The electrical sensitivity of glass fiber/multiwall carbon nanotube/vinyl ester hierarchical composites containing a tailored electrically-percolated network to self-sense accumulation of structural damage when subjected to cyclic tensile loading-unloading is investigated. The hierarchical composites were designed to contain two architectures differentiated by the location of the multiwall carbon nanotubes (MWCNTs), viz. MWCNTs deposited on the fibers and MWCNTs dispersed within the matrix. The changes in electrical resistance of the hierarchical composites are associated to their structural damage and correlated to acoustic emissions. The results show that such tailored hierarchical composites are able to self-sense damage onset and accumulation upon tensile loading-unloading cycles by means of their electrical response, and that the electrical response depends on the MWCNT location.
The influence of carbon nanotube (CNT) structural damage (CNTSD) on the axial and transverse electrical conductivities of CNT/polymer composites is explored through a hierarchical multiscale modeling strategy. The composite cylinder and Mori-Tanaka's methods are used to model effective representative volume elements of CNT/polymer composites containing different fractions of defects. The axial and transverse CNT conductivities are adversely influenced by CNTSD, with the decrease being more pronounced for small radius CNTs. The predictions indicate that an 8% fraction of CNTSD decreases the axial and transverse conductivities of composites containing randomly oriented CNTs by 25-30%. Similar reductions in conductivity are found for both random and clustered damage.
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