Two pairs of pet TIB twin eyeknots

[X1]

   When I had presented those two crossing knot + overhand knot post-eye-tiable eyeknots (1)(2) { the OH knot used as a hitch, in the sense of ABoK#1821 }, I had deliberately ignored some "similar" knots I had also tied at the same time, where the rim of the overhand knot is wrapped around both eye legs (3). I thought that this rim/collar/bight, trying to keep those legs crossed, would suffer during ring loading,  it would be forced to widen, and/or it would remain loose - so I decided that the eye legs should better leave the knot s nub from different exit points. If we relax this condition, we enter into a broader class of bowline-like loops, where the overhand knot is now tied around the "base" of both eye legs - while it still remains entangled within the crossing knot in the same secure way ( a way that forces its tail to pass through, and be squeezed in, the most constricting area of the knot snub, in between the standing part s and the returning eye leg s first curves ). These eyeknots are also simple, very stable and very secure knots - although, for unknown to me reasons, they have not yet received the attention they deserve by the knot tyers.
   Some days ago, Alan Lee has shown one of those knots (4), so I grasped the opportunity to study them again, more carefully. Surprize !  I had discovered that at least two pairs of very "similar" such crossing knot + overhand knot loops, happen to be TIB eyeknots - a fact I believe sheds some new light on them. Being so simple, most or even all of them would have been tied at the past, I guess, but I doubt that they were ever considered or presented as a group, as in this thread. The interested reader would find out how one can go from the one to the other reversing the clock-wise or counter-clockwise direction of the returning eye leg s turn/collar/bight around the "base", and/or the side by which the tail enters into the knot s nub.

1. http://igkt.net/sm/index.php?topic=3944.msg23427#msg23427
2. http://igkt.net/sm/index.php?topic=3944.msg23429#msg23429
3. http://igkt.net/sm/index.php?topic=4095.msg24592#msg24592
4. http://igkt.net/sm/index.php?topic=4125.msg27230#msg27230

[X1]

  Same pictures, inversed colours ( white background).

[X1]

   For an easy comparison, here are two other Crossing knot + Overhand knot post-eye-tiable knots (PET), which are not tiable-in-the-bight (TIB).
   ( The lower (L), and the higher (H) knots at the "front" view, have been flipped at the "back" view ).

[X1]

   A way of tying the A pet Twin, as a TIB loop. Form three bights. Reeve the third one through the first one, half-way ( first picture). Then, reeve the second one through the third one all the way ( second picture ).

[X1]

   I tried the pet TIB (A) eyeknot against its main TIB rival : the Angler s loop. In the 6 mm cord shown at the attached pictures, under cyclic loading ( = jumping with by full body weight... ), I was able to make the Angler s loop jam, but not the pet TIB eyeknot. In fact, while the nub of the former was made very compact and rock solid, I was always able to untie the later quite easily, by manipulating=twisting its "lower" collar ( the collar around the eye legs ), which remained much softer. The corresponding collar around the eye legs of the Angler s loop did not yield to this or any other untying technique I hade tried. The reason in simple : the collar around the eye legs of the Angler s loop is directly connected with the most tensioned segment of the standing part, while the corresponding collar of the pet TIB loop is not. I believe that this is a general characteristic of most, if not all the crossing knot eyeknots - the nipping structure of those knots is not so powerful as the single simple nipping loop of the common bowline, but it is much more stable and it can be secured against the main danger the bowlines face under heavy loading, the 'opening" and the subsequent degeneration into an helix of their nipping structure, much easier. It is a pity that knot tyers have not yet noticed the stability and safety a carefully designed crossing knot based pet eyeknot can offer.
    To the interested reader, I recommend to tie this very easily tiable loop - either in-the-bight or in-the-end - and comment about it here. In my previous post, I have shown what I believe is one very simple TIB tying method , but I do not doubt that there might be others, equally or even more easy to remember and to follow.

[SS369]

Thank you X1.

One thing I notice and causes me to suspect something, is the movement of the nipping loop around the entry stem as strain is increased. What I suspect is that this area of movement will be the location of breakage due to friction heat along with compression of that small place of contact.

The subject of untie-ability is a tough one unless we set a standard(s) of force/load versus diameter/material elasticity. Force retention of soft cordage is a game changer sometimes.

SS

[X1]

Thank you SS369,

   The subject of untie-ability is a tough one unless we set a standard(s) of force/load versus diameter/material elasticity.

   I have suggested that we use ONE measure only, that of the untie-ability or not under 50% of the rope s ultimate strength.
   My point in the previous post was that this pet TIB eyeknot does not jam, after the same amount and number the (cyclic) loading where the Angler s loop does. However, I have not confirmed this at the 50% of the rope s strength - which I do not know if it is above or below the loading I have applied.   

   

compression of that small place of contact.

   Notice that the tail is located in between the standing part s and the eye leg s first curves, as a "bumper" that dissipates the load across a greater area there. Due to the fact that those two curves embrace each other, around the pivot-like tail, their contact area is not small. Now, the contact area between the standing end and the rim of the crossing knot does not matter much, because those two segments are not squeezed upon each other - under heavy loading, they barely touch each other. The "heart" of the loading, which will generate the heat, is located around the penetrating-the-two-curves tail.
   Would you, please, try it with the famous HPPE ropes of yours ?  I guess that, with those slippery ropes, you should better pull the tail with some force before loading, so the knot s nub will have as a compact form as possible right from the start. 
   Did you follow the TIB method I have shown, with the three interlocked bights ?

[SS369]

Hi X1.

I have just tied the PET TIB (A) using the Titan 5.5mm cord with the three interlocked bight method (Very easy!).
It ties up nicely and with a 200 lbs. approximate load I was able to flex it loose and untie. Not the 50% for sure.

I still suspect the area of the incoming rub to be the weak point. As the load through the nipping collar increases, the friction on the stem will get severe. Even with the knot SStightened it has some movement that I feel will continue to destruction as the 50% plus is exceeded.

BTW, it seems to be a winner as a mid-span loop too.

SS

[X1]

   Not the 50%, for sure.

   Dan Lehman has pointed out that the 50% is too much, for knots tied on HDPE - their ultimate strengths can not reach such percentages. So I guess that, regarding knots tied on those very strong materials, we should be satisfied with an untie-ability of even a "mere" 1/3 = 33.3%.

   I still suspect the area of the incoming rub to be the weak point. As the load through the nipping collar increases, the friction on the stem will get severe.

  I misunderstood you, I thought you were talking about pressure, not friction. Regarding friction, you may be right. The standing part is almost tangent to the rim/stem of the crossing-knot-made nipping structure, so the surfaces of the two segments at their small contact area may suffer, indeed.

[SS369]

I think that area will indeed have and be a high pressure location as well. Compression at the stem to collar contact will be great, as in many other eye knots.

Yes, according to manufacturers information, HDPE does not like bends in the fibers. Stronger than steel when straight or gently curved.

SS

[X1]

HDPE does not like bends in the fibers. Stronger than steel when straight or gently curved.

  Why ? I do not understand this...The Dyneema/Spectra fibre itself is not inflexible, is it ? Perhaps this is due to the patterns used to weave those fibres together - 8 or 12 braids, that can not be tensioned evenly when they have been bent ?
  As mentioned in (1), ancient writes describe ropes in great detail, but, when it comes to knots, they are notoriously silent. It seems that, with modern writers, what is happening is the exact opposite ! One can see this tendency in this Forum, too. Too much talking about knots, and almost nothing about the things on which knots are tied, and which enable the existence of knots in the first place, the ropes. It would be great if the members of this Forum who happen to know more about ropes than the average knot tyer, share their knowledge with us - perhaps a Section named " Ropes : properties, materials and structures ", something like this, would trigger some response ?

1. http://nautarch.tamu.edu/pdf-files/Charlton-MA1996.pdf   

[SS369]

HDPE does not like bends in the fibers. Stronger than steel when straight or gently curved.

  Why ? I do not understand this...The Dyneema/Spectra fibre itself is not inflexible, is it ? Perhaps this is due to the patterns used to weave those fibres together - 8 or 12 braids, that can not be tensioned evenly when they have been bent ?

I think that this statement > "low elasticity translates to low toughness." sums part of it up to me. Read the article at http://en.wikipedia.org/wiki/Dyneema and ponder about the long chain molecules.

SS

[X1]

"low elasticity translates to low toughness."

   I hope you will elaborate on this a little more in your book !    I do not understand how flexibility is related to elasticity, and also how elasticity is related to ultimate strength... Nylon is much more elastic than polyethylene, yet it is not much stronger. Also, I think that if a material is not flexible ( and so it can not be bent ), it breaks - like ceramics do. Certainly HDPE fibres do not break when bent, they just lose a considerable portion of their maximum tensile strength - but right afterwards, when they are straightened again, they return to their previous state regarding this strength, is nt it that so ? Anyway, I reckon that if my knowledge about knots has reached 1 ( out of 10...), my knowledge about ropes is still around 0.01...

[SS369]

Give this a read. http://stuff.mit.edu/afs/athena.mit.edu/course/3/3.064/www/slides/Advanced_Fibers_MRS.pdf
On the first page - Mechanical properties of Fibers.

SS

[X1]

   Thanks. Go on ! 

The extension of the chain is determined by the stiff covalent bonds, while the shear deformation is governed by the much weaker interchain bonds.Thus, the shear failure of the interchain bonds, not the fracture of the covalent bonds in the chain, is the limiting factor for the strength of these fibers
However, because of the rather weak chain-to-chain attractional van der Waals forces, polyethylene fibers undergo creep and display poor compressive load-bearing behavior. These issues, combined with the poor adhesion of polyethylene, make these high-strength fibers unsuitable as reinforcing fibers. These fibers perform well only for short durations or for impact loading.
...the bonding between the chains in polymer fibers is established by van der Waals and hydrogen bonds. These bonds show elastic behavior up to the yield strain in the tensile curve of the fiber. For larger strains, some loosening or yielding of the interchain bonding occurs, resulting in the nonelastic (plastic) behavior of the fiber. This "softening" of interchain bonding allows stress relaxation by some local movement of the chains around flaws and impurities without severely deteriorating the creep behavior of the fibers. After unloading of the fiber before breakage, all interchain bonds are restored to their original strength.