View Video Presentation: https://doi.org/10.2514/6.2022-1116.vid
Electrically conductive polymer nanocomposites, consisting of an engineering polymer and an electrically conductive filler on the nanoscale, e.g. carbon nanotubes, offer vast design freedom for strain sensing applications. The resulting piezoresistivity of the nanocomposite has been successfully utilized in various fields, such as health and motion monitoring, but polymer composites suffer from hysteresis and drift under cyclic and long-term measurements respectively. Viscoelasticity of the polymer was identified as one of the underlying causes for hysteresis and drift, but the effect is not well understood. This paper investigates the influence of multiaxial linear viscoelasticity of the polymer on piezoresistivity. First, a review of uniaxial and multiaxial viscoelasticity is provided with regard to experimental limitations. Second, a multiaxial viscoelastic master curve is created with the time-temperature superposition principle from a series of tensile creep tests. Third, a recently developed finite element model for piezoresistivity in carbon nanotube/polymer composites is employed and viscoelasticity of the polymer matrix is incorporated. The piezoresistive behavior of the viscoelastic nanocomposite is studied specifically under stress relaxation to elucidate the macroscale resistance change originating from the nanoscale tunneling effect while the principal strain is maintained. Results show that matrix viscoelasticity by itself causes an electrical resistance relaxation during stress relaxation due to an increasing compaction of the conductive network in the transverse direction.
