I found this - https://www.sexyloops.com/index.php/ps/sunburnt-nylonI wrote a series of articles for Sexyloops regarding the strength testing of various materials and knot. I also did an ageing test on nylon that had been left in sunlight for a couple of months.
Firstly, I'll say that if you want accurate data then you need to be using a load frame such as an Instron mechanical tester, fortunately I have access to one of these. Here the material under test is wound onto 'spools' and these are loaded into the machine, thus the testing can be done in the absence of knots. This gets the true tensile strength of the material.
When it comes to knots, there are very, very few in my experience that retain anything like 90% of the materials strength. The exception is the Bimini Twist which retains all the lines strength due to the fact that knot itself twists the line into a multi-strand 'rope' that is stronger than the starting material. A simple knot like a overhand loop (i.e. a 'wind' knot), in contrast loses 30% of the lines strength immediately. From my fairly extensive testing, I think an angler should assume that they've retained 60% of the materials strength once they've finished making up their leader and attached the fly.
What a machine like an Instron produces is a stress/strain response of the material under test. It should be noted the strain is the physics term for stretch. As such, breaking strain is actually the extension at which a material ruptures quoted as a percentage of its starting dimension. This term has been bastardised by anglers to mean tensile strength though. For example, the breaking strain of nylon is typically about 50% (irrespective of diameter), but if you answer the question of 'what breaking strain are you using' with 50%, although technically correct, you'll get a blank stare
The stress/strain response gives some interesting information about the material. The area under the stress/strain curve is a measure of the energy required to rupture the material, i.e. the brittleness. This fracture energy/brittleness is important when it comes to shock resistance. At this point I should say that the stress/strain behaviour of most materials is affected by the strain rate. I think in practice we all know this - e.g. if you want to snap a piece of leader it's 'easier' to do so with a sharp jolt rather than a steady pull. Materials with higher fracture energies are more resistant to failing under shock-loading conditions, thus stretchy materials tend to do better in this respect. There is a difference in fracture energy between nylon and flourocarbon, but it's nothing like some of the estimates made in this thread.
Hope this is useful, James.
do you have any other links to the other articles? I couldn't find them. Maybe that would end the constant repetitive threads on tippet materials (ha ha!).