Lightning strike damage detection at a fastener using self-sensing TDR of composite plate

Carbon fibre reinforced polymer (CFRP) composites structures are widely used in aeroplane structures. When a lightning strike affects fasteners or leak electric current of the lightning strike arrives at fasteners, the fasteners play serve as conducting electrodes for the CFRP plate. This current might cause complicated damage in the CFRP plate. The authors have developed self-sensing TDR to detect damage. Self-sensing TDR is used in this study to monitor lightning strike damage around a CFRP plate fastener hole. The lightning strike electric current is applied directly to a fastener. Thereafter, self-sensing TDR is applied. The lightning strike damage is investigated using cross-sectional inspection to clarify the mechanisms of the monitoring using TDR. Results show that the method can detect a 30 kA strike. Peeling of the GFRP insulator causes a characteristic impedance change, which in turn causes signal reflection of the transmission line.