by Bob Thrun » Apr 6, 2012 9:04 pm
I wonder about the data. It would make a good technical article if you gave sources. Each manufacturer seems to give elongation data differently, if at all. To get the stretch at a given load, you need to find elongation curves. I found only one manufacturer that gives curves for all its ropes. The curves are printed so small that it would be hard to pick off 300 lbs on a curve that goes to 6000 lbs. There is some hysterisis, a rope does not shrink all the way back to its original length after being unloaded. Some manufacturers give the stretch at 15 % of the breaking strength.
You have some ropes listed as having a Technora sheath and nylon or polypropylene core. It is usually the other way around, with a Technora core. The Technora/Technora combinations are shown as having more stretch than nylon/nylon. Technora has extremely low stretch while nylon has the most stretch of the fibers listed.