Quantitative evaluation of the electrically conductive internal network in CFRP composites

The electrical resistance change of CFRP composite under mechanical loading condition can be used as an effective parameter to evaluate the accumulated internal damage. The internal electrically conductive network, which is constructed by the contacts between conductive carbon fibers, is very important in correlating the resistance change to mechanical damage state. The electrical ineffective length δ_ec, the mean distance between adjacent contact points, can be used as a useful parameter to evaluate the internal conductive network. In this study, a new methodology for the evaluation of the internal conducting network is proposed. For this purpose, the electrically anisotropic characteristics of the CFRP composite are measured using the DC 4 probe and the DC 6 probe methods and the values of δ_ec are estimated using the mechanical tensile test for various fiber volume fractions. Based on the experimental results, the empirical relationship between the electrical anisotropy and δ_ec is established. We also conduct the DC network circuit analysis using Kirchhoff's rule and the Monte Carlo simulation of the contact point distribution, and calculate the δ_ec for various contact configurations. By comparing the analytical and experimental results, the distribution configuration and the number of contact points, which constitute the internal electrically conductive network of CFRP composites, can be evaluated quantitatively.