What a great post Genghis, may I please ask a supplementary question about the use of composites in the modern era. I do understand that higher reserve factors were applied in the early days of composites because not much was known about failures. Also the inability to inspect for defects. (I am guessing during manufacture or damage/ overstress in use)
With 787 and A350 are the RFs still increased. I would have thought that with all the experience gained and modern NDT 1.1 would have been sufficient.
I am with you all the way about deflection being used to absorb energy. Local stiffening just moved the problem. When I was a student I recall a book entitled the New Science of Strong Materials. It was littered with cartoons and phrases such as "why wings bend" and the likes.
Had I still been a student I would have asked my Dad to buy me the Guy Gratton book for Christmas or my Birthday.