Abstract
Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. However, the CFRP structures are easily damaged by impact loading. It is quite difficult to detect internal damages caused by impacts by visual inspection. In the present paper, self-sensing time-domain reflectometry (TDR) is proposed as a damage detection method for large CFRP structures. In the TDR, a set of high-frequency impulse signals is applied to a structure and damage location is calculated from difference in time of arrival between an input signal and reflected signal from the structure end or the damage. The experiment using TDR is conducted in this paper. It is the experiment for detection of impact damage in a long quasi-isotropic CFRP (1600 mm^L×200 mm^W, [0/+45/0/-45/90/+45/0/-45/ 90]s) in the fiber direction. Microstrip Line (MSL) structure is utilized for damage detection of CFRP. It is the structure which is arranged the dielectric (Glass fiber reinforced polymer, GFRP) on CFRP and the five copper lines as waveguide of electric pulse on the top. Copper meshes used for lightning protection in composite aircraft are arranged on copper lines of MSL which are not the target for measurement during TDR measurement in order to investigate that TDR could detected impact damage even if copper meshes exist around MSL. As a result, the experiments indicated that the TDR could detect impact damage on the copper line of MSL which could be used as lightning protection system.
