Abstract
Strain measurements are vital for monitoring the load-bearing capacity and safety of structures. A common approach is to affix strain gages onto structural surfaces. On the other hand, most aerospace, automotive, civil, and mechanical structures are painted and coated, often with many layers, prior to their deployment. There is an opportunity to design smart and multifunctional paints that can be directly pre-applied onto structural surfaces to serve as a sensing layer among their other layers of functional paints. Therefore, the objective of this study was to design a strain-sensitive paint that can be used for structural monitoring. Carbon nanotubes (CNT) were dispersed in paint by high-speed shear mixing, while paint thinner was employed for adjusting the formulation’s viscosity and nanomaterial concentration. The study started with the design and fabrication of the CNT-based paint. Then, the nanocomposite paint’s electromechanical properties and its sensitivity to applied strains were characterized. Third, the nanocomposite paint was spray-coated onto patterned substrates to form “Sensing Meshes” for distributed strain monitoring. An electrical resistance tomography (ERT) measurement strategy and algorithm were utilized for reconstructing the conductivity distribution of the Sensing Meshes, where the magnitude of conductivity (or resistivity) corresponded to the magnitude of strain, while strain directionality was determined based on the strut direction in the mesh.
Highlights
Structures in the civil, mechanical, and aerospace industries deteriorate over time and can possibly result in unexpected failure when exposed to extreme loads
Structural health monitoring (SHM) provides techniques to streamline the measurement of real-time structural performance data [1], which can be used to identify structural degradation and provide maintenance guidance so that early signs of damage prior to structural failure can be flagged
The Raman spectrum of thermoplastic polyurethane (TPU) substrate shows the major Raman peaks of polyurethane, including the vibrational mode of aromatic rings (637 cm−1), out-of-plane bending of aromatic C-H (864 cm−1), C-O stretching of the alcohol (1183 cm−1) and the ester group (1252 cm−1), and C=C bonds in the aromatic rings (1615 cm−1) [36]
Summary
Structures in the civil, mechanical, and aerospace industries deteriorate over time and can possibly result in unexpected failure when exposed to extreme loads. Foil-based strain gages have many advantages, including high accuracy, low cost, stable performance, and an easy installation process They are discrete sensors that can only measure strains at the point of installation. High-precision data collection of large civil infrastructures requires installing dense sensor arrays Another approach, as described by Yao et al [5], is to fabricate a strain sensing sheet with a dense array of strain gages connected with full circuits. Many studies have extended the application of CNT thin films from point-based strain gages to distributed strain sensors. Whereas strain magnitudes can be estimated, strain fields (i.e., magnitudes and directionalities) cannot be reconstructed using classical EIT To address this limitation, a “sensing mesh” composed of directional elements by patterning a nanocomposite coating was developed [23]. The experimental results and plans for future work are discussed at the end
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