Metal component internal stress ultrasonic detection method fusing mechanism model

Abstract

The invention discloses a metal component internal stress ultrasonic detection method fusing a mechanism model, and relates to the technical field of ultrasonic stress detection, and the method comprises the following steps: S1, building a theoretical relationship between sound time difference and metal internal stress; s2, a wave propagation model; s3, ultrasonic signal acquisition: acquiring ultrasonic signals of incident waves and LCR waves, and circularly sampling the ultrasonic signals to obtain multiple groups of data; s4, analyzing a loading force signal: acquiring a loading force signal, and calculating a theoretical stress value at the measurement point by using the loading force signal; s5, signal screening and system stability analysis; s6, stress calculation; and S7, error analysis. According to the method, LCR waves which are good in stability, high in accuracy and sensitive to internal stress changes are obtained by establishing a mechanism model, a detection system is established on the basis of the LCR waves according to the acoustic elasticity principle, and metal internal stress detection based on the acoustic time difference is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of ultrasonic stress detection, and in particular to a method for ultrasonic detection of internal stress of metal components integrating a mechanism model. Background Art

[0002] During the manufacturing and processing process, the control of residual stress is crucial to improving the mechanical properties and service life of the product. Residual stress refers to the internal stress caused by plastic deformation, heat treatment or welding processes inside the material. This stress still exists in the absence of external loads and may have a significant impact on the strength, fatigue life, crack resistance and corrosion resistance of the material. Reasonable control and distribution of residual stress can improve the bearing capacity of the material and reduce the risk of deformation and cracking. Especially in the fields of high precision and high reliability requirements such as aerospace, automobiles and ships, the optimization of residual stress is particularly important. Therefore, how to accurately detect residual stress has become a key technical means to improve product quality and extend service life.

[0003] Effective detection of metal internal stress is the key to accurately reflect the residual stress state. At present, there are several methods for detecting residual stress: the blind hole method calculates the strain around the hole by observing the resistance change of the strain gauge, and indirectly measures the internal stress at the drilling position. The advantages of this method are accurate measurement and low cost, and the disadvantages are that it destroys the surface structure and changes the original stress field; the magnetoelastic method indirectly measures the stress state of the material by measuring the magnetic field performance, thereby converting the complex stress measurement problem into an electromagnetic problem, but it is only used for the measurement of ferromagnetic materials; the X-ray diffraction method calculates the magnitude of the internal stress by measuring the change in the diffraction angle of the ray, but the measurement depth is only 10-30 microns, and the measurement cost is relatively high; the ultrasonic method uses sound waves for detection, and the measurement depth is deeper than the diffraction method. It is suitable for various materials, even non-metallic materials, and will not damage the surface of the sample. It is low-cost in practical applications and suitable for large-scale promotion. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for ultrasonic detection of internal stress of metal components that integrates a mechanism model. By establishing a mechanism model, an LCR wave with good stability, high accuracy and sensitivity to internal stress changes is obtained. Based on this, the principle of acoustic elasticity is used to build a detection system, thereby realizing the detection of metal internal stress based on acoustic time difference.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for ultrasonic detection of internal stress of metal components integrating a mechanism model comprises the following steps:

[0007] S1: Establish the theoretical relationship between acoustic time difference and internal stress of metal;

[0008] S2: Wave propagation model: Establish a mechanism model of critical refraction longitudinal wave (LCR wave) propagation inside the metal and determine the first critical angle that can stably separate the LCR wave;

[0009] S3: Ultrasonic signal acquisition: Acquire ultrasonic signals of incident waves and LCR waves, perform cyclic sampling on the ultrasonic signals, and obtain multiple sets of data;

[0010] S4: Loading force signal analysis: Obtain the loading force signal and use the loading force signal to calculate the theoretical stress value at the measuring point;

[0011] S5: Signal screening and system stability analysis: Perform cross-correlation analysis on the multiple groups of ultrasonic signals collected in step S3, determine whether the system is stable based on the cross-correlation coefficient, and screen out ultrasonic signals that meet the conditions;

[0012] S6: Stress calculation: Calculate the acoustic time difference using the ultrasonic signal screened out in step S5, and then calculate the internal stress of the metal component according to the theoretical relationship between the acoustic time difference and the internal stress of the metal in step S1;

[0013] S7: Error analysis: Perform error analysis on the experimental results of step S6 according to step S4 to determine the source of the error and whether the error affects the experimental conclusion.

[0014] In the above scheme, the specific steps of S1 are:

[0015] S101: When there is no stress in the sample, the propagation velocity of the sound wave can be calculated by formula (1);

[0016]

[0017] Among them, V 0 is the acoustic wave velocity at zero stress, λ and μ are the second-order elastic coefficients of the material, ρ 0 is the density of the material;

[0018] The wave velocity of LCR wave satisfies equation (2):

[0019]

[0020] l and m are the third-order elastic coefficients of the material, V 111 is the wave velocity of LCR wave;

[0021] S102: Calculate the acoustic elastic coefficient k:

[0022] Substituting equation (1) into equation (2), we get

[0023]

[0024] make Formula (4)

[0025]

[0026] S103: Establish the relationship between metal internal stress and wave velocity:

[0027] Deriving both sides of equation (4) yields equation (5):

[0028]

[0029] S104: Establish the relationship between metal internal stress and acoustic time difference:

[0030] The calculation formula of wave speed is shown in formula (6);

[0031]

[0032] L is the distance between the transmitter and receiver in the wedge, t is the time required for the sound wave to travel a distance of L, and V is the current wave speed;

[0033] Deriving both sides of equation (6), we get equation (7);

[0034]

[0035] Substituting formula (7) into formula (5), we get formula (8)

[0036]

[0037] When t = t 0 When , we get formula (9), k is the stress coefficient of the aluminum alloy sample;

[0038]

[0039] S105: Get stress coefficient k

[0040] Substituting k in the previous formula into formula (9), we get formula (10);

[0041]

[0042] Because the expression of stress coefficient mostly contains fixed material parameters and experimental parameters, K is a constant, and there is a linear relationship between the internal stress of the metal and the acoustic time difference.

[0043] In the above scheme, the specific steps of S2 are:

[0044] The wave propagation model is established using COMSOL software. The wave propagation model can visually see the propagation of the wave pattern inside the metal through the cloud map. By continuously adjusting the angle until the LCR wave is clearly separated in the cloud map, the angle at this time is the first critical angle of the LCR wave.

[0045] S201: COMSOL is used to establish an LCR wave propagation mechanism model, which includes a sample, a wedge, a piezoelectric transducer, a matching layer and a damping block, and the parameters of the sample, the wedge, the piezoelectric transducer, the matching layer and the damping block are determined;

[0046] Select the signal frequency and set the coordinate system of the piezoelectric transducer so that the XY axes are orthogonal. Select the elastic wave-time domain explicit model when adding the physical field, and set the damping for the matching layer, damping block, wedge block and sample. Add piezoelectric material and low-reflection boundary in the physical field.

[0047] Add a physical field electrostatic model, select a piezoelectric transducer, set the piezoelectric transducer to charge conservation-piezoelectric, set the bottom of the piezoelectric transducer to ground, the top to a terminal, and select circuit as the terminal type; add a voltage source, close the voltage source and the terminal, and finally couple the elastic wave-time domain explicit model and the electrostatic model to form a multi-physics field;

[0048] Set the material parameters, select plastic for the wedge, PZT for the transducer, aluminum for the sample, matching material for the matching layer, and sound-absorbing material for the damping block;

[0049] Then, the damping layer, transducer, matching layer, wedge and sample were meshed respectively. The propagation efficiency of ultrasound between different materials is different, and the mesh density between different materials is also different. Ultrasonic propagation is faster in piezoelectric transducers and samples, while it is slower in other materials, so the mesh is encrypted for the faster propagation part.

[0050] In the above scheme, the sample width is 100mm, the height is 15mm, the side length of the wedge is 12mm, the width is 20mm, the height is 10mm, the piezoelectric transducer position angle is 0.48869rad (28°), the diameter is 9mm, the height is 1.55mm, and the matching layer height is 0.56mm; 1.5MHz is selected as the signal frequency.

[0051] In the above scheme, the specific steps of S3 are:

[0052] S301: Perform simple noise reduction processing on the ultrasonic signal, select 5 cycles each time for collection and storage; perform multiple cycle sampling to obtain multiple groups of data.

[0053] 6. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that:

[0054] The specific steps of S4 are:

[0055] S401: Using a dynamometer to observe and collect the force in the Z-axis direction in real time to obtain the external stress loaded on the sample;

[0056] The measured bending moment is calculated according to formula (11):

[0057] M=QL(11)

[0058] M is the bending moment, Q is the loading force, and L is the length of the lever arm;

[0059] According to formula (12), the stress value at the depth corresponding to the bending moment can be obtained:

[0060] σ=(My) / I (12)

[0061] σ is stress, y is the distance from the center axis of the cross section, and I is the moment of inertia of the cross section;

[0062] The moment of inertia of a rectangular cross section can be obtained from equation (13):

[0063]

[0064] b is the length of the rectangular section, and h is the height of the rectangular section.

[0065] 7. The method for ultrasonic detection of internal stress of metal components based on the fusion mechanism model according to claim 1, characterized in that the specific step S5 is:

[0066] S501: After the system is started, a delay of 10 seconds is performed to allow the coupling agent to stabilize, and the LCR wave data is read cyclically, and multiple LCR wave data are cross-correlated and analyzed; if the absolute value is ≤0.5 nanoseconds, the system as a whole tends to be stable, and samples in the zero stress state and the loading force state are cyclically sampled and cross-correlated and analyzed; if the absolute value of the cross-correlation is ≤0.5 nanoseconds, the acoustic time difference reaches accuracy, and the LCR waveform data in this state is obtained.

[0067] In the above scheme, the specific steps of S6 are:

[0068] S601: By comparing the waveform data at zero stress and after force application, determine the method for calculating the acoustic time difference. If the waveform has not changed, use the cross-correlation algorithm; if the waveform has changed, use the peak method. Finally, calculate the stress based on the acoustic time difference. The thickness of the measuring piece affects the number and amplitude of the LCR waves. When the measuring piece is thin, the longitudinal waves reflected from the bottom surface may overlap with the LCR waves, causing distortion. In addition, the refracted shear waves reflected back to the surface may also cause LCR wave distortion. To avoid distortion, the peak method is usually used at the first trough of the LCR wave.

[0069] In the above scheme, the specific steps of S7 are:

[0070] S701: The reason for the increase in error is the deformation of the specimen caused by excessive loading force. The theoretical model assumes that the specimen is a rigid body, but the stress value calculated theoretically is too high, which causes the error to increase with the increase of stress. In addition, the initial stress field of the specimen will change after each stress is applied during the test, which will increase the error. Except for the stage with large deformation, the error between the actual measured value and the theoretical value is small, so it does not affect the verification of the acoustic elastic model.

[0071] Beneficial effects:

[0072] 1. The present invention proposes an ultrasonic detection method that integrates a mechanism model to detect the internal stress of metal components. Compared with the prior art, the present invention has the following advantages: The present invention predicts the propagation of longitudinal and transverse waves in metals by constructing a propagation mechanism model of LCR waves, and can accurately obtain the first critical angle for separating LCR waves, and use a cross-correlation algorithm to determine the stability of the system, further ensuring the stability of the signal. The pulse burst period of the transmitting wave is lengthened to reduce the influence of the echo on the receiving wave, and the trough corresponding to the first peak of the LCR wave is used as the base point for calculating the acoustic time difference, further reducing the influence of the echo.

[0073] 2. The present invention can more accurately identify and quantify the internal stress in metal components by combining the mechanism model and ultrasonic detection technology, thereby improving detection accuracy and reducing errors.

[0074] 3. After the present invention is combined with the mechanism model, the ultrasonic detection process can interpret signals more efficiently, reduce the time required for complex signal processing, and improve the overall detection efficiency.

[0075] 5. The method of integrating the mechanism model in the present invention can expand the scope of application of ultrasonic testing, enabling it to be used on more types of metal materials and components, and adapt to the requirements of complex geometric shapes and different material properties.

[0076] 6. The method of the present invention maintains the non-destructive advantage of ultrasonic testing, while improving the reliability and accuracy of the test results through the mechanism model, avoiding the high cost and risk of destructive testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 A flow chart of a method for ultrasonically detecting internal stress of a metal component of a fusion mechanism model involved in an embodiment of the present invention;

[0078] Figure 2 2D modeling and mesh diagram for COMSOL;

[0079] Figure 3 Schematic diagram of the detection system;

[0080] Figure 4 Schematic diagram of loading system;

[0081] Figure 5 Diagram of experimental steps;

[0082] Figure 6 Schematic diagram of cross-correlation stability criterion;

[0083] Figure 7 Schematic diagram of ultrasonic signal;

[0084] Figure 8 Flowchart of acoustic time difference algorithm;

[0085] Fig. 9 Schematic diagram of the pulse signal generation process;

[0086] Fig.10 Schematic diagram of the LCR wave propagation process;

[0087] Fig.11 Schematic diagram of the signal reception process.

[0088] Reference numerals:

[0089] 1-fixture; 2-ultrasonic wedge; 3-sample; 4-loading device; 5-L-type fixture; 6-dynamometer; 7-support device. DETAILED DESCRIPTION

[0090] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0091] A method for ultrasonic detection of internal stress of metal components integrating a mechanism model comprises the following steps:

[0092] S1: Establish the theoretical relationship between acoustic time difference and internal stress of metal;

[0093] S2: Wave propagation model: Establish a mechanism model of critical refraction longitudinal wave (LCR wave) propagation inside metal, and determine the first critical angle that can stably separate LCR wave; Use COMSOL software to establish a wave propagation model. The wave propagation model can intuitively see the propagation of the wave type inside the metal through the cloud map. By continuously adjusting the angle until the LCR wave is clearly separated in the cloud map, the angle at this time is the first critical angle of the LCR wave;

[0094] S3: Ultrasonic signal acquisition: Acquire ultrasonic signals of incident waves and LCR waves, perform cyclic sampling on the ultrasonic signals, and obtain multiple sets of data;

[0095] S4: Loading force signal analysis: Obtain the loading force signal and use the loading force signal to calculate the theoretical stress value at the measuring point;

[0096] S5: Signal screening and system stability analysis: Perform cross-correlation analysis on the multiple groups of ultrasonic signals collected in step S3, determine whether the system is stable based on the cross-correlation coefficient, and screen out ultrasonic signals that meet the conditions;

[0097] S6: Stress calculation: Calculate the acoustic time difference using the ultrasonic signal screened out in step S5, and then calculate the internal stress of the metal component according to the theoretical relationship between the acoustic time difference and the internal stress of the metal in step S1;

[0098] S7: Error analysis: Perform error analysis on the experimental results of step S6 according to step S4 to determine the source of the error and whether the error affects the experimental conclusion.

[0099] Combined with Figure 1 As shown in the figure, a metal internal stress ultrasonic detection method integrating mechanism model is proposed. Based on the acoustic elasticity theory, piezoelectric effect and inverse piezoelectric effect as the mechanism model, a nondestructive detection system based on ultrasonic signal is designed and optimized. Figure 3 As shown in the figure. First, the acoustic elasticity theory is used to analyze the relationship between the stress field and the propagation of sound waves, which provides theoretical support for the determination of key parameters such as the critical angle, acoustic emission distance and pulse burst period. Secondly, the electrical signal is converted into an ultrasonic signal through the piezoelectric effect to ensure the stable transmission of the signal. At the same time, the ultrasonic signal is converted into an electrical signal by the inverse piezoelectric effect to realize the detection of the ultrasonic signal. After the parameters of the ultrasonic signal generated by the system are optimized, it is evaluated whether it meets the LCR wave separation accuracy requirements. If not, the key parameters and design schemes are further adjusted. Finally, based on the above theoretical model and key parameters, the design of the ultrasonic nondestructive testing system is completed, and high-precision monitoring of the stress field is achieved.

[0100] The following steps are involved:

[0101] S1: Establish the theoretical relationship between acoustic time difference and internal stress of metal:

[0102] The specific steps of S1 are:

[0103] S101: When there is no stress in the sample, the propagation speed of the sound wave can be calculated by formula (1):

[0104]

[0105] V 0 is the acoustic wave velocity at zero stress, λ and μ are the second-order elastic coefficients of the material, ρ 0 is the density of the material

[0106] The wave velocity of LCR wave satisfies equation (2):

[0107]

[0108] l and m are the third-order elastic coefficients of the material, V 111 is the wave velocity of the LCR wave,

[0109] S102: Calculate the acoustic elastic coefficient k:

[0110] Substituting equation (1) into equation (2), we get

[0111]

[0112] make Formula (4)

[0113]

[0114] S103: Establish the relationship between stress and wave velocity:

[0115] Deriving both sides of equation (4) yields equation (5):

[0116]

[0117] S104: Establish the relationship between stress and acoustic time:

[0118] The calculation formula of wave velocity is shown in formula (6):

[0119]

[0120] L is the distance between the transmitter and the receiver in the wedge, t is the time required for the sound wave to travel a distance of L, and V is the current wave speed.

[0121] By taking the derivative of both sides of formula (6), we get formula (7):

[0122]

[0123] Substituting formula (7) into formula (5), we get formula (8)

[0124]

[0125] When t = t 0 When , we get formula (9), where K is the stress coefficient of the aluminum alloy sample.

[0126]

[0127] S105: Obtain stress coefficient K;

[0128] Substituting k in the previous equation into equation (9), we obtain equation (10).

[0129]

[0130] Because the expression of stress coefficient mostly contains fixed material parameters and experimental parameters, K is a constant, and there is a linear relationship between stress and acoustic time difference.

[0131] S2: Constructing a model of LCR wave propagation mechanism

[0132] The specific steps of S2 are:

[0133] S201: COMSOL is used to establish the LCR wave propagation mechanism model. The geometric model includes the sample, wedge, piezoelectric transducer, matching layer and damping block. The sample width is selected as 100 mm, the height is 15 mm, the side length of the wedge is 12 mm, the width is 20 mm, and the height is 10 mm.

[0134] Since the 1.5MHz frequency has a deeper propagation distance than the 5MHz frequency, it is easier to observe the propagation of sound waves in the sample. Therefore, 1.5MHz is selected as the signal frequency, and the coordinate system of the transducer is set to make the XY axes orthogonal. When adding the physical field, the elastic wave-time domain explicit model is selected, and the matching layer, damping block, wedge block and sample are set to damp. Piezoelectric materials and low-reflection boundaries are added to the physical field.

[0135] S202: Add a physical field electrostatic model, select the transducer, set the transducer to charge conservation-piezoelectric, set the bottom of the piezoelectric transducer to ground, and the top to terminal, select circuit as the terminal type, add a voltage source, close the voltage source and the terminal, and finally couple the elastic wave-time domain explicit model and the electrostatic model to form a multi-physics field.

[0136] Set the material parameters, select plastic for the wedge, PZT material for the piezoelectric transducer, aluminum material for the sample, matching material for the matching layer, and sound-absorbing material for the damping block.

[0137] Then, the damping layer, transducer, matching layer, wedge and sample are meshed. Since the propagation efficiency of ultrasound is different between different materials, the mesh density between different materials is also different. Ultrasonic propagation is faster in piezoelectric transducers and samples, while it is slower in other materials. In order to improve the calculation accuracy, the mesh of the faster propagation part is encrypted. Figure 2 The LCR wave propagation mechanism model is adjusted by adjusting the parameters of the piezoelectric transducer, wedge and signal, such as selecting the piezoelectric transducer position angle as 0.48869 rad (28°), the wedge width as 20 mm, and the extended signal burst period.

[0138] S3: Ultrasonic signal acquisition

[0139] S301: The ultrasonic detection system includes a signal generator, a piezoelectric transducer, a signal amplifier, an ultrasonic wedge and an oscilloscope, which are responsible for collecting and storing signals during the stress loading process. The signal generator generates a Gaussian pulse current, which is released at the first critical angle by the piezoelectric transducer. Another piezoelectric transducer receives the signal and converts it into an electrical signal. After being amplified by the amplifier, the oscilloscope collects, stores and displays the electrical signals of the transmitted wave and the received wave. The schematic diagram of the ultrasonic detection system is shown in the figure. Figure 3 shown.

[0140] S4: Loading force signal analysis

[0141] S401: By designing a cantilever beam structure, a clamp is used to fix one end of the cantilever beam, and a vise is used to feed downward on the other end to apply pressure to the cantilever beam. Different pressures are applied by controlling the rotation distance of the bolt. At the same time, a dynamometer is placed under the vise, and the vise and dynamometer are fixed together to measure the pressure on the cantilever beam, thereby achieving the effect of accurate loading force. The schematic diagram of the loading system is shown in the figure. Figure 4 As shown, a supporting device 7 and a dynamometer 6 are provided on the experimental platform. An L-shaped fixing device 5 is provided on the dynamometer 6. The L-shaped fixing device 5 is used to fix the loading device 4. A fixing device 1 is provided on the supporting device 7. The fixing device is used to fix the supported sample 3. An ultrasonic wedge 2 is provided on the sample 3, and the sample 3 extends to the bottom of the loading device 4.

[0142] S5: Signal screening and system stability analysis

[0143] S501: This test uses a 5MHz frequency probe to apply a pressure of 50N to 600N to the cantilever beam, where the effective detection depth that the measuring probe can reach is 1.37mm.

[0144] The loading forces are 50N, 100N, 150N, 200N, 250N, 300N, 350N, 400N, 450N, 500N and 550N respectively.

[0145] The experiment uses a residual stress ultrasonic nondestructive testing system to measure the stress at the root of the cantilever beam under different loading forces. First, the cantilever beam is considered to be zero stress when it is not under stress. By rotating the bolt to apply pressure to the cantilever beam, stress is generated at the root of the cantilever beam and measured. After the measurement is completed, the next set of experiments is carried out in sequence until all measurements are completed. The schematic diagram of the test process is shown in the figure. Figure 5 shown.

[0146] S6: Stress calculation

[0147] S601: This system uses the acoustic time difference method to calculate residual stress and the cross-correlation algorithm to calculate acoustic time. After the system is started, it is delayed for 10 seconds to allow the coupling agent to stabilize, and then the LCR wave data is read in a circular manner. Multiple LCR wave data are cross-correlated and analyzed. Figure 6 As shown. If the absolute value is ≤0.5 nanoseconds, the system as a whole tends to be stable, and then the stress analysis begins. The samples in the zero stress state and the loading force state are sampled cyclically and cross-correlated. If the absolute value of the cross-correlation is ≤0.5 nanoseconds, the acoustic time difference reaches the accuracy, and the LCR waveform data in this state is obtained. The waveform diagrams of the transmitting signal and the receiving signal are shown in Figure 7 shown.

[0148] By comparing the waveform data of zero stress and after force application, the method of calculating the acoustic time difference is determined. If the waveform does not change, the cross-correlation algorithm is used; if the waveform changes, the peak method is used. Finally, the stress is calculated based on the acoustic time difference. The flow chart of the acoustic time difference algorithm is as follows: Figure 8 shown.

[0149] The thickness of the measured object affects the number and amplitude of LCR waves. When the measured object is thin, the longitudinal waves reflected from the bottom surface may overlap with the LCR waves, causing distortion. In addition, the refracted shear waves reflected back to the surface may also cause LCR wave distortion. To avoid distortion, the peak method is usually used at the first trough of the LCR wave.

[0150] S7: Verify the test results: compare the theoretical calculation values ​​with the test values ​​guided by the simulation.

[0151] S701: Fig. 9 As shown, the pulse signal is generated by a voltage source, which generates ultrasonic waves through a piezoelectric transducer and reaches the surface of the sample through a wedge. Fig.10 The figure shows the refraction process of ultrasonic waves in the sample. The shear wave propagates inside the sample. The LCR wave is red and has a faster propagation speed. Fig.11 As shown, the LCR wave is first received by the piezoelectric transducer at the other end due to its fast propagation speed, and then the shear wave is received.

[0152] The simulation results show that when the wedge angle is 0.48869 radians (28°), the refracted longitudinal wave is transformed into a critical refracted longitudinal wave, so the wedge angle should be set to 28°, which is equal to or greater than the first critical angle.

[0153] S702: Due to the difference between the actual loading force and the theoretical value, the test is based on the dynamometer measurement value, and the data is shown in Appendix 1. The test results of samples 2 and 4 are consistent with the theoretical values, while the measured values ​​of samples 1, 3, and 5 have obvious errors from the theoretical values, especially when the stress is greater than 130MPa. When the loading force is less than 400N (i.e., the stress value is less than 130MPa), the absolute value of the error is mostly less than 10MPa, and only a few exceed 10MPa but do not exceed 20MPa. When the loading force is greater than 400N, the errors of samples 2 and 4 are less than 20MPa, while the errors of samples 1, 3, and 5 are between 20-40MPa.

[0154] When the loading force is less than 400N, the error percentage is less than 15%, while when the loading force exceeds 400N, the error is magnified to more than 20%. The reason for the increase in error is the deformation of the specimen caused by the excessive loading force. The theoretical model assumes that the specimen is a rigid body, and the stress value calculated theoretically is too high, causing the error to increase with the increase in stress. In addition, the initial stress field of the specimen will change after each stress is applied during the test, further increasing the error. However, except for the stage with large deformation, the error between the actual measured value and the theoretical value is small, so it does not affect the verification of the acoustic elastic model.

[0155] Schedule 1

[0156]

[0157]

[0158]

[0159] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0160] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the broadest scope consistent with the principles and novel features disclosed herein.

[0161] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0162] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for ultrasonic detection of internal stress of metal components integrating a mechanism model, characterized in that: The steps include: S1: Establish the theoretical relationship between acoustic time difference and internal stress of metal; S2: Wave propagation model: Establish a mechanism model of critical refraction longitudinal wave (LCR wave) propagation inside the metal and determine the first critical angle that can stably separate the LCR wave; S3: Ultrasonic signal acquisition: Acquire ultrasonic signals of incident waves and LCR waves, perform cyclic sampling on the ultrasonic signals, and obtain multiple sets of data; S4: Loading force signal analysis: Obtain the loading force signal and use the loading force signal to calculate the theoretical stress value at the measuring point; S5: Signal screening and system stability analysis: Perform cross-correlation analysis on the multiple groups of ultrasonic signals collected in step S3, determine whether the system is stable based on the cross-correlation coefficient, and screen out ultrasonic signals that meet the conditions; S6: Stress calculation: Calculate the acoustic time difference using the ultrasonic signal screened out in step S5, and then calculate the internal stress of the metal component according to the theoretical relationship between the acoustic time difference and the internal stress of the metal in step S1; S7: Error analysis: Perform error analysis on the experimental results of step S6 according to step S4 to determine the source of the error and whether the error affects the experimental conclusion.

2. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S1 are: S101: When there is no stress in the sample, the propagation velocity of the sound wave can be calculated by formula (1); Where V0 is the speed of sound waves at zero stress, λ and μ are the second-order elastic coefficients of the material, and ρ0 is the density of the material; The wave velocity of LCR wave satisfies equation (2): l and m are the third-order elastic coefficients of the material, V 111 is the wave velocity of LCR wave; S102: Calculate the acoustic elastic coefficient k: Substituting equation (1) into equation (2), we get make Formula (4) S103: Establish the relationship between metal internal stress and wave velocity: Deriving both sides of equation (4) yields equation (5): S104: Establish the relationship between metal internal stress and acoustic time difference: The calculation formula of wave speed is shown in formula (6); L is the distance between the transmitter and receiver in the wedge, t is the time required for the sound wave to travel a distance of L, and V is the current wave speed; Deriving both sides of equation (6), we get equation (7); Substituting formula (7) into formula (5), we get formula (8) When t = t0, we get formula (9), where K is the stress coefficient of the aluminum alloy sample; S105: Get stress coefficient K Substituting k in the previous formula into formula (9), we get formula (10); Because the expression of stress coefficient mostly contains fixed material parameters and experimental parameters, K is a constant, and there is a linear relationship between the internal stress of the metal and the acoustic time difference.

3. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S2 are: The wave propagation model is established using COMSOL software. The wave propagation model can visually see the propagation of the wave pattern inside the metal through the cloud map. By continuously adjusting the angle until the LCR wave is clearly separated in the cloud map, the angle at this time is the first critical angle of the LCR wave. S201: COMSOL is used to establish an LCR wave propagation mechanism model, which includes a sample, a wedge, a piezoelectric transducer, a matching layer and a damping block, and the parameters of the sample, the wedge, the piezoelectric transducer, the matching layer and the damping block are determined; Select the signal frequency and set the coordinate system of the piezoelectric transducer so that the XY axes are orthogonal. Select the elastic wave-time domain explicit model when adding the physical field, and set the damping for the matching layer, damping block, wedge block and sample. Add piezoelectric material and low-reflection boundary in the physical field. Add a physical field electrostatic model, select a piezoelectric transducer, set the piezoelectric transducer to charge conservation-piezoelectric, set the bottom of the piezoelectric transducer to ground, the top to a terminal, and select circuit as the terminal type; add a voltage source, close the voltage source and the terminal, and finally couple the elastic wave-time domain explicit model and the electrostatic model to form a multi-physics field; Set the material parameters, select plastic for the wedge, PZT for the transducer, aluminum for the sample, matching material for the matching layer, and sound-absorbing material for the damping block; Then, the damping layer, transducer, matching layer, wedge and sample were meshed respectively. The propagation efficiency of ultrasound between different materials is different, and the mesh density between different materials is also different. Ultrasonic propagation is faster in piezoelectric transducers and samples, while it is slower in other materials, so the mesh is encrypted for the faster propagation part.

4. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 3 is characterized in that: The sample width is 100mm, the height is 15mm, the side length of the wedge is 12mm, the width is 20mm, the height is 10mm, the piezoelectric transducer position angle is 0.48869rad (28°), the diameter is 9mm, the height is 1.55mm, and the matching layer height is 0.56mm; 1.5MHz is selected as the signal frequency.

5. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S3 are: S301: Perform simple noise reduction processing on the ultrasonic signal, select 5 cycles each time for collection and storage; perform multiple cycle sampling to obtain multiple groups of data.

6. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S4 are: S401: Using a dynamometer to observe and collect the force in the Z-axis direction in real time to obtain the external stress loaded on the sample; The measured bending moment is calculated according to formula (11): M=QL (11) M is the bending moment, Q is the loading force, and L is the length of the lever arm; According to formula (12), the stress value at the depth corresponding to the bending moment can be obtained: σ=(My) / I (12) σ is stress, y is the distance from the center axis of the cross section, and I is the moment of inertia of the cross section; The moment of inertia of a rectangular cross section can be obtained from equation (13): b is the length of the rectangular section, and h is the height of the rectangular section.

7. The method for ultrasonic detection of internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S5 are: S501: After the system is started, a delay of 10 seconds is performed to allow the coupling agent to stabilize, and the LCR wave data is read cyclically, and multiple LCR wave data are cross-correlated and analyzed; if the absolute value is ≤0.5 nanoseconds, the system as a whole tends to be stable, and samples in the zero stress state and the loading force state are cyclically sampled and cross-correlated and analyzed; if the absolute value of the cross-correlation is ≤0.5 nanoseconds, the acoustic time difference reaches accuracy, and the LCR waveform data in this state is obtained.

8. The method for ultrasonic detection of internal stress of metal components based on the fusion mechanism model according to claim 1 is characterized in that: The specific steps of S6 are: S601: By comparing the waveform data at zero stress and after force application, determine the method for calculating the acoustic time difference. If the waveform has not changed, use the cross-correlation algorithm; if the waveform has changed, use the peak method. Finally, calculate the stress based on the acoustic time difference. The thickness of the measuring piece affects the number and amplitude of the LCR waves. When the measuring piece is thin, the longitudinal waves reflected from the bottom surface may overlap with the LCR waves, causing distortion. In addition, the refracted shear waves reflected back to the surface may also cause LCR wave distortion. To avoid distortion, the peak method is usually used at the first trough of the LCR wave.

9. The ultrasonic detection method for internal stress of metal components according to the fusion mechanism model of claim 1 is characterized in that: The specific steps of S7 are: S701: The reason for the increase in error is the deformation of the specimen caused by excessive loading force. The theoretical model assumes that the specimen is a rigid body, but the stress value calculated theoretically is too high, which causes the error to increase with the increase of stress. In addition, the initial stress field of the specimen will change after each stress is applied during the test, which will increase the error. Except for the stage with large deformation, the error between the actual measured value and the theoretical value is small, so it does not affect the verification of the acoustic elastic model.

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