Continuing their research on “smart skin” for structures after receiving a $300,000 grant from the National Science Foundation in 2012, affiliated faculty members of the University of Delaware, (UDEL) Erik Thostenson and Thomas Schumacher, have officially improved upon initial research and have developed a new approach to detecting hidden damage in bridges, roads, and a wide variety of different infrastructure. Four years later, the duo have coined a term for it, and they believe carbon nanotube “smart skin” is the solution to many a structural prognosis.
Thostenson and Schumacher, along with other engineers at UDEL, are actively working on the smart skin tech to monitor the structural health of all kinds of infrastructural needs. According to UDEL’s recent press release, the smart skin is made of a carbon nanotube composite.
The composite, a mechanically robust property, has the ability to adhere to almost any shape, with electrical properties that are isotropic (or in other words that are the same in all directions). The composite’s metaphorical DNA would theoretically allow the smart skin to be applied to anything, including roadways, bridges, and even other unorthodox-shaped structures, to monitor infrastructural health and deterioration.
Thostenson and Schumacher have added another technique to their initial research, however: Electrical Impedance Tomography (EIT). Broken down, EIT basically uses surface electrode measurements to create an image of the conductivity of a material or structure, according to UDEL’s press release. Taking the fundamental principle of EIT, Thostenson and Schumacher applied it to a carbon nanotube-based sensor for optimal data capture on infrastructure health.
According to Thostenson,
“While the feasibility of employing carbon-nanotube-based composites as sensors has been validated, the typical approach is to use a series of one-dimensional measurements collected from a two-dimensional sensing area. The problem is that this confines the possible damage locations to the grid points of the measurements. EIT, on the other hand, is a true 2-D algorithm.”
The idea is simpler than it sounds. When using carbon nanotube “smart skin” enhanced by EIT, Thostenson and Schumacher are really creating a 2D image of the skin’s electrical conductivity at two different times, for example, before and after an earthquake. (Engineering.com.) The 2D map is what gives engineers a true sense of the extent of structural damage resulting from said earthquake. In other words, smart skin gives a visual of a structure before and after a sustained amount of damage and has the ability to detect where the damage is via sensors and 2D imaging.
Schumacher, who envisions carbon nanotube “smart skin” as something that would be applied to in-service structures, cites some of its benefits as having the ability to be scaled up and being a “relatively” inexpensive tech to apply. No matter the scale, Schumacher says it does not require the use of many carbon nanotubes.
During their testing periods, engineers performed multiple tests on a variety of different types of simulated structural damage, including multiple square holes in the skin, a scratch to the skin to simulate a crack, and impact damage inflicted with a drop weight tester.
According to UDEL,
“ [Engineers] encountered some issues with the size of cracks being overestimated and their shapes not being well represented, [but] overall our EIT methodology was able to detect the initiation of damage well before it was visible with infrared thermography. We are in the process of making improvements to the EIT algorithm to increase its accuracy. After that, we plan to demonstrate it in the laboratory, with an aim toward scaling it up for future monitoring of real structures.”
If and how it could be applied to ongoing construction infrastructure or construction jobsites has yet to be explained or even addressed, but if carbon nanotube smart skin could be applied to in-service structures, it would be relevant to ask how they could be applied to ongoing projects, as well. But for now, Thostenson and Schumacher are strictly looking towards preventative use-cases by applying smart skin to structures to stop the collapse of bridges and general infrastructure degradation.
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