Characterization and modeling of in-plane mechanical and piezoresistive behavior of monolithic and sandwich composite structures

The electromechanical characterization of graphene-based multifunctional composites is important for understanding their behavior and optimizing their performance. This study focuses on the characterization and modelling of the in-plane mechanical and piezoresistive properties of rGO-coated unidirectional (UD) GFRPs. Through in-plane tensile tests at fiber orientations of 0°, 90°, and 45°, the mechanical and piezoresistive properties, including the elastic tensor, and the first order piezoresistive coefficients were obtained to calibrate the model parameters. The off-axis FCR, the fractional change in resistance measured at an angle θ to the principal material direction, and shear piezoresistive coefficient were obtained via the transformation matrix. The model employed a linear relation between the fractional change of resistivity and the mechanical stress. The UMAT-HT subroutine in Abaqus was used, considering the analogy between heat and electric conduction, to implement the model. The model was first validated using in-plane tensile tests on a series of laminates. It was subsequently used to simulate three-point bending tests on the GFRP facesheets in the sandwich structures subjected to three-point bending loads, where the bottom facesheet contained a single layer of rGO-coated fabric. The model matched experimental data in the linear region, effectively capturing the electromechanical behavior of rGO-coated GFRP at low strains, where fundamental piezoresistive mechanisms are characterized without damage complexities, crucial for sensor design and early-stage load monitoring.