CN115586245A - A Method for Crack Quantification of Ferromagnetic Materials Based on Pulsed Rotating Electromagnetic Field - Google Patents

Abstract

The invention discloses a ferromagnetic material crack quantification method based on a pulse rotating electromagnetic field, which is characterized in that a pulse excitation signal with a phase difference of 90 degrees is generated by developing a pulse rotating electromagnetic field ferromagnetic material crack quantification hardware system through an FPGA platform and acts on a piece to be measured, finally, a crack signal is extracted through the FPGA platform, the crack type is judged through crack extraction signals under reference signals with different frequencies, operation is carried out according to the crack signal, the signal characteristics of a magnetic leakage signal and a disturbance signal are recorded, and the crack length, the crack depth and the crack angle are calculated. The ferromagnetic material crack quantification method based on the pulse rotating electromagnetic field can solve the problems that the size of the ferromagnetic material crack cannot be quantified and the surface crack and the buried crack cannot be judged by the traditional rotating electromagnetic field detection technology.

Description

A Crack Quantification Method for Ferromagnetic Materials Based on Pulsed Rotating Electromagnetic Field

technical field

The invention relates to the technical field of rotating electromagnetic field detection, in particular to a method for quantifying cracks in ferromagnetic materials based on pulsed rotating electromagnetic fields.

Background technique

The rotating magnetic field is a magnetic field that does not change in size and rotates in space at a certain speed. When a symmetrical three-phase current flows in a symmetrical three-phase winding, a rotating magnetic field will be generated, and the magnetic field will continuously rotate in space as the current alternates. with. The rotating electromagnetic field detection technology uses the rotating uniform induced current field generated on the test piece to detect cracks. It has high detection sensitivity for small cracks and can quantify the size of cracks in any direction. Currently, the rotating electromagnetic field detection technology is used in non-ferromagnetic Mature research results have been achieved in the quantification of the single crack size of materials. However, for ferromagnetic materials, due to their own ferromagnetic properties, there will be complex magnetic fields composed of leakage magnetic fields and disturbance magnetic fields when detecting cracks. Therefore, rotating electromagnetic field detection is used. technology to quantify cracks poses difficulties.

When using rotating electromagnetic field detection technology to detect ferromagnetic materials, there is a complex magnetic field composed of disturbance magnetic field and leakage field caused by current, which makes it impossible to quantify cracks. Crack distinction.

Contents of the invention

The purpose of the present invention is to provide a method for quantifying cracks in ferromagnetic materials based on pulsed rotating electromagnetic fields, so as to solve the problems that the traditional rotating electromagnetic field detection technology cannot quantify the crack size of ferromagnetic materials and cannot judge surface cracks and buried deep cracks.

In order to achieve the above object, the present invention provides a method for quantifying cracks in ferromagnetic materials based on a pulsed rotating electromagnetic field, comprising the following steps:

Step 1, the pulse excitation signal generation module on the FPGA platform generates a pulse excitation signal with a phase difference of 90 degrees, and the pulse excitation signal passes through the MOS transistor drive circuit to form a unipolar pulse signal with a controllable duty cycle so that high current is applied to the On the pulse rotating probe, the sensor on the pulse rotating probe picks up the space-induced magnetic field signal above the DUT;

Step 2, the signal acquisition module on the FPGA platform transmits the electrical signal captured by the sensor on the pulse rotation probe to the FPGA platform, and at the same time generates the required reference signal through the reference signal control module on the FPGA platform, and then passes the phase-locked signal on the FPGA platform Amplifier module for crack signal extraction;

Step 3: Judging the type of cracks based on the crack extraction signals under different frequency reference signals, the frequency is from high to low, and deep-buried defects of different depths appear in sequence;

Step 4, calculating the amplitude information and phase information of the induced magnetic field contained in the extracted crack signal through the magnetic field reduction method to obtain the magnetic field strength of the induced magnetic field when the excitation magnetic field is at any angle;

Step 5, decomposing the extracted crack signal into a magnetic flux leakage signal and a disturbance signal, finding the maximum magnetic field intensity of the leakage magnetic field and the disturbance magnetic field, and recording the signal characteristics;

Step 6, calculating the crack length, crack depth, and crack angle according to the signal features.

Preferably, the MOS transistor drive circuit controls to generate a pulse signal with variable current magnitude to form a high-intensity induced magnetic field.

Preferably, the angle in step 4 is denoted as α _i (i=0, 1, 2, ..., 90), the decomposition accuracy is 1, and the magnetic field signal is decomposed in the range of 0° to 90°:

为激励磁场在角度为α_i时的感应磁场的磁场强度，A为感应磁场的幅值响应。in,

is the magnetic field strength of the induced magnetic field when the excitation magnetic field is at an angle of α _i , and A is the amplitude response of the induced magnetic field.

Preferably, the signal characteristics in step 5 are: a. when the disturbance signal is the largest, the magnetic field presents two circular magnetic fields, and the angle is denoted as α _d at this time; b. when the magnetic flux leakage signal is the largest, the magnetic field presents two strip magnetic fields, and at this time The angle is denoted as α _m .

Preferably, in step 6, when α _i =α _d , the crack length is quantified by the distance between the two peaks of the disturbance magnetic field signal, and the peak-to-peak coordinates of the disturbance magnetic field intensity are set as (X _k , Y _k ) and (X _l , Y _l ), the crack length is l, and the crack length is expressed as:

Among them, a is the proportional coefficient for converting the magnetic field signal coordinate difference to the physical length;

When α _i = α _m and α _i = α _d , the peak-to-peak value of the disturbance magnetic field and the leakage magnetic field are extracted to quantify the crack depth. Let the peak-to-peak value of the disturbance magnetic field intensity be Bz _d-max , and the peak-to-peak value of the leakage magnetic field intensity be Bz _{m -max} , the crack depth is h,

h＝(b _d Bz _d-max +b _m Bz _m-max )/2

Among them, b _d and b _m are the weight coefficients for the transformation of the disturbance magnetic field and the leakage magnetic field strength to the physical depth respectively. Quantity related;

When α _i = α _m and α _i = α _d , the strip-shaped leakage magnetic field signal clearly shows both sides of the crack. Assuming the crack angle is θ, we get:

Therefore, the present invention adopts a method for quantifying cracks in ferromagnetic materials based on the pulse rotating electromagnetic field with the above structure, which has the following beneficial effects:

1. The present invention proposes a pulse excitation method, which is realized by using FPGA combined with a MOS transistor drive circuit. The device is simple to implement, and can realize the output of a large current excitation signal, and realize the controllable excitation current;

2. Through the decomposition of the crack magnetic field signal of ferromagnetic material, it is divided into leakage magnetic field and disturbance magnetic field, and the crack size can be quantified by combining the two decomposition fields.

The technical solutions of the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

Description of drawings

Fig. 1 is the flow chart of the method for quantifying ferromagnetic material cracks based on pulse rotating electromagnetic field in the present invention;

Fig. 2 is the schematic structural diagram of the pulse rotating electromagnetic field ferromagnetic material crack quantification system developed based on the FPGA platform of the present invention;

Fig. 3 is the pulse excitation signal schematic diagram that the pulse excitation signal generation module of the present invention produces;

Fig. 4 is a schematic diagram of the surface crack Bz signal of the ferromagnetic material of the present invention;

Fig. 5 is a schematic diagram of the Bz signal of a deep-buried crack on the surface of a ferromagnetic material of the present invention;

Fig. 6 is a schematic diagram of Bz signal peak-to-peak coordinates when α _i =α _d of the present invention;

Fig. 7 is a schematic diagram of the peak-to-peak coordinates of the Bz signal when α _i =α _m according to the present invention.

reference sign

1. Pulse excitation signal generation module; 2. Signal acquisition module; 3. Reference signal control module; 4. Lock-in amplifier module; 5. MOS tube drive circuit; 6. Pulse rotating probe; 7. FPGA platform; pieces.

detailed description

The technical solutions of the present invention will be further described below through the accompanying drawings and embodiments.

Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by those skilled in the art to which the present invention belongs. "First", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Comprising" or "comprising" and similar words mean that the elements or items appearing before the word include the elements or items listed after the word and their equivalents, without excluding other elements or items. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "Down", "Left", "Right" and so on are only used to indicate the relative positional relationship. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

Example

Fig. 1 is the flow chart of the method for quantifying cracks in ferromagnetic materials based on pulsed rotating electromagnetic fields in the present invention; Fig. 2 is a schematic structural diagram of the quantification system for cracks in ferromagnetic materials in pulsed rotating electromagnetic fields developed by the present invention based on the FPGA platform; Fig. 3 is a pulse excitation signal generation module of the present invention Schematic diagram of the generated pulse excitation signal;

Fig. 4 is the ferromagnetic material surface crack Bz signal schematic diagram of the present invention; Fig. 5 is the ferromagnetic material surface deep buried crack Bz signal schematic diagram of the present invention; Fig. 6 is the Bz signal peak value coordinate schematic diagram when α _i = α _d of the present invention; Fig. 7 It is a schematic diagram of the peak-to-peak coordinates of the Bz signal when α _i =α _m in the present invention.

As shown in the figure, the present invention develops a rotating pulse eddy current ferromagnetic material crack quantification hardware system based on the FPGA platform. The hardware system mainly includes a pulse excitation signal generation module 1, a pulse rotation probe 6, a signal acquisition module 2, a reference signal control module 3 and a lock. phase amplifier module 4 etc.

A method for quantifying cracks in ferromagnetic materials based on pulsed rotating electromagnetic fields according to the present invention comprises the following steps:

Step 1, the pulse excitation signal generation module 1 on the FPGA platform 7 generates a pulse excitation signal with a phase difference of 90°, and the pulse excitation signal passes through the MOS tube drive circuit 5 to form a unipolar pulse signal with a controllable duty ratio so that A higher current is applied to the orthogonal excitation coil of the pulse rotating probe 6, so that a rotating pulse magnetic field is generated above the test piece 8, and an induced current is generated on the surface and inside of the test piece 8, and passes through the tunnel on the pulse rotating probe 6. The three-axis magnetoresistive sensor picks up the space-induced magnetic field signal above the test piece 8 . The MOS transistor drive circuit 5 controls the generation of pulse signals with variable current magnitudes to form a high-intensity induced magnetic field.

Step 2, the signal acquisition module 2 on the FPGA platform 7 transmits the electrical signal captured by the tunnel three-axis magnetoresistive sensor to the FPGA platform 7, and simultaneously generates the required reference signal through the reference signal control module 3 on the FPGA platform 7, and then passes the FPGA The lock-in amplifier module 4 on the platform 7 performs crack signal extraction.

Step 3: Judgment of crack type by crack extraction signals under different frequency reference signals, the frequency is from high to low, and deep-buried defects of different depths appear in sequence.

Step 4: Calculate the amplitude information and phase information of the induced magnetic field contained in the extracted crack signal by a magnetic field reduction method to obtain the magnetic field strength of the induced magnetic field when the excitation magnetic field is at any angle.

Step 5, decomposing the extracted crack signal into a magnetic flux leakage signal and a disturbance signal, finding the maximum magnetic field intensity of the leakage magnetic field and the disturbance magnetic field, and recording the signal characteristics.

Step 6, calculating the crack length, crack depth, and crack angle according to the signal features.

The selected part 8 to be tested has three defects, the size of which is 10mm×3mm (length×depth), and the buried depths are 0mm, 1mm and 2mm respectively. The pulse excitation signal generating module 1 generates two 300Hz, 5V pulse signal sources as excitation signals, and the phase difference between the two excitation signals is 90°. The orthogonal excitation coil is composed of two orthogonally wound coils, and receives the signal to be measured through the three-axis tunnel magnetoresistive sensor.

The signal to be measured passes through the lock-in amplifier module 4 built by FPGA to demodulate the specific frequency components of the signal to be measured. Here, 300Hz (the fundamental wave of the excitation signal) and 300300Hz (the 1001 harmonic wave of the excitation signal) sinusoidal signals are selected as reference signals to demodulate.

According to the principle that the ability of low-frequency electromagnetic signals to penetrate the DUT 8 is stronger than that of high-frequency signals, the type of defect is discriminated. It is known that the standard Bz amplitude signal is a double-peak signal. From the results in Figure 3, it can be seen that at 300Hz and 300300Hz, the Bz signal has two peak characteristics, which is the standard Bz amplitude signal curve. Therefore, the crack is the surface of the test piece. Crack; it is known that the standard Bz amplitude signal is a double-peak signal. From the results in Figure 4, it can be seen that at 300Hz, the Bz signal presents two peak characteristics, which is the standard Bz amplitude signal curve. At 300-300Hz, there is no crack signal feature. Therefore, it can be known that the crack is a deep crack in the test piece.

Crack quantification includes crack length, angle and depth information. A crack with a buried depth of 0 mm is selected for illustration, and defect quantification is performed at 300-300 Hz.

1. First, through the decomposition algorithm, the crack signal is decomposed according to the angle of the magnetic field signal, and the interval is 1, which is recorded as α ₀ , α ₁ , α ₂ ,..., α ₉₀ . The amplitude information and phase information of the induced magnetic field contained in the detection signal are calculated by the magnetic field reduction method to obtain the magnetic field strength of the induced magnetic field when the excitation magnetic field is at any angle:

为激励磁场在角度为α_i时的感应磁场的磁场强度，A为感应磁场的幅值响应。in,

is the magnetic field strength of the induced magnetic field when the excitation magnetic field is at an angle of α _i , and A is the amplitude response of the induced magnetic field.

2. Find the maximum disturbance signal and magnetic flux leakage signal: a. When the disturbance signal is the largest, the magnetic field presents two circular magnetic fields, and the angle at this time is recorded as α _d ; b. When the magnetic flux leakage signal is maximum, the magnetic field presents two strip magnetic fields, At this time, the angle is denoted as α _m .

In order to quantify the crack length, when α _i = α _d , record the peak-to-peak coordinates of the Bz signal as (X _k , Y _k ) and (X _l , Y _l ), and the crack length is l,

Among them, a is the proportional coefficient for transforming the magnetic field signal coordinate difference to the physical length.

In order to quantify the crack depth, when α _i =α _m and α _i =α _d , the peak-to-peak values of the disturbance magnetic field and the leakage magnetic field are extracted to quantify the crack depth. Let the peak-peak value of the disturbance magnetic field intensity be Bz _d-max , and the leakage magnetic field intensity be The peak-to-peak value is Bz _m-max , the crack depth is h,

h＝(b _d Bz _d-max +b _m Bz _m-max )/2

Among them, b _d and b _m are the weight coefficients for the conversion of the disturbance magnetic field and the leakage magnetic field strength to the physical depth, respectively.

In order to quantify the crack angle, when α _i = α _m , the strip-shaped magnetic flux leakage magnetic field signal clearly shows both sides of the crack. When α _i = α _d , the peak-to-peak coordinates of the Bz signal are (X _k , Y _k ) and ( X _l , Y _l ), record the crack angle as θ, and get

Therefore, the present invention adopts the method for quantifying ferromagnetic material cracks based on the pulsed rotating electromagnetic field with the above structure, which can solve the problems that the traditional rotating electromagnetic field detection technology cannot quantify the size of ferromagnetic material cracks and cannot judge surface cracks and buried deep cracks.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it still Modifications or equivalent replacements can be made to the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims (5)

1. A ferromagnetic material crack quantification method based on a pulse rotating electromagnetic field is characterized by comprising the following steps:

generating pulse excitation signals with a phase difference of 90 degrees by a pulse excitation signal generating module on an FPGA platform, forming unipolar pulse signals with controllable duty ratio by the pulse excitation signals through an MOS tube driving circuit so as to apply high current to a pulse rotating probe, and picking up space induction magnetic field signals above a piece to be detected by a sensor on the pulse rotating probe;

secondly, a signal acquisition module on the FPGA platform transmits an electric signal captured by a sensor on the pulse rotating probe into the FPGA platform, a reference signal control module on the FPGA platform generates a required reference signal, and then a phase-locked amplifier module on the FPGA platform extracts a crack signal;

judging the types of the cracks through the crack extraction signals under the reference signals with different frequencies, wherein the deep-buried defects with different depths sequentially appear from high to bottom in the frequency;

calculating the amplitude information and the phase information of the induced magnetic field contained in the extracted crack 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;

step five, decomposing the extracted crack signal into a leakage magnetic signal and a disturbance signal, finding the maximum magnetic field intensity condition of the leakage magnetic field and the disturbance magnetic field, and recording the signal characteristics;

and step six, calculating the crack length, the crack depth and the crack angle according to the signal characteristics.

2. The ferromagnetic material crack quantification method based on the pulsed rotating electromagnetic field as claimed in claim 1, wherein the MOS transistor driving circuit is controlled to generate a pulse signal with a variable current magnitude to form a high-intensity induced magnetic field.

3. The ferromagnetic material crack quantification method based on the pulsed rotating electromagnetic field as claimed in claim 1, wherein the angle in the fourth step is denoted as α _i (i =0,1,2, … …, 90), the resolution accuracy is 1, and the magnetic field signal resolution is performed in the range of 0 ° to 90 °:

wherein,

for exciting the magnetic field at an angle alpha _i The magnetic field strength of the induced magnetic field at the time, a, is the magnitude response of the induced magnetic field.

4. The ferromagnetic material crack quantification method based on the pulsed rotating electromagnetic field of claim 3, wherein the signal in the fifth step is characterized by: a. when the disturbance signal is maximum, the magnetic field presents two circular magnetic fields, and the angle is recorded as alpha _d (ii) a b. When the leakage signal is maximum, the magnetic field presents two strip magnetic fields, and the angle is recorded as alpha _m 。

5. The ferromagnetic material crack quantification method based on the pulsed rotating electromagnetic field of claim 4, wherein in step six, α is _i ＝α _d The crack length is quantified by the distance between two peak values of the disturbing magnetic field signal, and the peak-peak value coordinate of the disturbing magnetic field intensity is set as (X) _k ，Y _k ) And (X) _l ，Y _l ) The crack length is l, and the crack length is expressed as:

wherein a is a proportionality coefficient for converting the coordinate difference of the magnetic field signal into the physical length;

at alpha _i ＝α _m And alpha _i ＝α _d Extracting peak-to-peak values of the disturbing magnetic field and the leakage magnetic field to quantify the depth of the crack, and setting the peak-to-peak value of the disturbing magnetic field intensity as Bz _d-max Peak-to-peak value of the intensity of the leakage magnetic field is Bz _m-max The depth of the crack is h,

h＝(b _d Bz _d-max +b _m Bz _m-max )/2

wherein, b _d And b _m The coefficients are respectively weight coefficients for converting the intensity of the disturbance magnetic field and the intensity of the leakage magnetic field to physical depth, the coefficients are obtained by performing data fitting on the magnetic field intensity peak value and the crack depth value, and the accuracy of the coefficients is related to the fitting data volume;

at α _i ＝α _m And alpha _i ＝α _d And then, the strip-shaped magnetic leakage magnetic field signal clearly presents two sides of the crack, and the crack angle is set as theta to obtain:

。

Images