MICROWAVE TESTING OF CARBON FIBERS

THE GOAL OF THIS EXPLORATORY RESEARCH IS TO DEMONSTRATE THE FEASIBILITY OF USING INNOVATIVE MICROWAVE SENSORS AND MEASUREMENT TECHNIQUES TO NONDESTRUCTIVELY MONITOR VARIATIONS IN THE ELECTRICAL CONDUCTIVITY OF SINGLE AND MULTIFILAMENT CARBON FIBERS ON-LINE IN REAL TIME. THE CONDUCTIVITY IS OF DIRECT INTEREST IN END USE APPLICATIONS INVOLVING ELECTRICAL CONDUSTORS AND ELECTROMAGNETIC SHIELDING. BUT THE ELECTRICAL CONDUCTIVITY IS ALSO A SENSITIVE DIAGNOSTIC INDICATOR OF THE TENSILE MODULUS AND THERMAL CONDUCTIVITY. AT MICROWAVE FREQUENCIES, LOCAL INDUCTIVE COUPLING TO THE FIBERS BECOMES FEASIBLE, THEREBY AVOIDING PROBLEMS ASSOCIATED WITH CONDUCTIVE CONTACT TO THE FIBERS AND WITH FIBER TREATMENTS. THIS OPENS THE POSSIBILITY OF ON-LINE REAL-TIME MONITORING OF THE ELECTRICAL AND THERMAL CONDUCTIVITIES, AS WELL AS THE TENSILE MODULUS. THESE SENSORS ARE EXTREMELY SENSITIVE TO SMALL VARIATIONS IN THE CONDUCTIVITY, AND CAN BE DESIGNED FOR USE OVER DYNAMIC RANGES COVERING SEVERAL ORDERS OF MAGNITUDE CHANGE IN THE CONDUCTIVITY. THEY CAN BE USED IMMEDIATELY AFTER CARBONIZING, AFTER SURFACE TREATMENT, AFTER EPOXY SIZING OR BEFORE WEAVING AND LAYUP BY THE END USER.