Next-Generation Non-contact Strain-Sensing Method Using Strain-Sensing Smart Skin (S4) for Static and Dynamic Measurement

In this study, the next-generation non-contact strain-sensing method with the Strain-Sensing Smart Skin (S4), based on measuring strain-induced shifts in the emission near-infrared fluorescence spectra of single-walled carbon nanotubes (SWCNTs) embedded in a thin film (S4) on the surface of the specimen is presented. S4 is a direct sensing method. In the existing material and structural testing, strain mapping is performed using Digital Image Correlation (DIC), which is an indirect method that compares images of undeformed and deformed configurations to calculate strain maps. The results of the finite element method (FEM) analysis, measured S4, and DIC strain maps are presented. For static loading, the raster-scanned strain maps generated from S4 demonstrate more accurate strain maps (especially hotspots and stress/strain concentration areas with steep strain gradients), than DIC, when tested on acrylic specimens. Further, strain maps obtained from finite element analysis matched more closely with S4 as compared to DIC, demonstrating the superior quality of static strain mapping using S4. For dynamic loading, the single point S4 measurement also agreed well with the strain gauge at 3 Hz. The reference-free direct strain-sensing capability of S4 during static and dynamic loading presented in this study demonstrates the significant potential of the novel method as a promising next-generation strain measurement technology for field applications of structural non-destructive evaluation and structural health monitoring.