Carbon Nanomaterial-Based Polymer Composites as Large-Area Sensors for Intelligent Structural Health Monitoring

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Carbon Nanomaterial-Based Polymer Composites as Large-Area Sensors for Intelligent Structural Health Monitoring
Kim, Sang-Woo
Park, Young-Bin
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Graduate school of UNIST
This thesis presents an experimental study on the piezoresistive behavior of carbon nanomaterial-filled polymer composite sheets and multi-scale composite for their application in large-area strain and pressure sensing of structures subjected to flexural and pressure loading. The thermomechanical viscoelastic properties were characterized by dynamic mechanical analysis, and the fracture surfaces were observed under the scanning electron microscope to analyze the morphology and carbon nanomaterial dispersion. The inherent electrical conductivity of polymer nanocomposites imparted piezoresistivity, and the potential use of the nanocomposites as piezoresistive strain and pressure sensors was demonstrated. Mutiwalled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs) with two different sizes were used as conductive fillers. Conventional solution casting and coagulation methods were employed to fabricate nanocomposite sheets, and their influences on nanofiller dispersion and variation in electrical properties were compared. Nanocomposite sheets were bonded to the surfaces of polymeric plates, which were subjected to three-point bending. The changes in resistivities of nanocomposite sheets were measured in situ, which demonstrated large-area piezoresistivity. As compared to solution casting, coagulation showed higher repeatability and lower variability in electrical conductivity. Moreover, at the same loading, MWCNTs showed the highest sensitivity among the three types of filler, whereas the smaller xGnPs showed the lowest. In addition, the sensors exhibited excellent potential for pressure sensing, suggesting a possibility for tailoring to meet pressure range and large-area structural health monitoring using multiscale carbon nanomaterial-filled polymer composites. In addition to nanocomposites with randomly oriented MWCNTs, those with aligned MWCNTs were fabricated using a specially designed single-screw extruder. When bonded to a substrate that underwent flexural loading, the aligned nanocomposite sheets exhibited anisotropic piezoresistive behavior, that is, different sensitivities in directions parallel and perpendicular to the loaded direction, which suggested a useful application in strain sensing with preferred orientations.
School of Mechanical and Advanced Materials Engineering
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