Identifying crumbling physical infrastructure is sometimes as difficult as rectifying it, but that process could be much easier because of a new material under development.

The material responds to mechanical stimuli by recording stress history through a luminescent effect called an afterglow, said researchers at Tohoku University. This information ends up stored for a long time, and by applying the material to the surfaces of structures, researchers can observe changes in the afterglow to determine the amount of stress the material has experienced.

“What makes our material truly innovative is that it operates without a power supply, complex equipment, or on-site observation and easily combines with IoT technology,” said Tohoku University professor and corresponding author of a study on the subject, Chao-Nan Xu.

In Japan, aging infrastructure has become a significant problem, leading to an increased demand for new diagnostic technologies that prevent accidents and/or extend the life of structures.

Mechanoluminescent materials exhibit luminescence when mechanically stimulated, and technologies such as crack detection and stress visualization have been developed by applying this material to the surface of structures. But the luminescence can only end up observed at the moment of mechanical stimulation, and it is not possible to retrieve information about past mechanical stimuli.

Schneider Bold

Furthermore, researchers have explored various materials capable of recording past mechanical loading histories. These materials typically combine stress-luminescent materials with photosensitive materials, creating a system where the material emits light in response to mechanical stress, and this light can end up preserved and later analyzed to reconstruct the stress history. However, these materials face several challenges: Complex layering structures, dark reactions, and long-term recording performance. Additionally, while certain fluorophores reveal past loading history when subjected to heat, the application ended up limited to materials capable of withstanding high temperatures.

Xu and her colleagues discovered a simple and environmentally friendly method to record stress using Pr-doped Li0.12 Na0.88 NbO3 (LNNO). This LNNO had a mechanical recording functionality, meaning it could retrieve even past stress events.

Structural health diagnosis combined with IoT technology could mean safer infrastructure relying on less people.
Source: Tomoki Uchiyama, Chao-Nan Xu et al.

To retrieve past stress information, LNNO ends up applied as a coating on the surface of an object and then irradiated with a flashlight. The afterglow produced by LNNO can end up measured using cameras or light sensors.

The study demonstrated the afterglow image matches quantitatively with the results obtained through finite element method analysis. Additionally, the research confirmed LNNO retains this stress information even after a period of five months.

“Our findings are expected to alleviate the shortage of manpower in structural diagnosis, and lower costs,” Xu said.


Pin It on Pinterest

Share This