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patto
Jul 19, 2007, 1:57 AM
Post #51 of 54
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Registered: Nov 15, 2005
Posts: 1453
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rgold wrote: Patto, I may indeed be wrong; I did a force calculation based on a linear rope model. I am not an engineer and certainly not a materials scientist. Since you seem to know something about this, I'd find it very useful to have some references for three of your statements: 1. Ropes will survive many many more factor-1 falls than factor-2 falls. 2. Factor-1 falls cause negligible damage to the rope. 3. Factor-2 falls cause significant damage to the rope. If any of your references quantify "many many more," "negligible," and "significant," that would also be helpful, as would a description of the nature of the damage you refer to.
I knowingly used qualitative words as I do not have number available. However I'll try to back up my statements.
Ropes will survive many many more factor-1 falls than factor-2 falls.
This follows from the other two comments. Also talk to Dan Osman about his many factor 1 falls. Pitty the friction got to him. :(
Factor-2 falls cause significant damage to the rope.
Most ropes can hold fewer than 15 factor 2 falls many less than 10. Failure after less than 15 cycles indicates to me that damage the I would describe as significant. It quantifiably reduces the ropes life and strength.
Factor 1 falls cause negligable damage to the rope.
A factor 2 fall involes TWICE a much energy as a factor 1 fall. I don't have the numbers to show you but consider this:
If you have a rubber band that can hold a weight drop of 2kg 15 times how many times could it hold a 1kg weight drop. I would be estimate it would be well over 10x more times. Similiary you could drop oranges from 1m heights vs 2m heights and compare the survivability.
Good elastic mediums can have 1000s of cycles if the plastic yield point is not reached. I would be VERY surprised if a factor 1 fall pushes a rope into plastic deformation.
Check out for a quick description of strength vs strain. http://www.key-to-steel.com/Articles/Art43.htm
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greenketch
Jul 19, 2007, 4:17 AM
Post #52 of 54
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Registered: Jan 12, 2005
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Patto, I can definatley see that you do not have the numbers to demonstrate your theoury. I can also see that yu do not have the understanding of ropes or falls to postulate a plausible theory.
The change in fall factor does not directly relate to a change in fall forces, it is a ratio that is used in the calculation of peak forces.
A rope does not dissipate by plastic deformation. It is part of the construction of the rope (a spiral lay of the kern) that functions in this way. The spiral is disturbed as the force is applied and it does not return fully.
thanks for trying though
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jt512
Jul 19, 2007, 4:31 AM
Post #53 of 54
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Registered: Apr 12, 2001
Posts: 21904
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patto wrote: rgold wrote: Patto, I may indeed be wrong; I did a force calculation based on a linear rope model. I am not an engineer and certainly not a materials scientist. Since you seem to know something about this, I'd find it very useful to have some references for three of your statements: 1. Ropes will survive many many more factor-1 falls than factor-2 falls. 2. Factor-1 falls cause negligible damage to the rope. 3. Factor-2 falls cause significant damage to the rope. If any of your references quantify "many many more," "negligible," and "significant," that would also be helpful, as would a description of the nature of the damage you refer to. I knowingly used qualitative words as I do not have number available. However I'll try to back up my statements. Ropes will survive many many more factor-1 falls than factor-2 falls. This follows from the other two comments. Also talk to Dan Osman about his many factor 1 falls. Pitty the friction got to him. :( Factor-2 falls cause significant damage to the rope. Most ropes can hold fewer than 15 factor 2 falls many less than 10. Failure after less than 15 cycles indicates to me that damage the I would describe as significant. It quantifiably reduces the ropes life and strength. Factor 1 falls cause negligable damage to the rope. A factor 2 fall involes TWICE a much energy as a factor 1 fall. I don't have the numbers to show you but consider this: If you have a rubber band that can hold a weight drop of 2kg 15 times how many times could it hold a 1kg weight drop. I would be estimate it would be well over 10x more times. Similiary you could drop oranges from 1m heights vs 2m heights and compare the survivability. Good elastic mediums can have 1000s of cycles if the plastic yield point is not reached. I would be VERY surprised if a factor 1 fall pushes a rope into plastic deformation. Check out for a quick description of strength vs strain. http://www.key-to-steel.com/Articles/Art43.htm
In other words, you have no data, just a circular argument.
Jay
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knudenoggin
Jul 19, 2007, 5:01 PM
Post #54 of 54
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Registered: May 6, 2004
Posts: 596
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jt512 wrote: patto wrote: rgold wrote: [unneeded, deleted] [...... and, we just read all this--blip rather than echo to add one line  ] In other words, you have no data, just a circular argument.
There's enough lack of data here to go around on all sides of this debate, which keeps
the illusion that we only need speak of Fall Factor alone as relevant.
On the anecdotal side, we can look to Outdoor Knots from Mountaineers publishers
for these words of retirement guidance:
In reply to: Extensive data show the repeated short falls, whether sport climbing or top roping, quickly wear out dynamic ropes--owners of climbing gyms know this all too well. Likewise, frequent rappelling ... does a lot of damage. One study showed that just 50 rappels with a figure-8 device reduced the number of falls held by a third. [I wonder at the allowed recovery time in this study.] ... Heavy climbers do more wear and tear than lighter climbers. Frequent falls and lowering wallop a rope more than occasional falls when traditional climbing. Tests of ropes with known climbing histories indicate that after 100 50-meter pitches, a climbing rope loses half of its fall rating. And another 120 pitches (11,000 meters climbing total) reduces dynamic ability to one third of original.
to Patto's and my suggestions. But there's a lot to better understand, here.
(Re lowering, its effect I think could be lessened if the climber did the lowering
control, halving the load on the rope, rather than engaging the pulley effect's
greater tension at the top along with feed through the belay device.)
*kN*
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