a b s t r a c tIn this paper, the piezoresistive response (i.e. the change of resistance under the application of strain) of polymer composites reinforced by a novel material known as fuzzy fibers is characterized by using single tow piezoresistive fragmentation tests and modeled by using a 3D computational multiscale model based on the finite element analysis. In the characterization work, the fuzzy fiber tow is embedded in a dogbone specimen infused by epoxy, with resistance and displacement measured simultaneously to obtain its piezoresistive response. An approximately linear and stable piezoresistive response is observed within the fuzzy fiber tow region yielding gauge factors on average of 0.14. Using a 3D multiscale mechanicalelectrostatic coupled code and explicitly accounting for the local piezoresistive response of the anisotropic interphase region, the piezoresistive responses of the overall fuzzy fiber reinforced polymer composites are studied parametrically in an effort to provide qualitative guidance for the manufacture of fuzzy fiber reinforced polymer composites. It is observed from the model that the fuzzy fiber reinforced polymer composites with cylindrically orthotropic carbon nanotube interphase regions are dominated by the electrical tunneling effect between the nanotubes and can yield very large gauge factors while fuzzy fibers with randomly oriented carbon nanotubes in the interphase region yield smaller gauge factors as the material is electrically saturated by the carbon nanotubes. Finally, the modeling efforts provide plausible reasons for the observed small gauge factors in experiments in the form of a combination of high concentration randomly oriented carbon nanotube interphase regions separated by sparse nanotube regions along the fuzzy fiber length.

Hybrid piezoelectric composite structures that are able to convert mechanical energy into electricity have gained growing attention in the past few years. In this work, an energy harvesting composite beam is developed by growing piezoelectric zinc oxide nanowires on the surface of carbon fiber prior to forming structural composites. The piezoelectric behavior of the composite beam was demonstrated under different vibration sources such as water bath sonicator and permanent magnet vibration shaker. The beam was excited at its fundamental natural frequency (43.2 Hz) and the open circuit voltage and the short circuit current were measured to be 3.1 mV and 23 nA, respectively. Upon connecting an optimal resistor (1.2 kΩ) in series with the beam a maximum power output 2.5 nW was achieved.