Piezoresistivity analyses of GNP-filled composite piezoresistor under cycling loading and correlation with the Monte Carlo percolation model

This paper presents a composite piezoresistor made of graphite paste and graphene nano-platelets (GNP). We focused on fluctuations in the gauge factor of piezoresistive composites and their dependence on the amplitude of strain cycles. A three-dimensional Monte Carlo percolation model was created. The model examines how the interactions between fillers and deformation-driven geometric changes could affect piezoresistivity. The present model of the composite piezoresistor simulates the percolation path for conduction through tunneling and capacitive interaction of particle pairs. Strain cycles of different amplitudes (loading parameter) and Poisson's ratios (material parameter) are the variables of the analyses by the model. During the loading, the algorithm simulates the cross-sectional shrinkage of the matrix given the Poisson's ratio. Shrinkage of the matrix enhances the conductance while the extension decreases it. Simulations demonstrated that the impact of the shrinkage on piezoresistivity varies with the amplitude of the strain. The results of the experimental plan for the composite piezoresistors are qualitatively in line with the simulations verifying the dominant influence of variations in extension/shrinkage amplitude as the main reason for a degrading gauge factor.