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Self-Repairing Structural Stress Sensor Developed

Inspecting bridge damage (Oregon DOT/Flickr)A research team at North Carolina State University in Raleigh has built a sensor to measure the strain in structural materials and that can fix itself if broken. NCSU mechanical engineering student Young Song and faculty member Kara Peters published their findings in the June issue of the journal Smart Materials And Structures (paid subscription required).

Sensors measure the strain in real time on buildings, bridges, airplane wings, and other critical infrastructure, and can give advance warning of issues before they become too serious a problem.  But sensors can break if subjected to too much stress, even if the material they’re measuring holds up. Where sensors are placed in difficult to reach or remote locations, they become difficult or impossible to replace.

The sensor developed by the NCSU engineers is built to repair itself if subjected to too much force or strain, by stretching and compressing along with the material it monitors. An infrared (IR) light wave runs through the sensor and detects these changes, which tells us how much strain the material is undergoing.

The sensor contains two glass optical fibers that run through a reservoir filled with ultraviolet (UV)-curable resin. The ends of the glass fibers are aligned with each other, but separated by a small gap. Focused beams of IR and UV light run through one of the fibers.

When the focused UV beam hits the resin, the resin hardens, creating a thin polymer filament that connects the glass fibers. That connected filament then creates a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.

If the sensor remains intact, the liquid resin in the reservoir remains as a liquid. If the polymer filament breaks under stress, however, more liquid resin rushes into the gap, comes into contact with the UV beam and hardens, which repairs the sensor automatically.

Read more: Sensor Gives Faster Soil Erosion Test on Structures

Photo: Oregon Department of Transportation/Flickr

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