Author Topic: Boil In Oil (BIO)  (Read 2456 times)

X1

  • Inactive
  • Sr. Member
  • *
  • Posts: 1200
Boil In Oil (BIO)
« on: January 29, 2013, 11:32:27 PM »
   When one s theory is confronted with experimental results that do not quite fit smoothly into it ( to call the total dissonance as mildly as possible ), he has to choose whom he should follow : the dinosaurs (and their descendants, the birds), and bury his head in the sand - or the mammals, and try to create a new theory. I have used to imagine a more or less simplistic, "mechanistic" model of the strength of the knots, where invisible pre-existing mini-cracks looming into the bulk of the material, enlarge, propagate and emerge near the regions of maximal tension, and, finally, cause the catastrophic rupture.
   However, in this model, friction and the generated by friction temperature, are curiously absent - they do not play any role at all. If the rupture of the rope is due to the deterioration of the mechanical strength of the fibres by the local high temperatures generated by friction - which temperatures, in their turn, are causing the breaking of the molecular bonds -, the "mechanistic" theory of knots strength should be reconsidered ( to call the trajectory towards the wastebasket as mildly as possible, again... :)).
   In this theory, the fibres that are elongated more, i.e., the "outsiders" of the rope s path inside the knot s nub, are the only ones that are maximally loaded during the last stage of the loading. That would suggest that we should try to make the curvilinear paths they follow smoother, that is, try to make the standing part follow wider curves. So, more fibres would be offered the chance to be maximally elongated, and to be able to absorb the total loading, and so the knot s strength could be elevated.
   I have tried to figure out some bends with a geometric shape that would allow wider than average first curves of the standing part - in an effort to offer to the fibres that would be maximally loaded at the moment of rupture, the chance to absorb and dissipate the tensile forces along a more extended area. (1)(2)(3)(4)
   Is this the optimum strategy we should follow to elevate the strength of a knot ? I am not sure about it - in fact, I am even more sceptical about it than I was before the publication of J.P. results.
   It had even crossed my mind this crazy idea : to somehow insert some quantity of a lubricating substance ( oil, for example ) in between the fibres of the rope ( at least just before and along the standing part s first curve ), so the magnitude of the friction forces would be lowered there, and the temperature that would be generated and could lead to a local catastrophic melt down, would be dissipated more easily towards a longer segment.
   That was the meaning of the title of this thread - but I had to reveal only at the end of the post, in a hope that somebody would be forced, by sheer curiosity, to read it!  :)

1.  http://igkt.net/sm/index.php?topic=3148.msg18833
2.  http://igkt.net/sm/index.php?topic=2154.msg15144#msg15144
3.  http://igkt.net/sm/index.php?topic=2154.msg16808#msg16808
4.  The A4 bend, at : http://igkt.net/sm/index.php?topic=3611.msg20614#msg20614
« Last Edit: January 29, 2013, 11:47:53 PM by X1 »

X1

  • Inactive
  • Sr. Member
  • *
  • Posts: 1200
Re: Boil In Oil (BIO)
« Reply #1 on: January 30, 2013, 06:07:57 AM »
   So, what would be the ( conjectured ) benefit of the suggested oiled, most slippery individual threads and strands of a rope, free to slip along each other at the region just before and on the standing end s firs curve ?
   1. Those bundles of individual fibres would function much like small diameter individual ropes, running parallel to each other. J.P. s result have shown some very high strengths for knots tied on small diameter ropes - so the added strength of those many smaller diameter ropes working in parallel to each other could possibly be greater than the strength of one larger diameter rope (of the same cross sectional area ).
   2. Time and again it has been reported that, in a knot, the rope breaks just before or alongside the standing part s first curve. If the rupture of the rope is turned out to be caused by the deterioration of the mechanical strength of the material, due to the high temperature, which, by its turn, is generated by friction, we can suppose that a lower and able to be dissipated across a longer segment temperature, would transfer the "dangerous" zone somewhere after the first curve. So, the load would be confronted by more regions of the knot s nub, and not only by the first curve.
   Actually, this "theory" can be falsified very easily. One can insert some quantity of a lubricant fluid in between the threads and the strands of a thick rope, at the region of the standing part s first curve - inside its mantle, by a syringe or something. The point of rupture, will it remain at the usual area, or it will be transferred along the rope, after the first curve ? The strength of this "oiled" knot, will it remain the same, or not ?
   J.P. has a lot of work to do... :)
« Last Edit: January 30, 2013, 06:10:08 AM by X1 »

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1788
Re: Boil In Oil (BIO)
« Reply #2 on: January 30, 2013, 02:52:19 PM »
Having talked briefly with a man who owns a local (to me) rope manufacturing company and is the person who designs new configurations, I remember his talking about climbing rope fibers lubricity, how it has to be a balance. He mentioned that the core and sheath need to have a certain amount of friction to work with each other in regards to having a correct amount of elongation performance.

We got into a conversation about Spectra/Dyneema as well and ultimately why he had chosen to sew connections instead of using knots.

Other manufacturers seem to agree with this assessment and decision. http://www.sterlingrope.com/media/document/techmanual.pdf

The modern fibers show in literature, to have low friction coefficients and it makes me think that the addition of a lubricant would potential cause detrimental side effects.
ftp://compsweb.marine.usf.edu/pub/misc/jdorton/papers/090612-038.pdf

I agree that the first curve severity is the main detriment and the radius being increased is the first line of defense towards rope survival, or keeping the rope as straight as possible throughout.

S

X1

  • Inactive
  • Sr. Member
  • *
  • Posts: 1200
Re: Boil In Oil (BIO)
« Reply #3 on: January 30, 2013, 03:08:27 PM »
   Imagine that you are a single, individual thread of the rope, and the other threads around you with which you are in contact form the slippery sides of a narrow "canal", that follows the rope s path inside the knot s nub. If you are pulled by your one end, there is nothing to interrupt the flow of the tensile forces along your body, towards the other end. In a way, the slippery surfaces of the other threads play the role of many free-rotating pulleys, so you are a rope running inside a complicated simple machine, but a simple machine nevertheless. There is no reduction of the strength of a rope running within the pulleys of a block and tackle simple machine. Of course, the real word is not like this, and there would be a minimum friction along the sides of this canal - but even then, the friction will be dissipated across the curvilinear sides of each of the many left and right turns, not only across the sides of the first turn. Transfer some of the friction, and the generated temperature, towards the next to the first curve, that is the pottential benefit the freely-sliding-along-the-first-curve threads could actualize. So, no more wide first curve, but a slippery first curve, with less friction/lower temperature than elsewhere.
« Last Edit: January 30, 2013, 03:20:00 PM by X1 »

X1

  • Inactive
  • Sr. Member
  • *
  • Posts: 1200
Re: Boil In Oil (BIO)
« Reply #4 on: January 30, 2013, 03:17:35 PM »
it makes me think that the addition of a lubricant would potential cause detrimental side effects.

May be...but we should TEST this theory to be able to falsify it, do nt we ?  :)  And I beliieve this would be an easy thing to accomplish.

the core and sheath need to have a certain amount of friction to work with each other

  We are talking about the friction between the individual yarns, threads and strands, not between these and the envelope / mantle. I guess there is often some protective coating around those bundles of fibers, so they do not get wet easily. We should find a rope without this, so we will be able to insert a certain amount of lubricant in between the individual yarns, across the first curve - and see what happens !  :)
« Last Edit: January 30, 2013, 03:18:32 PM by X1 »