1. The test piece surface crack two-dimensional profile inversion method based on the current dipole is characterized by comprising the following steps of:

applying an excitation electromagnetic field to obtain a detection signal of the induced magnetic field on the surface of the test piece;

processing the detection signal to obtain the magnetic field intensity of the induction magnetic field when the rotating electromagnetic field is positioned at any angle;

reconstructing the current on the surface of the test piece by using an electric dipole model, and equivalently dividing the reconstructed test piece surface current to obtain a plurality of electric dipoles, wherein the reconstructed test piece surface current comprises a test piece surface uniform current and a test piece surface disturbance current;

calculating an induced magnetic field intensity distribution matrix of a unit electric dipole according to the Bio Saval law, and establishing a functional relation between the electric dipole and an induced magnetic field;

obtaining the disturbance current of the surface of the test piece by inverting the induction magnetic field;

superposing the disturbance current on the surface of the test piece and the uniform current on the surface of the test piece to obtain the current distribution on the surface of the test piece;

and drawing a test piece surface current distribution diagram, and obtaining a profile image of the test piece surface crack through the test piece surface current distribution diagram.

2. The method for inverting the two-dimensional profile of the crack on the surface of the test piece based on the current dipole as recited in claim 1, wherein the applying the excitation electromagnetic field and obtaining the detection signal of the induced magnetic field on the surface of the test piece comprises:

acquiring an excitation signal;

generating an excitation magnetic field according to the excitation signal, and rotating the excitation magnetic field on the surface of the test piece to form induction magnetic fields at a plurality of angles; and collecting detection signals of the induction magnetic field of each angle.

3. The method for inverting the two-dimensional profile of the crack on the surface of the test piece based on the current dipole as recited in claim 1, wherein the step of processing the detection signal to obtain the magnetic field strength of the induced magnetic field when the rotating electromagnetic field is positioned at any angle comprises the following steps:

calculating the amplitude information and the phase information of the induced magnetic field contained in the detection signal by a magnetic field reduction method to obtain the magnetic field intensity of the induced magnetic field when the excitation magnetic field is positioned at any angle:

wherein the content of the first and second substances,the magnetic field intensity of the induction magnetic field when the angle of the excitation magnetic field is alpha; a is the amplitude response of the induction magnetic field;

is the phase response of the induced magnetic field; α is the angle of the excitation field.

4. The method for inverting the two-dimensional profile of the surface crack of the test piece based on the current dipole as claimed in claim 3, wherein the step of calculating the distribution matrix of the induced magnetic field strength of the unit electric dipole according to the BioSaval's law and establishing the functional relationship between the unit electric dipole and the induced magnetic field comprises the following steps:

establishing the relation between the unit electric dipole on the surface of the test piece and the induction magnetic field, as shown in the following formula:

wherein C is a magnetic field distribution matrix generated by a unit electric dipole on the surface of the test piece; n is a magnetic field intensity error matrix between the detected induction magnetic field and the actual induction magnetic field; conv (·, ·) represents a convolution operation;the current is disturbed by the surface of the test piece when the magnetic field is excited at an angle alpha.

5. The method for inverting the two-dimensional profile of the crack on the surface of the test piece based on the current dipole as claimed in claim 4, wherein the obtaining of the disturbance current on the surface of the test piece by inverting the induced magnetic field comprises the following steps: converting convolution operation in the relation between the unit electric dipole on the surface of the test piece and the space disturbance magnetic field into product operation in a frequency domain, adding a regularization parameter to constrain an operation result, and obtaining an expression of disturbance current on the surface of the test piece:

wherein μ is a regularization parameter; f () represents the Fourier transform, F^-1() Representing an inverse fourier transform;

and (3) inverting to obtain a current matrix under the electric dipole model, and converting the obtained current matrix, wherein the conversion formula is as follows:

wherein i and j are positive integers not greater than the number of rows and columns of the matrix respectively;andthe elements of the ith row and the jth column of the surface disturbance current distribution matrix in the direction of the X, Y axis are respectively.

6. The method for inverting the two-dimensional profile of the test piece surface crack based on the current dipole as recited in claim 5, wherein the step of superposing the test piece surface disturbance current and the test piece surface uniform current to obtain the test piece surface current distribution comprises the steps of:

superposing the disturbance current on the surface of the test piece and the uniform current on the surface of the test piece, wherein the intensity of the uniform current on the surface of the test piece is obtained by calculating the maximum intensity value of the disturbance current on the surface, and the current distribution on the surface of the test piece is obtained:

wherein the content of the first and second substances,when the angle of the excitation magnetic field is a, the surface of the test piece is uniformly electrified;andx, Y respectively, are used for disturbing the current distribution matrix on the surface.

7. The method for inverting the two-dimensional profile of the crack on the surface of the test piece based on the current dipole as claimed in claim 6, wherein: and adding the test piece surface currents obtained from different angles to obtain an average value, and obtaining the final test piece surface current distribution.

8. The utility model provides a test piece surface crack two-dimensional profile inversion device based on current dipole which characterized in that includes:

a two-dimensional moving platform;

the signal generation module is arranged on the two-dimensional mobile platform, comprises a homologous orthogonal signal generation component, a voltage-controlled current source conversion component and a current measurement component, and is configured to receive a control signal and send out an excitation signal according to the control signal; the magnetic field detection probe is arranged on the two-dimensional moving platform, comprises an excitation coil assembly and an array detection coil assembly, is configured to generate an excitation magnetic field according to an excitation signal, detect an induction magnetic field generated by the excitation magnetic field on the surface of the test piece and send out a detection signal;

the signal processing module comprises a quadrature phase locking circuit and is configured to receive the detection signal and convert the detection signal into an electric signal;

and the upper computer is respectively connected with the signal generation module, the signal processing module and the two-dimensional mobile platform, is configured to control the two-dimensional mobile platform to move, outputs a control signal, receives the processed detection signal and obtains a two-dimensional profile of the surface crack of the test piece through inversion.

9. The current dipole-based test piece surface crack two-dimensional profile inversion device as recited in claim 8, wherein: the excitation coil assembly comprises a coil framework and two mutually orthogonal excitation coils wound on the coil framework, the excitation coil assembly is arranged above the test piece and close to the test piece, and the array detection coil assembly is positioned below the excitation coil assembly; two excitation signals with the same amplitude and 90-degree phase difference are generated by a homologous orthogonal signal generating component in the signal generating module, are converted into constant current signals by a voltage-controlled current source-to-current source component and then are respectively connected into two excitation coils to generate excitation magnetic fields; the two-dimensional moving platform drives the magnetic field detection probe to move to scan the test piece, and the upper computer controls the scanning range and the step length of the two-dimensional moving platform so that the array detection coil assembly detects the induced magnetic field generated by the test piece at a plurality of angles.

Background

At the initial stage of cluster crack formation, the individual cracks tend to be small, and it is difficult to cause large damage. However, as the crack grows, small cracks tend to grow continuously along the length direction, and a plurality of small cracks are combined into a large crack. When a large crack occurs, the crack can cause the rupture of the pipeline, and finally, the accident can occur. Taking the cluster cracks in the pipeline as an example, the pipeline cracks often appear in the form of adjacent, close and even crossed cluster cracks, and the cluster cracks are easy to accelerate to spread under the action of stress and a corrosive environment, so that the pipeline cracks. It is therefore necessary to monitor the cluster cracks at their early stages of development to prevent pipe rupture due to the propagation of the cracks from one another.

With the development of nondestructive testing technology, higher requirements are put forward on the precision of crack size parameters while the defect detection is realized. However, in the cluster-shaped cracks, the distance between every two cracks is small, and the disturbance signals of every crack are often superposed together to form a protective barrier. The inspector often approximates two adjacent defects as one defect. The existing nondestructive testing technology is difficult to realize accurate identification of each crack, only the labeling of crack regions can be realized for clustered cracks, and the misjudgment of the cracks is easy to occur. Therefore, a set of highly accurate inversion and analysis techniques for the surface profile of the clustered cracks is urgently needed to realize effective evaluation of the clustered cracks on the surface of the material.

Disclosure of Invention

In order to solve the problems, the invention provides a test piece surface crack two-dimensional profile inversion method and device based on a current dipole.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a test piece surface crack two-dimensional profile inversion method based on current dipoles comprises the following steps:

applying an excitation electromagnetic field to obtain a detection signal of the induced magnetic field on the surface of the test piece;

processing the detection signal to obtain the magnetic field intensity of the induction magnetic field when the rotating electromagnetic field is positioned at any angle;

reconstructing the current on the surface of the test piece by using an electric dipole model, and equivalently dividing the reconstructed test piece surface current to obtain a plurality of unit electric dipoles, wherein the reconstructed test piece surface current comprises a test piece surface uniform current and a test piece surface disturbance current;

calculating an induced magnetic field intensity distribution matrix of the unit electric dipole according to the Bio Saval law, and establishing a functional relation between the unit electric dipole and an induced magnetic field;

obtaining the disturbance current of the surface of the test piece by inverting the induction magnetic field;

superposing the disturbance current on the surface of the test piece and the uniform current on the surface of the test piece to obtain the current distribution on the surface of the test piece;

and drawing a test piece surface current distribution diagram, and obtaining a profile image of the test piece surface crack through the test piece surface current distribution diagram.

Further, the applying an excitation electromagnetic field and acquiring a detection signal of the induced magnetic field on the surface of the test piece includes:

acquiring an excitation signal;

generating an excitation magnetic field according to the excitation signal, and rotating the excitation magnetic field on the surface of the test piece to form induction magnetic fields at a plurality of angles;

and collecting detection signals of the induction magnetic field of each angle.

Further, the processing of the detection signal to obtain the magnetic field strength of the induced magnetic field when the rotating electromagnetic field is located at any angle includes:

calculating the amplitude information and the phase information of the induced magnetic field contained in the detection signal by a magnetic field reduction method to obtain the magnetic field intensity of the induced magnetic field when the excitation magnetic field is positioned at any angle:

wherein the content of the first and second substances,the magnetic field intensity of the induction magnetic field when the angle of the excitation magnetic field is alpha; a is the amplitude response of the induction magnetic field;is the phase response of the induced magnetic field; α is the angle of the excitation field.

Further, the calculating the distribution matrix of the induced magnetic field strength of the unit electric dipole according to the biotival law, and establishing the functional relationship between the unit electric dipole and the induced magnetic field includes:

establishing the relation between the unit electric dipole on the surface of the test piece and the induction magnetic field, as shown in the following formula:

wherein C is a magnetic field distribution matrix generated by a unit electric dipole on the surface of the test piece; n is a magnetic field intensity error matrix between the detected induction magnetic field and the actual induction magnetic field; conv (·, ·) represents a convolution operation;disturbance current is generated on the surface of the test piece when the angle of the excitation magnetic field is alpha; .

Further, the obtaining of the disturbance current of the surface of the test piece by inverting the induced magnetic field includes: converting convolution operation in the relation between the unit electric dipole on the surface of the test piece and the space disturbance magnetic field into product operation in a frequency domain, adding a regularization parameter to constrain an operation result, and obtaining an expression of disturbance current on the surface of the test piece:

wherein μ is a regularization parameter; f () represents the Fourier transform, F^-1() Representing an inverse fourier transform;

and (3) inverting to obtain a current matrix under the electric dipole model, and converting the obtained current matrix, wherein the conversion formula is as follows:

wherein i and j are positive integers not greater than the number of rows and columns of the matrix respectively;andthe elements of the ith row and the jth column of the surface disturbance current distribution matrix in the direction of the X, Y axis are respectively.

Further, superpose test piece surface disturbance current and test piece surface uniform current mutually, obtain test piece surface current distribution, include: superposing the disturbance current on the surface of the test piece and the uniform current on the surface of the test piece, wherein the intensity of the uniform current on the surface of the test piece is obtained by calculating the maximum intensity value of the disturbance current on the surface, and the current distribution on the surface of the test piece is obtained:

wherein the content of the first and second substances,when the angle of the excitation magnetic field is alpha, the surface of the test piece is uniformly electrified;andx, Y respectively, are used for disturbing the current distribution matrix on the surface.

Further, the test piece surface currents obtained from different angles are added to obtain an average value, and the final test piece surface current distribution is obtained.

A test piece surface crack two-dimensional profile inversion device based on current dipoles comprises:

a two-dimensional moving platform;

the signal generation module is arranged on the two-dimensional mobile platform, comprises a homologous orthogonal signal generation component, a voltage-controlled current source conversion component and a current measurement component, and is configured to receive a control signal and send out an excitation signal according to the control signal;

the magnetic field detection probe is arranged on the two-dimensional moving platform, comprises an excitation coil assembly and an array detection coil assembly, is configured to generate an excitation magnetic field according to an excitation signal, detect an induction magnetic field generated by the excitation magnetic field on the surface of the test piece and send out a detection signal;

the signal processing module comprises a quadrature phase locking circuit and is configured to receive the detection signal and convert the detection signal into an electric signal;

the upper computer is respectively connected with the signal generation module, the signal processing module and the two-dimensional mobile platform, is configured to control the two-dimensional mobile platform to move, outputs a control signal, receives the processed detection signal and obtains a two-dimensional profile of the surface crack of the test piece through inversion

Furthermore, the excitation coil assembly comprises a coil framework and two mutually orthogonal excitation coils wound on the coil framework, the excitation coil assembly is arranged above the test piece and close to the test piece, and the array detection coil assembly is positioned below the excitation coil assembly; two excitation signals with the same amplitude and 90-degree phase difference are generated by a homologous orthogonal signal generating component in the signal generating module, are converted into constant current signals by a voltage-controlled current source-to-current source component and then are respectively connected into two excitation coils to generate excitation magnetic fields; the two-dimensional moving platform drives the magnetic field detection probe to move to scan the test piece, and the upper computer controls the scanning range and the step length of the two-dimensional moving platform so that the array detection coil assembly detects the induced magnetic field generated by the test piece at a plurality of angles.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention adopts a current inversion method, thus solving the problem of multi-crack magnetic field interference;

(2) the invention uses the rotating excitation electromagnetic field detection technology, and improves the accuracy of cracks at any angle.

(3) According to the method, the crack outline is displayed in an image form by a visual means, so that the shape detection of the crack on the surface of the test piece is realized; the method has the advantages that the effective evaluation of the cluster cracks on the surface of the test piece is realized, the two-dimensional profile information such as the number, the interval, the distribution and the length of each crack in the cluster cracks is determined in detail, the important significance is realized for the subsequent accurate evaluation of the residual service life and the crack expansion, and the early warning can be effectively carried out on the accident.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a flow chart of a test piece surface crack two-dimensional profile inversion method based on current dipoles in the embodiment of the invention;

FIG. 2 is a schematic diagram of a square electric dipole model according to an embodiment of the present invention;

FIG. 3 is a diagram showing a surface current distribution of a test piece according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of inversion of a two-dimensional profile of a surface of a test piece according to an embodiment of the present disclosure;

FIG. 5 is a structural diagram of a test piece surface crack two-dimensional profile inversion device based on a current dipole in the embodiment of the invention;

FIG. 6 is a schematic diagram of a quadrature phase lock circuit according to an embodiment of the present invention;

FIG. 7 is a diagram illustrating a bobbin structure according to an embodiment of the present invention;

FIG. 8 is a schematic diagram illustrating a winding direction of an exciting coil according to an embodiment of the present invention;

in the figure: 1. a two-dimensional moving platform; 2. a signal generation module; 3. a magnetic field detection probe; 31. an excitation coil assembly; 311. a coil bobbin; 312. an excitation coil; 32. the array detects the magnetic field; 4. a signal processing module; 5. an upper computer; 6. a test piece; 7. and (5) collecting the card.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Referring to fig. 1, an embodiment of the present invention provides a current dipole-based two-dimensional profile inversion method for a surface crack of a test piece, including the following steps:

step 1: applying an excitation electromagnetic field to obtain a detection signal of the induced magnetic field on the surface of the test piece;

specifically, the method comprises the following steps:

step 101: the upper computer sends out a control signal to control the homography quadrature generation component to generate two sine signals with the same amplitude and 90-degree phase difference, the sine signals are converted into excitation signals in the form of constant-current electric signals by the voltage-controlled current conversion component, and the output excitation signals are monitored by the current measurement module; meanwhile, another excitation signal is led out from the signal generation module to be used as a reference signal, and the phase of the reference signal is used as an initial phase;

step 102: an excitation coil in the magnetic field detection probe generates an excitation magnetic field according to an excitation signal, the initial angle and the rotation direction of the excitation magnetic field are controlled by a signal generation module, and then the excitation magnetic field rotates on the surface of a test piece to form induction magnetic fields with a plurality of angles;

step 103: the array detection coil assembly is used for acquiring detection signals of the induction magnetic fields at all angles and sending the detection signals to the signal processing module, the signal processing module is used for carrying out quadrature phase locking on the detection signals to obtain amplitude and phase information of the induction magnetic fields contained in the detection signals, and the amplitude and phase information is transmitted to an upper computer for processing through the acquisition card;

step 2: calculating the amplitude information and the phase information of the induced magnetic field contained in the detection signal by a magnetic field reduction method to obtain the magnetic field intensity of the induced magnetic field when the excitation magnetic field is positioned at any angle:

wherein the content of the first and second substances,the magnetic field intensity of the induction magnetic field when the angle of the excitation magnetic field is alpha; a is the amplitude response of the induction magnetic field;is the phase response of the induced magnetic field; α is the angle of the excitation field.

And step 3: reconstructing the surface current of the test piece by using a square electric dipole model, changing the current distribution of the surface of the test piece after reconstruction from continuous current into a plurality of discrete independent square unit electric dipoles, and using a matrix [ I ]_α]Represents; and decomposing the scattered test piece surface current to obtain the test piece surface uniform current and the test piece surface disturbance current.

And 4, step 4: calculating an induced magnetic field intensity distribution matrix of the unit electric dipole according to the Bio Saval law, and establishing a functional relation between the unit electric dipole and an induced magnetic field, wherein the functional relation is shown as the following formula:

wherein C is a magnetic field distribution matrix generated by a unit electric dipole on the surface of the test piece; n is a magnetic field intensity error matrix between the detected induction magnetic field and the actual induction magnetic field; conv (·, ·) represents a convolution operation;the current is disturbed by the surface of the test piece when the magnetic field is excited at an angle alpha.

And 5: converting convolution operation in the relation between the unit electric dipole on the surface of the test piece and the space disturbance magnetic field into product operation in a frequency domain, adding a regularization parameter to constrain an operation result, and obtaining an expression of disturbance current on the surface of the test piece:

wherein μ is a regularization parameter; f () represents the Fourier transform, F^-1() Representing an inverse fourier transform;

inverting to obtain a current matrix under the square electric dipole model shown in fig. 2, and converting the obtained current matrix, wherein the conversion formula is as follows:

wherein i and j are positive integers not greater than the number of rows and columns of the matrix respectively;andthe elements of the ith row and the jth column of the surface disturbance current distribution matrix in the direction of the X, Y axis are respectively.

Because the angle of the detected crack is unknown, magnetic field data under a plurality of angles needs to be selected for inversion, the inversion precision is ensured, and the angles suitable for selection are as follows: 0 °, 45 °, 90 °, 135 °, 180 °; in the inversion of the embodiment, 90 ° is selected, and the intensity of the induced magnetic field is the maximum, so that the inversion result is more accurate.

Step 6: superposing the disturbance current on the surface of the test piece and the uniform current on the surface of the test piece, wherein the intensity of the uniform current on the surface of the test piece is obtained by calculating the maximum intensity value of the disturbance current on the surface, and the current distribution on the surface of the test piece is obtained:

wherein the content of the first and second substances,when the angle of the excitation magnetic field is alpha, the surface of the test piece is uniformly electrified;andx, Y respectively, are used for disturbing the current distribution matrix on the surface.

In this embodiment, the surface currents of the test pieces obtained from different angles are added to obtain an average value, so as to obtain the final surface current distribution of the test piece.

And 7: and drawing a test piece surface current distribution diagram, and obtaining a profile image of the test piece surface crack through the test piece surface current distribution diagram.

In the embodiment, the test piece surface disturbance current is reduced, and the set test piece surface uniform current is added to obtain the test piece surface current distribution under a specific angle, and as the test piece surface current distribution is influenced by the crack profile, no current distribution exists in the crack area, the crack distribution can be visually obtained according to the current density of the inversion result;

the final result is generated by current distribution superposition under multiple angles, as shown in fig. 3-4, the obtained current distribution diagram on the surface of the test piece reflects the current density distribution on the surface of the test piece, the current of a white area approaches to 0, the area where the crack is located is shown, and the two-dimensional profile distribution of the crack on the surface of the test piece is directly reflected.

Referring to fig. 5, another embodiment of the present invention provides a current dipole-based two-dimensional profile inversion apparatus for surface cracks of a test piece 6, including a two-dimensional moving platform 1, a signal generation module 2, a magnetic field detection probe 3, a signal processing module 4, and an upper computer 5; the signal generation module 2 and the magnetic field detection probe 3 are arranged on the two-dimensional mobile platform 1, and the signal generation module 2 comprises a homologous orthogonal signal generation component, a voltage-controlled current conversion component and a current measurement component, and is configured to receive a control signal and send out an excitation signal according to the control signal; the magnetic field detection probe 3 includes an excitation coil assembly 31 and an array detection coil assembly 32, and is configured to generate an excitation magnetic field according to an excitation signal and detect an induced magnetic field generated by the excitation magnetic field on the surface of the test piece 6, and to emit a detection signal; the signal processing module 4 comprises an orthogonal phase-locking circuit, as shown in fig. 6, and is configured to receive the detection signal, process the detection signal into an electric signal, and send the electric signal to the upper computer 5 through the acquisition card 7; the upper computer 5 is connected with the signal generating module 2, the signal processing module 4 and the two-dimensional moving platform 1 respectively, and is configured to control the two-dimensional moving platform 1 to move, output a control signal and receive the processed detection signal, and obtain a two-dimensional profile of the surface crack of the test piece 6 through inversion.

Preferably, referring to fig. 7-8, the excitation coil assembly 31 includes a coil frame 311 and two mutually orthogonal excitation coils 312 wound on the coil frame 311, the excitation coil assembly 31 is disposed above the test piece 6 and close to the test piece 6, and the array detection coil assembly 32 is disposed below the excitation coil assembly 31; two excitation signals with the same amplitude and 90-degree phase difference generated by the homologous orthogonal signal generating component in the signal generating module 2 are converted into constant current signals by the voltage-controlled current source-to-current source component and then are respectively connected into the two excitation coils 312 to generate excitation magnetic fields; the two-dimensional moving platform 1 drives the magnetic field detection probe 3 to move to scan the test piece 6, and the upper computer 5 controls the scanning range and the step length of the two-dimensional moving platform 1 to enable the array detection coil assembly 32 to detect the induced magnetic fields generated by the test piece at multiple angles.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.