EP0857291A1 - Jauge de contrainte - Google Patents

Jauge de contrainte

Info

Publication number
EP0857291A1
EP0857291A1 EP96935080A EP96935080A EP0857291A1 EP 0857291 A1 EP0857291 A1 EP 0857291A1 EP 96935080 A EP96935080 A EP 96935080A EP 96935080 A EP96935080 A EP 96935080A EP 0857291 A1 EP0857291 A1 EP 0857291A1
Authority
EP
European Patent Office
Prior art keywords
ofthe
supports
optical fibre
strain gauge
fibre
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP96935080A
Other languages
German (de)
English (en)
Inventor
Neil Richard Haigh
Simon Mark Rowland
Richard Stephen Linton
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Balfour Beatty PLC
Original Assignee
BICC PLC
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 BICC PLC filed Critical BICC PLC
Publication of EP0857291A1 publication Critical patent/EP0857291A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • G01L1/246—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 integrated gratings, e.g. Bragg gratings
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
    • G01B11/18—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge using photoelastic elements
    • 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 to strain gauges for engineering structures e.g. bridges, buildings, pipes, plant and the like whether made from steel or concrete, and in particular to strain gauges that inco ⁇ orate optical fibres as the strain sensing elements.
  • Strain gauges formed from optical fibres and having dimensions, in the order of 0.1 metre to 10 metres and especially in the order of 0.1 to 1 metre would be particularly useful in detecting and monitoring strain in large engineering structures.
  • one significant problem in the use of optical fibres for such purposes is the issue of supporting the fibres on the structure so that the fibres are subjected to strains in the structure but without damaging the fibres or requiring costly and time-consuming methods of mounting the fibres on the surface of the structure.
  • an optical fibre strain gauge for an engineering structure which comprises: a) a plurality of supports for the optical fibre that are, or can be, located on a surface ofthe structure and are spaced apart from one another over a part of the surface; and • b) at least one optical fibre that is looped around the supports so that it extends between the supports, the optical fibre being fixed to the supports so that the length ofthe part of the fibre extending between the supports will vary in accordance with strain ofthe surface ofthe structure.
  • the strain gauge according to the invention has the advantage that the optical fibres can be looped around the supports a number of times. This enables the optical fibre or fibres to be held by the supports more easily so that the fibre or fibres are subject to the strain ofthe surface ofthe structure without the necessity of complex attachment procedures such as metallising and welding.
  • the strain gauge according to the invention will inco ⁇ orate a length of optical fibre that is significantly greater than the dimension ofthe area ofthe structure that is being monitored. This increases the flexibility ofthe design and enables, for example, areas of structures to be monitored which have dimensions smaller than the resolution ofthe equipment employed to monitor them.
  • the optical fibre or fibres will normally contain one or more reflectors so that light will be caused to pass in both directions along that part ofthe optical fibre extending between the supports.
  • the increase in length may be measured by a reflectometry method in which light is sent along the fibre and reflected back to a detector and changes in the length ofthe fibre alter the time taken before the light is detected at the detector.
  • a detector may be formed by a mirror, a Bragg grating formed in the fibre, or even, in the broadest aspect ofthe invention, simply a cleaved end ofthe fibre.
  • the reflector, and any additional elements that may be present can be located at a position remote from the supports, so that if the structure to be monitored is subjected to very high temperatures or is otherwise located in a hostile environment, only that part ofthe or each optical fibre that is looped around the supports need be located in that environment.
  • the optical fibre may contain a strain-sensitive reflector such as a Bragg grating in that part ofthe fibre that extends between the supports.
  • the spacing ofthe grating will therefore vary in accordance with strain ofthe surface.
  • light of a broad wavelength spectrum could be launched into the optical fibre and the wavelength ofthe reflected light would vary in accordance with the strain ofthe surface.
  • optical fibre or optical fibres may simply be looped around the supports as a whole or they may additionally be wound around individual supports in a plurality of turns. This may enable the optical fibre or fibres to be held to the supports at least principally by friction, although it may be appropriate to provide some additional form of adhesion.
  • the or each optical fibre should be looped around the supports so that it is taut.
  • the fibre in many cases it is preferred for the fibre to be under tension so that it is in a stretched state even when the structure surface is not strained. In this way the strain gauge will be able to record a degree of compressive strain in the structure surface as the separation between the supports decreases.
  • the optical fibre or fibres would be stretched to an elongation of 0.2 to 0.5% at zero structural strain.
  • the supports for the fibre may take any appropriate form, although it is preferred for them to comprise protuberances that extend from the surface ofthe structure and around which the or each optical fibre is looped.
  • the supports preferably have no corners or edges that contact the optical fibre and which could cause light loss from the optical fibre by microbending.
  • the supports preferably have a curvature of radius of at least 30mm so that no light is lost from the fibre by macrobending.
  • the supports may, for example, be formed as cylindrical protuberances of circular cross- section. However, in some circumstances it may be preferable for the protuberances to have lateral dimensions that diminish in a direction (normal to the surface) that extends away from the surface, for instance they may be frusto-conical in shape.
  • the strain gauge may have supports for the optical fibre that are formed integrally with the structure surface. However, it is preferred for the gauge to be formed separately from the structure so that it can be attached to the structure at any convenient time.
  • the supports may be located on a base plate that can be attached to the structure, for instance by welding or bolting.
  • the optical fibres may be looped around the supports by hand in situ, but it is preferred to package the optical fibres in a more rugged arrangement that will withstand normal abuse to be expected on a construction site and in use. For this reason the optical fibres may be provided in a capping element that is located on the supports. If the supports are frusto-conical or otherwise taper, the degree to which the capping element is pushed on to the supports will determine the degree to which the optical fibre is stretched as it is installed.
  • the strain gauge may include any appropriate number of supports. If it has two supports, the optical fibre will extend between the supports in one direction and will therefore detect strain in a single direction only.
  • the strain gauge may alternatively include three or more supports arranged on the surface so that the optical fibre or fibres will be subject to strain occurring on the surface in two directions. For example they may be arranged to form the vertices of a triangle, preferably a right-angled triangle so that optical fibres extend over part ofthe surface in mutually perpendicular directions. It is possible for the strain gauge to have, for example, four supports arranged at corners of a rectangle, and for the optical fibre or optical fibres to extend between adjacent supports along the edges ofthe rectangle.
  • Figure 1 is a partially cut-away perspective view of one form of strain gauge
  • Figure 2. is a schematic top view of a second form of strain gauge
  • Figure 3 is a schematic top view of a third form of strain gauge.
  • figure 1 shows a strain gauge 1 which comprises a rectangular base plate 2 that can be firmly attached to a metal structure, for example, it can be welded to the structure along its edges 4 and 6 so that points on the base plate 2 follow strains on the underlying structure.
  • a pair of protuberances 8 and 10 stand up from the base plate 2 and act as supports for an optical fibre strain sensing element ofthe strain gauge 1.
  • the protuberances 8 and 10 are each frusto-conical in shape having a circular cross-section that is of minimum diameter of 60mm to prevent any light loss in the optical fibre by macrobending, and are each located at one end region ofthe base plate 2.
  • the strain gauge includes an optical fibre 12 that forms a strain sensing element, and is looped around the protuberances three times before being led away from the base plate 2 in a steel tube 14. Although only three loops ofthe optical fibre are shown for the sake of clarity, in practice the fibre may be looped around the protuberances many more times if desired, for example up to fifty or one hundred times. In addition the thickness ofthe optical fibre will be much less than as shown.
  • the optical fibre may have a polymeric jacket formed, for example, from an acrylic polymer, and will typically meter (including jacket) of about 125 ⁇ m.
  • the optical fibre may have a carbon coating or a metallic coating e.g. formed from aluminium or gold which will exhibit less creep, will give the fibre a higher degree of protection and will load to a reduced fibre diameter, thereby enabling a larger number of optical fibre loops if desired.
  • the protuberances 8 and 10 and the optical fibre 12 are enclosed in a steel capping element 16 that is also rectangular in shape and of substantially the same dimensions as the base plate 2.
  • a steel capping element 16 that is also rectangular in shape and of substantially the same dimensions as the base plate 2.
  • the interior ofthe capping element 16 is filled with a potting compound 18, for example polyurethane, a cured acrylic polymer or the like.
  • the strain sensor is manufactured and delivered to the installation site in two parts: the base plate with protuberances, and an assembly ofthe capping element 16 containing the optical fibre 12 and the potting compound 18.
  • the capping element part ofthe strain gauge is manufactured by looping the optical fibre 12 the required number of times around a former having the same shape and dimensions as the protuberances 8 and 10 or perhaps very slightly smaller diameters, placing the capping element over the former and optical fibre 12, filling the interior ofthe capping element 12 with the potting compound 18 and curing the potting compound After the potting compound 18 has fully cured the former is removed
  • the base plate 2 is attached to the surface of the structure for example by welding, and the capping element assembly is pushed on to the two protuberances 8 and 10 sufficiently to cause the taper ofthe protuberances to stretch the optical fibre 12 by a small amount e g 0 2 to 0.5%
  • the appropriate degree of stretch ofthe optical fibre 12 may, for example, be ensured by providing one ofthe base plate or the capping element assembly with a stop and the capping element assembly may be forced on to the protuberances, for example by hammering, until further movement is prevented by the stop
  • the capping element 16 is retained on the base plate by means of screws 20 that are received by tapped holes 22 in the protuberances
  • the length ofthe optical fibre will vary in accordance with changes in the separation ofthe protuberances 8 and 10, the total length ofthe fibre changing by 2n times the change in separation ofthe protuberances, where n is the number of times the optical fibre is looped around the protuberances
  • Appropriate choice of potting compound 18 and jacket material for the optical fibre 12 will cause adhesion between the two and will prevent or at least substantially reduce slippage ofthe fibre around the protuberances
  • Strain in the structure may be monitored by any ofthe following methods 1) by providing a pair of reflectors such as Bragg gratings in the parts ofthe optical fibre remote from the strain gauge, and using reflectometry methods to monitor the change in the overall length ofthe optical fibre,
  • Figure 2 shows schematically a second form of strain gauge according to the invention which can monitor strain in two orthogonal directions A and B as shown in the drawing.
  • the gauge is ofthe same construction as that of figure 1, and comprises a base plate 2 and three protuberances 8, 9 and 10, the protuberances subtending an angle of 90° about protuberance 9.
  • Two separate optical fibres 12 and 12' are looped about protuberances 8 and 9 and about protuberances 9 and 10 respectively so that each optical fibre lies predominantly parallel to one ofthe directions A or B and predominantly pe ⁇ endicular to the other ofthe directions.
  • Figure 3 shows schematically a third form of strain gauge according to the invention which can monitor strain in two orthogonal directions and is temperature compensated.
  • the strain gauge is also ofthe same general construction as that shown in figure 1 but comprises a generally square base plate 2 having four protuberances 8, 9, 10 and 1 1, one protuberance in the region of each comer ofthe base plate 2.
  • Four optical fibres 12, 12', 13 and 13' are wound around adjacent pairs ofthe protuberances so that each ofthe optical fibres extends generally along one edge ofthe base plate, optical fibres 12 and 13 being disposed along opposite parallel edges as are optical fibres 12' and 13'.
  • the base plate is welded to the underlying structure surface by weld 20 which extends along two adjacent edges 21 and 22 ofthe base plate 2 but not along the other adjacent edges 23 and 24 (although the weld 20 could, if desired, be extended along part ofthe edges 23 and 24 in the region of protuberances 9 and 1 1).
  • weld 20 extends along two adjacent edges 21 and 22 ofthe base plate 2 but not along the other adjacent edges 23 and 24 (although the weld 20 could, if desired, be extended along part ofthe edges 23 and 24 in the region of protuberances 9 and 1 1).
  • protuberances 8, 9 and 11 are fixed to the structure surface while protuberance 10 is decoupled from the surface and will maintain a constant separation from protuberances 9 and 1 1 other than due to variations in temperature.
  • Optical fibres 12 and 12' will therefore act as strain sensing elements in respect of directions A and B respectively, while optical fibres 13 and 13' can be used to compensate for temperature effects

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Optical Transform (AREA)

Abstract

Une jauge de contrainte (1) à fibres optiques destinée à un ouvrage d'art tel qu'un pont, un immeuble, une canalisation, une installation ou similaire, comporte: (a) une pluralité de supports (8, 10) destinés à la fibre optique, lesquels peuvent être situés sur une surface de la structure et sont espacés les uns des autres sur une partie de cette surface; et (b) au moins une fibre optique enroulée autour des supports de manière à s'étendre entre ces derniers, la fibre optique étant fixe par rapport aux supports de sorte que la longueur de la partie de la fibre s'étendant entre lesdits supports va varier en fonction de la contrainte de la surface de la structure. La ou les fibres optiques (12) peuvent être enroulées autour des supports (8, 10) un certain nombre de fois, ce qui permet un maintien plus aisé des fibres, et permet à la jauge d'intégrer une longueur de fibre notablement supérieure à la dimension de la surface de la structure contrôlée. La ou les fibres comportent normalement des réflecteurs tels que des réseaux de Bragg permettant le contrôle des signaux.
EP96935080A 1995-10-26 1996-10-24 Jauge de contrainte Withdrawn EP0857291A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9521957 1995-10-26
GBGB9521957.2A GB9521957D0 (en) 1995-10-26 1995-10-26 Strain gauge
PCT/GB1996/002606 WO1997015805A1 (fr) 1995-10-26 1996-10-24 Jauge de contrainte

Publications (1)

Publication Number Publication Date
EP0857291A1 true EP0857291A1 (fr) 1998-08-12

Family

ID=10782952

Family Applications (1)

Application Number Title Priority Date Filing Date
EP96935080A Withdrawn EP0857291A1 (fr) 1995-10-26 1996-10-24 Jauge de contrainte

Country Status (6)

Country Link
EP (1) EP0857291A1 (fr)
JP (1) JPH11513806A (fr)
AU (1) AU7317596A (fr)
CA (1) CA2235482A1 (fr)
GB (1) GB9521957D0 (fr)
WO (1) WO1997015805A1 (fr)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2461532A (en) * 2008-07-01 2010-01-06 Vestas Wind Sys As Sensor system and method for detecting deformation in a wind turbine component
US8234083B2 (en) 2008-09-22 2012-07-31 Vestas Wind Systems A/S Wind turbine rotor blade comprising an edge-wise bending insensitive strain sensor system
US8310657B2 (en) 2008-03-31 2012-11-13 Vestas Wind Systems A/S Optical transmission strain sensor for wind turbines
US8712703B2 (en) 2008-12-16 2014-04-29 Vestas Wind Systems A/S Turbulence sensor and blade condition sensor system
US8733164B2 (en) 2010-02-04 2014-05-27 Vestas Wind Systems A/S Wind turbine optical wind sensor
US8814514B2 (en) 2008-07-03 2014-08-26 Vestas Wind Systems A/S Embedded fibre optic sensor for wind turbine components
US9014863B2 (en) 2009-08-06 2015-04-21 Vestas Wind Systems A/S Rotor blade control based on detecting turbulence

Families Citing this family (13)

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Publication number Priority date Publication date Assignee Title
FR2807512B1 (fr) 2000-04-11 2002-05-24 Commissariat Energie Atomique Inclinometre a reseau de bragg
EP1709416B1 (fr) 2004-01-23 2018-03-07 LM Wind Power International Technology II ApS Dispositif comprenant un systeme concu pour etre utilise dans la compensation thermique de mesures de contrainte dans des structures renforcees par des fibres
JP4609836B2 (ja) * 2004-02-26 2011-01-12 古河電気工業株式会社 光ファイバセンサ
GB2440955A (en) * 2006-08-18 2008-02-20 Insensys Ltd Wind turbine blade monitoring
FR2909446B1 (fr) * 2006-11-30 2009-02-13 Commissariat Energie Atomique Dispositif et procede de mesure des deformations mecaniques d'un profile
KR100945149B1 (ko) * 2008-12-19 2010-03-08 주식회사 금륜방재산업 초고층 건물의 방재 시스템 및 방법
NL2002743C2 (nl) * 2009-04-10 2010-10-12 Stichting Energie Inrichting en werkwijze voor het meten van rek.
JP5409243B2 (ja) * 2009-10-09 2014-02-05 第一高周波工業株式会社 高温環境用光ファイバセンサ
GB2490086B (en) * 2010-11-08 2015-04-08 Silixa Ltd Fibre optic monitoring installation, apparatus and method
US9061425B2 (en) 2013-10-15 2015-06-23 Avago Technologies General Ip (Singapore) Pte. Ltd. Frame transfer device for an optical strain gauge structure
US10113862B2 (en) 2013-12-01 2018-10-30 Cmiws Co., Ltd. Strain sensor and manufacturing method for strain sensor
JP6784139B2 (ja) * 2016-10-25 2020-11-11 中国電力株式会社 ひずみ計測方法、及びひずみ計測システム
CN115266075B (zh) * 2022-09-26 2023-02-17 中交第一公路勘察设计研究院有限公司 鼓凸自感知的板式支座及制作方法、监测系统及监测方法

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US4996419A (en) * 1989-12-26 1991-02-26 United Technologies Corporation Distributed multiplexed optical fiber Bragg grating sensor arrangeement
US5250802A (en) * 1991-11-04 1993-10-05 Teledyne Ryan Aeronautical, Division Of Teledyne Industries, Inc. Fiber optic stress sensor for structural joints
FR2707754B1 (fr) * 1993-07-12 1995-10-06 Aerospatiale Structure embarquée sur véhicule spatial, ayant des capteurs dimensionnels intégrés.
GB9317576D0 (en) * 1993-08-24 1993-10-06 British Aerospace Fibre optic damage detection system

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8310657B2 (en) 2008-03-31 2012-11-13 Vestas Wind Systems A/S Optical transmission strain sensor for wind turbines
GB2461532A (en) * 2008-07-01 2010-01-06 Vestas Wind Sys As Sensor system and method for detecting deformation in a wind turbine component
US8348611B2 (en) 2008-07-01 2013-01-08 Vestas Wind Systems A/S Wind turbine having a sensor system for detecting deformation in a wind turbine rotor blade and corresponding method
US8814514B2 (en) 2008-07-03 2014-08-26 Vestas Wind Systems A/S Embedded fibre optic sensor for wind turbine components
US8234083B2 (en) 2008-09-22 2012-07-31 Vestas Wind Systems A/S Wind turbine rotor blade comprising an edge-wise bending insensitive strain sensor system
US8712703B2 (en) 2008-12-16 2014-04-29 Vestas Wind Systems A/S Turbulence sensor and blade condition sensor system
US9014863B2 (en) 2009-08-06 2015-04-21 Vestas Wind Systems A/S Rotor blade control based on detecting turbulence
US8733164B2 (en) 2010-02-04 2014-05-27 Vestas Wind Systems A/S Wind turbine optical wind sensor

Also Published As

Publication number Publication date
JPH11513806A (ja) 1999-11-24
CA2235482A1 (fr) 1997-05-01
WO1997015805A1 (fr) 1997-05-01
GB9521957D0 (en) 1996-01-03
AU7317596A (en) 1997-05-15

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