A high-frequency ultrasonic coating bonding strength detection method and device

Abstract

The present application discloses a high-frequency ultrasonic coating bonding strength detection method and device. The method realizes the detection of coating bonding strength when the medium / coating interface echo and the coating / substrate interface echo are aliased from the perspective of signal analysis. The echo signal is transformed into the frequency domain through time-frequency transformation, and the notch frequency of the signal spectrum and its difference are identified to calculate the characterization characteristics of the coating bonding strength for constructing a characteristic matrix. The characteristic matrix is ​​binarized to calculate the distribution of bonding strength of the tested sample in the tested area, and the coating bonding strength of the whole tested sample is characterized by calculating the proportion of the number of binary elements in the binary matrix. The method overcomes the interference of interface echo aliasing and realizes non-destructive graded detection of coating bonding strength.

Description

Technical Field

[0001] The invention belongs to the field of coating bonding strength detection, and specifically relates to a high-frequency ultrasonic coating bonding strength detection method and device. Background Art

[0002] Coating technology has been applied to various fields, such as anti-oxidation and corrosion-resistant coatings for engines, temperature control coatings for spacecraft, carbide coatings for cutting tools, and camouflage coatings for aircraft, etc. The bonding strength between the coating and the substrate affects the use effect and service life of the coating system. At present, the most commonly used method for testing the bonding strength of coatings is the cross-cutting test method, which is a destructive test and cannot test the entire area of ​​the sample. Therefore, it is of great significance to perform non-destructive testing and characterization of the bonding strength of coatings. Summary of the invention

[0003] Based on this, the present invention provides a high-frequency ultrasonic coating bonding strength detection method and device, which effectively realizes ultrasonic silent detection of coating bonding strength and overcomes the defects of the above-mentioned prior art.

[0004] The present invention provides a high-frequency ultrasonic coating bonding strength detection method, comprising:

[0005] Collecting the reflected echo signal of the sample under test according to a preset scanning step length, wherein the reflected echo signal includes a first interface echo signal of the coupling medium / coating interface and a second interface echo signal of the coating / substrate interface;

[0006] Performing time-frequency transformation on the reflected echo signal to obtain a signal spectrum, and confirming each notch frequency in the signal spectrum;

[0007] Establishing a relationship between the notch frequency and the echo signal phase difference, wherein the echo signal phase difference represents the phase difference between the first interface echo signal and the second interface echo signal; establishing a relationship between the coating bonding strength characterization feature and the echo signal phase difference based on the relationship between the notch frequency and the echo signal phase difference, and constructing a characteristic matrix, wherein the matrix elements represent the coating bonding strength characterization features corresponding to each reflected echo signal;

[0008] Convert the feature matrix into a binary matrix;

[0009] The number ratio of binary elements in the binary matrix is ​​calculated, and the coating bonding strength of the tested sample is determined according to the number ratio.

[0010] Preferably, the time-frequency transform uses fast Fourier transform.

[0011] Preferably, the relationship between the notch frequency and the echo signal phase difference is expressed as follows:

[0012] n represents the number of notches in the spectrum, f nrepresents the notch frequency, represents the phase difference between the first interface echo signal and the second interface echo signal, Δf represents the frequency difference between adjacent notches, Δf = f n -f n-1 ;

[0013] Then the frequency difference Δf=f n -f n-1 It can be expressed as

[0014] Preferably, the relationship between the coating bonding strength characterization feature and the echo signal phase difference is established as follows:

[0015] Calculate the characteristic factor a of each notch frequency n-1 =f n-1 / d n-1 , d n-1 =f n -f n-1 , n represents the number of notches in the spectrum, d n represents the frequency difference between adjacent notches, then

[0016]

[0017] Therefore, for n notches, the corresponding n characteristic factors can be expressed as

[0018] Take the fractional part b of the characteristic factor as follows n The average value is used as the characteristic of coating bonding strength

[0019] Preferably, the echo signal phase difference is expressed as follows:

[0020] Z2 and Z3 represent the acoustic impedance of the coating and the acoustic impedance of the substrate, respectively, ω represents the signal angular frequency, and K represents the coating interface stiffness.

[0021] Preferably, converting the feature matrix into a binary matrix includes:

[0022] The feature matrix is ​​binarized according to the intensity threshold. The feature matrix elements greater than or equal to the intensity threshold are set to 1, and the feature matrix elements less than the intensity threshold are set to 0. The feature matrix is ​​converted into a binary matrix with only 1 and 0 elements through binarization.

[0023] Preferably, calculating the number ratio of binary elements in the binary matrix, and determining the coating bonding strength of the tested sample according to the number ratio comprises:

[0024] The proportion of the number of element 1 in the binary matrix is ​​calculated, and the level of the proportion of element 1 is determined according to the preset strength classification to determine the level of the coating bonding strength of the tested sample.

[0025] The present invention also provides a high-frequency ultrasonic coating bonding strength detection device, comprising:

[0026] Ultrasonic transducer, three-dimensional motion platform, angle adjustment mechanism, sample slot, pulse transceiver, computer;

[0027] The angle adjustment mechanism is fixedly connected to the three-dimensional motion platform, the ultrasonic transducer is installed on the angle adjustment mechanism, the pulse transceiver is electrically connected to the ultrasonic transducer, and the computer is electrically connected to the pulse transceiver;

[0028] When the device is used for detection, a sample to be tested is placed in a sample slot, and the relative position of the ultrasonic transducer and the sample to be tested is adjusted by a three-dimensional motion platform and an angle adjustment mechanism, so that the ultrasonic transducer is located in the focal area, and the main sound beam is perpendicular to the surface of the sample to be tested. The sample slot is filled with a coupling medium, and the ultrasonic wave is incident on the sample to be tested through the coupling medium and returns a reflected echo signal to a pulse transceiver, and the reflected echo signal is transmitted to a computer through the pulse transceiver for signal detection;

[0029] The device is used to implement the above-mentioned high-frequency ultrasonic coating bonding strength detection method.

[0030] It can be seen from the above technical solutions that the present invention has the following beneficial effects:

[0031] The present invention provides a high-frequency ultrasonic coating bonding strength detection method and device, which realizes the detection of coating bonding strength when the medium / coating interface echo and the coating / substrate interface echo are aliased from the perspective of signal analysis, transforms the echo signal to the frequency domain through time-frequency transformation, identifies the notch frequency of the signal spectrum to calculate the characterization characteristics of the coating bonding strength, binarizes the characteristic matrix to distinguish the strength of the bonding strength, and realizes non-destructive graded detection of the coating bonding strength. The detection method provided by the present invention can overcome the interference of the aliasing of the medium / coating interface echo and the coating / substrate interface echo, and can effectively realize ultrasonic non-destructive detection of the coating bonding strength without the need for a reference signal. Not only can the coating bonding strength of the detected sample be graded, but also the imaging contrast is large and the detection accuracy is high. It can be applied in large-scale production lines and has good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0033] Figure 1 It is a schematic diagram of a high-frequency ultrasonic coating bonding strength detection device disclosed in the present invention;

[0034] Figure 2 It is a flow chart of the high-frequency ultrasonic coating bonding strength detection method disclosed in the present invention;

[0035] Figure 3 is a time domain diagram of a detection signal according to an embodiment of the present invention;

[0036] Figure 4 It is a frequency domain diagram of a detection signal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In order to realize the high-frequency ultrasonic coating bonding strength detection method provided by the present invention, refer to Figure 1 , this embodiment discloses a detection device, including:

[0039] Ultrasonic transducer 1, three-dimensional motion platform 2, angle adjustment mechanism 3, sample slot 4, pulse transceiver 5, computer 6;

[0040] The angle adjustment mechanism 3 is fixedly connected to the three-dimensional motion platform 2 , the ultrasonic transducer 1 is mounted on the angle adjustment mechanism 3 , the pulse transceiver 5 is electrically connected to the ultrasonic transducer 1 , and the computer 6 is electrically connected to the pulse transceiver 6 .

[0041] It should be understood that the electrical connection mentioned here can be either a wired electrical connection, such as signal transmission through a tangible cable, or a wireless electrical connection, such as signal transmission through a wireless network, Bluetooth, radio frequency communication, etc. The present invention is not limited to this.

[0042] When the device is used for detection, a sample to be tested is placed in the sample slot 4, and the relative positions of the ultrasonic transducer 1 and the sample to be tested are adjusted by the three-dimensional motion platform 2 and the angle adjustment mechanism 3, so that the ultrasonic transducer 1 is located in the focal area and the main sound beam is perpendicular to the surface of the sample to be tested. The sample slot 4 is filled with a coupling medium, and the ultrasonic wave is incident on the sample to be tested through the coupling medium and returns a reflected echo signal to the pulse transceiver 5. The reflected echo signal is transmitted to the computer 6 through the pulse transceiver 5 for signal detection.

[0043] Specifically, the ultrasonic transducer is aligned with the sample to be tested before the formal test. This embodiment uses an immersion-type high-frequency ultrasonic transducer. A three-dimensional motion platform 2 and an angle adjustment mechanism 3 are used according to the detection range to ensure that the main sound beam of the ultrasonic transducer 1 is perpendicular to the surface of the sample to be tested. The position of the Z axis is adjusted to place the transducer in the focal area.

[0044] The specific focusing process is as follows: perform an echo test on the sample to be tested, first move the Z-axis position to the position with obvious echo, then adjust the ultrasonic transducer in the X-axis direction to find the position with the largest echo amplitude, adjust in the Y-axis direction to find the position with the largest echo amplitude, and finally adjust the Z-axis direction to make the echo amplitude the largest. The position at this time is the focus of the transducer.

[0045] See also Figure 2 , the high-frequency ultrasonic coating bonding strength detection method disclosed in the present invention is introduced below.

[0046] The ultrasonic wave emitted by the ultrasonic transducer passes through the coupling medium (e.g. water) in the sample tank and is incident on the medium / coating interface and the coating / substrate interface. The scanning waveform P0(t) of the reflected echo signal of the sample under test is collected according to the preset scanning step length, where t represents time.

[0047] In some embodiments, the preset scanning step size can be determined by the inspector according to the inspection requirements, or the cutting spacing specified in the grid test in the national standard GB / T9286-1998 can be used, and the cutting spacing can be regarded as the ultrasonic scanning step size to obtain the reflected echo signals corresponding to multiple scanning points.

[0048] The multiple reflected echo signals obtained by scanning are represented by a signal matrix. The matrix has M×N elements, and the elements represent the reflected echo signals at the scanning points, which are generated by the ultrasonic wave incident on the sample under test through the coupling medium, including the first interface echo signal representing the medium / coating interface and the second interface echo signal representing the coating / substrate interface.

[0049] In some embodiments, in order to conveniently solve the phase difference of the echo signal, the comb filter effect can be used to express the time domain expression of the reflected echo signal in the form of a comb filter function.

[0050] The filter function of the comb filter is expressed as y(t)=b0x(t)+b d x(t)e iωΔt , y(t) represents the output signal, x(t) represents the input signal, b0 and b d represents the proportional coefficient, ω represents the signal angular frequency, and Δt represents the signal delay.

[0051] The reflected echo signal can be expressed as β1 and β2 represent the amplitudes of the first interface echo signal and the second interface echo signal, respectively. c is the center frequency, is the phase difference between the two interface echo signals, and Δt represents the arrival time difference between the two interface echo signals.

[0052] It can be seen that the echo signal is consistent with the function expression of the comb filter, which is convenient for obtaining in subsequent detection.

[0053] Phase difference between the first interface echo signal and the second interface echo signal It can be expressed as follows:

[0054] Z2 and Z3 represent the acoustic impedance of the coating and the acoustic impedance of the substrate, respectively, ω represents the signal angular frequency, and K represents the coating interface stiffness. Therefore, the bonding strength of the coating can be characterized by studying the phase relationship of the coating echo.

[0055] Perform fast Fourier transform on the filtered scanning waveform P0(t) to obtain the corresponding spectrum A(f), where f represents frequency in Hz. a ,f b ], assuming that the signal spectrum is in the frequency range [f a ,f b ], there are n notches, then there are notch frequencies f1, f2, ..., f n , n is a positive integer. Figure 3 and Figure 4 The time domain signal and frequency domain signal of the detection signal are shown respectively. Figure 4 The depression in the IF signal indicates a notch.

[0056] For notch frequencies f1, f2, ..., f n Next, we need to establish the phase difference of the interface echo signal The relationship between the notch frequency and the notch frequency can be expressed as f n Indicates the notch frequency, Δf=f n -f n-1represents the frequency difference between adjacent notches, then the frequency difference between adjacent notches Δf=f n -f n-1 It can be expressed as Therefore, when the notch frequency is determined, the phase difference of the interface echo can be obtained from the notch frequency.

[0057] In addition, the frequency difference between adjacent notches can also be expressed as follows:

[0058] d1=f2-f1

[0059] d2=f3-f2

[0060]

[0061] d n-1 =f n -f n-1

[0062] The quotient of the notch frequency and the corresponding frequency difference is as follows:

[0063] a1=f1 / d1

[0064] a2=f2 / d2

[0065]

[0066] a n-1 =f n-1 / d n-1

[0067] For the sake of distinction, this embodiment uses a n-1 Named as characteristic factor, through the above calculation, we can get the characteristic factor and the interface echo phase difference The relationship is as follows:

[0068]

[0069] Therefore, for n notches, the corresponding n characteristic factors can be expressed as

[0070] It is easy to see from the expression of the above characteristic factors that since n is a positive integer, only the decimal part is related to the phase difference, that is, related to the coating bonding strength, so the decimal part b of each characteristic factor is taken n And calculate the average value as the coating bonding strength characteristic That is:

[0071]

[0072] Each scanning waveform is processed as above to obtain the characteristic The M×N feature matrix composed of

[0073] An intensity threshold δ is used to define the strength of the coating bonding strength. Since the reflected echo signal is collected according to the preset scanning step length, it can be regarded as the main sound beam of the ultrasonic transducer incident on a certain point of the sample under test, and the above signal processing of the reflected echo signal is obtained It can characterize the bonding strength of the coating at that location of the sample being tested.

[0074] For the M×N feature matrix obtained by the above signal processing process, the elements greater than or equal to the threshold δ are set to 1, indicating that the bonding strength of the coating in the measured area is strong; the elements less than the threshold δ are set to 0, indicating that the bonding strength of the coating in the measured area is weak. It is easy to understand that the feature matrix can be converted into an M×N binary matrix through this process.

[0075] Record the number of 1 and 0 in the binary matrix, and count the percentages of the two elements 1 and 0. Since 1 indicates strong coating bonding strength, the higher the percentage of element 1, the higher the coating bonding strength of the sample as a whole. In order to better characterize the coating bonding strength of the tested sample as a whole, the percentage of 1 characterizes the proportion of the area with strong coating bonding strength in the sample test area. Therefore, this embodiment uses the percentage of 1 as a quantitative indicator for sample strength classification, and its value can be expressed as β=[W / (M×N)]×100%, where W represents the number of element 1.

[0076] In some embodiments, the coating bonding strength grading can be determined by statistics of multiple test results, or the grading standard specified in the national standard GB / T9286-1998 cross-cut test can be used, as shown in Table 1 below. The higher the coating bonding strength, the smaller the cross-cut area affected in the cross-cut test. In this case, it is sufficient to determine the relationship between the proportion of element 1 and the proportion of damaged area corresponding to each grade in the standard GB / T9286-1998.

[0077] Table 1

[0078]

[0079]

[0080] For example, if the β value of the sample being tested is 97%, its strength level is 1; if the β value of the sample being tested is 80%, its strength level is 3; if the β value of the sample being tested is 50%, its strength level is 4.

[0081] It is understandable that, in some embodiments, the coating bonding strength of the entire sample under test can also be characterized by the proportion of element 0. Further, when the strength is graded using the grading standard specified in the national standard GB / T9286-1998, its mapping relationship is exactly opposite to the proportion of element 1. For example, when characterized by the proportion η of element 0, if the η value of the sample under test is 3%, its strength grade is 1; if the η value of the sample under test is 20%, its strength grade is 3; if the η value of the sample under test is 45%, its strength grade is 4.

[0082] In some embodiments, the intensity threshold δ can be calculated and determined by measuring a standard sample, and one implementation method is given here.

[0083] The cross-cut test method is used to obtain standard samples with strength levels of 0 to 5, and all standard samples are subjected to ultrasonic nondestructive testing and signal processing as above to obtain M×N characteristic matrices R0, R1, R2, R3, R4, and R5 corresponding to each level. The initial strength threshold is 0, and the matrices R0 to R5 are binarized as above and the proportion of each matrix element 1 is calculated, expressed as β0, β1, β2, β3, β4, and β5. Compare the relationship between β0 to β5 and the proportion of damaged areas corresponding to each grade in the standard GB / T9286-1998, and determine whether it is consistent with the grade to which the standard sample itself belongs. For example, for a standard sample of grade 1, if its element proportion β1 is 95% or 98%, the test result is consistent with the cross-cut test result. When the test results of all standard samples are consistent with the grade to which they belong, the secondary threshold can be used as the strength threshold of the test method proposed by the present invention, and used for the strength detection of other tested samples; if the test result of any standard sample is inconsistent with the grade to which it belongs, the threshold is changed according to a fixed step size until the consistency condition is met. The threshold value can be changed in steps of 0.1 or other step values.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-frequency ultrasonic coating bonding strength detection method, characterized in that: include: The reflected echo signal of the sample under test is collected according to the preset scanning step length. The reflected echo signal includes a first interface echo signal of the coupling medium / coating interface and a second interface echo signal of the coating / substrate interface. The time domain signal of the reflected echo signal is expressed as follows: β1 and β2 represent the amplitudes of the first interface echo signal and the second interface echo signal, respectively. c is the center frequency, is the phase difference between the first interface echo signal and the second interface echo signal, and Δt represents the arrival time difference between the first interface echo signal and the second interface echo signal; Performing time-frequency transformation on the reflected echo signal to obtain a signal spectrum, and confirming each notch frequency in the signal spectrum; The relationship between the notch frequency and the echo signal phase difference is established as follows: n represents the number of notches in the spectrum, f n represents the notch frequency, represents the phase difference of the echo signal, Δf represents the frequency difference between adjacent notches, Δf=f n -f n-1 ; Then the frequency difference Δf=f n -f n-1 It can be expressed as Based on the relationship between the notch frequency and the phase difference of the echo signal, the relationship between the coating bonding strength characterization feature and the phase difference of the echo signal is established, and a characteristic matrix is ​​constructed, in which the matrix elements represent the coating bonding strength characterization features corresponding to each reflected echo signal; Convert the feature matrix into a binary matrix; Calculating the proportion of the number of binary elements in the binary matrix, and determining the coating bonding strength of the tested sample according to the proportion of the number; The relationship between the coating bonding strength characterization feature and the echo signal phase difference is established as follows: Calculate the characteristic factor a of each notch frequency n-1 =f n-1 / d n-1 , d n-1 =f n -f n-1 , n represents the number of notches in the spectrum, d n represents the frequency difference between adjacent notches, then Therefore, for n notches, the corresponding n characteristic factors can be expressed as Take the fractional part b of the characteristic factor as follows n The average value is used as the characteristic of coating bonding strength 2. The high-frequency ultrasonic coating bonding strength detection method according to claim 1, characterized in that: The time-frequency transformation adopts fast Fourier transformation.

3. The high-frequency ultrasonic coating bonding strength detection method according to claim 1, characterized in that: The echo signal phase difference is expressed as follows: Z2 and Z3 represent the acoustic impedance of the coating and the acoustic impedance of the substrate, respectively, ω represents the signal angular frequency, and K represents the coating interface stiffness.

4. The high-frequency ultrasonic coating bonding strength detection method according to claim 1, characterized in that: Converting the feature matrix into a binary matrix includes: The feature matrix is ​​binarized according to the intensity threshold, the feature matrix elements greater than or equal to the intensity threshold are set to 1, and the feature matrix elements less than the intensity threshold are set to 0, and the feature matrix is ​​converted into a binary matrix with only 1 and 0 elements through binarization.

5. The high-frequency ultrasonic coating bonding strength detection method according to claim 4 is characterized in that: Determining the coating bonding strength of the tested sample according to the number ratio includes: The proportion of the number of elements 1 in the binary matrix is ​​calculated, and the level of the proportion of the number of elements 1 is determined according to the preset strength classification to determine the level of the coating bonding strength of the tested sample.

6. A high-frequency ultrasonic coating bonding strength detection device, characterized in that: include: Ultrasonic transducer, three-dimensional motion platform, angle adjustment mechanism, sample slot, pulse transceiver, computer; The angle adjustment mechanism is fixedly connected to the three-dimensional motion platform, the ultrasonic transducer is mounted on the angle adjustment mechanism, the pulse transceiver is electrically connected to the ultrasonic transducer, and the computer is electrically connected to the pulse transceiver; When the detection device is used for detection, a sample to be tested is placed in the sample slot, and the relative position of the ultrasonic transducer and the sample to be tested is adjusted by the three-dimensional motion platform and the angle adjustment mechanism, so that the ultrasonic transducer is located in the focal area and the main sound beam is perpendicular to the surface of the sample to be tested. The sample slot is filled with a coupling medium, and the ultrasonic wave is incident on the sample to be tested through the coupling medium and returns a reflected echo signal to the pulse transceiver, and the reflected echo signal is transmitted to the computer through the pulse transceiver for signal detection; The pulse transceiver is used to collect the reflected echo signal of the sample under test according to the preset scanning step length. The reflected echo signal includes the first interface echo signal of the coupling medium / coating interface and the second interface echo signal of the coating / substrate interface. The time domain signal of the reflected echo signal is expressed as follows: β1 and β2 represent the amplitudes of the first interface echo signal and the second interface echo signal, respectively. c is the center frequency, is the phase difference between the first interface echo signal and the second interface echo signal, and Δt represents the arrival time difference between the first interface echo signal and the second interface echo signal; The computer executes the following high-frequency ultrasonic coating bonding strength detection method: Performing time-frequency transformation on the reflected echo signal to obtain a signal spectrum, and confirming each notch frequency in the signal spectrum; The relationship between the notch frequency and the echo signal phase difference is established as follows: n represents the number of notches in the spectrum, f n represents the notch frequency, represents the phase difference of the echo signal, Δf represents the frequency difference between adjacent notches, Δf=f n -f n-1 ; Then the frequency difference Δf=f n -f n-1 It can be expressed as Based on the relationship between the notch frequency and the phase difference of the echo signal, the relationship between the coating bonding strength characterization feature and the phase difference of the echo signal is established, and a characteristic matrix is ​​constructed, in which the matrix elements represent the coating bonding strength characterization features corresponding to each reflected echo signal; Convert the feature matrix into a binary matrix; Calculating the proportion of the number of binary elements in the binary matrix, and determining the coating bonding strength of the tested sample according to the proportion of the number; The relationship between the coating bonding strength characterization feature and the echo signal phase difference is established as follows: Calculate the characteristic factor a of each notch frequency n-1 =f n-1 / d n-1 , d n-1 =f n -f n-1 , n represents the number of notches in the spectrum, d n represents the frequency difference between adjacent notches, then Therefore, for n notches, the corresponding n characteristic factors can be expressed as Take the fractional part b of the characteristic factor as follows n The average value is used as the characteristic of coating bonding strength

Images