Strain sensing behaviors of epoxy nanocomposites with carbon nanotubes under cyclic deformation

The strain sensing behavior of multi-walled carbon nanotubes (MWCNT)/epoxy (EP) conductive composites subjected to tensile strain was studied in detail. With increasing the load to rupture, the responsivity (Delta R/R-0, R-0 is the original resistance, Delta R is instantaneous change in resistance) increased in a linear fashion and then began to decrease at a critical strain (epsilon(c)), which was remarkably different from the thermoplastic conductive composites only with a monotonic increase of the responsivity. It was attributed to the decrease of the nanotube contact points, the increase in the gaps before epsilon(c), and the reorientation and violent alignment of nanotubes in the zones of high local deformation (after epsilon(c)). In addition, when the extension-retraction cycles were applied, the values of max Delta R/R-0 showed a distinct tendency with different strains around the epsilon(c). These behaviors were attributed to the competition of network destruction and reconstruction during the cyclic deformation. The mechanism of this unique sensing behavior was proposed as well. (C) 2017 Elsevier Ltd. All rights reserved.