Influence of seawater ageing on the mechanical and damage self-sensing capability of glass fiber-MWCNT/epoxy laminates subjected to flexural loading by means of the electrical resistance approach

The self-sensing capability of multiscale composite laminates exposed to seawater ageing was investigated under monotonic and cyclic flexural loading. To this end, glass fiber fabrics were coated with multiwalled carbon nanotubes (MWCNTs) using different contents and then infused with epoxy resin under vacuum pressure. Dynamic mechanical analysis and three-point bending tests showed that the thermo-mechanical and flexural properties of composites were significantly affected due to seawater ageing as a consequence of plasticization of the matrix. However, the composites with 0.75 wt% MWCNTs help the composite to retain mayor part of its strength and strain to failure compared to the neat composite. Electromechanical tests of dry and wet composites under monotonic and cyclic flexural loading revealed that seawater ageing reduces the piezoresistive sensitivity, although the still were able to detect matrix cracking, fiber/matrix failure, delamination and fiber breakage. Cumulative counts of the residual change in resistance after each cycle were associated with plastic deformation for composites exposed to seawater ageing. Thus, the results demonstrated that electrical networks produced by spray-coated MWCNTs has good self-sensing capabilities for in situ damage detection and strain monitoring of composite laminates even after their exposition to seawater ageing, providing a feasible real- time monitoring technique of marine structures.