Does anybody remember how Rolls Royce nearly went bankrupt by a too early adoptions of composite materials ?.
The RB211 main fan blades were initially designed from Unidirectional graphite fibre . All was fine until they had the first bird strike test and the complete disc had a catastrophic failure . A very expensive lesson was learned . So the use of high strength composites is not really that new . Strength , fatigue and enviromental degradation factors are well established for the most commonly used materials which are based on resin systems developed in the early 70's. What still seems to be a "black art" is non destructive testing , and more importantly in service testing . Ultrasonic inspection still seems to rely to a great degree to expert interpretation of the results. ( we can see something unusual but we are not sure what it is ). Wheras an X ray or Zyglo inspection of a metal part in the most part gives results which are easily interpreted. There is not any new helicopter I know of that does not have composite blades and the safety record of these blades is impeccable , mainly because thay are made from low modulus glass which has a much more gradual failure mode than graphite. The other thing abour helicopter blades is that any change in stiffness will usually be detected by the pilot before it becomes a major problem , i am sure that in a fixed wing this is not the same case.