Damage monitoring in nanoenhanced composites using impedance spectroscopy

In the present work we propose a novel approach for damage detection in non-conductive composites via Impedance spectroscopy (IS). For that purpose carbon nanotube (CNT)-modified epoxy resins and their hybrid composites subjected to different levels damage via hygrothermal exposure and mechanical step loading respectively. The IS measurements were performed using a simple two-electrode method with no specialized modifications. The Electrode polarization (EP) effect which normally impedes impedance measurements for dielectric materials have been addressed via the incorporation of the conductive nanophase which tailors conductivity to the desired levels. The presence of CNTs shifted the electrical response of the material to AC towards higher frequencies resulting in a higher signal-to-noise ratio. The AC frequency response of the composites revealed a direct correlation between the level of damage as verified by optical microscopy and the hysteretic behaviour of the studied materials. Induced damage has been successfully modeled using a simple RC circuit in parallel providing an insight of the internal state of the material.