Flattening of cordage by descending rings

[CatSplat]

I don't believe the flattening would cause significant changes to the Amsteel's strength. Amsteel is commonly used for heavy (12,000lb+) recovery winches, and when using the synthetic line a Hawse fairlead is used. The Hawse is essentially just a smooth piece of metal the Amsteel slides over, and when it does so the Amsteel is flattened. This flattening has not, to my knowledge, been shown to reduce the strength of the Amsteel in these situations, even when loaded nearly to breaking strength.

I would consider abrasion from rough surfaces to be far more worrisome than flattening, especially considering the weight-rating safety factors typically designed into our hammock suspensions.

[Mouseskowitz]

This is talking about kernmantel rather than amsteel so it may or may not apply. This an except from Life on a Line by Dr. Merchant which is a cave rescue book.

"Several studies in the USA and Europe have shown that for kernmantel rope in particular, if it is left in a knot for an extended period it can take on a permanent residual stress, even when untied. Almost every caver knows that when you untie a rope that has been hanging on a pitch for a long time, the section of rope that was in the knot retains a bent and curly shape. Few realise that this section is now significantly weaker than the rest of the rope, and can remain so forever. Of most danger when tied in the middle of a rope (for example on a traverse line), long after the rope has been removed and reused and everyone has forgotten where the knots had been, it retains a point of weakness that could cost you your life. The same applies to webbing though to a far lesser extent. This residual memory is probably the cause of several mid-rope failures both in the real world and during load testing."

So, my thought is, if a portion of rope has been flattened it may cause a permanent weakening of that section at the microscopic level. Will this cause failure with our application? I'm speculating probably not. If you take degrade 1600lb by 60% you still have 640lb which should still hold us in most hammocking applications.

[Ramblinrev]

Warbonnet hasn't used those rings in a couple of years and I'm not aware of any hardware currently being used that has similar issues.

I used to use welded steel rings from the hardware store. They would have the same weld issues as well as an oxidation issue that climbing rated aluminum rings might not have. Aluminum can oxidize to be sure and the corrosion can be abrasive but I would expect climbing rated aluminum equipment is treated or hardened in a way to minimize that risk.

[DemostiX]

This is talking about kernmantel rather than amsteel so it may or may not apply. This an except from Life on a Line by Dr. Merchant which is a cave rescue book.

<snip>

So, my thought is, if a portion of rope has been flattened it may cause a permanent weakening of that section at the microscopic level. Will this cause failure with our application? I'm speculating probably not. If you take degrade 1600lb by 60% you still have 640lb which should still hold us in most hammocking applications.

Internal abrasion damage of fiber on fiber was a serious problem of early Kevlar cordage. it was particularly dangerous because disintegration was taking place within an outer protective cladding or outer braid.

Dyneema / Spectra (and probably current versions of other hi-tech synthetic fibers) don't have this characteristic. Testing of bending fatique resistance is done to thousands and tens of thousands of cycles.

[nothermark]

Everything I have been able to find leads me to expect flattening of Amsteel or any other loose braid rope. I see is as a good thing. The bend radius of the the rope is exceeded with rings but not strands. The strands are extremely tough, do not cold flow and are difficult to cut. The coating may rub a bit but that is largely cosmetic. The base material is Ultra-high-molecular-weight polyethylene (UHMWPE). Dyneema is the base material, Amsteel has a coating developed by Sampson Rope. Spectra is similar material but may have a processing difference.

It's worth pointing out that there are 3 basic types of rope commonly in use. Loose braid like Amsteel blue. Solid braid that is a harder rope and does not deform as much and kern mantle rope like climbing rope or a lot of the Harbor Freight cheap stuff. KM has a high strength core of parallel fibers sheathed in a braided cover for UV and abrasion protection. KM will deform under load similar to loose braid if the sheath is loose.
UHMWPE core with some sheath damage does not get me nervous as it does not cold flow and is very abrasion resistant. Climbing rope becomes instant trash as that has a nylon core that does cold flow and is more subject to other problems. Mystery rope has mystery problems. ;-)

[Mouseskowitz]

The more I'm thinking about this subject the more I wonder if we should differentiate between the flattening of amsteel over a smooth surface and the "pinching" mechanism found in a garda hitch.

I believe that nothermark and CatSplat are on the money with their observations about the flattening characteristics. If you just look at the rope new off the real it's more flattened than round. So, with this being the case, flattening against a non abrasive surface with a bend radius of at least the recommended 8:1 is not a problem.

The question in my mind, and where I was going with quote I posted above, is what effect the pinching action of a garda hitch has on the rope. As I have not seen this phenomenon I am making some assumptions, please correct me if any of them or wrong. I am thinking that the flattened area is localized to the area that was between the rings and that it does not easily return to its original form. I'm thinking this would be correlative to the curliness of a long term knot that has been untied. If this is the case, it can be assumed that there has been a permanent alteration to the rope fibers at that point creating a weakness.

I am far from being an expert. So, if I'm off please egimicate me.

[GrizzlyAdams]

...I am thinking that the flattened area is localized to the area that was between the rings and that it does not easily return to its original form. I'm thinking this would be correlative to the curliness of a long term knot that has been untied. If this is the case, it can be assumed that there has been a permanent alteration to the rope fibers at that point creating a weakness.

I am far from being an expert. So, if I'm off please egimicate me.

I am no expert either. But, after showing the garda hitch on woven cord in a video and later seeing this permanent pinching, made me retract the implicit garda hitch recommendation. I don't know whether it necessarily weakens the cord or not. But there are so many other viable alternatives that don't affect the cord this way, in the absence of any indication that it doesn't weaken the cord, it seems prudent to me to avoid the combination of Amsteel and the garda hitch.