View Video Presentation: https://doi.org/10.2514/6.2021-0402.vid
Engineering polymers combined with electrically conductive filler material offer an attractive way to design flexible and conductive nanocomposites. The resulting piezoresistivity of the composite can be utilized for strain sensing in various fields, such as health and motion monitoring but problems such as nonlinearity, viscoelasticity and plasticity in the matrix limit the stability and repeatability over loading cycles. This paper investigates the influence of viscoelasticity of the polymer matrix, beginning with a phenomenological model which is verified with a cyclic tension test. In addition, a new finite element modeling approach for piezoresistivity in polymers filled with carbon nanotubes is proposed and the effect of viscoelastic matrix properties on the resultant piezoresistive response is investigated. The piezoresistive behavior of the viscoelastic nanocomposite is studied specifically under cyclic tensile loading to elucidate the observed lack of repeatability in previous experimental studies. It is found that matrix viscoelasticity can lead to hysteresis in the piezoresistive behavior. In the case of a non-constant Poisson ratio the uniqueness of the relation between relative resistance change and corresponding strain is lost over time due to different time-dependencies of the axial and transverse strain respectively.
