/ 8.5mm rope breaking load?
Just tested some 8,5 mm dynamic half ropes to destruction on the tensile tester (because I can).
Double overhand knots both ends (uses less rope).
Breaking load was 8,0kN extension was measured at 230mm for a sample of around 250mm eye to eye.
Strain rate was 50mm / min.
Given that the double overhand de-rates the rope strength to 45-55% of the original strength then this would possibly suggest that the rope has a static strength of 14,4 - 17,8 kN.
A 10,5mm semi static EN1891 rope is required to make 22,0kN static.
Given a reduction in cross sectional area of 1,5 times, and similar core/sheath ratios I'd expect a reduction in strength proportional to the loss of cross sectional area. 22,0/1,5=14,7 kN.
I was surprised that the rope failed at 8kN I was expecting higher even with the evil overhand knots. I was impressed by the elasticity, and yes I know they are designed to stretch, Max Impact Force is quoted at 5,5kN.
My question is: Does anyone have any similar data from other ropes they can share?
On a vaguely related note... I used a retired mammut serenity 8.7 to tow a people carrier behind a land rover. Did the job surprisingly well. I wonder what peak force was through the rope... 3kn at a guess?
Yep probably very little peak force when towing to be fair.
I'm primarily interested in how we can measure deterioration of rope over time. I've read a lot of stuff about this on these and other forums.
Does anyone know where 8,5 dynamic rope is sold off the reel by the meter?
When you say double overhand both ends, did you form loops for 10mm pins to go through? Did it break at a knot?
Only rope I ever broke (10.5 Mammut) stopped a car (~60kJ into ~15m of rope), twice before it let go over an edge, it was also quite tired having spent a couple of years lying in a field after a full life on the crag. As anecdotes go I don't suppose it'll add a very useful data point to your collection but I've always found it reassuring
Pretty sure Dick's Climbing sell it off the reel.
Double overhand knots both ends to form loops, yes, I used 8mm pins though i appreciate that the standards say 12mm, and yes it broke at the knot all 4 samples. Ropes will, in my experience, always break at the knot unless damaged or cut, e.g. by an edge, and I've broken many in my time, mainly semi static.
Cheers, I'll check them out.
Yes they have a 10.2, but I'm interested in 8,5mm half ropes.
You can get Beal Verdon half rope by the meter, but its 9mm
> Given that the double overhand de-rates the rope strength to 45-55% of the original strength
Are you sure? A single overhand is widely quoted in angling literature as reducing the BS of fishing line by ~50%. It does this by its lack of internal friction allowing the knot to pull ridiculously tight into a tiny bend radius. A double overhand has loads more friction and wider bend radius.
have ordered some, will be very interesting to pull it.
> , will be very interesting to pull it.
Got the beal verdon 9mm this week.
Tested same method as above:
160mm test sample with double OH knots both ends:
4 samples tested:
Average BS 10,300N, extension was ~350mm from 10N to break.
This here dynamic rope is seriously stretchy.
20+ year old nylon fibres retain at least 90% of the strength of new nylon fibres based on a simple stress relation - Break load / Cross sectional Area. This relation also holds based on BS / mass per metre.
Differences in the rope types tested and core to sheath percentages 42/49% may skew these results.
The data is interesting, but ropes are cheap enough not to risk climbing on ropes that are suspect.
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