting limited resources into the knots testing.
(And I'd be curious how a 3-wrap fixing affected things--but, yes, then you're
deviating and in two tests have more a 1 & 1 situation.  But it's just that I cannot
figure how more wraps would make for a higher  break strength, UNLESS
a few-only wraps allowed sufficient force to be transmitted to the terminal knot
to put the break there--and even one and certainly two wraps I'd think would
significantly cut the transmitted load.  Adding more wraps just provides more
material to be elongated by load and thus more movement of the material
AND more time at each load (under a constant rate of pull) to reach higher
tensions--and duration at tension is a weakening condition!)

Quote
I could not undo these [Overhand stopper] knots by hand alone. They were easily untied with the aid of pointy nose pliers.

I suggest doing more finger execises!   ;D  (Though, seriously, I recently struggled with fingers in the
cold on Overhands set by fising useage in well-worn/-weathered 7mm marine kernmantle and was
able to get 'em all--using thumbnails was key, in forcing bits of movement (it was not quick).)
Good show!

Quote
BOWLINE ABoK #1010 TEST SERIES:
Observations:
The knot was cinched tight using hand force only.
A single 'tracer' thread of white cotton was weaved through the sheath to mark the exact mid point of the collar on each knot.

 ???  :-\  Sorry, but I cannot imagine this being a point of rupture--there's little
tension IN the collar.  But this is most interesting in terms of tightening :  for there
have been reports of jammed bowlines (also of unjammed tested-to-rupture partners (Lyon)),
and the only way it can jam is if the collar snugs up, under tension and elongated/thinned
cordage such that upon the relaxation of load the *swelling* rope binds solid.
And if the collar showed no movement at all, well, I can't see THIS rope jamming!

The markers need to be at Derek's "GeeSpot", and most importantly at the approximate
farthest-towards-EYE point of the knots "loop/hitch" --THERE is where the break will come.

Quote
Examination of the specimen after failure indicated that the break/rupture did not occur at the collar.

NB:  THIS IS AMBIGUOUS!  "at the collar" is where my worn CEO rope broke,
in one sense--but IN THE SPart, at the collar; not IN the collar.

Quote
Observations:
Only one of the #1010 knots failed. On this occasion, the knot that failed was closest ...

Mr. Grammar wants "closER"--there are but two.
How could it be otherwise, than "only one"?
Well, you could comment on the nature of the 2nd knot.  There IS a case--w/photo(!)--
of a webbing bend tested as I suggested with TWO knots (to have a survivor, to mitigate
tension imbalance in a sling/closed-circle-of-test-material) in which the surviving knot
shows the start of some rupture--and, quite oddly, at a different place than where
the broken knot broke!  Given your prior report of the rope seemingly breaking internally
and then holding to nearly the same load and breaking completely (I'll speculate that
there must have been core material to lend support to the mantle for at likely 50% or
less of the bulk, the mantle couldn't hold such a high force), you might have some
start of rupture in the survivor--not sure if you can feel or otherwise detect it.

Quote
to the end termination anchor point[/i] (and not the knot immediately adjacent to the load cell).

Ah, well, just as "bitter end" --despite Spydey's use otherwise :P -- means "at the bitts",
let's adopt a shorthand "anchor end" & "load end" here?!

Quote
Examination of the specimen after failure indicated that the BLUE tracer thread was missing.
I could locate the white and red tracer threads, ...

EXCELLENT:  for you'll want to mail that intact piece with the red thread
to Derek so he can work it into his promised essay on dangers of the GeeSpot!   :D

(Note that "blue" rhymes with "true".)

Quote
... but NOT the blue. This indicated that failure/rupture was occurring at a region on and/or
around the blue tracer thread. A further test with a fourth tracer thread will be required to more
accurately home in on the region of failure/rupture.

The fact that the other #1010 knot remained intact enabled location and comparison of the tracer thread positions.

Good job, but you should have photos of the knots under high (50-70% of THEIR breakpoint) tension
--looking at the positions of things w/o tension won't pinpoint the spot at crunch time,
for it DOES move, some.

Quote
TEST #3:  ...
[ ] Peak force recorded at failure: 3.76 kN ...

I notice that each break is weaker than the prior one:
you've disproved the old adage Practice makes Perfect --let's all break for tea!   ;)

Quote
EDIT: I would like to add the comment that this whole testing procedure is very time
consuming and labor intensive. In particular, weaving the tracer threads through the sheath in strategic
positions is tedious and testing both my eye sight and patience... I hope its worth the effort Dan!

Hey, look at it as developing another job (or survival  skill (i.e., sewing)) in a time of
downturned economy!

But, seriously, has anyone EVER seen any testing done like this, intelligently
answering some rather fundamental questions (which have had bogus answers
given to them and parroted, for AGES--eyes / minds closed shut tight!) ?!

You are narrowing in on a break point by simple means (NOT by a hi-tech super-speed camera,
which in the Katherine Milne (draft) report was deemed not-quite-adequate-to-see... ) :   by
needle & thread (& some needling from the cheap seats over the ocean) and a camera (yes?),
AND a 2nd-tested-but-surviving knot.  All simple enough for any of the many testers to have
done decades ago, but ... no.  So, yes:  today, 2009-01-... and counting, we are generating
a STEP FORWARD in UNDERSTANDING KNOTS.  And all quite repeatable --say, of
a crude, brute-force ("shock load") break unconcerned about calibrated force measure,
but only point-of-rupture discovery--with thread(s), or a marker.  (And you are confirming
K.Milne's observations, but with greater surety (and different material).)

I say that is quite worthwhile.

--and red-threaded bits for Derek, to boot!

 :)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 12, 2009, 08:04:51 AM
Thanks for your feedback Dan...

I can indeed mail the test specimens to DerekSmith if that's what you want... can we confirm this as postage costs to overseas destinations from Australia aren't cheap (if its to go via airmail not snail mail).

I am only going to post via an edit... rather than creating a new post each time.

I've completed two more ultimate breaking strength tests on the 5mm cord (see post).

I have purchased another 20m of accessory cord. Have cut a series of 500.0mm lengths in preparation for the joining knot (bends) tests. This will include:
[ ] Rosendahl
[ ] Double fishermans

I am quite interested in testing Bowlines with 3 rope diameters fed through the nipping loop - we'll see how they perform in comparison to ABoK #1010...

I'll keep you updated with results... weather is bad here in 'sunny' Nth Queensland at the moment - lighting conditions are poor so no photography at this stage...

agent smith
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 12, 2009, 08:43:07 PM
I can indeed mail the test specimens to DerekSmith if that's what you want...

THAT is a joke (a barb , even).  Chisholm posited the Bowline's break right at the
SPart's entry point; Derek moved one point further into the knot, at the Crossing Point.

Quote
I am only going to post via an edit... rather than creating a new post each time.

I'd rather you NOT do this:  perhaps what you can do is post a new, updated/full report;
then go back and edit down prior post to minimal info.  But having to go back to a continually
updated post, which in the meantime has been quoted, etc., doesn't make a good plan.

Hmmm, we can do without repeated information, such as:
> [ ] Construction: Kernmantel / accessory cord
> [ ] Material: Nylon
> [ ] Diameter: 5.0mm
> [ ] MBS: 5.2kN (1169 LBS)
> [ ] Certification: EN 564
> [ ] Batch coding: A050AS0100  Lot #R6-092507KT
> [ ] Condition: New
> [ ] Purchase date: 02 Jan 2009
> [ ] Cord length: 1.0m
> [ ] 2 x identical #1010 Bowlines were tied - to form an eye at each end of the cord
> [ ] Tails: 100mm on each knot

More helpful to know is the span between the knots and the length of the eyes
==>  Anchor +> | <--5cm eye--> | nub@A-end | <--30cm span between--> | nub@L-end | <--5cm eye--> | <+ LOADcell

--something like this schema above, for what does "1m" tell us, as it is divided
into several distinct sections.  Also, I think that you can be safely assured by
much use & prior testing that YOUR TAILS CAN BE QUITE **SHORT**,
saving you several cm per knot (2 per test (how you work this w/bends might
be by making a sling/runner tying two short lengths)).

Quote
I am quite interested in testing Bowlines with 3 rope diameters fed through the nipping loop

Agreed!
Also, note how the Bowline (#1010) moves the end out of the line of fire and hence puts
such load at the blue-threaded area (which I suspect shifts SPartwards w/force); if the
end is dressed to anticipate this "draw" by the SPart by being set leftwards under the
other bight leg (ref. your "front" perspective), then it will only come to the presented
position after considerable force, and it--the tail--isn't under such tension as the other
bight-leg (which is an eye-leg), and so should be compressed and more yielding to
the SPart and maybe provide some cushioning/padding effect which might increase
strength!?  Similarly, for the Cowboy Bowline (1034.5), the SPart's draw should pull
the end down around rightwards behind the bight-side eye-leg, and get cushioning
in this way (one might need to dress the knot so as to ensure that this behavior occurs).

At this point, you have experienced the consequences of rupturing this material:
what happens--how *explosive* is it, how have your defences fared, et cetera?

I was going to also point out that it wasn't necessarily the case that you needed to add
more marker threads, if you have photos (flash?), as with a reasonably proximate marker,
you can see that the breaks are coming at about such'n'such distance(s) from it.  And I'll
guess that the broken *edges*/rupture point/ends are fairly NON-sharp, some fibres
longer, others shorter, suggesting a cut & tear covering a cm or two?!

Are you sewing the thread through the mantle only, or straight through the rope in one
strand, or through, u-turn and back through?  Maybe the best marking is just a brief
stitch through the mantle, more likely to stay put, and quicker to make--make a couple
about 90deg apart and cut the connecting thread and move on:  more likely some
small set of so-joined sheath fibres will move in the same direction than a larger
bunch. !?

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 15, 2009, 10:05:49 PM
Quote
ighting conditions are poor so no photography at this stage

Let me remind you of one hoped-for benefit of photographs:  even though it
might be impossible for you to test actual rockclimbing rope (because of the
greater strength of that rope compared to the test mechanism), it could be
helpful to have images of the tested rope's knots at some various loadings
with which to make comparisons & estimates vis-a-vis witness similar
knot geometry in climbing rope.  E.g., suppose it is found that the 5mm
low-elongation cord obtains a certain geometry at 50% of tensile, but
that the climbing rope does so much sooner:  that might be a good reason
to be less confident that the climbing rope will have similar knot strength.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: alpineer on January 21, 2009, 08:25:44 AM
Would anyone care to test what i describe as a "Triple Tuck Bowline" against any other loopknot. To form the knot you simply retuck the tail through the nipping loop an additional two times to form a three-wrap coil around the "crossing part" of the nipping loop structure. The resulting knot will be bulkier, but in my very meager comparative tests with small diameter cordage I have found it to be stronger than even the Rethreaded Figure Eight (aka Figure Eight Follow Through). This particular variation appears to add both greater security and greater strength to the knot.

I am very interested if anyone else would be able to verify my test results and also be able to assess the relative efficiency of this bowline variation.
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 22, 2009, 12:57:24 AM
Would anyone care to test what i describe as a "Triple Tuck Bowline" against any other loopknot.

Have you looked at the pdf document associated with the secured bowlines of issue
with this thread?  Several of the newly presented knots entail an additional diameter
of rope through the central loop.  --and can serve you for description by reference,
if you're lacking an image to share:  words can work!

 :)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 26, 2009, 03:19:54 AM
Reporting in here with some new test results... my children, holidays and life's daily duties keep getting in the way of my little project to contribute to world knowledge.

Now that is an honorable thought - contributing to world knowledge!


Commentary:

Testing initially was carried out by forming a loop with 2 x ABoK #1415 (Double Fishermans) knots tied with 2 x 500.0mm lengths of 5.0mm accessory cord. This is the test method Dan Lehman proposed and in principle it is a brilliant idea.

However, I ran into 2 problems with this technique:
1. The force required to cause knot failure was much higher - and therefore the risks also increased.
2. The results did not directly correlate with the cord MBS of 5.2kN - and therefore it was difficult to calculate a relative % strength for the knot. Details of the initial round of 'loop tests' are as follows:

[ ] Test date: 12 Jan 2009
[ ] Test geometry: 2 x 500mm lengths of cord formed into a loop
[ ] Loop size: 200 +- 10mm
[ ] Tails: 30 +- 5mm
[ ] Application of force: Applied with lever action winch - continuous pumps of lever until failure occurred
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz

ABoK #1415 (Double Fishermans)
Test 1: 7.86kN (loop strength with dual knots)
Test 2: 7.76kN (loop strength with dual knots)
Test 3: 7.74kN (loop strength with dual knots)


Rosendahl (Zeppelin)
Test 1: 6.62kN (loop strength with dual knots)
Test 2: 7.22kN (loop strength with dual knots)
Test 3: 6.48kN (loop strength with dual knots)


As usual, in every test only one of the knots failed, leaving the other knot intact. The intact knot of course is maximally loaded, and its highly compressed form is worth photographing (the position of the cotton tracer threads will be interesting to compare to the surviving knot specimen). I have packaged and labeled all knot specimens.

The recoil force was violent - and the load cell was jarred by the recoil shock. There was no discernible fragmentation of the specimen knot - and I was not injured on any occasion. The test bed that I set up was intended for lower forces - so these 'loop tests' strained me and my equipment considerably, but still within working load limits. Note: I would not be able to perform loop tests with 6mm diameter cord as the forces would exceed 10kN...

EDIT: Another important point is that the end termination anchor pins are a crucial factor in performing ultimate break strength tests on the cord and in any test where a free (unkotted) tail end needed to be secured. Anyone trying to reproduce my results would do well to learn from this post. I initially tried 20mm diameter anchor pins with a 5 wrap tensionless hitch and then a 6 wrap hitch. I discovered that this was insufficient. Breaks were occurring at the pins which indicates that stress and strain was occurring at the pins and not isolated at the knot. Obviously, it is important to ensure that tensile force concentrates at the specimen knot, and not at the standing part end terminations.

I purchased larger Bow shackles with 30mm diameter pins. This enabled me to use an 8 wrap tensionless hitch. That did the trick! All the stress and strain was now focussed at the knots and not the anchor pins. The 30mm pin diameter provides a 6:1 ratio with respect to the cord diameter.

...

I therefore ran another series of tests, this time in linear fashion with only one knot.

ABoK #1415 (Double Fishermans)

TEST #1:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 2 x 1.5m lengths of cord
[ ] Test geometry: Linear test with a single knot specimen
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tails: 70mm +- 10mm
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Standing Part end terminations: 8 wrap tensionless hitches around 30mm anchor pins
[ ] Application of force: Applied with lever action winch - continuous pumps of lever until failure occurred
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.16 kN


TEST #2:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 2 x 1.5m lengths of cord
[ ] Test geometry: Linear test with a single knot specimen
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tails: 70mm +- 10mm
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Standing Part end terminations: 8 wrap tensionless hitches around 30mm anchor pins
[ ] Application of force: Applied with lever action winch - continuous pumps of lever until failure occurred
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.58 kN


TEST #3:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 2 x 1.5m lengths of cord
[ ] Test geometry: Linear test with a single knot specimen
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tails: 70mm +- 10mm
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Standing Part end terminations: 8 wrap tensionless hitches around 30mm anchor pins
[ ] Application of force: Applied with lever action winch - continuous pumps of lever until failure occurred
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.20 kN


TEST #4: - special test to determine effects of dressing (knot loosely tied)

EDIT: The difference in this knot compared to the other 3 tests is the degree of hand force used to set and dress the specimen knot. With the other 3 knots, considerable effort was applied to cinch the knots tight (as tight as I could pull by hand). In the present case, I did not use such effort - the knot was simply tied/dressed without applying muscular force. Whereas the former knots were tightened by hand until I could no longer pull any harder. Note: Perhaps I should test my hand strength using the load cell - and then I could report that I cinched the knot tight by applying 0.5kN force...etc!

[ ] Test date: 15 Jan 2009
[ ] Cord length: 2 x 1.5m lengths of cord
[ ] Test geometry: Linear test with a single knot specimen
[ ] The knot specimen was dressed loosely, with minimal cinching by hand. However, due attention was still paid to form and symmetry
[ ] Tails: 70mm +- 10mm
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Standing Part end terminations: 8 wrap tensionless hitches around 30mm anchor pins
[ ] Application of force: Applied with lever action winch - continuous pumps of lever until failure occurred
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 3.52 kN


...


ABoK #1047 (Figure 8 loop / eye knot)

TEST #1:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 Fig 8 loop knots were tied in order to form a connective eye at each end. Eye to eye length = 315 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.26 kN


TEST #2:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 Fig 8 loop knots were tied in order to form a connective eye at each end. Eye to eye length = 315 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.00 kN


TEST #3:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 Fig 8 loop knots were tied in order to form a connective eye at each end. Eye to eye length = 315 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.32 kN


...


End Bound Single Bowline - EBSB with yosemite finish (3 rope diameters placed inside nipping loop)

TEST #1:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 EBSB Bowlines were tied in order to form a connective eye at each end. Eye to eye length = 300 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] Tracer threads: 3 different colours inserted after knot was dressed by hand
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 3.84 kN


TEST #2:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 EBSB Bowlines were tied in order to form a connective eye at each end. Eye to eye length = 300 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] No tracer threads
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 4.02 kN


TEST #3:
[ ] Test date: 15 Jan 2009
[ ] Cord length: 1 x 1.0m length of cord was used
[ ] Test geometry: 2 EBSB Bowlines were tied in order to form a connective eye at each end. Eye to eye length = 300 +- 5mm; Eye size = 60+- 5mm; Tails = 60+- 5mm
[ ] The knot specimen was dressed very tight by hand strength only - pulled as tight as possible with due attention to form and symmetry
[ ] No tracer threads
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)
[ ] Force measuring instrument: Dynafor load cell - set to record peak force achieved with sampling rate of 40hz
[ ] Peak force recorded at failure: 3.96 kN

...

I also performed one more test to determine the ultimate strength of the Sterling 5.0mm accessory cord. I used the 30mm diameter anchor pins with 8 wrap tensionless hitches.

Test result:
[ ] Peak force recorded at failure: 5.48 kN

Previously, I was recording lower break values using 20mm anchor pins. This proves that larger diameter anchor pins are a crucial factor in determining MBS for various cords.

MBS is taken to mean "Minimum Breaking Strength".


...

A side note: This is a very labor intensive and tedious process. It is also self-funded (no, I am not asking for donations). Is it worth the effort? Yes, because it is contributing to our collective knowledge of knots...


agent smith
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 26, 2009, 07:44:41 AM
Testing initially was carried out by forming a loop with 2 x ABoK #1415 (Double Fishermans) knots tied with 2 x 500.0mm lengths of 5.0mm accessory cord. This is the test method Dan Lehman proposed and in principle it is a brilliant idea.

However, I ran into 2 problems with this technique:
1. The force required to cause knot failure was much higher - and therefore the risks also increased.
2. The results did not directly correlate with the cord MBS of 5.2kN - and therefore it was difficult to calculate a relative % strength for the knot.

Ah, we'd been so eager for more results ... !

I appreciate your concern for the closed-loop-w/2-knots doubling of force.
Conceivably, you could reduce pull force of hauler by using a pulley (and
so the hauler has 2:1 advantage, roughly; but 1:2 speed).
However, single-line specimens can have TWO knots, just as those for
the eyeknots do.  (I think that one can raise some technical concerns about
the distance between knots, but that's likely getting a tad picky for our purposes
--like pixel-peeping at camera results.)  And thus you'll have both two-knots'
results per loading, and a survivor.

One might speculate that part of the discrepancy between the trio of results
got for the two-in-a-loop Grapevines vs. the single-line ones could arise
from some imbalance of tension, which would see the even division of
force an unachieved ideal, with actually the broken side presumably
having borne more of the load, a little.  I can see thus that the average
approx. 3.9kN then being 4.0 & 3.8 !?  --but unlikely more.  (If the knot's
compress at different rates, one side of the loop can get relief from this
that the other lacks!?)  Otherwise I'll wonder if the rates of loading, for
whatever reason(s), differed; for the knots should be showing equal
strengths, loop'd or single-strand'd.


Quote
I have packaged and labeled all knot specimens.

Excellent.  But you're not mentioning PHOTOGRAPHY, and that worries me.
NB:  even if you take a few samplings of photos, you do a LOT more than if
none is taken.  And we can advance to believing your observations that
"all of the knots looked generally just like this (even though I didn't photograph
them all--why should I, if they're all the same?)."  Of course, in the case of surviving,
highly loaded knots, you can still get a photo, well past test time.

Quote
Another important point is that the end termination anchor pins are a crucial factor in performing knot break tests. Anyone trying to reproduce my results would do will to learn from this post. I initially tried 20mm diameter anchor pins with a 5 wrap tensionless hitch and then a 6 wrap hitch. I discovered that this was insufficient. Breaks were occurring at the pins which indicates that stress and strain was occurring at the pins and not isolated at the knot.

I don't follow you here:  was there any case where the break occurred at the pin
instead of in the knot?  (Not for the 2-eyeknots-per-specimen, and not for the
Grapevine & Rosendahl tests, right.)
Note that I recommended that you use a FEWER-wraps Tensionless hitch,
not more!?  More wraps only reduces the force transmitted to the ultimate
terminus; it in all likelihood (IMO) reduces the strength of the hitch (unless
the break occurs at the terminus).

Quote
This enabled me to use an 8 wrap tensionless hitch. That did the trick!

Again, I don't follow this.  A larger dia. pin, yes, should yield higher breaks;
but NOT the superfluous wraps, if the terminus isn't tied back to this line.

...

Quote
this time in linear fashion with only one knot.

Although two knots in "linear fashion" should be possible, as noted above.

Quote
TEST #4: - special test to determine effects of dressing (knot loosely tied)

Esp. here, we can only really appreciate this if we have photos of the actual
geometry.  "loosely dressed" is highly unspecific.  (And one of Tom Moyer's
like cases for the Grapevine got I think one of his higher results.)


Quote
ABoK #1047 (Figure 8 loop / eye knot)

And, speaking of "unspecific", this is a particular sore point case:  there is the
dressing, and then there is the choice of which end to load.  We almost never
get these things specified.

Quote
End Bound Single Bowline - EBSB with yosemite finish (3 rope diameters placed inside nipping loop)
[ ] Peak force recorded at failure: 3.84 kN
[ ] Peak force recorded at failure: 4.02 kN
[ ] Peak force recorded at failure: 3.96 kN

And so, with the first of the 3-diameters-in-loop bowlines, we see a gain of about 0.2kN.
Well, that's something.  (Actual geometry at break time unknown.)

Quote
[ ] Anchor pins: 10mm diameter (to simulate a carabiner)

I very much fail to see the point of this?  It was raised above and I thought
adequately rebuked:  what is it you expect of this?

Quote
MBS is taken to mean "Minimum Breaking Strength".

That much I guessed; but what exactly IS "minimum breaking strength"
--how is that figured?  (I have seen one figuring of it as being some
number of standard deviations below the mean (as opposed to, say,
the lowest break value obtained).)  [I suppose I can ask Sterling directly.]

Also, what is the construction of the 5mm cord?  The mantle is I guess
something like 24 single-strands over/under-2; but what is the kern?
--laid, or braid?

Great to have another set of numbers; l00king forward to fotos,I hope hope hope!

 ;)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 26, 2009, 10:15:01 AM
Sorry Dan,

Made a typo with respect to the anchor pins. I have edited my post above...

What I meant to state is that in any test which requires an unknotted standing part to be anchored, a tensionless hitch is essential and so is the correct anchor pin diameter. For example, when trying to measure the MBS of the unknotted cord, I found that 30mm diameter anchor pins were required. I reached 5.48kN in one test using 30mm diameter anchor pins with an 8 wrap tensionless hitch. The tail ends of both tensionless hitches were terminated with ABoK #515 fed through a hole in the pin of an adjoining shackle.

I can confirm that after the test was completed, the #515 stopper knots were loose and easily untied. When I used 20mm diameter pins with a 6 wrap tensionless hitch, the #515 stopper knots were cinched tight and could not be untied by hand (needed a pointy nose pliers). In my view, this is a indication that the relative distribution of force was not concentrated around the pin, but rather at the linear portion of the cord (which is what I wanted to test).

Does this make sense?

When I tested knots in tandem so that each end termination was in fact the eye of a knot, I used 10mm diameter anchor pins to simulate a carabiner. Obviously, with eye knots, the end termination is not an issue - particularly since a knot NEVER failed at the eye.

...

As for photos, I still do not have the proper lighting conditions...I want to take quality photos. Dont worry, all the knot specimens are packaged & preserved in their original condition after failure... I recognise the importance of photography!

With respect to the higher forces to break a loop, it doesn't matter what the geometry is (ie a 2:1 pulley) - keep in mind that the actual force at the specimen knot must reach a certain value to achieve failure...therefore you still get a violent recoil at the instant of failure.

agent smith
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 26, 2009, 06:26:05 PM
I can confirm that after the test was completed, the #515 stopper knots were loose and easily untied.
When I used 20mm diameter pins with a 6 wrap tensionless hitch, the #515 stopper knots were cinched tight ... .
In my view, this is a indication that the relative distribution of force was not concentrated around the pin,
but rather at the linear portion of the cord (which is what I wanted to test).

Does this make sense?

It is expected, but does NOT make sense in terms of the objective of getting
the break strength of the rope.  A larger pin, YES; more wraps, NO.  Again,
all the added wraps do is consume material and ease the tension into the
terminus--but that isn't the point of the exercise.  Maybe it doesn't much matter
for strength determination:  in the few-wraps case, material moves around
the pin and builds tension at the terminal side and tightens the knot;
in the many-wraps case, material moves around the pin until it just
gets exhausted by continued friction, leaving the terminal side slack.

My hunch, though, was that the many-wraps case will give excessive
material movement, which if nothing else, will delay the rise of tension,
putting material at-tension (whatever) longer, and that tends to lead
to lesser break figures (with some balance between the allowing of
fibres to settle into an evenness of sharing load--though I think one
might need cyclic preloading at say 50% to achieve this--, and the
added weakening agent of duration).  --and that few-wraps deprives
the specimen of this material contribution into the main loaded part,
and reaches higher forces sooner.  In either case, it's expected that
the break won't come on the terminal side.

Quote
As for photos, I still do not have the proper lighting conditions...I want to take quality photos.
Dont worry, all the knot specimens are packaged & preserved in their original condition after failure...
I recognise the importance of photography!

This sounds like perfection being the enemy of good:  SOMEthing is better than nothing;
I can't imagine that any modern camera--from $80, 3mb P&S, to <sky's the limit>--won't
produce  d e c e n t  photos for capturing the knot geometry during test, and the
positions of the marker threads (and the photo of the broken knot showing such
markers).  We're not insisting on Medium-Format Hasselblads or a Nikon D3 w/14-24mm lens!
Post-mortem  specimens have lost the transitional state (and also much of
the high-tension geometry, since tension is gone, SPart/eye-legs relaxed).

Quote
With respect to the higher forces to break a loop, it doesn't matter what the geometry is (ie a 2:1 pulley)

It matters to the force on the hauler and partner anchor, though resistance on the
opposite anchor will be doubled; recoil should be half-load to each of them,
but that pulley sure wants to be constrained!!

What steps are you aking to redress recoil?
I could see tying some anchor line, perhaps w/shock cord in its system, and that
to a 5#  bag of <sand?>, to the midpoint of line between knots (or having actually
a pair of lines tied at this point, each angled to resist recoil in one direction).

Good job, this is enlightening!

(-;
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 26, 2009, 09:42:12 PM
Might I be allowed to indulge in a little 'dot counting' or 'pixel-peeping' as Dan calls it.

1.   MBF, in my book it stands for Mean Breaking Force, not Max.  There would be no value in comparing the strength of knots against the single highest figure recorded for the breaking of the cord, when the majority of the knots would likely never have been tied in that one strongest piece of cord.

2. Expecting two knots to break simultaneously is like expecting a needle to balance on its point.  Both are possible, but the probability of all forces and factors being so perfectly balanced is just a little bit improbable.  You should expect one to break but if both broke, then you should look carefully for a fault in your set-up to explain why the the near impossible just happened.

3. If you test two knots against one another the weaker one will always fail first.  If the two knots are essentially the same (in statistical terms you would say they were from the same population), then by testing one against another, you are filtering out the weakest knots and almost never testing the strongest.  This will skew your results into the lowest quadrants of results.   If you do enough tests, eventually you will test a strong knot against another strong knot and get what seems to be a spuriously high result, while all the tests involving weak knots will be recorded in your data.  You can compensate for this filtering effect, but it is far better not to inject it into the results in the first place.

You might argue that it is important to measure only how weak a knot is, because only the weak knots will fail.  That is a logical argument but it is weak science.  If a knot has a broad slew of possible strengths, then we should determine this and give ourselves the opportunity of also discovering just what it is that both imparts and takes away this strength.

4. Photography is critical just before failure in the loaded situation, because an unloaded knot cannot be expected to display the same geometry as it would under load.  Images also have to be captured from different perspectives because one shot cannot capture the 3D nature of the directions, angles and vectors involved in a knot.  This is especially important when you consider the time effort and cost going into creating a single breaking strain figure and the fact that photography today is ridiculously inexpensive per picture (ca 10p per gigabyte), takes but a few seconds to record, and offers a means of sharing the information of the event via the internet.

5.  The suggestion that anchor point diameter influences MBL and knot strength.  The 'Weak Point' of a cord  depends on two factors a) the physical strength of the cord at any given point and b) the focus or magnitude of force at that point.  A physically strong point can become a weak point if there is a concentration of load at that same point.

In testing a straight piece of cord, the weakest point can be anywhere along it.  The chance that the physical weak point being at the anchor point goes down proportional to the length of the test cord (increasing the MBL) and the longer the cord the greater the chance it will contain a a rare weak point (decreasing the MBL).

Increasing the anchor point diameter will reduce the load concentration so it will lessen the effect of stress concentration upon happenstance location of a physical weak spot at the anchor 'bend'.  However, this should not translate into the cord in such a way as to alter knot characteristics unless core / sheath characteristics have a propagation ability and this reaches a closely tied knot.

Happy knotting
Derek

Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 27, 2009, 12:25:43 AM
Might I be allowed to indulge in a little 'dot counting' or 'pixel-peeping' as Dan calls it.

1.   MBF, in my book it stands for Mean Breaking Force, not Max. ...

Clean your glasses before peeping at anything:  nOne has said "max", but, rather,
"MIN"; and the question is What does "Minimum Breaking Strength"  mean
--it might be defined statistically re standard deviations, and not as a lowest datum.

Quote
2. Expecting two knots to break simultaneously is ...

..., again, not part of any discussion here:  so, what's the point of discussion?
(What we expect is that two knots enduring tension X are better than having
one do so, re data/stat.s, and also yield the benefit of a survivor.)

Quote
3. If you test two knots against one another the weaker one will always fail first.

--a tautology.

Quote
4. Photography is critical just before failure in the loaded situation, because an unloaded knot cannot be expected to display the same geometry as it would under load.  Images also have to be captured from different perspectives because one shot cannot capture the 3D nature of the directions, angles and vectors involved in a knot.

I'm thinking of a mirror involved, like the extra knot in a test specimen:  two things
for the effort for one!

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 27, 2009, 09:51:05 AM
Might I be allowed to indulge in a little 'dot counting' or 'pixel-peeping' as Dan calls it.

1.   MBF, in my book it stands for Mean Breaking Force, not Max. ...

Clean your glasses before peeping at anything:  nOne has said "max", but, rather,
"MIN"; and the question is What does "Minimum Breaking Strength"  mean
--it might be defined statistically re standard deviations, and not as a lowest datum.

--dl*
====

Thanks for the kind words Dan, but I think it must be the clot behind the glasses that is at fault here - either I am going to have to lay off that 30 yo Glenfarclas or there has been a sneaky Edit ? ?

Anyway, we probably need to bottom this one out before moving on to any strength calculations.

In terms of defining a ropes usable strength, manufacturers declare the rating that fewer than one rope in a thousand will fail to reach.  It is called the 3-Sigma Minimum Breaking Strength, and you are right that it is not the lowest datum, it is in fact much lower than the lowest recorded value.  The manufacturer measures a number of break strengths, then calculates the average (Mean) and the Standard Deviation (Sigma).  They then step down from the Mean by three Standard Deviations which (for a 'Normal Distribution') gives the once in a thousand safety limit. (see http://www.sterlingrope.com/faq.asp (http://www.sterlingrope.com/faq.asp) )

However, for the purpose of declaring knot strength, this figure is nearly as meaningless as a Max BS because you are comparing the knot breakage with rope you are almost never going to come into contact with.

For the purpose of assessing the effect of the knot on the rope, we should compare like with like, i.e. the strength of the rope unknotted with the strength of the rope knotted, and for this comparison when there are not many test values, the mean is the most meaningful comparison (calculating Sigma on two or three values is as silly as reading max when the text says minimum).  We should be careful not to mix up rope safety strength claims with what is being performed here - a comparative test.

Derek
AKA 'Dot Counter'
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 27, 2009, 11:31:11 AM

snip...

Quote
2. Expecting two knots to break simultaneously is ...

..., again, not part of any discussion here:  so, what's the point of discussion?
(What we expect is that two knots enduring tension X are better than having
one do so, re data/stat.s, and also yield the benefit of a survivor.)

Quote
3. If you test two knots against one another the weaker one will always fail first.

--a tautology.
snip...
--dl*
====

"so, what's the point of discussion?"  The point is that if AS is intending to publish his results he should not expose himself to criticism that he failed High School Stats.  Even the claim that the method generates a valuable surviving sample is questionable because the shockwave caused by failure might have altered the structure in some way impossible to predict.

Luckily the problem is very easy to demonstrate.

Assume we have a length of reasonably uniform cord, we divide it up and make ten test samples.  If we test each one to destruction we might for example get the following set of results (modelled roughly on a Normal distribution) --

47, 53, 44, 56, 59, 47, 41, 51, 49, 53.

The average strength of these samples is 50.

Now let's do a paired test, you can do it easily for yourselves.  Write the values on scraps of paper and put them into a hat, pull out two at random and write down the lowest of the two, then throw them both away (tested).  Repeat this four more times till you have the five double knot test results.

Here are a set I drew out.

53 vs 47    result  47
44 vs 53    result  44
47 vs 59    result  47
51 vs 56    result  51
49 vs 41    result  41

Average              46

@A Fluke of the draw' you cry - OK do it again several times and you will see that you are getting a result which is focussed towards the average of the low values, or roughly 10% lower than the true average for that knot in that cord.  The reason is that the method filters out the high values and discards them, biasing the result away from the real value.

If you counter argue that you want to declare the statistically weakest strength, then again you have to measure all ten individually to be able to determine the mean and a value for Sigma, then take the 3-Sigma value, but agian you must not skew the data before calculating the mean and sigma.

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on January 27, 2009, 05:03:14 PM
Just some comments here...

[ ] Photography: I have preserved all the knot specimens - the surviving knots (from the dual knot test series) have been cinched very tight - and their shape and structure has not altered with the passage of a few weeks. There are a few very good reasons why i haven't taken photos; i) I ran out of time - I am currently at work and away from home; ii) I want to take photos in the right conditions (using combination of flash + natural sunlight) but North Queensland (Australia) has had a deluge of rain/storms the past month. There are a few  perfectionists on this forum and I for one dont want to send out sub-standard images of my work!

I'm on to it guys, just be patient a bit longer - I will be back home in 3 days and it will be the weekend...

[ ] The lever action winch: I purchased a $AUD 100.00 winch and it consists of a 2:1 pulley configuration. I always mount the load cell at the knot specimen side - so it measures what is going on right there at the knot. I cant be specific about the speed of increasing load - I simply crank on the lever and keep cranking away. I cant for example state a speed of say 300mm per minute or whatever. So there is always going to be some degree of lack of measurable quantities in my tests... The 2:1 configuration of the winch doesn't alter the force bearing down on the specimen knots...and there is still cable length run out from anchor point to anchor point...whichever way you look at it, there is force in the system and it has to be treated with respect.

[ ] Recoil at instant of knot failure: Linear type knot tests with 5.0mm diameter accessory cord are easy to manage - the anti-recoil system I use is simple. I have an old punch bag (boxing) which I lay down on the driveway to which is attached an old (retired) dynamic climbing rope. The punch bag acts as a 'dead weight' - and absorbs the shock. I also lay down foam padding underneath the load cell - because it jumps a bit - I don't like it jarring on a concrete surface. The recoil force in the loop style tests a little more scary due to the force hovering around 7-8kN. I use the same system, only with more caution thrown in. Hearing protection is not required. I don't bother to wear eye protection in the linear tests, but I do wear them in the loop tests.

[ ] Dual knot testing: I still support the concept of testing dual knots - because there is always a surviving specimen. With tracer threads woven in both knots, it makes it easy to draw comparisons and determine the region of knot failure. Its just that I HATE inserting the cotton threads. I now know that my calling in life wasn't sewing! I wish that I could mail all my knots to Dan Lehman (by the bag full) and let him do the weaving (and then mail them all back to me)...

i find it hard to understand the test results of loop style tests - eg 2 x ABoK #1415 Double Fishermans joined from 2 x 500mm lengths of cord. Sterling report an MBL of 5.2 for their 5.0mm diameter cord...but the test results are up around 7-8kN... I would have to get a harness manufacturer in Australia to form a loop out of the cord by using a stitched join. Then I'd have to break the darn loop (3 times) to get some figures...and then compare it to the looped knot tests... too expensive and too time consuming.

[ ] Knot security/stability Vs raw strength - Although its interesting to go through this exercise, at the end of the day I think security and stability are more important factors with life support knots. I don't think any knot is ever going to break in the field...

[ ] MBS: Minimum Breaking Strength.. have not researched into how Sterling derive their published figures (ie 5.2kN for 5.0mm diameter cord). I dont know about the technical detail of the composition & weave pattern of the sheath either. Perhaps Dan/Derek could write to Sterling and aks for more detail???

[ ] Anchor pins / tensionless hitch: Can we ask how Sterling anchor the standing Parts of their cordage for linear pull tests? I used 30mm diameter anchor pins with the 5.0mm accessory cord, and I found this worked for me...I got an immediate increase to 5.48kN using an 8 wrap tensionless hitch around a 30mm diameter pin... again, what do Sterling use?



agent smith
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 27, 2009, 09:51:40 PM
Quote
2. Expecting two knots to break simultaneously is ...
..., again, not part of any discussion here:  so, what's the point of discussion?
(What we expect is that two knots enduring tension X are better than having
one do so, re data/stat.s, and also yield the benefit of a survivor.)

Quote
3. If you test two knots against one another the weaker one will always fail first.
--a tautology.
--dl*
====

"so, what's the point of discussion?"  The point is that if [A_]S is intending to publish his results he should not expose himself to criticism that he failed High School Stats.  Even the claim that the method generates a valuable surviving sample is questionable because the shockwave caused by failure might have altered the structure in some way impossible to predict.

Ah, well, implying that we expected simultaneous/equal breaks was an odd
way of stating this concern.  But I don't give it much value, anyway.

Quote
Luckily the problem is very easy to demonstrate.  ...
the following set of results (modelled roughly on a Normal distribution)

Holy haphazard hypothesis, Batman!!
You are spewing results that differ in extremes of the lowest being 75% of the highest!!
That is quite some diversity, which makes your lament seem worthwhile.

But even so, the conclusions you want to draw are simply not those that should
be drawn.  Knowing that the surviving knot is stronger, one can (as I suggested
above) toss in some bit of statistical hocus-pocus to adjust for that; it is of some
comfort to realize that one's data is in this sense a bit of "worst-case" values.
Given a more reasonable set of values, there isn't all that much difference to
have to worry about, anyway.  (Perhaps one could take Dave Richards's
results from kernmantle-rope breaking and figure a reasonably likely maximum
difference--it will be well shy of 25%!!--, and then use that to guesstimate some
2- or 3-stnd-dev. below Mean value (by bumping Mean; or, by going just 2 vs. 3
stnd. dev. below.)

What you miss is that this project requires EFFORT of breaking, COST or MATERIALS:
PER UNIT TEST SPECIMEN WE FIND A VALUE THAT **TWO** KNOTS ENDURE
rather than just one.
Now, taking my logic to extreme, I guess we should urge a stringing together
of some 10-20-50-100 knots in a row, and ... .  That goes beyond practical,
but might give a more believable Min value than statistical figuring from merely
5 knots.

Quote
you must not skew the data before calculating the mean and sigma.

Sad to think that adding information degrades the result; I don't.

And I also don't lose sight of the purpose of this plan,
which is to:
  compare various knots (this consistent method does so);
  learn about knot behavior (statistics aren't invited here);
  and gain confidence in some seldom-tested, "new" knots.

Considering that other results to which these arguably improperly figured
values might be compared come without the basic information to assess
the tested items, I don't see any loss of value here.

As for the value of the surviving knot, photos can show whether there
is any deformation of structure from some shock wave--I doubt it.
--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 27, 2009, 10:28:56 PM
[ ] Photography: I have preserved all the knot specimens - the surviving knots (from the dual knot test series) have been cinched very tight - and their shape and structure has not altered with the passage of a few weeks.
...  There are a few  perfectionists on this forum and I for one dont want to send out sub-standard images of my work!

A moderately good photo is infinitely better than none.  I reiterate prior urgings.
As for knot change, while I don't think so much of the post-rupture geometry will
be lost, I do not believe that in-tension geometry survives rupture--especially for
bowlines, whose collar won't hold the full tension of the SPart.

Quote
I have an old punch bag (boxing) ...

This is good to know:  I will henceforth let Derek argue w/you about results.   ;D

Quote
to which is attached an old (retired) dynamic climbing rope. The punch bag acts as a 'dead weight' - and absorbs the shock.

I don't follow.  There's (lots of!) mass, and a climbing rope:  but what's tied to what?

Quote
I HATE inserting the cotton threads. I now know that my calling in life wasn't sewing!
I wish that I could mail all my knots to Dan Lehman (by the bag full) and let him do
the weaving (and then mail them all back to me)...

Well, maybe it's the insertion at in-tension time rather than prior, making an
estimate of position (and a photo to document where they *happen* to end
up).  Again, I'm curious as to what sort of sewing you do.  At first, I thought
one would just pull a thread through once or twice; but then it occurred to
me that it might be better to just try to make a nipping loop of thread around
a few of the mantle fibres (thinking it less likely then that the thread would
be pulled in two directions--odds being that those few fibres would all go
in the same direction).

Quote
i find it hard to understand the test results of loop style tests - eg 2 x ABoK #1415 Double Fishermans joined from 2 x 500mm lengths of cord. Sterling report an MBL of 5.2 for their 5.0mm diameter cord...but the test results are up around 7-8kN... I would have to get a harness manufacturer in Australia to form a loop out of the cord by using a stitched join. Then I'd have to break the darn loop (3 times) to get some figures...and then compare it to the looped knot tests... too expensive and too time consuming.

???  Um, the knots  broke under a load of the loop of 8kn, which implies a load
on the knot (i.e., on each side of the loop) of 4kN.  And we can wonder at the difference
between this derived value and that of the individual tests (which were higher).  It's not
huge, and I gave some reasoning that might explain.  --no reason to create a loop of
original material:  that makes no sense, unless your break is at the pin.

Quote
MBS: Minimum Breaking Strength.. have not researched into how Sterling derive their published figures (ie 5.2kN for 5.0mm diameter cord). I dont know about the technical detail of the composition & weave pattern of the sheath either. Perhaps Dan/Derek could write to Sterling and aks for more detail???

Re "MBS", yes, we (I) can.  Re weave:  you have busted (and cut) bits right in
your hands!  Can't you take a peek at this--esp. in the ruptures, the kern should
be plainly visible.  --and a collection of twisted (or braided?) strands, or maybe
a braided unit (sort of a rope within a rope (which would break my definition
of "kernmantle", but that's just me)).

Quote
Anchor pins / tensionless hitch: Can we ask how Sterling anchor the standing Parts of their cordage for linear pull tests? I used 30mm diameter anchor pins with the 5.0mm accessory cord, and I found this worked for me...I got an immediate increase to 5.48kN using an 8 wrap tensionless hitch around a 30mm diameter pin... again, what do Sterling use?

Okay.  Again, I question the value, to strength, of extra wraps;
they have value in absorbing force transmitted to the end,
but that isn't a great issue here.  (I suspect Sterling use an
even larger bollard--maybe 6" diameter?)

Cheers,
(-;
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 28, 2009, 01:39:13 PM
snip...

Quote
I have an old punch bag (boxing) ...

This is good to know:  I will henceforth let Derek argue w/you about results.   ;D

snip...


Dan, even in jest I am not here to 'argue' with anyone.  It is Agent Smith's project and he has posted here to attract input and comment from other minds.  From past contact with him I have found that he demands a very high standard of himself and for his publications, and to achieve this he willingly subjects his work to open review, then makes his own balanced judgement as to what his final publications will contain.

I have also found your good self to be a perfectionist, so I am more than a little surprised to see you advocating "Guestimation" and "hocus pocus" rather than the simple application of a little bit of rigour to eliminate an effect documented in studies which you have referenced before on this forum.

Just because a piece of work is not being carried out in an accredited laboratory does not mean that it has to be sloppy or that it cannot present the very highest standard of professionalism.  Often in the Amateur world, cutting edge work has been produced well in advance of any standard industry could afford to achieve.

This trial uses a concrete drive as its testbed and a hand winch as it force source, but what does that matter so long as these factors can be shown not to distort the results?  In my test rig, I use a 50 KN hydraulic car jack as the force source, but it does not detract from the quality of work that is possible, provided knowledge, ingenuity and peer input are fully utilised.

Your comment about stacking multiple knots to find the weakest in a single test is completely valid, but it does not tell us how weak it was against the other knots and because it was destroyed in testing, we cannot infer anything from the structure of the remaining knots, because they were all stronger than it was.  Their structure may well have been different in some  significant aspect, such as to bestow the additional strength on them.  We just finish up with an unknown situation which weakens a knot to a known low value. 

You also state that "hocus pocus" can be utilised to take the biased 'pair results' back to full population results - fine, how about pointing us then to how this should be done or to someone who can do it as I would not be able to advise Agent Smith how to do it.

How many times have we seen reports from professional labs or Universities where the test set up and statistical analysis has been exemplary but all detail of knot structure, dressing etc has been ignored - virtually every time.  So when the job is approached from the other direction - from the knot tyers perspective, should we fall into the same trap of ignoring aspects which are not particularly interesting to us or not within our sphere of expertise, resorting to a little bit of "Guestimation" and "hocus pocus"?   I would suggest not, particularly when the solution is so easy to achieve.

How large is the effect?  I have no idea.  The hypothetical data set I used in the example was simply to demonstrate the existence and mechanism of the effect for you.  We cannot know the significance of this effect unless we have access to unbiased data and we cannot begin to postulate reasons for strength variations unless we have access to images of the knots from several perspectives under near terminal load.  Whether Agent Smith decides if any of this is relevant to his final report, is up to him, and I have no intention of arguing with him or yourself over the issue.  The facts are more than capable of arguing for themselves.

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 28, 2009, 07:16:51 PM
I have also found your good self to be a perfectionist, so I am more than a little surprised
to see you advocating "Guestimation" and "hocus pocus" rather than the simple application
of a little bit of rigour to eliminate an effect documented in studies which you have
referenced before on this forum.

There is a simple matter of making X number of loadings of X test specimens:
I want to increase the information got from that, and believe that including two
knots per does that.  By your insistence on that pristine-for-statistics 1-per-1
work you have X broken knots & data; by the current test plan we have that
AND add X more load-enduring knots, which hold some form that can be
analyzed.   Statistics, as you point out, can point out that the latter sample
of 2X knots got data from the weaker of each pairing; well, then, we can
be happy that our results are more *solid* in finding minimum values (as
one tends to have a bigger complaint for things weaker than expected).
I'll surmise--w/o knowledge--that there is some statistical analysis that
can accommodate the unknown strengths of the surviving knots; and
that especially in a population where differences (stnDev) are small,
ultimate values are not going to change much:  and, again, one could
use the X-values-only and proceed with a confidence of conservatism.
As this method can be applied I think for all knots (bends--2 in line--,
hitches), they all can be compared.

And you would prefer to have half the number of knots tested?
(And, yes, yet, I have not urged FOUR knots per test.)

AND, again, we are not seeking to make huge inferences or promotions
with these values vis-a-vis other tested values, about which a great
deal is unknown (in some cases, e.g., I wonder at transposition of
the digits!).  And my Perfectionism relaxes there in realization that
such fine-tuned scrutinizing just cannot have much sway in anything
that matters (for one, conditions of material and loading in practical
cases will vary greatly).

I do urge the jettison of wanting photographer-studio conditions and
losing all capture of images in its absence--much is lost to us, now.

Quote
very highest standard of professionalism.
I've never thought that this was an issue, so I don't understand your words
on this point.

Quote
Their structure may well have been different in some  significant aspect,
such as to bestow the additional strength on them.

But this has nothing to do with examination of a survivor, but everything to do
with photographing knots during testing!

Quote
You also state that "hocus pocus" can be utilised to take the biased 'pair results'
back to full population results - fine, how about pointing us then to how this should be
done or to someone who can do it as I would not be able to advise Agent Smith how to do it.

I'll see if some statistically adept person has a definite answer,
beyond my remarks above about at least simply noting that the
data comes from a selectively weaker set than the survivor set.

Quote
"Guestimation" and "hocus pocus"?
I would suggest not, particularly when the solution is so easy to achieve.

You're making more of the words than is intended--I'm happy enough to use
them for statistics in general, after all.  The "solution" of losing results doesn't
appeal; I will hope that statistics shows some way(s) to deal.

Quote
The hypothetical data set I used in the example was simply to demonstrate
the existence and mechanism of the effect for you.  We cannot know the significance
of this effect unless we have access to unbiased data ...

Oh, but you can.  You have unbiased weakest-knot data--i.e., the range of values
of randomly selected pairings.  You also have Richards's results in some similar
cordage (i.p., 7mm accessory nylon kernmantle).
here:  www.caves.org/section/vertical/nh/50/knotrope.html (http://www.caves.org/section/vertical/nh/50/knotrope.html)
The largest stnDev in the 7mm (and about largest throughout, ignoring those
knots that required back-up knots to arrest slippage) is 3.2%.  The smallest
value is 93% of the largest; in your set, it was 75%.  Absent the exagerated
difference, there really is little to fuss about, other than the *purity* of the statistics
for statistics sake.  Again, I'm happy to put a footnote "* NB:  these values are
probably slightly understated." (or simply "understated").  We're not hiding
anything, anyway.

Quote
and we cannot begin to postulate reasons for strength variations ...

Oh?!  I distinctly recall someone's red-painting a "GeeSpot" and vowing to get
water from rock on that!  --even lacking some obvious aspects of the issue.
 ::)

Quote
unless we have access to images of the knots from several perspectives under near terminal load.

It might well turn out  that for some knots the strength-determining geometry
is set well shy of near-terminal load; but it will take some scrutiny of knots
preferably with sharable photos in order to understand this.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 29, 2009, 06:42:05 PM
So if I might paraphrase:-

You accept that you have corrupted your data by weakest pair testing, but you hold that, (based on someone else's unbiased data from different cord) that the corruption is small, and besides it is in the right direction (understating true mean strength).

And you have a set of destruction fragments with known failure strengths and a set of intact knots, known to be stronger than a given value but of unknown strength.

I don't think there is any point flogging this one any further, you understand the data is corrupt and want to stick with it.

Ho Hum
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on January 30, 2009, 07:11:42 AM
Speaking of data, here's what we have, so far, concisely:
(avg. % values figured for both the rated, 5.2kN, & tested, 5.48kN tensile)

((interesting is the discrepancey between the Grapevine when tied to
join TWO ropes into a sling vs. tied in-line of single strand!?))
(((interesting is that A_S didn't re-test Rosendahl's bend similarly!)))

Bowline (#1010):
  3.98  3.78  3.76  avg.~= 3.84  ~= 74 {70}%  (per 5.2 rating  {or 5.48 test} )

Bowline (EBSB):
  3.84  4.02  3.96  avg.~= 3.94  ~= 76 {72}%

Grapevine (#1415) in LOOP:
  7.86  7.76  7.74  avg.~= 3.9   ~= 75 {71}%
in single-knot/-line:
  4.16  4.58  4.20  avg.~= 4.3   ~= 83 {78}%

Rosendahl's Zeppelin Bend in LOOP:
  6.62  7.22  6.48  avg.~= 3.4   ~= 65 {62}%

Fig.8 EyeKnot:
  4.00  4.26  4.32  avg.~= 4.2   ~= 80 {76} %


 :)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: DerekSmith on January 30, 2009, 07:08:30 PM
snip...

((interesting is the discrepancey between the Grapevine when tied to
join TWO ropes into a sling vs. tied in-line of single strand!?))
(((interesting is that A_S didn't re-test Rosendahl's bend similarly!)))

snip...

Grapevine (#1415) in LOOP:
  7.86  7.76  7.74  avg.~= 3.9   ~= 75 {71}%
in single-knot/-line:
  4.16  4.58  4.20  avg.~= 4.3   ~= 83 {78}%

snip...


You state that TWO ropes were joined to make a sling, i.e. you are testing the weakest again so in that respect no surprise.

However, I am surprised at the magnitude.  Are you SURE that there was no friction at the sling anchor points which would have caused uneven tension in one leg over the other.  Even the slightest disparity will load one leg while releaving the other.  i.e. 4.3 + 3.5 = 7.8  only +/- 5% of the total load displaced.  unless the anchor pin is free to rotate under load, it is easy to generate this sort of disparity, but then, it is strange that the disparity is so reproducible ? ?  Short of seeing a video of the testing process it is hard to pinpoint what error is being incorporated.

Note : although I know what you mean, even the approximation notation does not give justice to the statement "7.86  7.76  7.74  avg.~= 3.9"

PS.  What method was used to test the single knot/-line bends ?

Derek
Title: Re: Knot testing - Life support knots - procedures and results
Post by: R Statistician on March 18, 2009, 07:56:10 PM
The R in R Statistician stands for retired.  There are procedures for analyzing this type of data (some values known, other values are a lower limiit on the breaking strength).  The problem occurs in product life testing: the test is terminated before all the items fail.  Some times are failure times (when the item failed), other times are how long an item was on test, but it didn't fail.  The times for the non-failing items are called censored times or censored data.  The computations are very complicated, so they are done by a computer package.  The calculations depend on the type of distribution.  I compared the fit of Normal, Lognormal, Extreme Value, and Weibull distributions to the data listed in this thread.  Of the six small data sets (5 knots and re-test in single-knot line), the Weibull fit best in 2 cases, the Extreme Value fit best in 1.5 cases (the result of a tie between two distributions), the Normal fit best in 1.5 case, and the Lognormal fit best in 1 case.  I also checked the fit of these distributions to the 7mm accessory cord data: the Weibull fit best for 5 of the 8 knots, the Extreme Value for 2 knots, and the Lognormal for 1 knot.   So I used the Weibull distribution.  Here are the results.
 knot         mean   95% confidence interval (approximate)
Bowline       3.90   (3.79-4.02)
EBSB          3.98   (3.91-4.05)
Grapevie     3.91   (3.88-3.94)
in 1 line      4.31    (4.05-4.58)
Zeppelin     3.49    (3.31-3.68)
Fig 8 Eye    4.27   (4.16-4.39)

I believe that the retest of the grapevine in single-knot line gave a different result due to a calibration problem between the two levels of testing: the sling or rope ring requires twice the force to break it as does a single line.  If the re-test was done after all the other tests were finished, then there could have been a calibration problem between the times of the two tests.  The usual solution to this problem is to prevent it by testing all the knots once before testing any knot the second time, then test every knot the second time before testing any knot for the 3rd time, and so on.  The order of testing the knots within each set is often determined by a random draw (for example, ace-2-3-4-5-6 from a shuffled deck of cards for six knots).

I am not only retired, I have an old computer (Windows 95 operating system) and ancient software; I suggest you get somebody else to verify the results.  For Internet access I use the computers at the public library, so my Internet visits are short and infrequent.  I am interested in data abouts knots: strength, security, stability, ease of tying and untying.

Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on March 18, 2009, 11:17:55 PM
There are procedures for analyzing this type of data (some values known, other values are a lower limiit on the breaking strength).  The problem occurs in product life testing: the test is terminated before all the items fail.
Ah, good, thanks; I thought that there must be something to this effect.

I don't mean to go overboard in exercising your expertise,
but might you show the results for, say, a couple of the above
knots--i.p., one w/greatest variance (bowline?)--, and one with
much less--, as though those results were in fact for FOUR knots per specimen?
--just to get an idea of what we might be missing (probably not great) by the
current limit of two.  (Putting four knots into a specimen I think would raise
or aggravate concerns about physical proximity and other behavior.)

Quote
I believe that the retest of the grapevine in single-knot line gave a different result due to a calibration problem between the two levels of testing: the sling or rope ring requires twice the force to break it as does a single line.  If the re-test was done after all the other tests were finished, then there could have been a calibration problem between the times of the two tests.
Good points.  But, to reiterate, there is a valid thought that if the knots'
compression rates differed--say, side-A loses more material (maybe was
less tightly set)--, friction at the pins could sustain an imbalanced loading,
and perhaps have 100% + 80% of knot strength, giving a value (by halving
the total force pulling both sides of sling) of 90% of actual force in the breaking
side.  --conceivably.  Or, as you point out, other factors could be at work.

[edit:  It must be noted that by my reasoning above the in-loop values should higher, not lower! ]

Quote
The order of testing the knots within each set is often determined by a random draw
 (for example, ace-2-3-4-5-6 from a shuffled deck of cards for six knots).
Here is where Statistics & I have a disagreement:  IF there is some bias resulting from
test-device *ageing* during activity, I'd think that likely it is somewhat linear and going
from one state towards another (as it accrues usage); and that to balance results,
one must be deliberate in spreading particular knots-testing across this possible
range of readings--whereas random ordering could do poorly at this!


Quote
my Internet visits are short and infrequent.  I am interested in data about
 knots: strength, security, stability, ease of tying and untying.

We will enjoy what visits you can make, and hope to keep or build your interest
maybe to raise the frequency.  I just lost one computer and have yet to set up
its replacement, so I know well about this modern benefit of a local library!
--AND books, to boot (have two at hand from the 4-sale shelf).

Thanks, & happy to meet you,
--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on August 22, 2009, 08:16:20 PM
 :)   Here's a "bump" to remind folks of this thread, and Agent_Smith in our
continued interest in its development -- such as photos of tensioned knots,
and, of course, further data to chew on.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on August 28, 2009, 08:28:32 AM
Hello...I'm back again.

I have created a 'public downloads' page at www.paci.com.au (hopefully any traffic attracted to the site wont clog my bandwidth and cause me financial pain!).

From the home page, click on 'public downloads' and then the first 2 files you see in the table will be about knots.

I have given kudos to Derek Smith and Dan Lehman for their critical reviews of my work which spurred me on.

I consider the work good enough to open up to the public domain...and no doubt I'll receive some more feedback.

This site is all about giving back to the public and contributing to our collective knowledge on all things knots.

Some files are password protected...the knot study guide is 'thankyou' (without the quotation marks).


Mark
Title: Re: Knot testing - Life support knots - procedures and results
Post by: capt larry on August 28, 2009, 04:05:21 PM
Mark,

First welcome back.  I have been following this thread - though without posting since for me it has been a learning experience.

Personally, it has been worth the wait.  Your work is a fine contribution to knotting.

Have only had an opportunity for cursory review at this point but am impressed by the detail and clarity of your presentation, the illustrations are very well done.

One critical observation that popped out at me is in respect to the "Butterfly" - a favorite knot of mine.  As I read it, the knot was not referenced as ABoK "lineman's" and it was attributed to W&G.  A recent thread on this forum has shown that it was published  a few years before (1917) in a paper by Burger at Iowa State Univ.  Also, there has been a thread here where Alpiner showed an extremely easy alternative to tying it that seems to give easier control over the sizing of the loop.

Will be awaiting Dan L's reaction.

Larry   
Title: Re: Knot testing - Life support knots - procedures and results
Post by: roo on August 28, 2009, 04:16:34 PM
Hello...I'm back again.

I have created a 'public downloads' page at www.paci.com.au (hopefully any traffic attracted to the site wont clog my bandwidth and cause me financial pain!).


When clicking on the first file, I get a message that the file is damaged and cannot be repaired.  Maybe I can try again later with a different brand of reader.
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on August 28, 2009, 05:31:19 PM
I have created a 'public downloads' page at www.paci.com.au ... .
When clicking on the first file, I get a message that the file is damaged and cannot be repaired.
Maybe I can try again later with a different brand of reader.

I just clicked on the URLink and after a long (dial-up:  about 6min?) period
in which things appeared to be in fact loading (modem indication, and the
locator-window URL text being gradually highlighted ("filling")), I ended up
with the browser window *done* and ... no sign of a file anywhere!?
-- no nastygrams, either; just no productive result, so far as I can tell.

!?!?

OH, this attempt was for the KNOTS (not Bowlines) file, as I was looking for
updated test data.  (Which it might be helpful to post to this thread in the
format of my previous summary update (i.e., w/o reiterating the tedious
detail of device/rate/attire-of-tester...).   "Just the facts"

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on August 28, 2009, 06:13:49 PM
One critical observation that popped out at me is in respect to the "Butterfly" - a favorite knot of mine.
As I read it, the knot was not referenced as ABoK "lineman's" and it was attributed to W&G.
A recent thread on this forum has shown that it was published  a few years before (1917)
in a paper by Burger at Iowa State Univ.  Also, there has been a thread here where Alpiner showed
an extremely easy alternative to tying it that seems to give easier control over the sizing of the loop.

Will be awaiting Dan L's reaction.

Capt.Larry, about the Lineman's Loop aka "Butterfly knot" aka "Alpine Butterfly",
what we have is a case where a knot was discovered in two separate places (at
not all so different times).   One can postulate that there must've been many other
like discoveries, but who knows.  (I was remiss in missing CLDay's note, and am
quite glad that Bob Thrun read more attentively, in addition to pursuing that lead
so well (and now having not only e-copy but also --courtesy a link from Nautile--
hardcopy of the earlier work.  (It was Bob also who had gotten W&G and put
it into e-form, which Charles Hamel has kindly put up on-line for access.)  And
we can reflect on the multiple discoveries --over a 2-3 decades-- of SmitHunter's
Bend:  Smith, Hunter, Lehman (and ... ?).  Despite Phil Smith's publication in
a book (limited circulation, but still ...), it was a "new" knot to many, taking
Edward Hunter's revelation via the Times & perhaps also IGKT-informed authors
to become more public.  (resp. circa 1955, 1964, 1973, for S-H-L, I think)
So, I think that W&G deserve both merit for discovery (not exclusive, but
authentic) and publication, and perhaps their efforts were what can be
traced into the acceptance by rockclimbers, and thus into other disciplines;
whereas, despite use & publicity, perhaps --I don't know-- the knot's life
waned in the lineman world (or can we find in then-current & following
years/decades published guidance for such workers to continue it use?) !?

And I concur in your assessment of Alpiner's (initial, at least -- were there two?)
improved tying method.  In fact, that was put out to some rockclimbers and
got a bit of a nod of approval; the other methods are simply not so neat.

And, now, I have found a sort of *brother* to the Butterfly, in which there
is one seeming superfluous wrap of one eye leg around the body of the
knot (whereas in the original the eye legs flow into collars; this extra
wrap is quite helpful if the orientation of eye loading can be foreseen, as
it fairly well prevents the (effective) end's collar from collapsing around
it -- i.e., in a case where one end is loaded (so is "S.Part") and the other
completely slack, the collar on the slack end has no resistance and can
be drawn tight around it, to the point of jamming.  (And I've discovered
a great many similar but "directional" eye knots, using a Slip-knot
base, as well as a #1408 equivalent to the Butterfly (which comes about
also with that eye-leg wrap).)

--dl*
====

postscript:  How Creation Works (one case)

I just conceived a **New & Improved** Directional Fig.8 eye knot,
led to such fancy by mulling over this topic and then the formation
from the Slip-Knot and so on.  Had to keep closing my eyes to "see"
this, to double-check that it wasn't illusory, and then to manifest it
in rope.  Ta-da!  doesn't look bad.

Partly what led me into invention was reflection on the CMC Rope Rescue
Manual
data in which the usual, Fig.8 eye knot tested a few %-pt.s STRONGER
in end-2-end loading than the Directional Fig.8 (!!)  -- quite surprising, as both
the former is deemed bad as a knot, and even too bad to even sustain pulling
by two persons(!), and the latter's raison d'etre is supposed fitness for such
loading (where, however, I've noted that it has the form of a SquaREef knot
w/one slip-tuck) !?  I think that CMC might've gotten lucky on their test,
and would love to know how their Fig.8 was dressed & set (since I believe
that those accounts of its failing to how qua bend --and here the only
difference is whether the eye is cut or not (irrelevant if holding)-- are not
jokes.  TMoyer's testing of the Offset Fig.8 bend (the so-called "EDK"-like form)
show it holding and not holding, variously; though it didn't seem strong.

(Hmmmm, now it occurs to me that this recent invention might be one
I have previously done  -- rather behind on recording, or if done long ago,
forgetful of it (or perhaps the knot form then came about not by tying in
the bight (or even if doing so not considering it for "directional" use),
and not being aware of the potential).)

((double-HmmmMMM:  Moreover, this variation of the Fig.8 is what
I think some rockclimbers tie as a sort of "backed-up" and easier to
untie version (and it might be more vulnerable to ring-loading),
similar to another such version.))

argh:  now it's getting to be work ...   :(
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on August 29, 2009, 04:31:51 AM
Thanks for the comment re Butterfly knot...am aware of the historical significance and am working on the knot study guide to update it asap. Will upload revised pdf file very soon and announce it on this forum.

To Dan: There does seem to be a glitch with the way Mozilla Firefox downloads and reads PDF files in the browser window. I tried clicking on the first 2 knot links in the table and they both 'froze'. I then closed Firefox and re-opened it and cleared the history. On second try it opened normally and asked for a password. I have no rational explanation for this strange behaviour.

However, an alternative way to access all the files is to right click and then choose 'Save link as' (for Firefox) or right click and then choose 'Save target as' (for Internet Explorer). The right click method always works with all browsers.

Make sure you are using the latest version of Adobe Acrobat Reader (we're up to Ver 9). Also make sure you are using the latest version of firefox or internet explorer... (just my suggestions).

Dan/Derek, I am expecting some serious critique from you guys...will take on board any comments and fix/update my work accordingly. I noted that you are silent on my EBSB variant Bowline! I was definitely expecting a few remarks re this alternative tie-in knot for climbers... (I have been using it for some time now with good success - always easy to untie after repeated loading events and is stable and secure). Learning to tie it is more difficult than the F8 eye knot, but nothing like a bit of repetition, repetition, repetition to sort out the long term memory issue!

I am also going to place more emphasis on the properties of knot security and stability (rather than pure strength). This will feature in my next update.


Mark
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on August 29, 2009, 06:16:45 AM
Thanks for the comment re Butterfly knot...am aware of the historical significance and am
working on the knot study guide to update it asap.

To be clear:  the evidence so far is consistent with W&G originating the knot
for themselves (not sure how this would be disproven; have no reason to
doubt it -- they seem honest), and I surmise that by them it became known
in climbing circles.; beyond that world's horizons, however, it is clear that
the knot was known to others (who happen to have earlier dates of publication).

Quote
To Dan: There does seem to be a glitch with the way Mozilla Firefox

Safari here, so far.  (Though working w/Yahoo Mail is getting very annoying.)

Quote
I noted that you are silent on my EBSB variant Bowline!

I thought I'd lambasted that previously?!  This is the EBSB +Yo finish, yes?
(Fig.s #26-7 of pdf#6)
To my mind, it is gratuitously complex and suboptimal; you did have the Janus
Cowboy Bwl, and that is vastly simpler.  I just gave a token of that a good
load with the pulley, and the Janus C-Bwl looked good in S.Part curvature.

--dl*
====


Title: Re: Knot testing - Life support knots - procedures and results
Post by: capt larry on August 29, 2009, 03:14:59 PM
Dan,

Thanks for the info on origin of the "Butterfly". Don't want to contribute to further inaccuracies in the knot tying history.

Mark,

I use Firefox and had no problems. Should note that the second time I used your link and don't think I needed the password.

CL
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on August 29, 2009, 07:04:38 PM
Thanks for the info on origin of the "Butterfly". Don't want to contribute to further inaccuracies in the knot tying history.

I should remark that much of the problem is our lack of objectivity in
reporting:  if we say "W&G invented the knot in 1928", or assert that
theirs was the first public presentation of it, we are saying more than
we have a right to -- or using "invent" in an arguably legitimate way but
without care that it can be interpreted otherwise.  So, saying simply and
clearly that, e.g., "The first-known publication of the Butterfly knot, so
far as the authors are aware, was in 1928 ..." is clearer; and, as Joop K.
remarked, is the unassertive way in which W&G themselves introduced
it -- as new to them though conceivably known elsewhere.

Further, note that we can credit W&G with invention (i.e., innovation
regardless of that done by others previously); we cannot credit Burger
with that, only of having published what he alleges to have found or
known about -- and so for the earlier emergence of the "Lineman's Rider",
we have yet to trace beginnings (one can wonder about some old
industrial manuals for linemen).  Similarly, re the Constrictor knot,
although we might believe that "Tom Bowling" presented it in his
old knots book, that he did so as almost an aside -- lacking an image
to correspond with the text, odd for the book (and as did, likewise,
Ohrvall (!! -- what is about this knot?!)) -- , in both cases the authors
seem to be merely conveying information known in some way and
not presenting a novelty originating with themselves.  So, there is
yet further tracing to do.

Btw, verbally:  if you tie the Butterfly by the old "twirly flop" method
--i.e., of twisting the line and then bringing the bight around to tuck
into the twist--, at the point immediately prior to this finishing tuck
if you give the one side that can do it a half twist (doing so for one
side will UNtwist it, for the other ... work), you will orient the two
S.Parts so that they draw into the knot in the same rotation (whereas
the Butterfly usually had one pulling opposite other, rotationally).
You will find that this line w/extra half twist forms a Fig.8 to the
other's Overhand; and it will be less able to jam if being the end
that is not loaded when the eye is loaded.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on August 30, 2009, 02:50:45 AM
I have uploaded VER 4.0 of my knot study guide. It is now live and ready for download. Password = thankyou

Go here to access files: www.paci.com.au and then click on 'public downloads'

I have made amendments to the following areas:
[ ] Section on knot stability and security - warnings and emphasis that security and stability are of greater important than raw strength in human life support applications
[ ] Section on the Butterfly knot - added historical note re the AA Burger book published April 1917 and the reference to the 'Lineman's Rider'
[ ] Section on the Bowline - added information about alternative name (Right hand Bowline per Ashley)
[ ] Added acknowledgment to those who assisted me in preparing my work (eg Derek Smith and Dan Lehman)
[ ] Added information about copyright laws


I have also added AA Burger's work as a downloadable PDF file...


Feedback is always welcome.


Mark

Title: Re: Knot testing - Life support knots - procedures and results
Post by: dfred on September 17, 2009, 06:48:39 PM
I have uploaded VER 4.0 of my knot study guide. It is now live and ready for download. Password = thankyou
[...]
Feedback is always welcome.

I lost track of this thread at some point and was just catching-up.  The Knot Study Guide is looking great, here are a few comments:

Page 23: The strength section of the Zeppelin Bend reads: "...this knot is strong, but quite as strong as the double fishermans..." -- should this read "but not quite as strong"?

Page 29: The comments about Burger look good, however there is actually a slightly earlier publication date, August 1, 1914, for Rope and Its Uses.  Here's a link to that edition on Google books; note that it is embedded in a much larger collection within the single PDF document:  Rope and Its Uses (http://books.google.com/books?id=Ju4sAAAAYAAJ&as_brr=1&pg=RA2-PA19), A.A. Burger, 1914.  (Direct link to page where description of Lineman's Rider begins (http://books.google.com/books?id=Ju4sAAAAYAAJ&as_brr=1&pg=RA3-PA24#v=onepage&q=&f=false))

Page 44: The name "Slipped Double Overhand Knot" seems like it could be misleading.  The term slipped often means the final tuck of the knot is a bight, so as to facilitate a quick-release.  In the case of a double overhand knot, this could mean that the slipped portion was the working end rather than the standing part.  It's a minor point and probably unlikely to cause confusion in reality, but have you considered using "Double Overhand Noose" for the primary name instead?  (I see you do mention "noose" in the alternate names.)

Those were the things that jumped out, but I'll keep looking through it.  I also have forwarded it to my cousin (not the one with the hanging tomatoes :) ) who is a climbing guide and instructor in the western US.  I'll let you know if he has any feedback.

Thanks for posting this and all those other interesting documents on the public downloads page!
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on September 18, 2009, 04:51:57 AM
Page 23: The strength section of the Zeppelin Bend reads: "...this knot is strong, but quite as strong as the double fishermans..." -- should this read "but not quite as strong"?

As this document takes software (Apple's Preview doesn't handle it) that won't
be coming down the dial-up line anytime soon (IIRC, Adobe's latest is a load),
I'll be a while taking a gander.
For now, though, I think that the right question to the above text is "Says who?"!
And I made this point previously:  on what basis is Rosendahl's Zeppelin bend
judged to be "strong" (typically interpreted relative to others) ?  Beyond this is
the point to being strong vis-a-vis the intended application(s), which I recall
including abseiling -- where strength is irrelevant in the usual cordage for it.

Quote
Page 44: The name "Slipped Double Overhand Knot" seems like it could be misleading.  The term slipped often means the final tuck of the knot is a bight, so as to facilitate a quick-release.  In the case of a double overhand knot, this could mean that the slipped portion was the working end rather than the standing part.  It's a minor point and probably unlikely to cause confusion in reality, but have you considered using "Double Overhand Noose" for the primary name instead?  (I see you do mention "noose" in the alternate names.)

I believe this comment gives sufficient illumination to the issue:  the name I push
for this is "Strangle (knot) Noose (-hitch)".  (Yeah, a rather variable/optional name.)
The Strangle knot can be found, w/o confusion, I think; "noose-hitch" is a name of
a structure (vs. knot) which naming lends itself to comprehension (of a
structure that employs the named knot tied to its S.Part to effect the attachment);
and "Dbl.Overhand" can have more range, if left as a more topological denotation
(where the Anchor Hitch and Strangle are Dbl.Overhands; I've seen the former form
used qua stopper in Com.Fish.Knotting, btw).  (Chances of "Clove hitch noose"
overtaking "Two Half-hitches" is pretty slim, huh.)

Quote
Thanks for posting this and all those other interesting documents on the public downloads page!

Yes, much!

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on September 25, 2009, 04:12:11 PM
Thanks for feedback dFred.

I have made amendments as recommended. VER 4.1 is uploaded to the site: www.paci.com.au (then click on 'public downloads').

Was unable to download 1914 ed of AA Burger book (Rope and its uses). Seems locked out to me here in Australia. Was able to obtain the 1917 ed was search through google but not by clicking on the link embedded in this forum. Would be keen to grab a hold of the 1914 edition...

Dan, I have changed the name to Double overhand noose (ABoK #409).

Also improved references to 'strength'. Made specific warning that stability and security are the most important features in life support knots.


Mark
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on September 26, 2009, 04:34:16 AM
Thanks, Agent_Smith.  Do keep in mind what the title of this thread is about
(as we look for further progress on that).

 ::)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: beau on January 31, 2011, 12:17:14 PM
*bump*
Any progress on these tests? There seems to be a lot of conflicting information on which bowline variant or which life support knot is the best.
Hardly any sites includes some real sources/test data. ie the yosemite finish is supposed to make the normal (claimed to be rather weak) bowline strong but I can't find any source.

Wouldn't the YF just lock the normal bowline? How does it make it stronger besides locking it?

The same goes for the double(-knotted) bowline. Is it actually proven to be stronger (and why?) or is it just harder to capsize?

Beau
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on February 01, 2011, 05:38:41 PM
Hi, Beau.  Agent_Smith has been silent & inactive for some time,
and I suppose that is answer enough to your question insofar as
his testing is concerned.

For may part, I have not yet sought testing of this particular focus,
but did include a sort of *Fig.8/false bowline* among 5 eyeknots I had
tested in 8mm(5/16") 12-strand urethane-coated HMPE (Dyneema
SK-75); it did not slip, but was unremarkable re strength (somewhere
in the range of results from 33-42% (37%) for the five, each test
specimen having the same knot on each end (so, one survivor).

As for the bowline with Yosemite finish (which exact finish one can
see differing between various references, as to which side of the
S.Part it lies --tighter vs. less tight final turn), I concur in your
questioning of how that could influence strength --though it is
an assertion made by Craig Connally, author of The Mountaineering
Handbook
, there and in posts to RC.com (www.rockclimbing.com).

Quote
The same goes for the double(-knotted) bowline. Is it actually proven to be stronger (and why?) or is it just harder to capsize?

By which name I assume you mean what is also named "Round turn" &
"Double" bowline --an extra (round) turn for the central nipping part,
same end-forms-bight finish.  Tests have shown this to be stronger, I
believe, and about the same strength --so, YMMV.  What you almost
NEVER see in test reports is a clear indication of the exact geometry
of the tested item : no, you have a name --e.g., "Fig.8 on a bight"--
and that can denote all sorts of dressings of some general knot.
Capsizing I don't think is much an issue with bowlines, though for
some reason, many in the mooring hawsers of trawlers within my
periodic inspection seem to have them(!?).  What the extra turn
in the Dbl.Bwl. does is provide a better grip (for security) and
the extra turn helps impede loosening, in that any slack feeding
into the knot had 2 vs. 1 loop to loosen --the slack is *amortized*
over twice the looping --so, some small benefit.

Quote
which bowline variant or which life support knot is the best

Define "best" --there's the rub.  Or, for that matter, how much better
one knot should be over others in order to gain such acclaim?  Often
there are trade-offs between !!!

E.g., the Fig.8 eyeknot is often promoted over the bowline because
--in part-- it is supposedly easier to inspect (for correct tying)
(even though precise geometries of this common knot are seldom
presented for instruction --anything is correct enuff!), but MUCH
of the problem with the bowline, IMO, is the way it is presented,
showing it from a side in which the crossing of the central
nipping loop is beneath the easily understood/perceived paths
of the legs of the end bight!  --geeesh, just flip that knot around!
But presentation after presentation show the bowline from the
wrong perspective, and ... people have difficulty understanding
the knot.  Then, with the result of a sort of corollary, non-practice
makes imperfect --self-fulfilling prophesy.  (Concerns about Bwl.
security are valid, but many solutions are available; but then it's
the "many" aspect that frustrates learning and common understanding.)

As for
Quote
... claimed to be rather weak [bowline, i.e.]

no, the bowline is not all so weak, maybe esp. in the cordage used
(perhaps esp. in dynamic rope).  But the figures do have a range,
enough again to make you want to know the unreported details
of knot geometry and so on.

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: agent_smith on February 10, 2011, 02:06:44 AM
Silent and inactive - I'm afraid Dan is correct.

Reasons: Work load too high, global financial crisis hit me, have been in hospital 3 times in 2010 with blood clots in my lungs, cost and time given to this project became too high...etc etc.

I am slowly getting back on track and will return with more test data soon.

Random comments:

[ ] I have developed what might be a new joining knot (ie bend) - but I haven't really looked too hard to check if it already exists or has already been discovered (eg by xarax or someone else) - if it is 'new', I'd like to put it through its paces...
[ ] I had some issues with violent recoil of my load cell during knot break tests - and I was concerned about risk of damage (it cost over $2000.00 AUD to buy).
[ ] I hate threading tracer cotton threads through the test specimen knots - its time consuming and damn tedious, not to mention eye strain for a 49 yr old! (but yes, Dan Lehman is correct that it is a cheap and effective marker system)
[ ] Quality photos of knots has always been an issue - but i solved that problem last year and figured out how to achieve good resolution images with neutral white background - check my 'knot study guide' out at my www.paci.com.au website (under public downloads) to see the image quality I am now achieving.
[ ] I agree with Dan Lehman in that most so-called 'knot testers' publish ambiguous or inaccurate results - or results that cannot be reproduced (after all, any scientist will want to be able reproduce another testers results in order to 'validate' or disprove it). I have taken all of his comments on board so that i do not make the same mistakes others before me have made. For example, I consider pure knot strength to be almost irrelevant - of greater importance is security and stability (my theory only). Tests must capture the elements of stability and security - rather than simple breaking loads
[ ] All my testing to date has been with 'thin' 5.0mm or 6.0mm diameter kernmantel construction synthetic cord (yes Dan, I spell it the German way since it is a German word). I have a feeling (not very scientific) that results obtained with larger diameter rope - eg 11.0mm - may be different. My theory is that larger rope diameters will produce larger radius bends/turns/wraps when compared to thinner diameter cords - which in turn should reduce compression/tension (ie outer radius stretching) of rope fibres. I would expect to see variations in results with knots that employ 3 rope diameters inside nipping loops/turns. Testing will either prove or disprove this theory.
[ ] I am self-funded - and sometimes money is tight.

Mark Gommers
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on February 10, 2011, 04:54:50 AM
[ ] I hate threading tracer cotton threads through the test specimen knots - its time consuming and damn tedious, not to mention eye strain for a 49 yr old! (but yes, Dan Lehman is correct that it is a cheap and effective marker system)
[ ] Quality photos of knots has always been an issue - but i solved that problem last year and figured out how to achieve good resolution images with neutral white background - check my 'knot study guide' out at my www.paci.com.au website (under public downloads) to see the image quality I am now achieving.

Firstly, very sorry to hear of your health problems; may they forever
be behind you.

As for threading, well, I got to taste my own medicine,
"to feel your pain" --had some knots tested and of course
wanted to know something more than numbers associated
with them.  I'm attaching a photo taken pre-testing.
AND you'll note that there are also --all eyeknots-- two
knots per specimen : one will break, the other will help
answer the question of Where & thus Why.
(8mm 12-strand Dyneema SK-75)

Good to hear from you, Mark!


 :)
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on February 18, 2011, 06:37:54 PM
Random comments:

[1 ] I have developed what might be a new joining knot (ie bend)
 - but I haven't really looked too hard to check if it already exists
...
[2 ] Quality photos of knots has always been an issue - but i solved that problem last year

Putting 1 & 2 together, I think that we should be seeing
an image of this potential *new* knot, then!  Where is it?

Quote
check my 'knot study guide' out at my
 www.paci.com.au website (under public downloads)

I tried --four times--, but each time, as the downloading small
indicator with a filling-up-left-to-right bar moves to near completion,
it POOPH abruptly stops and quits, almost finished.  I don't know if
my system is bumping into some 4mb (or less) cache-ing limit or
what; I'm just not seeing this file
Anybody else able to view this "knots" (Oct'10) PACI Dowload (top item)?

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: SS369 on February 18, 2011, 07:18:12 PM
Hello Dan,

I am able to view the pdf file.
I could save it and email it to you if you wish.
It is only 4.16MB

SS
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Sweeney on February 18, 2011, 07:32:28 PM
The pdf on this web page may be of interest. http://www.hse.gov.uk/research/crr_htm/2001/crr01364.htm (http://www.hse.gov.uk/research/crr_htm/2001/crr01364.htm). The HSE is the Health and Safety Executive in the UK (a government body who enforce health & safety legislation but who also sponsor research). The paper was done in 2001 but has some data about knot testing which may be of interest.

Barry
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on February 19, 2011, 06:11:38 AM
I am able to view the pdf file.
I could save it and email it to you if you wish.
It is only 4.16MB

SS

Thanks, I might have to try that.

Agent_Smith, I see that bloody "password" now, but nothing
in my course of trying to download the file asked for any
password.  I do seem to have landed a file but Preview cannot
read it, and ... .  Got the Bowlines one w/o trouble.  Is the
Knots one a different PDF version?


 ???
Title: Re: Knot testing - Life support knots - procedures and results
Post by: SS369 on February 19, 2011, 02:22:43 PM
Hello Dan,

the password for the 01 knots pdf file is            thank you.
The file is safe by very updated virus scan.

I suspect since it is password protected, your preview pane will just show the Acrobat icon.
Let me know if I can help.

SS
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Dan_Lehman on February 20, 2011, 02:57:56 AM
I saw the password ; but I never have a point in which to USE it
(tried tacking '?=password=thankyou' onto the URLink --it made
no difference (which itself is interesting!)).

I've heard from another that this seems to be an issue of different
versions of Adobe PDF --this requiring 8.0 maybe, as it reportedly
doesn't work on 6.0.  (I have viewed the file in the library, btw.)
(And that upgrading Adobe requires updating an OS --PITA just for
incompatible PDF  >:(   (this for a windows user; I don't know that
from Apple's Leopard it's not possible)

--dl*
====
Title: Re: Knot testing - Life support knots - procedures and results
Post by: SS369 on February 20, 2011, 03:05:13 AM
For me, all I had to do was double click the file, a small password requesting window opens,  typed in the password and voila.

I don't know what version of Acrobat you're using, but I would update it soon. The newer versions of the reader plug up some of the vulnerabilities that nogoodnicks can exploit.

If you need this literature, we can think of some way to get it to you.

SS
Title: Re: Knot testing - Life support knots - procedures and results
Post by: Bob Thrun on February 22, 2011, 05:07:38 AM
For me, all I had to do was double click the file, a small password requesting window opens,  typed in the password and voila.

I don't know what version of Acrobat you're using, but I would update it soon. The newer versions of the reader plug up some of the vulnerabilities that nogoodnicks can exploit.
The vulnerabilities are of concern mainly for PDFs of unknown origin that may be malicious.  Acrobat can make password-protected PDFs that are compatible with earlier versions of the Reader.  I note that none of the other PDFs on the PACI site are password protected.