Jock
Composite structures are a very different thing from metal and this is a big problem within the industry, a lot of the major players within GA have a very worrying lack of knowlage and ability when it comes to composites.
Almost all of the Daimond and cirrus approved maintenance shops in the UK are not capable of all but the most minor repair work, this leads to the aircraft becoming expensive to insure as the aircraft get written off for damage that could be fixed. One example is a DA40 that was scrapped on the south coast simply because the maintenance company had no idea that the damage was repairable, the aircraft could have been back in the air within a month or so had it been looked at by the right people. (NOTE this sort of damage would be repaired IAW a manufactures repair scheme ). Unfortunatly this also is true of parts, things that should be repaired are being scrapped due to lack of Repair knowlage within the industry and it is the owners that are bearing the cost!
The knowlage of the long term durability of composite structures is mostly to be found in the renewable energy industry as these structures are having to last up to thirty years with minimal inspection, I know of one aviation based company that is in the renewable energy sector and they have fatigue numbers for composite water turbines that say the turbines are good for thirty years running. The boss of this company is of the opinion that compared to water turbines aircraft get a very easy life with lots of inspection and so are far easier to maintan safely.