CN100417963C - Distributed long gauge length optical fibre Bragg optical grating strain sensor and mfg. process thereof - Google Patents

Abstract

The invention relates to distributivity long gauge length optical fiber Prague grating strain gage and its manufacturing method. It is formed by many long gauge length optical fiber Prague grating strain gages with series connection. The two ends of the each long gauge length optical fiber Prague grating are respectively connected with mono-mode fiber without coating. Their outer is hitched by annular tube of which two ends are fixed on the mono-mode fiber respectively by optical fiber and annular tube, which two ends are connected with outer mono-mode fiber optical cable by welding point. Composite material packaging layer is covered at the outside of the above structure.

Description

Distributed long gauge length optical fibre Bragg optical grating strain sensor and manufacture method thereof

Technical field

The present invention is a kind of health detection of structure facility and the distributed long gauge length optical fibre Bragg optical grating strain sensor and manufacture method thereof of monitoring of being used for, and belongs to the technical field that fibre optic strain sensor is made.

Background technology

The health monitoring of structure comprises integral body and area monitoring.The sensor of whole monitoring that with the accelerometer is representative is comparatively ripe, show that but a large amount of research and engineering are actual only the whole monitoring method based on mode (frequency, the vibration shape etc.) still faces bigger difficulty on diagnosing structural damage and parameter recognition.And based on the area monitoring of stress (strain), on the one hand because corresponding sensor can not satisfy the needs of structure long term monitoring far away on stability and permanance, on the other hand, traditional " point " foil gauge often occurs losing efficacy because of stress raisers and crack, and distributing on large-scale civil structure, it is unactual to arrange yet, but the local damage in the structure is difficult to be detected exactly within the sensor test scope that appears at arrangement, thereby can't capture prior unpredictable structural failure effectively.

Summary of the invention

Technical matters: the purpose of this invention is to provide a kind of distributed long gauge length optical fibre Bragg optical grating strain sensor and manufacture method thereof, the fusion of structural entity information and local message in the realization health monitoring process, realization is to Crack Monitoring and reinforcement corrosion and the integrality performance of the structure evaluation of the local failure of large scale structure diagnosis as xoncrete structure, realize under the small strain situation high precision measurement under the ambient vibration for example, solve installation cheap property, stability and the endurance issues of sensor.

Technical scheme: distributed long gauge length optical fibre Bragg optical grating strain sensor of the present invention is in series by a plurality of long gauge length optical fibre Bragg optical grating strain sensors; Wherein single long gauge length optical fibre Bragg optical grating is connected with the single-mode fiber of removing coat respectively at the two ends of Fiber Bragg Grating FBG, be with sleeve pipe in Fiber Bragg Grating FBG and the outside of removing the single-mode fiber of coat, the two ends of sleeve pipe are fixed on the single-mode fiber of removing coat by the point of fixity of optical fiber and sleeve pipe respectively, the two ends of removing the single-mode fiber of coat are connected by the signal mode fiber cable of welding point with the outside respectively, and the compound substance encapsulated layer is coated on the outside of above structure.

At first make single long gauge length FBG sensor package structure:

The manufacture craft concrete steps are as follows:

1) peel off near the coating of a segment length (greater than gauge length L) the optical fiber naked grating, after the alcohol cleaning, passing length is the long sleeve pipe of gauge length, two ends and optical cable welding;

2) with glue optical fiber is fixed on an end of sleeve pipe, at other end prestretching to satisfy the needs that compressive strain is measured, fixed fiber and sleeve pipe then.With glue sleeve pipe is fixed on CFRP wire rod or the sheet material afterwards, guarantees that sleeve pipe is not crooked;

3) epoxy resin is evenly smeared along CFRP wire rod or sheet material, treat resin bonded sclerosis after, the total co-operation that becomes one.

Key is the use of sleeve pipe, make and comprise FBG and be in free state at inside pipe casing at interior optical fiber, and optical fiber is fixed on the two ends of sleeve pipe, thus form the homogeneous strain of the long gauge length scope of sensor internal inner fiber, guarantee that the strain that FBG measures represented the interior mean strain of long gauge length scope.

Optical fiber prestretching before being fixed in the sleeve pipe two ends produces certain primary stress, helps measuring compression deformation;

Utilize the synthetic compound substance of fiber-resin to do permanance and the long-time stability that encapsulated layer helps sensor, and with the bonds well and the co-operation of various civil engineering materials;

This method for packing is linked to be integral body with sensor and general commercial optical cable, and volume is little, and light weight can be used the optical cable of existing comparative maturity and connection is installed and lay standard, convenient on-the-spot the installation;

Compare with similar long mark square FBG strain transducer, can stick on the surface of works easily with resin comprehensively, need not weld at on-the-spot two ends, and what is more important can be imbedded the inside of works.

For the performance (as anticorrosion, waterproof, enhanced sensitivity and temperature compensation) of improving above-mentioned single long gauge length FBG sensor, the optical fiber in the gauge length scope can be carried out recoat before being inserted in sleeve pipe.The surface of Fiber Bragg Grating FBG scribbles the first recoat layer, scribbles the second recoat layer on the surface of the other single-mode fiber of removing coat of Fiber Bragg Grating FBG, and casing pipe sleeve is in the outside of the first recoat layer and the second recoat layer.At the requirement of enhanced sensitivity, adopt two kinds of naked gratings of material recoat with different elastic modulus, for example use resin recoat FBG part (L ₀), with the compound substance recoat remainder of resin and fiber; (2) at the requirement of temperature compensation, adopt two kinds of material recoat bare fibres with different temperatures expansion coefficient, the temperature sensitive coefficient of combination that makes sensor is zero; (3) recoat material requirements water-tight corrosion-proof.

The long gauge length FBG strain transducer manufacture craft concrete steps that are used for the small strain test are as follows:

1) peels off near the coating of a segment length (greater than gauge length L) the optical fiber naked grating, the alcohol cleaning;

2) adopt two kinds of naked gratings of material recoat, for example use resin recoat FBG part (L with different elastic modulus ₀), with the compound substance recoat remainder of resin and fiber;

3) optical fiber behind the recoat being passed length is long sleeve pipe, two ends and optical cable welding of gauge length

4) with glue optical fiber is fixed on an end of sleeve pipe, at other end prestretching to satisfy the needs that compressive strain is measured, fixed fiber and sleeve pipe then.With glue sleeve pipe is fixed on CFRP wire rod or the sheet material afterwards, guarantees that sleeve pipe is not crooked.

5) epoxy resin is evenly smeared along CFRP wire rod or sheet material, treat resin bonded sclerosis after, the total co-operation that becomes one.

Temperature compensation about long gauge length FBG strain transducer

1) key is that the material recoat bare fibre that adopts two kinds to have the different temperatures expansion coefficient, the temperature sensitive coefficient of combination that makes sensor are zero, and promptly ambient temperature changes does not have influence to sensor.

2) use sleeve pipe, the optical fiber of recoat be in free state at inside pipe casing, and be fixed on the two ends of sleeve pipe;

3) optical fiber prestretching before being fixed in the sleeve pipe two ends produces certain primary stress, helps measuring compression deformation;

4) utilize the synthetic compound substance of fiber-resin to do permanance and the long-time stability that encapsulated layer helps sensor, and with the bonds well and the co-operation of various civil engineering materials;

5) this method for packing is linked to be integral body with sensor and general commercial optical cable, and volume is little, and light weight can be used the optical cable of existing comparative maturity and connection is installed and lay standard, convenient on-the-spot the installation;

6) compare with similar long mark square FBG strain transducer, can stick on the surface of works easily with resin comprehensively, need not weld at on-the-spot two ends, and what is more important can be imbedded the inside of works.

Distributed long gauge length FBG strain transducer

Distributed long gauge length optical fibre Bragg optical grating strain sensor is in series by a plurality of long gauge length optical fibre Bragg optical grating strain sensors.

Being described in detail of manufacturing process:

1) peels off near the coating of a segment length (greater than gauge length L) optical fiber a series of naked gratings, the alcohol cleaning;

2) adopt two kinds of naked gratings of material recoat with different elastic modulus and temperature expansion coefficient;

3) optical fiber behind the recoat is passed one with each segment mark apart from serving as the sleeve pipe that leaves hole at interval, passing end and optical cable welding;

4) with glue optical fiber is fixed on an end of sleeve pipe, at other end prestretching to satisfy the needs that compressive strain is measured, then in the position of each hole with glue fixed fiber successively and sleeve pipe:

5) after being fixed on a series of sleeve pipes on CFRP wire rod or the sheet material with glue, unification is smeared with epoxy resin.After treating resin bonded sclerosis, the total co-operation that becomes one.

The mounting arrangements mode:

The FBG sensor small, light of compound substance encapsulation can bond with other structured material well, has guaranteed that sensor can be imbedded easily or mounted on surface does not influence its original mechanical property in tested works.Consider the characteristic of distributed long gauge length FBG strain transducer, proposed two kinds of modes of arranging along tested works:

1) full distributed layout.Because the damage position and the degree of structure can't be predicted in advance, and strain has local characteristics, for total is monitored, distributed long gauge length FBG strain transducer is carried out distributed arrangement along tested works.

2) the local distribution formula is arranged.Binding isotherm calculates and practical engineering experience, in advance the Strain Distribution of structure is predicted, only at the relatively large location arrangements FBG sensor of strain.

Characteristics:

1) key is to select two kinds of suitable material recoat bare fibres, and elastic modulus difference on the one hand makes the distortion of (L) in the long gauge length scope most of or all by the middle body (L that comprises FBG ₀) bear, temperature expansion coefficient difference on the other hand, the temperature sensitive coefficient of combination that makes sensor is zero, promptly ambient temperature changes does not have influence to sensor.

2) use sleeve pipe, the optical fiber of recoat is in free state at inside pipe casing, and is fixed on the two ends of sleeve pipe;

3) optical fiber prestretching before being fixed in the sleeve pipe two ends produces certain primary stress, helps measuring compression deformation;

4) utilize the synthetic compound substance of fiber-resin to do permanance and the long-time stability that encapsulated layer helps sensor, and with the bonds well and the co-operation of various civil engineering materials;

5) this method for packing is linked to be integral body with sensor and general commercial optical cable, and volume is little, and light weight can be used the optical cable of existing comparative maturity and connection is installed and lay standard, convenient on-the-spot the installation;

6) compare with similar long mark square FBG strain transducer, can stick on the surface of works easily with resin comprehensively, need not weld at on-the-spot two ends, and what is more important can be imbedded the inside of works.

7) will realize distributed measurement, Fig. 6 shows that structure can be directly installed on and guarantees on the works that transducing part is continuous.The basic sensing principle of Fiber Bragg Grating FBG (FBG)

Light in the transmission of Fiber Bragg Grating FBG (FBG) as shown in Figure 7, theoretical derivation can prove to have maximum reflectivity and minimum transmissivity for making FBG, its centre wavelength should satisfy

λ _B＝2n _eΛ

N wherein _eBe the grating index modulation degree of depth, Λ is a grid cycle.Existing various sensors based on FBG all are the centre wavelength of utilizing strain or temperature change FBG directly or indirectly basically at present, reach the purpose of test physical quantity.

1) strain sensitivity

Δλ _B＝λ _B(1-P _e)*ε

Wherein, P _eIt is the strain optical coefficient of material.For silica fibre, P _e≈ 0.22.Therefore for wave band λ commonly used _B=1550nm has:

Δλ _B＝(1.2pm/με)*ε

2) temperature control

Δλ _B＝λ _B(α+ξ)*ΔT

Wherein, α makes the thermal expansivity of fiber optic materials, and ξ is a thermo-optical coeffecient.Generally speaking, α＜＜ξ.For multiple optical fiber, when temperature is between 20～150 ℃, ξ ≈ 7.2 * 10 ^-6/ ℃; In the time of between 400 ℃, ξ ≈ 10 * 10 ^-6/ ℃.Therefore for wave band λ commonly used _B=1550nm has:

λ _B＝(11pm/℃)*ΔT

The present invention has mainly used the strain sensitivity characteristics of FBG, i.e. the strained influence of centre wavelength is drifted about.And attempt mode, the influence that makes FBG not changed by ambient temperature by temperature compensation.

The realization principle that is used for the long gauge length FBG strain transducer of small strain test

Suppose that the gauge length two ends of sensor and tested works bonding is good, no relative displacement, the detailed derivation of equation and being described as follows:

If the optical fiber in the sleeve pipe adopts two kinds of different encapsulating materials.δ ₁, δ ₀Be two-part displacement, ε ₁, ε ₀Be corresponding strain, E ₁, E ₀Be corresponding elastic modulus, A ₁, A ₀Be corresponding cross-sectional area.

The total displacement at gauge length two ends: δ=δ ₁+ δ ₀=ε ₁L ₁+ ε ₀L ₀

Each point is stressed all identical in the sleeve pipe, therefore has:

${\mathrm{\ϵ}}_1:{\mathrm{\ϵ}}_0=\frac{N_0}{E_1{A}_1}:\frac{N_0}{E_0{A}_0}=\frac{1}{E_1{A}_1}:\frac{1}{E_0{A}_0}$

So the strain of FBG part is ${\mathrm{\ϵ}}_0=\frac{\mathrm{\δ}}{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}$

Mean strain $\stackrel{\‾}{\mathrm{\ϵ}}=\frac{\mathrm{\δ}}{L}=\frac{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}{L}{\mathrm{\ϵ}}_0=((1-\frac{E_0{A}_0}{E_1{A}_1})\frac{L_0}{L}+\frac{E_0{A}_0}{E_1{A}_1})\·{\mathrm{\ϵ}}_0$

Order ${\mathrm{\α}}_E=\frac{E_0{A}_0}{E_1{A}_1},$ ${\mathrm{\α}}_L=\frac{L_0}{L}$ ε=(α is then arranged _L+ α _E-α _Lα _E) ε ₀, so far can obtain following important conclusion:

A) ε ₀=η ε, wherein $\mathrm{\η}=\frac{1}{{\mathrm{\α}}_L+{\mathrm{\α}}_E-{\mathrm{\α}}_L{\mathrm{\α}}_E}$ Be called amplification coefficient

Here, ε is that the distortion by tested works causes, size has nothing to do with sensor itself; ε ₀Strain for the FBG measurement.By following formula as seen, as long as select suitable α _E, α _L, promptly select suitable encapsulating material and length, the strain size that is reflected on the FBG can be amplified.This has greatly improved the too small rough sledding of being flooded by noise easily of the strain measurement value of works under the ambient vibration, for the ambient vibration strain testing has been opened up new approach.If α _E=1, promptly adopt identical material package sensor, ε=ε is then arranged ₀The encapsulation manufacturing method of Here it is our the initial long gauge length FBG sensor that proposes.

B) consider E ₀＜＜E ₁, i.e. α _E→ 0, then $\mathrm{\η}\≈\frac{1}{{\mathrm{\α}}_L}=\frac{L}{L_0},$ The distortion that is equivalent to sensor gauge length L scope is fully by inside pipe casing L ₀The part of length is born.

C) at present adopt high-elastic modulus fibre compound substance encapsulation diagram green portion during actual package, with the red part that comprises FBG of ordinary epoxy resin encapsulation diagram.E under this situation is verified in experiment ₀＜＜E ₁, the strain that FBG measures and the mean strain of practical structures thing are satisfied: ${\mathrm{\ϵ}}_0=\frac{L}{L_0}\stackrel{\‾}{\mathrm{\ϵ}}$

The realization principle of long gauge length FBG strain transducer temperature compensation

Suppose that it is that promptly temperature variation is to the not influence of tested works on zero the tested works that sensor is installed in temperature expansion coefficient.Suppose that in addition tested works is not subjected to external force, the gauge length two ends of sensor and tested works bonding are good, and no relative displacement is zero here.If the temperature sensitive coefficient of FBG is γ _T, the strain sensitive coefficient is γ _ε

Suppose that the optical fiber in the sleeve pipe adopts two kinds of different encapsulating materials, δ ₁, δ ₀Be two-part displacement, ε ₁, ε ₀Be corresponding strain, E ₁, E ₀Be corresponding elastic modulus, C ₁, C ₀Be corresponding temperature expansion coefficient, A ₁, A ₀Be corresponding cross-sectional area.

The only total displacement that causes of temperature variation ${\mathrm{\δ}}^T={\mathrm{\δ}}_1^T+{\mathrm{\δ}}_0^T=(C_1(L-L_0)+C_0{L}_0)T$

Because total displacement δ=δ ^T+ δ ^N=0, so must there be an external force at the sensor two ends, be made as N.Therefore, the drift of FBG centre wavelength is made up of three parts in this encapsulating structure that is caused by temperature:

λ＝λ ₁+λ ₂+λ ₃

λ ₁Temperature expansion by FBG part encapsulating material causes; λ ₂N causes by external force; λ ₃Be the influence of temperature to FBG itself.

Obvious λ ₁=C ₀T γ _ε

From the exploitation of the above-mentioned long gauge length FBG strain transducer that is used for small strain test as can be known, the strain of the FBG that is caused by external force N is:

${\mathrm{\ϵ}}_0^N=\frac{{\mathrm{\δ}}^N}{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}=-\frac{{\mathrm{\δ}}^T}{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}$

Therefore ${\mathrm{\λ}}_2={\mathrm{\ϵ}}_0^N{\mathrm{\γ}}_{\mathrm{\ϵ}}=-\frac{{\mathrm{\δ}}^T{\mathrm{\γ}}_{\mathrm{\ϵ}}}{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}=-\frac{(C_1(L-L_0)+C_0{L}_0)T{\mathrm{\γ}}_{\mathrm{\ϵ}}}{L_0+\frac{E_0{A}_0}{E_1{A}_1}(L-L_0)}$

Order ${\mathrm{\α}}_E=\frac{E_0{A}_0}{E_1{A}_1},$ ${\mathrm{\α}}_L=\frac{L_0}{L},$ ${\mathrm{\α}}_C=\frac{C_0}{C_1},$ Then ${\mathrm{\λ}}_2=-\frac{C_1(1-{\mathrm{\α}}_L)+C_0{\mathrm{\α}}_L}{{\mathrm{\α}}_E(1-{\mathrm{\α}}_L)+{\mathrm{\α}}_L}{\mathrm{T\γ}}_{\mathrm{\ϵ}}$

λ ₃＝Tγ _T

Comprehensive above various getting: $\mathrm{\λ}={\mathrm{\λ}}_1+{\mathrm{\λ}}_2+{\mathrm{\λ}}_3=(C_0{\mathrm{\γ}}_{\mathrm{\ϵ}}-\frac{C_1(1-{\mathrm{\α}}_L)+C_0{\mathrm{\α}}_L}{{\mathrm{\α}}_E(1-{\mathrm{\α}}_L)+{\mathrm{\α}}_L}{\mathrm{\γ}}_{\mathrm{\ϵ}}+{\mathrm{\γ}}_T)T$

Here to eliminate Temperature Influence, i.e. temperature variation, FBG centre wavelength does not have drift, then

${\mathrm{\η}}_T=C_0{\mathrm{\γ}}_{\mathrm{\ϵ}}-\frac{C_1(1-{\mathrm{\α}}_L)+C_0{\mathrm{\α}}_L}{{\mathrm{\α}}_E(1-{\mathrm{\α}}_L)+{\mathrm{\α}}_L}{\mathrm{\γ}}_{\mathrm{\ϵ}}+{\mathrm{\γ}}_T=0$

η _TBe only relevant with a material coefficient, visible as long as select suitable encapsulating material, temperature can be eliminated the influence of this long gauge length FBG strain transducer.

Consider to adopt a kind of material package, i.e. A ₁=A ₀, E ₁=E ₀, C ₁=C ₀, α then _E=1, α _L=1, η then _T=γ _T≠ 0, obviously can't realize temperature compensation.So adopting two or more different encapsulating materials is the necessary conditions that realize temperature compensation.

Consider E ₀＜＜E ₁, i.e. α _E→ 0, by η _T=0 can get $C_1=\frac{{\mathrm{\γ}}_T}{{\mathrm{\γ}}_{\mathrm{\ϵ}}}\·\frac{{\mathrm{\α}}_L}{1-{\mathrm{\α}}_L},$ With C ₀Irrelevant.

Have generally speaking: γ _T=11pm/ ℃, γ _ε=1.2pm/ μ m, then $C_1\≈\frac{10{\mathrm{\α}}_L}{1-{\mathrm{\α}}_L}$ (μ m/ ℃), wherein 0＜α _L＜1.If ${\mathrm{\α}}_L=\frac{1}{2},$ C then ₁≈ 10

Beneficial effect: compared with prior art, the encapsulating structure of the distributed long mark square FBG strain transducer that the present invention proposes has following advantage:

Distributed long gauge length FBG strain transducer can be realized following important measurement: a) mean strain is measured.Mean strain can avoid the stress/strain that causes because of factors such as cracks to concentrate, thereby makes the strain value of measurement can reflect the curvature of member intuitively.B) distributed measurement.Can contain structure as much as possible in a big way, obtain a vector that constitutes by all mean strain components, thereby complete relatively structural information is provided.C) kinetic measurement.High speed FBG demodulating system can be obtained the time-history curves of distributed mean strain efficiently, be converted to frequency domain after, can obtain the wide cut spectrum curve, thereby obtain the natural frequency of vibration and the mode mean strain of high-order.This provides advantage for the structure for health diagnosis based on vibration.

The present invention is used for large structures such as RC (reinforced concrete) or other composite structure are carried out the distribution monitoring of local failure, as monitor generation, position and the degree in crack, creeping of monitoring of structures material, whether the monitoring reinforcing bar corrodes, and whether the monitoring concrete strength degenerates.

The present invention can utilize the high precision strain measurement result of long gauge length sensor to replace the overall performance evaluation that deformation test methods such as fleximeter are used for works.Although fleximeter be generally acknowledge at present integrality performance of the structure is measured the most directly effective sensor, but need a reference position to limit the use of its reality during owing to installation, for example can not have such " reference point " to place fleximeter in the bridge span.

The present invention is used for the measurement environment vibration dynamic strain time-histories of bridge and other works down, extracts the feature modal parameter of works with this, for the health monitoring of structure provides foundation.And be worth particularly pointing out be, in flexure mode structure, the measurement that is actually a kind of amount of deflection degree of freedom with acceleration is similar, mean strain is actually the measurement of the difference of rotational degree of freedom, thereby a kind of metering system of rotational degree of freedom is provided indirectly.That is to say that distributed long gauge length FBG strain transducer can provide the kinetic measurement with the accelerometer equivalence, the former emphasizes rotational degree of freedom, and the latter emphasizes the amount of deflection degree of freedom.

The present invention be used to realize high-acruracy survey under the environmental baseline such as temperature variation complexity and works in good time and long term monitoring.

Description of drawings

Fig. 1 is common commercialization Fiber Bragg Grating FBG (FBG) synoptic diagram.

Fig. 2 is signal mode fiber cable (SMC) synoptic diagram.

Fig. 3 is single long gauge length FBG sensor package structural representation.

Fig. 4 is the long gauge length FBG sensor package structural representation that is used for the small strain test.

Fig. 5 is the temperature compensation encapsulating structure synoptic diagram of long gauge length FBG sensor.

Fig. 6 is a distributed long gauge length FBG sensor package structural representation.

Fig. 7 is the test philosophy synoptic diagram of FBG.

Have among the above figure: Fiber Bragg Grating FBG 1, remove the single-mode fiber 2 of coat, single-mode fiber 3; protective seam 4, cushion 5, sleeve pipe 6; point of fixity 7, welding point 8, compound substance encapsulated layer 9; encapsulation point 10, the first recoat layers 11, the second recoat layer 12 of signal mode fiber cable; sandwich layer 13; covering 14, coat 15, FBG grid cycle 16.

Embodiment

This strain transducer is in series by a plurality of long gauge length optical fibre Bragg optical grating 1 strain transducers; Wherein single long gauge length optical fibre Bragg optical grating 1 is connected with the single-mode fiber 2 of removing coat respectively at the two ends of Fiber Bragg Grating FBG 1, be with sleeve pipe 6 in Fiber Bragg Grating FBG 1 and the outside of removing the single-mode fiber 2 of coat, the two ends of sleeve pipe 6 are fixed on the single-mode fiber 2 of removing coat by the point of fixity 7 of optical fiber and sleeve pipe respectively, the two ends of removing the single-mode fiber 2 of coat are connected by the signal mode fiber cable of welding point 8 with the outside respectively, and compound substance encapsulated layer 9 is coated on the outside of above structure.The surface of described Fiber Bragg Grating FBG 1 scribbles the first recoat layer 11, and the surface of the single-mode fiber of removing coat 2 by Fiber Bragg Grating FBG 1 scribbles the second recoat layer 12, and sleeve pipe 6 is enclosed within the outside of the first recoat layer 11 and the second recoat layer 12.The first recoat layer 11, the second recoat layer 12 adopt two kinds of naked gratings of material recoat with different elastic modulus at the requirement of enhanced sensitivity, for example use resin recoat FBG part (L ₀), with the compound substance recoat remainder of resin and fiber; Requirement at temperature compensation, adopt two kinds of resin and fibrous material recoat bare fibres with different temperatures expansion coefficient, for example resin adopts epoxy resin, and fiber adopts carbon fiber or PBO polymer composites such as (poly-p-phenylenebenzobisoxazole); The temperature sensitive coefficient of combination that makes sensor is zero.

Recoat material requirements water-tight corrosion-proof.

The simple and easy long gauge length FBG strain transducer of making

The simple and easy long gauge length FBG strain transducer of present making in laboratory, the specific implementation process is as follows:

1) peel off near the coating of a segment length (greater than gauge length L) the optical fiber naked grating, after the alcohol cleaning, the steel sleeve that to pass the about 1mm length of diameter be gauge length L is passing end and optical cable welding;

2) with the end fixed fiber of 502 glue at steel pipe, at other end prestretching to satisfy the needs that compressive strain is measured, the other end of fixed fiber and steel pipe then;

3) guarantee that at the counterweight of quality such as CFRP wire rod two ends extension wire rod is straightened, the steel pipe that will be with optical fiber with 502 glue is fixed on the CFRP wire rod, guarantees that it is not crooked, and then covers on the steel pipe with identical wire rod;

4) evenly smear along the CFRP wire rod with epoxy resin, treat resin bonded sclerosis after, total becomes one.

Fiber Bragg Grating FBG 1 (FBG), proper length are generally 1-2 centimetre

Remove the single-mode fiber 2 of coat, 0.25 millimeter of diameter

Single-mode fiber 3 (SMF), 0.5 millimeter of diameter

Sleeve pipe 6, about 0.5 millimeter of diameter

The first recoat layer 11 (containing the FBG part), length L ₀

The second recoat layer 12 (not containing the FBG part), effective length is (L-L ₀)

Application example in the RC beam

The application of distributed long gauge length FBG Fibre Optical Sensor in the reinforced concrete structure health monitoring may be summarized to be two levels.The one, be the damage of representative with the Crack Monitoring, the 2nd, the overall performance evaluation of structure.The part important conclusion of following brief overview FBG sensor in the RC beam is used.

As mentioned above, traditional " point " foil gauge often occurs losing efficacy because of stress raisers and crack, and on large-scale civil structure, distribute arrange unactual yet.Long gauge length FBG sensor can remedy the deficiency of this two aspect, and on the one hand the strain equalization has relaxed the local stress sudden change that causes after the crack occurs, and guarantees that sensor still can effectively work; On the other hand, being connected in series long gauge length FBG sensor can carry out distribution measuring in certain zone of total or structure, contains complete relatively crack information.Test shows the common RC beam of a span 2m, and the FBG sensor of gauge length 0.2m can be monitored appearance, position and the degree in crack effectively.

The overall performance evaluation that can be used for structure is the most outstanding advantage of distributed long gauge length FBG sensor.Test shows, the common RC beam of a span 2m, and 4 are curved, and the mean strain of the FBG sensor measurement that gauge length 0.4m is above and the mid-span deflection of RC beam have good linear relationship.This important phenomenon explanation, as long as gauge length and position suitable, long gauge length FBG sensor can replace displacement meter fully, and it is well-known, displacement meter is that integrality performance of the structure is measured the most directly effective sensor, but need a reference position to limit the use of its reality during owing to installation, for example can not have such " reference point " to place displacement meter in the bridge span.In addition, relatively find with the result of Theoretical Calculation, mean strain and theoretical value in the 0.2m length of actual measurement are more identical, the strain of 0.8 length that obtains after the actual measurement mean strain in the strain of the 0.4m length that obtains after the actual measurement mean strain in two 0.2m length is average and four the 0.2m length is average is more consistent with theoretical value, this is for carrying out such as load assessment reinforced concrete structure based on the mean strain of actual measurement, rigidity is with fixed, and contrary analysis the such as reinforcement stresses estimation provides important evidence.In conjunction with above Crack Monitoring as seen, the common RC beam of a span 2m, the FBG sensor of gauge length 0.2m not only can be monitored the crack effectively but also can assess the whole member performance through the postpone of distribution cloth.

The vibration-testing example

1) girder steel

One long 1m, wide 50mm, the Steel Cantilever vibration of beam test shows of high 3mm: a gauge length is 10cm's

The accelerometer of a FBG sensor and a corresponding frequencies 50Hz is installed in the free end of beam, the knocking vibration can be measured the strain and the reaction of acceleration time-histories of girder steel down, through fast Fourier transform, can obtain the spectrum curve of structure, thereby can utilize peak value to find out the natural frequency of Tongliang County simply.Can find that the structural natural frequencies that FBG sensor and accelerometer obtain is very identical.

2) shaketalle test of RC bridge pier

One high 2m, xsect is that the shaketalle test of the RC bridge pier of 45cm * 80cm shows: the top that sticks on two sides of test specimen when the FBG sensor with epoxy resin, the position that foil gauge with identical gauge length is attached to its parallel sided is in order to relatively the time, the earthquake strain-responsive that both measure overlaps substantially, and the time domain under the simple harmonic oscillation also has good consistent with frequency curve.

Claims (4)

1. a distributed long gauge length optical fibre Bragg optical grating strain sensor is characterized in that this strain transducer is in series by a plurality of long gauge length optical fibre Bragg optical gratings (1) strain transducer; Wherein single long gauge length optical fibre Bragg optical grating (1) is connected with the single-mode fiber (2) of removing coat respectively at the two ends of Fiber Bragg Grating FBG (1), be with sleeve pipe (6) at the Fiber Bragg Grating FBG (1) and the outside of removing the single-mode fiber (2) of coat, the two ends of sleeve pipe (6) are fixed on the single-mode fiber (2) of removing coat by the point of fixity (7) of optical fiber and sleeve pipe respectively, the two ends of removing the single-mode fiber (2) of coat are connected by the signal mode fiber cable of welding point (8) with the outside respectively, and compound substance encapsulated layer (9) is coated on the outside of above structure.

2. based on the described long gauge length optical fibre Bragg optical grating strain sensor of claim 1, the surface that it is characterized in that described Fiber Bragg Grating FBG (1) scribbles the first recoat layer (11), surface at the other single-mode fiber of removing coat (2) of Fiber Bragg Grating FBG (1) scribbles the second recoat layer (12), and sleeve pipe (6) is enclosed within the outside of the first recoat layer (11) and the second recoat layer (12).

3. long gauge length optical fibre Bragg optical grating strain sensor according to claim 2 is characterized in that the requirement at enhanced sensitivity of the first recoat layer (11), the second recoat layer (12), adopts two kinds of naked gratings of material recoat with different elastic modulus; At the requirement of temperature compensation, adopt two kinds of material recoat bare fibres with different temperatures expansion coefficient, the temperature sensitive coefficient of combination that makes sensor is zero.

4. the manufacture method of a distributed long gauge length optical fibre Bragg optical grating strain sensor as claimed in claim 1, step is as follows:

1) peel off near the bare fibre Bragg grating (1) a segment length greater than the optical fiber coating of gauge length L, after the alcohol cleaning, pass one with each segment mark apart from serving as the sleeve pipe (6) that leaves hole at interval, two ends and optical cable welding;

2) single-mode fiber (2) that will have Fiber Bragg Grating FBG (1) with glue is fixed on an end of sleeve pipe (6), at other end prestretching to satisfy the needs that compressive strain is measured, then in the position of each hole with glue fixed fiber successively and sleeve pipe, with glue sleeve pipe (6) is fixed on CFRP wire rod or the sheet material afterwards, guarantees that sleeve pipe is not crooked;

3) epoxy resin is evenly smeared along CFRP wire rod or sheet material, treated the resin bonded sclerosis after being fixed on a series of sleeve pipes on CFRP wire rod or the sheet material with glue.

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