An electronic speckle local heating type residual stress nondestructive testing device and method

Abstract

The application discloses a kind of local heating type residual stress nondestructive testing device and method of electronic speckle, belong to surface residual stress nondestructive testing field.Nondestructive testing device includes heating system, displacement measurement optical path system.Heating system front end vertical irradiation is tested sample surface, and the circular area covered by light spot is heating zone;In displacement measurement optical path system, first light splitting prism, first laser, second light splitting prism, second laser are sequentially arranged behind heating laser, and first mirror and second mirror are arranged on the two sides of light splitting prism along X direction, and third mirror and fourth mirror are arranged on the two sides of second light splitting prism along Y direction;CCD camera and polarizer are arranged on the side of tested sample.The residual stress of sample surface is released by the method of local heating, and the nondestructive testing device is designed, and the inversion method of residual stress is given, and the nondestructive testing of residual stress on the surface of complex structure can be realized.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing of surface residual stress, and relates to a local heating non-destructive testing device and method for residual stress using electron speckle. Background Technology

[0002] In the aerospace field, residual stress introduced during the manufacturing process of large components (such as fuselage frames, wing spars, and rocket fuel tanks) can accelerate component deformation and crack initiation, ultimately leading to component fracture and seriously threatening the safety and reliability of the equipment. Therefore, accurate detection of residual stress in large components is of great significance for ensuring the service performance of aerospace equipment.

[0003] Currently, commonly used methods for residual stress measurement include neutron diffraction, X-ray diffraction, and the pinhole method. However, these methods are significantly limited in practical applications by the size and structure of the components: neutron diffraction and X-ray diffraction require sophisticated equipment, have limited detection areas, and are difficult to apply to large components; the pinhole method is a micro-destructive testing method and is not suitable for the non-destructive evaluation of in-service components. Therefore, there is an urgent need to develop a residual stress testing technology that is not limited by space and can achieve in-situ non-destructive testing, especially for measuring residual stress on the surface of large structures, which has urgent and important engineering value.

[0004] In recent years, some patented technologies have been developed for nondestructive testing, but certain limitations still exist.

[0005] Chinese invention patent CN1793872A discloses a "non-destructive testing method for residual stress in micro-regions," which measures the change in lattice spacing (strain) using X-ray diffraction and then calculates the residual stress based on the principles of elasticity. However, this method is sensitive to the lattice distribution and surface morphology of the material, which can introduce measurement errors, leading to inaccurate residual stress measurements. Chinese invention patent CN120121192A discloses a "non-destructive testing method, device, and system for three-dimensional deformation field, residual strain field, and residual stress field." This method directly captures displacement values ​​using a CCD camera by utilizing changes in the surface grating before and after sample processing or heat treatment, and then infers the residual stress in the structure. However, the surface deformation caused by the release of residual stress only corresponds to elastic strain, and its strain amplitude is typically as low as 10. -5For deformations on the order of magnitude or even smaller, relying solely on a CCD camera system is insufficient to guarantee the accuracy of observation. Furthermore, due to the difficulty in creating grating marks on the surface during processing, this method cannot effectively detect residual stress in already processed samples. Chinese invention patent CN121521323A discloses a "Non-destructive Measurement Method for Residual Stress in Epoxy Insulators Based on Local Pyrogenetic Strain," which uses local pyrogenetic strain technology to acquire strain signals through strain gauges, thereby achieving non-destructive testing of residual stress. However, in actual testing, the strain amplitude is typically as low as 10... -5 The magnitude of the residual strain is even smaller, and the measurement accuracy of conventional strain gauges is insufficient to meet the detection requirements at this level. Furthermore, this method can only measure uniaxial residual strain and cannot directly measure multiaxial residual strain, thus making it unsuitable for working conditions under multiaxial residual stress states.

[0006] In summary, existing non-destructive testing methods for residual stress are limited by the microstructure of the surface and subsurface, the resolution of small strains, and the methods for non-destructive release of residual stress, making them difficult to apply in experimental engineering. Therefore, a non-destructive testing method for residual stress that is not limited by space, does not require structural damage, and can accurately capture micro-elastic strain information was designed. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a localized heating non-destructive testing device and method for residual stress using electron speckle. This invention achieves elastic release of residual stress on the sample surface through localized heating, designs a localized heating non-destructive testing device for residual stress using electron speckle, and provides an inversion method for residual stress, enabling non-destructive testing of residual stress on complex structural surfaces.

[0008] To achieve the above objectives, the technical solution adopted by the present invention includes the following: A localized heating non-destructive testing device for residual stress using electronic speckle, comprising a heating system and a displacement measurement optical path system.

[0009] The heating system is a heating laser used to heat the test sample.

[0010] The displacement measurement optical path system includes a first reflecting mirror, a second reflecting mirror, a first beam splitter, a first laser, a third reflecting mirror, a second beam splitter, a fourth reflecting mirror, a second laser, a CCD camera, a polarizing mirror, and a heating zone. The incident direction of the heating laser is defined as the Z-direction, the optical path directions of the first reflecting mirror, second reflecting mirror, and first beam splitter are defined as the X-direction, and the optical path directions of the third reflecting mirror, second beam splitter, and fourth reflecting mirror are defined as the Y-direction. The first reflecting mirror, second reflecting mirror, first beam splitter, and first laser form the X-direction displacement measurement optical path system, which is arranged in the XOZ plane. The third reflecting mirror, second beam splitter, fourth reflecting mirror, and second laser form the Y-direction displacement measurement optical path system, which is arranged in the YOZ plane. The front end of the heating laser perpendicularly illuminates the surface of the sample to be tested. The plane of residual stress to be measured on the sample lies in the XOY plane, and the circular area covered by the laser spot is the heating zone. The first beam splitter, the first laser, the second beam splitter, and the second laser are sequentially positioned behind the heating laser. The two sides of the beam splitter are provided with a first reflector and a second reflector along the X direction, and the two sides of the second beam splitter are provided with a third reflector and a fourth reflector along the Y direction. The CCD camera and the polarizing filter are positioned on the side of the sample to be tested.

[0011] In the X-direction displacement measurement optical path system: the laser emitted from the first laser passes through the first beam splitter and is divided into two coherent beams of equal energy. These beams are reflected by the first and second mirrors onto the entire surface of the test sample. The coherent light in the observation area of ​​the CCD camera on the test sample surface is diffusely reflected, first entering the polarizing mirror and then the target surface in the CCD camera to form an interference fringe pattern in the X direction.

[0012] In the optical path system for measuring displacement in the Y direction: the laser emitted from the second laser passes through the second beam splitter and is divided into two coherent beams of equal energy. These beams are reflected by the third and fourth mirrors onto the entire surface of the sample to be tested. The coherent light in the observation area of ​​the CCD camera on the sample surface is diffusely reflected and first enters the polarizing mirror before entering the target surface in the CCD camera to form an interference fringe pattern in the Y direction.

[0013] Furthermore, the XOZ plane where the X-direction displacement measurement optical path system is located is at a 90° angle to the YOZ plane where the Y-direction displacement measurement optical path system is located. The interference fringe patterns in the X-direction and Y-direction are perpendicular to each other.

[0014] A localized heating method for nondestructive testing of residual stress using electron speckle, based on the aforementioned localized heating method for nondestructive testing of residual stress using electron speckle, includes the following steps: Step 1: Spray white paint on the entire surface of the test sample to enable the CCD camera to capture the light intensity change before and after the deformation of the heated area. Coaxially clamp the Z-axis of the test sample and the Z-axis of the displacement measurement optical path system. Adjust the CCD camera so that it can capture the entire heated area on the test sample. Then, adjust the CCD camera to move the heated area to the center of the field of view. Step 2: After the test sample is clamped, measure the interference fringes in the X and Y directions before heating. Then, irradiate the heated area with a heating laser. After heating, turn off the heating laser and measure the interference fringes in the X and Y directions after heating. Output the light intensity of each pixel in the interference fringes before and after heating. The specific steps are as follows: Step 2.1: Before heating after the test sample is clamped: The first laser emits a 532nm wavelength laser beam, which is split into two coherent beams by the first beam splitter. These beams are reflected by the first and second mirrors, respectively, onto the test sample. After diffuse reflection, the two coherent beams first enter the polarizing mirror and then the 532nm wavelength channel in the CCD camera. By changing the deflection angle of the polarizing mirror to 0°, 90°, 180°, and 270°, the CCD camera captures the interference fringes formed by the mutual interference in the X direction at the corresponding angles, and outputs the light intensity of the corresponding pixel under the corresponding interference pattern. The 472nm wavelength laser emitted by the second laser is split into two coherent beams by the second beam splitter. These beams are reflected onto the test sample by the first and second mirrors, respectively. After diffuse reflection, the two coherent beams first enter the polarizing mirror and then the 472nm wavelength channel in the CCD camera. By changing the deflection angle of the polarizing mirror to 0°, 90°, 180°, and 270°, the CCD camera captures the interference fringes formed by the mutual interference at the corresponding angles, and outputs the light intensity of the corresponding pixel under the corresponding interference pattern. Step 2.2: Heat the heating area for 10~30s using a heating laser; Step 2.3: After heating, repeat step 2.1 to obtain the interference fringe patterns in the X and Y directions after heating, as well as the light intensity of the corresponding pixel under the corresponding interference pattern; Step 3: Combining the light intensity obtained from the CCD camera at 0°, 90°, 180°, and 270° in Steps 2.1 and 2.3, the phase corresponding to each pixel is obtained through a four-step phase-shifting method, and the phase difference of each pixel before and after heating is calculated. The specific calculation steps are as follows: Step 3.1: Calculate the phase of each pixel before and after heating using the four-step phase-shifting method, as shown in the following formula: (1) in, This indicates that the phase of each pixel is obtained by a four-step phase-shifting method before and after heating. I 1 represents the light intensity corresponding to each pixel at 0°; I 2 represents the light intensity corresponding to each pixel at 90°. I 3 represents the light intensity corresponding to each pixel at 180°. I 3 represents the light intensity corresponding to each pixel at 270°; Step 3.2: Subtract the phase difference before and after heating to calculate the phase difference of each pixel before and after heating. The calculation formula is as follows: (2) Where, ΔΦ( x , y ) represents the phase difference between each pixel before and after heating, Φ 加热后 ( x , y ) represents the phase of each pixel obtained by the four-step phase-shifting method after heating, Φ 加热前 ( x , y () indicates the phase of each pixel obtained by the phase shifting method in the first four steps of heating; Step 4: Based on the phase difference of each pixel calculated in Step 3.2, establish the X-direction displacement. u and displacement in the Y direction v The relationship between phase difference and phase difference is calculated using the following formula: (3) in, u Indicates displacement in the X direction. v Indicates displacement in the Y direction. i This indicates the incident angle of the laser beam from the first or second laser. l Indicates the wavelength of the laser light from the first or second laser; Step 5: Combining formula (3), by... u and v Perform differentiation, calculate the difference step size in the X and Y directions, then calculate the phase difference change in the X and Y direction difference step size directions, and finally obtain the strain components in the X and Y directions. Step 5.1: For u and v The specific formula for differentiation is as follows: (4) in, e res,x This represents the strain caused by residual stress in the X direction. e res,y ΔΦ represents the strain caused by residual stress in the Y direction. R ( x ,y ) represents the change in phase difference along the X-direction differential step size, ΔΦ G ( x , y ) represents the change in phase difference along the Y-direction differential step size, Δ x and Δ y This represents the difference step size in the X and Y directions. l R and l G This indicates the laser wavelengths corresponding to the first and second lasers. i R and i G This indicates the incident angle of the first and second lasers relative to the test sample; Step 5.2: Calculate the difference step size in the X and Y directions. The specific formula is as follows: (5) (6) in, n x This indicates the number of pixels during the X-direction differencing process. n y This indicates the number of pixels during the Y-direction differencing process. L This indicates the field of view of a CCD camera. W This indicates the field of view width of a CCD camera. N x This indicates the X-axis resolution of the CCD camera. N y This indicates the resolution in the Y direction of the CCD camera; Step 5.3: Calculate the phase difference change in the X and Y directions along the differential step size. The specific formula is as follows: (7) (8) Where, ΔΦ(Δ x , y ) represents the phase difference of the corresponding pixels after the X-direction differentiation, ΔΦ( x ,Δ y () represents the phase difference of the corresponding pixels after differential analysis in the Y direction; Step 5.4: Substitute formulas (5~8) into formula (4) to calculate the strain in the X and Y directions; Step 6: Based on the classic plane stress model and combined with the thermal strain caused by heating, the difference between the strain in the material calculated by the plane stress model and the thermal strain is the strain caused by residual stress. Step 6.1: Using the classic plane stress model, calculate the strain in the material. The specific formula is as follows: (9) in, E Indicates the elastic modulus. m Represents Poisson's ratio. s x This represents the stress component in the X direction. s y This represents the stress component in the Y direction. e x This represents the strain component in the X direction. e y Represents the strain component in the Y direction; Step 6.2: Calculate the thermal strain caused by heating. The specific formula is as follows: (10) Step 6.3: Subtract the thermal strain from the strain calculated using the plane stress model to calculate the strain caused by residual stress. The specific formula is as follows: (11) in, e T This represents the thermal strain at the corresponding temperature. α The coefficient of thermal expansion, Δ T This indicates a temperature rise.

[0015] Step 7: Solve the stress and strain equations in formula (11) to calculate the residual stress. The specific formula is as follows: (12) in, s res,x This represents the residual stress in the X direction. s res,y This represents the residual stress in the Y direction.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses local heating to achieve elastic release of residual stress, avoiding mechanical or chemical damage to the sample surface, which is beneficial to protecting the surface integrity and original state of the sample.

[0017] (2) The present invention is based on thermal stress inversion of residual stress. The measurement results of this method are not affected by the morphological fluctuations of the measured surface and the differences in the crystal orientation of the material, and have good applicability.

[0018] (3) This invention utilizes electronic speckle interferometry (ESPI) to reconstruct the strain generated by local heating. Since this strain is on the nanometer scale, the resolution of traditional CCD cameras combined with digital image correlation (DIC) or strain rosettes is difficult to meet the measurement accuracy requirements, while ESPI can achieve high-sensitivity full-field non-contact measurement. Attached Figure Description

[0019] Figure 1 This invention relates to a localized heating type non-destructive testing device for residual stress based on electronic speckle patterns. Figure 2 The pattern is an interference fringe. Figure 2 (a) in the image shows the interference fringe pattern in the X direction before heating; Figure 2 (b) in the image shows the interference fringe pattern in the Y direction before heating; Figure 3 This is a flowchart of a localized heating method for nondestructive testing of residual stress using electronic speckle. In the diagram: 1 heating laser, 2 first reflecting mirror, 3 second reflecting mirror, 4 first beam splitter, 5 first laser, 6 third reflecting mirror, 7 second beam splitter, 8 fourth reflecting mirror, 9 second laser, 10 CCD camera, 11 polarizing mirror, 12 heating zone. Detailed Implementation

[0020] The technical solutions in the design process of this invention will be clearly and completely described below in conjunction with the design concept of this invention.

[0021] This embodiment provides a localized heating type non-destructive testing device for residual stress using electronic speckle, such as... Figure 1 As shown, it includes a heating system and a displacement measurement optical path system. The heating system is a heating laser 1, which is used to heat the test sample.

[0022] The displacement measurement optical path system includes a first reflecting mirror 2, a second reflecting mirror 3, a first beam splitter 4, a first laser 5, a third reflecting mirror 6, a second beam splitter 7, a fourth reflecting mirror 8, a second laser 9, a CCD camera 10, a polarizing mirror 11, and a heating zone 12. The incident direction of the heating laser 1 is defined as the Z-direction, the optical path directions of the first reflecting mirror 2, the second reflecting mirror 3, and the first beam splitter 4 are defined as the X-direction, and the optical path directions of the third reflecting mirror 6, the second beam splitter 7, and the fourth reflecting mirror 8 are defined as the Y-direction. The first reflecting mirror 2, the second reflecting mirror 3, the first beam splitter 4, and the first laser 5 form the X-direction displacement measurement optical path system, which is arranged in the XOZ plane. The third reflecting mirror 6, the second beam splitter 7, the fourth reflecting mirror 8, and the second laser 9 form the Y-direction displacement measurement optical path system, which is arranged in the YOZ plane. The specific arrangement of the displacement measurement optical path system is as follows: The front end of the heating laser 1 vertically illuminates the surface of the test sample. The plane of the residual stress to be measured of the test sample is in the XOY plane, and the circular area covered by the laser spot is the heating area 12. The first beam splitter 4, the first laser 5, the second beam splitter 7, and the second laser 9 are sequentially arranged behind the heating laser 1. The beam splitter 4 has a first reflector 2 and a second reflector 3 arranged on both sides along the X direction, and the second beam splitter 7 has a third reflector 6 and a fourth reflector 8 arranged on both sides along the Y direction. The CCD camera 10 and the polarizing filter 11 are arranged on the side of the sample to be tested.

[0023] In the X-direction displacement measurement optical path system: the laser emitted from the first laser 5 passes through the first beam splitter prism 4 and is split into two coherent beams of equal energy. These beams are reflected by the first reflector 2 and the second reflector 3 onto the entire surface of the test sample. The coherent light in the observation area of ​​the CCD camera 10 on the surface of the test sample is diffusely reflected and first enters the polarizer 11 before entering the target surface in the CCD camera 10 to form an interference fringe pattern in the X direction.

[0024] In the optical path system for measuring displacement in the Y direction: the laser emitted from the second laser 9 is split into two coherent beams of equal energy by the beam splitter prism 7, and is reflected onto the entire surface of the test sample by the third reflector 6 and the fourth reflector 8, respectively. The coherent light in the observation area of ​​the CCD camera 10 on the surface of the test sample is diffusely reflected and first enters the polarizer 11 and then enters the target surface in the CCD camera 10 to form an interference fringe pattern in the Y direction.

[0025] In this embodiment, the XOZ plane where the X-direction displacement measurement optical path system is located is at a 90° angle to the YOZ plane where the Y-direction displacement measurement optical path system is located. The interference fringes in the X-direction are perpendicular to each other.

[0026] A localized heating nondestructive testing method for residual stress using electron speckle, the flowchart of which is shown below. Figure 3 As shown, the local heating type residual stress nondestructive testing device based on the above-mentioned electronic speckle includes the following steps: Step 1: Spray white paint on the surface of the 20mm×20mm test sample, clamp the Z-axis of the test sample plane to be measured coaxially with the Z-axis of the displacement measurement optical path system, and adjust the angle of the CCD camera 10 to move the heating area 12 to the center of the field of view. Step 2: After the test sample is clamped, measure the interference fringes in the X and Y directions before heating, as shown below. Figure 2 As shown, the heating area 12 is then irradiated by heating laser 1. After heating, heating laser 1 is turned off. The interference fringe patterns in the X and Y directions after heating are measured, and the light intensity of each pixel in the interference fringe patterns before and after heating is output. The specific steps are as follows: Step 2.1: After the test sample is clamped and before heating, the 532nm wavelength laser emitted by the first laser 5 is split into two coherent beams by the first beam splitter 4. These beams are reflected onto the test sample by the first reflecting mirror 2 and the second reflecting mirror 3, respectively. After diffuse reflection, the two coherent beams first enter the polarizer 11 and then the 532nm wavelength channel in the CCD camera 10. By changing the deflection angle of the polarizer 11, the CCD camera 10 captures the interference fringe patterns formed by mutual interference in the X direction at deflection angles of 0°, 90°, 180°, and 270°, and outputs the corresponding interference diagrams. The light intensity of the corresponding pixel under the case; the laser with a wavelength of 472nm emitted by the second laser 9 is split into two coherent beams by the second beam splitter 7, and reflected onto the test sample by the first reflector 6 and the second reflector 8 respectively. The two coherent beams enter the polarizer 11 first and then enter the 472nm channel of the CCD camera 10 after diffuse reflection. By changing the deflection angle of the polarizer 11, the CCD camera 10 captures the interference fringe pattern formed by mutual interference in the Y direction at deflection angles of 0°, 90°, 180° and 270°, and outputs the light intensity of the corresponding pixel under the corresponding interference pattern. Step 2.2: Use heating laser 1 to heat heating area 12 for 20 seconds, so that the temperature rises by 52K; Step 2.3: Increase the temperature by 52K, repeat step 2.1, and obtain the interference fringe patterns in the X and Y directions after heating, as well as the light intensity of the corresponding pixel under the corresponding interference pattern; Step 3: Combining the light intensity obtained by CCD camera 10 in Steps 2.1 and 2.3, the phase corresponding to each pixel is obtained through a four-step phase-shifting method, and the phase difference of each pixel before and after heating is calculated. The specific calculation steps are as follows: Step 3.1: Using the four-step phase-shifting method, substitute the light intensity obtained by CCD camera 10 in steps 2.1 and 2.3 to calculate the phase of each pixel before and after heating. The formula is as follows: (1) in, This indicates that the phase of each pixel is obtained by a four-step phase-shifting method before and after heating. I 1 represents the light intensity corresponding to each pixel at 0°; I 2 represents the light intensity corresponding to each pixel at 90°. I 3 represents the light intensity corresponding to each pixel at 180°. I 3 represents the light intensity corresponding to each pixel at 270°; Step 3.2: Subtract the phase of each pixel before and after heating to calculate the phase difference between the pixels before and after heating. The calculation formula is as follows: (2) Where, ΔΦ( x ,y ) represents the phase difference between each pixel before and after heating, Φ 加热后 ( x , y ) represents the phase of each pixel obtained by the four-step phase-shifting method after heating, Φ 加热前 ( x , y () indicates the phase of each pixel obtained by the phase shifting method in the first four steps of heating; Step 4: Based on the phase difference of each pixel calculated in Step 3.2, establish the X-direction displacement. u and displacement in the Y direction v The relationship between phase difference and phase difference is calculated using the following formula: (3) in, u Indicates displacement in the X direction. v Indicates displacement in the Y direction. i This indicates the incident angle of the laser from either the first laser 5 or the second laser 9. l This indicates the wavelength of the laser beam from the first laser 5 or the second laser 9; Step 5: Combining formula (3), by... u and v Perform differentiation, calculate the difference step size in the X and Y directions, then calculate the phase difference change in the X and Y direction difference step size directions, and finally obtain the strain components in the X and Y directions. Step 5.1: For u and v The specific formula for differentiation is as follows: (4) in, e res,x This represents the strain caused by residual stress in the X direction. e res,y ΔΦ represents the strain caused by residual stress in the Y direction. R ( x , y ) represents the change in phase difference along the X-direction differential step size, ΔΦ G ( x , y ) represents the change in phase difference along the Y-direction differential step size, Δ x and Δ y This represents the difference step size in the X and Y directions. l R and l G This indicates the laser wavelengths corresponding to the first laser 5 and the second laser 9. i R and iG This indicates the incident angle of the first laser 5 and the second laser 9 relative to the sample under test; Step 5.2: Calculate the difference step size in the X and Y directions. The specific formula is as follows: (5) (6) in, n x This indicates the number of pixels during the X-direction differencing process. n y This indicates the number of pixels during the Y-direction differencing process. L This indicates the field of view of a CCD camera. W This indicates the field of view width of a CCD camera. N x This indicates the X-axis resolution of the CCD camera. N y This indicates the resolution in the Y direction of the CCD camera; Step 5.3: Calculate the phase difference change in the X and Y directions along the differential step size. The specific formula is as follows: (7) (8) Where, ΔΦ(Δ x , y ) represents the phase difference of the corresponding pixels after the X-direction differentiation, ΔΦ( x ,Δ y () represents the phase difference of the corresponding pixels after differential analysis in the Y direction; Step 5.4: Substitute formulas (5~8) into formula (4), and input the CCD camera resolution in the X and Y directions, the length and width of the CCD phase field of view, the incident angle and wavelength of the first laser and the second laser, the phase difference of the corresponding pixel points after the X and Y directions are differentiated, and the number of pixel points during the X and Y directions differentiation process, so as to calculate the strain in the X and Y directions. Step 6: Using the plane stress model, combined with the thermal strain caused by heating, the difference between the strain in the material calculated by the plane stress model and the thermal strain is the strain caused by residual stress. Step 6.1: Using the classical plane stress model, substitute the elastic modulus and Poisson's ratio of the sample to be tested to calculate the strain in the material. The specific formula is as follows: (9) in, E Indicates the elastic modulus. m Represents Poisson's ratio. s x This represents the stress component in the X direction. sy This represents the stress component in the Y direction. e x This represents the strain component in the X direction. e y Represents the strain component in the Y direction; Step 6.2: Increase the temperature by 52K and calculate the thermal strain caused by heating. The specific formula is as follows: (10) Step 6.3: Calculate the strain caused by residual stress by subtracting formulas (9) and (10). The specific formula is as follows: (11) in, e T This represents the thermal strain at the corresponding temperature. α The coefficient of thermal expansion, Δ T This indicates a temperature rise of 52K.

[0027] Step 7: Solve the stress and strain equations in formula (11) to calculate the residual stress. The specific formula is as follows: (12) in, s res,x This represents the residual stress in the X direction. s res,y This represents the residual stress in the Y direction; The residual stress generated on the surface of the test sample due to processing can then be calculated. The residual stress in the X direction is -216.3 MPa, and the residual stress in the Y direction is -163.6 MPa.

[0028] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A localized heating non-destructive testing device for residual stress using electron speckle, characterized in that, The local heating type residual stress non-destructive testing device includes a heating system and a displacement measurement optical path system; The displacement measurement optical path system includes a first reflector (2), a second reflector (3), a first beam splitter (4), a first laser (5), a third reflector (6), a second beam splitter (7), a fourth reflector (8), a second laser (9), a CCD camera (10), and a polarizer (11); the incident direction of the heating laser (1) is defined as the Z direction, the optical path directions of the first reflector (2), the second reflector (3), and the first beam splitter (4) are defined as the X direction, and the optical path directions of the third reflector (6), the second beam splitter (7), and the fourth reflector (8) are defined as the Y direction; The heating system is a heating laser (1). The front end of the heating laser (1) is perpendicularly irradiated to the surface of the test sample. The plane of the residual stress to be tested of the test sample is in the XOY plane. The circular area covered by the light spot is the heating area (12). The first beam splitter (4), the first laser (5), the second beam splitter (7), and the second laser (9) are arranged in sequence behind the heating laser (1). The first beam splitter (4) has a first reflector (2) and a second reflector (3) arranged on both sides along the X direction. The second beam splitter (7) has a third reflector (6) and a fourth reflector (8) arranged on both sides along the Y direction. The CCD camera (10) and the polarizer (11) are arranged on the side of the sample to be tested.

2. The localized heating residual stress nondestructive testing device for electron speckle according to claim 1, characterized in that, The first reflector (2), the second reflector (3), the first beam splitter (4), and the first laser (5) form an X-direction displacement measurement optical path system, which is arranged in the XOZ plane. The third reflector (6), the second beam splitter (7), the fourth reflector (8), and the second laser (9) form a Y-direction displacement measurement optical path system, which is arranged in the YOZ plane. In the X-direction displacement measurement optical path system: the laser emitted by the first laser (5) passes through the first beam splitter (4) and is divided into two coherent beams of equal energy. They are reflected onto the surface of the sample to be tested by the first mirror (2) and the second mirror (3), respectively. The CCD camera (10) then enters the target surface in the CCD camera (10) through diffuse reflection, first entering the polarizing mirror (11) and then entering the target surface in the CCD camera (10), forming an interference fringe pattern in the X direction. In the optical path system for measuring displacement in the Y direction: the laser emitted from the second laser (9) passes through the second beam splitter (7) and is divided into two coherent beams of equal energy. These beams are reflected by the third mirror (6) and the fourth mirror (8) respectively onto the surface of the sample to be tested. The beams then enter the target surface of the CCD camera (10) through diffuse reflection, first entering the polarizer (11) and then entering the target surface of the CCD camera (10), forming an interference fringe pattern in the Y direction.

3. The local heating type non-destructive testing device for residual stress of electron speckle according to claim 2, characterized in that, The XOZ plane where the X-direction displacement measurement optical path system is located is distributed at 90° with the YOZ plane where the Y-direction displacement measurement optical path system is located, and the interference fringe pattern in the X direction is perpendicular to the interference fringe pattern in the Y direction.

4. A localized heating nondestructive testing method for residual stress using electron speckle, characterized in that, Based on the locally heated residual stress nondestructive testing device according to any one of claims 1-3, the method includes the following steps: Step 1: Spray white paint on the surface of the test sample, so that the CCD camera (10) can capture the light intensity change before and after the deformation of the heating area (12). The Z-axis of the test sample and the Z-axis of the displacement measurement optical path system are coaxially clamped. The CCD camera (10) is adjusted so that it can capture the complete heating area (12) on the test sample. The CCD camera (10) is then adjusted to move the heating area (12) to the center of the field of view. Step 2: After the test sample is clamped, measure the interference fringe pattern in the X direction and the interference fringe pattern in the Y direction before heating. Then, irradiate the heating area (12) through the heating laser (1). After heating, turn off the heating laser (1), measure the interference fringe pattern in the X direction and the interference fringe pattern in the Y direction after heating, and output the light intensity of each pixel in the interference fringe pattern before and after heating. Step 3: Combine the light intensity obtained by the CCD camera (10), obtain the phase corresponding to each pixel point through the four-step phase shift method, and calculate the phase difference of each pixel point before and after heating; Step 4: Based on the phase difference of each pixel, establish the relationship between the X-direction displacement u and the Y-direction displacement v and the phase difference. The calculation formula is as follows: in, u Indicates displacement in the X direction. v Indicates displacement in the Y direction. θ This indicates the incident angle of the laser from the first laser (5) or the second laser (9). λ Indicates the wavelength of the laser from the first laser (5) or the second laser (9); Step 5: Combining the calculation formula from Step 4, by... u and v Perform differentiation, calculate the difference step size in the X and Y directions, then calculate the phase difference change in the X and Y direction difference step size directions, and finally obtain the strain components in the X and Y directions. Step 6: Based on the classical plane stress model and the thermal strain caused by heating, obtain the equations of stress and strain, and calculate the difference between strain and thermal strain based on the plane stress model as the strain caused by residual stress. Step 7: Solve the stress and strain equations from Step 6 to calculate the residual stress. The specific formula is as follows: in, σ res,x This represents the residual stress in the X direction. σ res,y This represents the residual stress in the Y direction.

5. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 4, characterized in that, Step 2 specifically involves: Step 2.1: Before heating, the laser emitted by the first laser (5) is split into two coherent beams by the first beam splitter (4), which are reflected onto the test sample by the first reflector (2) and the second reflector (3), respectively. The two coherent beams are diffusely reflected and enter the CCD camera (10) through the polarizer (11). The deflection angle of the polarizer (11) is changed to 0°, 90°, 180° and 270°, respectively. The interference fringe pattern formed by mutual interference in the X direction is captured by the CCD camera (10) at the corresponding angle, and the corresponding pixel under the corresponding interference pattern is output. The light intensity of the point; the laser emitted by the second laser (9) is split into two coherent beams by the second beam splitter (7), which are reflected onto the test sample by the first reflector (2) and the second reflector (3), respectively. The two coherent beams are diffusely reflected and enter the CCD camera (10) through the polarizer (11). The deflection angle of the polarizer (11) is changed. The deflection angles are 0°, 90°, 180° and 270°, respectively. The CCD camera (10) captures the interference fringe pattern formed by mutual interference in the Y direction at the corresponding angles, and outputs the light intensity of the corresponding pixel point under the corresponding interference pattern. Step 2.2: Heat the heating area (12) using a heating laser (1); Step 2.3: After heating, repeat step 2.1 to obtain the interference fringe patterns in the X and Y directions after heating, as well as the light intensity of the corresponding pixel points under the corresponding interference patterns.

6. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 5, characterized in that, In step 2.1, the first laser (5) emits a laser with a wavelength of 532nm and enters the 532nm channel of the CCD camera (10); the second laser (9) emits a laser with a wavelength of 472nm and enters the 472nm channel of the CCD camera (10).

7. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 6, characterized in that, In step 2.2, the heating time is 10~30s.

8. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 7, characterized in that, Step 3 specifically involves: Step 3.1: Calculate the phase of each pixel before and after heating using the four-step phase-shifting method, as shown in the following formula: in, This indicates that the phase of each pixel is obtained by a four-step phase-shifting method before and after heating. I 1 represents the light intensity corresponding to each pixel at 0°; I 2 represents the light intensity corresponding to each pixel at 90°; I 3 represents the light intensity corresponding to each pixel at 180°. I 3 represents the light intensity corresponding to each pixel at 270°; Step 3.2: Subtract the phase difference before and after heating to calculate the phase difference of each pixel before and after heating. The calculation formula is as follows: Where, ΔΦ( x , y ) represents the phase difference between each pixel before and after heating, Φ 加热后 ( x , y ) represents the phase of each pixel obtained by the four-step phase-shifting method after heating, Φ 加热前 ( x , y ) represents the phase of each pixel obtained by the phase shifting method in the first four steps before heating.

9. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 8, characterized in that, Step 5 specifically involves: Step 5.1: For u and v The specific formula for differentiation is as follows: in, ε res,x This represents the strain caused by residual stress in the X direction. ε res,y ΔΦ represents the strain caused by residual stress in the Y direction. R ( x , y ) represents the change in phase difference along the X-direction differential step size, ΔΦ G ( x , y ) represents the change in phase difference along the Y-direction differential step size, Δ x and Δ y This represents the difference step size in the X and Y directions. λ R and λ G This indicates the laser wavelengths corresponding to the first laser (5) and the second laser (9). θ R and θ G This indicates the incident angle of the first laser (5) and the second laser (9) relative to the sample under test; Step 5.2: Calculate the difference step size in the X and Y directions. The specific formula is as follows: in, n x This indicates the number of pixels during the X-direction differencing process. n y This indicates the number of pixels during the Y-direction differencing process. L This indicates the field of view of a CCD camera. W This indicates the field of view width of a CCD camera. N x This indicates the X-axis resolution of the CCD camera. N y This indicates the resolution in the Y direction of the CCD camera; Step 5.3: Calculate the phase difference change in the X and Y directions along the differential step size. The specific formula is as follows: Where, ΔΦ(Δ x , y ) represents the phase difference of the corresponding pixels after the X-direction differentiation, ΔΦ( x ,Δ y () represents the phase difference of the corresponding pixels after differential analysis in the Y direction; Step 5.4: Substitute the formulas from Step 5.2 and Step 5.3 into the formula from Step 5.1 to calculate the strain in the X and Y directions.

10. The method for localized heating residual stress nondestructive testing of electron speckle according to claim 9, characterized in that, Step 6 specifically involves: Step 6.1: Calculate the strain in the material using a plane stress model. The specific formula is as follows: in, E Indicates the elastic modulus. μ Represents Poisson's ratio. σ x This represents the stress component in the X direction. σ y This represents the stress component in the Y direction. ε x This represents the strain component in the X direction. ε y Represents the strain component in the Y direction; Step 6.2: Calculate the thermal strain caused by heating. The specific formula is as follows: Step 6.3: Subtract the thermal strain from the strain calculated using the plane stress model to calculate the strain caused by residual stress. The specific formula is as follows: in, ε T This represents the thermal strain at the corresponding temperature. α The coefficient of thermal expansion, Δ T This indicates a temperature rise.

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