A novel fiber optic bolt loosening monitoring sensor is proposed and applied to an experimental model of aircraft lug assemblies. The lug assembly is fabricated with a stainless steel lug, a composite sandwich panel, and 10 carbon-steel bolts, nuts, and washers. The bolt loosening monitoring system is configured with a single-mode fiber and an optical time-domain reflectometer. Sections of the single-mode fiber line are mounted on the respective 10 bolt/nut joints and function as bending sensor nodes to detect bolt loosening events. Then, the other end of the single-mode fiber is connected to the optical time-domain reflectometer, to measure optical loss in the backscattering light attenuation trace, induced by the macro-bending of the sensor nodes. In addition, the bolt loosening angle and locations can be determined, by analyzing the optical time-domain reflectometer traces. The experiments for multi-bolt monitoring demonstrate that the single single-mode fiber line incorporated with optical time-domain...

A novel fiber optic bolt loosening monitoring sensor system for aircraft bolt joints

Bolted joints of aircraft lug assembly play an important role in connecting the wing and fuselage of an aircraft structure. Generally, the bolted joints get loosened because they are frequently exposed to the dynamic loads induced when an aircraft is in service. For this reason, it is important to monitor the condition of the bolted joints to avoid any critical defect that will lead to any risk in human life. However, it is difficult to conduct the bolted joints’ loosening inspection by an operator. In past few decades, optical fiber based sensor has been widely used due to its advancement over a conventional piezoelectric (PZT) sensor, especially due to its small size and light weight. With regard to this, a loosening monitoring of bolted joints using optical fiber bending sensor for aircraft lug assembly is proposed in this paper. The lug assembly specimen, which consists of a stainless steel lug, CFRP/Nomex honeycomb sandwich panel, carbon-steel bolt, nut and washer, and the monitoring system, which consists of a single mode fiber with ten optical fiber bending sensor nodes and an Optical Time-domain Reflectometer (OTDR) were used to determine the bolt loosening at every 1 degree interval.

Loosening Monitoring of Bolted Joints Using Optical Fiber Bending Sensor for Aircraft Lug Assembly

SHMTools is a free, open-source set of standardized MATLAB software tools for Structural Health Monitoring (SHM) research. The software package includes a library of compatible SHM algorithms. This paper is a report of an initial investigation into application of SHMtools for tracking and monitoring the integrity of bolted joints using piezoelectric active-sensors. The target application of this study is a fitting lug assembly of unmanned aerial vehicles (UAVs), where a composite wing is mounted to a UAV fuselage. The SHM methods deployed in this study are time-series analysis, and high-frequency response functions measured by piezoelectric activesensors. In addition, this software is also used for monitoring the functionality of piezoelectric transducers in SHM. Practical implementation issues, including temperature changes, are also considered in this study.

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SHMTools"" for SHM and sensor diagnostics: lug assembly applications

This paper is a report of an initial investigation into tracking and monitoring the integrity of bolted joints using piezoelectric active-sensors. The target application of this study is a fitting lug assembly of unmanned aerial vehicles (UAVs), where a composite wing is mounted to a UAV fuselage. The SHM methods deployed in this study are impedance-based SHM techniques, time-series analysis, and high-frequency response functions measured by piezoelectric active-sensors. Different types of simulated damage are introduced into the structure, and the capability of each technique is examined and compared. Additional considerations encountered in this initial investigation are made to guide further thorough research required for the successful field deployment of this technology.

Seung Moon Jun

Papers

Monitoring of bolted joints using piezoelectric active-sensing for aerospace applications