Electrical Impedance Characterization for Damage Detection in Carbon Fiber-Reinforced Polymer (CFRP) Laminated Composites

Abstract

The use of modern carbon fiber-reinforced polymer (CFRP) composite materials is becoming increasingly widespread recently. However, the failure modes of such composite structures are extremely complex and, unlike metals, they may suffer significant degradation with barely visible surface damage. Since the damage may cause serious decrease in material strength and lead to catastrophic failure, the development of reliable structural health monitoring techniques is indispensable and has a tremendous impact on the life-cycle cost spent for inspection and repair.

Such techniques that are based on the change in the electrical properties of materials are promising and viable approach for maintaining the structural integrity. They are low-cost, fast, effective, and have high potential to be applicable on real structures where they can be monitored online and real-time. The topic of this PhD dissertation is mainly focused on a number of key developments and milestones towards monitoring damage in CFRP laminated composites and making electrical-based methods practical on real structures.

One of the major components of these methods is the electrode, which is the interface between the external hardware and the monitored structure. We develop a novel method for surface preparation of composite laminates for better electrode quality using pulsed laser irradiation. Further, we provide a new insight on the anisotropic behavior of the contact impedance for the electrodes on CFRP laminated composites. Another major component for achieving reliable monitoring techniques is the in-depth understanding of impedance response of these materials when subjected to an alternating electrical excitation, information that is only partially available in the literature. For more efficient electrical signal-based inspections, we investigate the electrical impedance spectroscopy response at various frequencies of laminates chosen to be representative of classical layups employed in composite structures. Finally, we use different electrodes configurations on CFRP plates applied to one side mimicking the case of real structures that is undergoing a quasi-static indentation representative of the impact load. We investigate the coupling between the electrical measurements and the type of mechanical degradation using an in-house built electro-mechanical system that measures the change in impedance and phase angle in-situ and real-time.