Damage detection in CFRP by electrical conductivity mapping

Carbon-fiber-reinforced polymer (CFRP) composites derive their excellent me chanical 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 st ructure needs to be constructed and the relationships between the conductiv ity and various use- and damage-related variables need to be established. E xperimental results demonstrate that internal damage, such as fiber fractur e and delamination, decreases the conductivity of composite laminates. In g eneral, 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 hi ghly anisotropic electrical conductivity. Above a certain level of anisotro py, 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 comple x calculations, thus enabling damage detection in real time. Experimental o bservations indicate that a practical EIT has a potential of being a cost-e ffective health and usage monitoring technique (HUMT) for CFRPs. (C) 2001 E lsevier Science Ltd. All rights reserved.