Damage Quantification and Location Detection in Carbon Nanotube Enhanced Composite Panels

Epoxy resin based composite panels enhanced with carbon nanotube were subjected to damage while their electrical resistivity was monitored. The objective of the study was to utilize the composite piezoresistivity as means of damage quantification and location detection. Two different multi walled CNT-epoxy composites were manufactured for this study: one was CNT enhanced epoxy resin and the second was glass fabric reinforced CNT epoxy resin. Rectangular panels of various proportions were studied. Disks made out of copper foil were affixed to surfaces of CNT epoxy specimen, while in glass fabric CNT epoxy specimen the disks were embedded inside the samples. The disks acted as electrodes, enabling resistivity measurements using Kelvin in-line four-probe technique. The technique minimizes contact resistance between electrodes and the composite. Two different configurations of electrode network were employed to scan resistivity of entire samples. The networks included evenly spaced electrodes that spanned the entire surface of the panel, and one that covered the panel’s diagonals and its edges. To further investigate influence of electrodes distribution, finite element methods were employed to solve for the electrical potential distribution in the panel simulating various damage location and extent. Pre and post damage resistivity change was used as gauge in determining the damage location and its extent quantification. The finite element method simulation results matched experimental data closely allowing further studies with electrodes distribution, damage geometry and location. The results indicated that a relatively small spaced electrode network is capable of determining location and quantification of visible and hardly visible damages. As spacing between electrodes is increased they become less responsive to smaller damages.