Contract number : FA 2386 - 09 - 1 - 4038 Research title : Damage detection of laminated CFRP structures using electric pulse wave transmission

Carbon Fiber Reinforced Polymer (CFRP) laminates are applied to many aerospace structures. For these laminated CFRP structures, it is quite difficult to detect internal damage such as delamination, matrix cracks, and local fiber breakages. Carbon fibers are adopted as reinforcement in CFRP and it is an excellent electric conductor at the same time. The carbon fiber has been used as a strain sensor for decades. Electrical resistance change measurement has advantages over other methods of structural health monitoring. The electrical resistance change method, however, requires a lot of electrodes on the target CFRP structures to measure electrical resistance change at multiple segments of the CFRP structure. The present approach adopts a pulse electric wave that transmits in a CFRP plate structure. CFRP has high conductivity in the fiber direction and the very low conductivity in the transverse direction. A pulse wave transmits in the carbon fiber to the end of the fiber. When fiber damages occur, the pulse wave is reflected by the damage. By the reflected pulse wave, we can detect the damages in the CFRP structures. A parallel plate cathode and a directional coupler were used here. The proposed new method was adopted for the unidirectional CFRP in the present study. Several modifications to obtain high performance of the reflected pulse wave were performed here. As a result, the method was experimentally proved to be effective for detections of carbon fiber damages.