mathew said..MarkSSC said..
I wonder if the most proactive thing we can do is to work out how much life is added to a sail by using the crossply panels. My observation is that there is a substantial increase in the life of a sail simply by having crossply panels
^^ this. Sort of.
X-ply does crack, but those cracks tend to not puncture. Monofilm cracks, then punctures along the crack.
X-ply has one particular downside -> it distorts the view. This never really bothered me until I tried ariel-off-the-lip where I couldn't judge the the whitewater.
I've been saying for a few years now -> what we need is x-ply without the thread. It is the glue-layer that allows the partial cracks to not puncture, while also not being distorted.
Every material has a life expectancy. Fatigue cracking was something peculiar to the aircraft industry when the materials they were using cracked and failed due to the stresses involved in general use. With that in mind, the continual bending, stretching and flexing of the monofilm may be the catalyst for eventual failure. Other factors are also involved, like the brittleness caused by the sun and unexpected large objects (people) impacting the surface. I still think, because there is a lot of variation in how long each sail will last, that stress fatigue has a part to play. I am not sure that your thesis about the laminations is valid, because laminating a surface always leads to greater strength. The advantage with laminations is that one layer can be damaged, but not compromise the structure. A crack always goes through a material, but it does not mean the material will continue to tear. I think you will find that it is not the glue that stops further tearing, it is the other material that has been bonded for that purpose. Effectively, in the case you describe, the cross-ply material has prevented a crack from developing further, maintaining the integrity of the sail.
