Herman wrote: ↑
Tue Jan 28, 2020 5:58 pm
I doubt that the normal forces and coefficient of friction know whether they are knotted or spliced.
Friction, deformation, and stretch extremely different in dyneema / Spectra versus nylon and Dacron.
For instance, when making a bend over a shiv or other type of contact surface where the line makes a sharp direction change, dyneema can actually be weaker than the same strength nylon line. This is specifically because there is no stretch in dyneema on very small scales such as the distance over a turning block or other object. The effect this has is that the fibers taking the longest route on the outside of the bend will carry all of the load and break first with dyneema. But in nylon or Dacron, the stretch will allow the fibers on the inside of the bend to be loaded and thus not all of the load is taken up by just a few fibers at a time. Another reason that dyneema uses flat braids is to combat this property. Round braids in dyneema running over a turning block or other object would put an extreme load on those outside fibers.
So again the physics are definitely different with respect to dyneema vs. Nylon / Dacron lines.
As for knots, I think it's pretty evident that dyneema knots fail by slow slippage, as opposed to Breaking at the knot or a quick slip of the knot.
So after establishing that the physics are different, I think it is fair to treat dyneema in an knot situation differently than lines that have a large amount of stretch. The elasticity of nylon / Dacron helps with knot retention. The lack of elasticity prevents even some of the most reliable knots from holding in dyneema / Spectra.
I would think that it is fairly obvious that the action of cinching down in a knot is much different then the action wear a splice cinches down on the line inside of it.
Could there be a degree to which the slipperiness of the dyneema surface comes into play? I would think so, but the main culprit of knot slippage in dyneema / Spectra, is that there is no significant stretch with regards to very small scales of length in that material.