Large area distributed strain monitoring using patterned nanocomposite sensing meshes

The ability to measure, monitor, and prevent catastrophic failure has made structural health monitoring crucial for aerospace, civil, and marine structures. Spatial strain sensing is necessary for quantifying distributed damage in structural systems. Previous studied that coupled electrical impedance tomography (EIT) algorithms with piezoresistive coatings opened up vast opportunities for distributed strain sensing. However, these approaches could not extract strain directionalities from the reconstructed EIT conductivity maps, and sensing resolution remained rather low. Therefore, this study aims to develop next-generation "sensing meshes" capable of resolving both spatial strain magnitudes and directionalities for distributed strain field monitoring. The approach is to design and fabricate piezoresistive graphenebased thin films and then patterning them to form a grid or mesh. The nanocomposite grid lines were designed to be of a high-aspect ratio so that each grid element could sense distributed strain along its length and direction. Various sensing mesh specimens were fabricated, and a load frame was employed to strain them in a controlled manner. Similar to conventional EIT, boundary voltage measurements were acquired when electrical current was applied between two boundary electrodes. The boundary voltage dataset was then used as inputs to the EIT inverse algorithm to reconstruct the conductivity distribution of the sensing mesh. For verification, these experimental results were compared to an elastic finite element model subjected to the same strain states. Good agreement between the experimental tests and numerical simulations were observed, thereby demonstrating the potential of this technology for distributed strain field monitoring.