Non-linear ultrasonic zero-frequency component-based residual stress damage identification method and system

Abstract

The invention discloses a residual stress damage identification method and system based on a nonlinear ultrasonic zero-frequency component in the field of ultrasonic early damage detection. The method comprises the following steps: S1, adopting a model without residual stress damage as a standard model; s2, adopting a model containing residual stress damage as a model to be detected; s3, setting a signal excitation point and a signal receiving point at the same position of the standard vertebra model and the to-be-detected model; s4, performing low-pass filtering processing on the signal received by the signal receiving point to extract a zero-frequency signal, and respectively obtaining a standard zero-frequency signal and a damaged zero-frequency signal; s5, calculating and obtaining a difference signal between the damaged zero-frequency signal and the standard zero-frequency signal, and recording the difference signal as a residual zero-frequency signal; s6, damage analysis: judging the type of residual stress damage by utilizing concavity and convexity of the residual zero-frequency signal, and judging the size of the residual stress damage according to the strength of the residual zero-frequency signal; and related difficulties of hybrid wave and second harmonic technologies are overcome.

Description

Technical Field

[0001] The present invention belongs to the field of ultrasonic early damage detection, and specifically relates to a method and system for identifying residual stress damage based on the zero-frequency component of non-linear ultrasonic waves. Background Art

[0002] During the manufacturing process of various machines and apparatuses, residual stresses will be generated inside parts. Therefore, detecting residual stresses is an important criterion for determining the internal stress balance state of workpieces after processing.

[0003] Among the existing methods for residual stress, ultrasonic detection of material residual stress is a method that utilizes the change in the sound velocity of ultrasonic waves in a material containing residual stress during propagation to reflect the magnitude of the stress by measuring the change in the sound velocity of ultrasonic waves in a stressed workpiece. It has the advantages of fast detection speed, no radiation harm to the human body, low cost, excellent spatial resolution, a wide detection depth range, and the ability to perform on-site handheld operation, being portable, and being able to complete the detection of the magnitude and tensile / compressive state of macroscopic residual stresses on the surface and subsurface.

[0004] The methods for ultrasonic detection of material residual stress mainly include pure longitudinal waves, pure transverse waves, a combination of transverse and longitudinal waves, surface waves, guided waves, non-linear ultrasonic waves, and LCR waves.

[0005] Among them, the pure longitudinal wave method is mainly used to detect the overall average stress inside components with relatively parallel end faces and a relatively short distance between the two end faces, such as bolts. If the component is too long or there are no relative end faces, or if it is impossible to place a probe on the relative end faces, effective stress measurement cannot be performed. The pure transverse wave method calculates the plane stress distribution by utilizing the photoelastic birefringence effect of transverse waves. The result is obtained through the relationship between the wave velocities in the two polarization directions of transverse waves and stress. However, longitudinal waves are the most sensitive to stress, while transverse waves are less sensitive to stress. Since the detection principle of the combination of transverse and longitudinal waves is the same as that of the pure longitudinal wave method, there are similar limitations, that is, it can only be applied to the detection of components such as bolts and cannot meet the actual needs of detecting the processing residual stresses of most workpieces such as welding.

[0006] The penetration depth of surface waves is relatively small. Like transverse waves, surface waves are less sensitive to stress, resulting in low detection accuracy and limited practical application value. Due to the complex dispersion characteristics and numerous modes of guided waves, there are many limitations in practical applications, and it is difficult to ensure the detection accuracy. LCR wave detection of residual stress is a very practical, economical, and accurate detection method, but it has not been widely applied in on-site actual measurements, and there are still many hotspots and difficulties that need to be studied in depth.

[0007] Traditional methods for non-linearly detecting residual stress are only limited to the high-harmonic method. When it is necessary to judge the type of tensile / compressive damage of residual stress damage, the traditional non-linear ultrasonic detection method is not applicable. Summary of the Invention

[0008] The object of the present invention is to solve the problem of difficult identification of types of different residual stress damages in tension / compression, and to propose a method and system for identifying types of residual stress damages by using the zero-frequency component of non-linear ultrasonic waves.

[0009] To achieve the above object, the technical solution of the present invention is as follows:

[0010] A method for identifying residual stress damages based on the zero-frequency component of non-linear ultrasonic waves includes the following steps: S1: Using a model without residual stress damages as a standard model;

[0011] S2: Using a model containing residual stress damages as a model to be detected;

[0012] S3: Setting a signal excitation point and a signal reception point at the same position of the standard model and the model to be detected, emitting a fundamental wave at the signal excitation point, and then receiving the signal through the signal reception point;

[0013] S4: Performing low-pass filtering on the received signal to extract the zero-frequency signal. Among them, the zero-frequency signal obtained from the standard model is the standard zero-frequency signal, and the zero-frequency signal obtained from the damaged model is the damaged zero-frequency signal;

[0014] S5: Calculating and obtaining the difference signal between the damaged zero-frequency signal and the standard zero-frequency signal, denoted as the residual zero-frequency signal;

[0015] S6: Damage analysis, using the concavity and convexity of the residual zero-frequency signal to judge the type of residual stress damage, and judging the size of the residual stress damage according to the strength of the residual zero-frequency signal.

[0016] Further, in S3, the fundamental wave signal is:

[0017]

[0018] where f is the center frequency, N is the number of pulse waves, t is the time, and A is the amplitude of the excitation pulse.

[0019] Further, in S6, the manifestation form of the residual zero-frequency signal corresponding to the residual stress is that when the stress is compressive stress and continuously decreases to zero and the direction evolves into tensile stress and continuously increases, the magnitude and sign of the non-linear coefficient will change (for example, from positive to negative), and it is approximately linearly changed.

[0020] Further, in S3, the center frequency f is 200 KHz, N is 10, and A is 0.0001 mm.

[0021] Further, in S6, there is a positive correlation between the magnitude of the non-linear coefficient and the amplitude of the zero-frequency signal.

[0022] Furthermore, in S1 to S6, the intensity of the zero-frequency component increases linearly with the propagation of the fundamental wave.

[0023] Furthermore, the thickness and size of the model without residual stress damage and the model with residual stress damage are the same.

[0024] Furthermore, based on the residual stress damage identification system of the zero-frequency component of nonlinear ultrasonic waves, according to the system based on the above-mentioned method for identifying residual stress damage of the zero-frequency component of nonlinear ultrasonic waves, it includes a model clamping module, an information acquisition module, and an information processing module;

[0025] The model clamping module is used to fixedly clamp the standard model or the model to be detected;

[0026] The information acquisition module includes a signal excitation point and a signal reception point located on both sides of the model clamping module. Based on the position of the signal excitation point, the fundamental wave is cyclically emitted to measure the standard model or the model to be detected, and the ultrasonic signal is received in real time through the signal reception point and sent to the information processing module;

[0027] The information processing module performs low-pass filtering on the ultrasonic signal to extract the zero-frequency signal and draws the corresponding ultrasonic diagram based on the zero-frequency signal.

[0028] After adopting the above scheme, the following beneficial effects are achieved: When the material has residual stress damage, different types of tensile / compressive residual stress damage can cause different signs of the third-order nonlinear coefficient (third-order elastic constant) of the material, and the morphology of the zero-frequency component is extremely sensitive to the change of the sign of the third-order elastic constant of the material. The type of residual stress damage can be identified by measuring the concavity and convexity of the morphology of the zero-frequency component. Moreover, the strength of the zero-frequency component is positively correlated with the magnitude of the nonlinear coefficient (third-order elastic constant), and measuring the strength of the zero-frequency signal can also reflect the degree of residual stress damage. Other nonlinear detection methods cannot identify the type of residual stress. Without identifying the type of residual stress, using the nonlinear ultrasonic detection method to judge the size of residual stress damage based on the signal strength is prone to misjudgment of damage. The detection of residual stress damage based on the zero-frequency component, identifying the type of tensile / compressive stress damage of residual stress damage according to the concavity and convexity of the zero-frequency component, and further being able to measure the size of residual stress damage, overcomes the problems of traditional nonlinear detection techniques.

[0029] This scheme can judge the type of residual tensile / compressive stress damage and measure the size of residual stress damage by analyzing the concavity and convexity and the signal strength of the zero-frequency component, overcomes the difficulties of traditional nonlinear detection techniques based on high-order harmonics, and has the characteristics of simple and efficient measurement. Description of the Drawings

[0030] Figure 1Schematic diagram of the excitation signal of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0031] Figure 2 Schematic diagram of the simulation model of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0032] Figure 3 Schematic diagram of the relationship between the material nonlinear coefficient and stress of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0033] Figure 4 Time image of the nonlinear wave displacement components of each pair of points on the cross-section of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0034] Figure 5 Time image of the zero-frequency displacement x1 component of each pair of points on the cross-section of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0035] Figure 6 Schematic diagram of the relationship between the morphology of the excited zero-frequency component signal and the material nonlinear coefficient of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0036] Figure 7 Relationship between the zero-frequency component and the nonlinear coefficient of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention.

[0037] Figure 8 Relationship between the zero-frequency component and the nonlinear coefficient of the residual stress damage identification method and system based on the zero-frequency component of nonlinear ultrasonic waves according to the embodiments of the present invention. Detailed implementation manners

[0038] The following is a further detailed description through specific implementation manners:

[0039] Embodiment 1

[0040] The embodiment is basically as shown in the appendix Figures 1 to 8 as follows:

[0041] The residual stress damage identification method based on the zero-frequency component of nonlinear ultrasonic waves includes the following steps: S1: Using a model without residual stress damage as the standard model;

[0042] S2: Using a model containing residual stress damage as the model to be detected;

[0043] S3: Set signal excitation points and signal reception points at the same positions of the standard model and the model to be detected, emit the fundamental wave at the signal excitation points, and then receive the signals through the signal reception points;

[0044] S4: Perform low-pass filtering on the received signals to extract zero-frequency signals. Among them, the zero-frequency signal obtained from the standard model is the standard zero-frequency signal, and the zero-frequency signal obtained from the damaged model is the damaged zero-frequency signal;

[0045] S5: Calculate and obtain the difference signal between the damaged zero-frequency signal and the standard zero-frequency signal, denoted as the residual zero-frequency signal;

[0046] S6: Damage analysis. Use the concavity and convexity of the residual zero-frequency signal to judge the type of residual stress damage, and judge the size of the residual stress damage based on the strength of the residual zero-frequency signal.

[0047] Due to the dispersion and multimodal characteristics, the theoretical derivation of the solution of nonlinear Lamb waves is relatively complex. Now consider the propagation of finite-amplitude ultrasonic guided waves in an isotropic, homogeneous thin plate with a thickness of 2h. The normal direction of the free boundaries on the upper and lower sides of the thin plate is along the u direction, and the ultrasonic waves propagate along the x1 direction. Lamb waves are a type of plane strain wave, and the vibration of the medium particles remains in the x1-x3 plane during the propagation process. Considering the material constitutive model as second-order weakly nonlinear hyperelasticity, when the amplitude of the nonlinear component of Lamb waves is much smaller than the amplitude of its fundamental wave, the solution of the nonlinear component of Lamb waves can be obtained using the perturbation method, modal expansion method, and complementary principle. The total displacement field u of the particle motion can be decomposed into the fundamental wave displacement field u (1) and the second harmonic wave displacement field u (2) The sum, and the total displacement field satisfies u = u (1) (X, t) + u (2) (X, t), and |u (2) | << |u (1) | (|*| represents the magnitude of the quantity '*'). According to the relevant theoretical reviews and derivations by the inventor in the literature "Sun X Q. Locating mutation damage based on the zero-frequency component of nonlinear Lamb waves[J]. Mechanical Systems and Signal Processing, 2023, 197: 110384", the motion control equation of Lamb waves can be expressed as:

[0048]

[0049]

[0050] Among them,

[0051]

[0052] T(H) = T L (H) + T NL (H),

[0053] T L (H) = λtr(H)I + μ(H + H T ),

[0054]

[0055] n3 is the unit vector normal to the thin plate, T is the second Piola - Kirchhoff stress tensor, λ and μ are Lame constants, A, B, and C are third - order elastic constants respectively, and the superscript 'T' is the transpose operator.

[0056] Consider two fundamental waves excited at x1 = 0 with angular frequencies ω a and ω b and wave vectors k a and k b respectively. The fundamental waves propagate along the x1 direction. The excitation signal can be expressed as:

[0057]

[0058] where c.c. represents the complex conjugate. The solution of the secondary wave field for this wave problem is:

[0059]

[0060] where the subscripts m and n represent the m - th and n - th modes (ω a ±ω b ), a m (x1) represents the amplitude of the velocity field of the m - th mode, the superscript '*' represents taking the complex conjugate of the corresponding physical quantity, and there are:

[0061]

[0062]

[0063]

[0064] And:

[0065]

[0066]

[0067]

[0068] where v m is the particle velocity field in the m - th mode, k and are the wave vectors of the fundamental wave and the nth-order mode, respectively, and P mn is the energy flux of the mth-order propagating mode wave. And when P mn = 0, that is, the mth-order mode is orthogonal to any other order mode. and are the bulk energy flux and the surface energy flux from the fundamental wave flows of (ω a , k a ), (ω a , k a ) to the second-order wave (ω a ±ω b , k a ±k b ), respectively. If f n ≠0 and that is, the non-zero energy flux and phase velocity matching conditions are satisfied. At this time, internal resonance will occur in the second-order wave field, and the amplitude solution of the second-order wave field will increase linearly with the propagation distance of the fundamental wave.

[0069] In the above formula, taking the limit k a →k b = k, then the solution a of the second harmonic component corresponding to (k b + k is:

[0070] ,

[0071]

[0072] In the above formula, taking the limit k a →k b = k and then the solution a of the zero-frequency component corresponding to (k b - k is:

[0073]

[0074] Since the change of the sign of f n does not affect P mn , and f n is an odd function of λ, μ, A, B, C:

[0075] f n = f n (λ, μ, A, B, C, u(x1, x3, t)) = f n (∑(α λ λ + α μ μ + α A A + α B B + α cC)·g(u(x1, x3, t)))

[0076] where α λ , α μ , α A , α B and α C are the coefficients of λ, μ, A, B, and C respectively, and g(u(x1, x3, t)) is a function of u(x1, x3, t). Thus, the sign of f n can be changed through the relationship shown in the following equation:

[0077] -f n = f n (-λ, -μ, -A, -B, -C, u(x1, x3, t)). Obviously, A, B, and C are related to the material non-linearity where the function represents geometric non-linearity, and the function represents material non-linearity. For material non-linearity, generally, geometric non-linearity can be ignored. Thus, when the signs of the third-order elastic constants A, B, and C change, the sign of f n changes accordingly, resulting in:

[0078] It can be seen that the sign of f can be changed by changing the third-order elastic

[0079] According to the literature "Pau A, Lanza di Scalea F. Nonlinear guided wave propagation in prestressed plates[J]. The Journal of the Acoustical Society of America, 2015, 137(3): 1529-1540.", residual stress can not only change the absolute value of the third-order elastic constant but also change its sign. As Figure 1 shown, for the two stress cases of A and C, that is, when the stress loading direction is consistent with the wave propagation direction and during dilatational stress loading, as the compressive stress decreases continuously to zero and then changes direction to tensile stress and increases continuously, the non-linear coefficient (third-order elastic constant) gradually decreases from positive to negative and changes approximately linearly.

[0080] Therefore, measuring the concavity and convexity of the zero-frequency component morphology can identify the types of residual stress damage, and measuring the strength of the zero-frequency component signal can also reflect the degree of residual stress damage.

[0081] The finite element simulation is carried out below. Without considering damping, a commercial finite element analysis software Abaqus (Version 6.14, Dassault Systems Simulia Corp., Providence, RI, USA) is used for modeling. The specific parameters of the material constitutive model are shown in Table 1.

[0082] Table 1 Material parameters of aluminum plate

[0083]

[0084] Figure 2 The upper part shows the simulation model diagram. The model thickness is 2 mm. To eliminate the influence of reflected waves, the model length is set to 2400 mm. To eliminate the rigid displacement of the overall simulation model during loading, a displacement fixed constraint is applied to the right end of the model.

[0085] The equation is satisfied through the Hann window displacement excitation function:

[0086]

[0087] where f(=200 kHz) is the center frequency of the excitation signal, N(=10) is the number of cycles contained in a single excitation pulse, t is the time, and A(=0.0001 mm) is the amplitude of the excitation pulse.

[0088] By changing f and N, a pulse signal with a center frequency of f and a number of cycles of N modulated by the Hann window function can be obtained.

[0089] From Figure 1 As shown, it is an example of a pulse signal modulated by a Hann window function with a center frequency of 200 kHz and a number of cycles of 10. This displacement excitation is directly applied to the left end of the model, which can excite the S0 mode Lamb wave. 19 signal receiving points are set in the model. The first signal receiving point is set at a position 150 mm away from the left end boundary, and then a signal receiving point is set every 100 mm. The model mesh size is 0.05 mm, and the shortest wavelength of the wave to be simulated is approximately 2.7 mm. At least 54 elements are included in one wavelength range, which is sufficient to ensure the calculation accuracy. Figure 2 The lower part shows the displacement nephogram at a certain moment after the displacement excitation is applied to the left end of the model. From the nephogram, it can be roughly judged that the displacement in the x1 direction is symmetric about the neutral plane of the aluminum plate, that is, the displacement law satisfies the characteristics of the S0 mode Lamb wave.

[0090] When establishing two models, the initial excitation wave phase of one model is zero, and the initial excitation wave phase of the other model is π, that is, the two initial excitation wave phases are opposite. By controlling variables, the fundamental wave can be removed through anti-phase superposition at the same signal extraction point, and a non-linear wave signal containing zero-frequency components and second-harmonic components can be obtained. Draw a transverse line at any position in the model, that is, the x1 coordinates of the points on the vertical line are the same (150 mm), extract the signals of the points on the transverse line, and perform analysis and processing. Figure 4 and Figure 5 The data graph of the transverse line shown is the result obtained by anti-phase superposition.

[0091] Among them, in Figure 4 and Figure 5 , x1 = 150 mm; Figure 4 is the non-linear wave signal obtained by superposing fundamental waves with opposite phases. The quadratic-square property of material non-linearity results in the non-linear wave being in a symmetric mode. The x1 components of the particle displacements at different thickness positions on the transverse line are the same, and the second harmonic is attached to the zero frequency, or rather, the zero frequency depicts the equilibrium position of the particle vibration of the second harmonic. By performing low-pass filtering on the data in Figure 4 , filtering out the high-frequency components, that is, filtering out the second harmonic, the approximate morphology of the zero frequency is obtained as shown in Figure 5 . Figure 5 In, the morphology of the zero frequency is convex upward. It should be noted that by directly performing low-pass filtering on the fundamental wave, Figure 4 and Figure 5 can also be obtained. Therefore, in subsequent data processing, directly perform low-pass filtering on the fundamental wave to extract the zero frequency.

[0092] According to the previous description, changing the type of residual stress damage can change the third-order elastic constant of the material, and thus cause a change in the concavity and convexity of the zero-frequency signal. Now, perform a simulation verification for identifying the type of residual stress damage, that is, it is necessary to change the sign of the third-order elastic constant to see if it causes a change in the concavity and convexity of the zero-frequency signal. To further verify the sensitivity of the zero-frequency signal to the magnitude of residual stress damage, record the values of the third-order elastic constants A, B, and C in Table 1 of the material parameters as 1TOE, and multiply A, B, and C by the same factors -3, -2.5, -2, -1.5, -1, -0.5, 0, 0.5, 1, 1.5, 2, 2.5, and 3 respectively to obtain new third-order elastic constants, which are denoted as -3TOE, -2.5TOE, -2TOE, -1.5TOE, -1TOE, 0TOE, -0.5TOE, 0.5TOE, 1TOE, 1.5TOE, 2TOE, 2.5TOE, and 3TOE respectively. In a completely ideal situation, in this embodiment, 0TOE is set as the model without damage, and other models are all damaged models.

[0093] Extract the zero-frequency signal morphologies of different TOEs respectively. Denote the zero-frequency component signal extracted from the damaged model as the damaged zero-frequency signal, and the zero-frequency signal extracted from the undamaged model as the standard zero-frequency signal. Subtract the extracted damaged zero-frequency signal from the standard zero-frequency signal to obtain the differential zero-frequency signals of each model as follows Figure 6 shown. It is easy to know that the concavity and convexity of the differential zero-frequency signal are extremely sensitive to the types of residual stress damage, and the amplitude intensity of the differential zero-frequency signal is also very sensitive to the magnitude of residual stress damage. When the sign of the nonlinear coefficient changes, the concavity and convexity of the zero-frequency signal also change. Further, there is a positive correlation between the magnitude of the nonlinear coefficient and the amplitude of the zero-frequency signal, indicating that the zero-frequency component can not only identify the types of residual stress damage but also measure the magnitude of residual stress damage.

[0094] Extract the zero-frequency component intensities at different points of each model, that is, perform a Fourier transform on the fundamental wave signal, extract the value of the ordinate at zero frequency in the frequency domain diagram, and make a diagram showing the relationship between the zero-frequency component intensity and the propagation distance of the fundamental wave as follows Figure 7 and Figure 8 shown (β in the figure is the ratio of the zero-frequency component intensity to the square of the fundamental wave amplitude intensity, or the intensity of the zero-frequency component can also be directly used). Obviously, the zero-frequency component increases linearly with the propagation of the fundamental wave, indicating that the zero-frequency component can perform high-efficiency large-area residual stress damage detection on the plate structure. At the same time, according to the slope magnitude of the straight line of the zero-frequency component intensity varying with the fundamental wave, different magnitudes of nonlinear coefficients can also be measured, that is, different degrees of residual stress damage can be measured.

[0095] It should be noted that when simulating, the zero-frequency component signal of the model with the third-order elastic constant being zero is used as the standard zero-frequency signal, and some adjustments are required in actual applications. Generally, the material nonlinear coefficient of the standard undamaged model is not zero, that is, the third-order elastic constant of the material without damage is not zero. Since the third-order elastic constant of the standard model of the material to be measured is non-zero, the standard zero-frequency component signal is not a horizontal line but a pulse with a certain concavity and convexity. At this time, it is necessary to first measure the concavity and convexity of the morphology of the standard zero-frequency component of the model without residual stress damage.

[0096] In this embodiment, common aluminum materials are taken as an example (as shown in Figure 3 ), where, A: the stress direction is consistent with the wave propagation direction; B: the stress direction is perpendicular to the wave propagation direction; C: isotropic stress; Figure 3

[0097] When the material is undamaged, α is zero, and at this time the third-order elastic constant is not zero but a negative value. First measure the corresponding to Figure 3 Figure 3When α is zero, the zero-frequency component of the sample without residual stress damage is used as the standard zero-frequency component, and then the damage zero-frequency signals of other samples to be measured are obtained. The damage zero-frequency component signal is subtracted from the standard zero-frequency component signal to obtain the differential zero-frequency component signal: if the differential zero-frequency signal is a horizontal straight line, there is no damage; if the concavity and convexity of the differential zero-frequency signal are the same as those of the standard zero-frequency signal, it is tensile residual stress damage, and the greater the amplitude of the differential zero-frequency signal, the greater the tensile residual stress damage stress; if the concavity and convexity of the differential zero-frequency signal are opposite to those of the standard zero-frequency signal, it is compressive residual stress damage, and the greater the amplitude of the differential zero-frequency signal, the greater the compressive residual stress damage stress. This solution can judge the types of residual tensile / compressive stress damage and measure the magnitude of residual stress damage by analyzing the concavity and convexity of the zero-frequency component and the signal strength, overcoming the difficulties of traditional non-linear detection techniques based on high-order harmonics.

[0098] Embodiment 2

[0099] A residual stress damage identification system based on the zero-frequency component of non-linear ultrasonic waves. According to the system based on the method for identifying residual stress damage using the zero-frequency component of non-linear ultrasonic waves described above, it includes a model clamping module, an information acquisition module, and an information processing module;

[0100] The model clamping module is used to fixedly clamp the standard model or the model to be detected;

[0101] The information acquisition module includes a signal excitation point and a signal reception point located on both sides of the model clamping module. The fundamental wave is cyclically emitted based on the position of the signal excitation point to measure the standard model or the model to be detected, and the ultrasonic signal is received in real time through the signal reception point and sent to the information processing module;

[0102] The information processing module performs low-pass filtering on the ultrasonic signal to extract the zero-frequency signal and draws the corresponding ultrasonic diagram based on the zero-frequency signal.

[0103] This embodiment is a supplementary description of the above embodiment, and the beneficial effects are the same as those of the above embodiment, so they will not be repeated in this embodiment.

[0104] The above are only the embodiments of the present invention. Specific structures and / or common knowledge such as characteristics well known in the art are not described in detail here. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. A method for identifying residual stress damage based on the zero-frequency component of nonlinear ultrasonic waves, characterized in that, It includes the following steps: S1: Use a model without residual stress damage as the standard model; S2: Use a model with residual stress damage as the model to be detected; S3: Set a signal excitation point and a signal reception point at the same position of the standard model and the model to be detected, emit a fundamental wave at the signal excitation point, and then receive the signal through the signal reception point; S4: Perform low-pass filtering on the received signal to extract the zero-frequency signal. Among them, the zero-frequency signal obtained from the standard model is the standard zero-frequency signal, and the zero-frequency signal obtained from the damaged model is the damaged zero-frequency signal; S5: Calculate and obtain the difference signal between the damaged zero-frequency signal and the standard zero-frequency signal, denoted as the residual zero-frequency signal; S6: Damage analysis. Use the concavity and convexity of the residual zero-frequency signal to judge the type of residual stress damage, and judge the size of the residual stress damage based on the strength of the residual zero-frequency signal.

2. The method for identifying residual stress damage based on the zero-frequency component of non-linear ultrasonic waves according to claim 1, wherein: In S3, the fundamental wave signal used is: ， where f is the center frequency, N is the number of pulse waves, t is the time, and A is the amplitude of the excitation pulse.

3. The method for identifying residual stress damage based on the zero-frequency component of non-linear ultrasonic waves according to claim 1, characterized in that: In S6, the manifestation form of the residual zero-frequency signal corresponding to the residual stress is that when the stress is compressive stress and continuously decreases to zero and the direction evolves into tensile stress and continuously increases, the magnitude and sign of the nonlinear coefficient will change, and it is approximately linearly changing.

4. The method for identifying residual stress damage based on the zero-frequency component of nonlinear ultrasonic waves according to claim 2, wherein: In S3, the center frequency f is 200KHz, N is 10, and A is 0.0001mm.

5. The method for identifying residual stress damage based on the zero-frequency component of nonlinear ultrasonic waves according to claim 1, wherein: In S6, there is a positive correlation between the magnitude of the nonlinear coefficient and the amplitude of the zero-frequency signal.

6. The method for identifying residual stress damage based on the zero-frequency component of nonlinear ultrasonic waves according to claim 1, wherein: In S1 to S6, the intensity of the zero-frequency component increases linearly with the propagation of the fundamental wave.

7. The method for identifying residual stress damage based on the zero-frequency component of non-linear ultrasonic waves according to claim 1, characterized in that: The thickness and size of the model without residual stress damage and the model with residual stress damage are the same.

8. Nonlinear ultrasonic zero-frequency component residual stress damage identification system, characterized in that, The system for identifying residual stress damage based on the zero-frequency component of nonlinear ultrasonic waves according to any one of claims 1-7 includes a model clamping module, an information acquisition module, and an information processing module; The model clamping module is used to fixedly clamp the standard model or the model to be detected; The information acquisition module includes a signal excitation point and a signal reception point located on both sides of the model clamping module. Based on the position of the signal excitation point, a fundamental wave is cyclically emitted to measure the standard model or the model to be detected, and the ultrasonic signal is received in real time through the signal reception point and sent to the information processing module; The information processing module performs low-pass filtering on the ultrasonic signal to extract the zero-frequency signal and draws a corresponding ultrasonic diagram based on the zero-frequency signal.

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