Mood Ring Sensors Could Detect Damages in Failing Structures

Scientists are working with “mood ring” materials as a potential way to minimize and mitigate damage to the nation’s failing infrastructure.

The American Society of Civil Engineers has estimated that more than $3.6 trillion in investment is needed by 2020 to rehabilitate and modernize the nation’s failing infrastructure.

An important element in any modernization effort will be the development of new and improved methods for detecting damage in these structures before it becomes critical. That is where “mood ring” materials come in.

Sprinkle some nanoparticles into a batch of clear polymer resin and you get “a smart material that changes color when it is damaged or about to fail, what I call a ‘mood ring material,’” explains Cole Brubaker, a doctoral student in civil engineering and part of the team at Vanderbilt University’s Laboratory for Systems Integrity and Reliability (LASIR) developing the new sensing system.

A person with a flashlight

Smart sensing technologies are one of the hot new fields in civil, mechanical, and aerospace engineering.

These efforts have generally focused on developing networks of physical sensors that are attached to structures of interest. However, high costs and power- and data-processing requirements have hindered this approach.

The LASIR researchers are taking a different tack by incorporating fluorescent nanoparticles into the material itself that react to stress by changing their optical properties in order to create a new kind of detection system that can monitor these structures in an efficient and cost-effective fashion.

“Currently, there are two ways to keep everything from bridges to aircraft safe,” says Douglas Adams, director of LASIR and professor of civil and environmental engineering.

“One is to send people out to look at them with a flashlight. The problem with this is that it is labor-intensive and the people can’t see very small cracks when they form.

“The other is to install elaborate sensor networks that constantly look for small cracks and detect them before they grow too large. The problem is that these networks are very expensive and, in the case of aircraft, add a lot of weight. So we need to somehow change the materials we are using so they illuminate these tiny cracks.”

The team’s initial studies, published in the Proceedings of the SPIE Conference on Sensors and Smart Structures Technologies for Civil, Mechanical and Aerospace Systems, determined that adding a tiny concentration of special nanoparticles (1 to 5 percent by weight) to an optically clear polymer matrix produces a distinctive light signature that changes as the material is subjected to a broad range of compressive and tensile loads.