Author Topic: Knot Strength  (Read 16267 times)

SS369

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Re: Knot Strength
« Reply #15 on: October 08, 2011, 11:43:07 PM »
I am thinking even less costly than accessory cord and weaker by far.
A more generic cord to most people is what they can purchase at the hardware/supply type stores. Lowe's, Home Depot and the like.
Something that everyone who wants to do, or even repeat, the testing can find and not hock the arm to buy it.

A simple diamond braid like Wellington/Lehigh of nylon & polyester. And some twisted cord of similar size and breakage rating. My thinking is that these microcosm sizes could reflect the characteristics enough of their respective big brothers and sisters to show the viability of what the tested knot is trying to do.

I believe that we want to be able to break this material easy enough and the working load of 40 lbs. makes this achievable.

It would be a collective start on something that as it grew, if it does, will combine all the input of many minds. Sort of "cloud knot testing".

Input on the test apparatus/procedures?

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xarax

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Re: Knot Strength
« Reply #16 on: October 09, 2011, 01:35:27 AM »
   What does this "I" in the title of IGKT stands for ? Will IGKT Forum adopt the International System of Units, or we will have to wait, in the good company of Burma and Liberia, another two millennia or so for this miracle to happen ?  :)
   http://en.wikipedia.org/wiki/International_System_of_Units
 
   I suggest the use of a cord that breaks at 500-1000 N , the weight of an average man. So, we can easily perform a destructive test of a knot, by stepping/jambing on a vertically hung loop, at the end of our knotted line. The price difference would be negligible, and we will be able to inspect the local deformations of the cord - and spear the cost of a magnifying glass.  :)
   I suppose that we are talking about a "knots war" comparative / simultaneous test of two (or more) knots here, because we do not have the means to measure absolute loads accurately (?)

   
This is not a knot.

SS369

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Re: Knot Strength
« Reply #17 on: October 09, 2011, 02:58:12 AM »
This all well and good, though the places I purchase rope or cord don't indicate the specs in SI.
We could provide a conversion chart and then all be on the same page, so to speak.

As long as we know the break strength of the test piece, be it of international units or whatever, we will have a standard at least to go with.

I am not suggesting the use of apparatus that will be devoid of safety and am not recommending jumping/stepping or the like. Perhaps a simple device such as a lever of sufficient length to provide the necessary forces and distance from the subjects. Using a zoom lens, if you want "action" photos, it can be documented as such.
I am interested in getting some basic understanding of the failure(s) and successes of the specimen choices that we all can agree with. A collective test. It will take into consideration the minor possible discrepancies of the various testers, e.g., dressing and how tight, rate of force applied, and a few other influences.

Any ideas on the test machine(s)?

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xarax

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Re: Knot Strength
« Reply #18 on: October 09, 2011, 04:37:48 AM »
  I am not suggesting the use of apparatus that will be devoid of safety and am not recommending jumping/stepping or the like.

  I do not believe that there will be any safety problem, with 3 mm cords, and a height of the loop - rung of, say, 0.20 meters from the ground...A mechanical apparatus, using levels, would probably be more dangerous, not less...If we do not need to actually measure  the exact amount of the force, but only to load the line as much as needed, to whatever point the weakest knot breaks first ( the weakest knot in a series of two or more knots, tied on the same line), then a simple arrangement of tensioned cords, using body s weight, or some compound - or block and tackle - pulley configuration, would be sufficient, I believe.
This is not a knot.

SS369

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Re: Knot Strength
« Reply #19 on: October 09, 2011, 02:52:19 PM »
Not so much the lack of safety from dropping to your doom, but the break when it happens can be a fairly hurtful whip.

I personally would rather test a single knot each time, for the purpose than a series. Unless that is a decided (by the collective) test criteria.
Isolated, the test knot will show exactly what its performance is.
If we want we can have a the tug-of-war type "knot wars" tests as well to see what beats what.

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knot4u

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Re: Knot Strength
« Reply #20 on: October 09, 2011, 04:58:29 PM »
The test machine doesn't have to be an invention, right?  There must be plenty of literature for making a test machine.  If not, here's a setup that's doable with materials from a hardware store:

The major obstacles are the connections on each side of the rope.  The knots or connections holding the rope must be stronger than the knot(s) being tested.  Try securing each end of the rope with relatively large Round Turns.  Use large strong pipes or whatever.  On one end, construct a Windlass for turning the Round Turns and, thereby, loading the rope until the tested knot(s) break.  If a hitch is being tested, tie the hitch on the anchor that doesn't have the Windlass.

The next obstacle is measuring the precise force on the knot.  Instead, if you just want to get started with some results without too much effort, you can just do a tug-of-war with two or more knots and see which knot breaks first.
« Last Edit: October 09, 2011, 05:54:57 PM by knot4u »

xarax

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Re: Knot Strength
« Reply #21 on: October 09, 2011, 05:20:17 PM »
Use large strong pipes or whatever. 

  I have thought of Coke Zero cans filled with cement  :) , and two round turns and two half hitches on each of them. For 3-5mm cord, the diameter of those drums would be more than adequate.

If you just want to get started with some results without too much effort, you can just do a tug-of-war with two or more knots and see which knot breaks first.

   I think that this is much simpler, and might even be much more interesting, too. Place-your-bets !
« Last Edit: October 09, 2011, 05:25:21 PM by xarax »
This is not a knot.

xarax

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Re: Knot Strength
« Reply #22 on: October 09, 2011, 09:56:06 PM »
   A simple knot testing apparatus, and six simple instructions :

1. Wear protective glasses.
2. Use your old bicycle, not the brand new one.
3. Choose the biggest gear .
4. With the knotted cord, make some turns around the axle of the pedal, ( at the bottom bracket ) with the one end, and around any of the other three vertices of the diamond-shape frame ( the head tube, the top tube near the seat lug, ot at some point of the frame near the rear wheel axle).
5. Rotate the rim of the rear wheel, until you hear a "bang".
6. Do not sue the author of this article (please).

See the attached pictures, for a succesful destructive test of a 4mm auxilliary cord.
« Last Edit: October 09, 2011, 10:08:17 PM by xarax »
This is not a knot.

SS369

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Re: Knot Strength
« Reply #23 on: October 09, 2011, 10:58:44 PM »
Was that your bicycle or the neighbor's child? lol
Ingenious.

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SS369

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Re: Knot Strength
« Reply #24 on: October 09, 2011, 11:31:53 PM »
Good old "Object D".
Hope your bicycle lasted longer. ;-)

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xarax

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Re: Knot Strength
« Reply #25 on: October 10, 2011, 01:37:14 AM »
  It lasted only 3 months, but completed 1440 orbits around the earth !
Wikipedia says there is only one remaining piece of it, at the Smithsonian.
This is not a knot.

SS369

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Re: Knot Strength
« Reply #26 on: October 10, 2011, 03:06:56 AM »
Sometimes competition is good.