Aircraft Health Monitoring:
The primary aging mechanisms that are known to reduce the economic service life of both civilian and military aircraft are corrosion, stress corrosion cracking and fatigue. In the past, foil strain gauges have worked well for this evaluation but they require multiple lead wires per gauge, which consumes time in installation and provides for undesirable masses of cables. Foil gauges are also prone to drift and tend to have problems with electromagnetic interference. When compared to conventional foil gauges, Luna’s fiber optic sensors offer substantially reduced size and weight, greatly simplified installation and immunity to electromagnetic interference. Not only are substantial cost savings realized due to labor and material reduction in the installation process, increased coverage viaÂ distributed sensingÂ means higher spatial resolution and an increased probability of early damage detection.
Aircraft manufacturers are continuing to incorporate more carbon fiber reinforced materials into their new aircraft structures. These composite structures weigh less than metal structures and they are stronger. However, composites can still deteriorate, often in the form of fractures, cracks or delaminations. Due to the construction of the composites, these faults are often invisible to the naked eye. Luna’s Rayleigh Backscatter technology is excellent for structural health monitoring of composite structures.
Wind Turbine Health Monitoring:
Luna’s sensors are robust, tolerate in harsh environments, immune to lighting strikes, highly multiplexable, inexpensive, fast, embeddable and lightweight. With a LunaÂ Distributed Sensing Systemâ„¢,Â thousands of sensors can be multiplexed providing strain and temperature information with high spatial resolution which provides early detection of cracks, disjoints and dislocations on a wind turbine blade. This would in turn reduce labor costs for turbine inspection; eliminate the need for unnecessary replacement based on time of use; and reduce the chances of catastrophic failure.
Power Generator Health Monitoring:
As electrical generators age, they become increasingly prone to failure. The failure of a single generator can greatly reduce the output of a power plant while the unit is down for evaluation and repair. Failure from overheating can result from operating the machines beyond their specifications or by problems such as ventilation blockage due to excessively dirty environments. To extend operational life, power plants often intentionally run their electrical generators at less than optimal efficiencies during non-peak usage times. Applying Luna’s distributed sensing technology allows numerous sensors to be multiplexed along the length of a single optical fiber allowing for inexpensive, detailed real-time temperature monitoring of the generator
Cavity Detection / Sinkhole Monitoring:
Embedded cavities, or sink holes that may induce soil collapse present a major risk to the French railway system. Current technologies such as ground penetrating radar, seismic analysis or infrared thermography are increasing in use to locate cavities, but do not offer continuous embedded cavity monitoring, a major concern for rail companies. Luna’s Optical Backscatter Reflectometerâ„¢ (OBR) 4400 device with distributed Rayleigh sensing, was used in an experiment in France for the possible use as a cavity detection or sink hole warning system on railway track beds and tunnels. The experiment conducted a full-scale laboratory investigation of Luna’s OBR, which uses Optical Frequency Domain Reflectometry, together with a competing technology that uses Brillouin scattering. For more information, read the release “Luna’s Fiber Optic Sensing Used in Railway Test in France.”
“Fatigue Performance Comparison between OFDR-based Distributed Fiber Optic Sensing and Strain Gages”
This engineering note presents comparative measurements between foil gages and fiber optic sensors in two experimental configurations. The superior characteristics of fiber optic strain sensors pave the way for overcoming fatigue limitations of traditional foil gages and support their use for fatigue testing and other high-strain cyclic monitoring.
“Distributed Fiber Optic Sensing:Â Measuring Strain Along a Leaf Spring”
This engineering note demonstrates the ability of fiber optic sensors to measure strain profiles along the length of a leaf spring. Results show that fiber optic strain data correlates well to foil gage strain data while providing a more complete profile of strain events over the length of the spring.
“Distributed Fiber Optic Sensing: Applications in Composites Test and Measurement”
As the push for stronger and lighter materials permeates through industry, the necessity to fully understand the structural properties of materials being used grows ever more important. Given the non-homogenous nature of composite materials, the concept that there is a uniformly distributed strain across a test article is not a valid assumption. The nature of Lunaâ€™s distributed fiber optic sensing (DFS) technology provides high spatial resolution strain measurements. This engineering note describes applications that illustrate how a high spatial resolution measurement provides insight that cannot be practically achieved using single point sensors such as conventional foil strain gauges.
“Measuring Liquid Level Using Fiber Optic Sensing”
Fiber optic sensing can be used to measure changes in liquid level when there is a temperature difference between the liquid and surrounding air. One example is measuring the level of fuel in a tank, where fiber is especially advantageous as a sensor because it is chemically inert and does not pose an ignition hazard. This engineering note describes a test of fuel level measurements using the ODiSI strain sensing system.
“Distributed Fiber Optic Sensing: Measuring Strain Across Welds”
While strain gages adhered to welds will average the strain across the gage area, utilizing fiber optic sensing allows the user to measure the strain profile across a weld with a very high spatial resolution. This engineering note demonstrates measurement of strain across the welding joints of a motorcycle handle bar instrumented with a fiber optic sensor.
“Measuring Small Strains with the ODiSI B”
This engineering note discusses results from a simple experiment that was performed to demonstrate the capability of measuring very small strains using Lunaâ€™s ODiSI B fiber sensing system.
“Distributed Fiber Optic Sensing: Measuring Strain with PEEK-Buffered Fiber Optic Sensors”
Optical fibers are manufactured with a variety of coatings to shield the fibers from abrasion and preserve their strength. The userâ€™s end application and environmental conditions inform the choice in fiber coatings. This engineering note discusses strain measurements obtained from PEEK fiber compared to polyimide fiber, when bonded onto a fiberglass coupon and loaded in tension.
“Distributed Fiber Optic Sensing: Strain Measurements on Powder Coated Metal”
Powder coating is a method for electrostatically binding dry powder onto surfaces. While providing better protection for surfaces, this tough finish makes it difficult and time consuming to sand off when preparing the surface for strain sensor bonding. This engineering note shows that fiber optic sensors give accurate strain measurements even when bonded directly onto well adhered powder coated surfaces.
“Distributed Fiber Optic Sensing: Measuring Temperature on a Printed Circuit Board”
This engineering note discusses results from a simple experiment that was conducted to demonstrate how distributed temperature sensing with Lunaâ€™s ODiSI-B can be used to identify a possible point of failure in an integrated electrical component system.
“Temperature Compensation of Strain Measurement”
This engineering note describes some methods that can be employed to correct for this temperature-induced apparent strain. Various compensation schemes are discussed, based on fiber layout and environmental conditions.