Damage detection in CFRP by electrical conductivity mapping

Carbon-fiber-reinforced polymer (CFRP) composites derive their excellent mechanical strength, stiffness and electrical coductivity from carbon fibers. The mechanical deformation acid electrical resistance are coupled in these fibers that make them inherently sensors. Thus CFRPs can be considered as a self-monitoring material without any need for additional sensing elements. However, for this to become reality the conductivity map of the entire structure needs to be constructed and the relationships between the conductivity and various use- and damage-related variables need to be established. Experimental results demonstrate that internal damage, such as fiber fracture and delamination, decreases the conductivity of composite laminates. In general, the information about the damage size and position can be obtained by utilizing electrical impedance tomography (EIT), but the traditional EIT is not capable of extracting this information when the medium possesses highly anisotropic electrical conductivity. Above a certain level of anisotropy, it is advantageous to modify the traditional EIT. This paper presents a method of extracting the damage size and position for highly orthotropic (unidirectional) CFRPs. The results are obtained without the need for complex calculations, thus enabling damage detection in real time. Experimental observations indicate that a practical EIT has a potential of being a cost-effective health and usage monitoring technique (HUMT) for CFRPs. (C) 2001 Elsevier Science Ltd. All rights reserved.