Nondestructive measurement method and system for residual stress of basin-type insulator

Abstract

The invention belongs to the technical field of stress detection, and relates to a nondestructive measurement method and system for residual stress of a basin-type insulator. The method comprises the following steps: acquiring a transverse wave acoustic elastic birefringence coefficient and a dual-frequency longitudinal wave acoustic elastic coefficient of a standard test block made of the same material as an insulator in different uniaxial stress states; obtaining the transverse wave propagation time of the polarization direction of the target point in the annular direction, the transverse wave propagation time of the polarization direction in the radial direction and the dual-frequency longitudinal wave propagation time of the insulator in the state of no external load; and acquiring circumferential residual stress and radial residual stress at the target point according to the transverse wave acoustic elasticity birefringence coefficient, the dual-frequency longitudinal wave acoustic elasticity coefficient, the transverse wave propagation time of which the polarization direction is in the circumferential direction, the transverse wave propagation time of which the polarization direction is in the radial direction and the dual-frequency longitudinal wave propagation time. Nondestructive testing of the residual stress of the epoxy resin part of the basin-type insulator is achieved, and directional analysis and independent measurement of a complex stress field are achieved.

Description

A non-destructive measurement method and system for residual stress in basin-type insulators Technical Field

[0001] This invention belongs to the field of stress detection technology, and relates to a non-destructive measurement method and system for residual stress in basin-type insulators. Background Technology

[0002] Pot-type insulators are critical insulating components in gas-insulated metal-enclosed switchgear (GIS). During manufacturing (e.g., cutting, casting) and subsequent service, their epoxy resin components are prone to residual stress due to process stresses, assembly forces, or temperature fields. Circumferential and radial residual stresses are the main concentrated and significantly harmful stress directions. These stresses severely weaken the dielectric strength and mechanical properties of the material, posing a significant threat to early insulator failures and the long-term reliability of GIS operations. Therefore, residual stress testing of the epoxy resin components of pot-type insulators is an important means of condition assessment, quality control, and preventative maintenance.

[0003] Currently, residual stress detection methods are mainly divided into two categories: destructive and non-destructive. Destructive methods (such as drilling and core drilling) can cause irreversible damage to components and are not suitable for in-service or pre-shipment testing. Among non-destructive methods, techniques such as X-ray diffraction and neutron diffraction are limited by equipment cost, environmental conditions, and radiation safety, making them difficult to apply in engineering sites. In contrast, ultrasonic testing technology based on the acoustoelastic effect has significant advantages such as being non-destructive, fast, low-cost, and highly adaptable, making it easy to implement in the field. Among these, piezoelectric ultrasonic methods, due to their flexible probe size and high excitation and reception efficiency, have become an important development direction for stress non-destructive testing.

[0004] However, directly applying existing ultrasonic methods to residual stress detection in basin-type insulators still faces challenges. First, the complex structure of basin-type insulators makes it difficult to accurately determine the actual stress distribution at the test point when external loads are applied. Second, their withstandable stress load range is limited (damage values ​​are only in the MPa range), far lower than that of regular epoxy resin samples (tensile stress damage values ​​are typically 60 to 80 MPa, and compressive stress damage values ​​are generally higher than 100 MPa), making direct calibration experiments for ultrasonic velocity information and stress unsuitable. Furthermore, the large thickness and curved geometry of basin-type insulator components impose specific requirements on the size, frequency, and other parameters of the contact piezoelectric ultrasonic probe. Meanwhile, existing quantitative models based on acoustoelastic effects typically rely on precise measurements of the absolute value of ultrasonic velocity, making them extremely sensitive to the measurement accuracy of material thickness or sound propagation path, thus limiting their engineering applicability to complex components in the field. Furthermore, existing ultrasonic testing methods for basin-type insulators generally lack the ability to resolve the directionality of residual stress fields. Most methods can only obtain a single index or equivalent value reflecting the overall stress level, but it is difficult to effectively separate and quantitatively characterize the actual, specifically oriented residual stress components within the insulator. Therefore, there is an urgent need for a residual stress detection method that can adapt to the structural characteristics of basin-type insulators, meet the requirements of on-site testing, and possess directional resolution and independent quantitative capabilities. Summary of the Invention

[0005] The purpose of this invention is to provide a non-destructive measurement method and system for residual stress in pot-type insulators, in order to solve the technical problems of how to achieve non-destructive, on-site, and high-precision quantitative measurement of residual stress inside epoxy resin in pot-type insulators, and how to independently and accurately separate and quantify the residual stress components in the circumferential and radial directions of epoxy resin.

[0006] To achieve the above objectives, the present invention employs the following technical solution: Firstly, the present invention provides a non-destructive measurement method for residual stress in a basin-type insulator, comprising the following steps: obtaining the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient of a standard test block made of the same insulating material as the insulator under different uniaxial stress states; obtaining the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time at a target point of the insulator under no external load conditions; and obtaining the circumferential residual stress and radial residual stress at the target point based on the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, the second frequency longitudinal wave acoustoelastic coefficient, the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time.

[0007] Secondly, the present invention provides a non-destructive testing system for residual stress in a basin-type insulator, comprising: an ultrasonic probe group, including a transverse wave probe with variable polarization direction, a first center frequency longitudinal wave probe, and a second center frequency longitudinal wave probe, wherein the first center frequency longitudinal wave probe and the second center frequency longitudinal wave probe are longitudinal wave probes with different center frequencies; the transverse wave probe, the first center frequency longitudinal wave probe, and the second center frequency longitudinal wave probe are used to emit and receive ultrasonic waves of corresponding types after contacting the surface of the insulator or standard test block under test; an ultrasonic excitation / receiving module, electrically connected to the ultrasonic probe group, is used to drive each probe in the ultrasonic probe group to emit ultrasonic waves and receive echo signals from each probe; and a standard test block data processing module is used to obtain data based on the echo signals received by the ultrasonic excitation / receiving module, the data being processed by the insulator using materials identical to those of the insulator. The standard test block has transverse wave acoustoelastic birefringence, first-frequency longitudinal wave acoustoelastic coefficient, and second-frequency longitudinal wave acoustoelastic coefficient under different uniaxial stress states; an insulator data processing module is used to obtain the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first-frequency longitudinal wave propagation time, and the second-frequency longitudinal wave propagation time at the target point of the insulator under no external load state, based on the echo signal received by the ultrasonic excitation / reception module; a residual stress acquisition module is used to obtain the circumferential residual stress and radial residual stress at the target point based on the transverse wave acoustoelastic birefringence, the first-frequency longitudinal wave acoustoelastic coefficient, the second-frequency longitudinal wave acoustoelastic coefficient, the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first-frequency longitudinal wave propagation time, and the second-frequency longitudinal wave propagation time.

[0008] Compared with existing technologies, this invention has the following advantages: By selecting a standard sample made of the same material as the epoxy resin insulation component of the basin insulator for wave velocity-stress calibration, this invention eliminates the need to apply external loads to the complex basin insulator body, effectively avoiding the engineering limitations of its small load-bearing range and difficulty in determining actual stress, thus improving the feasibility and accuracy of the calibration process. The invention employs a dual-frequency longitudinal wave method and calculations based on the relative wave velocity values ​​of acoustic anisotropy, replacing the requirement for precise measurement of the absolute material thickness in traditional acoustoelastic methods. This reduces the requirements for on-site testing conditions and improves the method's engineering applicability and on-site operability. By integrating ultrasonic transverse wave birefringence and dual-frequency longitudinal wave measurement technologies, the circumferential and radial residual stress components inside the epoxy resin insulation component of the basin insulator can be separated and quantitatively detected, achieving directional analysis and independent measurement of complex stress fields. This provides more accurate key parameters for insulator manufacturing process quality assessment and service reliability analysis. This invention enables non-destructive testing of residual stress in the epoxy resin portion of pot-type insulators, avoiding damage to the insulator structure caused by destructive methods such as drilling, and ensuring the integrity of the equipment and subsequent operational safety.

[0009] The system of this invention includes: an ultrasonic probe group, an ultrasonic excitation / receiving module, a standard test block data processing module, an insulator data processing module, and a residual stress acquisition module. The ultrasonic probe group includes a transverse wave probe with variable polarization direction, a first center frequency longitudinal wave probe, and a second center frequency longitudinal wave probe. The first and second center frequency longitudinal wave probes have opposite center frequencies. The transverse wave probe, the first center frequency longitudinal wave probe, and the second center frequency longitudinal wave probe are used to emit and receive corresponding types of ultrasonic waves after contacting the surface of the insulator or standard test block under test. The ultrasonic excitation / receiving module is electrically connected to the ultrasonic probe group and is used to drive each probe in the ultrasonic probe group to emit ultrasonic waves and receive echo signals from each probe. The standard test block data processing module is used to acquire, based on the echo signals received by the ultrasonic excitation / receiving module, the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient of a standard test block with the same insulating material as the insulator under different uniaxial stress states. By analyzing the changes under different known stresses, the transverse wave acoustoelastic birefringence coefficient and the dual-frequency longitudinal wave acoustoelastic coefficient are calculated, providing accurate model parameters for subsequent stress calculations. The insulator data processing module, based on the output of the signal processing module, acquires the circumferential transverse wave propagation time, radial transverse wave propagation time, first-frequency longitudinal wave propagation time, and second-frequency longitudinal wave propagation time at the target point under no external load conditions. The residual stress acquisition module acquires the circumferential and radial residual stresses at the target point based on the transverse wave acoustoelastic birefringence coefficient, the first-frequency longitudinal wave acoustoelastic coefficient, the second-frequency longitudinal wave acoustoelastic coefficient, the circumferential transverse wave propagation time, the radial transverse wave propagation time, the first-frequency longitudinal wave propagation time, and the second-frequency longitudinal wave propagation time. These modules work together to achieve non-destructive testing of the residual stress in the epoxy resin portion of the basin insulator, realizing directional analysis and independent measurement of complex stress fields. Attached Figure Description

[0010] Figure 1 is a flowchart of the method according to an embodiment of the present invention; Figure 2 is a system block diagram according to an embodiment of the present invention; Figure 3 is a flowchart of a non-destructive measurement method for residual stress of a basin-type insulator according to another embodiment of the present invention; Figure 4 is a waveform diagram of the transverse ultrasonic signal of a standard test block of epoxy resin composite material; Figure 5 is a waveform diagram of the longitudinal ultrasonic signal of a standard test block of epoxy resin composite material; Figure 6 is the acoustic anisotropy and stress linear fitting results of epoxy resin composite material; Figure 7 is the linear fitting results of the longitudinal wave velocity and stress at the first center frequency of epoxy resin composite material; Figure 8 is a schematic diagram of the circumferential-radial local coordinate system of a basin-type insulator; Figure 9 is a schematic diagram of the radial-axial local coordinate system of a basin-type insulator; Figure 10 is a waveform diagram of the ultrasonic signal of an epoxy resin insulating component of a basin-type insulator.

[0011] Among them, 1. Insulator; 2. Target point. Detailed Implementation

[0012] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0013] It should be noted that the terms "first," "second," etc., in the specification and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0014] The present invention will be further described in detail below with reference to the accompanying drawings: Embodiment 1: Referring to Figure 1, this embodiment discloses a non-destructive measurement method for residual stress of a basin-type insulator, including the following steps: S1, obtaining the transverse wave acoustoelastic birefringence coefficient of a standard test block with the same insulating material as the insulator 1 under different uniaxial stress states. First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient This method achieves high-precision and repeatable calibration of the intrinsic acoustoelastic properties of materials. It avoids the problem of destructive or inaccurate stress loading on complex and fragile basin-type insulators, ensuring the integrity of the equipment and the safety of subsequent operation.

[0015] In a preferred embodiment of the present invention, the transverse wave acoustoelastic birefringence coefficient of a standard test block made of the same insulating material as the insulator 1 under different uniaxial stress states is obtained. First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient This includes: acquiring multiple sets of different uniaxial stresses collected from the standard test block in the pulse-echo mode of the ultrasonic testing system. The ultrasonic data includes: shear wave data with polarization direction perpendicular to the stress direction, shear wave data with polarization direction parallel to the stress direction, longitudinal wave data at a first frequency, and longitudinal wave data at a second frequency; the shear wave velocity with polarization direction perpendicular to the stress direction is obtained based on the shear wave data with polarization direction perpendicular to the stress direction. Based on the transverse wave data with polarization direction parallel to stress direction, obtain the transverse wave velocity with polarization direction parallel to stress. The first frequency longitudinal wave velocity is obtained based on the first frequency longitudinal wave data. The second frequency longitudinal wave velocity is obtained based on the second frequency longitudinal wave data. In a preferred embodiment of the present invention, the method further includes: extracting the peak time of the first echo and the peak time of the second echo from the ultrasound data, and obtaining a time interval based on the peak time of the first echo and the peak time of the second echo. According to the first time interval The thickness of the standard test block and the transverse wave data with polarization direction perpendicular to the stress direction are used to obtain the transverse wave velocity with polarization direction perpendicular to the stress. According to the second time interval The thickness of the standard test block and the transverse wave data with polarization direction parallel to the stress direction are used to obtain the transverse wave velocity with polarization direction parallel to the stress. According to the third time interval The thickness of the standard test block and the first frequency longitudinal wave data are used to obtain the first frequency longitudinal wave velocity. According to the fourth time interval The thickness of the standard test block and the second frequency longitudinal wave data are used to obtain the second frequency longitudinal wave velocity. .

[0016] In a preferred embodiment of the present invention, the formulas for obtaining the transverse wave velocity perpendicular to the stress, the transverse wave velocity parallel to the stress, the first frequency longitudinal wave velocity, and the second frequency longitudinal wave velocity are as follows:

[0017]

[0018] in, This represents the peak moment of an echo; This is the peak moment of the second echo; For time intervals; The transverse wave velocity is the one whose polarization direction is perpendicular to the stress. The transverse wave velocity is the one whose polarization direction is parallel to the stress. The first frequency longitudinal wave velocity, The second frequency longitudinal wave velocity; The thickness is the standard test block thickness.

[0019] Based on the transverse wave velocity whose polarization direction is perpendicular to the stress... and the transverse wave velocity whose polarization direction is parallel to the stress. Obtaining acoustic anisotropy The acoustic anisotropy The formula for obtaining it is as follows:

[0020] in, For the first Uniaxial stress Acoustic anisotropy at the following levels; The transverse wave velocity is the one whose polarization direction is perpendicular to the stress. The transverse wave velocity is the one whose polarization direction is parallel to the stress.

[0021] Multiple sets of different uniaxial stresses Acoustic anisotropy First frequency longitudinal wave velocity Second frequency longitudinal wave velocity respectively with the corresponding uniaxial stress Linear fitting was performed to obtain the transverse wave acoustoelastic birefringence coefficient. First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient .

[0022] The transverse wave acoustic elastic birefringence coefficient First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient The linear fitting formula is as follows:

[0023]

[0024]

[0025] in, For the first Uniaxial stress Acoustic anisotropy at the following levels; For the first Group of uniaxial stresses; The reference wave velocity of the first frequency longitudinal wave under zero stress is given. This is the reference wave velocity of the second frequency longitudinal wave under zero stress. The transverse wave acoustoelastic birefringence coefficient; The first frequency longitudinal wave acoustic elastic coefficient; The second frequency longitudinal wave acoustic elastic coefficient; The first frequency longitudinal wave velocity, The second frequency longitudinal wave velocity.

[0026] S2, obtain the transverse wave propagation time along the circumferential direction of the polarization direction at target point 2 of the insulator 1 under no external load condition. Transverse wave propagation time along the radial direction of polarization First frequency longitudinal wave propagation time and the propagation time of the second frequency longitudinal wave This step is mainly used to obtain the ultrasonic wave propagation time at target point 2 of insulator 1, realizing non-destructive data acquisition of the stress state at the test point of the basin insulator.

[0027] In a preferred embodiment of the present invention, the method of obtaining the transverse wave propagation time along the circumferential direction of the polarization direction of the target point 2 of the insulator 1 under no external load is described. Transverse wave propagation time along the radial direction of polarization First frequency longitudinal wave propagation time and the propagation time of the second frequency longitudinal wave The method includes: acquiring the transverse wave signal along the circumferential direction, the transverse wave signal along the radial direction, the first frequency longitudinal wave signal, and the second frequency longitudinal wave signal of the target point 2 of the insulator 1 under no external load conditions; and acquiring the transverse wave propagation time along the circumferential direction based on the transverse wave signal along the circumferential direction, the transverse wave signal along the radial direction, the first frequency longitudinal wave signal, and the second frequency longitudinal wave signal. Transverse wave propagation time along the radial direction of polarization First frequency longitudinal wave propagation time and the propagation time of the second frequency longitudinal wave .

[0028] S3, based on the transverse wave acoustoelastic birefringence coefficient The first frequency longitudinal wave acoustic elastic coefficient The second frequency longitudinal wave acoustic elastic coefficient The propagation time of the transverse wave along the circumferential direction of the polarization direction. The propagation time of the transverse wave along the radial direction of the polarization direction. The propagation time of the first frequency longitudinal wave and the propagation time of the second frequency longitudinal wave Obtain the circumferential residual stress at the target point. and radial residual stress This method enables independent and quantitative calculation of residual stress components in two directions, overcoming the limitation of previous methods that could only provide equivalent uniaxial stress, and achieving accurate analysis of the direction of the residual stress field.

[0029] In a preferred embodiment of the present invention, the circumferential residual stress at the target point and radial residual stress The formula for obtaining it is as follows:

[0030] in, The circumferential residual stress component to be determined; Let be the radial residual stress component to be determined; The propagation time of the transverse wave along the circumferential direction of polarization; The propagation time of the transverse wave along the radial direction of polarization; The propagation time of the first frequency longitudinal wave; The propagation time of the second frequency longitudinal wave; The reference wave velocity of the first frequency longitudinal wave under zero stress is given. This is the reference wave velocity of the second frequency longitudinal wave under zero stress. The transverse wave acoustoelastic birefringence coefficient; The first frequency longitudinal wave acoustic elastic coefficient; The second frequency longitudinal wave acoustic elastic coefficient is denoted as .

[0031] This invention enables non-destructive testing of residual stress in the epoxy resin portion of basin-type insulators, avoiding damage to the insulator structure caused by destructive methods such as drilling, thus ensuring the integrity of the equipment and subsequent operational safety. By selecting a standard sample of the same material as the epoxy resin insulation component of the basin-type insulator for wave velocity-stress calibration, this invention eliminates the need to apply external loads to the complex basin-type insulator body, effectively circumventing the engineering limitations of its limited load-bearing range and difficulty in determining actual stress, thereby improving the feasibility and accuracy of the calibration process. This invention employs a dual-frequency longitudinal wave method and calculates and analyzes wave velocities based on acoustic anisotropy, replacing the requirement for precise measurement of the absolute material thickness in traditional acoustoelastic methods, reducing the requirements for on-site testing conditions, and improving the method's engineering applicability and on-site operability. This invention integrates ultrasonic transverse wave birefringence and dual-frequency longitudinal wave measurement technologies, enabling the separation and quantitative detection of circumferential and radial residual stress components within the epoxy resin insulation component of the basin-type insulator. It achieves directional analysis and independent measurement of complex stress fields, thus providing more accurate key parameters for insulator manufacturing process quality assessment and service reliability analysis.

[0032] Referring to Figure 2, based on the above method, the present invention also discloses a non-destructive measurement system for residual stress of a basin-type insulator, comprising: an ultrasonic probe group, including a transverse wave probe with variable polarization direction, a first center frequency longitudinal wave probe, and a second center frequency longitudinal wave probe, wherein the first center frequency longitudinal wave probe and the second center frequency longitudinal wave probe are longitudinal wave probes with different center frequencies; the transverse wave probe, the first center frequency longitudinal wave probe, and the second center frequency longitudinal wave probe are used to emit and receive ultrasonic waves of corresponding types after contacting the surface of the insulator or standard test block under test.

[0033] An ultrasonic excitation / receiving module is electrically connected to the ultrasonic probe group and is used to drive each probe in the ultrasonic probe group to emit ultrasonic waves and receive echo signals from each probe.

[0034] The standard test block data processing module is used to obtain the transverse wave acoustoelastic birefringence coefficient of a standard test block made of the same insulating material as the insulator under different uniaxial stress states, based on the echo signal received by the ultrasonic excitation / reception module. First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient By analyzing the variations under different known stresses, the acoustoelastic birefringence coefficient of transverse waves and the acoustoelastic coefficient of longitudinal waves with two frequencies were calculated, providing accurate model parameters for subsequent stress calculations.

[0035] The insulator data processing module is used to obtain the transverse wave propagation time along the circumferential direction of the polarization direction at target point 2 of the insulator under no external load condition, based on the echo signal received by the ultrasonic excitation / reception module. Transverse wave propagation time along the radial direction of polarization First frequency longitudinal wave propagation time and the propagation time of the second frequency longitudinal wave .

[0036] The residual stress acquisition module is used to obtain the residual stress based on the shear wave acoustoelastic birefringence coefficient. The first frequency longitudinal wave acoustic elastic coefficient The second frequency longitudinal wave acoustic elastic coefficient The propagation time of the transverse wave along the circumferential direction of the polarization direction. The propagation time of the transverse wave along the radial direction of the polarization direction. The propagation time of the first frequency longitudinal wave and the propagation time of the second frequency longitudinal wave Obtain the circumferential residual stress at target point 2. and radial residual stress .

[0037] The system of the present invention further includes: a rectangular coordinate system constructed with the target point 2 as the center and the circumferential, radial, and axial directions, as shown in Figures 8 and 9, wherein the x-axis is located in the radial direction, the y-axis is located in the circumferential direction, and the z-axis is located in the axial direction; during measurement, the polarization direction of the transverse wave probe is aligned with the circumferential and radial directions in the local rectangular coordinate system of the circumferential, radial, and axial directions; the material formulation and curing process of the standard test block are exactly the same as those of the epoxy resin insulating part of the pot insulator to be tested.

[0038] The various modules of this invention work together to achieve non-destructive testing of residual stress in the epoxy resin portion of basin-type insulators, and to realize directional analysis and independent measurement of complex stress fields.

[0039] Example 2: The purpose of this example is to ensure that the basin-type insulator structure is not damaged and no external stress load is applied, while measuring the acoustoelastic coefficient of the epoxy resin insulation material of the basin-type insulator based on the acoustoelastic birefringence effect and the principle of dual-frequency longitudinal wave measurement technology, and calculating the circumferential and radial residual stresses at the measurement points of the basin-type insulator. Referring to Figure 3, the specific steps are as follows: Step 1, Material acoustoelastic coefficient calibration: S11, Construct an ultrasonic testing system, including an ultrasonic excitation / receiving module, a signal processing module, and an ultrasonic probe group; the probe group includes a transverse wave probe with variable polarization direction and two longitudinal wave probes with different center frequencies; since the load-bearing range of the basin-type insulator is small, and the actual external stress at the measurement point is difficult to determine, directly performing wave velocity-stress calibration on it would result in a large error. Therefore, a standard test block with the same material and process as the epoxy resin insulation material of the basin-type insulator under test is used, and the experiment is conducted under uniaxial stress loading conditions.

[0040] S12, using the ultrasonic testing system in pulse-echo mode, acquire data on the standard test block under m different uniaxial stresses. Ultrasound data below; defined in the first Group stress Next, from the first The ultrasound data acquired by the probe is ,in This indicates a transverse wave probe whose polarization direction is perpendicular to the direction of stress application. This indicates a transverse wave probe whose polarization direction is parallel to the direction of stress application. This indicates the first center frequency longitudinal wave probe. This indicates the second center frequency longitudinal wave probe. See Figure 4 for the ultrasonic shear wave signal waveform of the epoxy resin composite standard specimen; see Figure 5 for the longitudinal wave ultrasonic signal waveform of the epoxy resin composite standard specimen.

[0041] S13, for each set of stresses Ultrasound data below (j=1, 2, 3, 4), extract the peak time of each echo. Peak time of the second echo Calculate the time interval The This indicates the propagation time of the ultrasonic wave from the top surface to the bottom surface and then back to the top surface within the test block; based on the thickness of the test block. The propagation path length of the ultrasonic signal in the test block is 2. Calculate according to the following formula;

[0042] The calculated transverse wave velocity is perpendicular to the stress direction. transverse wave velocity with polarization direction parallel to stress First frequency longitudinal wave velocity Second frequency longitudinal wave velocity Subsequently, the same stress The transverse wave velocities obtained in the two polarization directions and Substitute acoustic anisotropy The calculation formula is used to calculate the acoustic anisotropy. ;

[0043] S14, based on the m sets of experimental data, the acoustic anisotropy degree First frequency longitudinal wave velocity and the second frequency longitudinal wave velocity respectively with the corresponding uniaxial stress Perform linear fitting, where the fitting relationships are as follows:

[0044]

[0045]

[0046] in, Let be the reference wave velocity of the first frequency longitudinal wave under zero stress. The reference wave velocity of the second frequency longitudinal wave under zero stress is used; the transverse wave acoustoelastic birefringence coefficient of the material is determined by fitting. First frequency longitudinal wave acoustic elastic coefficient and the second frequency longitudinal wave acoustic elastic coefficient See Figure 6 for the acoustic anisotropy and stress linear fitting results of the epoxy resin composite material, and see Figure 7 for the longitudinal wave velocity and stress linear fitting results of the epoxy resin composite material at the first center frequency.

[0047] Step 2, Stress Measurement and Inversion of the Insulator Under Test: S21, using the same ultrasonic testing system, the target area of ​​the basin-type insulator under test, which is in a state without external load, is tested. The transverse wave signal with polarization direction along the circumferential direction, the transverse wave signal with polarization direction along the radial direction, the first frequency longitudinal wave signal, and the second frequency longitudinal wave signal are acquired sequentially at the measurement point. See Figure 10 for the ultrasonic signal waveform diagram of the epoxy resin insulation component of the basin-type insulator.

[0048] S22, Process the above measurement signal according to the method described in S13, and calculate the circumferential shear wave propagation time corresponding to the measurement point. Radial transverse wave propagation time First frequency longitudinal wave propagation time and the propagation time of the second frequency longitudinal wave S23, Based on the acoustoelastic birefringence effect and the principle of dual-frequency longitudinal wave measurement technology, establish a set of equations, and substitute the obtained propagation time and the original wave velocity and corresponding coefficients calibrated in step one into the equations:

[0049] in, and These represent the circumferential and radial residual stress components to be determined. Solving the above system of equations yields the circumferential residual stress at the measurement point of the basin-type insulator. and radial residual stress .

[0050] To ensure the consistency of the measurement benchmark, the directionality mentioned in the method of this invention is clearly defined: a circumferential-radial-axial local rectangular coordinate system is established at the measurement point of the epoxy resin insulating component of the basin insulator. This coordinate system is centered on the measurement point, with the circumferential and radial axes located within the tangent plane at that point on the insulating component, and the axial axis perpendicular to this tangent plane. The shear wave probe involved in the method of this invention has its polarization direction strictly aligned with the circumferential and radial axes of this coordinate system for measurement. See Figure 8, which is a schematic diagram of the circumferential-radial-axial local coordinate system of the basin insulator.

[0051] The above method is based on the premise that the acoustic anisotropy of the material in the tested part of the basin insulator is entirely caused by stress, and not by the grain orientation or other non-stress factors. When using the piezoelectric ultrasonic testing system to test the GIS basin insulator, considering its large thickness, certain curvature, and the strong attenuation of ultrasonic waves by the epoxy resin material, a suitable ultrasonic probe with appropriate crystal size and signal frequency should be selected to verify the sample before implementing the testing steps, ensuring that a valid ultrasonic echo signal can be received.

[0052] This invention enables non-destructive testing of residual stress in the epoxy resin portion of basin-type insulators, avoiding damage to the insulator structure caused by destructive methods such as drilling, thus ensuring the integrity of the equipment and subsequent operational safety. By selecting a standard sample of the same material as the epoxy resin insulation component of the basin-type insulator for wave velocity-stress calibration, this invention eliminates the need to apply external loads to the complex basin-type insulator body, effectively circumventing the engineering limitations of its limited load-bearing range and difficulty in determining actual stress, thereby improving the feasibility and accuracy of the calibration process. This invention employs a dual-frequency longitudinal wave method and calculates and analyzes wave velocities based on acoustic anisotropy, replacing the requirement for precise measurement of the absolute material thickness in traditional acoustoelastic methods, reducing the requirements for on-site testing conditions, and improving the method's engineering applicability and on-site operability. This invention integrates ultrasonic transverse wave birefringence and dual-frequency longitudinal wave measurement technologies, enabling the separation and quantitative detection of circumferential and radial residual stress components within the epoxy resin insulation component of the basin-type insulator. It achieves directional analysis and independent measurement of complex stress fields, thus providing more accurate key parameters for insulator manufacturing process quality assessment and service reliability analysis.

[0053] Example 3: The specific implementation of the present invention is illustrated in conjunction with Figures 2 to 10, demonstrating the experimental process and results of measuring the residual stress of epoxy resin insulation components of basin insulators using the described method.

[0054] The experiment employed an arbitrary waveform ultrasonic module (UT-WAVE, TECLAB) to construct the detection system. The excitation signal was set as a sinusoidal modulated wave with a center frequency matched to the probe's nominal frequency and a cycle count of 5. The probes used included a shear wave probe with a center frequency of 1 MHz and longitudinal wave probes with center frequencies of 1 MHz and 5 MHz, respectively. The epoxy resin standard specimen used for calibration was 100 mm × 40 mm × 10 mm in size. A uniaxial gradient stress was applied to the standard specimen using an electro-hydraulic servo universal testing machine, with the stress change rate controlled within 0.5 MPa / min to ensure quasi-static loading conditions. At each set stress level, five sets of ultrasonic echo signals were repeatedly acquired, with each set representing the result of 100 synchronous averages to improve the signal-to-noise ratio.

[0055] The acquired raw ultrasonic signals were digitally bandpass filtered. The passband was set according to the probe frequency: 0.5-1.5 MHz for a 1 MHz shear wave signal; 0.5-2 MHz for a 1 MHz longitudinal wave signal; and 2-10 MHz for a 5 MHz longitudinal wave signal. By processing the filtered signals, the ultrasonic velocity under different stress states was calculated. Then, the wave velocity (and acoustic anisotropy) was linearly least-squared-fitted with the applied stress to calibrate the shear wave acoustoelastic birefringence coefficient of the epoxy resin material, as well as the longitudinal wave acoustoelastic coefficients corresponding to 1 MHz and 5 MHz.

[0056] Figures 2 and 3 show typical transverse and longitudinal ultrasonic signal waveforms collected on epoxy resin specimens, respectively. Figures 4 and 5 show the acoustic anisotropy calculated from the transverse wave data and the relationship and fitting curves of longitudinal wave velocity with stress. Experimental data show that the correlation coefficients of each fitting curve are all above 0.91, confirming a good linear relationship between acoustic parameters and stress, satisfying the basic assumptions of acoustoelasticity theory.

[0057] Based on the acoustoelastic coefficient obtained from the above calibration, this testing system was applied to actual pot-type insulator specimens. By measuring the circumferential and radial transverse wave acoustic time and the dual-frequency longitudinal wave acoustic time at the test point, and substituting these measurements into a set of equations that integrate the principles of acoustoelastic birefringence and dual-frequency longitudinal waves, a rapid, quantitative, and non-destructive assessment of the circumferential and radial residual stress components inside the epoxy resin component of the insulator can be achieved.

[0058] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A non-destructive measurement method for residual stress in a basin-type insulator, characterized in that, Includes the following steps: Obtain the transverse wave acoustoelastic birefringence, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient of a standard test block made of the same insulating material as the insulator under different uniaxial stress states; obtain the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time at the target point of the insulator under no external load conditions; based on the transverse wave acoustoelastic birefringence, the first frequency longitudinal wave acoustoelastic coefficient, the second frequency longitudinal wave acoustoelastic coefficient, the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time, obtain the circumferential residual stress and radial residual stress at the target point.

2. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 1, characterized in that, The acquisition of the transverse wave acoustoelastic birefringence, the first-frequency longitudinal wave acoustoelastic coefficient, and the second-frequency longitudinal wave acoustoelastic coefficient of a standard test block made of the same insulating material as the insulator under different uniaxial stress states includes: acquiring multiple sets of ultrasonic data under different uniaxial stresses collected by the standard test block in the pulse-echo mode of an ultrasonic testing system; the ultrasonic data includes: transverse wave data with polarization direction perpendicular to the stress direction, transverse wave data with polarization direction parallel to the stress direction, first-frequency longitudinal wave data, and second-frequency longitudinal wave data; acquiring the transverse wave velocity with polarization direction perpendicular to the stress direction based on the transverse wave data with polarization direction perpendicular to the stress direction; and acquiring the transverse wave velocity with polarization direction perpendicular to the stress based on the... The transverse wave velocity with the polarization direction parallel to the stress direction is obtained from the transverse wave data. The first frequency longitudinal wave velocity is obtained from the first frequency longitudinal wave data. The second frequency longitudinal wave velocity is obtained from the second frequency longitudinal wave data. The acoustic anisotropy is obtained from the transverse wave velocity with the polarization direction perpendicular to the stress and the transverse wave velocity with the polarization direction parallel to the stress. The acoustic anisotropy, the first frequency longitudinal wave velocity, and the second frequency longitudinal wave velocity under multiple sets of different uniaxial stresses are linearly fitted with the corresponding uniaxial stresses to obtain the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient.

3. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 2, characterized in that, Also includes: The peak times of the first and second echoes are extracted from the ultrasound data. A time interval is obtained based on the peak times of the first and second echoes. The transverse wave velocity with a polarization direction perpendicular to the stress direction is obtained based on the time interval, the thickness of the standard test block, and the transverse wave data with a polarization direction parallel to the stress direction. The transverse wave velocity with a polarization direction parallel to the stress direction is obtained based on the time interval, the thickness of the standard test block, and the transverse wave data with a polarization direction parallel to the stress direction. The first frequency longitudinal wave velocity is obtained based on the time interval, the thickness of the standard test block, and the first frequency longitudinal wave data. The second frequency longitudinal wave velocity is obtained based on the time interval, the thickness of the standard test block, and the second frequency longitudinal wave data.

4. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 3, characterized in that, The formulas for obtaining the transverse wave velocity perpendicular to the stress, the transverse wave velocity parallel to the stress, the first frequency longitudinal wave velocity, and the second frequency longitudinal wave velocity are as follows: in, This represents the peak moment of an echo; This is the peak moment of the second echo; For time intervals; The transverse wave velocity is the one whose polarization direction is perpendicular to the stress. The transverse wave velocity is the one whose polarization direction is parallel to the stress. The first frequency longitudinal wave velocity, The second frequency longitudinal wave velocity; The thickness is the standard test block thickness.

5. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 2, characterized in that, The formula for obtaining the acoustic anisotropy is as follows: in, For the first Acoustic anisotropy under uniaxial stress; The transverse wave velocity is the one whose polarization direction is perpendicular to the stress. The transverse wave velocity is the one whose polarization direction is parallel to the stress.

6. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 2, characterized in that, The linear fitting formulas for the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient are as follows: in, For the first Acoustic anisotropy under uniaxial stress; For the first Group of uniaxial stresses; The reference wave velocity of the first frequency longitudinal wave under zero stress is given. This is the reference wave velocity of the second frequency longitudinal wave under zero stress. The transverse wave acoustoelastic birefringence coefficient; The first frequency longitudinal wave acoustic elastic coefficient; The second frequency longitudinal wave acoustic elastic coefficient; The first frequency longitudinal wave velocity, The second frequency longitudinal wave velocity.

7. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 1, characterized in that, The step of obtaining the circumferential transverse wave propagation time, radial transverse wave propagation time, first frequency longitudinal wave propagation time, and second frequency longitudinal wave propagation time of the target point of the insulator under no external load condition includes: obtaining the circumferential transverse wave signal, radial transverse wave signal, first frequency longitudinal wave signal, and second frequency longitudinal wave signal of the target point of the insulator under no external load condition; and obtaining the circumferential transverse wave propagation time, radial transverse wave propagation time, first frequency longitudinal wave propagation time, and second frequency longitudinal wave propagation time based on the circumferential transverse wave signal, radial transverse wave signal, first frequency longitudinal wave signal, and second frequency longitudinal wave signal.

8. The non-destructive measurement method for residual stress in a basin-type insulator according to claim 1, characterized in that, The formulas for obtaining the circumferential and radial residual stresses at the target point are as follows: in, The circumferential residual stress component to be determined; Let be the radial residual stress component to be determined; The propagation time of the transverse wave along the circumferential direction of polarization; The propagation time of the transverse wave along the radial direction of polarization; The propagation time of the first frequency longitudinal wave; The propagation time of the second frequency longitudinal wave; The reference wave velocity of the first frequency longitudinal wave under zero stress is given. This is the reference wave velocity of the second frequency longitudinal wave under zero stress. The transverse wave acoustoelastic birefringence coefficient; The first frequency longitudinal wave acoustic elastic coefficient; The second frequency longitudinal wave acoustic elastic coefficient is denoted as .

9. A non-destructive measurement system for residual stress in a basin-type insulator, characterized in that, include: An ultrasonic probe assembly includes a transverse wave probe with variable polarization, a longitudinal wave probe with a first center frequency, and a longitudinal wave probe with a second center frequency. The first and second longitudinal wave probes have different center frequencies. The transverse wave probe, the first longitudinal wave probe, and the second longitudinal wave probe are used to emit and receive corresponding types of ultrasonic waves after contacting the surface of the insulator or standard test block under test. An ultrasonic excitation / receiving module is electrically connected to the ultrasonic probe assembly and is used to drive each probe in the ultrasonic probe assembly to emit ultrasonic waves and receive echo signals from each probe. The standard test block data processing module is used to obtain, based on the echo signal received by the ultrasonic excitation / receiving module, the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, and the second frequency longitudinal wave acoustoelastic coefficient of a standard test block with the same insulating material as the insulator under different uniaxial stress states; the insulator data processing module is used to obtain, based on the echo signal received by the ultrasonic excitation / receiving module, the transverse wave propagation time along the circumferential direction, the transverse wave propagation time along the radial direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time of the target point of the insulator under no external load state. The residual stress acquisition module is used to acquire the circumferential residual stress and radial residual stress at the target point based on the transverse wave acoustoelastic birefringence coefficient, the first frequency longitudinal wave acoustoelastic coefficient, the second frequency longitudinal wave acoustoelastic coefficient, the transverse wave propagation time along the circumferential direction of the polarization direction, the transverse wave propagation time along the radial direction of the polarization direction, the first frequency longitudinal wave propagation time, and the second frequency longitudinal wave propagation time.

10. The non-destructive testing system for residual stress in a basin-type insulator according to claim 9, characterized in that, Also includes: A rectangular coordinate system is constructed with the target point as the center and the circumferential, radial, and axial directions as the coordinates. During measurement, the polarization direction of the transverse wave probe is aligned with the circumferential and radial directions in the local rectangular coordinate system of the circumferential, radial, and axial directions. The material formula and curing process of the standard test block are exactly the same as those of the epoxy resin insulation part of the pot insulator to be tested.

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