Department: Structural Engineering
Research Institute Affiliation: Agile Center for Extreme Events Research (CEER)
Faculty Advisor(s): Kenneth J. Loh

Primary Student
Email: s8gupta@ucsd.edu
Phone: 858-822-0431
Grad Year: 2018

Aerospace, civil, marine, and mechanical structures are susceptible to damage due to degradation, excessive loading, and extreme events. Structural health monitoring (SHM) is crucial for ensuring safety, reliability, and overall performance. While visual inspection and nondestructive evaluation technologies are employed in practice, they suffer from limitations such as accuracy, precision, and the ability to identify damage location, particularly if damage is hidden beneath structural surfaces. Thus, the objective of this research is to develop nano-engineered structural materials that are endowed with damage sensing properties and, when coupled with tomographic algorithms, are able to use limited measurements for identifying the severity, location, and type of damage. Three examples are showcased here. First, multifunctional carbon nanotube (CNT)-polymercoatings were developed, and they can be spray-coated (like paint) onto metallic, cementitious, and fiber-reinforced polymer (FRP) composite surfaces. The nanocomposite was designed such that its conductivity changed in response to deformation or corrosion, depending on its design and constituents.In addition, an electrical impedance tomography (EIT) algorithm was implemented, which used boundary electrical excitations and measurements for estimating the coating?s spatial conductivity map. Since the coating?s conductivity at every location is sensitive to damage,the resulting EIT maps directly enable damage visualization to show the severity and location of distributed damage. Lab tests conducted on metallic and FRP structural elements validatedtheir applicability for SHM of aerospace, marine, and civil structures. Second, besides applying coatings onto surfaces, they were integrated with concrete for scaling up the technology for large-scale civil structures. The approach was by modifying cement-aggregate interfaces or interfacial transition zones in concrete with CNT-polymer thin films. It was found from concrete cylinder compression and beam flexural tests that film-enhanced concrete exhibited improved mechanical performance as well as self-sensing properties. The modified interfaces allowed electrical current to propagate throughout the bulk material, which permitted EIT spatial conductivity mapping. Damage detection tests showed that EIT was able to resolve the severities and locations of damaged induced by cracks and drilled holes of different depths. Lastly, following the same principles that govern EIT, a non-contact, nondestructive damage assessment technique was implemented. Instead of applied electrical current, different patterns of electrical field were propagated over a pre-determined sensing space. Using boundary measurements of electrical response, the permittivity distribution within that space could be reconstructed. Highly localized damage due to permittivity changes (e.g., voids in FRPs, corrosion of metals, and manufacturing defects) could be accurately detected.

Industry Application Area(s)
Aerospace, Defense, Security | Civil/Structural Engineering | Materials

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