What good is an instrument if it breaks while in use? As anÂ article inÂ Plastics Today reports, researchers fromÂ North Carolina State University (NCSU) have made a new type of sensor based on polymers that can fix itself if it literally cracks under pressure.
Engineers face a vexing problem when using conventional sensors for measuring the strain, or forces, experienced by materials. The sensors, while measuring the strain in structures like airplanes or buildings, can break under stress and stop working.
To address this issue, the NCSU researchers came up with a new type of sensor that repairs itself. The ability to fix itself lets the sensor keep collecting data from structures about the strain they experience during unanticipated events, such as earthquakes and explosions.
The sensor contains two glass optical fibers that run through a reservoir filled with a ultraviolet (UV)-curable resin. The ends of the glass fibers are aligned with each other, but separated by a small gap. Focused beams of infrared and UV light run through one of the fibers, and when the UV beam hits the resin, the plastic hardens, creating a polymer filament that re-connects the glass fibers and creates a closed circuit for the IR light. The rest of the resin in the reservoir remains in liquid form, surrounding the filament.
The leftover liquid resin is critical in the sensor’s design. If the polymer filament cracks and breaks under stress, the remaining resin flows in and fills the gap. Under the UV beam, the liquid resin then turns solid and fixes the sensor.
Peters described to Plastics Today the situations in which the sensors would be useful:
‘Events that can break a sensor, but don’t break the structure being monitored, are important,’ Peters said. ‘These events could be bird strikes to an airplane wing or earthquake damage to a building. Collecting data on what has happened to these structures can help us make informed decisions about what is safe and what is not. But if those sensors are broken, the data aren’t available. Hopefully, this new sensor design will help us collect this sort of data in the future.’
Source: “UV-curable plastic makes self-healing sensor possible,” Plastics Today, 06/13/11
Source: “Aerospace Research @ NC State’s Centennial Campus,” YouTube
Rajendrani "Raj" Mukhopadhyay is a science writer and editor who contributes news stories and feature articles on scientific advances to a variety of magazines. Raj holds Ph.D. in biophysics from Johns Hopkins University.