Plane stress detection method based on phased array-critical refraction longitudinal wave

Abstract

The invention belongs to the field of material detection and evaluation, and discloses a phased array-critical refraction longitudinal wave-based plane stress detection method, which comprises the following steps: estimating a material sound velocity range, optimizing a phased array ultrasonic delay rule, obtaining a change curve of different excitation sound velocities and critical refraction longitudinal wave amplitudes, and extracting an optimal excitation sound velocity; critical refraction longitudinal waves are excited in the sample with the optimal excitation sound velocity, and processing such as interpolation and filtering is carried out on signals received by array elements of a receiving probe; obtaining the amplitude and sound time of critical refraction longitudinal waves, and calculating the sound velocity of the critical refraction longitudinal waves and the sound time difference of different array elements for receiving the critical refraction longitudinal waves; establishing the change relation of the critical refraction longitudinal wave sound velocity, the amplitude and the sound time difference along with the stress. According to the method, the critical refraction longitudinal wave acoustic time-stress relation in a traditional stress test method is improved into the critical refraction longitudinal wave acoustic time-stress-array element spacing relation, and the problems that in the traditional method, material adaptability is poor, acoustic time calculation stability is poor, and stress test reliability is low are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the field of material detection and evaluation, and relates to a plane stress detection method based on phased array - critically refracted longitudinal wave. Background Art

[0002] Residual stress can affect the mechanical properties of workpieces such as strength and stiffness, significantly affecting the service reliability and life of workpieces. It is a performance index that must be concerned during the forming, processing, assembly, service, and maintenance of key components in fields such as electronics, aviation, aerospace, rail transit, and automobiles. Therefore, non - destructive testing of residual stress has important scientific and engineering value.

[0003] The critically refracted longitudinal wave is a wave that propagates along the material surface at the first critical angle. According to the photo - elastic theory, since it is a longitudinal wave propagating parallel to the material surface, it has great advantages in the detection of plane stress on the material surface. Traditional evaluation methods use a one - transmit - one - receive method. After fixing the acoustic path, the change in acoustic time of the critically refracted longitudinal wave under different stresses is extracted to characterize the stress magnitude. This evaluation method requires designing wedges with different angles for different materials, and the acoustic evaluation parameter is single. The acoustic time is prone to large fluctuations during the test, and it cannot meet the requirements of accurate stress detection during the manufacturing and service processes of high - end equipment.

[0004] In our previous research - a multi - material detection system for critically refracted longitudinal wave based on a single - angle wedge and its sound velocity measurement method (CN112903820A) and an anisotropic material damage evaluation method based on phased array - critically refracted longitudinal wave (CN115200755A), effective excitation methods using phased array ultrasonic detection were recorded. However, neither of the above two methods involves the problem of stress detection, and the calculation and processing of acoustic time cannot achieve the accuracy and reliability required for stress detection.

[0005] The present invention evaluates the plane stress on the material surface through the phased array - critically refracted longitudinal wave method, effectively solving problems such as poor material adaptability, poor stability of acoustic time calculation, and low reliability of stress test in traditional methods. It can be widely used for stress detection and evaluation of various materials, and is of great significance for the development of stress evaluation methods for high - end equipment. Summary of the Invention

[0006] The present invention proposes a plane stress detection method based on phased array - critically refracted longitudinal wave. Through the phased array - critically refracted longitudinal wave method, problems such as the need to frequently replace wedges for different types of materials, poor stability of acoustic time calculation, and low reliability of stress results are avoided, and effective evaluation of plane stress is achieved.

[0007] The technical solution of the present invention:

[0008] A method for detecting plane stress based on phased array - critically refracted longitudinal wave determines the optimal excitation sound velocity of the critically refracted longitudinal wave based on the phased array - critically refracted longitudinal wave method, measures the maximum amplitude and sound velocity of the critically refracted longitudinal wave under different stresses, obtains the acoustic time difference of the critically refracted longitudinal wave with different element spacings by the method of taking differences between different elements, establishes the corresponding relationship between the above - mentioned acoustic characteristic parameters and stress, and calculates the stress coefficient of the material. The specific steps are as follows:

[0009] (1) Surface treatment of the material specimen;

[0010] Grind the surface of the material specimen to make its surface flat and smooth;

[0011] (2) Excite the critically refracted longitudinal wave;

[0012] Estimate the sound velocity range of the material specimen, change the transmitting - end delay rule by setting the excitation sound velocity, establish the variation relationship between the excitation sound velocity and the amplitude of the critically refracted longitudinal wave within the estimated sound velocity range, narrow the excitation - sound - velocity step and continue to excite within the sound velocity range where the amplitude of the critically refracted longitudinal wave is relatively high, obtain the variation curve of the amplitude of the critically refracted longitudinal wave with the excitation sound velocity, and take the highest point to obtain the optimal excitation sound velocity;

[0013] (3) Conduct a tensile loading experiment on the specimen;

[0014] Using the optimal excitation sound velocity in step (2), use a tensile testing machine to apply stress to the specimen, keep the load stable, conduct acoustic testing, and obtain ultrasonic signals of different elements;

[0015] (4) Calculate the amplitude, sound velocity, and acoustic time difference of the critically refracted longitudinal wave;

[0016] Filter, interpolate, and smooth the ultrasonic signals received in step (3), read the amplitude and acoustic time of the critically refracted longitudinal wave of different elements, linearly fit the acoustic time to obtain the slope k of the straight line, and calculate the sound velocity v of the critically refracted longitudinal wave. The calculation formula is as follows:

[0017]

[0018] Where v w is the wedge sound velocity, θ w is the wedge inclination angle, and P is the element spacing;

[0019] The elements at the receiving end of the phased - array ultrasonic detection system are arranged at equal intervals. By taking the difference between the acoustic times of the critically refracted longitudinal wave received by any one element and all other elements, the acoustic time difference of the critically refracted longitudinal wave with different element spacings is obtained;

[0020] (5) Obtain the acoustic characteristics of the critically refracted longitudinal wave under different stress states;

[0021] Repeat steps (2) to (4) for the material specimens under different stress states, and establish the variation curves of the amplitude of the critically refracted longitudinal wave and the excitation sound velocity under different stresses, as well as the variation curves of the amplitude, sound velocity and acoustic time difference of the critically refracted longitudinal wave under different stresses;

[0022] (6) Stress coefficient calibration

[0023] Based on the acoustoelastic theory and geometric relationship, the acoustic time difference varies linearly with both stress and element spacing. The stress coefficient of the material is obtained by analyzing the slopes of the curves of the acoustic time difference varying with stress and element spacing:

[0024] y = Ax1x2 + Bx1 + Cx2 + D (2)

[0025]

[0026] where: x1 is the stress, x2 is the element spacing, y is the acoustic time difference of the critically refracted longitudinal wave, A is the stress coefficient, and B, C, and D are stress constants;

[0027] (7) Extract stress evaluation parameters

[0028] Combined with the sound velocity, amplitude and acoustic time difference of the critically refracted longitudinal wave in step (5), establish the variation laws of the three acoustic parameters with stress to evaluate the plane stress state of the material surface.

[0029] The beneficial effects of the present invention: Based on the phased array - critically refracted longitudinal wave plane stress detection method, by predicting the material sound velocity range, optimizing the phased array ultrasonic delay rule, obtaining the variation curves of different excitation sound velocities and the amplitudes of the critically refracted longitudinal waves, obtaining the highest amplitude and the corresponding optimal excitation sound velocity; exciting the critically refracted longitudinal wave in the specimen at the optimal excitation sound velocity, and performing interpolation, filtering and smoothing processing on the ultrasonic signals received by each element; obtaining the amplitude and acoustic time of the critically refracted longitudinal wave, calculating the sound velocity of the critically refracted longitudinal wave, and obtaining the acoustic time difference of different element spacings by taking the difference of the acoustic times of the critically refracted longitudinal waves received by different elements; establishing the variation relationships of the sound velocity, amplitude and acoustic time difference with stress. On the basis of the traditional acoustic time - stress correspondence relationship, it is improved to the correspondence relationship of acoustic time - stress - element spacing, and stress evaluation is carried out by combining three acoustic parameters including sound velocity and amplitude. The method proposed by the present invention has the advantages of high detection accuracy, high efficiency and low cost, and provides a comprehensive and effective method for the ultrasonic non - destructive evaluation of plane stress. Description of the drawings

[0030] Figure 1 is a schematic diagram of an aluminum alloy specimen (unit: mm).

[0031] Figure 2 is a schematic diagram of a phased array - critically refracted longitudinal wave stress detection system.

[0032] Figure 3 It is a curve graph showing the relationship between the initial state excitation sound velocity and the amplitude of the critically refracted longitudinal wave.

[0033] Figure 4 It is a flow chart of stress loading and ultrasonic testing.

[0034] Figure 5 It is a curve graph showing the relationship between the excitation sound velocity and the amplitude of the critically refracted longitudinal wave under different stresses.

[0035] Figure 6 It is a curve graph of the amplitude change under different stresses.

[0036] Figure 7 It is a curve graph of the sound velocity change under different stresses.

[0037] Figure 8 It is a curve graph of the change of acoustic time difference with stress under different element spacings.

[0038] Figure 9 It is a curve graph of the change of acoustic time difference with element spacing under different stresses.

[0039] Figure 10 It is an error analysis diagram of the phased array - critically refracted longitudinal wave stress detection result. Specific implementation manners

[0040] The following further describes the specific implementation method of the present invention in combination with the accompanying drawings and technical solutions.

[0041] The technical method for plane stress detection based on phased array - critically refracted longitudinal wave is as follows:

[0042] (1) Surface treatment of the material specimen

[0043] Taking aluminum alloy as an example, the geometric specifications of the specimen are designed as Figure 1 shown. The total length of the specimen is 140 mm, the thickness is 5 mm, the length of the parallel section is 60 mm, and the width is 12 mm. The specimen is mechanically polished to ensure the surface is smooth and flat.

[0044] (2) Excitation of the critically refracted longitudinal wave

[0045] Using the M2M phased array ultrasonic testing equipment to build a stress detection platform as Figure 2 shown. Conduct acoustic performance testing on the specimen, search for the optimal excitation sound velocity in the sound velocity range from 5800 m / s to 6800 m / s with a step of 50 m / s, and obtain that the sound velocity range when the amplitude of the critically refracted longitudinal wave is the largest is between 6200 m / s and 6400 m / s. Search for the optimal excitation sound velocity with a step of 10 m / s in this interval, and as Figure 3 shown, the optimal excitation sound velocity is 6340 m / s.

[0046] (3) Perform a tensile loading experiment on the specimen

[0047] Use a tensile testing machine to perform tensile loading on the specimen. The experimental procedure is as Figure 4 shown. The entire tensile process uses stress control. The maximum stress loading is 40 MPa, and the loading step is 20 MPa. Keep the load for 4 minutes for ultrasonic testing each time. The probe frequency is 5 MHz, and the sampling frequency of the ultrasonic signal is 125 MHz.

[0048] (4) Calculate the amplitude, sound velocity, and acoustic time difference of the critically refracted longitudinal wave

[0049] Perform cubic spline interpolation on the obtained ultrasonic signal, then perform 10 MHz low-pass filtering and smoothing processing. Truncate the critically refracted longitudinal wave, and extract the acoustic time and amplitude information of the critically refracted longitudinal wave received by each element based on the peak value. Obtain the acoustic time difference of the critically refracted longitudinal wave at different element spacings by taking the difference in the acoustic time of the critically refracted longitudinal wave of each element.

[0050] (5) Obtain the acoustic characteristics of the critically refracted longitudinal wave under different stress states

[0051] Repeat steps (2) to (4) for the material specimens under different stress states, establish the relationship curve between the amplitude of the critically refracted longitudinal wave and the excitation sound velocity under different stresses, and the change curves of the amplitude, sound velocity, and acoustic time difference of the critically refracted longitudinal wave from 0 MPa to 40 MPa, as Figures 5 to 9 .

[0052] (6) Extract stress evaluation parameters

[0053] Combine the sound velocity, amplitude, and acoustic time difference of the critically refracted longitudinal wave in step (5) to establish the variation law of the three acoustic parameters with stress, and evaluate the plane stress state of the material surface.

[0054] (7) Stress coefficient calibration

[0055] Calculate the stress coefficient of the material through equations (2) to (5). It can be calculated that A = -0.0194 ns· / (MPa·mm), B = 7.97×10 -5 ns / MPa, C = 30.27 ns / mm, D = 0.474 ns. The stress coefficient of aluminum alloy is -0.0194 ns· / (MPa·mm), Figure 10 as shown in the stress detection error analysis under uniaxial tensile stress. The results show that the error of the phased array - critically refracted longitudinal wave stress detection system is less than 9.26 MPa, and the detection standard deviation is 5.44 MPa.

Claims

1. A plane stress detection method based on phased array - critically refracted longitudinal waves, characterized in that The steps are as follows: (1) Surface treatment of the material specimen; (2) Exciting the critically refracted longitudinal wave; Estimate the sound velocity range of the material specimen. By changing the emission end delay rule through the exciting sound velocity setting, establish the variation relationship between the exciting sound velocity and the amplitude of the critically refracted longitudinal wave within the estimated sound velocity range. Narrow the exciting sound velocity step size and continue to excite within the sound velocity range where the amplitude of the critically refracted longitudinal wave is relatively high, obtain the variation curve of the amplitude of the critically refracted longitudinal wave with the exciting sound velocity, and take the highest point to obtain the optimal exciting sound velocity; (3) Conduct a tensile loading experiment on the specimen; Using the optimal exciting sound velocity in step (2), use a tensile testing machine to apply stress loading to the specimen, keep the load stable, conduct acoustic testing, and obtain ultrasonic signals of different array elements; (4) Calculate the amplitude, sound velocity, and acoustic time difference of the critically refracted longitudinal wave; Perform filtering, interpolation, and smoothing processing on the ultrasonic signals received in step (3), read the amplitude and acoustic time of the critically refracted longitudinal wave of different array elements, perform linear fitting on the acoustic time to obtain the straight line slope k, and calculate the sound velocity v of the critically refracted longitudinal wave; The array elements at the receiving end of the phased array ultrasonic detection system are arranged at equal intervals. By taking the difference between the acoustic times of the critically refracted longitudinal wave received by any one array element and all other array elements, obtain the acoustic time difference of the critically refracted longitudinal wave at different array element spacings; (5) Obtain the acoustic characteristics of the critically refracted longitudinal wave under different stress states; Repeat steps (2) to (4) for the material specimen under different stress states, establish the variation curves of the amplitude of the critically refracted longitudinal wave and the exciting sound velocity under different stresses, and the variation curves of the amplitude, sound velocity, and acoustic time difference of the critically refracted longitudinal wave under different stresses; (6) Stress coefficient calibration Based on the photoelastic theory and geometric relationship, the acoustic time difference varies linearly with both stress and array element spacing. Analyze the slopes of the variation curves of the acoustic time difference with stress and array element spacing to obtain the stress coefficient of the material; (7) Extract stress evaluation parameters Combined with the sound velocity, amplitude, and acoustic time difference of the critically refracted longitudinal wave in step (5), establish the variation laws of the three acoustic parameters with stress to evaluate the plane stress state of the material surface.

2. The plane stress detection method based on phased array-critical refraction longitudinal wave according to claim 1, wherein The specific process of step (1): Grind the surface of the material specimen to make its surface flat and smooth.

3. The method for plane stress detection based on phased array-critical refraction longitudinal wave according to claim 1, wherein The calculation formula for the sound velocity v in step (4) is as follows: where v w is the sound velocity of the wedge, θ w is the wedge angle, and P is the element pitch.

4. The plane stress detection method based on phased array-critical refraction longitudinal wave according to claim 1, characterized in that The stress coefficient in step (4): y = Ax1x2 + Bx1 + Cx2 + D (2) Where: x1 is the stress, x2 is the array element spacing, y is the acoustic time difference of the critically refracted longitudinal wave, A is the stress coefficient, and B, C, and D are stress constants.

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