Resistive loss considerations in the finite element analysis of eddy current attenuation in anisotropic conductive composites

The penetration depth of eddy current is widely recognized as a guide in the nondestructive testing (NDT) methods using eddy current, which is often treated as equivalent to the skin effect depth. This paper takes the resistive loss of eddy current into account, and clearly points out the discrepancy between the two terms, especially in the case of carbon fiber reinforced plastic (CFRP) composites, which are less conductive and show strong anisotropy. Based on the theoretical modeling of skin depth and resistive loss according to Poynting's theorem, this paper adopts finite element numerical simulation to study the attenuation characteristics of current density and magnetic field strength under the conditions of different conductivity, frequency and anisotropy ratio. In addition, a set of experiments are conducted to verify the simulation results semi-quantitatively. The results show that the resistive loss dominates the eddy current attenuation in less conductive and high anisotropic composites, resulting in a frequency independent attenuation law, which is very different from skin effect. Meanwhile, the resistive loss in the orthotropic laminate is greatly reduced due to the existence of the interface between the adjacent layers. This research provides a theoretical basis for the realization of high frequency eddy current testing method for anisotropic CFRP composite materials.