Another topic raised from the dead.
Over on another forum, there's an account of a sudden and unexpected failure of 5mm Dyneema which was being used on a cascaded backstay arrangement on an average white yacht. The consensus was that this was probably caused by heat generated by friction because of a seized-up block.
This then developed into a discussion about the physical properties of Dyneema, which is alleged to liquify quite readily if sufficient heat is applied. Certainly true if cut with a heated rope blade but then all strings melt when faced with that. What really caught my attention was the suggestion that small diameter Dyneema and "low" friction rings are not really the best combination in bits of rigging which can move under high stress. That's got me thinking about places on my boat where this is the case. So far, I've come up with my modified mizzen outhaul arrangement and my jib boom topping lift. Probably something to be aware of rather than a major worry, as a boat with failures in either area can still sail perfectly well. On the other hand, what about Dyneema soft shackles?
Dyneema used to be miracle string but as we use it more, its weaknesses become more apparent: it doesn't stretch but unless specially heat-treated it can creep, which can be irritating; it can degrade quite quickly under strong UV (not a problem in my part of the world at present) unless specially coated; even bog-standard untreated Dyneema string is expensive; and now this.