using vibrations of some machine (washer?);
! ! 
Good idea.
You should attach the knot to the limbs of a small bow,
which will keep the ends tensioned,
and see if it will come out in one piece after the washing ( and drying ! )...
But I don't want the ends tensioned --I want to test
"slack security", resistance to shaking/jostling/idle_loosening.
And so my thought re the machine was to have a series
of knotted specimens tied to a rigid pole, dangling, and
being shaken by the machine's vibrations transferred
via the pole (or, via flag-shaken line to which specimens
are attached, similarly --but where to put one's monetary
tokens to generate a breeze?!
).
Hmmm, thinking of my in-the-pocket non-testing but
effectively a sort of testing ... , I can thus suggest that
one has a
bag of speciments, perhaps also weighted balls,
that one repeatedly lets roll down a slope --the point being
to mimic my in-the-pocket circumstance, and to use what
CAN be depended upon --a slope (which won't change angle,
alter gravity, or move away, time to time!). The "weighted"
(better, maybe, "weighty" ?) balls are there to help ensure
that this bag o' knots does roll down the slope, while also
providing some additional "jostling" effect internally?
(maybe just one old bowling ball!).
And grading would be pretty coarse --as befits this quite
non-finely-graduated test-- : do the knots stay tied?
--or loosen but only up to a point? --or only in some
of the materials? --... some of the settings? et cetera.
[Currently, I'm awarding myself Bright Idea of the Week for this!][[note : award precedes actual attempt to DO ... ! ]]
--dl*
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