http://iopscience.iop.org/1367-2630/3/1/310It is a common macroscopic observation that knotted ropes or fishing lines under tension
easily break at the knot. However, a more precise localization of the breakage point
in knotted macroscopic strings is a difficult task. In the present work,
the tightening of knots was numerically simulated, a comparison of strength
of different knots was experimentally performed and a high velocity camera
was used to precisely localize the site where knotted macroscopic strings break.
In the case of knotted spaghetti, the breakage occurs at the position with
high curvature at the entry to the knot. This localization results
from joint contributions of loading, bending and friction forces
into the complex process of knot breakage. The present simulations
and experiments are in agreement with recent molecular dynamics
simulations of a knotted polymer chain and with experiments performed
on actin and DNA filaments. The strength of the knotted string is greatly
reduced (down to 50%) by the presence of a knot, therefore reducing
the resistance to tension of all materials containing chains of any sort.
The present work with macroscopic strings revels some important aspects,
which are not accessible by experiments with microscopic chains.
