Direct printing of graphene sensors for health monitoring of additively manufactured structures

Abstract

Graphene, the first discovered and most studied two-dimensional material, has gained increasing interest in the research community due to a combination of unique optical, electronic transport, and structural properties. Single layer graphene is transparent, conductive, strong and flexible. In this work the mechanical flexibility, conductivity, and solution processing of the material are coupled resulting in direct printing of reduced graphene oxide (RGO) strain sensors using 3D printer platforms. Monolayer flakes of commercially available graphene oxide dispersed in water are ink-jet printed and then reduced to form the sensors. The chemical reduction process using ascorbic acid is performed at temperatures compatible with additively manufactured thermoplastics, enabling direct sensor printing during part fabrication. The temperature dependence and piezo-resistance of the sensors are characterized and presented in terms of the variable range hopping model. Experimental results including coupon testing and full-scale flight tests are discussed.