<title>Conductivity of CFRP as a tool for health and usage monitoring</title>

Abstract

Carbon fibers used in advanced composite structures are piezoresistive. These fibers are inherently sensors because of this property. Therefore, carbon fiber reinforced polymer (CFRP) composites can be considered 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 relationship between the conductivity and various usage and damage related variables need to be established. Experimental results are given to demonstrate that internal damage, such as fiber fracture and delamination, decreases the conductivity of the 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 preliminary results from the modified EIT applied to highly orthotropic (unidirectional) CFRP. These results indicate that a practical EIT has a potential of being a cost effective health and usage monitoring technique (HUMT) for CFRPs.