Author Topic: FYI test results for misc. Fig.8 EyeKnots (4x2)  (Read 4075 times)

Dan_Lehman

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FYI test results for misc. Fig.8 EyeKnots (4x2)
« on: August 01, 2020, 04:36:15 PM »
www.blackdiamondequipment.com/en_US/experience-story?cid=qc-lab-can-i-use-a-sharpie-to-mark-the-middle-of-my-rope

Just a blip in the radar in testing.  It's not possible for me
to surely discern what state of dressing/setting the various
Fig.8 EKs were in, though the survivors do (or 3/4 do) show
a telltale untensioned eye collar that suggests *interior*
loading (but, then, of what sort of imperfectly dressed knot?).

Of the pre-test layout, L & R I see:

Interior dive of exterior approach   vs. same
 [ "  meaning that the twin that WOULD've taken the
   exterior path judged by its entry has tucked down
   into interior position at the U-turn ]

perfect form exterior loaded   vs   <ditto of above>

<again>   vs  similar re loaded strand, but the eye bight swings out of perfect form

<same but eye bight ... IMperfect finish>  vs. <like above, exterior at critical point>

Now, I hesitate to match pre- & post-tested knots --i.e., that the
layout is intended to match (though noting that it does seem deliberately done).

!?

Ah, in all cases the rope "broke at the bottom knot",
and in another posting by the Black Diamond site I see
that the (same, presumably, by looks) test device
MOVES THE UPPER UPWARDS,
so the breaks reported came at the stationary end.

And in a test of 20yr-old UNUSED climbing rope,
which performed "as though made yesterday" in
tensile (Fig.8 EK) & drop testing (impact forces),
one has a good look at the two Fig.8 eye knots:
the broken one (again at bottom) is in my "perfect
form", *exterior* loaded,
and the upper, surviving knot is imperfectly formed
with the loaded strand swinging out wide around
its twin --which gives it the larger diameter at the
critical u-turn bend.  IMO, consistent with one
theory of knots weakening.
This imagery is a couple scrolls down, on this page:
www.blackdiamondequipment.com/en_US/experience-story?cid=qc-lab-old-vs-new-gear-testing

TO EMPHASIZE, IMO were the lower knot in the
"perfect form, exterior loaded" FIRST SET BY
hauling hard ON THE TAIL,
then the loaded strand would not so readily crush
inwards to its hard, 2-diameter (and really more
like ONE dia. with other just *behind* this) bend.
Note the difference as seen in the center image with
loaded knots with the upper knot where the loaded
strand in swinging wide encompasses another diameter.


--dl*
====
« Last Edit: August 01, 2020, 04:54:16 PM by Dan_Lehman »

agent_smith

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Re: FYI test results for misc. Fig.8 EyeKnots (4x2)
« Reply #1 on: November 17, 2020, 03:21:38 AM »
With regard to the link to the Black diamond test report:
The underlying intent of the testing was to determine the effect of a permanent marker pen (eg 'Sharpie pen') on a synthetic human rated climbing rope (EN892).
In my view, knot geometry was secondary in the testers mind - so not much attention was paid to precisely how each knot was tied (the F8 knots are there simply to provide a convenient attachment point).
The test articles did not point to any measurable effect caused by a permanent marker pen.

Criticisms of the Black Diamond testing:
1. The test sample size was relatively small - and there has been no peer reviewed follow up testing by other testers to confirm or refute the results.
2. It was not reported as to the duration that test articles were exposed to the sharpie marker pen.. eg was it 5 minutes? Was it 1 hour? Were ropes marked and then left for 24 hours or longer (eg a week)? Who knows?
3. No MSDS (or just 'SDS') info on the formulation of the sharpie pen was provided! In other words, we have absolutely no idea what the chemical constituents were in the 'sharpie' pen.
They could have at least done a litmus paper pH test - litmus paper would at least provide some clue on the pH of the sharpie pen. (A PH of 7 is neutral.. a pH less than 7 is acidic). The pH scale runs from 0-14. Note: It is well understood that acids have an immediate destructive affect on human rated synthetic ropes (eg EN892 rope).

Given the cheap cost and easily obtainable status of litmus paper - I am somewhat astounded that Black diamond did not check the pH of the 'sharpie' pen. You can even purchase digital pH test devices for less than $30 USD.

...

With regard to the reported positions where the knots yielded to load - the tester simply stated
Quote
As expected, the ropes always broke at the knot
The test configuration was a mirror (dual) test article - ie, same knot tied at each end of the rope.
It was reported that the test article that failed was the "bottom knot".

What does "bottom knot: actually mean?
We can only take a guess because (as is usual with these types of tests) - specificity is lacking.

Lets say we speculate and 'assume' the break occurred at the knot fixed to the stationary pin.
In most tensile testing machines, there will be a stationary (fixed) end and a moving end where the force generating machine is located.

I have noted before that it is rare for a tester to declare which knot and at which end broke first.
I have also pointed out that no one appears to have carried out extensive testing to look into this issue - ie which knot yields first - or is it random - or is it indeed affected by the test configuration where one end is fixed and the other end is 'moving'.

NOTE:
Those of you who now wish to interject and shout loudly that reference frames and Newtons laws point to both ends actually moving from the perspective of the knot specimen (even though one end of the test rig is fixed) can take a nice slow calming breath.
Yes - from one point of view within a moving reference frame - both pins on the test machine are 'moving'.
Please remain seated and remain calm :)

Please read very carefully before replying to this post:
All I am suggesting is that someone needs to conduct peer reviewed lab testing to rule out any test rig bias.
What if there is indeed a measurable bias caused by having a test rig that employs a fixed pin on one side and a moving pin on the opposite side?
Right now, I am confident enough to state that we are not 100% certain that such a test rig induced bias.
And further food for thought...
Could any experimental bias be introduced due to the spacial orientation of the test rig?
That is, a vertically oriented test rig versus a horizontally oriented test rig? Could gravity cause some slight bias in a test rig that is vertically oriented?

...

As to the precise geometry of the hand tied test knots - this is another matter.
Upon closer analysis of a blown up image (which pixelates) it does appear that there is variation in the way the F8 knots are tied.
#1047 F8 can be tied in different geometries - predominantly in where the SPart is positioned.
In my view, the orientation/position of the SPart segment has no statistically significant impact on MBS yield.
However, it does affect the jamming threshold.
That is, the position/orientation of the SPart segment plays a role in how the knot responds to load - and one way yields greater resistance to jamming.
I therefore respectfully disagree with Dan Lehman that the position/orientation of the SPart segment should be described as (quote) "strong Vs weak form" (unquote).
Rather, it is best described as; "jam resistant Vs vulnerable to jamming".

The j#1047 F8 is more vulnerable to jamming when the SPart segment lies 'on top of' adjacent segments so it is located closest to the fixed eye of the knot.

« Last Edit: November 17, 2020, 03:29:54 AM by agent_smith »

Dan_Lehman

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Re: FYI test results for misc. Fig.8 EyeKnots (4x2)
« Reply #2 on: December 03, 2020, 01:55:08 AM »
As to the precise geometry of the hand tied test knots - this is another matter.
Upon closer analysis of a blown up image (which pixelates) it does appear that there is variation in the way the F8 knots are tied.
#1047 F8 can be tied in different geometries - predominantly in where the SPart is positioned.
In my view, the orientation/position of the SPart segment has no statistically significant impact on MBS yield.
What basis do you have for this assertion?
Surely, knot geometry exactly determines behavior.
Now, it might be the case that for some knots there
are like results for different geometries, but this needs
to be (first, recognized!) tested.  (There is recent testing
that shows my "weak form" to be better on both strength
AND untying/less-jamming.  But that is sans my setting!)
And do keep in mind my insistence on hard setting
so to give a more solid *nub* for the exterior strand
to be deflected around!  --a test case of the significance
of this maybe would pit elastic/deformable cordage vs.
less-so cordage, to see if the former partly defeated
the curvature effort in its deformation,
while the latter reaped its benefits!?

Quote
I therefore respectfully disagree with Dan Lehman that the position/orientation of the SPart segment should be described as (quote) "strong Vs weak form" (unquote).
Rather, it is best described as; "jam resistant Vs vulnerable to jamming".
I have ceased (much) using those terms,
precisely for want of solid grounds, among
other reasons; I now use, respectively,
"exterior"/"interior" loading --where these refer
to the proximity to the knot center.  (Note that
there are geometries not so simply discribed,
but these two cases apply to the "perfect form".)


--dl*
====

agent_smith

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Re: FYI test results for misc. Fig.8 EyeKnots (4x2)
« Reply #3 on: December 03, 2020, 01:48:20 PM »
per Dan Lehman:
Quote
What basis do you have for this assertion?
?
Which part?
If you are referring to the test article hand tied knots - have a closer look at the images in the Black Diamond website.
Although image quality isn't exactly perfect - it is good enough to see variation.

I assert again that perfect knot geometry likely wasn't foremost on the testers mind.
The issue that was of primary concern was the use of permanent marker ink on a synthetic human rated rope.
In other words -the tester was focused on examining the effects of a permanent marker pen (ie 'sharpie' pen).

The tester was directing his mind to the effects of a sharpie pen.
His mind was not specifically directed to achieving absolute geometric precision with his hand tied knots.

I also assert to you that it is remarkable that the tester didn't bother to check the pH of the sharpie pen formulation.
The cost of litmus paper is negligible.

Dan_Lehman

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Re: FYI test results for misc. Fig.8 EyeKnots (4x2)
« Reply #4 on: May 11, 2021, 08:10:07 PM »
per Dan Lehman:
Quote
What basis do you have for this assertion?
?
Which part?
THIS part ::
> In my view, the orientation/position of the SPart segment
> has no statistically significant impact on MBS yield.



At THIS time (May'21), one can point to the detailed/repetitive
testing done by those Czech (is it?) folks, in which they
found that the INterior ("O" loading per them) form
was stronger --though we can question how hard the
knot was set so to give advantage to the SPart, in
either form.  (Ditto, btw, for the overhand.)

--dl*
====
« Last Edit: May 11, 2021, 08:10:57 PM by Dan_Lehman »