Titanium alloy plate thickness measuring method based on low-frequency eddy current phase characteristic model and application thereof

Abstract

The invention belongs to the technical field of eddy current nondestructive testing, and discloses a titanium alloy plate thickness measuring method based on a low-frequency eddy current phase characteristic model and application of the titanium alloy plate thickness measuring method.The titanium alloy plate thickness measuring method comprises the steps that S1, the conductivity sigma is determined according to a titanium alloy mark, S2, sigma is substituted into a penetration depth formula, the excitation current frequency f is determined, and the thickness of a titanium alloy plate is measured; s3, connecting the detection coil, the isolation resistor, the reference coil and the excitation signal source in series; the detection coil is vertically placed on the surface of a plate, and the reference coil is parallel above the detection coil. And S4, generating excitation current with frequency f, obtaining Z and Zair, and calculating delta Z = Zair-Z. And S5, extracting a real part Re (delta Z) and an imaginary part Im (delta Z) of delta Z, and calculating tan (theta) = Im (delta Z) / Re (delta Z). S6, the tan (theta) is substituted into the explicit inversion analysis model, and the thickness c is calculated. According to the method, under low-frequency excitation, when the eddy current penetration depth is three times larger than the thickness, an explicit inversion model is established through the approximate linear relation between the coil phase and the titanium alloy thickness. Based on the model, the measurement does not need iteration or calibration, and the thickness is calculated directly through coil impedance, which is fast and simple.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of eddy current nondestructive testing, and particularly relates to a titanium alloy plate thickness measurement method based on a low-frequency eddy current phase feature model and application thereof. BACKGROUND

[0002] Titanium alloy is an alloy composed of titanium and other elements, and has the advantages of high strength, small density and good corrosion resistance. In titanium alloy processing materials, the yield of plate accounts for more than 50% of the total, and its application is the most extensive. In the production process of titanium alloy plate, the thickness deviation may be caused by the instability of the production process, the insufficient equipment precision, the fluctuation of raw material quality and the like, which may lead to problems such as decreased processing precision and intensified equipment wear.

[0003] At present, common detection methods for titanium alloy plates include ultrasonic wave, ray and eddy current method. Eddy current detection is a nondestructive testing technology based on electromagnetic induction phenomenon, and has the advantages of high speed, non-contact, no pollution, low cost and no need for coupling agent compared with other nondestructive testing methods. In the process of material detection by using the eddy current detection technology, when the thickness of the measured material changes, the magnetic flux of the eddy current coil will change, and the impedance change of the induction coil is reflected. The thickness of the measured plate can be indirectly judged by relying on the impedance change.

[0004] However, the traditional eddy current thickness measurement method has obvious limitations. The traditional eddy current detection method relies on complex calibration and iterative calculation, and it is difficult to meet the online high-precision measurement requirement. For example, the reference master curve is obtained through the previous experiment, and the measured thickness is obtained by comparing the detection signal with the master curve during measurement. Such a way is tedious in the previous experiment, and the precision is not high. Although most of the measurement methods based on the model improve the precision, the complex nonlinear expression or ill-conditioned equation needs to be solved through iteration, the calculation efficiency is low, and it is difficult to meet the online high-speed measurement requirement. At the same time, the existing model is mostly aimed at high-conductivity metals, and the influence of the low-conductivity characteristics of titanium alloy on the eddy current response is not fully considered, so the measurement precision is difficult to guarantee. Therefore, a new analytical model needs to be established, and a corresponding new measurement method needs to be designed to solve the above problems. SUMMARY

[0005] In view of the background, the titanium alloy plate thickness measurement method based on the low-frequency eddy current phase feature model and application thereof are provided. Under low-frequency excitation, the ratio of the real part and the imaginary part of the impedance change of the eddy current coil is approximately linearly related to the thickness of the titanium alloy, an explicit inversion analytical model based on the phase feature is established, and a corresponding measurement method is designed. The method does not need iteration or calibration of the master curve, and the thickness can be directly calculated through the measured impedance.

[0006] To achieve the object of the application, the following technical solutions are adopted:

[0007] In a first aspect, the present application provides a titanium alloy plate thickness measurement method based on a low-frequency eddy current phase characteristic model, and the specific steps are as follows:

[0008] S1, according to the grade of the measured titanium alloy plate, determine its conductivity σ;

[0009] S2, substitute the conductivity σ into the penetration depth formula to determine the low-frequency excitation current frequency f of the eddy current coil;

[0010] The excitation frequency determination criterion is that the excitation frequency should satisfy that the penetration depth is greater than 3 times the range thickness , and the excitation frequency is calculated by the formula , wherein is the vacuum permeability;

[0011] S3, the detection coil, the isolation resistor, the reference coil and the excitation signal source are connected in series to form a magnetic field loop, the detection coil is vertically placed on the surface of the titanium alloy plate to be measured, and the reference coil is parallelly placed above the detection coil, wherein the sizes of the detection coil and the reference coil are the same.

[0012] S4, the excitation signal source generates an excitation current with a frequency of f, and obtains the detection coil impedance Z and the reference coil impedance Z air , and calculates the impedance change signal ΔZ=Z air -Z;

[0013] S5, extract the real part Re(ΔZ) and the imaginary part Im(ΔZ) of the impedance change signal, and calculate the phase characteristic tan(θ)=Im(ΔZ) / Re(ΔZ) of the impedance change;

[0014] S6, substitute the phase characteristic tan(θ) obtained in S5 into the explicit inversion analytical model to directly calculate the thickness c of the titanium alloy plate.

[0015] Preferably, the explicit inversion analytical model in step S6 is:

[0016] ;

[0017] Wherein, ξ is a comprehensive factor related to the geometric size of the detection coil. The comprehensive factor ξ is related to the inner radius r1, the outer radius r2 and the height of the detection coil, and its expression is as follows:

[0018] .

[0019] In a second aspect, the present application provides a flash memory medium embedded with a burning program to realize the method as described in the first aspect, for rapid online measurement of titanium alloy plates and application of portable instruments.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0021] 1. High efficiency: It abandons the traditional thickness inversion measurement method and is based on an explicit inversion formula. The thickness can be calculated from the measured impedance in one step without iterative calculation or reference calibration master curve.

[0022] 2. High precision: Low-frequency excitation conditions are optimized for the low conductivity of titanium alloys, and the phase characteristics are strongly linearly correlated with the thickness.

[0023] 3. Wide applicability, suitable for various grades of titanium alloys such as TA1, TA2, and TC4.

[0024] 4. Low cost: The thickness of titanium alloy plates can be measured simply by adjusting the excitation frequency according to the conductivity, and the measurement time is short. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of eddy current measurement of titanium alloy plate thickness according to the present invention.

[0026] Figure 2 This is a flowchart of the titanium alloy plate thickness measurement method based on a low-frequency eddy current phase characteristic model according to the present invention.

[0027] In the diagram: 1. Titanium alloy plate under test; 2. Detection coil; 3. Isolation resistor; 4. Reference coil; 5. Excitation signal source. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The principle of eddy current measurement of titanium alloy plate thickness in this embodiment is as follows: Figure 1 As shown, a circuit is formed by connecting the detection coil 2, isolation resistor 3, reference coil 4, and excitation signal source 5 in series. The detection coil 2 is placed vertically on the surface of the titanium alloy plate 1 to be tested, and the reference coil 4 is placed parallel above the detection coil 2. The detection coil 2 and reference coil 4 are of the same size. The distance between the reference coil 4 and the detection coil 2 is twice the diameter of the detection coil 2. When the excitation signal source 5 generates an alternating current with frequency f, the detection coil 2 generates a magnetic field. Eddy currents are generated in the titanium alloy plate 1 due to electromagnetic induction. When the thickness of the plate changes, the magnetic flux of the detection coil 2 changes, which is reflected as a change in the coil's impedance. By comparing the impedance change of the detection coil 2 with that of the reference coil 4, the thickness of the plate can be indirectly determined.

[0030] The frequency f output by the excitation signal source 5 can be selected as a low-frequency signal in the range of 0.5kHz to 5kHz. This frequency range ensures that the penetration depth of the eddy current in the titanium alloy plate covers the common thickness range to be measured (0.5mm-10mm). The impedance difference between the detection coil 2 and the reference coil 4 is converted into a phase difference signal in the circuit. This phase difference is extracted and amplified by an impedance analyzer. No calibration is required before actual measurement. The precise thickness value of the titanium alloy plate 1 to be measured can be calculated by substituting the phase difference extracted by the final lock-in amplifier into the explicit inversion analytical model.

[0031] Based on the aforementioned detection principle, this application provides a method for measuring the thickness of titanium alloy plates based on a low-frequency eddy current phase characteristic model, such as... Figure 2 As shown, the steps are as follows:

[0032] S1. Determine the electrical conductivity based on the grade of the titanium alloy being tested. The electrical conductivity σ of the known material is given.

[0033] S2. Substitute the conductivity σ into the penetration depth formula to determine the frequency f of the low-frequency excitation current supplied to the eddy current coil;

[0034] S3. Connect the detection coil, isolation resistor, reference coil, and excitation signal source in series to form a circuit. Place the detection coil vertically on the surface of the titanium alloy plate to be tested, and place the reference coil parallel above the detection coil. The detection coil and reference coil are of the same size.

[0035] S4. An excitation signal source generates an excitation current with frequency f, which passes through the coil to obtain the impedance Z of the detection coil and the impedance Z of the reference coil. air Calculate the impedance change signal ΔZ=Z air -Z.

[0036] Impedance signals can be acquired by devices such as impedance analyzers and data acquisition cards, but are not limited to these devices;

[0037] S5. Extract the real part Re(ΔZ) and imaginary part Im(ΔZ) of the impedance change signal, and calculate the phase characteristic of the impedance change tan(θ)=Im(ΔZ) / Re(ΔZ).

[0038] S6. Substitute the phase characteristic tan(θ) obtained in S5 into the explicit inversion analytical model to directly calculate the thickness c of the titanium alloy plate.

[0039] The accurate conductivity σ can be obtained by consulting the material handbook corresponding to the titanium alloy grade being tested or by using the four-probe method for actual measurement, ensuring the accuracy of subsequent frequency calculations. The penetration depth formula is δ=√(2 / (2πfμ0σ)) (where μ0 is the magnetic permeability of the titanium alloy; for non-magnetic materials, μ0≈4π×10). -7Substituting H / m into σ, a low-frequency f is selected to ensure the penetration depth δ covers 1.5-2 times the thickness to be measured, balancing measurement sensitivity and linear range. Both the detection coil and reference coil are wound with the same number of turns (50-100 turns recommended) and a wire diameter of 0.1-0.3mm enameled copper wire; the isolation resistor value must match the internal resistance of the excitation signal source (usually 50Ω); the distance between the detection coil and the surface to be measured is controlled within 0.5mm, and the parallel distance between the reference coil and the detection coil is maintained at 2-5mm to avoid mutual inductance interference. The impedance analyzer is set to AC impedance measurement mode with a sampling rate of 2kHz; the Z-axis is measured... air To minimize random errors, the coil is moved to air free of metallic interference and the process is repeated three times. Before extracting the real and imaginary parts, high-frequency noise is removed using a low-pass filter to ensure a signal-to-noise ratio ≥30dB. The explicit inversion analytical model is derived based on a quasi-static eddy current field, and its error has been experimentally calibrated to ≤2%. It is necessary to confirm that tan(θ) is within the model's applicable range (thickness 0.5-10mm, conductivity 1-5 MS / m); if it exceeds this range, a correction factor is used.

[0040] S7. Repeated measurement verification: Repeat S3-S6 at 5 uniform measurement points on the plate to be tested, and take the average value as the final thickness. The relative standard deviation should be ≤1%.

[0041] S8. Error Correction and Output: Introduce temperature compensation (0.002 / ℃) or surface roughness correction factor to adjust the deviation; the result is retained to two decimal places and output to the recording system or report.

[0042] Preferably, the criterion for determining the excitation frequency in step S2 is:

[0043] The excitation frequency must satisfy the requirement that the penetration depth is greater than the range thickness. Three times that of the excitation frequency, which can be expressed by the formula Calculation. Among them... is the vacuum permeability.

[0044] Preferably, the explicit inversion analytical model described in step S6 is:

[0045]

[0046] Wherein, ξ is a comprehensive factor related to the geometric dimensions of the detection coil. The comprehensive factor ξ is related to the inner radius r1, outer radius r2, and height of the detection coil, and its expression is as follows:

[0047] .

[0048] Furthermore, in a specific example, ten TC4 titanium alloy plates were used as samples for measurement. Their thickness ranged from 0.5 mm to 4.0 mm, their conductivity was 0.61 MS / m, and their dimensions were 200*200 mm. The excitation frequency was determined to be 1.85 kHz based on the frequency selection criterion. The sensor was vertically attached to the sample, and each sample was measured 30 times, with the average value taken. The comparison between the measured thickness and the actual thickness is shown in Table 1.

[0049] Table 1

[0050]

[0051] Based on the results in Table 1, the measurement results of the embodiments of this application are described in detail. Comparing the measured values ​​with the actual values, the relative error range of the experimental measurements was 0.0110 to 0.0647 mm, with an average of 0.0286 mm; the relative error range was 0.314 to 3.235%, with an average of 1.696%. The error values ​​are all within a reasonable and very small range, and the measured values ​​are in high agreement with the actual values, demonstrating the effectiveness of the embodiments of this application in the actual measurement of titanium alloy plate thickness.

[0052] Looking at the specific data for each number, the 3.5mm thick sample corresponding to number 7 has the smallest relative error, at only 0.314%, demonstrating the outstanding fitting accuracy of this method in this thickness range. The 2.0mm thick sample of number 4 has the largest relative error, but it still does not exceed 3.235%, far below the error threshold commonly found in industrial testing. This result is highly consistent with the principle of the low-frequency eddy current phase characteristic model: by extracting phase characteristic quantities directly related to thickness, the model effectively avoids the problem of impedance amplitude being easily affected by material uniformity in traditional eddy current methods, ensuring that the measurement error in different thickness ranges remains within a controllable range. Furthermore, the operation of measuring each sample 30 times and taking the average value further suppresses the influence of random factors such as environmental noise and minor sensor installation deviations, ensuring the stability and repeatability of the data. Considering the application scenarios of titanium alloy plates in aerospace, high-end equipment manufacturing, and other fields, the accuracy of this method fully meets the requirements for component thickness quality control—for example, the wall thickness detection of titanium alloy blades for aero-engines typically allows an error of no less than 5%, while the average relative error of this method is only 1.696%, providing reliable data support for the performance evaluation of key components. These results fully verify the feasibility and superiority of the titanium alloy plate thickness measurement method based on the low-frequency eddy current phase characteristic model in practical engineering applications.

[0053] The specific embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for measuring the thickness of titanium alloy plates based on a low-frequency eddy current phase characteristic model, characterized in that, Includes the following steps: S1. Determine the conductivity σ of the titanium alloy plate being tested based on its grade. S2. Substitute the conductivity σ into the penetration depth formula to determine the frequency f of the low-frequency excitation current supplied to the eddy current coil; The criterion for determining the excitation frequency is that the penetration depth must be greater than the range thickness. Three times that, the formula for excitation frequency. Calculation; where Permeability of free space; S3. Connect the detection coil, isolation resistor, reference coil, and excitation signal source in series to form a circuit. Place the detection coil vertically on the surface of the titanium alloy plate to be tested, and place the reference coil parallel above the detection coil. The detection coil and the reference coil are the same size. S4. The excitation signal source generates an excitation current with frequency f, and obtains the impedance Z of the detection coil and the impedance Z of the reference coil. air Calculate the impedance signal change value ΔZ=Z air -Z; S5. Extract the real part Re(ΔZ) and imaginary part Im(ΔZ) of the impedance change signal, and calculate the phase characteristic of the impedance change as tan(θ) = Im(ΔZ) / Re(ΔZ); S6. Substitute the phase characteristic tan(θ) obtained in S5 into the explicit inversion analytical model to directly calculate the thickness c of the titanium alloy plate.

2. The method for measuring the thickness of titanium alloy plates based on a low-frequency eddy current phase characteristic model according to claim 1, characterized in that, The explicit inversion analytical model mentioned in step S6 is: ； Where ξ is a comprehensive factor related to the geometric dimensions of the detection coil.

3. The method for measuring the thickness of titanium alloy plates based on a low-frequency eddy current phase characteristic model according to claim 2, characterized in that, The comprehensive factor ξ is related to the inner radius r1, outer radius r2, and height of the detection coil, and its expression is as follows: 。 4. A time-lapse storage medium, embedded and programmed to implement the method as described in any one of claims 1-4, characterized in that, Applications of rapid online measurement and portable instruments for titanium alloy plates.

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