On the dynamic acquisition of electrical signals for structural health monitoring of carbon nanotube doped composites

In the last decades, the interest on fiber reinforced polymers (FRPs) has increased due to their mechanical properties and weight saving potential. This has led to the development of novel inspection techniques, being the failure modes of composite structures complex to identify. In this regard, carbon nanotubes (CNTs) have been widely used for Structural Health Monitoring (SHM) purposes, thanks to their excellent electrical properties and piezoresistive behavior, which ensure for SHM higher sensitivities than other conventional techniques. The correlation between electrical properties and mechanical behavior on CNT doped nanocomposites is well known, and several analytical and numerical models have been proposed. However, most of these studies considered static and quasi-static load configuration, whereas the dynamic electromechanical behavior still unknown. This work aims to develop a novel technique for dynamic acquisition of electrical signals for SHM using CNTs. For this purpose, impact and vibration analyses on multiscale CNT-doped glass FRP have been performed. Besides, fatigue tests on CFRP lap joints bonded by a CNT-doped adhesive have been carried out. SHM is carried out by means of voltage measurement during the tests. A potentiometer is used to keep the current constant so that voltage variations correspond to resistance changes across the specimen. Dynamic acquisition is carried out using a high frequency acquisition system. The results of impact, vibration and fatigue tests prove the validity and applicability of the acquisition system. The electrical signals have been correlated with the mechanical behavior of the material, providing information on the system dynamic response and, simultaneously, on damage propagation mode.