Fabrication, polarization, and characterization of PVDF matrix composites for integrated structural load sensing

The focus of this work is to evaluate a new carbon fiber reinforced composite structure with integrated sensing capabilities. In this composite structure, the typical matrix material used for carbon fiber reinforced composites is replaced with the thermoplastic polyvinylidene difluoride (PVDF). Since PVDF has piezoelectric properties, it enables the structure to be used for integrated load sensing. In addition, the electrical conductivity property of the carbon fabric is harnessed to form the electrodes of the integrated sensor. In order to prevent the carbon fiber electrodes from shorting to each other, a thin Kevlar fabric layer is placed between the two carbon fiber electrode layers as a dielectric. The optimal polarization parameters were determined using a design of experiments approach. Once polarized, the samples were then used in compression and tensile tests to determine the effective d₃₃ and d₃₁ piezoelectric coefficients. The degree of polarization of the PVDF material was determined by relating the effective d₃₃ coefficient of the composite to the achieved d₃₃ of the PVDF component of the composite using a closed form expression. Using this approach, it was shown that optimal polarization of the composite material results in a PVDF component d₃₃ of 3.2 pC N^-1. Moreover, the Young's modulus of the composite structure has been characterized.