Analysis and structural evaluation of seawater-aged composite tidal turbine blades using multi-walled carbon nanotubes and acoustic emission

The main objective of this research was to evaluate the piezoresistive response and mechanical performance of seawater-aged blades manufactured with glass fiber/epoxy resin incorporating multi-walled carbon nanotubes (MWCNTs). MWCNTs content was 0.75 wt. %, which was sufficient to form an electric percolation network. MWCNTs were dispersed in the fiber using the spray-coating method, allowing the entire blade outer surface to gain strain self-sensing capability. Exposure of the blades with and without MWCNT to seawater caused a moisture absorption of 1.67% and 1.56%, respectively. This caused damage such as matrix cracking, and fiber/matrix interfacial debonding. These effects were manifested by an increase in tip displacement of 13% and 1.43% in the blades with and without MWCNTs, also local deformations on the blade increased. The MWCNTs induced a positive effect on piezoresistive capability, resulting in the development of sensitivity to deformation. This showed that MWCNTs in the specified content is efficient for damage detection in complex structural components even after seawater aging while retaining maximum electrical resistance change of 0.45% and 0.26% on the tensile and compressive side, respectively. With acoustic emission (AE), it was confirmed that the presence of MWCNTs acts as toughening mechanisms reducing damage such as micro-cracks in the matrix.