Thanks for these!
On the first site, I note that this fellow (a teacher
w/grad students?) has been producing misc. knotty
test reports for a while.
At the 2nd site, I found among other-reports listed,
one that ...
Feasibility of Knots to Reduce the Maximum Dynamic Arresting Load in Rope Systems
Daniel A. Martin, K. Boron, +2 authors G. Horn
Published 2015
Materials Science
Journal of Dynamic Behavior of Materials
Impact loads to the human body due to falls from height can be mitigated
by well-designed and characterized fall protection systems. While energy
absorption methods using rope deformation and/or accessory components
have previously been evaluated, the ability for simple knots tied in the
system to alter impact loads has not been studied in detail. We quantify
the effectiveness of various common knots to reduce dynamic loads in
typical fall scenarios for which the systems are designed, and interpret
this change in the context of rope strength reduction due to the knot.
Knots are shown to significantly (45?60 %) reduce the quasistatic strength
of rope when compared to a manufactured sewn-eye (40 %). A single
exception to this outcome is with the quadruple overhand on a bite (30?35 %).
Knots significantly reduce the maximum arresting load due to a dynamic impact
event when compared to ropes without knots, providing significantly more energy
absorption than the sewn-eye alone. In nearly all rope/knot combinations,
the ratio of maximum arrest load (MAL) to breaking strength was lower with
the knotted ropes when compared to the sewn-eye terminations. In particular,
the quadruple overhand on a bite tied in the Technora?Technora rope resulted
in MALs that were only 33 % of the minimum breaking strength (MBS).
Ropes with sewn-eye terminations resulted in MALs that were 80 % of the MBS.
From the scenarios investigated, the quadruple overhand on a bite provides
a favorable reduction in arrest loads with the smallest associated loss of strength.
I've not looked at the report to see if there is some measure
of the amount of material coming out of each knot. Considering
the length of a rockclimber's fall, one must question how much
effect the yield of a small amount of cordage from the knot
can have! --fall of say 3metres and yield of 3cm and ... !?
TO this I'll remark that in using such a STATIC rope as one
made w/Technora (4% elongation at rupture?) they give
knot compression --which is I think more absolute in yield--
to figure more prominently, in % terms. (HMPE might be
even more dramatic, the slickness enabling much pull-out
compression of a knot!?)
"on a bite" [sic] is a sad thing to see.
--dl*
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