Thin plate residual stress detection method and system based on thickness resonance mode

Abstract

The invention discloses a thin plate residual stress detection method and system based on a thickness resonance mode, and relates to the technical field of stress detection, and the method comprises the steps: obtaining a frequency dispersion curve of a to-be-detected thin plate, and determining the theoretical thickness resonance frequency of the S1 thickness resonance mode according to the frequency dispersion curve; carrying out a stress coefficient calibration experiment on the to-be-tested thin plate, and determining experimental Lamb wave A-scanning data of different stresses; determining a stress-thickness resonance normalized amplitude curve associated with a theoretical thickness resonance frequency according to the resonance wave time domain signal of the A-scan data of each experimental Lamb wave; exciting a Lamb wave signal to a preset excitation point of the thin plate to be measured, and determining corresponding actually measured Lamb wave A-scan data; and determining the residual stress of the to-be-measured thin plate by adopting a stress-thickness resonance normalized amplitude curve based on an actually measured thickness resonance normalized amplitude determined by actually measured Lamb wave A-scanning data. The residual stress of the thin plate is measured by using the characteristic that the amplitude in the S1 thickness resonance mode is gradually increased along with the change of the stress value, and the detection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of stress detection, and in particular to a method and system for detecting residual stress of a thin plate based on thickness resonance mode. Background Art

[0002] Thin plate parts are widely used in many industries such as automobiles, mechanical equipment shells, aircraft skins, and sheet metal products. Such long-serving metal structures may cause stress concentration in key parts under external loads, which in turn leads to crack formation, material failure, and even sudden fracture, posing a threat to life and property safety. Therefore, in order to ensure the quality of thin plate parts during the production and acceptance stages, as well as to accurately evaluate their structural life throughout their entire service life, it is necessary to perform residual stress testing on thin plate parts.

[0003] Residual stress measurement technology can be divided into destructive testing methods and non-destructive testing methods. Destructive testing methods obtain residual stress by removing sample materials and based on displacement or strain in the area, including drilling method, ring core method and peeling method. Although destructive testing methods are relatively mature in theory and the measurement accuracy is usually high, they will cause irreversible damage to the workpiece during implementation. Non-destructive testing methods (NDT) can more accurately evaluate the microstructure and mechanical properties of the material without damaging the tested sample, and effectively identify and locate potential defects such as bubbles, cracks and material inhomogeneity. Nondestructive testing methods mainly include diffraction (X-ray Diffraction, XRD), ultrasonic method, magnetic method, Raman spectroscopy and nanoindentation method. Among them, the diffraction method has a complete detection standard but the instrument is expensive. The magnetic method has high detection sensitivity but is only applicable to ferromagnetic workpieces. Raman spectroscopy can measure microstructures but the accuracy is easily affected by external conditions. Nanoindentation detection is convenient and fast but the theory is not perfect. The ultrasonic method is widely recognized in industrial applications because of its advantages such as high safety, pollution-free, fast response speed and easy to carry equipment.

[0004] At present, the ultrasonic stress detection method based on zero-group-velocity Lamb Waves (ZGV Lamb Waves) performs stress detection through the zero-group-velocity mode (ZGV). The mechanism is that the frequency of the ZGV mode will undergo a monotonic change, namely, frequency shift, as the stress in the thin plate changes. Since the thickness change of the thin plate during the stretching process will affect the frequency shift, thickness compensation processing is required. The detection process is relatively cumbersome, resulting in low efficiency in residual stress detection of the thin plate. Summary of the invention

[0005] The present invention provides a thin plate residual stress detection method and system based on thickness resonance mode, which solves the technical problem that the existing ultrasonic stress detection method needs to perform thickness compensation processing for stress detection through zero group velocity mode, resulting in low efficiency of thin plate residual stress detection.

[0006] A first aspect of the present invention provides a method for detecting residual stress of a thin plate based on thickness resonance mode, comprising:

[0007] Obtaining a dispersion curve of the thin plate to be tested, and determining a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve;

[0008] Performing a stress coefficient calibration experiment on the thin plate to be tested to determine experimental Lamb wave A-scan data of different stresses;

[0009] Determining a stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each of the experimental Lamb wave A-scan data;

[0010] Exciting a Lamb wave signal to a preset excitation point of the thin plate to be tested, and determining corresponding measured Lamb wave A-scan data;

[0011] Based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, the residual stress of the thin plate to be measured is determined using the stress-thickness resonance normalized amplitude curve.

[0012] Optionally, the obtaining of a dispersion curve of the thin plate to be tested and determining a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve comprises:

[0013] Acquiring structural parameters of the thin plate to be tested, and determining a dispersion curve of the thin plate to be tested based on the structural parameters;

[0014] Determine the theoretical frequency-thickness product of the S1 thickness resonance mode according to the dispersion curve;

[0015] The plate thickness is extracted from the structural parameters, and a ratio operation is performed between the theoretical frequency-thickness product and the plate thickness to output a theoretical thickness resonance frequency.

[0016] Optionally, determining the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each of the experimental Lamb wave A-scan data comprises:

[0017] Extracting the corresponding resonance wave time domain signal from each of the experimental Lamb wave A-scan data according to a preset time range;

[0018] After windowing the time domain signals of the resonance waves by using the Hanning window function, fast Fourier transform is performed respectively, and amplitude normalization is performed using the amplitude of the S1 zero group velocity Lamb wave modal frequency as an indicator, and multiple experimental frequency domain graphs are output;

[0019] The peak amplitude in each experimental frequency domain diagram that is closest to the theoretical thickness resonance frequency is taken as the corresponding theoretical thickness resonance normalized amplitude;

[0020] The theoretical thickness resonance normalized amplitude and the associated stress are used to perform curve fitting to generate a stress-thickness resonance normalized amplitude curve.

[0021] Optionally, the residual stress of the thin plate to be measured is determined by using the stress-thickness resonance normalized amplitude curve based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, including:

[0022] Performing a windowed fast Fourier transform on the resonance wave time domain signal in the measured A-scan data within a preset time range, and outputting a measured frequency domain graph;

[0023] Determining a measured thickness resonance normalized amplitude of the S1 thickness resonance mode from the measured frequency domain diagram according to the theoretical thickness resonance frequency;

[0024] The measured thickness resonance normalized amplitude is input into the stress-thickness resonance normalized amplitude curve for solution, and the residual stress of the thin plate to be measured is output.

[0025] Optionally, there are multiple excitation points; further comprising:

[0026] The thin plate to be tested is mechanically scanned to determine the residual stresses at multiple excitation points, and the residual stresses are used to construct the residual stress field of the thin plate to be tested.

[0027] A second aspect of the present invention provides a thin plate residual stress detection system based on thickness resonance mode, comprising a waveform generator, an amplifier, an incident probe, a receiving probe, an incident wedge, a receiving wedge, an oscilloscope, a processor and a universal testing machine;

[0028] The waveform generator is connected to the amplifier, and the amplifier is connected to the incident probe;

[0029] The processor is connected to the oscilloscope, and the oscilloscope is connected to the receiving probe;

[0030] The incident probe is connected to the thin plate to be tested through the incident wedge according to a preset incident angle, the receiving probe is connected to the thin plate to be tested through the receiving wedge, and the universal testing machine is connected to the thin plate to be tested;

[0031] The universal testing machine is used to perform stress coefficient calibration experiments of different stresses on the thin plate to be tested;

[0032] The waveform generator is used to generate an excitation signal, which is amplified by an amplifier and then transmitted to the incident probe to generate an incident ultrasonic signal;

[0033] The incident wedge is used to convert the ultrasonic signal into a Lamb wave signal and excite the thin plate to be tested;

[0034] The receiving wedge is used to transmit the Lamb wave signal returned by the thin plate to be tested to the receiving probe to generate a receiving ultrasonic signal;

[0035] The oscilloscope is used to generate experimental Lamb wave A-scan data or measured Lamb wave A-scan data of different stresses according to the received ultrasonic signal;

[0036] The processor is used to obtain a dispersion curve of the thin plate to be tested, and determine the theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve; determine the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each experimental Lamb wave A-scan data; and determine the residual stress of the thin plate to be tested using the stress-thickness resonance normalized amplitude curve based on the measured thickness resonance normalized amplitude determined based on the measured Lamb wave A-scan data.

[0037] Optionally, when determining the measured Lamb wave A-scan data, the incident wedge and the receiving wedge may both be air or water.

[0038] Optionally, the process of determining the incident angle includes:

[0039] Determining the phase velocity of the S1 zero group velocity Lamb wave mode based on the dispersion curve;

[0040] The incident angle is determined by performing an inverse sine operation on the ratio of the longitudinal wave velocity in the incident wedge or water or air to the phase velocity.

[0041] A third aspect of the present invention provides a computer device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the thin plate residual stress detection method based on thickness resonance mode as described in any one of the above items.

[0042] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed, implements the thin plate residual stress detection method based on thickness resonance mode as described in any one of the above items.

[0043] A fifth aspect of the present invention provides a computer program product, comprising a computer program / instruction, which, when executed by a processor, implements a thin plate residual stress detection method based on thickness resonance mode as described in any one of the above.

[0044] It can be seen from the above technical solutions that the present invention has the following advantages:

[0045] The above scheme of the present invention provides a thin plate residual stress detection method based on thickness resonance mode, including: obtaining the dispersion curve of the thin plate to be tested, and determining the theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve; performing a stress coefficient calibration experiment on the thin plate to be tested, and determining the experimental Lamb wave A-scan data of different stresses; determining the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each experimental Lamb wave A-scan data; exciting the Lamb wave signal to the preset excitation point of the thin plate to be tested, and determining the corresponding measured Lamb wave A-scan data; based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, using the stress-thickness resonance normalized amplitude curve to determine the residual stress of the thin plate to be tested. The above scheme accurately measures the residual stress of the thin plate by utilizing the characteristic that the amplitude increases with the change of the stress value under the S1 thickness resonance mode, and does not need to consider the thickness change of the thin plate, thereby improving the efficiency of the residual stress detection of the thin plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 A flowchart of a method for detecting residual stress of a thin plate based on thickness resonance mode provided by an embodiment of the present invention;

[0048] Figure 2 A schematic diagram of a frequency-thickness product-phase velocity dispersion curve provided by an embodiment of the present invention;

[0049] Figure 3 A technical flow chart of a thin plate residual stress detection method based on thickness resonance mode provided by an embodiment of the present invention;

[0050] Figure 4 It is a structural schematic diagram of a two-dimensional finite element model with point source excitation;

[0051] Figure 5 It is the dispersion curve of 6061 aluminum alloy;

[0052] Figure 6 Schematic diagram of time domain signal at 0MPa and 200MPa;

[0053] Figure 7 This is a frequency domain comparison diagram under 0MPa and 200MPa stress;

[0054] Figure 8 Schematic diagram of the variation of S1 thickness resonance mode frequency with stress;

[0055] Fig. 9 Schematic diagram of the variation of S1 thickness resonance mode amplitude with stress;

[0056] Fig.10 It is the stress cloud diagram of the uniform sample under the tensile force of 10.5kN;

[0057] Fig.11 It is the stress distribution diagram of the uniform specimen under the tensile force of 10.5kN;

[0058] Fig.12 This is a typical frequency domain diagram under 100MPa stress;

[0059] Fig.13 Reconstructed diagram of stress field for uniform plate;

[0060] Fig.14 A schematic structural diagram of a thin plate residual stress detection system based on thickness resonance mode provided by an embodiment of the present invention;

[0061] Fig.15 A structural diagram of a thin plate residual stress detection system based on thickness resonance mode using different propagation media provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0062] The embodiments of the present invention provide a method and system for detecting residual stress of a thin plate based on thickness resonance mode, which is used to solve the technical problem that the existing ultrasonic stress detection method needs to perform thickness compensation processing when performing stress detection through zero group velocity mode, resulting in low efficiency of residual stress detection of thin plates.

[0063] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] See also Figure 1 , Figure 1A flowchart of the steps of a method for detecting residual stress of a thin plate based on thickness resonance mode is provided in an embodiment of the present invention.

[0065] The present invention provides a thin plate residual stress detection method based on thickness resonance mode, comprising:

[0066] Step 101: Obtain a dispersion curve of the thin plate to be tested, and determine a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve.

[0067] Step 101 includes the following sub-steps:

[0068] Acquire structural parameters of the thin plate to be tested, and determine the dispersion curve of the thin plate to be tested based on the structural parameters;

[0069] Determine the theoretical frequency-thickness product of the S1 thickness resonance mode based on the dispersion curve;

[0070] The plate thickness is extracted from the structural parameters, and the theoretical frequency-thickness product is used to perform ratio calculation with the plate thickness to output the theoretical thickness resonance frequency.

[0071] It should be noted that there are many ways to obtain the dispersion curve of the thin plate to be tested. In one implementation, COMSOL Multiphysics finite element software can be used to solve the Rayleigh-Lamb equation by inputting the thickness, geometric shape, elastic modulus, density and Poisson's ratio of the thin plate to be tested, which reflect the geometric properties and material properties of the template to be tested, so as to determine the dispersion curve of the thin plate to be tested. The Rayleigh-Lamb equation includes:

[0072] For the symmetric mode (S):

[0073] ;

[0074] For the antisymmetric mode (A):

[0075] ;

[0076] In the formula, is half the plate thickness, is the first propagation constant, is the second propagation constant, is the wave number; where the propagation constant satisfies the following formula:

[0077] ;

[0078] ;

[0079] In the formula, is the angular frequency, is the longitudinal wave velocity in the thin plate, is the shear wave velocity in the thin plate;

[0080] According to the calculation results of the above equations, the calculation results are processed by MATLAB commercial software to draw the required dispersion curve, and then simulate and analyze the dispersion characteristics; it can be understood that the dispersion curve can have many forms, for example: with the frequency-thickness product as the horizontal coordinate and the phase velocity as the vertical coordinate (such as Figure 2 As shown), with the frequency-thickness product as the abscissa and the group velocity as the ordinate, with the wave number as the abscissa and the frequency as the ordinate;

[0081] In this embodiment, the focus is on the S1 thickness resonance mode, that is, the cutoff frequency of the S1 mode. Based on the dispersion curve, the frequency-thickness product of the S1 thickness resonance mode can be determined as the theoretical frequency-thickness product. Combined with the thickness of the thin plate to be tested, the theoretical thickness resonance frequency can be calculated using the following formula:

[0082] ;

[0083] In the formula, is the theoretical thickness resonance frequency, is the theoretical frequency product, For the plate thickness.

[0084] Step 102: Perform a stress coefficient calibration experiment on the thin plate to be tested to determine experimental Lamb wave A-scan data of different stresses.

[0085] Step 102 includes the following sub-steps:

[0086] It should be noted that the stress coefficient calibration experiment can be carried out on the thin plate to be tested under different set stress conditions through the universal testing machine. It can be understood that the stress coefficient calibration experiment includes a tensile test and a compression test. Lamb wave signals are emitted by instruments such as waveform generators, probes and wedges to stimulate the S1 thickness resonance mode of the thin plate to be tested, and the corresponding A-scan data can be determined by an oscilloscope as experimental Lamb wave A-scan data.

[0087] Step 103: Determine a stress-thickness resonance normalized amplitude curve associated with a theoretical thickness resonance frequency according to the resonance wave time domain signal of each experimental Lamb wave A-scan data.

[0088] Step 103 includes the following sub-steps:

[0089] From the Lamb wave A-scan data of each experiment, the corresponding resonance wave time domain signal is extracted according to the preset time range;

[0090] After windowing the time domain signals of each resonant wave through the Hanning window function, fast Fourier transform is performed respectively, and the amplitude of the S1 zero group velocity Lamb wave modal frequency is used as an indicator for amplitude normalization, and multiple experimental frequency domain diagrams are output;

[0091] The peak amplitude closest to the theoretical thickness resonance frequency in each experimental frequency domain diagram is taken as the corresponding theoretical thickness resonance normalized amplitude;

[0092] The normalized amplitude of each theoretical thickness resonance and the associated stress are used for curve fitting to generate a stress-thickness resonance normalized amplitude curve.

[0093] It should be noted that the resonance wave time domain signal within a preset time range is selected from the Lamb wave A-scan data of each experiment, and the Hanning window function is used to perform windowing processing on each resonance wave time domain signal and perform fast Fourier transform. Then, the amplitude of the S1 zero group velocity Lamb wave mode (S1-ZGV) frequency is used as an indicator for amplitude normalization processing, thereby obtaining multiple experimental frequency domain diagrams. In the experimental frequency domain diagram, the frequency is used as the horizontal coordinate and the thickness resonance normalized amplitude is used as the vertical coordinate. The thickness resonance normalized amplitude can be understood as the ratio of the thickness resonance frequency amplitude to the S1-ZGV frequency amplitude. By using Hanning windowing, spectrum leakage can be prevented during the Fourier transform process, thereby improving the transform efficiency. The frequency accuracy after the test is improved. By normalizing the amplitude with the amplitude of the S1-ZGV frequency, the voltage change of the excitation signal can be avoided to affect the size of the thickness resonance mode amplitude, and then affect the value of the fitting curve, thereby improving the stability of the curve fitting. The peak amplitude closest to the theoretical thickness resonance frequency of the S1 thickness resonance mode is extracted from the experimental frequency domain diagram as the corresponding theoretical thickness resonance normalized amplitude. The theoretical thickness resonance normalized amplitude under different stresses is fitted with the stress-amplitude curve. The relationship between stress and the amplitude of the S1 thickness resonance mode can be established to obtain the stress-thickness resonance normalized amplitude curve, thus completing the stress calibration process.

[0094] Step 104 , exciting a Lamb wave signal to a preset excitation point of the thin plate to be measured, and determining the corresponding measured Lamb wave A-scan data.

[0095] It should be noted that after the stress calibration index is determined, the Lamb wave signal should be excited at a preset excitation point set on the thin plate to be tested, and the measured Lamb wave A-scan data at the location of the excitation point can be collected.

[0096] Step 105 : Based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, the residual stress of the thin plate to be measured is determined using a stress-thickness resonance normalized amplitude curve.

[0097] Step 105 includes the following sub-steps:

[0098] Performing a windowed fast Fourier transform on the resonance wave time domain signal in the preset time range in the measured A-scan data, and outputting a measured frequency domain graph;

[0099] According to the theoretical thickness resonance frequency, the measured thickness resonance normalized amplitude of the S1 thickness resonance mode is determined from the measured frequency domain diagram;

[0100] The measured thickness resonance normalized amplitude is input into the stress-thickness resonance normalized amplitude curve for solution, and the residual stress of the thin plate to be measured is output.

[0101] It should be noted that the measured frequency domain diagram is generated by windowing the resonance wave time domain signal of the measured A-scan data in the preset time range with a windowing function and then performing a fast Fourier transform. The amplitude of the S1 thickness resonance mode is obtained from the frequency domain diagram according to the theoretical thickness resonance frequency as the measured thickness resonance normalized amplitude, and then the residual stress in the thin plate to be measured is calculated using the stress-thickness resonance normalized amplitude curve obtained by stress calibration.

[0102] Preferably, there are multiple excitation points; the method further comprises:

[0103] The thin plate to be tested is mechanically scanned to determine the residual stresses at multiple excitation points, and the residual stresses are used to construct the residual stress field of the thin plate to be tested.

[0104] It should be noted that the residual stress of a single excitation point only reflects the stress state of the thin plate to be tested in a local range. In order to obtain the stress distribution of the entire thin plate to be tested, multiple excitation points can be set on the thin plate to be tested, and the residual stress of each excitation point can be obtained according to step 105, thereby obtaining the residual stress distribution in the global range.

[0105] To better explain, Figure 3 A schematic diagram of the technical process of the thin plate residual stress detection method based on thickness resonance mode provided by an embodiment of the present invention is shown; it should be noted that the technical process is only briefly described, and the specific implementation process of each step can be understood by referring to the relevant content in the aforementioned embodiment:

[0106] 1. Excite the S1 thickness resonance mode: In this process, first solve the dispersion curve of the thin plate to be tested, select a probe with a suitable center frequency according to the theoretical thickness resonance frequency determined by the dispersion curve, and select the optimal incident angle of the probe to ensure that the S1 thickness resonance mode of the thin plate to be tested can be excited;

[0107] 2. Establish the relationship between stress-thickness resonance modal amplitude: In this process, a tensile test is performed on the thin plate to be tested under different stresses, and the probe is used to excite the thin plate to be tested and transmit the signal returned from the thin plate to the oscilloscope, thereby obtaining A-scan data under different stresses, and the resonance wave time domain signal in each A-scan data is processed by windowed fast Fourier transform to obtain the corresponding frequency domain diagram, and the theoretical thickness resonance normalized amplitude is extracted from each frequency domain diagram and curve fitted with the corresponding stress, thereby obtaining the stress-amplitude relationship formula;

[0108] 3. Solve local stress: In this process, the probe is moved to detect a certain excitation point set on the thin plate to be tested. After obtaining the corresponding measured thickness resonance normalized amplitude, the stress-amplitude relationship formula is used to solve the local residual stress of the thin plate to be tested;

[0109] 4. Scan the stress in the entire range: In this process, the entire surface of the thin plate to be tested is scanned by automatically or manually moving the probe. Multiple excitation points set on the surface of the thin plate to be tested are processed according to the steps of solving local stress, so as to obtain the residual stress value of the global range of the thin plate to be tested.

[0110] In order to clearly illustrate the effect of the thin plate residual stress detection method based on thickness resonance mode provided by the embodiment of the present invention, a numerical simulation experiment is carried out through finite element modeling:

[0111] First, the thin plate workpiece was numerically simulated using COMSOL Multiphysics commercial software to construct Figure 4 The point source excitation two-dimensional finite element model shown in the figure has a geometric shape of a 3 mm thick thin plate, and the material is 6061 aluminum alloy. Increasing damping absorption layers are set on the left and right sides of the thin plate of the model to effectively eliminate the influence of sound reflection from the boundary. At the same time, in order to obtain the stress values ​​of the thin plate workpiece at multiple positions, a total of 80 equally spaced (interval of 2 mm) normal displacement signals are collected on the model surface (including the excitation point). The linear array method can be used to receive the signals of multiple excitation points. In addition, tensile stress is applied in the thin plate workpiece in the range of 0-200 MPa with a step size of 20 MPa to simulate the different stresses in the stress coefficient calibration experiment.

[0112] Secondly, according to the known structural parameters of the thin plate workpiece, the Rayleigh-Lamb equation is solved by COMSOL Multiphysics finite element software, and the calculation results are processed by MATLAB commercial software to draw the following figure: Figure 5The dispersion curve shown in the figure; in the dispersion curve diagram, it can be seen that when the wave number k=0, it represents the cutoff frequency, that is, the thickness resonance mode. From the marked box in the figure, it can be obtained that the theoretical thickness resonance frequency of the S1 thickness resonance mode is 1.0567MHz; on this basis, the center frequency of the excitation signal can be selected near the theoretical thickness resonance frequency. In the simulation, the excitation signal is a 3-cycle sinusoidal signal modulated by the Hanning window with a center frequency of 0.9MHz. This excitation signal is a broadband signal, and its frequency domain also contains the frequency components of the thickness resonance mode;

[0113] Then, the test was carried out under the loading conditions of 0MPa and 200Mpa tensile stress, and the receiving signal of the model at the first excitation point, namely the A-scan data, was extracted; Figure 6 (a) It can be observed that there is a resonance wave that lasts for a period of time in the A-scan data at 0 MPa. The resonance wave time domain signal of 4-50 μs is intercepted from the A-scan data, as shown in Figure 6 (b) shows that the resonance wave exhibits a uniform amplitude decrease. The analysis results show that the signal contains the S1-ZGV mode and the extremely weak S1 thickness resonance mode. Under the tensile stress of 200Mpa, Figure 6 (c) It can be seen that there is also a resonance wave that lasts for a period of time in the A-scan data. The resonance wave time domain signal of 4-50μs is intercepted as shown in Figure 6 As shown in (d), in comparison, the amplitude of the resonance wave time domain signal under tensile stress shows obvious periodic changes, which is due to the superposition of the S1-ZGV mode and other modes with similar frequencies under stress, which means that there may be an S1 thickness resonance mode in the resonance wave;

[0114] Next, in order to further determine whether there is an S1 thickness resonance mode in the resonance wave, the two intercepted resonance wave time domain signals are subjected to windowed fast Fourier transform to obtain the frequency domain comparison under 0MPa and 200MPa stress. Figure 7 As shown in the figure; the resonance peak with a larger amplitude is the S1-ZGV mode, but after applying a tensile stress of 200MPa in the simulation, a new resonance peak appears at 1.0497MHz, which is quite close to the theoretical thickness resonance frequency of the S1 thickness resonance mode of 1.0567MHz. In addition, the frequency of the S1 thickness resonance mode is higher than that of the S1-ZGV mode, which can be clearly distinguished in the frequency domain diagram; According to existing research, changes in excitation conditions will affect the coupling efficiency of the S1-ZGV mode, which may lead to the emergence of new modes near the cutoff frequency of the Lamb wave. In this study, the application of stress destroys the optimal coupling condition of the S1-ZGV mode. Under the induction of stress, the S1-ZGV mode will undergo mode conversion, thereby triggering the generation of the S1 thickness resonance mode;

[0115] Furthermore, under the action of tensile stress of 0-200MPa (step size of 20MPa), the resonant wave time domain signal in the range of 110-250μs is subjected to windowed fast Fourier transform. It can be understood that the selection of different time ranges has little effect on the results, but it is necessary to ensure that the intercepted time range is long enough. If the intercepted time range is too short, the spectrum will be wider, thereby masking the S1 thickness resonance mode; the frequency and amplitude of the resonance peak of the S1 thickness resonance mode under different stresses are extracted, and the trend change is constructed as follows: Figure 8 and Fig. 9 As shown, according to Figure 8 It can be seen that the change in the S1 thickness resonance mode frequency under the action of 0-200MPa is small, while Fig. 9 The amplitude change of the S1 thickness resonance mode shows a relatively smooth increasing trend, and its change amount is also quite sensitive with the change of stress value. Therefore, it can be seen that the amplitude change under the modal conversion is an effective indicator for detecting stress, and compared with the frequency offset of the Hz / MPa level without thickness compensation in the existing S1-ZGV frequency domain method, the amplitude change indicator is more advantageous; by performing cubic curve fitting on the simulation data, the stress-thickness resonance normalized amplitude curve of the relationship between stress (X) and amplitude (Y) can be obtained as follows: ;

[0116] Finally, for a uniform 6061 aluminum plate with a material yield strength of 275 MPa, a thickness of 3 mm, and a width of 35 mm in the middle, a tensile force of 10.5 kN is applied to the workpiece in COMSOL software. The stress cloud diagram and stress distribution diagram are as follows: Fig.10 and Fig.11 As shown; under the action of 10.5kN tensile force, according to the formula ,in, is stress, is the applied force, is the cross-sectional area, the expected theoretical stress in the middle of the aluminum plate is 100 MPa, which is consistent with the static analysis results. At this time, an external stress of 100 MPa is applied to the point source excitation two-dimensional finite element model, the A-scan data of the receiving point (excitation point) is extracted, and the resonant wave time domain signal in the range of 110-250 μs is subjected to windowed fast Fourier transform. The obtained frequency domain diagram is shown in the figure below: Fig.12 As shown in Figure 1, the amplitude of the S1 thickness resonance mode under the action of 100 MPa is 0.1557. According to the fitted stress-thickness resonance normalized amplitude curve, the stress σ≈93.702 MPa can be solved, which is very close to the expected stress. The same operation is performed on multiple equally spaced points to obtain the stress field reconstruction diagram of the uniform thin plate as shown in Figure 1. Fig.13As shown in the figure, the stress field has a good detection effect; referring to the standard deviation formula, the thickness resonance modal stress measurement method error is defined as: ,in, To measure stress, is the theoretical stress calculated by the formula, For the stress, and the standard deviation of the detected stress is calculated to be 8.7457MPa. The error of this stress detection method is less than 10MPa, which proves that this method has high accuracy.

[0117] In the embodiment of the present invention, the residual stress of the thin plate is accurately measured by utilizing the characteristic that the amplitude of the thickness resonance mode increases with the change of the stress value, so that the stress field inside the thin plate can be reconstructed by using the Lamb wave technology of the thickness resonance mode. This method does not need to consider the thickness change of the thin plate, and does not need to perform thickness compensation processing. It is relatively more convenient, thereby improving the efficiency of residual stress detection of the thin plate. At the same time, it has a wider applicability and strong practical value in local and global stress measurement, provides a new method and theoretical basis for evaluating the residual stress in the workpiece, and shows potential application prospects in the field of non-destructive testing.

[0118] See also Fig.14 , Fig.14 A schematic structural diagram of a thin plate residual stress detection system based on thickness resonance mode provided in an embodiment of the present invention.

[0119] The present invention provides a thin plate residual stress detection system based on thickness resonance mode, comprising:

[0120] Waveform generator, amplifier, incident probe, receiving probe, incident wedge, receiving wedge, oscilloscope, processor and universal testing machine;

[0121] The waveform generator is connected to the amplifier, and the amplifier is connected to the incident probe;

[0122] The processor is connected to the oscilloscope, and the oscilloscope is connected to the receiving probe;

[0123] The incident probe is connected to the thin plate to be tested through the incident wedge according to the preset incident angle, the receiving probe is connected to the thin plate to be tested through the receiving wedge, and the universal testing machine is connected to the thin plate to be tested;

[0124] The universal testing machine is used to perform stress coefficient calibration experiments of different stresses on the thin plates to be tested;

[0125] The waveform generator is used to generate an excitation signal, which is amplified by the amplifier and then transmitted to the incident probe to generate an incident ultrasonic signal;

[0126] The incident wedge is used to convert the ultrasonic signal into a Lamb wave signal and excite the thin plate to be tested;

[0127] The receiving wedge is used to transmit the Lamb wave signal returned by the thin plate to be tested to the receiving probe to generate a receiving ultrasonic signal;

[0128] The oscilloscope is used to generate experimental Lamb wave A-scan data or measured Lamb wave A-scan data of different stresses according to the received ultrasonic signal;

[0129] The processor is used to obtain the dispersion curve of the thin plate to be tested, and determine the theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve; determine the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each experimental Lamb wave A-scan data; based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, the residual stress of the thin plate to be tested is determined using the stress-thickness resonance normalized amplitude curve.

[0130] It should be noted that the theoretical thickness resonance frequency of the S1 thickness resonance mode is first determined by the processor based on the dispersion curve of the thin plate (workpiece to be tested), and then a probe with a suitable frequency is further selected for the experiment, and the calculation formula of Snell's law is used. , for the longitudinal wave velocity in the propagation medium The phase velocity of the S1 zero group velocity Lamb wave mode The incident angle of the incident probe is determined by performing an arc sine operation on the ratio of , to effectively excite the thickness resonance mode;

[0131] After selecting the appropriate probe and incident angle, the detection operation can be carried out. In the experimental system, when the propagation medium is in the form of a wedge, the probe and the wedge, as well as the wedge and the thin plate to be tested, are contact-coupled using an ultrasonic coupling agent to improve the ultrasonic propagation efficiency and the signal-to-noise ratio of the detection results; a waveform generator and an amplifier are used as excitation modules, and an oscilloscope and a processor are used as receiving modules. When performing signal detection, the waveform generator generates an excitation signal, which is amplified by the amplifier and then transmitted to the incident probe. The incident probe emits an incident ultrasonic signal into the thin plate to be tested at a certain incident angle. The ultrasonic signal is incident on the thin plate to be tested through the incident wedge and is converted into a Lamb wave signal in the thin plate. The Lamb wave propagates in the thin plate and returns to the receiving module. The receiving probe in the wedge block receives and generates a receiving ultrasonic signal, and the receiving probe transmits the receiving ultrasonic signal to the oscilloscope to generate A-scan data. The receiving angle of the receiving probe can be set according to the incident angle. According to the above signal detection process, when the universal testing machine performs stress coefficient calibration experiments of different stresses on the thin plate to be tested, the corresponding experimental Lamb wave A-scan data are detected, and the processor determines the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonant wave time domain signal of each experimental Lamb wave A-scan data, and then determines the measured thickness resonance normalized amplitude according to the measured Lamb wave A-scan data detected at the preset excitation point position, and then solves the residual stress of the thin plate to be tested through the stress-thickness resonance normalized amplitude curve.

[0132] Alternatively, the processor may be a computer.

[0133] Optionally, when determining the measured Lamb wave A-scan data, the incident wedge and the receiving wedge may both be air or water.

[0134] It should be noted that when conducting stress coefficient calibration experiments, the propagation medium can be in the form of a wedge, and in the actual measurement process after stress calibration, if Fig.15 As shown, in addition to using wedges, water or air can also be used as propagation media to excite the mode of interest at oblique incidence.

[0135] Optionally, obtaining a dispersion curve of the thin plate to be tested, and determining a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve, includes:

[0136] Acquire structural parameters of the thin plate to be tested, and determine the dispersion curve of the thin plate to be tested based on the structural parameters;

[0137] Determine the theoretical frequency-thickness product of the S1 thickness resonance mode based on the dispersion curve;

[0138] The plate thickness is extracted from the structural parameters, and the theoretical frequency-thickness product is used to perform ratio calculation with the plate thickness to output the theoretical thickness resonance frequency.

[0139] Optionally, according to the resonant wave time domain signal of each experimental Lamb wave A-scan data, a stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency is determined, including:

[0140] From the Lamb wave A-scan data of each experiment, the corresponding resonance wave time domain signal is extracted according to the preset time range;

[0141] After windowing the time domain signals of each resonant wave through the Hanning window function, fast Fourier transform is performed respectively, and the amplitude of the S1 zero group velocity Lamb wave modal frequency is used as an indicator for amplitude normalization, and multiple experimental frequency domain diagrams are output;

[0142] The peak amplitude closest to the theoretical thickness resonance frequency in each experimental frequency domain diagram is taken as the corresponding theoretical thickness resonance normalized amplitude;

[0143] The normalized amplitude of each theoretical thickness resonance and the associated stress are used for curve fitting to generate a stress-thickness resonance normalized amplitude curve.

[0144] Optionally, based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, the residual stress of the thin plate to be measured is determined using a stress-thickness resonance normalized amplitude curve, including:

[0145] Performing a windowed fast Fourier transform on the resonance wave time domain signal in the preset time range in the measured A-scan data, and outputting a measured frequency domain graph;

[0146] According to the theoretical thickness resonance frequency, the measured thickness resonance normalized amplitude of the S1 thickness resonance mode is determined from the measured frequency domain diagram;

[0147] The measured thickness resonance normalized amplitude is input into the stress-thickness resonance normalized amplitude curve for solution, and the residual stress of the thin plate to be measured is output.

[0148] Optionally, there are multiple excitation points; the processor is further configured to:

[0149] The thin plate to be tested is mechanically scanned to determine the residual stresses at multiple excitation points, and the residual stresses are used to construct the residual stress field of the thin plate to be tested.

[0150] It should be noted that, by automatically or manually moving the probe to scan the entire surface of the thin plate to be tested, the residual stresses of multiple excitation points set on the surface of the thin plate to be tested can be obtained, and then the residual stress value of the global range of the thin plate to be tested can be determined.

[0151] An embodiment of the present invention also provides a computer device, including a memory and a processor, wherein a computer program is stored in the memory; when the computer program is executed by the processor, the processor executes the steps of a thin plate residual stress detection method based on thickness resonance mode as in any of the above embodiments.

[0152] An embodiment of the present invention further provides a computer-readable storage medium having a computer program / instruction stored thereon. When the computer program / instruction is executed by a processor, the steps of the thin plate residual stress detection method based on thickness resonance mode as in any of the above embodiments are implemented.

[0153] An embodiment of the present invention further provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of a thin plate residual stress detection method based on thickness resonance mode as in any of the above embodiments.

[0154] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described system and module can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0155] In the several embodiments provided in the present application, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0156] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0157] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0158] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0159] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting residual stress of a thin plate based on thickness resonance mode, characterized in that: include: Obtaining a dispersion curve of the thin plate to be tested, and determining a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve; Performing a stress coefficient calibration experiment on the thin plate to be tested to determine experimental Lamb wave A-scan data of different stresses; Determining a stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each of the experimental Lamb wave A-scan data; Exciting a Lamb wave signal to a preset excitation point of the thin plate to be tested, and determining corresponding measured Lamb wave A-scan data; Based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, the residual stress of the thin plate to be measured is determined using the stress-thickness resonance normalized amplitude curve.

2. The thin plate residual stress detection method based on thickness resonance mode according to claim 1 is characterized in that: The step of obtaining a dispersion curve of the thin plate to be tested and determining a theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve comprises: Acquiring structural parameters of the thin plate to be tested, and determining a dispersion curve of the thin plate to be tested based on the structural parameters; Determine the theoretical frequency-thickness product of the S1 thickness resonance mode according to the dispersion curve; The plate thickness is extracted from the structural parameters, and a ratio operation is performed between the theoretical frequency-thickness product and the plate thickness to output a theoretical thickness resonance frequency.

3. The thin plate residual stress detection method based on thickness resonance mode according to claim 1 is characterized in that: Determining the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each of the experimental Lamb wave A-scan data comprises: Extracting the corresponding resonance wave time domain signal from each of the experimental Lamb wave A-scan data according to a preset time range; After windowing the time domain signals of the resonance waves by using the Hanning window function, fast Fourier transform is performed respectively, and amplitude normalization is performed using the amplitude of the S1 zero group velocity Lamb wave modal frequency as an indicator, and multiple experimental frequency domain graphs are output; The peak amplitude in each experimental frequency domain diagram that is closest to the theoretical thickness resonance frequency is taken as the corresponding theoretical thickness resonance normalized amplitude; The theoretical thickness resonance normalized amplitude and the associated stress are used to perform curve fitting to generate a stress-thickness resonance normalized amplitude curve.

4. The thin plate residual stress detection method based on thickness resonance mode according to claim 1 is characterized in that: The residual stress of the thin plate to be measured is determined by using the stress-thickness resonance normalized amplitude curve based on the measured thickness resonance normalized amplitude determined by the measured Lamb wave A-scan data, including: Performing a windowed fast Fourier transform on the resonance wave time domain signal in the measured A-scan data within a preset time range, and outputting a measured frequency domain graph; Determining a measured thickness resonance normalized amplitude of the S1 thickness resonance mode from the measured frequency domain diagram according to the theoretical thickness resonance frequency; The measured thickness resonance normalized amplitude is input into the stress-thickness resonance normalized amplitude curve for solution, and the residual stress of the thin plate to be measured is output.

5. The thin plate residual stress detection method based on thickness resonance mode according to claim 1 is characterized in that: The excitation points are multiple; and further include: The thin plate to be tested is mechanically scanned to determine the residual stresses at multiple excitation points, and the residual stresses are used to construct the residual stress field of the thin plate to be tested.

6. A thin plate residual stress detection system based on thickness resonance mode, characterized in that: It includes a waveform generator, an amplifier, an incident probe, a receiving probe, an incident wedge, a receiving wedge, an oscilloscope, a processor and a universal testing machine; The waveform generator is connected to the amplifier, and the amplifier is connected to the incident probe; The processor is connected to the oscilloscope, and the oscilloscope is connected to the receiving probe; The incident probe is connected to the thin plate to be tested through the incident wedge according to a preset incident angle, the receiving probe is connected to the thin plate to be tested through the receiving wedge, and the universal testing machine is connected to the thin plate to be tested; The universal testing machine is used to perform stress coefficient calibration experiments of different stresses on the thin plate to be tested; The waveform generator is used to generate an excitation signal, which is amplified by an amplifier and then transmitted to the incident probe to generate an incident ultrasonic signal; The incident wedge is used to convert the ultrasonic signal into a Lamb wave signal and excite the thin plate to be tested; The receiving wedge is used to transmit the Lamb wave signal returned by the thin plate to be tested to the receiving probe to generate a receiving ultrasonic signal; The oscilloscope is used to generate experimental Lamb wave A-scan data or measured Lamb wave A-scan data of different stresses according to the received ultrasonic signal; The processor is used to obtain a dispersion curve of the thin plate to be tested, and determine the theoretical thickness resonance frequency of the S1 thickness resonance mode according to the dispersion curve; determine the stress-thickness resonance normalized amplitude curve associated with the theoretical thickness resonance frequency according to the resonance wave time domain signal of each experimental Lamb wave A-scan data; and determine the residual stress of the thin plate to be tested using the stress-thickness resonance normalized amplitude curve based on the measured thickness resonance normalized amplitude determined based on the measured Lamb wave A-scan data.

7. The thin plate residual stress detection system based on thickness resonance mode according to claim 6 is characterized in that: When determining the measured Lamb wave A-scan data, the incident wedge and the receiving wedge may also be both air or water.

8. The thin plate residual stress detection system based on thickness resonance mode according to claim 6 or 7, characterized in that: The process of determining the incident angle includes: Determining the phase velocity of the S1 zero group velocity Lamb wave mode based on the dispersion curve; The incident angle is determined by performing an inverse sine operation on the ratio of the longitudinal wave velocity in the incident wedge or water or air to the phase velocity.

9. A computer device, characterized in that: It comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the thin plate residual stress detection method based on thickness resonance mode as described in any one of claims 1 to 5.

10. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the thin plate residual stress detection method based on thickness resonance mode as described in any one of claims 1 to 5 are implemented.

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