CN110243922B - ACFM visual imaging method for irregular cracks of ferromagnetic material - Google Patents
ACFM visual imaging method for irregular cracks of ferromagnetic material Download PDFInfo
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Abstract
The invention discloses an ACFM visual imaging method for irregular cracks of ferromagnetic materials, which relates to the technical field of nondestructive testing defect imaging and comprises the following steps: the method comprises the steps of obtaining a magnetic field signal Bz amplitude matrix of an irregular crack alternating current electromagnetic field surface scanning result by means of a grid scanning method, obtaining an X-direction gradient field matrix and a Y-direction gradient field matrix of a distorted magnetic field signal Bz by means of a gradient field, reflecting the aggregation condition of induced currents around the irregular crack and the leakage magnetic field formed by an original excitation magnetic field, obtaining two-direction normalization matrixes by further obtaining extremum, removing background and normalizing the two-direction gradient field matrices, and summing the two-direction normalization matrixes, so that visual imaging results of the surface profile of the irregular crack of the ferromagnetic material can be achieved, and visual evaluation and accurate prediction of residual life of the crack of the ferromagnetic material are facilitated.
Description
Technical Field
The invention relates to the technical field of nondestructive testing defect imaging, in particular to an ACFM visual imaging method for irregular cracks of ferromagnetic materials.
Background
The marine structure is in service in seawater for a long time, and various crack defects are easily generated on the surface of the structure under the combined actions of corrosion, storm, ocean current, alternating load, dead weight and the like, so that the safe service of the structure is threatened. The alternating current magnetic field detection (Alternating Current Field Measurement is abbreviated as ACFM) technology is an emerging electromagnetic nondestructive detection technology, has the characteristics of non-contact detection, no need of cleaning attachments, quantitative evaluation and the like, is widely applied to the defect detection of marine structures, and utilizes uniform current induced by a detection probe on the surface of a conductive test piece, the current generates disturbance around the defect to cause spatial magnetic field distortion, and the defect detection and evaluation are carried out by measuring a distorted magnetic field. When no defect exists, the surface current of the conductive test piece is in a uniform state, and the space magnetic field is free from disturbance.
When the induced current is perpendicular to the crack, the current disturbance is obvious, and the space distortion magnetic field presents larger disturbance. When the induced current is parallel to the crack, the current disturbance is not obvious, but the original excitation magnetic field is perpendicular to the crack, so that a leakage magnetic field is formed. The secondary distortion magnetic field and the primary leakage magnetic field of the original excitation caused by the current disturbance around the irregular cracks on the surface of the ferromagnetic material structure exist simultaneously, so that a plurality of challenges are brought to the judgment and evaluation of the irregular cracks. The existing alternating current electromagnetic field detection technology judges according to characteristic signals Bx and Bz or butterfly patterns formed by the characteristic signals, wherein the Bx and Bz signals are magnetic field signals parallel to the surface of a test piece (parallel to the scanning direction of a probe) and perpendicular to the surface of the test piece respectively, the characteristic signals can only judge that cracks perpendicular to induced current exist, and imaging display of irregular cracks cannot be achieved. The electromagnetic field around the irregular cracks of the ferromagnetic material is distorted and complicated, and the surface profile of the irregular cracks cannot be visually displayed by the prior art means.
Therefore, it is necessary to provide a method for imaging irregular cracks on the surface of a ferromagnetic material, which has good intuitiveness, can display the surface profile visualization morphology of the irregular cracks, and provides accurate data support for irregular crack evaluation and service life prediction of the ferromagnetic material.
Disclosure of Invention
Aiming at the problems, the invention provides the ACFM visual imaging method for the irregular cracks of the ferromagnetic material, which visually presents the visual appearance of the surface profile of the irregular cracks of the ferromagnetic material and provides accurate visual data support for the evaluation and life prediction of the irregular cracks of the ferromagnetic material.
The invention provides an ACFM visual imaging method for irregular cracks of a ferromagnetic material, which comprises the following steps:
step one, acquiring magnetic field signal Bz amplitude values of the same plane and different positions above irregular cracks of ferromagnetic materials by using an alternating current magnetic field detection probe in a grid scanning mode, defining the scanning direction of the probe as the X direction, extracting n position points from scanning paths in the X direction, extracting the number of scanning paths in the direction perpendicular to the scanning direction of the probe as m, and forming an m-row n-column matrix by the magnetic field signal Bz amplitude values of the position pointsFor each row element [ a ] of matrix A i1 a i2 …a in ]Gradient +.>Obtaining an X-direction gradient field matrix of the matrix AFor each column element of matrix A +.>Gradient determination along Y-direction (matrix A-column direction)Obtaining a Y-direction gradient field matrix of matrix A>
Step two, obtaining an extreme value PGX in all elements of the X-direction gradient field matrix GX Bz Determining an extremum PGX Bz If the value is smaller than 0, multiplying by-1 to obtain an X-direction positive peak matrix CX; obtaining an extreme value PGY in all elements of the Y-direction gradient field matrix GY Bz Determining an extremum PGY Bz If the value is smaller than 0, multiplying by-1 to obtain a Y-direction positive peak matrix CY;
step three, judging whether each element in the X-direction positive peak matrix CX is smaller than 0, if so, multiplying by 0 to obtain an X-direction removal background matrix DX; judging whether each element in the Y-direction positive peak matrix CY is smaller than 0, if so, multiplying by 0 to obtain a Y-direction removal background matrix DY;
normalizing the amplitude values of all elements of the X-direction removal background matrix DX to a 0-1 interval to obtain an X-direction normalization matrix EX; normalizing the amplitude values of all elements of the Y-direction removal background matrix DY to a 0-1 interval to obtain a Y-direction normalization matrix EY;
summing the X-direction normalization matrix DX and the Y-direction normalization matrix DY to obtain a comprehensive matrix E, and drawing an irregular crack surface profile color image F by a coordinate position corresponding to each element of the comprehensive matrix E;
and step six, converting the color image F into a gray level image G to obtain an irregular crack surface profile image of the ferromagnetic material.
According to the method for visualizing the irregular crack ACFM of the ferromagnetic material, provided by the invention, the X-direction gradient and the Y-direction gradient are obtained through the characteristic signal Bz amplitude matrix, the current disturbance distortion extremum position and the leakage extremum position of the leakage magnetic field of the irregular crack of the ferromagnetic material are obtained, the extremum is obtained through the two-direction gradient field matrix elements, the background field is removed and the normalization treatment is carried out, the surface contours of the irregular crack in two vertical directions are reflected, the normalization results in the two directions are further summed to obtain a color map reflecting the surface contours of any angle position of the irregular crack of the ferromagnetic material, and the visual contours of the irregular crack can be visually displayed through gray scale map conversion.
Drawings
FIG. 1 is a flow chart of an ACFM visual imaging method for irregular cracks of a ferromagnetic material;
FIG. 2 is a photograph of irregular cracks on the surface of a carbon steel test block according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an ACFM probe grid scanning path provided by an embodiment of the present invention;
fig. 4 is a color chart formed by scanning magnetic field signal Bz amplitude matrixes of different positions by using a grid based on an alternating current magnetic field detection technology according to an embodiment of the present invention;
FIG. 5 is an image formed by an X-direction gradient field matrix GX provided in an embodiment of the present invention;
FIG. 6 is an image formed by a Y-direction gradient field matrix GY provided by an embodiment of the present invention;
FIG. 7 is a graph of an X-direction removal background matrix DX obtained by obtaining extremum and removing background from an X-direction gradient field matrix GX according to an embodiment of the present invention;
FIG. 8 is a graph of a Y-direction removed background matrix DY obtained by obtaining extremum and removing background from a Y-direction gradient field matrix GY according to an embodiment of the present invention;
FIG. 9 is an image formed by an amplitude X-direction normalized matrix EX for removing all elements of a background matrix DX in the X-direction according to an embodiment of the present invention;
FIG. 10 is a diagram showing an image formed by a normalized matrix EY of the amplitude Y-direction of all elements of a background matrix DY removed in the Y-direction according to an embodiment of the present invention;
FIG. 11 is a diagram showing a color image F drawn by a synthesis matrix E according to an embodiment of the present invention;
fig. 12 is a visual image showing an irregular crack surface profile provided by an embodiment of the present invention.
Detailed Description
For the purpose of promoting an understanding of the principles and advantages of the invention, reference will now be made in detail to the drawings and specific examples, it is to be understood that the embodiments described are merely illustrative of some, but not all of the embodiments. Based on the embodiments of the present invention, other embodiments that may be obtained by those skilled in the art without performing inventive efforts are within the scope of this invention.
In the embodiment of the invention, the method is applied to the visual imaging of the surface profile of the irregular crack of the ACFM ferromagnetic material, firstly, an alternating electromagnetic field surface scanning result magnetic field signal Bz amplitude matrix is obtained by means of a grid scanning method, when induced current on the surface of the ferromagnetic material gathers and disturbances are obvious during vertical crack, and when the induced current is parallel to the crack, the current disturbance is not obvious, but the original excitation magnetic field forms a leakage magnetic field, namely, the disturbance magnetic field formed by the current disturbance and the leakage magnetic field formed by the original excitation magnetic field respectively play a leading role in two mutually perpendicular directions, in order to realize the visual imaging of any angle crack on the surface of the irregular crack, gradients are needed to be obtained for the distortion magnetic fields in the two directions, the magnetic field distortion positions in the X direction and the Y direction are obtained, the surface profile reflecting the irregular crack in the two directions is obtained through the operations of obtaining of extreme values of the X direction and the normalization, and further, the visual image of any angle profile of the irregular crack of the ferromagnetic material is obtained through summation, and the visual image of the irregular crack is obtained through gray map conversion, thereby being beneficial to realize the visual evaluation and accurate prediction of the residual life of the irregular crack of the ferromagnetic material.
Example 1
Fig. 1 is a flowchart of an ACFM visual imaging method for irregular cracks of a ferromagnetic material, provided by an embodiment of the present invention, including:
s1, preparing a carbon steel test block, wherein an irregular crack is formed on the surface of the test block, the irregular crack consists of four sections of cracks of 0 degree, 30 degree, 60 degree and 90 degree, the crack depth is 2.0mm, and the width is 0.8mm, as shown in figure 2. A schematic diagram of a scanning path of a probe grid is shown in fig. 3, a scanning direction of the probe is defined as an X direction, a grid scanning method is adopted, an alternating current magnetic field detection probe is utilized to detect an area of 89.0mm multiplied by 88.0mm along the scanning path on the same height plane of the irregular crack surface of a test block, the scanning step length in the X direction is 1.0mm, the number of equidistant position points on the X direction scanning path is 90, the distance between the Y direction scanning paths is 2.0mm, the number of equidistant path points in the Y direction scanning is 45, the amplitude of a magnetic field signal Bz of the position points is obtained, the number of lines m is 45, the number of columns n is 90, and a matrix A comprises the following partial elements:
in order to visually represent the sizes of the elements in the matrix a, the magnitudes of the magnetic field signals Bz of the corresponding position points of the abscissa (X direction) and the ordinate (Y direction) are used to draw a planar color chart, as shown in fig. 4. It can be seen that the amplitude of the magnetic field signal Bz in the matrix a is disturbed around the irregular crack, and positive and negative peaks are presented, so that the surface profile of the crack cannot be visually displayed.
Gradient determination for each line of elements in matrix A according to X direction (matrix A line direction) An X-direction gradient field matrix GX is obtained, and an X-direction gradient field matrix image is drawn using the X-direction gradient field matrix GX corresponding to the coordinate position points, as shown in fig. 5. It can be seen that the X-direction gradient field matrix reflects the 60 DEG and 90 DEG section crack morphology, is insensitive to 0 DEG and 30 DEG section cracks, and cannot display the complete irregular crack surface profile visualization morphology.
Gradient is obtained for each column of elements in matrix A according to Y direction (column direction of matrix A) A Y-direction gradient field matrix GY is obtained, and a Y-direction gradient field matrix image is drawn using the Y-direction gradient field matrix GY of the corresponding coordinate position point, as shown in fig. 6. It can be seen that the Y-direction gradient field matrix reflects crack morphology of 0 degree, 30 degree and 60 degree, is insensitive to crack of 90 degree, and cannot display the complete irregular crack surface profile visualization morphology.
As can be seen from fig. 5 and 6, positive and negative peaks appear in the X-direction gradient field and the Y-direction gradient field, and in order to find the maximum distortion extremum, extremum processing needs to be performed on the gradient field matrix, and the process proceeds to step S2.
S2: obtaining extreme value PGX in all elements of X-direction gradient field matrix GX Bz Extreme value PGX in the present embodiment Bz Positive value due to PGX Bz When the gradient field matrix GX is larger than 0, element replacement processing is not needed, and the gradient field matrix GX in the X direction is converted into a positive peak matrix CX in the X direction; obtaining the extreme value PGY in all elements of the Y-direction gradient field matrix GY Bz In the present embodimentExtreme value PGY Bz Positive value due to PGX Bz When the gradient field matrix GY is larger than 0, the Y-direction gradient field matrix GY is converted into a Y-direction positive peak matrix CX without element replacement processing. In order to remove the negative value of the element in the positive peak matrix, it is necessary to go to step S3 to remove the background value from the element in the positive peak matrix.
S3: and judging whether each element in the X-direction positive peak matrix CX is smaller than 0, if so, multiplying by 0, changing all elements smaller than 0 in the X-direction positive peak matrix CX into 0, and realizing unified return-to-0 processing of all element background values of the X-direction positive peak matrix CX to obtain an X-direction removal background matrix DX, and drawing an image by utilizing the X-direction removal background matrix DX of the corresponding coordinate position point, as shown in fig. 7. Compared with fig. 5, it can be seen that fig. 7 removes the influence of background interference noise, and significantly improves the contrast of the outline of the defect region;
and judging whether each element in the Y-direction positive peak matrix CY is smaller than 0, if so, multiplying by 0, changing all elements smaller than 0 in the Y-direction positive peak matrix CY into 0, and uniformly returning all element background values of the Y-direction positive peak matrix CY to 0 to obtain a Y-direction removal background matrix DY, and drawing an image by utilizing the Y-direction removal background matrix DY of the corresponding coordinate position point, as shown in fig. 8. Compared with fig. 6, it can be seen that fig. 8 removes the influence of background interference noise, and significantly improves the contrast of the outline of the defective region.
Because fig. 7 and 8 only show partial irregular crack surface contours, all visual imaging of the irregular crack surface contours cannot be realized, normalization processing of the X-direction removal background matrix DX and the Y-direction removal background matrix DY can be performed, elements of the two matrices are normalized to a 0-1 interval, and summation under the same scale is convenient to realize.
S4, dividing the amplitude values of all elements of the X-direction removal background matrix DX by the extremum PGX Bz Normalizing to 0-1 interval to obtain an X-direction normalized matrix EX, and drawing an image by the coordinate position corresponding to each element of the X-direction normalized matrix EX, as shown in FIG. 9. Fig. 9 is a view capable of visually displaying the surface profile of an irregular crack 60 ° and a 90 ° segment crack;
dividing the amplitude values of all elements of the Y-direction removal background matrix DYAt the extreme value PGY Bz Normalizing to 0-1 interval to obtain a Y-direction normalized matrix EY, and drawing an image by the coordinate position corresponding to each element of the Y-direction normalized matrix EY, as shown in FIG. 10. Fig. 10 can intuitively show the surface profile of the irregular crack 0 °, 30 °, 60 ° segment crack. To achieve a visual imaging display of the crack segments at all positions of the irregular crack, the X-direction normalization matrix EX and the Y-direction normalization matrix EY are summed.
S5, summing the X-direction removing background matrix DX and the Y-direction removing background matrix DY to obtain a comprehensive matrix E, and drawing an irregular crack surface profile color image F by the coordinate position corresponding to each element of the comprehensive matrix E, as shown in FIG. 11. It can be seen that fig. 11 can show the surface profile of all the sections of the surface crack of the carbon steel test block.
S6, converting the color image F into a gray scale image G by utilizing Matlab to obtain a ferromagnetic material irregular crack surface profile visualization image, as shown in FIG. 12. The visual appearance of the irregular cracks can be clearly shown in fig. 12, the visual appearance of the irregular cracks is better matched with the irregular cracks on the surface of the carbon steel test block, and the higher accuracy of the contour reconstruction is achieved.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (1)
1. An ACFM visual imaging method for irregular cracks of ferromagnetic materials is characterized by comprising the following steps:
acquiring magnetic field signal Bz amplitude values of the same plane and different positions above irregular cracks of ferromagnetic materials by using an alternating current magnetic field detection probe, defining the scanning direction of the probe as X direction, extracting n position points from scanning paths in the X direction, extracting the number of scanning paths as m from the direction perpendicular to the scanning direction of the probe, and forming an m-row n-column matrix by the magnetic field signal Bz amplitude values of the position pointsFor each row element [ a ] of matrix A i1 a i2 ···a in ]Gradient +.>Obtaining an X-direction gradient field matrix of matrix A>For each column element of matrix A +.>Gradient +.>Obtaining a Y-direction gradient field matrix of matrix A>
Step two:
obtaining an extreme value PGX in all elements of the X-direction gradient field matrix GX Bz Determining an extremum PGX Bz If the value is smaller than 0, multiplying by-1 to obtain an X-direction positive peak matrix CX; obtaining an extreme value PGY in all elements of the Y-direction gradient field matrix GY Bz Determining an extremum PGY Bz If the value is smaller than 0, multiplying by-1 to obtain a Y-direction positive peak matrix CY;
step three:
judging whether each element in the X-direction positive peak matrix CX is smaller than 0, if so, multiplying by 0 to obtain an X-direction removal background matrix DX; judging whether each element in the Y-direction positive peak matrix CY is smaller than 0, if so, multiplying by 0 to obtain a Y-direction removal background matrix DY;
step four:
normalizing the amplitude values of all elements of the X-direction removal background matrix DX to a 0-1 interval to obtain an X-direction normalization matrix EX; normalizing the amplitude values of all elements of the Y-direction removal background matrix DY to a 0-1 interval to obtain a Y-direction normalization matrix EY;
step five:
summing the X-direction normalization matrix DX and the Y-direction normalization matrix DY to obtain a comprehensive matrix E, and drawing an irregular crack surface profile color image F by the coordinate position corresponding to each element of the comprehensive matrix E;
step six:
and converting the color image F into a gray level image G to obtain an irregular crack surface profile image of the ferromagnetic material.
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| CN111189905B (en) * | 2020-01-09 | 2023-09-05 | 中国石油大学(华东) | Three-dimensional size assessment method for corrosion defect of underwater structure based on alternating-current electromagnetic field |
| CN111189906B (en) * | 2020-01-09 | 2023-09-29 | 中国石油大学(华东) | On-line intelligent judging and classifying identification method for alternating current magnetic field defects |
| CN112964777B (en) * | 2021-04-14 | 2024-02-06 | 中国特种设备检测研究院 | Double-excitation detection method for surface crack trend |
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| CN114234785A (en) * | 2021-12-23 | 2022-03-25 | 中国特种设备检测研究院 | Method for detecting cracks on surface and near surface of connecting pipe fillet weld based on field gradient imaging |
| CN117074513B (en) * | 2023-10-13 | 2023-12-15 | 中国石油大学(华东) | Defect identification method based on alternating current electromagnetic field and array detection probe |
| CN117235433B (en) * | 2023-11-10 | 2024-01-26 | 中国石油大学(华东) | Metal surface crack quantitative evaluation method based on alternating current magnetic field |
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