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by siliconunit 1196 days ago
Interesting behaviour, usually any normal rope knot makes the rope weaker at the point of maximum curvature/choking etc. Would be enlightening to get a comparison why the different behaviours, just a scale/friction non linearities?
2 comments
mihaaly 1196 days ago
They claim the structure is tougher (absorbs more energy) not stronger (maximum force before breaks). As far as I see they say nothing about if it is stronger or weaker than straight lines. Likely because it is weaker due to the curvatures leading to stress peaks in the material before the ultimate force of two straight filaments was reached. They should have presented the force-displacement diagram too which is essential data (maybe the original article has it). I'd be curious seeing the force-displacement diagram of the two illustrated experiment compared to the diagram of two straight fibres tested.

Also I guess the toughness is just a relative matter to the dimensions of the structure but since uses much more material than two straigh fibres it is less tough by weight (due to the decreased strength). If the same amount of material was connecting the top and bottom with straight lines then that would lead to the toughest situation of all (absorbing the most energy). Again, guessing.

In the video the woven material may have tighter threads with stronger friction or more uneven friction distribution leading to reaching the yield limit of the filaments quicker. The woven with some 'lubrication' should have had similar properties assuming the same amount (length or weight) of material included. I'd also be curious then about the reproducibility of the results on the same kind of structure. Like if making the same knotted pattern would lead to the same results or slight deviation of geometry was affecting the end results significantly.

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cwillu 1196 days ago
It looks like the loop of the knot permits slack which in turn causes stress on the fiber to be taken up by straining neighbouring weaves, rather than causing the stressed fiber to immediately strain to its failure point.
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