Printed Carbon Resistive Strain Sensor for Structural Health Monitoring

Structural health monitoring (SHM) of large-scale engineering structures increasingly relies on flexible hybrid electronics (FHE) systems to enable conformal, lightweight, low-cost and scalable sensing solutions capable of sustained performance under repeated mechanical stress. This work presents the design, fabrication, and characterization of printed carbon-based resistive strain sensors for crack detection application. Serpentine trace test coupons were fabricated by dispensing carbon-based conductive pastes onto polyimide and PET substrates and evaluated under tensile loading and extended fatigue cycling with real-time four-wire resistance monitoring. Of ten conductive inks screened, two carbon pastes on polyimide demonstrated the most favorable balance of printability, gauge factor and resistance drift (5% for the best configurations). Extended fatigue testing to 15,000 cycles confirmed stable gauge factors of 4–5.7 with no significant degradation. Thin lamination encapsulation outperformed dielectric encapsulation in signal stability, with resistance drift as low as 1.4% compared to up to 15% for dielectric samples. Thermo-pressing post-processing further reduced baseline resistance by over 50% and improved gauge factor consistency, lowering standard deviation from 0.87 to 0.37. These results establish printed carbon resistive sensors with thin lamination and thermo-pressing as a scalable, low-cost platform for flexible structural health monitoring.