EMBEDDED FIBER OPTIC SENSOR FOR COMPOSITE FLEXBEAMS

A NOVEL FIBER OPTIC SENSOR SYSTEM TO MONITOR THE STRUCTURAL INTEGRITY OF COMPOSITE FLEXBEAMS IN BEARINGLESS HELICOPTER MAIN ROTOR HUBS IS PROPOSED. THE SENSOR SYSTEM UTILIZES A SHORT GAUGE LENGTH BRAGG GRATING SENSOR AND A MANUFACTURING TECHNIQUE WHICH PERMITS THROUGH THE THICKNESS (Z-DIRECTION) INSERTION OF THE SENSOR IN THE COMPOSITE FLEXBEAM WITHOUT DEGRADATION OF PART PROPERTIES. FIBER OPTIC STRESS/STRAIN SENSORS PLACED IN THE Z-DIRECTION WILL BE FAR MORE SENSITIVE TO PLY DELAMINATION THAN CONVENTIONAL IN-PLANE SENSORS. ADDITIONALLY, THE COMPLETE SENSOR SYSTEM WILL PERMIT THE INSPECTION OF THE FLEXBEAM WITH A GROUND BASED INSTRUMENT WITHOUT THE REMOVAL OF THE PITCH CASE ENCLOSURE. THE PHASE I PROGRAM WILL DEMONSTRATE THAT FOSTER-MILLER'S FIBER INSERTION TECHNOLOGY CAN SUCCESSFULLY INSERT SELECTED FIBER OPTIC SENSORS INTO A TYPICAL FLEXBEAM LAMINATE IN THE TRANSLAMINAR DIRECTION AND DEMONSTRATE THAT THE SENSOR SYSTEM IS CAPABLE OF SENSING PLY DELAMINATION PRIOR TO FAILURE.