CN111707735B - Method for quantifying transverse cracks of fan spindle by using dual-mode diffraction waves - Google Patents

Method for quantifying transverse cracks of fan spindle by using dual-mode diffraction waves Download PDF

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CN111707735B
CN111707735B CN202010405654.8A CN202010405654A CN111707735B CN 111707735 B CN111707735 B CN 111707735B CN 202010405654 A CN202010405654 A CN 202010405654A CN 111707735 B CN111707735 B CN 111707735B
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main shaft
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CN111707735A (en
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程俊
何存富
吕炎
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Beijing University of Technology
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0421—Longitudinal waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0422—Shear waves, transverse waves, horizontally polarised waves
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction

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Abstract

The invention discloses a method for quantifying transverse cracks of a fan spindle by utilizing dual-mode diffraction waves, which comprises the steps of arranging an excitation sensor on the end surface of the spindle and radiating ultrasonic longitudinal waves; an electromagnetic acoustic sensor is disposed inside the central bore of the main shaft for receiving longitudinal and transverse waves diffracted by the crack. An elliptical trajectory of the diffraction point of the longitudinal wave is determined by the excitation sensor position, the electromagnetic acoustic sensor position and the transit time of the diffracted longitudinal wave. A circular locus of diffraction points for the transverse waves is determined by the electromagnetic acoustic sensor locations, and the differences in transit time of the diffracted transverse waves and the longitudinal waves. And determining the position of the diffraction point by utilizing the intersection point of the two tracks, thereby realizing quantitative characterization of the axial position and the expansion depth of the transverse crack of the surface opening.

Description

Method for quantifying transverse cracks of fan spindle by using dual-mode diffraction waves
Technical Field
The invention relates to a diffraction wave quantitative detection method for transverse cracks of an opening on the surface of a main shaft of an in-service wind driven generator, and belongs to the field of nondestructive detection.
Background
Wind power becomes a third largest power source in China, the proportion in the national power source structure is improved year by year, and the running condition of the wind turbine generator is related to national energy safety. The main shaft of the wind driven generator is a core component of a transmission system of the wind turbine, and the structural health state of the main shaft directly influences the operation safety of a fan. The main shaft of the fan has a severe service environment and very complex working conditions, and can bear complex stress effects such as torque, axial thrust, pneumatic bending moment and the like for a long time. In the long-term running process of the main shaft, transverse cracks with surface openings are easily generated in the matching area between the main shaft and the bearing, so that the safety of the wind turbine generator is seriously endangered, and a plurality of safety accidents are caused. The transverse crack detection of the surface opening of the fan spindle not only needs to find cracks, but also needs to quantify the expansion depth of the cracks. Since crack propagation depth is one of the important indicators for evaluating spindle damage.
The fan main shaft is a large revolving body with a central hole characteristic, which consists of a plurality of shaft sections. For the detection of the main shaft of the in-service fan, the difficulty of quantitative characterization exists in that the size of cracks relative to the main shaft is small. At present, the ultrasonic flaw detection is carried out by adopting the end face of the main shaft, and has larger limitations, such as: based on the quantitative technology of the amplitude of the reflected sound wave, the crack quantification precision is low, and the measurement of the crack propagation depth cannot be realized. The invention patent discloses a method for quantifying transverse cracks of a main shaft of a wind driven generator, which is characterized in that sensors are respectively arranged at two positions in a central hole of a fan to receive diffraction longitudinal waves of the cracks, and quantitative detection of the transverse cracks of the opening of the main shaft surface is realized through two elliptical tracks formed by the receiving sensors and the transmitting sensors. However, this method requires two measurements of the diffracted longitudinal wave to achieve detection; the method for realizing quantitative characterization of the crack by using the crack diffraction longitudinal wave and the transverse wave at the same time by using only a single sensor arranged in the central hole is not involved; moreover, a specific mathematical model of the elliptical trajectory is not given, and the method of drawing the elliptical trajectory is dependent on a manual drawing method. In summary, for the quantitative characterization of the cracks of the main shaft of the fan, an algorithm which depends on fewer sensors and carries out quantitative evaluation on the cracks more rapidly is developed, which is beneficial to the progress of crack detection technology and has very important practical significance for the accurate detection of the transverse cracks of the opening of the surface of the actual main shaft.
Aiming at the current state of the art, a crack quantification method is required to be further developed, longitudinal waves and transverse waves of crack diffraction are fully utilized, and the evaluation of the depth and the position of the transverse crack growth of the surface opening of the main shaft of the fan is realized more rapidly and accurately through fewer sensors. Aiming at the problem of quantification of transverse cracks on the surface opening of a main shaft of a wind driven generator, the invention creatively provides a method for realizing accurate quantification of crack positions and expansion depths by utilizing longitudinal waves and transverse waves of crack diffraction.
Disclosure of Invention
The invention provides a method for precisely evaluating the axial position and the expansion depth of a transverse crack on the surface of a main shaft by utilizing the diffraction characteristic of a crack tip to sound waves. And the end face of the main shaft radiates the ultra-longitudinal wave, and the sensor at a single position of the central hole of the main shaft receives the crack diffraction longitudinal wave and the transverse wave, so that the quantitative characterization of the transverse crack of the opening on the circumferential surface of the main shaft is realized. The method can solve the problem that transverse cracks are difficult to quantify in the detection of the end face of the main shaft, and can achieve the purpose of accurately measuring the positions and the expansion depths of the cracks. Compared with the existing method for detecting shaft workpieces, the method provided by the invention has the advantages that the crack diffraction longitudinal wave and transverse wave are utilized to evaluate the transverse crack propagation depth and the axial position of the opening on the surface of the main shaft, the defect that echo amplitude quantitative cracks exist is avoided, the configuration of the sensor is simplified, and the accuracy of the detection result is improved. The method can play an important role in the health monitoring of the main shaft structure of the wind driven generator, and is a further development and innovation of the existing main shaft crack quantifying technology.
In order to achieve the purpose, the technical scheme adopted by the invention is that the method for quantifying the transverse crack of the main shaft of the fan by utilizing the double-mode diffraction waves is adopted, and the device required by the detection method comprises an ultrasonic signal excitation source, a piezoelectric sensor, an electromagnetic acoustic sensor and signal acquisition equipment. The method comprises the following specific implementation steps of:
step one: obtaining the outline dimension of a main shaft of the wind driven generator; determining the detection area, i.e. the distance L between the spindle and the bearing-engaging shaft section (distance L from the end face of the spindle 1 ～L 2 ) And a maximum radius R of the shaft segment; actually measuring the diameter d of the central hole; actual measurement of spindle longitudinal wave sound velocity c L And transverse wave sound velocity c s 。
Step two: selecting a proper piezoelectric sensor according to the general principle of ultrasonic detection, and fixing the piezoelectric sensor at the position with the radius R of the end surface of the main shaft; when the radius of the end face is smaller than R, the end face is fixed at the position with the maximum radius of the end face.
Step three: in the central hole of the main shaft, is away from the end face L of the main shaft 1 ～L 2 Any position L in the range E An electromagnetic sound receiving sensor is arranged for receiving the crack diffraction longitudinal wave and the transverse wave. The piezoelectric sensor, the electromagnetic sound receiving sensor and the spindle axis are ensured to be in the same plane.
Step four: exciting a piezoelectric sensor by using an ultrasonic signal excitation source, and recording the zero point moment t of a trigger pulse 0 The method comprises the steps of carrying out a first treatment on the surface of the Collecting electromagnetic acoustic sensor output signals, respectively extracting crack diffraction longitudinal waves and diffraction transverse waves, and corresponding time t of two diffraction wave peaks L And t s . Wherein t is 0 、t L 、t s Is in nanosecond order.
Step five: by the main partThe center point of the shaft end surface is used as a circle center, the central shaft of the main shaft is used as an x-axis, the radius of the end surface is used as a y-axis, and a plane rectangular coordinate system is established; according to the position coordinates F (0, R) of the piezoelectric sensor and the position coordinates of the electromagnetic sound receiving sensorAnd diffraction longitudinal wave transit time (t L -t 0 ) Calculating parameters of the elliptical trajectory:
wherein a is 1 Is a long half shaft of an ellipse; b 1 Is an ellipse short half shaft c 1 Is the semicoke length of ellipse, (x) 0 ,y 0 ) Is the coordinates of the central point of the elliptical track, theta 1 Is the included angle between the major axis of the ellipse and the center line of the main shaft.
According to the parameters, an elliptic orbit equation is established:
and drawing an elliptic track through an elliptic equation.
Step six: according to the transition time difference (t s -t L ) Calculating a circular track radius r:
receiving sensor coordinates with electromagnetic soundFor the circle center and radius r, a circular track equation is established:
(x-x E ) 2 +(y-y E ) 2 ＝r 2 (c)
the circular trajectory is plotted by the circular equation.
Step seven: parameterizing the circular trajectory equation (c) obtained in the step six:
wherein eta is a parameter, eta is 0,180 degrees.
Bringing formula (d) into equation (a), finding the appropriate η by dichotomy p The following formula is satisfied:
wherein epsilon is more than 0 and less than or equal to 10 -4 。
Further calculating to obtain the intersection point P (x p ,y p )。
Step eight: the position of the surface opening transverse crack in the main axis passes through the point P abscissa x p A representation;
step nine: obtaining the distance end face x p Radius R of shaft segment at position c Through R c -y p The crack growth depth was calculated.
Step ten: and (3) obtaining the positions and the expansion depths of the transverse cracks on the spindle in different circumferential directions according to the steps four to nine on different azimuth angles of the end face of the spindle.
The axial position and the expansion depth of the crack are determined by the sound path of the diffraction longitudinal wave and the diffraction transverse wave at the crack tip to the electromagnetic sound receiving sensor respectively. The total sound path of the sound emission source-crack tip-receiving source can be determined by the diffraction longitudinal wave transit time, so that an elliptical track is obtained; determining a circular track by the time difference of the diffraction transverse wave and the diffraction longitudinal wave; the intersection point of the two tracks is a crack tip diffraction point; the abscissa of the diffraction point determines the position of the main shaft where the crack is located, and the ordinate determines the depth of the crack extending to the axis;
the method is that the longitudinal wave radiated by the end face of the main shaft interacts with the crack tip to diffract the dual-mode sound wave (namely the longitudinal wave and the transverse wave) so as to position the crack position and the expansion depth. The electromagnetic acoustic sensor with the longitudinal wave and transverse wave receiving capability is arranged in the central hole of the main shaft and receives diffraction waves of cracks, so that the purpose of quantifying the cracks is achieved.
Compared with the prior art, the invention has the following beneficial effects.
1. The method utilizes longitudinal waves and transverse waves diffracted by crack tips, and solves the quantitative characterization problem of transverse cracks on the surface opening of the main shaft of the wind driven generator. In the prior art, crack detection is performed only by using the diffraction longitudinal wave, and the effect of the diffraction transverse wave is ignored. The invention fully utilizes the diffraction characteristic of the crack to the sound wave, quantitatively characterizes the main shaft crack, and innovates on the detection mechanism.
2. According to the invention, the transmitting sensor and the receiving sensor are respectively arranged in the end face and the central hole of the main shaft, so that the measurement of the axial position and the expansion depth of the crack is completed, the defect that the equivalent of the crack is evaluated by echo amplitude is overcome, and the purpose that the crack is quantized by single measurement is realized.
3. The method establishes mathematical models of diffraction point ellipses and circular tracks, provides a rapid and feasible diffraction point position calculation method, and provides a set of rapid algorithm for crack quantitative characterization.
4. The invention reduces the number of sensors used, only adopts the diffraction signal collected by the same receiving sensor, reduces the measurement error of the transit time of the diffraction wave, and improves the crack quantification precision.
Drawings
FIG. 1 is a view of the dimensions and detection area of a spindle to be inspected in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of the present invention quantifying crack axial location and propagation depth;
FIG. 3 is a time domain waveform acquired by an electromagnetic acoustic sensor in an embodiment of the present invention;
FIG. 4 is a graph of crack location and propagation depth obtained with an embodiment of the present invention;
in the figure: 1-a detection zone; 2-a piezoelectric sensor; 3-an elliptical trajectory determined by the diffracted longitudinal wave; 4-surface open transverse crack; 5-diffraction of circular trajectories determined by longitudinal and transverse waves; 6-the central line of the main shaft; 7-electromagnetic acoustic sensor; 8-wind driven generator main shaft
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
The invention is described in detail below with reference to the drawings and the detailed description.
According to the embodiment of the invention, a method for quantifying transverse cracks of a fan spindle by diffraction double-mode sound waves is provided.
In the long-term service process of the wind driven generator, transverse cracks with open surfaces are easy to generate on the pressed surfaces of the main shaft and the bearing, the mechanical property of the main shaft is directly reduced by the cracks, and whether the quality of the main shaft can continuously meet the use requirement or not is checked by means of nondestructive detection.
The main shaft of the wind driven generator adopted in the embodiment is the main shaft (8) to be detected in fig. 1, and the main shaft material is 42CrMo4. There was a transverse crack of depth 5mm at 700mm from the end face of the spindle. The detection surface selects the end surface at the left side of the main shaft and the inner wall of the central hole.
The equipment adopted by the embodiment comprises 1 ultrasonic signal excitation source, 1 piezoelectric sensor, 1 electromagnetic acoustic sensor and 1 signal acquisition equipment, and the specific implementation steps are as follows:
step one: obtaining the outline dimension of a main shaft of the wind driven generator, as shown in figure 1; the detection area is determined, namely a shaft section (1) which is positioned at a distance of 650-850 mm from the end face of the main shaft, and the maximum half of the shaft sectionDiameter r=283 mm; measured centre hole diameter d=75mm; actual measurement of spindle longitudinal wave sound velocity c L 5928.000m/s, transverse wave sound velocity c s ＝3260.000m/s。
Step two: according to the general principle of ultrasonic detection, a piezoelectric sensor with the frequency of 2.5MHz and the diameter of phi 20mm is selected. The piezoelectric sensor (2) is fixed at a position with the radius of 283mm on the end face of the main shaft.
Step three: in the central hole of the main shaft, is away from the end face L of the main shaft E An electromagnetic sound receiving sensor (7) for receiving crack diffraction longitudinal waves and transverse waves is arranged at a position of 725 mm. The azimuth angle of the electromagnetic sound receiving sensor (7) in the central hole is adjusted to be coplanar with the piezoelectric sensor (2) and the spindle center line (6).
Step four: exciting a piezoelectric sensor (2) by using an ultrasonic signal excitation source, and recording the zero point moment t of a trigger pulse 0 =0.000 μs, electromagnetic acoustic sensor output signals were acquired by a signal acquisition device, as shown in fig. 2. Respectively extracting crack diffraction longitudinal wave and diffraction transverse wave, and extracting time t corresponding to two diffraction wave crest values L = 158.813 μs and t s ＝192.235μs。
Step five: and taking the central point of the end face of the main shaft as the center of a circle, taking the central axis of the main shaft as the x axis and the radius of the end face as the y axis, and establishing a plane rectangular coordinate system. Calculating an ellipse parameter from piezoelectric sensor position coordinates F (0, 283), electromagnetic sound receiving sensor position coordinates E (725, 37.5) and diffracted longitudinal wave transit time: elliptic orbit long half shaft a 1 = 470.722mm; short half shaft b 1 = 274.053mm; half focal length c 1 382.719mm, the coordinates of the center point of the elliptical track are (362.500,160.250), and the included angle θ between the major axis of the ellipse and the center line of the principal axis 1 ＝-18.707°。
The elliptic orbit equation determined according to the above parameters is:
according to the elliptic equation, an elliptic locus (3) is drawn as shown in fig. 3.
Step six: according to diffraction transverse wave and diffractionTime difference of transit of the radial longitudinal wave (t s -t L ) The circular track radius r= 242.085mm is calculated = 33.422 μs. Establishing a circular track equation by taking the coordinate E (725,37.5) of the electromagnetic sound receiving sensor as the circle center:
(x-725) 2 +(y-37.5) 2 ＝242.085 2
the circular trajectory (5) is plotted according to the circular trajectory equation, as shown in fig. 3. .
Step seven: and D, parameterizing the circular trajectory equation obtained in the step six:
wherein eta is a parameter, eta is 0,180 degrees.
The parametric equation for circular trajectories is brought into the elliptical trajectory equation. In the interval [0,180 ]]Finding proper eta by adopting a dichotomy numerical method p The absolute value of the following expression is made smaller than 10 -4 。
And (3) obtaining: η (eta) p ＝96.086°
Further calculating to obtain the intersection point coordinates of the elliptical track and the circular track as follows:
step eight: the surface opening transverse crack is 699.332mm away from the main shaft end face;
step nine: obtaining radius R of the shaft segment at a position from the end face 699.332 c =283 mm, and the crack growth depth was calculated to be 4.779mm.
Step ten: and (3) obtaining the positions and the expansion depths of the transverse cracks on the spindle in different circumferential directions according to the steps four to nine on different azimuth angles of the end face of the spindle.

Claims (5)

1. A method for quantifying transverse cracks of a fan spindle by using dual-mode diffraction waves is characterized by comprising the following steps: the method comprises the following specific implementation steps:
step one: acquiring the outline dimension of a main shaft of the wind driven generator, and determining a detection area;
step two: fixing the piezoelectric sensor at the position with the radius R of the end face of the main shaft;
step three: in the central hole of the main shaft, is away from the end face L of the main shaft 1 ～L 2 Any position L in the range E An electromagnetic sound receiving sensor is arranged for receiving the crack diffraction longitudinal wave and the crack diffraction transverse wave; the piezoelectric sensor and the electromagnetic sound receiving sensor are positioned on the same plane with the axis of the main shaft;
step four: exciting a piezoelectric sensor by using an ultrasonic signal excitation source, and recording the zero point moment t of a trigger pulse 0 The method comprises the steps of carrying out a first treatment on the surface of the Collecting electromagnetic acoustic sensor output signals, respectively extracting crack diffraction longitudinal waves and diffraction transverse waves, and corresponding time t of two diffraction wave peaks L And t s ；
Step five: taking the center point of the end face of the main shaft as the center of a circle, the central shaft of the main shaft as the x-axis, and the radius of the end face as the y-axis, and establishing a plane rectangular coordinate system; calculating parameters of the elliptical track according to the position coordinates of the piezoelectric sensor, the position coordinates of the electromagnetic sound receiving sensor and the transition time of the diffraction longitudinal wave: drawing an elliptical track through an elliptical equation; taking the center point of the end face of the main shaft as the center of a circle, the central shaft of the main shaft as the x-axis, and the radius of the end face as the y-axis, and establishing a plane rectangular coordinate system; according to the position coordinates F (0, R) of the piezoelectric sensor and the position coordinates of the electromagnetic sound receiving sensorAnd diffraction longitudinal wave transit time (t L -t 0 ) Calculating parameters of the elliptical trajectory:
wherein a is 1 Is a long half shaft of an ellipse; b 1 Is an ellipse short half shaft c 1 Is the semicoke length of ellipse, (x) 0 ,y 0 ) Is the coordinates of the central point of the elliptical track, theta 1 Is the included angle between the ellipse major axis and the center line of the main shaft; actually measuring the diameter d of the central hole; actual measurement of spindle longitudinal wave sound velocity c L ；
Elliptic trajectory equation:
step six: according to the transition time difference (t s -t L ) Calculating a circular track radius r: receiving sensor coordinates with electromagnetic soundEstablishing a circular track equation for the circle center and the radius r, and drawing a circular track through the circular track equation;
(x-x E ) 2 +(y-y E ) 2 ＝r 2
step seven: parameterizing the circular track equation obtained in the step six to obtain an intersection point P (x) of the elliptical track and the circular track p ，y p )；
Step eight: the position of the surface opening transverse crack in the main axis passes through the point P abscissa x p A representation;
step nine: obtaining the distance end face x p Radius R of shaft segment at position c Through R c -y p Calculating crack propagation depth;
step ten: and (3) obtaining the positions and the expansion depths of the transverse cracks on the spindle in different circumferential directions according to the steps four to nine on different azimuth angles of the end face of the spindle.
2. A method for quantifying fan spindle cross-cracks using dual mode diffraction waves as recited in claim 1, wherein: the axial position and the expansion depth of the crack are determined by the sound path that the longitudinal wave and the transverse wave diffracted by the crack tip reach the electromagnetic sound receiving sensor respectively; the total sound path of the acoustic emission source-crack tip-receiving source is determined by the diffraction longitudinal wave transit time, so that an elliptical track is obtained; determining a circular track by the time difference of the diffraction transverse wave and the diffraction longitudinal wave; the intersection point of the two tracks is a crack tip diffraction point; the abscissa of the diffraction point at the tip of the crack determines the position of the main shaft where the crack is located, and the ordinate determines the depth of the crack extending to the axis.
3. A method for quantifying fan spindle cross-cracks using dual mode diffraction waves as recited in claim 1, wherein: the longitudinal wave radiated by the end face of the main shaft interacts with the crack tip and then diffracts the longitudinal wave and the transverse wave to position the crack and expand the depth; the electromagnetic acoustic sensor with the capability of receiving longitudinal waves and transverse waves is arranged in the central hole of the main shaft, and receives diffracted longitudinal waves and transverse waves of cracks, so that the purpose of quantifying the cracks is achieved.
4. A method for quantifying fan spindle cross-cracks using dual mode diffraction waves as recited in claim 1, wherein: the device for realizing the method comprises an ultrasonic signal excitation source, a piezoelectric sensor, an electromagnetic acoustic sensor and signal acquisition equipment; the ultrasonic signal excitation source is connected with the piezoelectric sensor, and the electromagnetic acoustic sensor is connected with the signal acquisition equipment.
5. A method for quantifying fan spindle cross-cracks using dual mode diffraction waves as recited in claim 1, wherein: and in the second step, when the radius of the end face is smaller than R, the end face is fixed at the position with the maximum radius of the end face.
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