Impact Resistance of Composite Fan Blades.

This report presents the results of a program to determine the impact resistance of composite fan blades subjected to foreign object damage FOD while operating under conditions simulating a short takeoff and landing STOL engine at takeoff. The full-scale TF39 first-stage fan blade was chosen as the base design for the demonstration component since its configuration and operating tip speeds are similar to a typical STOL fan blade and several composite configurations had already been designed and evaluated under previous programs. The first portion of the program was devoted toward fabricating and testing high impact resistant, aerodynamically acceptable composite blades which utilized only a single material system in any given blade. The material systems utilized were a graphiteepoxy system AUPR 288 and a boronepoxy system 4.0 mil5505. It was determined that the blades of each material system were both capable of sustaining impact equivalent to a half bite of a 624 gram 22ounce bird without total failure. Beyond this point, both blades broke off at the root at impact. In order to increase the blade impact capability beyond this point, several mixed material hybrid designs were investigated using S-glass and Kevlar as well as boron and graphite fibers. These hybrid composite blades showed a marked improvement in resistance to bird impact over those blades made of a single composite material.