Kevlar fatigue limit

[lw395]

Does anybody know if there is a lower limit below which kevlar rope does not have fatigue problems?
I want to use it in a system where its low stretch and lack of creep are useful, but it has to go around several blocks.
Vectran would be better, but I have a load of kevlar I got very cheap!
I think it would be loaded to around 5% of break strain.

Thanks!

 

[vyv_cox]

I found this one, which may answer your question. http://www-civ.eng.cam.ac.uk/cjb/papers/p12.pdf

 

[lw395]

Thanks Vyv, that's a very good start!

 

[wklein]

Does anybody know if there is a lower limit below which kevlar rope does not have fatigue problems?
I want to use it in a system where its low stretch and lack of creep are useful, but it has to go around several blocks.
Vectran would be better, but I have a load of kevlar I got very cheap!
I think it would be loaded to around 5% of break strain.

Thanks!

What is the application? I would say that the degree and radius of the turns would be at least as important as the load. And obviously be very careful with UV.

 

[lw395]

It is for control systems on a dinghy.
I think it we be OK, as it will only be changed at most twice per lap, so not thousands of cycles.
The load will be below 5% of breaking strain.
Some of the sheaves will be quite small though. Typical 28mm dinghy blocks.
I don't think UV will be too much of a problem as it lives under a cover most of the week and the systems are below deck.
I will use Vectran for the critical bits (where failure would cause the mast to fall down), but I don't want to spend on Vectran for everything until I know the design is right.