Midea develops fiber laser sensor for structural monitoring

[China Instrument Network Instrument R&D] Recently, researchers from the Department of Optical Science and Materials Science of the United States Naval Research Laboratory (NRL) have successfully used distributed feedback fiber laser acoustic emission sensors to detect cracks in riveted lap joints. The resulting acoustic emission signal.

Defect detection of riveted lap joints using fiber laser acoustic emission sensors: This figure shows the initiation and growth of cracks between rivets in the upper left lap joint. The fiber laser sensor is mounted on the detection structure and measures the acoustic emission signal generated by the crack defect. The software records it as an acoustic event (AE event).

“We have researched an on-site structural health monitoring (SHM) automation system that can effectively monitor key structural parameters such as temperature, internal stress, impact, and crack defects; and can reliably ensure that structural damage conditions reach a critical level It was detected to increase structural safety and speed of information feedback while reducing operational costs for the naval platform,” said Dr. Geoffrey Cranch, a physicist from the Department of Optical Sciences. “At present, there is no U.S. service that uses in-situ technology to manage it. Equipment structure health." To achieve this goal, the most critical is the need for a sensor that can detect near-real-time acoustic emission signals associated with the appearance and growth of defects such as cracks. Moreover, these sensors must be smaller, lighter, easier to handle, and have comparable or increased sensitivity than most existing electronics. The ultimate goal is to make these components have a small system footprint and high reliability.

Part of the research funding provided by the Department of Materials Science of the US Naval Research Office (ONR), NRL is developing a laser sensor whose width is about the width of a human hair filament. During the test, the researchers installed a distributed feedback fiber laser acoustic emission sensor in a set of aluminum rivets and measured a 0.5 MHz bandwidth acoustic emission signal generated in a two-hour accelerated fatigue test. An equivalent electrical sensor measures.

This embedded sensor can be used to resolve the periodic “fretting” acoustic events of the rivets and to detect acoustic emission information from cracks. Time-lapse imaging of the lap will allow the observed fracture to be correlated with the measured signal.

In addition to crack detection, this fiber laser sensor can also effectively detect impact damage effects. In addition, the sensor has the potential to integrate with existing fiber strain and temperature sensing systems. This provides a multi-parameter sensing capability to meet the operational safety requirements of the field structure health monitoring system. It is worth mentioning that this will also significantly reduce the overall cost.

"Our research team has demonstrated the ability of this fiber laser sensing technology to detect crack-generated ultrasonic acoustic emission signals in a simulated fatigue environment," said Cranc. "The novelty of this research is mainly fiber laser transmission. Sense technology and its application methods etc."

Acoustic signals generated from flaws such as cracks can also be measured using piezoelectric sensors, and this technique also facilitates existing fault prediction work. However, piezoelectric sensing technology is not very practical in many aspects due to its large device size and limited distributed monitoring capabilities.

It is emphasized that this technology will likely be applied in many areas other than the military field. "Our research and application focus is on defenses such as the Navy, such as aircraft, ships, and submarines. If some bridges or building structures contain critical components that are vulnerable to fatigue and failure, then this technology can also be applied to these. Continuous monitoring of the structure."

At present, no other intrinsic optical fiber sensor can match the performance achieved by the fiber laser acoustic emission sensor in the laboratory. Compared with some existing electrical sensing technologies, fiber laser sensors have been shown to have comparable or even higher acoustic emission signal sensitivity. The system has been able to integrate multiple fiber laser sensors into a bundle of fibers. At present, the work of the research team is mainly to understand and explain these acoustic emission data to calculate some useful index parameters (such as failure probability, etc.). The direction of future improvement is mainly focused on the realization of phased array beamforming technology to effectively determine the specific location of cracks and other defects.

(Original title: US Military First Fiber Laser Sensor for Structural Health Monitoring)

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