CN110044682A - Unilateral gap aluminium alloy test specimen crack Propagation monitoring method based on FBG sensor - Google Patents

Unilateral gap aluminium alloy test specimen crack Propagation monitoring method based on FBG sensor Download PDF

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CN110044682A
CN110044682A CN201910255191.9A CN201910255191A CN110044682A CN 110044682 A CN110044682 A CN 110044682A CN 201910255191 A CN201910255191 A CN 201910255191A CN 110044682 A CN110044682 A CN 110044682A
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fbg2
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CN110044682B (en
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曾捷
郑丁午
吴肖
于惠勇
杨钰敏
张旭苹
吴心怡
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Nanjing University of Aeronautics and Astronautics
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    • 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
    • G01B11/165—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by means of a grating deformed by the object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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    • G01N2203/0058—Kind of property studied
    • G01N2203/006—Crack, flaws, fracture or rupture
    • G01N2203/0062—Crack or flaws
    • G—PHYSICS
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    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0073—Fatigue
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/0641—Indicating or recording means; Sensing means using optical, X-ray, ultraviolet, infrared or similar detectors

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Abstract

The unilateral gap aluminium alloy test specimen crack Propagation monitoring method based on FBG sensor that the invention discloses a kind of, using crack Propagation in distribution type fiber-optic Bragg grating sensor network aware structure, FBG sensor center wavelength shift amount is extracted as characteristic parameter, using different location FBG sensor center wavelength shift amount with crack propagation changing rule, fatigue crack length projected relationship model is established, realizes crack Propagation length prediction.The features such as crack Propagation monitoring method in the present invention realizes the prediction of On Crack Propagation position by calculating FBG sensor center wavelength shift amount, has quickly, intuitively, and be not necessarily to a large amount of priori knowledges.

Description

Unilateral gap aluminium alloy test specimen crack Propagation monitoring based on FBG sensor Method
Technical field
The present invention relates to the fatigue damage detection technical fields of monitoring structural health conditions, more particularly to a kind of FBG that is based on to sense The unilateral gap aluminium alloy test specimen crack Propagation monitoring method of device.
Background technique
Currently, the materials of aluminium alloy account for exhausted large scale in aerospace vehicle structural material dosage, and in aluminium alloy material Expect in the complex mechanical structures such as spacecraft and aircraft, mechanical critical tissue and component are due to for a long time by extraneous heat or power etc. The effect of various reversed fatigue load easily causes structural wear, failure, so as to cause fatigue damage and fracture.Fatigue crack is It is the original state form of fatigue damage fracture.Although aerospace vehicle there are still being continued to use when fine crack, It is that its performance can be declined, if can then eventually lead to housing construction for a long time without monitoring and safeguarding and disintegrate and more serious Catastrophic effect.
With the rapid development of aerospace field, more more and more urgent are also become to the monitoring structural health conditions of aerospace vehicle With it is important.And fiber-optic grating sensor, because it is with light weight, flexibility is good, small in size, electromagnetism interference, collects signal transmission With sensing in one, be easy to the particular advantages such as distributed cloth networking, overcome many deficiencies of traditional electrical sensor, more meet existing For the demand of aerospace field sensing technology, under especially extremely complicated application environment, its unique advantage has even more been shown. Therefore in recent years, fiber grating sensing technology is rapidly developed, and fiber-optic grating sensor already becomes aerospace field knot One of the sensor of structure health monitoring most mainstream.
Currently in the prediction of fatigue crack damage monitoring, be mostly in a manner of using neural network and support vector machines etc., With great amount of samples data training network, although precision is higher, by being then based on large sample, Generalization Capability is bad, real-time and Bad practicality.
Summary of the invention
The technical problem to be solved by the present invention is to provide one kind and be based on for defect involved in background technique The unilateral gap aluminium alloy test specimen crack Propagation monitoring method of FBG (Fiber Bragg Grating, FBG) sensor, is adopted With crack Propagation in distribution type fiber-optic Bragg grating sensor network aware structure, FBG sensor central wavelength is extracted Offset as characteristic parameter, using different location FBG sensor center wavelength shift amount with crack propagation changing rule, Fatigue crack length projected relationship model is established, realizes crack Propagation length prediction.
The present invention uses following technical scheme to solve above-mentioned technical problem:
Unilateral gap aluminium alloy test specimen crack Propagation monitoring method based on FBG sensor, comprising the following steps:
Step 1) carries out finite element modeling to unilateral gap aluminium alloy test specimen:
According to preset elasticity modulus, Poisson's ratio, size, Circularhole diameter, unilateral gap length, the building of precrack length Unilateral gap aluminum alloy specimen part finite element model, wherein unilateral gap direction and test specimen edge are vertical, direction of check and unilateral Notch direction is identical；
Step 2), the intersection point for defining two center of circular hole line of test specimen and direction of crack propagation is crackle starting point, by FBG1, Between tri- strain transducers of FBG2, FBG3 equidistantly arrange along direction of check, and sensor is vertical with crack propagation path Away from for preset distance threshold, tri- sensor axis of FBG1, FBG2, FBG3 are to vertical with direction of check；
Step 3), tri- strain transducer reflection kernel wavelength of FBG1, FBG2, FBG3 before acquiring fatigue test are as former Primordium calibration signal, is denoted as λRi, wherein i=1,2,3, i indicate sensor numbers；The FBG sensor pasted is passed through into wire jumper again Series connection access fiber Bragg grating (FBG) demodulator, and two circular holes of clamping test pieces, using permanent load tensile test specimen, obtain different crackles Length corresponds to tri- strain transducer central wavelength data of FBG1, FBG2, FBG3, is denoted as { Wi,j, wherein i=1,2,3, indicate Sensor number, j indicate crack length；
Step 4), according to { Wi,jAnd tri- strain transducer archicenter wavelength standard signal λ of FBG1, FBG2, FBG3Ri, Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3 are calculated, the corresponding each sensing of different crack lengths is obtained Device center wavelength shift amount response characteristic set { Si,j, wherein i=1,2,3, indicate that sensor number, j indicate crack length；
Step 5), according to { Si,j, using center wavelength shift amount as dependent variable y, using crack length be independent variable x in two dimension Described point one by one in rectangular coordinate system, utilization index function expressionFitting The relationship of FBG1, FBG2 center wavelength shift amount and crack length calculates fitting expression parameter a1、a2、b1、b2、c1、c2、 c3；Recycle polynomial expression y=a3x6+b3x5+c4x4+d1x3+d2x2+d3x+d4It is fitted FBG3 center wavelength shift amount and splits Line length relation calculates fitting expression parameter a3、b3、c4、d1、d2、d3、d4, it is corresponding thus to establish three FBG sensors Fatigue Crack Propagation Prediction functional relationship model；
Step 6), the central wavelength and step that unknown crackle is responded according to tri- strain transducers of FBG1, FBG2, FBG3 3) tri- strain transducer archicenter wavelength standard signal λ of FBG1, FBG2, FBG3 inRi, it is corresponding to calculate unknown crack length Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3, are denoted as △ λ respectivelyFBG1、△λFBG2、△λFBG3；
Step 7) is divided according to crack length projected relationship Model on Crack line extended area in step 5), is compared The center wavelength shift amount size of tri- strain transducers of FBG1, FBG2, FBG3 determines unknown crack propagation region, tool Body includes:
Step 7.1), the x augment direction along two-dimensional Cartesian coordinate system, successively by FBG1 matched curve and FBG2 matched curve Intersection point be denoted as (xa,ya), the intersection point of FBG1 matched curve and FBG3 matched curve is denoted as (xb,yb), FBG2 matched curve with The intersection point of FBG3 matched curve is denoted as (xc,yc), the intersection point of FBG2 matched curve and FBG1 matched curve is denoted as (xd,yd), counterincision Line extended area is divided, region division principle are as follows:
x≤xaRegion, be denoted as region I；xa<x<xbRegion, be denoted as region II；xb≤x≤xcRegion, be denoted as region III；xc<x<xdRegion, be denoted as region IV；x≥xdRegion, be denoted as region V；
Step 7.2), according to 3 FBG sensor center wavelength shift amount △ λ in step 6)FBG1、△λFBG2、△λFBG3's Sensor fitting function relational model in numerical values recited relationship and step 5, determines crack propagation region, specific to determine Principle are as follows:
If △ λFBG1>△λFBG2>△λFBG3, determine crack propagation in region I；
If △ λFBG2>△λFBG1>△λFBG3, determine crack propagation in region II；
If △ λFBG2>△λFBG3>△λFBG1, determine crack propagation in region III；
If △ λFBG3>△λFBG2>△λFBG1, determine crack propagation in region IV；
If △ λFBG3>△λFBG1>△λFBG2, determine crack propagation in region V；
Step 8), 3 FBG sensor center wavelength shift amount △ λ being calculated according to step 6)FBG1、△λFBG2、△ λFBG3, three FBG center wavelength shift amounts of gained and crack length fitting function relation curve in step 5) are substituted into, is determined not Know three preliminary crack length values of crackle, then using FBG sensor center wavelength shift amount absolute value accounting as weight, calculates Obtain final unknown crack extending length:
Step 8.1), in the unknown crack propagation region determined by step 7), three FBG that step 6 is calculated Center sensor wavelength shift △ λFBG1、△λFBG2、△λFBG3, substitute into the resulting three Function Fitting curved line relations of step 5) In formula, three preliminary crack length values are calculated；
Step 8.1.1), it is non-monotonic, i.e. same center there are certain fitting function curve in identified segment Corresponding two different crack lengths of wavelength shift, remember the coordinate point in the non-monotonic curve with identical central wavelength shift It Wei not (xq,yq)、(xq’,yq), wherein q=1,2,3, q indicate that sensor numbers, the peak of curve coordinate are (xpq,ypq), there is xq <xpq<xq'；Define the crack length and central wavelength on the corresponding fitting function curve of other two FBG sensor in the section Offset relationship is respectively (xi,yi)、(xj,yj), i, j=1,2,3, i, j expression sensor number, then:
If xi、xj≤xpq, with xq、xi、xjAs preliminary crack length calculated value；
If xi、xj>xpq, with xq’、xi、xjAs preliminary crack length calculated value；
If xi≤xpq≤xj, compare | xi-xq| with | xj-xq' | size, when | xi-xq| it is smaller, then with xqWith xi、xjAs first Crack length calculated value is walked, when | xj-xq' | it is smaller, then with xq' and xi、xjAs preliminary crack length calculated value；
If xj≤xpq≤xi, compare | xj-xq| with | xi-xq' | size, when | xj-xq| it is smaller, then with xqWith xi、xjAs first Crack length calculated value is walked, when | xi-xq' | it is smaller, then with xq' and xi、xjAs preliminary crack length calculated value；
Step 8.1.2), when being monotonous curve in identified segment, note FBG1, FBG2 and FBG3 sensor is corresponding Fitting function curve on crack length and center wavelength shift magnitude relation be respectively (x1,y1)、(x2,y2)、(x3,y3), directly It connects with x1、x2、x3As preliminary crack length calculated value；
Step 8.2), the center wavelength shift amount that tri- strain transducers of FBG1, FBG2, FBG3 respond unknown crackle Absolute value accounting is as weight factor, i.e.,
Wherein △ λFBG1、△λFBG2、△λFBG3Respectively indicate calculated by step 6 it is resulting associated with unknown crack length FBG1, FBG2, FBG3 center sensor wavelength shift；To calculated just by each FBG matched curve institute in step 8.1) Step crack length calculated value is weighted, and determines final unknown crack length value X:
Or
The invention adopts the above technical scheme compared with prior art, has following technical effect that
1. the present invention uses fiber Bragg grating sensor, it is only necessary to which 3 fiber-optic grating sensors constitute series network, i.e., It can be achieved to monitor aluminium alloy single edge notched specimen crack Propagation, it is negative to reduce system compared to piezoelectric type sensor array Load has the remarkable advantages such as the simple, electromagnetism interference of structure；
2. carrying out crack Propagation prison as characteristic parameter using fiber Bragg grating sensor reflection kernel wavelength Surveying has good linear relationship with prediction, and strain, compared to other signal characteristic processing methods, certainly using sensor The optical characteristics of body is a kind of easier, intuitive physical monitoring method；
3. in current many progress fatigue crack damage monitoring research methods, it usually needs establish in a large amount of priori knowledges On the basis of.And this method only needs less sample using the center sensor wavelength shift and crack length relationship of different location This point can establish crack propagation prediction fitting function relational model, and weight factor is combined to carry out crack length prediction, enhancing Engineering practicability.
Detailed description of the invention
Fig. 1 is the structure of unilateral gap aluminium alloy test specimen, specification schematic diagram in the present invention；
Fig. 2 is the schematic layout pattern of tri- strain transducers of FBG1, FBG2, FBG3 in the present invention；
Fig. 3 is the unilateral gap aluminium alloy test specimen crack Propagation monitoring method flow chart based on FBG sensor；
Fig. 4 is crack Propagation region division schematic diagram in the present invention；
Fig. 5 is unknown crack length identification schematic diagram in the present invention.
Specific embodiment
Technical solution of the present invention is described in further detail with reference to the accompanying drawing:
The present invention can be embodied in many different forms, and should not be assumed that be limited to the embodiments described herein.On the contrary, It is thorough and complete to these embodiments are provided so that the disclosure, and model of the invention will be given full expression to those skilled in the art It encloses.In the accompanying drawings, for the sake of clarity it is exaggerated component.
Unilateral gap aluminium alloy test specimen crack Propagation monitoring method flow chart based on FBG sensor as shown in figure 3, Specific implementation steps are as follows:
Step 1) carries out finite element modeling to test specimen:
Building unilateral gap aluminum alloy specimen part finite element model, elasticity modulus 70Gpa, Poisson's ratio 0.33, having a size of 240mm × 200mm × 15mm, Circularhole diameter 25mm, test specimen unilateral gap length be 37mm, the long 2.5mm of precrack, It is identical with unilateral gap direction, since unilateral gap tip, as shown in Figure 1；
Step 2) rises as shown in Fig. 2, defining the intersection point of two center of circular hole line of test specimen and direction of crack propagation for crackle Tri- strain transducers of FBG1, FBG2, FBG3 are sequentially arranged in apart from the position notch 20mm, 40mm and 60mm, i.e. distance by point Crackle starting point is followed successively by 32.5mm, 52.5mm and 72.5mm, and setting sensor and crack propagation path vertical interval are 10mm, Tri- sensor axis of FBG1, FBG2, FBG3 are to vertical with direction of check；
Step 3), tri- strain transducer reflection kernel wavelength of FBG1, FBG2, FBG3 before acquiring fatigue test are as former Primordium calibration signal, is denoted as λRi, wherein i=1,2,3, i indicate sensor numbers；The FBG sensor pasted is passed through into wire jumper again Series connection access fiber Bragg grating (FBG) demodulator, and two circular holes of clamping test pieces, 20KN permanent load tensile test specimen is utilized, it obtains different Crack length corresponds to tri- strain transducer central wavelength data of FBG1, FBG2, FBG3, is denoted as { Wi,j, wherein i=1,2,3, Indicate that sensor number, j indicate crack length；
Step 4), according to { Wi,jAnd tri- strain transducer archicenter wavelength standard signal R of FBG1, FBG2, FBG3f, Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3 are calculated, the corresponding each sensing of different crack lengths is obtained Device center wavelength shift amount response characteristic set { Si,j, wherein i=1,2,3, i expression sensor numbers, j indicate crack length；
Step 5), according to { Si,j, using center wavelength shift amount as dependent variable y, using crack length be independent variable x in two dimension Described point one by one in rectangular coordinate system, utilization index function expressionFitting The relationship of FBG1, FBG2 center wavelength shift amount and crack length calculates fitting expression parameter a1、a2、b1、b2、c1、c2、 c3；Recycle polynomial expression y=a3x6+b3x5+c4x4+d1x3+d2x2+d3x+d4It is fitted FBG3 center wavelength shift amount and splits Line length relation calculates fitting expression parameter a3、b3、c4、d1、d2、d3、d4, it is corresponding thus to establish three FBG sensors Fatigue Crack Propagation Prediction functional relationship model；
Step 6), the central wavelength and step that unknown crackle is responded according to tri- strain transducers of FBG1, FBG2, FBG3 3) tri- strain transducer archicenter wavelength standard signal λ of FBG1, FBG2, FBG3 inRi, it is corresponding to calculate unknown crack length Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3, are denoted as △ λ respectivelyFBG1、△λFBG2、△λFBG3；
Step 7) is divided according to crack length projected relationship Model on Crack line extended area in step 5), is compared The center wavelength shift amount size of tri- strain transducers of FBG1, FBG2, FBG3 determines unknown crack propagation region, such as Shown in Fig. 4, specifically include:
Step 7.1), the x augment direction along two-dimensional Cartesian coordinate system, successively by FBG1 matched curve and FBG2 matched curve Intersection point be denoted as (xa,ya), the intersection point of FBG1 matched curve and FBG3 matched curve is denoted as (xb,yb), FBG2 matched curve with The intersection point of FBG3 matched curve is denoted as (xc,yc), the intersection point of FBG2 matched curve and FBG1 matched curve is denoted as (xd,yd), counterincision Line extended area is divided, region division principle are as follows:
x≤xaRegion, be denoted as region I；xa<x<xbRegion, be denoted as region II；xb≤x≤xcRegion, be denoted as region III；xc<x<xdRegion, be denoted as region IV；x≥xdRegion, be denoted as region V.
Step 7.2), according to 3 FBG sensor center wavelength shift amount △ λ in step 6)FBG1、△λFBG2、△λFBG3's Sensor fitting function relational model in numerical values recited relationship and step 5), determines crack propagation region, specific to determine Principle are as follows:
If △ λFBG1>△λFBG2>△λFBG3, determine crack propagation in region I；
If △ λFBG2>△λFBG1>△λFBG3, determine crack propagation in region II；
If △ λFBG2>△λFBG3>△λFBG1, determine crack propagation in region III；
If △ λFBG3>△λFBG2>△λFBG1, determine crack propagation in region IV；
If △ λFBG3>△λFBG1>△λFBG2, determine crack propagation in region V；
Step 8), 3 FBG sensor center wavelength shift amount △ λ being calculated according to step 6)FBG1、△λFBG2、△ λFBG3, three FBG center wavelength shift amounts and crack length fitting function relation curve obtained by step 5) are substituted into, is determined unknown The preliminary crack length calculated value of three of crackle, in conjunction with FBG sensor center wavelength shift amount absolute value accounting as weight, really Fixed final unknown crack extending length；
Step 8.1) enables △ λ in step 6)FBG1=y1, △ λFBG2=y2, △ λFBG3=y3, in FBG1, FBG2 and FBG3 tri- Its corresponding coordinate points is respectively (x in matched curve1,y1)、(x2,y2) and (x3,y3), therewith with the coordinate of identical y value Respectively (x1’,y1)、(x2’,y2) and (x3’,y3), to be illustrated as shown in Figure 5:
(a) when crack propagation to region I, there are non-monotonic section, FBG1 curve and FBG2 curves to exist for FBG1 matched curve I, the line of demarcation intersection point in the region II is denoted as (xi,yi), the peak coordinate of FBG1 curve is denoted as (xp1,yp1)；
If y1<yi, then by x1、x2、x3As preliminary crack length calculated value；
If yi≤y1<yp1, then for same y1Value, there are two different crack length x1And x1', it need to be according to x2、x3With xp1 Between size relation determination be x on earth1Or x1', and further determine that preliminary crack length calculated value, rule are as follows:
1. if x2、x3≤xp1, then by x1、x2、x3As preliminary crack length calculated value；
2. if x2、x3>xp1, then by x1’、x2、x3As preliminary crack length calculated value；
3. if x2≤xp1≤x3, compare | x1-x2| with | x3-x1' | size, when | x1-x2| when smaller, then with x1With x2、x3Make For preliminary crack length calculated value, when | x3-x1' | when smaller, then with x1' and x2、x3As preliminary crack length calculated value；
4. if x3≤xp1≤x2, compare | x3-x1| with | x2-x1' | size, when | x3-x1| when smaller, then with x1With x2、x3Make For preliminary crack length calculated value, when | x2-x1' | when smaller, then with x1' and x2、x3As preliminary crack length calculated value；
If y1=yp1, then by xp1、x2、x3As preliminary crack length calculated value；
(b) when crack propagation to region II, then directly by x1、x2、x3As preliminary crack length calculated value；
(c) similar with region I method for solving when prediction crack propagation to region III, FBG2 peak of curve coordinate is denoted as (xp2,yp2), FBG1 matched curve is denoted as x in II, III area limit line intersection point abscissa with FBG3 matched curvej, then by xjGeneration Enter FBG2 curve, it is (x that corresponding coordinate point, which is calculated,j,yj)；
If y2<yj, then by x1、x2、x3As preliminary crack length calculated value；
If yj≤y2<yp2, then for same y2Value, there are two different crack length x2And x2', it need to be according to x1、x3With xp2 Between size relation determine on earth be x2Or x2', and further determine that preliminary crack length calculated value, rule are as follows:
1. if x1、x3≤xp2, then by x1、x2、x3As preliminary crack length calculated value；
2. if x1、x3>xp2, then by x1、x2’、x3As preliminary crack length calculated value；
3. if x1≤xp2≤x3, compare | x2-x1| with | x3-x2' | size, when | x2-x1| when smaller, then with x2With x1、x3Make For preliminary crack length calculated value, when | x3-x2' | when smaller, then with x2' and x1、x3As preliminary crack length calculated value；
4. if x3≤xp2≤x1, compare | x3-x2| with | x1-x2' | size, when | x3-x2| when smaller, then with x2With x1、x3Make For preliminary crack length calculated value, when | x1-x2' | when smaller, then with x2' and x1、x3As preliminary crack length calculated value；
If y2=yp2, then by xp2、x1、x3As preliminary crack length calculated value；
(d) similar with region III method for solving when crack propagation to region IV, FBG3 peak of curve coordinate is denoted as (xp3,yp3), FBG1 matched curve is denoted as x in IV, V area limit line intersection point abscissa with FBG2 matched curvek, then by xkIt substitutes into FBG3 curve, it is (x that corresponding coordinate point, which is calculated,k,yk)；
If y3<yk, then by x1、x2、x3As preliminary crack length calculated value；
If yk≤y3<yp3, then for same y3Value, there are two different crack length x3And x3', it need to be according to x1、x2With xp3 Between size relation determine on earth be x3Or x3', and further determine that preliminary crack length calculated value, rule are as follows:
1. if x1、x2≤xp3, then by x1、x2、x3As preliminary crack length calculated value；
2. if x1、x2>xp3, then by x1、x2、x3' it is used as preliminary crack length calculated value；
3. if x1≤xp3≤x2, compare | x3-x1| with | x2-x3' | size, when | x3-x1| when smaller, then with x3With x1、x2Make For preliminary crack length calculated value, when | x2-x3' | when smaller, then with x3' and x1、x2As preliminary crack length calculated value；
4. if x2≤xp3≤x1, compare | x3-x2| with | x1-x3' | size, when | x3-x2| when smaller, then with x3With x1、x2Make For preliminary crack length calculated value, when | x1-x3' | when smaller, then with x3' and x1、x2As preliminary crack length calculated value；
If y3=yp3, then by xp3、x1、x2As preliminary crack length calculated value；
(e) when crack propagation is in region V, directly by x1、x2、x3As preliminary crack length calculated value.
Step 8.2), the center wavelength shift amount that tri- strain transducers of FBG1, FBG2, FBG3 respond unknown crackle Absolute value accounting is as weight, i.e.,
Wherein △ λFBG1、△λFBG2、△λFBG3For calculated FBG1, FBG2, FBG3 tri- to unknown crackle of step 6 Strain transducer center wavelength shift amount；It will tentatively be split in step 8.1) by FBG1, FBG2 and FBG3 matched curve are obtained Line length computation value is denoted as x respectivelyFBG1、xFBG2And xFBG3, three preliminary crack length calculated values are weighted, it may be determined that go out Final unknown crack length calculated value:
Those skilled in the art can understand that unless otherwise defined, all terms used herein (including skill Art term and scientific term) there is meaning identical with the general understanding of those of ordinary skill in fields of the present invention.Also It should be understood that those terms such as defined in the general dictionary should be understood that have in the context of the prior art The consistent meaning of meaning will not be explained in an idealized or overly formal meaning and unless defined as here.
Above-described specific embodiment has carried out further the purpose of the present invention, technical scheme and beneficial effects It is described in detail, it should be understood that being not limited to this hair the foregoing is merely a specific embodiment of the invention Bright, all within the spirits and principles of the present invention, any modification, equivalent substitution, improvement and etc. done should be included in the present invention Protection scope within.

Claims (1)

1. the unilateral gap aluminium alloy test specimen crack Propagation monitoring method based on FBG sensor, which is characterized in that including with Lower step:
Step 1) carries out finite element modeling to unilateral gap aluminium alloy test specimen:
It is unilateral according to preset elasticity modulus, Poisson's ratio, size, Circularhole diameter, unilateral gap length, the building of precrack length Notch aluminum alloy specimen part finite element model, wherein unilateral gap direction and test specimen edge are vertical, direction of check and unilateral gap Direction is identical；
Step 2), the intersection point for defining two center of circular hole line of test specimen and direction of crack propagation is crackle starting point, by FBG1, FBG2, Tri- strain transducers of FBG3 are equidistantly arranged along direction of check, and sensor and crack propagation path vertical interval are pre- If distance threshold, tri- sensor axis of FBG1, FBG2, FBG3 are to vertical with direction of check；
Step 3), tri- strain transducer reflection kernel wavelength of FBG1, FBG2, FBG3 before acquiring fatigue test are as original base Calibration signal is denoted as λRi, wherein i=1,2,3, i indicate sensor numbers；The FBG sensor pasted is connected by wire jumper again Incoming fiber optic grating demodulation instrument, and two circular holes of clamping test pieces, using permanent load tensile test specimen, obtain different crack lengths Corresponding tri- strain transducer central wavelength data of FBG1, FBG2, FBG3, are denoted as { Wi,j, wherein i=1,2,3, indicate sensing Device number, j indicate crack length；
Step 4), according to { Wi,jAnd tri- strain transducer archicenter wavelength standard signal λ of FBG1, FBG2, FBG3Ri, calculate Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3 out obtain in the corresponding each sensor of different crack lengths Heart wavelength shift response characteristic set { Si,j, wherein i=1,2,3, indicate that sensor number, j indicate crack length；
Step 5), according to { Si,j, using center wavelength shift amount as dependent variable y, using crack length be independent variable x at two-dimentional right angle Described point one by one in coordinate system, utilization index function expressionFitting FBG1, The relationship of FBG2 center wavelength shift amount and crack length calculates fitting expression parameter a1、a2、b1、b2、c1、c2、c3；Again Utilize polynomial expression y=a3x6+b3x5+c4x4+d1x3+d2x2+d3x+d4It is fitted FBG3 center wavelength shift amount and crackle is long Degree relationship calculates fitting expression parameter a3、b3、c4、d1、d2、d3、d4, thus establish the corresponding fatigue of three FBG sensors Crack propagation anticipation function relational model；
Step 6), in the central wavelength and step 3) responded according to tri- strain transducers of FBG1, FBG2, FBG3 to unknown crackle Tri- strain transducer archicenter wavelength standard signal λ of FBG1, FBG2, FBG3Ri, it is corresponding to calculate unknown crack length Tri- strain transducer center wavelength shift amounts of FBG1, FBG2, FBG3, are denoted as △ λ respectivelyFBG1、△λFBG2、△λFBG3；
Step 7) is divided according to crack length projected relationship Model on Crack line extended area in step 5), compare FBG1, The center wavelength shift amount size of tri- strain transducers of FBG2, FBG3, determines unknown crack propagation region, specific to wrap It includes:
Step 7.1), the x augment direction along two-dimensional Cartesian coordinate system, successively by the friendship of FBG1 matched curve and FBG2 matched curve Point is denoted as (xa,ya), the intersection point of FBG1 matched curve and FBG3 matched curve is denoted as (xb,yb), FBG2 matched curve and FBG3 are quasi- The intersection point for closing curve is denoted as (xc,yc), the intersection point of FBG2 matched curve and FBG1 matched curve is denoted as (xd,yd), On Crack Propagation Region is divided, region division principle are as follows:
x≤xaRegion, be denoted as region I；xa<x<xbRegion, be denoted as region II；xb≤x≤xcRegion, be denoted as region III； xc<x<xdRegion, be denoted as region IV；x≥xdRegion, be denoted as region V；
Step 7.2), according to 3 FBG sensor center wavelength shift amount △ λ in step 6)FBG1、△λFBG2、△λFBG3Numerical value Sensor fitting function relational model in size relation and step 5, determines crack propagation region, specifically determines principle Are as follows:
If △ λFBG1>△λFBG2>△λFBG3, determine crack propagation in region I；
If △ λFBG2>△λFBG1>△λFBG3, determine crack propagation in region II；
If △ λFBG2>△λFBG3>△λFBG1, determine crack propagation in region III；
If △ λFBG3>△λFBG2>△λFBG1, determine crack propagation in region IV；
If △ λFBG3>△λFBG1>△λFBG2, determine crack propagation in region V；
Step 8), 3 FBG sensor center wavelength shift amount △ λ being calculated according to step 6)FBG1、△λFBG2、△λFBG3, Three FBG center wavelength shift amounts of gained and crack length fitting function relation curve in step 5) are substituted into, determines unknown split The preliminary crack length value of three of line, then using FBG sensor center wavelength shift amount absolute value accounting as weight, be calculated Final unknown crack extending length:
Step 8.1), in the unknown crack propagation region determined by step 7), three FBG that step 6 is calculated are sensed Device center wavelength shift amount △ λFBG1、△λFBG2、△λFBG3, it substitutes into the resulting three Function Fittings curved line relation formula of step 5), Three preliminary crack length values are calculated；
Step 8.1.1), it is non-monotonic, i.e. same central wavelength there are certain fitting function curve in identified segment Corresponding two different crack lengths of offset, remember that the coordinate in the non-monotonic curve with identical central wavelength shift is respectively (xq,yq)、(xq’,yq), wherein q=1,2,3, q indicate that sensor numbers, the peak of curve coordinate are (xpq,ypq), there is xq<xpq< xq'；Define the crack length and center wavelength shift on the corresponding fitting function curve of other two FBG sensor in the section Magnitude relation is respectively (xi,yi)、(xj,yj), i, j=1,2,3, i, j expression sensor number, then:
If xi、xj≤xpq, with xq、xi、xjAs preliminary crack length calculated value；
If xi、xj>xpq, with xq’、xi、xjAs preliminary crack length calculated value；
If xi≤xpq≤xj, compare | xi-xq| with | xj-xq' | size, when | xi-xq| it is smaller, then with xqWith xi、xjAs tentatively splitting Line length computation value, when | xj-xq' | it is smaller, then with xq' and xi、xjAs preliminary crack length calculated value；
If xj≤xpq≤xi, then compare | xj-xq| with | xi-xq' | size, when | xj-xq| it is smaller, then with xqWith xi、xjAs preliminary Crack length calculated value, when | xi-xq' | it is smaller, then with xq' and xi、xjAs preliminary crack length calculated value；
Step 8.1.2), when being monotonous curve in identified segment, note FBG1, FBG2 and FBG3 sensor is corresponding quasi- The crack length and center wavelength shift magnitude relation closed on function curve is respectively (x1,y1)、(x2,y2)、(x3,y3), then directly With x1、x2、x3As preliminary crack length calculated value；
Step 8.2), the center wavelength shift amount that tri- strain transducers of FBG1, FBG2, FBG3 respond unknown crackle are absolute It is worth accounting as weight factor, i.e.,
Wherein △ λFBG1、△λFBG2、△λFBG3Respectively indicate calculated by step 6 it is resulting associated with unknown crack length FBG1, FBG2, FBG3 center sensor wavelength shift；To calculated preliminary by each FBG matched curve institute in step 8.1) Crack length calculated value is weighted, and determines final unknown crack length value X:
Or
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