A Comparative Study on the Pattern Effect of Screen-Printed Carbon Nanotubes/Cellulose Nanocrystals Strain Sensors

One-step fabrication technique for printing piezoresistive strain sensors on glass fiber-reinforced polymers (GFRPs) using a scalable screen-printing method was demonstrated. Using cellulose nanocrystals to disperse carbon nanotubes (CNTs) in an aqueous medium, various inks were prepared and tested for shear thinning, thixotropic, and viscoelastic properties. Turning the ink consistency from liquid-like to paste-like led to printability on the surface of GFRPs. The electrical stability of the printed sensors was evaluated by testing different thicknesses under various conditions. Results showed that electrical stability depended on the number of printed layers and applied voltage. Furthermore, the influence of pattern design on the sensors' electromechanical performance was studied for line, grid, o-line, and omnidirectional patterns. During cyclic tensile loading, the pattern geometry affected both reliability and sensitivity, whereas linearity remained unaffected. Reliability and sensitivity demonstrated strain-dependent behavior, while linearity improved due to additional linear piezoresistive contribution from individual CNT-bridging. Additionally, the omnidirectional sensors were printed at three different angles and subjected to cyclic loading, revealing their ability to detect strains from multiple directions. It was also visually demonstrated that the sensors can detect tensile and compressive strains resulting from bending, showing good potential for structural health monitoring of advanced structures.