Damage Quantification in Electrically Conductive Composite Laminate Structures

摘要

This paper presents an approach for assessing damage in electrically conductive reinforced polymers that is based on feature changes in the current flow and overall conductivity of the structure under damage conditions such as internal fiber fracture and delamination cracks. Through monitoring the integral resistance of the structure, changes in a selected feature set related to the inherent conductivity is directly correlated to the location and extent of the damage present. The technique employed uses a relatively simple analysis process and requires a network of electrodes to apply electric potential to the external surfaces of the structure. A Finite Element Model (FEM) of the structure enables the calculation of the predicted electrostatic environment inside multidirectional laminates with highly anisotropic plies. Orientation of the electrically conductive fibers is accounted for by introducing the corresponding anisotropic conductivity tensor for each ply. Multiple parametric analyses of unidirectional and multidirectional laminates show significant influence of anisotropy on current flow trajectories, and overall resistivity. The influence of holes, cracks and delaminations have been determined by measurements and compared with the theoretical FEM model results. A comparison of the potential and current distribution for damaged and undamaged laminates shows a substantial difference around the damaged area, as well as the difference in a set of overall resistivities. The difference induced by small cracks produces subtle deviations in measurements. The corresponding sensitivities are used to deduce the requirement precision of the measurement instrument, which forms the basis of a damage detection system. Finally, selected experimental results are provided that verify the basis of the model- based analysis technique presented.