The GE90-115b has flown on the 747 test bed at it's rated power, so I believe that the required tests (bird strike and blade off tests would have already been proved.
For the current engine (-76b and on!) the bird strike tests were no major problem. For the blade out test it was released (from memory) a third way up.
The blade is manufactured from composite layers, layered at 0^ 45^ and 90^ with metal pins inserted to add to the strength. The leading edge and trailing edge are titanium. with the blade (aft of the L/E strip) coated with polyurethane to prevent erosion.
The fan is extremely good with no major problems, unfortunately it's let down by the rest of the engine at the moment
