Expanding the Vision of Sensor Materials (1995) / Chapter Skim
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CHAPTER 4: SELECTED SENSOR APPLICATIONS FOR STRUCTURAL MONITORING AND CONTROL
CHAPTER 4: SELECTED SENSOR APPLICATIONS FOR STRUCTURAL MONITORING AND CONTROL
Pages 47-61
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From page 47... ...
Four disparate applications (condition monitoring of equipment, control and condition monitoring of aeronautical jet engines, structural monitoring of test prototypes, and structural monitoring during operation) are discussed below to illustrate the broad range of current LCM applications and associated sensor technology requirements.
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The sensor framework described in Chapter 2 can be used very effectively in developing a core set of sensor specifications and in comparing the attributes of candidate sensors. Condition monitoring requires periodic polling of the sensors and analysis of the data.
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The sensors and actuators can be TABLE 4-1 Functions of a let Engine Diagnostic Unit Function Typical Stored Parameters Engine event detection Engine performance determination Life-usage data collection Control-system fault detection Low-pressure turbine rotor speed High-pressure turbine rotor speed Turbine airfoil over-temperature Hot start Engine stall Augmentor blowout or mix-light Fuel flow rat . tingle pressures Mach number Thrust-level request Engine operating time Engine flight time Hot section time Electronic control faults System faults 50
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From page 51... ...
Use of these smart devices would eliminate the need for point-to-point wiring for sensors and actuators at extended distances from the engine controller and would, in turn, greatly reduce engine harness weight (Tiliman and Ikeler, 1991~. The use of smart sensors and actuators for jetengine control is currently limited by the availability of mature high-temperature electronic components that can withstand the engine operating environment.6 As this technology advances, smart devices will increasingly appear in engine applications.
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. res~shve wire thin film ultrasonic 53 Structural Health Monitoring Structural health monitoring involves the evaluation of a structure's capability to carry useful load.
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From page 54... ...
are not a comprehensive list of the many different sensor methods that could be employed to accomplish this task but are representative of sensor approaches that have been or are being applied to satisfy this particular requirement. 54 Two different approaches have been used: embedded fiberoptic sensors8 (passive)
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From page 55... ...
Second, moisture was absorbed over time in the epoxy and ultimately permeated to the silica fiber; this caused surface microcracks that resulted in light Toss and eventually fiber breakage. A materials development effort resulted in improved reliability and survivability for the optical fibers due in part to the development of hermetic coatings for the fibers.
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From page 56... ...
The use of optical fibers to perform intrinsic sensing in smart structures was first investigated in 1979 at the National Aeronautics and Space Administration's Langley Research Center. In this early research, optical fibers were used to measure strain in low-temperature composite materials.
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From page 57... ...
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From page 58... ...
Some of the preliminary research involves using active ferromagnetic tagging to determine the complex moclulus of polymer specimens using magnetostrictive tagging particles to detect delamination in thermoplastic composites, using active ferromagnetic tagging particles to monitor the curing process of composite specimens and using ferroelectric particles 58 to monitor adhesive bonds. Using the tagging method for nondestructive evaluation usually requires the selection of the appropriate sensor particles, determination of the quantity of particles, preparation of the proper transducers (to pick up signatures resulting from the tagging particles)
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From page 59... ...
Flexible optical fibers with a broad passband were required (conventional optical fibers do not transmit infrared radiation) , as well as a very capable image transTa tion system.
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From page 60... ...
Existing sensor technology is often less advanced than required for many of the envisioned smart structures applications. However, major advances in control technology are also needed; a discussion of these is outside the scope of this report, but Appendix A contains appropriate references.
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From page 61... ...
8. Optical fiber sensor technology is discussed in Appendix D of this report.
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