Author Topic: Knot testing - Life support knots - procedures and results  (Read 38484 times)

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #15 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*
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agent_smith

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Re: Knot testing - Life support knots - procedures and results
« Reply #16 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!
« Last Edit: January 10, 2009, 10:33:32 AM by agent_smith »

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #17 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*
====

DerekSmith

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Re: Knot testing - Life support knots - procedures and results
« Reply #18 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

agent_smith

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Re: Knot testing - Life support knots - procedures and results
« Reply #19 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!
« Last Edit: January 12, 2009, 07:57:49 AM by agent_smith »

DerekSmith

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Re: Knot testing - Life support knots - procedures and results
« Reply #20 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

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #21 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!

 :)

agent_smith

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Re: Knot testing - Life support knots - procedures and results
« Reply #22 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

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #23 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*
====

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #24 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*
====

alpineer

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Re: Knot testing - Life support knots - procedures and results
« Reply #25 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.
« Last Edit: December 08, 2012, 05:53:08 PM by alpineer »

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #26 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!

 :)

agent_smith

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Re: Knot testing - Life support knots - procedures and results
« Reply #27 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
« Last Edit: January 26, 2009, 02:57:17 PM by agent_smith »

Dan_Lehman

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Re: Knot testing - Life support knots - procedures and results
« Reply #28 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!

 ;)

agent_smith

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Re: Knot testing - Life support knots - procedures and results
« Reply #29 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
« Last Edit: January 26, 2009, 10:18:31 AM by agent_smith »