Electrical measurements of carbon nanotube multiscale GFRPs have been carried out for the monitoring of low velocity impact dynamics. To achieve that purpose, several plates have been fed by a power supply and a high frequency acquisition system has been used. Electrical measurements show that there is an initial decrease of electrical resistance due to plate compression, followed by an increase due to tunneling effect of carbon nanotubes. Finally, the effect of mechanical rebound is correlated to drop rise cycles of the electrical resistance. The sensitivity of the measured signals is also correlated with the impact energy and the electrodes disposition. Thus, the proposed method proves the validity and applicability of carbon nanotubes to characterize the low-velocity impact dynamics of a composite laminate.
SHM is defined as the process of acquiring and analyzing data from on-board sensors to evaluate the health of a structure. Most common damages on aircrafts are local cracks and delaminations, that do not change strongly the overall strain field, but that will act as the failure initiation point. Fiber optic sensors act primarily as strain sensors, so unless damage happens very close to the sensor location, it may go undetected. Currently, three main approaches for detecting damage from strain measurements are being investigated: 1) High resolution fibre optic distributed sensing (OFDR Rayleigh scattering). 2) Strain mapping with a dense network of sensors. Statistical analysis tools, like PCA, have been successfully used. 3) Hybrid FBG/PZT systems. FBGs must detect the ultrasonic elastic waves.