I was told this info came from Yale many years ago and is only for Polyester and Nylon ropes. I cannot however provide anything that looks like an official Yale publication to support this claim. I do trust my source though as a person with a daunting amount of first hand knowledge on this subject.Phil, what is source for the bend radius table please?
>>is it by chance an eye radius and not bit/bollard/pulley radius table?
In an attempt to expand my own knowledge, and because you mentioned the 4:1 50% strength loss was from Samson, I reached out directly to Samson to see what they had to say. I did not mention the 50% loss number. I just sent them my chart and asked if they had any published research or charts that could validate the numbers I had for polyester and nylon cordage. One of the application engineers responded back with the following:
"There are no standard set of recommendations across various rope types / constructions. Phil is correct that rope design will have an effect, but this is not typically investigated for every type of rope. Samson has a proprietary model for our AmSteel Blue product design (Dyneema HMPE 12-strand w/ specific twist / braid structure) that is utilized to confirm strength for specific use configurations (i.e., lifting slings w/specific bends). We do not have this same model across all types of products.
Not sure where the listed estimates come from, but they appear to be less restrictive than our AmSteel Blue model or similar high performance rope or wire bend loss factors published in IMCA / DNV / ISO standards. At the listed boundary cases for example, the 1:1 ratio would be closer to 50% strength loss and the 8:1 per our model for AmSteel Blue would be closer to 15%. These losses are generally expected to be less severe for traditional fiber types, due to the higher elongation of the material providing increased load sharing around tight bends, but we do not have a similar empirical model developed."
That statement is copied straight from my email.
Based on the last statement, I trust my chart to be close to accurate in a generalized sort of way.