Optical Technology Center develops new fiber optic systems for structural health testing in extreme environments

Now, at the Virginia Tech University in Virginia, researchers at its Optical Technology Center have developed a new type of optical fiber technology that is expected to improve the ability to monitor structures under extreme conditions. Specifically, the new system is designed to sense some environmental factors ...

Structural health monitoring systems traditionally use piezoelectric transducers, a device that converts pressure to voltage signals. These sensors usually have good reliability, except in corrosive environments or at high temperatures, ie above 300 degrees Celsius. Therefore, in these harsh environments, their accuracy and practicability are limited.

Now, at the Virginia Tech University in Virginia, researchers at its Optical Technology Center have developed a new type of optical fiber technology that is expected to improve the ability to monitor structures under extreme conditions. Specifically, the new system is designed to sense environmental factors such as strain, temperature and deformation in the structure, as well as cracks in the appearance of the structure.

"Fiber components have proven to work reliably at very high temperatures," explains Hu Chennan, the lead author of the paper, as the fiber material is made of simple quartz fiber. "This development of fiber optic technology will greatly enhance the monitoring of structural health conditions in critical infrastructure such as modern superheaters or nuclear power plants in critical environments and will help ensure continuous operation of power plants and help prevent possible The structural failure that occurred, to prevent catastrophic consequences. "

Together with Hu, there is Yu Zhihao, the co-author of this dissertation, a postdoctoral fellow and Wang Anbo, the director of the center. This technique is described in the Optical Journal of the American Optical Society.

The system uses two optical fiber serial connection of multiple optical fiber lossless sensing unit, and the sensing unit attached to the surface of the structure for sensing and monitoring. Each sensing element includes a sounding unit located within a fiber optic cable, and an acoustic detection unit, also within a fiber optic housing.

When excited by a laser pulse transmitted by an optical fiber, the sound generating unit generates an acoustic vibration wave propagating in the structure. These vibrations are received by the sounding unit, a device called a fiber Bragg grating (FBG) which forms the acoustic features of the structure. In addition, fiber gratings also provide structural strain and temperature information.

"By analyzing the structure's acoustic signature and the additional information features obtained from the fiber grating, we can monitor multiple environmental parameters simultaneously," Hu explained. This is based on the theory of a paper published in the Optical Letters in 2009.

In the study described in this paper, monitoring experiments were performed on an aluminum block with changes in temperature, strain and thickness, and the appearance of an artificial crack. The document does not prove monitoring at high temperatures, "but we believe the system can work at high temperatures, ie replacing low temperature epoxy with high temperature adhesives, and we have obtained promising high temperature monitoring results," Nonsense.

One possible application of distributed sensing systems, researchers say, is on the outer surface of a so-called P91 steel pipe, which is widely used in the power industry.

"These pipes are commonly used to transport corrosive high-temperature, high-pressure steam," Hu explained. However, the integrity of these pipes and other critical materials can deteriorate in the power generation system and over time the rate of deterioration is likely to pick up rapidly as the operating temperature of the system is pushed higher, so the monitoring of these materials becomes More important. "

The sensor system can also be used on an aircraft to monitor the health of multi-point structures in gas turbine engines or other critical components, the researchers said.

Next, the team plans to develop a compact and powerful sensor system that will be field-tested in a real power plant to suit its commercial use, Hu explained.