A new material developed by Tohoku University records and stores stress history in structures through a luminescent effect, offering an innovative solution to monitor aging infrastructure without needing power or complex equipment.
Identifying deteriorating infrastructure can be as challenging as fixing it. However, researchers at Tohoku University have made this process easier with the development of an innovative new material.
The material responds to mechanical stimuli by recording stress history through a luminescent effect called an afterglow. This information is 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 is easily combined with IoT technology,” points out Tohoku University professor and corresponding author of the study, 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 and Challenges
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 be observed at the moment of mechanical stimulation, and information about past mechanical stimuli cannot be retrieved.
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 be 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 has been limited to materials capable of withstanding high temperatures.
Breakthrough With LNNO
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.
To retrieve past stress information, LNNO is applied as a coating on the surface of an object and then irradiated with a flashlight. The afterglow produced by LNNO can be measured using cameras or light sensors. The study demonstrated that the afterglow image matches quantitatively with the results obtained through finite element method analysis. Additionally, the research confirmed that 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,” adds Xu.
Reference: “Direct recording and reading of mechanical force by afterglow evaluation of multi-piezo mechanoluminescent material Li0.12Na0.88NbO3 on well-designed morphotropic phase boundary” by
Tomoki Uchiyama, Taisei Atsumi, Koki Otonari, Yuki Fujio, Xu-Guang Zheng and Chao-Nan Xu, 25 April 2024, Applied Physics Letters.
DOI: 10.1063/5.0209065
Also involved in the study was Tomoki Uchiyama, an assistant professor at Tohoku University, along with undergraduate students Taisei Atsumi and Koki Otonari. Yuki Fujio from the National Institute of Advanced Industrial Science and Technology and Xu-Guang Zheng from Saga University and Tohoku University.
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