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  • 1
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    Use of 3000 Bragg Grating Strain Sensors Distributed on Four Eight-meter Optical Fibers During Static Load Tests of a Composite Structure (2001)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: This paper describes the use of a fiber optic system to measure strain at thousands of locations along optical fibers where weakly reflecting Bragg gratings have been photoetched. The optical fibers were applied to an advanced composite transport wing along with conventional foil strain gages. A comparison of the fiber optic and foil gage systems used for this test will be presented including: a brief description of both strain data systems; a discussion of the process used for installation of the optical fiber; comparative data from the composite wing test; the processes used for the location and display of the high density fiber optic data. Calibration data demonstrating the potential accuracy of the fiber optic system will also be presented. The opportunities for industrial and commercial applications will be discussed. The fiber optic technique is shown to be a valuable augmentation to foil strain gages providing insight to structural behavior previously requiring reliance on modeling.
    Keywords: Aircraft Design, Testing and Performance
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    High-precision buffer circuit for suppression of regenerative oscillation (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Precision analog signal conditioning electronics have been developed for wind tunnel model attitude inertial sensors. This application requires low-noise, stable, microvolt-level DC performance and a high-precision buffered output. Capacitive loading of the operational amplifier output stages due to the wind tunnel analog signal distribution facilities caused regenerative oscillation and consequent rectification bias errors. Oscillation suppression techniques commonly used in audio applications were inadequate to maintain the performance requirements for the measurement of attitude for wind tunnel models. Feedback control theory is applied to develop a suppression technique based on a known compensation (snubber) circuit, which provides superior oscillation suppression with high output isolation and preserves the low-noise low-offset performance of the signal conditioning electronics. A practical design technique is developed to select the parameters for the compensation circuit to suppress regenerative oscillation occurring when typical shielded cable loads are driven.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-4658 , L-17453 , NAS 1.15:4658
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Optical Fiber Distributed Sensing Structural Health Monitoring (SHM) Strain Measurements Taken During Cryotank Y-Joint Test Article Load Cycling at Liquid Helium Temperatures (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper outlines cryogenic Y-joint testing at Langley Research Center (LaRC) to validate the performance of optical fiber Bragg grating strain sensors for measuring strain at liquid helium temperature (-240 C). This testing also verified survivability of fiber sensors after experiencing 10 thermal cool-down, warm-up cycles and 400 limit load cycles. Graphite composite skins bonded to a honeycomb substrate in a sandwich configuration comprised the Y-joint specimens. To enable SHM of composite cryotanks for consideration to future spacecraft, a light-weight, durable monitoring technology is needed. The fiber optic distributed Bragg grating strain sensing system developed at LaRC is a viable substitute for conventional strain gauges which are not practical for SHM. This distributed sensing technology uses an Optical Frequency Domain Reflectometer (OFDR). This measurement approach has the advantage that it can measure hundreds of Bragg grating sensors per fiber and the sensors are all written at one frequency, greatly simplifying fiber manufacturing. Fiber optic strain measurements compared well to conventional strain gauge measurements obtained during these tests. These results demonstrated a high potential for a successful implementation of a SHM system incorporating LaRC's fiber optic sensing system on the composite cryotank and other future cryogenic applications.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: SPIE Optics East 2007; Sep 09, 2007 - Sep 12, 2007; Boston, MA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Evaluation of GE-167 Silicone Rubber (RTV) For Possible Service As A Moisture-Barrier For Certain Strain Gage Applications (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The Langley Research Center uses strain gages in a wide variety of demanding test environments. Strain gage installations, depending on the testing scenario, may see high temperatures, cryogenic temperature, moisture accumulation, mechanical abuse, or any combination of these conditions. At Langley, there is often a need to provide protection for strain gages against moisture and mechanical abuse, especially when large-scale, harsh environment testing is to be encountered. This technical memorandum discusses the evaluation of a room temperature curing silicone rubber sealant manufactured by the General Electric Company for consideration as a moisture-barrier for certain strain gage installations.
    Keywords: Instrumentation and Photography
    Type: NASA/TM-2000-210087 , L-17931 , NAS 1.15:210087
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Characteristics of Extrinsic Fabry-Perot Interferometric (EFPI) Fiber-Optic Strain Gages (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The focus of this paper is a comparison of the strain-measuring characteristics of one type of commercially available fiber-optic strain sensor with the performance of conventional resistance strain gages. Fabry-Perot type fiber-optic strain sensors were selected for this testing program. Comparative testing is emphasized and includes load testing at room temperature with apparent strain characterization cryogenically and at elevated temperatures. The absolute accuracy of either of these types of strain gages is not addressed.
    Keywords: Instrumentation and Photography
    Type: NASA/TP-2000-210639 , L-17979 , NAS 1.60:210639
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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