All-printed strain sensors: Building blocks of the aircraft structural health monitoring system

Characterization of all-printed strain gages to assess their suitability for structural state monitoring of large structures is presented. Strain sensor response, transverse strain sensitivity and long-term reliability are key performance parameters of printed strain sensors on flexible substrates. These key performance parameters are evaluated for inkjet and screen printed strain sensors on polyethylene-terephthalate (PET) flexible substrates. More specifically, printing characteristics of commercially available inks, gage factor of serpentine strain sensors with transverse strain and temperature sensitivity, and sensor reliability under unidirectional tensile and fatigue loading is assessed. Maximum strain to which both inkjet and screen printable formulations can be reliably used for long-term repeatable measurements is recommended based on tensile and fatigue testing. Variation in gage factor is attributed to micro- and macro-scale fracture of printed traces under mechanical loading. Substrate, ink and printing process parameters are identified to further improve strain sensing characteristics of low-cost, large area strain mapping systems. Reliable, low-cost, and large-area strain mapping systems are sought for continuous or on-demand real-time diagnosis and prognosis of complex structural components.