Natural rope friction and snapping

[conaire]

Ok, so there is a little discussion going on in my circle of associates at the moment regarding rope break dynamics:

http://esinem.com/news/rope-friction-break-tests

If you watch both videos, you can see that some ropes (usually the synthetic ones) will saw through the static bight of the rope, while others (usually the natural fibres) will break on the dynamic portion.

Linen hemp, however acted like a syntheyic rather than a natural and sawed through the bight.

So can anyone explain to me why:

A) natural fibres break in the dynamic section

B) linen hemp broke the bight like a syntheyic rope.

Thanks and praise will be lavished upon whomever is able to increase my understanding.

 

[Bystander]

A) natural fibres break in the dynamic section

Bending failure.

 

[conaire]

Bending failure.

Is there anywhere I could find the concept in laymans terms?

 

[Bystander]

Compare the number of times you can bend a green twig before it breaks to the number for a dead twig. The moving bight is being bent repeatedly around the static bight, and a lot of natural fibers used for rope are brittle. What the actual failure mode of a bundle of natural fibers would be is a little difficult to determine from first principles, or from the videos: it could be pure tensile on the outside radius of the bundle as it goes around the bend; it could be longitudinal (axial) shearing of rough fiber surfaces against each other around the bend; transverse shear of fiber lays against each other around the bend; but, probably a mix of all of the above plus other effects. Natural fibers are generally not going to be as elastic as the artificial, so they can't handle the high tensile strain of repeated bending in the moving bight as well as the synthetics do.

 

[conaire]

Compare the number of times you can bend a green twig before it breaks to the number for a dead twig. The moving bight is being bent repeatedly around the static bight, and a lot of natural fibers used for rope are brittle. What the actual failure mode of a bundle of natural fibers would be is a little difficult to determine from first principles, or from the videos: it could be pure tensile on the outside radius of the bundle as it goes around the bend; it could be longitudinal (axial) shearing of rough fiber surfaces against each other around the bend; transverse shear of fiber lays against each other around the bend; but, probably a mix of all of the above plus other effects. Natural fibers are generally not going to be as elastic as the artificial, so they can't handle the high tensile strain of repeated bending in the moving bight as well as the synthetics do.

Awesome! Thank you so much. :-D

 

[Bystander]

This analysis is worth exactly what you paid for it --- it's where I'd start, but I wouldn't hang the future of the company on it.