Non-contact strain measurement system and method in high-temperature strong-noise environment

Abstract

The application provides a non-contact strain measurement system in a high-temperature strong-noise environment, comprising: a traveling wave tube for simulating a high sound intensity sound field, the traveling wave tube comprising a test section, a test piece being installed on a side wall plate of the test section, and a deformation measurement region of the test piece being provided with a speckle coating; a radiation heater being arranged on a side wall of the test section opposite to the test piece; an illumination light source being arranged on the side wall of the test section on both sides of the radiation heater; an endoscope probe being partially inserted into the test section and being aligned with the speckle coating of the test piece; a cooling device being arranged on the endoscope probe outside the test section; and an imaging device comprising a filter, a focusing ring, a high-speed camera, an acquisition terminal and a display at a tail end of the endoscope probe, the high-speed camera acquiring images of the deformation measurement region of the test piece through the endoscope probe, and the images before and after deformation being processed through the acquisition terminal to obtain displacement results which are displayed through the display.

Description

Technical Field

[0001] This application belongs to the field of high temperature and high noise environment measurement technology, and specifically relates to a non-contact strain measurement system and method under high temperature and high noise environment. Background Technology

[0002] Hypersonic vehicles are flight devices that travel at speeds several times Mach. During hypersonic flight, the surface of the vehicle structure experiences high temperatures due to friction, and simultaneously generates a strong noise environment under aerodynamic loads. Therefore, it is essential to conduct structural strength tests on hypersonic vehicles under combined aerodynamic heat and noise loads. However, accurately obtaining the structural response characteristics under harsh service environments such as high temperature and strong noise has become a key technical challenge restricting ground testing and analysis.

[0003] Currently, there are limited methods for measuring deformation in high-temperature acoustic fatigue testing of structures. Traditional contact-type high-temperature strain gauge measurements generally use the method of pasting strain gauges, but this method has shortcomings in terms of heat output, pasting process, and resistance to airflow impact. The survival rate of strain gauges and the effectiveness of measurement results are poor, and it will directly affect the heating effect on the structural surface. Especially in the high-temperature environment of 1200℃, there is a lack of means for strain sensor preparation, pasting, and calibration.

[0004] Non-contact digital image correlation (DIC) is an advanced optical measurement method with unique advantages, and it has been applied in room-temperature static tests. However, under conditions of high-temperature radiation and strong noise background airflow disturbance, this measurement method is not adaptable enough. Specifically, high-temperature frontal radiation causes image decorrelation, and optical path disturbance causes significant image distortion. Therefore, general digital image correlation measurement methods are not suitable for high-temperature acoustic fatigue tests. Summary of the Invention

[0005] The purpose of this application is to provide a non-contact strain measurement system for high-temperature and high-noise environments to solve or mitigate at least one of the problems in the prior art.

[0006] The technical solution of this application is: 1. A non-contact strain measurement system under high temperature and high noise environment, comprising:

[0007] A traveling wave tube (TWT) is used to simulate a high-intensity sound field. The TWT includes a test section, and a test piece is mounted on the side wall of the test section. The deformation measurement area of ​​the test piece is provided with a speckle coating.

[0008] A radiation heater, which is disposed on the side wall of the test section opposite the test specimen, is used to irradiate the test specimen to provide the required temperature for the test specimen;

[0009] An illumination source is provided on the sidewalls of the test section on both sides of the radiant heater, for illuminating the speckle coating of the test piece;

[0010] An endoscope probe, the portion of which extends into the test section and is aligned with the speckle coating of the test piece;

[0011] A cooling device, wherein the cooling device is arranged on the endoscope probe outside the test section, is used to cool the endoscope probe; and

[0012] An imaging device is provided, comprising a filter, a focusing ring, a high-speed camera, a data acquisition terminal, and a display located at the end of an endoscope probe. The high-speed camera acquires images of the deformation measurement area of ​​the test piece through the endoscope probe, and the data acquisition terminal processes the images before and after deformation to obtain displacement results, which are then displayed on the display. The filter is used to eliminate non-measurement wavelengths in the images acquired by the high-speed camera, and the focusing ring enables the high-speed camera to obtain clear images of the deformation measurement area.

[0013] In a preferred embodiment of this application, the radiant heater uses a quartz lamp for heating.

[0014] In a preferred embodiment of this application, the wavelength of the lighting source does not completely overlap with the radiation wavelength of the radiant heater.

[0015] In a preferred embodiment of this application, the illumination source is ultraviolet light.

[0016] In a preferred embodiment of this application, there are two lighting sources, distributed on both sides of the radiant heater.

[0017] In a preferred embodiment of this application, the endoscope probe has a double-walled structure;

[0018] The cooling device includes an air-cooled flow path and a water-cooled flow path. The water-cooled flow path includes a water-cooled inlet and a water-cooled outlet. The water-cooling medium flows in from the water-cooled inlet, flows along the internal flow path formed by the inner wall of the endoscope tube, and flows out from the water-cooled outlet. The air-cooled flow path includes an air-cooled inlet. The air-cooling medium flows in from the air-cooled inlet, flows along the gap channel formed between the two layers of the endoscope tube, and flows out from the end of the endoscope tube.

[0019] In a preferred embodiment of this application, the air-cooled inlet is located on the side of the cooling device near the tail of the endoscope probe.

[0020] Furthermore, this application also provides a method for non-contact strain measurement using any of the above-mentioned high-temperature and high-noise environments, the method comprising:

[0021] 1) Determine the experimental conditions

[0022] According to the test requirements, the magnitude of high temperature and strong noise loads and the target area for deformation measurement of the test piece are determined, and the corresponding traveling wave tubes and radiation heaters are installed and arranged. The traveling wave tubes provide the strong noise environment required for the test, and the radiation heaters provide the high temperature environment required for the test.

[0023] 2) Configure lighting sources

[0024] The specifications of the lighting source are determined according to the test temperature range. The wavelength λ of the selected photo light source avoids the radiation wavelength of the radiation heater. The lighting source is arranged on both sides of the radiation heater.

[0025] 3) Fabrication of speckled coating

[0026] The speckle coating fabrication scheme on the test piece is determined based on the test temperature, and speckle spraying is performed on the target area for deformation measurement on the test piece. The substrate material of the speckle coating meets the life requirements under the test temperature and noise conditions.

[0027] 4) Configure endoscope probe

[0028] Based on the target area for deformation measurement of the test specimen and the location of the radiation heater, determine the diameter of the endoscope probe, insert the endoscope probe into the traveling wave tube test section, and ensure that the distance between the head of the endoscope probe and the test specimen is ≥50mm.

[0029] 5) Select a filter

[0030] Based on the wavelength of the lighting source and the radiation wavelength of the radiation heater, the filtering range of the filter is selected so that the high-speed camera can acquire a clear image.

[0031] 5) Connect the cooling circuit

[0032] The cooling circuit connected to the cooling device enables the cooling device to cool the endoscope probe while stabilizing the optical path acquired by the endoscope probe.

[0033] 7) Equipped with a high-speed camera

[0034] A high-speed camera is connected to the end of the endoscope probe. The pixel count and frame rate of the high-speed camera are selected according to the measurement requirements. The focus is adjusted by the focusing ring according to the observation distance between the endoscope probe and the speckle coating, so that the high-speed camera can obtain a clear image.

[0035] 8) Image transmission and processing

[0036] Images acquired by the high-speed camera are transmitted to the acquisition terminal via a data cable. The acquisition terminal uses digital image correlation algorithms to compare images before and after deformation and calculate displacement. The initial deformation value adopts an integer pixel search method. Based on this, a suitable subpixel algorithm is selected to obtain the subpixel precision displacement value. Finally, the displacement field is differentially divided by a differential algorithm to obtain the full-field strain, which is then displayed on a monitor.

[0037] The technical solution of this application provides a feasible method for measuring the deformation field of structural surfaces in environments with high-temperature frontal radiation and strong noise background airflow interference. It effectively makes up for the lack of deformation measurement methods in high-temperature and strong noise environments. Moreover, the deformation measurement of structural surfaces has good stability and accuracy. It avoids the problems of heat output interference, bonding process influence, and radiation heating light path obstruction in the existing contact strain gauge measurement. It effectively overcomes the influence of harsh heat and noise environments, greatly improves the environmental applicability, and can be used for deformation measurement in environments with combined loads exceeding 1500℃ and 170dB, which greatly saves test costs. Attached Figure Description

[0038] To more clearly illustrate the technical solutions provided in this application, the accompanying drawings will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application.

[0039] Figure 1 This is a schematic diagram of the non-contact strain measurement system of this application.

[0040] Figure 2 This is a test temperature load environment control curve in one embodiment of this application.

[0041] Figure 3 This is a test noise load control curve in one embodiment of this application.

[0042] Figure 4 This is an image of the target area of ​​a test specimen according to an embodiment of this application.

[0043] Figure 5 This is a contour map of the target area of ​​the test specimen before displacement measurement in this embodiment of the application.

[0044] Figure 6 This is a cloud map showing the displacement of the target area of ​​the test piece in this embodiment of the application.

[0045] Figure label:

[0046] 1-Traveling wave tube, 11-Test section

[0047] 2-Test specimen, 21-Spot coating

[0048] 3-Radiation heater

[0049] 4-Lighting source

[0050] 5-Cooling device, 51-Air-cooled inlet, 52-Water-cooled inlet, 53-Water-cooled outlet

[0051] 6-Filter

[0052] 7-Focusing ring

[0053] 8-High-speed camera, 81-Data cable, 82-Acquisition terminal, 83-Display

[0054] 9-Endoscopic probe Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0056] This application provides a non-contact deformation measurement system and method for structural surfaces that can be used in high-temperature and high-noise environments, enabling accurate measurement of structural surface deformation under high-temperature frontal radiation of 1200℃ and above and strong noise background airflow interference of 165dB.

[0057] like Figure 1 As shown, the non-contact strain measurement system provided in this application includes: a traveling wave tube 1, a radiation heater 3, an illumination source 4, a cooling device 5, an endoscope probe 9, and an imaging device.

[0058] The traveling wave tube 1 is used to simulate a high-intensity sound field. It includes a test section 11, and the test piece 2 is mounted on the side wall of the test section 11 of the traveling wave tube 1. The background airflow in the traveling wave tube 1 is compressed air. In this embodiment of the application, the flow rate of the compressed air is 43 m³ / s. 3 / min.

[0059] The test piece 2 is a plate-shaped structure. In this embodiment of the application, the test piece 2 is an alumina system TPS (Thermal Protection System) test piece with a length, width and thickness of 500mm×100mm×30mm. The test piece 2 needs to be subjected to surface displacement measurement in an environment of high temperature radiation of 1250℃ and strong noise of 165dB. The high temperature and strong noise are applied to the same surface of the test piece 2 - that is, the left side surface of the test piece 2.

[0060] The middle area of ​​the left side of the test piece 2 is set as the target measurement area. A speckle coating 21 is provided in the target measurement area. The speckle coating 21 is sprayed with a high temperature resistant material, which can withstand a test temperature of 1250℃.

[0061] A radiant heater 3 is disposed on the traveling wave tube wall plate opposite to the test specimen 2. The radiant heater 3 irradiates the surface of the test specimen 2 to simulate a high-temperature environment of up to 1250°C on the surface of the test specimen 2. In one embodiment of this application, the radiant heater 3 may use a quartz lamp for radiant heating.

[0062] An illumination source 4 is also arranged on the traveling wave tube wall plate opposite the test piece 2 to illuminate the speckle coating of the measurement area of ​​the test piece 2. In a preferred embodiment of this application, the specifications of the illumination source 4 are determined according to the test temperature range, and the wavelength of the illumination source 4 is designed to avoid the radiation wavelength of the radiation heater 3 as much as possible. For example, in one embodiment of this application, an ultraviolet lamp is selected as the illumination source 4 to minimize overlap with the radiation wavelength of the radiation heater 3.

[0063] The endoscope probe 9 extends through the radiant heater 3 on the traveling wave tube wall and into the traveling wave tube test section 11, with the probe tip of the endoscope probe 9 aligned with the speckle coating of the test piece 2. In a preferred embodiment of this application, the distance between the probe tip of the endoscope probe 9 and the test piece 2 is no greater than 50 mm.

[0064] A cooling device 5 is located on the non-probe end of the endoscope tube 9, and cools the endoscope tube 9 through the cooling device 5. The cooling device 5 includes an air-cooled flow path and a water-cooled flow path. The endoscope tube 9 has a double-walled structure. The water-cooled flow path includes a water-cooled inlet 52, an internal flow path 54 formed by the inner wall of the endoscope tube 9, a water-cooled outlet 53, and pressure gauges, flow meters, valves (not shown), etc. By introducing a cooling medium into the water-cooled flow path, the probe portion exposed in the high-temperature radiation zone of the radiant heater 3 is cooled, thereby increasing the operating temperature of the endoscope tube 9. It is understood that the cooling medium introduced in the above method can be water, or other transparent cooling media, such as alcohol or ethylene glycol.

[0065] The air-cooled flow path includes an air-cooled inlet 51, a sandwich flow path 55 formed between the double walls of the endoscope probe 9, and an air-cooled outlet (not shown) at the end of the endoscope probe 9. By introducing cooling gas into the air-cooled flow path, gas is introduced into the gap between the probe head of the endoscope probe 9 and the circulating water-cooled flow path pipe. This not only further cools the probe head of the endoscope probe 9 but also stabilizes the detection optical path of the endoscope probe 9. In a preferred embodiment of this application, the air-cooled inlet 51 is located at the end of the cooling device 5 near the imaging device.

[0066] The imaging device includes a filter 6, a focusing ring 7, a high-speed camera 8, a data acquisition terminal 82, and a display 83. The filter 6, focusing ring 7, and high-speed camera 8 are sequentially positioned at the tail end of the endoscope probe 9. The filter 6 eliminates non-measurement wavelengths acquired by the probe end of the endoscope probe 9. The focusing ring 7 adjusts the imaging focal length. The high-speed camera 8 acquires images of the speckle coating 21 of the test piece 2 obtained by the probe end of the endoscope probe 9. The high-speed camera 8 is connected to the data acquisition terminal 82 via a data cable 81. The data acquisition terminal 82 transmits the images acquired by the high-speed camera 8 to the display 83, thus completing the image display. Specifically, the images acquired by the high-speed camera 8 are transmitted to the data acquisition terminal 82 via the data cable 81. The data acquisition terminal 82 uses digital image correlation algorithms to compare images before and after deformation and calculate displacement. Finally, a differential algorithm is used to differentiate the displacement field to obtain the full-field strain, which is then displayed on the display 83.

[0067] In addition, this application also provides a measurement method for the above-mentioned non-contact strain measurement system, including the following process:

[0068] 1) Determine the experimental conditions

[0069] According to the test requirements, determine the level of high temperature and strong noise load, as well as the target area for deformation measurement of test piece 2, and install and arrange the corresponding traveling wave tube 1 and radiation heater 3. The traveling wave tube 1 should be able to provide the strong noise environment required for the test, and the radiation heater 3 should be able to provide the high temperature environment (1200℃) required for the test.

[0070] 2) Configure lighting source 4

[0071] The specifications of the illumination source 4 are determined according to the test temperature range. The main wavelength λ of the selected light source 4 should avoid the radiation wavelength of the radiation heater 3 as much as possible. Ultraviolet light is used in the 1200℃ high temperature environment. The ultraviolet light source is arranged on both sides of the radiation heater 3.

[0072] 3) Fabrication of speckled coating

[0073] The fabrication scheme of speckle coating 21 on test piece 2 is determined according to the test temperature, and speckle spraying is performed on the deformation measurement target area on test piece 2. The substrate material should have sufficient life under the highest test temperature and noise conditions. Under the condition of not exceeding 1250℃, high temperature ceramic adhesive and matte paint and other high temperature resistant materials can be selected as speckle substrate.

[0074] 4) Configure 9 endoscope probes

[0075] Based on the deformation measurement target area of ​​test piece 2 and the position of radiation heater 3, an endoscope probe 9 of appropriate diameter is configured and inserted into the traveling wave tube test section. The distance between the head of the endoscope probe 9 and the test piece is ≥50mm.

[0076] By adjusting the number and distance of the lamps in the radiant heater 3, the positions of the endoscope probe 9, the radiant heater 3, and the target area for measuring the deformation of the test piece need to be coordinated.

[0077] 5) Select filter 6

[0078] Based on the wavelength of the lighting source 4 and the radiation wavelength characteristics of the radiation heater 6, a filter 6 with a suitable filtering range is selected. The filter 6 can be optimized according to the image effect of the computer terminal. For the case of ultraviolet light irradiating the light source under the high temperature of 1200℃, the filter 6 can be selected with a filtering range of λ±10nm, where λ is the main wavelength of the irradiating light source. For example, in this embodiment of the application, the filtering range of the filter can be 365nm±10nm.

[0079] 5) Connect the cooling circuit

[0080] The cooling of the endoscope probe 9 includes both air cooling and water cooling. The water cooling flow path covers the endoscope probe 6 exposed to the high temperature radiation area, thereby increasing the operating temperature of the endoscope probe 6. The air cooling gas passes through the gap between the endoscope probe 9 head and the circulating water cooling flow path to stabilize the optical path.

[0081] The air-cooling inlet is located at the end of the endoscope probe 9 near the filter 7. In this embodiment of the application, the water-cooling flow path has a pressure greater than 1 bar and a flow rate of 14 L / min, while the air-cooling circulation pressure is maintained at approximately 1.2 bar. Before the test, the cooling circuit must be correctly connected before high-temperature loading can be performed.

[0082] 7) Equipped with a high-speed camera

[0083] A high-speed camera 8 is connected to the end of the endoscope probe 9. The pixel count and frame rate of the high-speed camera 8 are selected according to the measurement requirements. The focus is adjusted by the focusing ring 7 according to the observation distance between the endoscope probe 9 and the speckle coating 21, so that the high-speed camera 8 can obtain a clear image.

[0084] 8) Image transmission and processing

[0085] The image acquired by the high-speed camera 8 is transmitted to the acquisition terminal 82 via the data cable 81. The acquisition terminal 82 uses a digital image correlation algorithm to compare the images before and after deformation and calculate the displacement. The initial value of the deformation adopts the integer pixel search method. On this basis, a suitable subpixel algorithm is selected to obtain the displacement value with subpixel precision. Finally, the displacement field is differentially divided by the differential algorithm to obtain the full-field strain, which is finally displayed on the display 83.

[0086] like Figure 2 and Figure 3The image shown illustrates the temperature and noise loads applied during the test in this embodiment of the application. The image of the target area for deformation measurement of the test piece, obtained by detecting the deformation through the endoscope probe 9 and imaging it with the high-speed camera 8, is shown below. Figure 4 The measurement results of the target area displacement of the test piece before and after deformation measurement are as follows: Figure 5 and Figure 6 The experimental results show that, under the conditions of high-temperature frontal radiation at 1250℃ and a total sound pressure level of 165dB noise, high-fidelity images and displacement measurement cloud maps of the target area for deformation measurement of the test piece can be successfully obtained.

[0087] The non-contact strain measurement system provided in this application overcomes the image decorrelation effect under high-temperature frontal radiation conditions on the one hand, and directly captures images using an optical probe on the other hand, overcoming the problems of high-speed cameras not being directly applicable in high-temperature environments and distortion caused by optical path disturbances. This enables the extraction of structural surface images under strong radiation and strong airflow disturbance environments, and further utilizes image correlation algorithms to complete the deformation measurement of the structural surface.

[0088] The technical solution of this application provides a feasible method for measuring the deformation field of structural surfaces in environments with high-temperature frontal radiation and strong noise background airflow interference. It effectively makes up for the lack of deformation measurement methods in high-temperature and strong noise environments. Moreover, the deformation measurement of structural surfaces has good stability and accuracy. It avoids the problems of heat output interference, bonding process influence, and radiation heating light path obstruction in the existing contact strain gauge measurement. It effectively overcomes the influence of harsh heat and noise environments, greatly improves the environmental applicability, and can be used for deformation measurement in environments with combined loads exceeding 1500℃ and 170dB, which greatly saves test costs.

[0089] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A non-contact strain measurement system for high-temperature and high-noise environments, characterized in that, include: A traveling wave tube (TWT) is used to simulate a high-intensity sound field. The TWT includes a test section, and a test piece is mounted on the side wall of the test section. The deformation measurement area of ​​the test piece is provided with a speckle coating. A radiation heater, which is disposed on the side wall of the test section opposite the test specimen, is used to irradiate the test specimen to provide the required temperature for the test specimen; An illumination source is provided on the sidewalls of the test section on both sides of the radiant heater, for illuminating the speckle coating of the test piece; An endoscope probe, a portion of which extends into the test section and is aligned with the speckle coating of the test specimen; A cooling device, wherein the cooling device is arranged on the endoscope probe outside the test section, is used to cool the endoscope probe; and An imaging device is provided, comprising a filter, a focusing ring, a high-speed camera, a data acquisition terminal, and a display located at the end of an endoscope probe. The high-speed camera acquires images of the deformation measurement area of ​​the test piece through the endoscope probe, and the data acquisition terminal processes the images before and after deformation to obtain displacement results, which are then displayed on the display. The filter is used to eliminate non-measurement wavelengths in the images acquired by the high-speed camera, and the focusing ring enables the high-speed camera to obtain clear images of the deformation measurement area.

2. The non-contact strain measurement system under high temperature and high noise environment as described in claim 1, characterized in that, The radiant heater uses a quartz lamp for heating.

3. The non-contact strain measurement system under high temperature and high noise environment as described in claim 1, characterized in that, The wavelength of the lighting source does not completely overlap with the radiation wavelength of the radiant heater.

4. The non-contact strain measurement system under high temperature and high noise environment as described in claim 3, characterized in that, The lighting source is ultraviolet light.

5. The non-contact strain measurement system under high temperature and high noise environment as described in claim 3 or 4, characterized in that, There are two lighting sources, located on both sides of the radiant heater.

6. The non-contact strain measurement system under high temperature and high noise environment as described in claim 1, characterized in that, The endoscope probe has a double-walled structure; The cooling device includes an air-cooled flow path and a water-cooled flow path. The water-cooled flow path includes a water-cooled inlet and a water-cooled outlet. The water-cooling medium flows in from the water-cooled inlet, flows along the internal flow path formed by the inner wall of the endoscope tube, and flows out from the water-cooled outlet. The air-cooled flow path includes an air-cooled inlet. The air-cooling medium flows in from the air-cooled inlet, flows along the gap channel formed between the two layers of the endoscope tube, and flows out from the end of the endoscope tube.

7. The non-contact strain measurement system under high temperature and high noise environment as described in claim 6, characterized in that, The air-cooled inlet is located on one side of the cooling device near the tail of the endoscope probe.

8. A method for non-contact strain measurement using the non-contact strain measurement system described in any one of claims 1 to 7 under high temperature and high noise conditions, characterized in that, include: 1) Determine the experimental conditions According to the test requirements, the magnitude of high temperature and strong noise loads and the target area for deformation measurement of the test piece are determined, and the corresponding traveling wave tubes and radiation heaters are installed and arranged. The traveling wave tubes provide the strong noise environment required for the test, and the radiation heaters provide the high temperature environment required for the test. 2) Configure lighting sources The specifications of the lighting source are determined according to the test temperature range. The wavelength λ of the selected lighting source avoids the radiation wavelength of the radiation heater. The lighting source is arranged on both sides of the radiation heater. 3) Fabrication of speckled coating The speckle coating fabrication scheme on the test piece is determined based on the test temperature, and speckle spraying is performed on the target area for deformation measurement on the test piece. The substrate material of the speckle coating meets the life requirements under the test temperature and noise conditions. 4) Configure endoscope probe Based on the target area for deformation measurement of the test specimen and the location of the radiation heater, determine the diameter of the endoscope probe, insert the endoscope probe into the traveling wave tube test section, and ensure that the distance between the head of the endoscope probe and the test specimen is ≥50mm. 5) Selecting a filter Based on the wavelength of the lighting source and the radiation wavelength of the radiation heater, the filtering range of the filter is selected so that the high-speed camera can acquire a clear image. 6) Connect the cooling circuit The cooling circuit connected to the cooling device enables the cooling device to cool the endoscope probe while stabilizing the optical path acquired by the endoscope probe. 7) Equipped with a high-speed camera A high-speed camera is connected to the end of the endoscope probe. The pixel count and frame rate of the high-speed camera are selected according to the measurement requirements. The focus is adjusted by the focusing ring according to the observation distance between the endoscope probe and the speckle coating, so that the high-speed camera can obtain a clear image. 8) Image transmission and processing Images acquired by the high-speed camera are transmitted to the acquisition terminal via a data cable. The acquisition terminal uses digital image correlation algorithms to compare images before and after deformation and calculate displacement. The initial deformation value adopts an integer pixel search method. Based on this, a suitable subpixel algorithm is selected to obtain the subpixel precision displacement value. Finally, the displacement field is differentially divided by a differential algorithm to obtain the full-field strain, which is then displayed on a monitor.

Images