Strain Sensing and Structural Health Monitoring Using Nanofilms and Nanocomposites

Structures can develop damage throughout their operational lifetimes, typically due to excessive loading, harsh environmental and loading conditions, and long-term deterioration. To evaluate the condition of structures, conventional structural health monitoring (SHM) systems employ discrete sensors such as accelerometers, displacement transducers, and strain gages, among others. Although these sensors provide quantitative data that can be correlated to structural behavior, it remains challenging to accurately detect and locate damage effectively. This chapter presents a summary of recent developments in using carbon nanotubes for the design of nanocomposite thin films that are sensitive to damage (specifically strain). In particular, the chapter presents in great detail the design and strain-sensing properties of three different types of nanofilms: buckypaper, layer-by-layer, and spray-coated films. In addition, nanofilms were also deposited on aggregates, and these nanofilm-coated aggregates were used for casting multifunctional cementitious composites that could bear loads while their electrical properties were sensitive to damage. The chapter also includes a brief discussion of the electrical impedance tomography (EIT) algorithm, which enables one to estimate the spatial conductivity (or resistivity) distribution of a conductive body. When applied to nanofilms or nanofilm-enhanced cementitious composites, it was shown that this technique allowed for the detection of damage severity and the identification of damage location in a precise and efficient manner. The chapter concludes with a summary of other avenues of research and a discussion of future research challenges that need to be addressed in order for this technology to be adopted for real-world SHM applications.