Author Topic: Response of F8 eye knot in EN892 drop test  (Read 438 times)

agent_smith

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Response of F8 eye knot in EN892 drop test
« on: August 02, 2023, 03:30:51 AM »
I have been corresponding with Dan Lehman in relation to the EN892 drop test.

EN892 is the default world standard for the manufacture and testing of dynamic ropes use in mountaineering and rock climbing.
Ropes are required to be drop tested - until failure - the number of falls being counted and recorded.

There are 3 categories of dynamic rope as follows:
1. Single ropes - must survive 5 test falls using 80kg drop mass
2. Half ropes - must survive 5 test falls using 55kg drop mass
3. Twin ropes - must survive 12 test falls using 80kg drop mass (tested as a double strand).

An F8 knot (#1047) is used to attach to the drop mass.
The test mass is raised to a height and released, generating a factor 1.77 fall.
The rope passes through an orifice - which simulates a carabiner of radius 5.0mm.

Eventually, the rope breaks.

What is of interest is precisely where the rope breaks.


That is, does rope failure occur at the F8 knot interface with the test mass?
OR;
Does rope failure occur at the orifice (the rope deflects through an orifice which simulates a carabiner).

I have been corresponding with Mr Lehman about this matter.
Dan has suggested that 'SS369' - a member of this forum - whom might have 'insider knowledge'.
It is very difficult to find first hand reports about where the breaks are occurring - as information does not appear to be in the general public domain.

Significant rope manufacturers include:
[ ] Sterling (USA)
[ ] Bluewater (USA)
[ ] Edelrid (Germany)
[ ] Beal (France)

Does anyone reading this post have direct personal contact (or a close working business relationship) with any of these rope manufacturers?
If yes, can you please make contact with their R&D department and obtain first hand reported data about where the rope breaks are occurring (ie at the orifice or at the F8 knot).
Can you then report the information in this thread?

NOTE: It is difficult for an 'outsider' to obtain this kind of detailed information. I know from experience that manufacturers generally don't respond to outsider enquiries.
I am trying to move beyond 'hearsay' information or second-hand information.
I need actual reported data - ie factual, first-hand evidence.

EN892 extract:
If breakage occurs at the knot, the test is declared invalid, and the test shall be repeated starting with a new test sample. If further test samples break at the knot, the fact shall be recorded, but the test results stand. Only one repeat test due to breakage at the knot is allowed.
« Last Edit: August 05, 2023, 09:10:13 AM by agent_smith »

Dan_Lehman

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Re: Response of F8 eye knot in EN892 drop test
« Reply #1 on: August 07, 2023, 08:22:23 PM »
There are 3 categories of dynamic rope as follows:
1. Single ropes - must survive 5 test falls using 80kg drop mass
2. Half ropes - must survive 5 test falls using 55kg drop mass
3. Twin ropes - must survive 12 test falls using 80kg drop mass (tested as a double strand).

Ahhh, I'd not realized #3 --a distinct, higher (much) requirement
for twin ropes !! ?!  (Rather, I thought that they were req'd to be
= single ropes in drop-test forces,
and typically DID register more drops,
and otherwise had the benefit of being
more cut-resistant (and allowing full abseil
on the halved rope vs. knotting single lengths
together --possibly of different types & sizes).
((or I forget that I knew this))  )

Hmmm, makes me wonder about fall-catch efficiency
PER WEIGHT of rope!?  --and getting frustrated in
a now quick attempt to get grams-per-metre or
other comparative weight info.  Seems like the
12-falls limit shows considerable gain in efficiency
for the twin ropes!?

Quote
Eventually, the rope breaks.

What is of interest is precisely where the rope breaks.


That is, does rope failure occur at the F8 knot interface with the test mass?
OR;
Does rope failure occur at the orifice (the rope deflects through an orifice which simulates a carabiner).
///
EN892 extract:
If breakage occurs at the knot, the test is declared invalid,
and the test shall be repeated starting with a new test sample.
If further test samples break at the knot, the fact shall be recorded,
but the test results stand.
Only one repeat test due to breakage at the knot is allowed.

Another news-to-me and surprising information
--breaking in the knot is considered bad form??!!
Most interesting.
(Another datum to have is break force --to see e.g.
if breaks at the bar (expected per test) come anywhere
near what we'd expect for a Fig.8 EKnot (65%, say). )

Thanks,
--dl*
====
« Last Edit: August 08, 2023, 05:34:42 PM by Dan_Lehman »

SS369

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Re: Response of F8 eye knot in EN892 drop test
« Reply #2 on: August 07, 2023, 10:35:55 PM »
I no longer have access to the BlueWater facility, but when my children worked there, I eyeballed everything when I visited them. (Quite often.)
If memory serves well, I remember watching a number of drop tests and did not witness many failures in the standard tests. A few tests were run till destruction, the rope breaking after the formal test was over and recorded. I only saw the breaks occur at the provided "edge". The spot on the rope was pretty shiny, glazed and hardened.

I have read a Sterling Rope report on drop testing that also indicates that the greater number of breaks occur at the edge of their test apparatus, although a few outliers at the F8.

In real world usage, there are so many things that can influence the rope's longevity.
Thing to remember; the cyclic impact point of the test is in the same place, thus it is an isolated test.

SS

 

anything