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WO1993004350A1 - Transducteur d'effort en fibre optique presentant un rayon de courbure equivalent ou inferieur a un rayon de courbure critique - Google Patents

Transducteur d'effort en fibre optique presentant un rayon de courbure equivalent ou inferieur a un rayon de courbure critique Download PDF

Info

Publication number
WO1993004350A1
WO1993004350A1 PCT/US1992/004275 US9204275W WO9304350A1 WO 1993004350 A1 WO1993004350 A1 WO 1993004350A1 US 9204275 W US9204275 W US 9204275W WO 9304350 A1 WO9304350 A1 WO 9304350A1
Authority
WO
WIPO (PCT)
Prior art keywords
optical fiber
curvature
radius
transducer
set forth
Prior art date
Application number
PCT/US1992/004275
Other languages
English (en)
Inventor
James Richard Houghton
Dale Alan Wilson
Robert Lee Wood
Andrew Khung-Chue Tay
Abdullah Caner Demirdogen
Original Assignee
Avco Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Avco Corporation filed Critical Avco Corporation
Publication of WO1993004350A1 publication Critical patent/WO1993004350A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/083—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT]
    • G01M11/085—Testing mechanical properties by using an optical fiber in contact with the device under test [DUT] the optical fiber being on or near the surface of the DUT
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/24—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
    • G01L1/242—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre
    • G01L1/243—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis
    • G01L1/245—Measuring force or stress, in general by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet the material being an optical fibre using means for applying force perpendicular to the fibre axis using microbending

Definitions

  • This invention relates generally to strain transducers and, in particular, to a fiber optic strain transducer having a specific geometry.
  • the invention also relates to structures, including composite structures, having one or more of the strain transducers disposed upon or within the structure.
  • structures employed as external surfaces for manned and unmanned vehicles.
  • Such structures are known in the art as “smart structures” and “smart skins”.
  • vehicles benefitting from such technology include, but are not limited to, aircraft, space platforms, off shore oil drilling platforms, bridges, buildings, and submarines.
  • Structures of particular interest are composite structures comprised of a number of plies or layers of material that are bonded together into a strong yet light-weight integral member.
  • modern aircraft wing sections may be comprised of composite materials.
  • integral strain transducers embedded between the plies of the structure, or bonded on the surface of the structure is of particular interest in that such transducers allow for in-flight damage assessment, routine maintenance checks of composite structure internal integrity, and also enable a dynamic determination of wing stress to be made during flight.
  • Fiber optic-based transducers are particularly attractive for such applications for a number of reasons. Firstly, optical fibers typically have diameters that are compatible with the inter-ply spacing of many composite structures. Secondly, optical fibers are inexpensive, lightweight and, when properly supported, are sufficiently rugged to withstand the stresses experienced during use. A third important consideration is that transducer systems that employ optical wavelengths do not radiate any significant amount of detectable electromagnetic or thermal radiation into the environment. Nor are such transducer systems subject to false readings or damage due to external electrical or thermal radiation.
  • a still further object of the invention is to provide a component that is comprised of a composite structure including one or more integral optical fiber strain transducer(s) , each of the transducers including at least one curved region having a curvature that is equal to or less than a critical radius of curvature for the optical fiber.
  • the transducer includes an optical fiber having an input port for coupling to a source of optical radiation and an output port for coupling to a receiver of the optical radiation.
  • the transducer is coupled to an optical time domain reflectometer (OTDR) or equivalent signal processor.
  • the optical fiber has at least one region that has a radius of curvature that is equal to or less than a critical radius of curvature for the optical fiber. This region induces a detectable loss in the optical signal in response to being deflected.
  • the optical fiber is mounted in a plane and the detectable loss is shown to be greater for an out-of-plane bending than for an in-plane bending.
  • the optical fiber includes a plurality of regions each having a radius of curvature that is equal to or less than the critical radius of curvature for the optical fiber, each of the plurality of regions being separated by a segment of the optical fiber having a radius of curvature that is greater than the critical radius of curvature.
  • the optical fiber includes a plurality of contiguous regions each having a radius of curvature that is equal to or less than the critical radius of curvature.
  • Fig. la is a block diagram showing a serpentine optical fiber strain transducer that is coupled to input and output devices in accordance with one embodiment of the invention
  • Fig. lb is a block diagram showing a serpentine optical fiber strain transducer that is coupled to input and output devices in accordance with another embodiment of the invention
  • Fig. 2 is a graph showing a change in optical fiber transmission as a function of fiber bending radius and illustrates a critical radius where a slope of the transmittance curve changes abruptly;
  • Fig. 5 illustrates the changes of radius of curvature on a circular loop due to bending around the y axis, Ryy, with the curvature direction being indicated in Fig. 3b;
  • Fig. 10 is a cut-away view of a composite structure showing several embodiments of an optical fiber strain transducer embedded within the composite structure.
  • a strain measuring system 10 that includes a substrate 12 upon which an optical fiber strain transducer 14 is mounted.
  • the transducer 14 has an undulating, serpentine shape comprised of a plurality of curved regions 14'.
  • the transducer 14 has an input coupler 16 that is optically coupled to a source 18 of electromagnetic radiation.
  • the source 18 is comprised of a light emitting diode (LED) or a laser diode which may be operated in either a pulsed mode or a continuous wave mode.
  • the transducer 14 also includes an output coupler 20 that is optically coupled to a receiver 22.
  • the receiver 22 is typically a photodetector such as a silicon photodiode.
  • Fig. lb the components of Fig. la are arranged such that the input coupler 16 and the output coupler 20 are located at the same end of the transducer 14.
  • the opposite end of the transducer 14 is made optically flat.
  • This embodiment of the system 10 operates by detecting back-scattered radiation from a transducer probe pulse in accordance with an Optical Time Domain Reflectometry (OTDR) method.
  • OTDR Optical Time Domain Reflectometry
  • OFDR Optical Frequency Domain Reflectometry
  • the strain sensing optical transducer 14 is provided as a plurality of half circles having a common initial radius.
  • the mathematical examples are presented for one circular loop and an independent variable (t) that is expressed in
  • strain is considered to be a difference in an extended length (1.) from an unstrained gage length (1 ), - > the difference being divided by the unstrained gage length.
  • FIG. 3a-3d Diagrams of the circular loop transducer 14 in three positions, which are referred to as a 20 model A and a model B, are shown in Figs. 3a-3d.
  • the circular loop transducer can also be provided with straight sections between two half circular loops or as a contiguous string of half circular loops disposed in a sinusoidal fashion.
  • transducer 14 model B (Fig. 3d) has a very low net change of attenuation due to the effects of in-plane bending of the structure. For a sinusoidal transducer the distortion effects tend to be equal and opposite across the length of the transducer and to effectively cancel one another. As a result, the transducer of the invention is most advantageously employed for detecting bending induced by a force applied from without, rather than within, the plane of the transducer.
  • the transducer 14 is also assumed to include a single mode optical fiber in that multi-mode fibers have many variables that contribute to attenuation and shifting of modes as the light passes around the curved path.
  • a useful description of the physics of bend loss in a single mode optical fiber as a function of wavelength and bend radius can be found in an article by A. J. Harris and P.F. Castle, "Bend Loss Measurements on High Numerical Aperture Single-Mode Fibers as a Function of Wavelength and Bend Radius", IEEE Journal of Lightwave Tech., Vol. LT-4, Jan. 1986, pp. 34-40 and in a text on Single-Mode Fiber Optics by L. B. Jeun Subscribe Single-Mode Fiber Optics, Marcel Dekker, Inc., 1983, pp. 88-94.
  • a and B wavelength of light and the optical fiber material property terms, as described by A. J. Harris et al. in the above-referenced article.
  • V the velocity along the path
  • A the acceleration on the path
  • FIG. 7 A demonstration of the light attenuation due to the radius of curvature changes from bending and compressive stress is shown in Fig. 7.
  • This figure represents a uniform stress field in a full loop (360 degrees) of fiber optics, as stressed in Fig. 3b, and shows the amount of attenuation increasing as the bending moment increases, i.e. the radius of curvature decreases.
  • the representation in Fig. 7 is the distributed attenuation performance in its best position.
  • FIG. 8 Another illustration of the net attenuation measured at the end of a 180° loop of optical fiber is shown in Fig. 8. This figure shows pure bending effects, uniform compression effects, and uniform tension effects, and how these effects change as the radius of curvature associated with the bending moment becomes larger.
  • Fig. 9 shows insignificant sensitivity to tensile and compressive stress fields acting on the optical fiber loop.
  • the difference in stress sensitivity between Fig. 8 and Fig. 9 is the direction to stress vector indication, and is an important aspect of the invention.
  • a function of the processor 24 of Fig. 1 is to determine the magnitude of the applied strain or stress from a change in the transducer 14 output signal. This determination is accomplished in accordance with the principles and relationships described above.
  • a cut-away view of a composite structure 30 comprised of a plurality of individual plies or layers 32.
  • Such laminated structures may be comprised of, by example, graphite-epoxy or fiberglass-resin and may include from tens to hundreds of individual layers.
  • Structure 30 may be a portion of an aircraft wing or may be any structural component where it is desirable to measure strain.
  • Between two of the layers 32 are shown several embodiments of the optical fiber transducer 1 .
  • Transducer 14a has a continuous serpentine shape that is approximately sinusoidal. A wavelength of the sinusoidal pattern is equal to or greater than approximately four times (CR) , where CR is the critical radius of the optical fiber at the wavelength of the source 18.
  • Transducer 14b has sinusoidal regions interspersed with linear regions.
  • Transducer 14c has a plurality of regions that describe half-circles interspersed with linear regions. For region 14c it should be 19
  • transducer embodiments 14a-14c
  • Transducers may also be provided between several pairs of adjacent layers 32.
  • these various transducer embodiments may be employed with other transducer types, such as temperature sensors, within a given structure.
  • the strain transducer 14 is most sensitive, as described in detail above, to bending induced by a force applied out of the plane of the fiber and is less sensitive to a force applied in the plane of the fiber. Furthermore, and as is indicated in Fig. 2, for the embodiments of 14b and 14c a localized strain is more readily detected in that a greater optical attenuation is obtained for deflections imposed at the curved fiber regions as opposed to the linear regions. That is, the curved region(s) may be provided at known locations such that any change in the optical signal that is extracted from the transducer indicates that a deflection has occurred at the known location.
  • the substrate 12 is comprised of a flexible material that is compatible with being incorporated within, or upon a surface of, the composite structure 30.
  • strain transducer of the invention is not limited to only composite structures but may instead be employed with, for example, metallic and masonry structures.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Optical Transform (AREA)

Abstract

Un transducteur d'effort (14) est sensible à un fléchissement auquel il est soumis afin de produire un signal de sortie pouvant être détecté et dont une caractéristique exprime le fléchissement. Le transducteur comprend une fibre optique ayant une entrée (16) devant être accouplée à une source (18) d'un rayonnement optique, ainsi qu'une sortie (20) devant être accouplée à un récepteur (22) du rayonnement optique. La fibre optique comprend au moins une région (14') dont le rayon de courbure est égal ou inférieur à un rayon de courbure critique de la fibre optique. Cette ou ces région(s) produit une perte détectable dans le signal optique en réponse à un fléchissement. La fibre optique est disposée dans un plan, et il est démontré que la perte détectable est plus importante pour un fléchissement hors du plan que pour un fléchissement dans le plan. Il est également démontré que le transducteur est particulièrement adapté pour être inclus dans une structure composite laminée, telle qu'un élément d'une aile d'avion.
PCT/US1992/004275 1991-08-25 1992-05-20 Transducteur d'effort en fibre optique presentant un rayon de courbure equivalent ou inferieur a un rayon de courbure critique WO1993004350A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US73602491A 1991-08-25 1991-08-25
US736,024 1991-08-25

Publications (1)

Publication Number Publication Date
WO1993004350A1 true WO1993004350A1 (fr) 1993-03-04

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995002273A1 (fr) * 1993-07-06 1995-01-19 British Nuclear Fuels Plc Rotor pour dispositif de stockage et de conversion d'energie
EP0943906A1 (fr) * 1998-03-20 1999-09-22 Talltec Technologies Holdings S.A. Capteur d'effort à fibre optique, procédé de fabrication d'un tel capteur, et dispositif de détection d'effort utilisant ce capteur
EP3173758A1 (fr) * 2015-11-24 2017-05-31 The Boeing Company Système et procédé pour une détection tactile utilisant des réseaux de détection optique à film mince

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4560016A (en) * 1983-12-14 1985-12-24 Anco Engineers, Incorporated Method and apparatus for measuring the weight of a vehicle while the vehicle is in motion
US4692610A (en) * 1986-01-30 1987-09-08 Grumman Aerospace Corporation Fiber optic aircraft load relief control system
US4781056A (en) * 1985-03-07 1988-11-01 Sopha Praxis Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales
US4812645A (en) * 1981-08-24 1989-03-14 G2 Systems Corporation Structural monitoring system using fiber optics
US4880970A (en) * 1987-02-26 1989-11-14 Jones Gordon R Optical sensors for measurement of a variable parameter
US4990769A (en) * 1988-09-27 1991-02-05 U.S. Philips Corp. Continuous cable fiber optical pressure sensor

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4812645A (en) * 1981-08-24 1989-03-14 G2 Systems Corporation Structural monitoring system using fiber optics
US4560016A (en) * 1983-12-14 1985-12-24 Anco Engineers, Incorporated Method and apparatus for measuring the weight of a vehicle while the vehicle is in motion
US4781056A (en) * 1985-03-07 1988-11-01 Sopha Praxis Optical device for strain detection, method for the measurement of strain by means of the said device and their application to scales
US4692610A (en) * 1986-01-30 1987-09-08 Grumman Aerospace Corporation Fiber optic aircraft load relief control system
US4880970A (en) * 1987-02-26 1989-11-14 Jones Gordon R Optical sensors for measurement of a variable parameter
US4990769A (en) * 1988-09-27 1991-02-05 U.S. Philips Corp. Continuous cable fiber optical pressure sensor

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995002273A1 (fr) * 1993-07-06 1995-01-19 British Nuclear Fuels Plc Rotor pour dispositif de stockage et de conversion d'energie
EP0943906A1 (fr) * 1998-03-20 1999-09-22 Talltec Technologies Holdings S.A. Capteur d'effort à fibre optique, procédé de fabrication d'un tel capteur, et dispositif de détection d'effort utilisant ce capteur
WO1999049287A1 (fr) * 1998-03-20 1999-09-30 Talltec Technologies Holdings S.A. Capteur d'effort a fibre optique, procede de fabrication d'un tel capteur, et dispositif de detection d'effort utilisant ce capteur
EP3173758A1 (fr) * 2015-11-24 2017-05-31 The Boeing Company Système et procédé pour une détection tactile utilisant des réseaux de détection optique à film mince
TWI718166B (zh) * 2015-11-24 2021-02-11 美商波音公司 使用薄膜光學感測網路之用於觸覺感測的系統和方法

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