Strain Testing Apparatus and Method for Metallic Materials in the Liquid Hydrogen Temperature Range

Abstract

This invention proposes a strain testing device and method for metallic materials at liquid hydrogen temperatures. The strain testing device includes a universal tensile testing machine, a Dewar cavity, and a support. The support is used to hold the metallic sample. The device also includes: a fiber optic imaging module located inside the Dewar cavity, comprising an imaging fiber and a transmission fiber, with the imaging fiber aligned with the gauge length of the metallic sample; a flange, detachably sealed to the top of the Dewar cavity, equipped with a bidirectional adapter; an image acquisition module located outside the Dewar cavity, connected to the imaging fiber via the bidirectional adapter, used to generate digital image signals based on analog image signals; and an image processing device, communicatively connected to the image acquisition module, used to determine the strain test results of the metallic sample based on the digital image signals. According to the technical solution of this invention, the fiber optic imaging module located inside the Dewar cavity enables image acquisition of the gauge length from within the Dewar cavity, avoiding damage to the image acquisition module due to low temperatures.

Description

Technical Field

[0001] This invention relates to the field of metal testing technology, and in particular to a strain testing device and method for metallic materials in the liquid hydrogen temperature range. Background Technology

[0002] Liquid hydrogen storage involves liquefying hydrogen gas and storing it in a cryogenic, insulated metal container. This facilitates large-scale, long-distance hydrogen energy storage and transportation. To select suitable metal materials for liquid hydrogen storage, strain test results of the metal materials at the liquid hydrogen temperature range (20K) are required.

[0003] Currently, strain tests are performed on metallic materials placed inside a Dewar cavity using a universal tensile testing machine in the liquid hydrogen temperature range. Two methods are used to measure strain data: contact extensometers and video extensometers. Contact extensometers are fixed to the surface of the metallic material to obtain strain data at liquid hydrogen temperatures. However, contact extensometers must be removed before the material fractures, making it impossible to directly measure the elasto-plastic stress and strain behavior during the post-yield, necking, and fracture stages, resulting in incomplete strain test results. Therefore, video extensometers are often used. A video extensometer includes a camera positioned outside the Dewar cavity with a transparent window on the cavity surface. The camera is aligned with this window, and the video extensometer obtains strain test results based on the image of the metallic material captured by the camera. However, the window in the Dewar cavity leads to poor insulation, resulting in low reliability of strain test results at liquid hydrogen temperatures. Furthermore, placing the camera inside the Dewar cavity risks damage due to the liquid hydrogen temperature environment. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a strain testing device and method for metallic materials in the liquid hydrogen temperature range, which can acquire images of metallic samples inside the Dewar cavity through a fiber optic imaging module located inside the Dewar cavity.

[0005] In a first aspect, embodiments of the present invention provide a strain testing device for metallic materials at liquid hydrogen temperatures. The strain testing device includes a universal tensile testing machine, a Dewar cavity, and a support, wherein the support is used to hold a metallic sample. The device further includes:

[0006] A fiber optic imaging module is located inside the Dewar cavity. The fiber optic imaging module includes an imaging fiber and a light transmission fiber. The imaging fiber is aligned with the gauge length of the metal sample. The imaging fiber is used to acquire image analog signals, and the light transmission fiber is used to provide illumination.

[0007] A flange, which is detachably sealed to the top of the Dewar cavity, and the flange is provided with a bidirectional adapter.

[0008] An image acquisition module is located outside the Dewar cavity and is connected to the imaging fiber via the bidirectional adapter. The image acquisition module is used to generate digital image signals based on the image analog signals.

[0009] An image processing device is communicatively connected to the image acquisition module, and the image processing device is used to determine the strain test results of the metal sample based on the image digital signal.

[0010] According to some embodiments of the present invention, the gauge length section is provided with speckle; the support is vertically provided with a guide post and a guide rail, the guide rail is mounted on the guide post, the fiber optic imaging module is mounted on the guide rail, the fiber optic imaging module is movable along the guide rail, and the fiber optic imaging module is aligned with the speckle.

[0011] According to some embodiments of the present invention, the image acquisition module includes a visible light compensation light source, an infrared light source, and a hybrid image transcription unit. The visible light compensation light source and the infrared light source are connected to the optical fiber. The hybrid image transcription unit includes a CMOS sensor. The image analog signal includes a visible light analog signal and an infrared light analog signal. The CMOS sensor is used to generate the image digital signal based on the visible light analog signal and the infrared light analog signal.

[0012] Secondly, embodiments of the present invention provide a method for testing the strain of metallic materials in the liquid hydrogen temperature range, applied to the strain testing apparatus for metallic materials in the liquid hydrogen temperature range described in the first aspect, the method comprising:

[0013] After the metal sample is mounted on the support, it is placed in the Dewar cavity, and the fiber optic imaging module is adjusted to align with the gauge length of the metal sample.

[0014] The Dewar cavity is sealed by a flange. After evacuating and filling the Dewar cavity with helium in sequence, the internal temperature of the Dewar cavity is reduced to the liquid hydrogen temperature range.

[0015] The fiber optic imaging module and the universal tensile testing machine are activated to acquire the image simulation signal of the gauge length segment through the imaging fiber while the optical fiber provides illumination to the Dewar cavity.

[0016] The image acquisition module acquires the image analog signal, generates the image digital signal based on the image analog signal, and sends the image digital signal to the image processing device so that the image processing device can determine the strain test result of the metal sample based on the image digital signal.

[0017] According to some embodiments of the present invention, the gauge length section is provided with speckle; the bracket is vertically provided with a guide post and a guide rail, the guide rail is mounted on the guide post, the fiber optic imaging module is mounted on the guide rail, the fiber optic imaging module is movable along the guide rail, and the fiber optic imaging module is aligned with the speckle;

[0018] After mounting the metal sample onto the support, it is placed inside the Dewar cavity. The fiber optic imaging module is then adjusted to align with the gauge length of the metal sample, including:

[0019] The metal sample is installed onto the support, the metal sample is adjusted to align the coaxiality of the metal sample and the support, and the support is placed into the Dewar cavity;

[0020] The fiber optic imaging module is mounted on the guide rail, and the imaging fiber is aligned with the speckle pattern.

[0021] The imaging fiber is connected to the bidirectional adapter, the bidirectional adapter is sealed, and the imaging fiber is calibrated to ensure that the image analog signal is distortion-free and the gauge length segment is fully imaged.

[0022] According to some embodiments of the present invention, an image acquisition module acquires the image analog signal, generates an image digital signal based on the image analog signal, and sends the image digital signal to an image processing device, so that the image processing device determines the strain test result of the metal sample based on the image digital signal, including:

[0023] The image processing device acquires the image analog signal, performs analog-to-digital conversion on the image analog signal, and obtains the image digital signal;

[0024] The image digital signal is filtered and denoised to obtain a denoised image;

[0025] Based on the denoised image, the feature points and feature coordinates of the gauge segment are determined, and a calibration image is generated. The calibration image includes the feature points, the feature coordinates, and a first timestamp. The feature coordinates represent the coordinates of the feature points.

[0026] Acquire multiple frames of the calibration images, and sort the multiple frames of the calibration images based on the first timestamp;

[0027] The displacement of the feature points in adjacent frames is determined based on multiple feature coordinates, and the strain test results of the metal sample are generated in real time based on the displacement.

[0028] According to some embodiments of the present invention, the image acquisition module includes a visible light compensation light source, an infrared light source, and a hybrid image transcription unit. The visible light compensation light source and the infrared light source are connected to the optical fiber. The hybrid image transcription unit includes a CMOS sensor. The image analog signal includes a visible light analog signal and an infrared light analog signal. The CMOS sensor is used to generate the image digital signal based on the visible light analog signal and the infrared light analog signal.

[0029] The image analog signal is acquired through an image acquisition module, and an image digital signal is generated based on the image analog signal, including:

[0030] When the optical fiber provides visible light illumination and infrared light illumination to the imaging fiber, the imaging fiber acquires the image simulation signal, which includes a visible light simulation signal and an infrared light simulation signal.

[0031] The CMOS sensor acquires the visible light analog signal and the infrared light analog signal, and performs photoelectric conversion on the visible light analog signal and the infrared light analog signal respectively to obtain a visible light image and an infrared radiation image respectively;

[0032] The CMOS sensor performs infrared image transcription on the infrared radiation image to obtain an infrared image;

[0033] The CMOS sensor performs multispectral image fusion on the visible light image and the infrared image to obtain a fused image;

[0034] The strain test results of the metal sample are generated based on the fused images from multiple frames.

[0035] According to some embodiments of the present invention, the image digital signal is sent to an image processing device so that the image processing device determines the strain test result of the metal sample based on the image digital signal, including:

[0036] The fused image is acquired, and the fused image is filtered and denoised to obtain a denoised image;

[0037] Based on the denoised image, the speckle center and speckle coordinates are determined, and a calibration image is generated, wherein the calibration image includes the speckle center, the speckle coordinates, and a first timestamp;

[0038] Acquire multiple frames of the calibration images, and sort the multiple frames of the calibration images based on the first timestamp;

[0039] The displacement of the speckle center in adjacent frames is determined based on multiple speckle coordinates, and the strain test results of the metal sample are generated in real time based on the displacement.

[0040] According to some embodiments of the present invention, the universal tensile testing machine includes a servo motor connected to the support, and the servo motor is used to load the metal sample;

[0041] After activating the fiber optic imaging module and the universal tensile testing machine, the following is also included:

[0042] A loading signal is generated by the servo motor, wherein the loading signal includes a second timestamp and loading data of the servo motor on the metal sample;

[0043] The multiple loading signals are sorted based on the second timestamp, and the stress test results of the metal sample are generated in real time based on the sorted multiple loading signals.

[0044] According to some embodiments of the present invention, after generating the stress test results of the metal sample in real time, the method further includes:

[0045] The strain test results and the stress test results are obtained, wherein the strain test results include the first timestamp and the stress test results include the second timestamp;

[0046] By matching the first timestamp and the second timestamp, the stress-strain test results of the metal sample are generated in real time.

[0047] The strain testing device for metallic materials in the liquid hydrogen temperature range according to embodiments of the present invention has at least the following beneficial effects: the strain testing device for metallic materials includes a universal tensile testing machine, a Dewar cavity, and a support. The support is used to hold the metallic sample. The device further includes: a fiber optic imaging module located inside the Dewar cavity, the fiber optic imaging module including an imaging fiber and a transmission fiber, the imaging fiber being aligned with the gauge length of the metallic sample, the imaging fiber being used to acquire an analog image signal, and the transmission fiber being used to provide illumination; a flange detachably sealed to the top of the Dewar cavity, the flange being provided with a bidirectional adapter; an image acquisition module located outside the Dewar cavity, the image acquisition module being connected to the imaging fiber through the bidirectional adapter, the image acquisition module being used to generate an image digital signal based on the image analog signal; and an image processing device communicatively connected to the image acquisition module, the image processing device being used to determine the strain test result of the metallic sample based on the image digital signal. According to the technical solution of the present invention, by placing the imaging fiber inside the Dewar cavity, and with the light transmission fiber providing the light source, the imaging fiber acquires the image analog signal of the gauge length segment and transmits it to the image acquisition module located outside the Dewar cavity, thereby realizing the acquisition of the gauge length segment image inside the Dewar cavity and avoiding damage to the image acquisition module due to low temperature. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a strain testing device for metallic materials in the liquid hydrogen temperature range provided in one embodiment of the present invention;

[0049] Figure 2 This is a flowchart of a method for testing the strain of metallic materials in the liquid hydrogen temperature range, provided in another embodiment of the present invention. Detailed Implementation

[0050] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0051] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0052] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0053] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0054] The strain testing device for metallic materials in the liquid hydrogen temperature range according to embodiments of the present invention has at least the following beneficial effects: the strain testing device for metallic materials includes a universal tensile testing machine, a Dewar cavity, and a support. The support is used to hold the metallic sample. The device further includes: a fiber optic imaging module located inside the Dewar cavity, the fiber optic imaging module including an imaging fiber and a transmission fiber, the imaging fiber being aligned with the gauge length of the metallic sample, the imaging fiber being used to acquire an analog image signal, and the transmission fiber being used to provide illumination; a flange detachably sealed to the top of the Dewar cavity, the flange being provided with a bidirectional adapter; an image acquisition module located outside the Dewar cavity, the image acquisition module being connected to the imaging fiber through the bidirectional adapter, the image acquisition module being used to generate an image digital signal based on the image analog signal; and an image processing device communicatively connected to the image acquisition module, the image processing device being used to determine the strain test result of the metallic sample based on the image digital signal. According to the technical solution of the present invention, by placing the imaging fiber inside the Dewar cavity, and with the light transmission fiber providing the light source, the imaging fiber acquires the image analog signal of the gauge length segment and transmits it to the image acquisition module located outside the Dewar cavity, thereby realizing the acquisition of the gauge length segment image inside the Dewar cavity and avoiding damage to the image acquisition module due to low temperature.

[0055] First, refer to Figure 1 The strain testing device for metallic materials in the liquid hydrogen temperature range provided in this application embodiment includes a universal tensile testing machine 1, a Dewar cavity 2, and a support 3. The support 3 is used to hold the metallic sample. The device also includes:

[0056] Fiber optic imaging module 4 is located inside the Dewar cavity 2. Fiber optic imaging module 4 includes an imaging fiber and a light transmission fiber. The imaging fiber is aligned with the gauge length of the metal sample. The imaging fiber is used to acquire image analog signals, and the light transmission fiber is used to provide illumination.

[0057] Flange 5 is detachably sealed to the top of Dewar cavity 2, and flange 5 is provided with a bidirectional swivel interface.

[0058] Image acquisition module 6 is located outside the Dewar cavity 2. Image acquisition module 6 is connected to the imaging fiber through a bidirectional adapter. Image acquisition module 6 is used to generate digital image signals based on image analog signals.

[0059] Image processing device 7 is communicatively connected to image acquisition module 6. Image processing device 7 is used to determine the strain test results of metal samples based on image digital signals.

[0060] It should be noted that the universal tensile testing machine 1 performs strain testing on the metal sample through the support 3; multiple digital image signals of the gauge length segment during the strain test are acquired through the imaging fiber located inside the Dewar cavity 2 and the image acquisition module 6 located outside the Dewar cavity 2, and the strain test results of the metal sample are determined based on the multiple digital image signals.

[0061] It should be noted that the Dewar cavity 2 is an insulated container with an internal cavity, which contains a hollow cavity that can accommodate the support 3.

[0062] It should be noted that the fiber optic imaging module 4 has a cylindrical structure, composed of multiple imaging fibers and multiple transmission fibers. The imaging fiber is located at the center of the fiber optic imaging module 4, and transmission fibers are arranged around it. A low-temperature polymer protective layer is placed on the outside of the transmission fibers to prevent the fiber optic imaging module 4 from being affected by the low temperature in the liquid hydrogen temperature range. One end of the imaging fiber is aligned with the gauge length section to acquire the analog image signal of the gauge length section, and the other end is connected to a bidirectional adapter to transmit the analog image signal to the image acquisition module 6 through the bidirectional adapter. The diameter of one imaging fiber or one transmission fiber is 1 mm to 1.5 mm, and the resolution of the imaging fiber is no less than 5 megapixels.

[0063] It should be noted that the acquisition and processing of the image analog signal in this application are jointly completed by the separate fiber optic imaging module 4 and image acquisition module 6. Because the fiber optic imaging module 4 is not easily affected by the low temperature in the liquid hydrogen temperature range, it is placed inside the Dewar cavity 2. The imaging fiber acquires the image analog signal of the gauge length segment of the metal sample. The imaging fiber transmits the image analog signal to the image acquisition module 6 located outside the Dewar cavity 2 via a bidirectional adapter, where the image acquisition module 6 processes the image analog signal. This application separates the image analog signal acquisition module and the image analog signal processing module. The fiber optic imaging module 4 completes the acquisition of the image analog signal, and the image acquisition module 6 completes the processing. The fiber optic imaging module 4 and the image acquisition module 6 are respectively located inside and outside the Dewar cavity 2 to achieve the acquisition of the gauge length segment image inside the Dewar cavity 2 and the processing of the image analog signal outside the Dewar cavity 2.

[0064] It should be noted that the image simulation signal of the gauge length is acquired in real time through the imaging fiber. The deformation of the gauge length is analyzed based on the image simulation signal by the image acquisition module 6 and the image processing device 7. The complete strain data of the metal sample during the strain test is dynamically acquired, realizing non-contact full-field strain measurement of the metal sample in the liquid hydrogen temperature zone (20K, i.e., 20 K) to obtain the strain test results of the metal sample.

[0065] It should be noted that a display screen is installed outside the Dewar cavity 2. The imaging fiber transmits the image analog signal to the display screen outside the Dewar cavity 2 through a bidirectional adapter, so that the tester can obtain the image digital signal of the imaging fiber in real time. This facilitates the tester to control the entire strain test process of the metal sample and allows the tester to calibrate the imaging fiber before the strain test of the metal sample to ensure the smooth conduct of the strain test.

[0066] It should be noted that the metal sample is equipped with a gauge length section, which is a specific area of ​​the metal sample used to measure deformation during the test.

[0067] It should be noted that the Dewar cavity 2 is an insulated container used in low-temperature environments. After the support 3, which is installed on the metal sample, is placed inside the Dewar cavity 2, the Dewar cavity 2 is sealed by the flange 5. The inside of the Dewar cavity 2 is then evacuated and filled with helium in sequence, using helium as the cooling medium, so that the internal temperature of the Dewar cavity 2 drops to the liquid hydrogen temperature range.

[0068] It should be noted that by setting a bidirectional adapter, there is no need to open a through hole in flange 5 to allow the imaging fiber to pass through. This allows the Dewar cavity 2 and the flange to form a vacuum-insulated, sealed space, thus keeping the strain test environment temperature of the metal sample in the liquid hydrogen temperature range, thereby improving the reliability of the strain test results of the metal sample.

[0069] It should be noted that this application separates the image analog signal acquisition module and the image analog signal processing module. The image analog signal acquisition is completed by the fiber optic imaging module 4, and the image acquisition module 6 completes the image analog signal processing. The bidirectional adapter on the flange 5 is the basis for the separation of the fiber optic imaging module 4 and the image acquisition module 6 in this application. Through the bidirectional adapter of this application, the communication connection basis for transmitting image analog signals in the vacuum-sealed environment of the Dewar cavity 2 can be guaranteed, so that the application can acquire image analog signals inside the Dewar cavity 2 and process image analog signals outside the Dewar cavity 2. The fiber optic imaging module 4, which can withstand the low temperature of liquid hydrogen, is located inside the Dewar cavity 2, while the image acquisition module 6 and the image processing module, which cannot withstand the low temperature of liquid hydrogen, are located in the normal temperature environment outside the Dewar cavity 2.

[0070] It should be noted that the bidirectional adapter includes a first port and a second port, with the first port communicatively connected to the second port. The first and second ports are respectively located at the bottom and top of the flange 5. Before sealing the Dewar cavity 2 through the flange 5, the end of the imaging fiber that is not aligned with the gauge length is connected to the first port. After sealing the Dewar cavity 2 through the flange 5, the image acquisition module 6 is connected to the second port, enabling the imaging fiber to transmit the analog image signal to the image acquisition module 6 through the bidirectional adapter. After connecting the imaging fiber to the bidirectional adapter, the bidirectional adapter is vacuum-sealed to ensure the airtightness of the flange 5 and the Dewar cavity 2.

[0071] It should be noted that, in order to better control the temperature inside the Dewar cavity 2, a temperature sensor is installed inside the Dewar cavity 2, and a sensor adapter is installed on the flange 5. The temperature sensor transmits the temperature data inside the Dewar cavity 2 to the outside of the Dewar cavity 2 through the sensor adapter. The internal temperature of the Dewar cavity 2 can be controlled manually or by a controller, thereby maintaining the temperature of the strain test environment of the metal sample in the liquid hydrogen temperature range, which helps to improve the reliability of the strain test results of the metal sample.

[0072] It should be noted that the image acquisition module 6 is located outside the Dewar cavity 2, so that the image acquisition module 6 is in a normal temperature environment, which can prevent the image acquisition module 6 from being affected by low temperature, thereby preventing the image acquisition module 6 from being damaged due to low temperature.

[0073] It should be noted that the image processing device 7 is located outside the Dewar cavity 2. The image processing device 7 can be a computer or processor or other devices. This application does not limit the specific type of the image processing device 7, as long as it can determine the strain test results of the metal sample based on the image digital signal.

[0074] It should be noted that, through the strain testing device for metal materials in the liquid hydrogen temperature range of this application, the fiber optic imaging module 4 can acquire images of the gauge length of the metal sample inside the Dewar cavity 2, ensuring the insulation effect of the Dewar cavity 2, stabilizing the test environment temperature during the strain testing process of the metal sample, realizing non-contact, high-precision full-field strain measurement of the metal sample in the sealed and insulated Dewar cavity 2, preventing the image acquisition module 6 from being damaged by the low temperature of the liquid hydrogen temperature range, and improving the reliability of the strain test results of the metal sample in the liquid hydrogen temperature range.

[0075] Additionally, in one embodiment, reference is made to Figure 1 The gauge length section is provided with speckle; the inside of the bracket 3 is vertically provided with guide post 8 and guide rail 9, the guide rail 9 is installed on the guide post 8, the fiber optic imaging module 4 is installed on the guide rail 9, the fiber optic imaging module 4 can move along the guide rail 9, and the fiber optic imaging module 4 is aligned with the speckle.

[0076] It should be noted that a speckle pattern is sprayed onto the gauge length of the metal sample using a mixture of titanium dioxide and carbon black powder. The mixing of titanium dioxide and carbon black increases the contrast of the speckle and suppresses interference from reflected light on the surface of the metal sample. This helps the Digital Image Correlation (DIC) algorithm to more accurately track the speckle center, thereby determining the strain test results of the metal sample. The speckle particle size is 10 to 50 micrometers, and the speckle density is greater than or equal to 200 points / square millimeter.

[0077] It should be noted that by vertically setting the guide post 8 and guide rail 9 inside the bracket 3, the fiber optic imaging module 4 installed on the guide rail 9 can slide on the guide rail 9. That is, the fiber optic imaging module 4 can be arbitrarily adjusted and fixed in the vertical direction along the sliding guide rail 9. Since this application performs image analog signal acquisition inside the Dewar cavity 2 and image analog signal processing outside the Dewar cavity 2, the imaging field of view of the image analog signal depends on the position of the acquisition end of the imaging fiber. Therefore, the guide rail 9 is set to enable the imaging fiber to slide on the guide rail 9 to adapt to metal samples of different sizes and ensure the integrity of the image acquisition of the metal sample by the imaging fiber.

[0078] It should be noted that before sealing the Dewar cavity 2 with flange 5, a metal sample with speckle patterns on the surface of the gauge section is installed onto the support 3. The metal sample is adjusted to align its coaxiality with the support 3, and then the support 3 is placed into the Dewar cavity 2. The fiber optic imaging module 4 is installed on the guide rail 9, aligning the imaging fiber with the speckle pattern. The imaging fiber is connected to the bidirectional adapter and calibrated. If there is imaging distortion based on the image analog signal, or if the speckle pattern in the image is incomplete, the imaging fiber is slid along the guide rail 9 until the imaging fiber acquires an image analog signal without distortion and the speckle pattern is complete. After calibrating the imaging fiber, the Dewar cavity 2 is sealed with flange 5.

[0079] Additionally, in one embodiment, reference is made to Figure 1 The image acquisition module 6 includes a visible light compensation light source, an infrared light source, and a hybrid image transcription unit. The visible light compensation light source and the infrared light source are connected to the optical fiber. The hybrid image transcription unit includes a CMOS sensor. The image analog signal includes a visible light analog signal and an infrared light analog signal. The CMOS sensor is used to generate an image digital signal based on the visible light analog signal and the infrared light analog signal.

[0080] It should be noted that the interior of the Dewar cavity 2, sealed by flange 5, is only illuminated by the optical fiber. However, the light intensity of the optical fiber is limited. Therefore, an adjustable visible light compensation light source is set up to make the speckle contrast high when the imaging fiber acquires the image simulation signal, thereby improving the accuracy of the DIC algorithm in tracking the speckle center and improving the reliability of the strain test results of the metal sample.

[0081] It should be noted that a layer of condensate will condense on the surface of the metal sample in the liquid hydrogen temperature zone, which will cause light reflection interference to the image simulation signal. The image acquisition module 6 obtains visible light and infrared images based on the image simulation signal, and performs multispectral image fusion through a weighted fusion algorithm to obtain a fused image, so as to eliminate the reflection interference of the condensate of the metal sample in the liquid hydrogen temperature zone, improve the signal-to-noise ratio of the image processed by the DIC algorithm, obtain better imaging effect of the gauge length segment, ensure the identification accuracy of feature points or speckle centers, and further improve the reliability of strain test results of metal samples in the liquid hydrogen temperature zone.

[0082] It should be noted that the image acquisition module 6 includes a visible light compensation light source, an infrared light source, and a hybrid image transcribing unit. The wavelength range of the visible light compensation light source is 400 nm to 700 nm, and the wavelength range of the infrared light source is 850 nm to 150 nm. The visible light compensation light source and the infrared light source support dynamic adjustment of light intensity to adapt to the reflection characteristics of different temperatures and achieve better imaging results.

[0083] It should be noted that the visible light compensation light source uses an LED array with an adjustable light intensity range of 0 lux to 5000 lux, while the infrared light source uses a narrow-band filter to enhance contrast.

[0084] It should be noted that the optical fiber is connected to the visible light compensation light source and the infrared light source. Visible light and infrared light are transmitted to the interior of the Dewar cavity 2 through the optical fiber, thereby providing visible light illumination and infrared light illumination for the imaging fiber. The imaging fiber can acquire visible light analog signals and infrared light analog signals.

[0085] It should be noted that the CMOS sensor of the hybrid image transcription unit can achieve photoelectric conversion between analog and digital image signals, and can also achieve multispectral image fusion of visible light and infrared images. The hybrid image transcription unit includes a CMOS sensor with a frame rate of ≥1000fps and a resolution of ≥5 micrometers / pixel.

[0086] It should be noted that the imaging fiber acquires a visible light analog signal under illumination by a visible light compensation light source, and the CMOS sensor photoelectrically converts the visible light analog signal to obtain a visible light digital image. Similarly, the imaging fiber acquires an infrared light analog signal under illumination by an infrared light source, and the CMOS sensor photoelectrically converts the infrared light analog signal to obtain an infrared radiation image. An infrared image is then obtained based on this infrared radiation image using infrared conversion technology. The infrared radiation image is invisible to the human eye, while the infrared image is a visible digital image.

[0087] In addition, embodiments of the present invention provide a method for strain testing of metallic materials in the liquid hydrogen temperature range, applicable to... Figure 1 The strain testing apparatus for metallic materials in the liquid hydrogen temperature range of the embodiment shown is based on... Figure 2 The method includes, but is not limited to, the following steps:

[0088] S10, after installing the metal sample into the support, place it into the Dewar cavity and adjust the fiber optic imaging module to align with the gauge length of the metal sample.

[0089] S20, the Dewar cavity is sealed by the flange, and after evacuating and filling the Dewar cavity with helium in sequence, the internal temperature of the Dewar cavity is reduced to the liquid hydrogen temperature range.

[0090] S30, start the fiber optic imaging module and universal tensile testing machine to acquire the image simulation signal of the gauge length through the imaging fiber while the optical fiber provides illumination to the Dewar cavity;

[0091] S40: The image acquisition module acquires the image analog signal, generates the image digital signal based on the image analog signal, and sends the image digital signal to the image processing device so that the image processing device can determine the strain test result of the metal sample based on the image digital signal.

[0092] It should be noted that the fiber optic imaging module located inside the Dewar cavity is used to acquire the analog image signal of the gauge length segment of the metal sample, while the image acquisition module located outside the Dewar cavity is used to process the analog image signal of the gauge length segment. Since the fiber optic imaging module and the image acquisition module in this application are not an integrated structure, the imaging fiber is aligned with the gauge length segment before being installed on the bracket, and the bracket with the imaging fiber is then placed inside the Dewar cavity. In existing technology, since the camera is located outside the Dewar cavity, it is not necessary to adjust the camera's shooting area before sealing the Dewar cavity with the flange.

[0093] It should be noted that the Dewar cavity is sealed by a flange and air is evacuated to make the inside of the Dewar cavity a vacuum insulated cavity. Since the internal temperature of the Dewar cavity needs to be lowered from room temperature to the liquid hydrogen temperature range, the required cooling time is long, and the strain test environment temperature required for the metal sample is extremely low, helium with a low boiling point is used as the cooling medium. Helium is filled into the Dewar cavity, and the internal temperature of the Dewar cavity is lowered to the liquid hydrogen temperature range by controlling the helium.

[0094] It should be noted that when the fiber optic imaging module and the universal tensile testing machine are started, during the strain test of the metal sample by the universal tensile testing machine, the imaging fiber acquires the image simulation signal of the gauge length segment while the transmission fiber provides illumination to the inside of the Dewar cavity.

[0095] It should be noted that the imaging fiber is located inside the Dewar cavity. Inside the Dewar cavity, the imaging fiber acquires the image analog signal of the gauge length segment and transmits the image analog signal to the image acquisition module located outside the Dewar cavity through a bidirectional adapter. The image acquisition module acts as the receiving end of the imaging fiber and is used to process the image analog signal without performing imaging based on the image analog signal.

[0096] It should be noted that in this application, the full-field displacement field and strain tensor data of the metal sample are dynamically and in real time calculated using the DIC algorithm, thereby determining the strain test results of the metal sample based on the image digital signal. Exemplarily, the image processing device acquires the image digital signal, extracts feature points based on the natural texture of the gauge length surface, tracks the feature points in multiple image digital signals, and determines the displacement of feature points in adjacent image digital signals by acquiring multiple image digital signals arranged in chronological order. Based on the displacement, the strain data of the metal sample is obtained, thereby determining the strain test results of the metal sample. The measurement accuracy of the displacement is ±0.01 mm, and the strain measurement accuracy is ±0.05%.

[0097] It should be noted that the technical principle of acquiring analog image signals of the gauge length segment inside the Dewar cavity through separate imaging fibers and image acquisition modules, obtaining digital image signals based on the analog image signals outside the Dewar cavity, and obtaining strain test results of the metal sample based on the digital image signals outside the Dewar cavity can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0098] The technical solution of this embodiment separates the imaging fiber and the image acquisition module, placing the imaging fiber inside the Dewar cavity where the internal temperature is in the liquid hydrogen temperature range. The imaging fiber is aligned with the gauge length of the metal sample to acquire the image simulation signal of the gauge length. The imaging fiber transmits the image simulation signal to the image acquisition module through a bidirectional adapter on the flange. The image acquisition module and the image processing device obtain the strain test results of the metal sample based on the image simulation signal. Thus, the image of the gauge length can be acquired inside the Dewar cavity, and the image acquisition module is not affected by the low temperature of the liquid hydrogen temperature range. Furthermore, the imaging fiber is directly aligned with the gauge length, resulting in higher imaging quality. The test environment temperature inside the Dewar cavity is stably maintained in the liquid hydrogen temperature range, making the strain test results of the metal sample in the liquid hydrogen temperature range more reliable.

[0099] In another embodiment, step S10 may include, but is not limited to, the following steps:

[0100] S11, Install the metal sample onto the support, adjust the metal sample to align the coaxiality of the metal sample and the support, and place the support into the Dewar cavity;

[0101] S12, Install the fiber optic imaging module on the guide rail, aligning the imaging fiber with the speckle;

[0102] S13, connect the imaging fiber to the bidirectional adapter, seal the bidirectional adapter, and calibrate the imaging fiber to ensure that the image analog signal is distortion-free and the gauge length segment is fully imaged.

[0103] It should be noted that before performing strain testing on the metal sample, the image simulation signal from the imaging fiber is first acquired through the display screen. Based on the image displayed on the screen, the position of the imaging fiber and the image acquisition end are adjusted to ensure that the image based on the image simulation signal is distortion-free and that the gauge length segment is fully imaged, thus guaranteeing the imaging effect during the strain testing of the metal sample. After the imaging fiber is adjusted, the Dewar cavity is sealed with a flange.

[0104] It should be noted that, since the fiber optic imaging module is located inside the Dewar cavity and the image acquisition module is located outside the Dewar cavity, the position of the imaging fiber needs to be adjusted based on the imaging of the image analog signal before the Dewar cavity is sealed by the flange. After determining the imaging quality of the image analog signal of the imaging fiber, the Dewar cavity is sealed by the flange to make the inside of the Dewar cavity a heat-insulated and sealed cavity, which provides a basis for the subsequent implementation of controlling the internal temperature of the Dewar cavity to be reduced to the liquid hydrogen temperature range by helium.

[0105] It should be noted that the technical principle of installing metal samples and fiber optic imaging modules to provide the basis for strain testing of metal samples can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0106] In another embodiment, step S40 may include, but is not limited to, the following steps:

[0107] S411, The image processing device acquires the image analog signal, performs analog-to-digital conversion on the image analog signal, and obtains the image digital signal;

[0108] S412 performs filtering and noise reduction processing on the digital image signal to obtain a denoised image;

[0109] S413, Based on the denoised image, determine the feature points and feature coordinates of the gauge length segment, and generate a calibration image, wherein the calibration image includes feature points, feature coordinates and a first timestamp, and the feature coordinates represent the coordinates of the feature points;

[0110] S414, acquire multiple calibration images, and sort the multiple calibration images based on the first timestamp;

[0111] S415 determines the displacement of feature points in adjacent frames based on multiple feature coordinates, and generates strain test results of metal samples in real time based on the displacement.

[0112] It should be noted that the feature points of the gauge length segment are determined based on the denoised image. The feature points are points extracted from the natural surface texture of the gauge length segment. Multiple feature points can be extracted to obtain the full-field strain data of the gauge length segment of the metal sample based on the displacement of multiple feature points.

[0113] It should be noted that the technical principle of generating strain test results for metal samples based on image-simulated signals can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0114] In another embodiment, in step S40, an image analog signal is acquired by the image acquisition module, and an image digital signal is generated based on the image analog signal. This process may include, but is not limited to, the following steps:

[0115] S421, when the optical fiber provides visible light illumination and infrared light illumination for the imaging fiber, the imaging fiber acquires an image analog signal, which includes a visible light analog signal and an infrared light analog signal.

[0116] S422, the CMOS sensor acquires visible light analog signals and infrared light analog signals, performs photoelectric conversion on the visible light analog signals and infrared light analog signals respectively, and obtains visible light images and infrared radiation images respectively;

[0117] S423, the CMOS sensor performs infrared image transcription on the infrared radiation image to obtain an infrared image;

[0118] The S424 CMOS sensor performs multispectral image fusion on visible light and infrared images to obtain a fused image.

[0119] S425, strain test results of metal samples generated based on multi-frame fused images.

[0120] It should be noted that after the Dewar cavity is sealed by the flange, the inside of the Dewar cavity is a closed, dark space, and the optical fiber can provide a light source for the inside of the Dewar cavity. In order to further improve the contrast of speckle in the image simulation signal, an additional visible light compensation light source is set. The light intensity of the visible light compensation light source is adjustable, and the optical fiber and the visible light compensation light source together provide illumination for the inside of the Dewar cavity. By improving the contrast of speckle in the image simulation signal, the tracking accuracy of the DIC algorithm on the speckle center is improved, thereby improving the accuracy of the strain test results of the metal sample.

[0121] It should be noted that the internal temperature of the Dewar cavity is extremely low, equivalent to liquid hydrogen temperature. A layer of condensate will condense on the surface of the metal sample inside the Dewar cavity. Under illumination from the optical fiber and the visible light compensation light source, this condensate reflects the light from both sources, resulting in light reflection interference and a low signal-to-noise ratio in the image simulation signal. This is detrimental to obtaining strain test results for the metal sample based on the image simulation signal. Therefore, an additional infrared light source is used. The imaging fiber acquires an infrared light simulation signal under infrared illumination. The image acquisition module obtains a fused image of the visible light and infrared images based on the image simulation signal. The fused image eliminates the light reflection interference from the condensate, improves the signal-to-noise ratio of the image, and enhances the accuracy of the DIC algorithm in identifying speckle centers, thereby improving the accuracy of the strain test results for the metal sample.

[0122] It should be noted that high-resolution image acquisition is achieved through the fiber optic imaging module located inside the Dewar cavity, and multispectral image fusion and DIC algorithm tracking of feature point displacement are achieved through the image acquisition module and image processing device outside the Dewar cavity 2, combined with visible light compensation light source, infrared light source and infrared image transcription technology, as well as data calculation based on displacement field and strain tensor, thereby obtaining the strain test results of the metal sample.

[0123] It should be noted that the strain test results of the metal sample are generated based on multi-frame fused images using the DIC algorithm. The DIC algorithm is existing technology, and this application does not make any formal improvements to the specific steps of the DIC algorithm, so they will not be elaborated here. For ease of understanding, the specific implementation steps of the DIC algorithm in this application are provided as follows: High-contrast speckle patterns are sprayed onto the gauge length of the metal sample; the DIC algorithm calibrates the speckle center based on the speckle surface; or, feature points are extracted using the natural surface texture of the gauge length; the displacement of the speckle center or feature points in adjacent frames is calculated using sub-pixel interpolation, where the displacement accuracy reaches 0.01 pixels; based on the Green-Lagrange strain tensor, the full-field strain distribution of the metal sample is calculated using the displacement gradient matrix.

[0124] It should be noted that, under conditions of visible light and infrared light illumination, the technical principle of generating strain test results for metal samples based on image simulation signals can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0125] In another embodiment, step S425 may include, but is not limited to, the following steps:

[0126] S4251: Obtain the fused image, filter and denoise the fused image to obtain the denoised image;

[0127] S4252, Based on the denoised image, determine the speckle center and speckle coordinates, and generate a calibration image, wherein the calibration image includes the speckle center, speckle coordinates and a first timestamp, and the speckle coordinates represent the coordinates of the speckle center;

[0128] S4253, acquire multiple calibration images, and sort the multiple calibration images based on the first timestamp;

[0129] S4254 determines the displacement of the speckle center in adjacent frames based on multiple speckle coordinates, and generates strain test results of metal samples in real time based on the displacement.

[0130] It should be noted that the fused image is denoised by applying Gaussian filtering.

[0131] It should be noted that the technical principle of generating strain test results for metal samples based on multi-frame fused images can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0132] In another embodiment, the universal tensile testing machine includes a servo motor connected to a support. The servo motor is used to load the metal sample. In step S30, after starting the fiber optic imaging module and the universal tensile testing machine, the following steps are included, but are not limited to:

[0133] S31, output a loading signal through the servo motor, wherein the loading signal includes a second timestamp and loading data of the servo motor on the metal sample;

[0134] S32 sorts multiple loading signals based on the second timestamp, and generates stress test results for the metal sample in real time based on the sorted multiple loading signals.

[0135] It should be noted that the loading data includes the output parameters of the servo motor, such as the output power of the servo motor, the time, and the magnitude of the stress applied to the metal sample.

[0136] It should be noted that in existing universal tensile testing machines, the metal sample is loaded by a servo motor and a support. The servo motor generates a loading signal, which includes the loading data of the servo motor on the metal sample. Based on the loading data, the stress test results of the metal sample can be obtained in real time. By obtaining the strain test results and stress test results of the metal sample, the strain-stress test results of the metal sample can be obtained.

[0137] In another embodiment, after generating the stress test results of the metal sample in real time in step S32, the steps include, but are not limited to, the following:

[0138] S33, Obtain strain test results and stress test results, wherein the strain test results include a first timestamp and the stress test results include a second timestamp;

[0139] S34 generates stress-strain test results for metal samples in real time by matching the first and second timestamps.

[0140] It should be noted that the strain test results include a first timestamp, and the stress test results include a second timestamp. Through the timestamp and hardware synchronization triggering mechanism, multiple loading signals of the servo motor and multiple frames of images of the gauge segment are matched to ensure that the stress data and strain data are synchronized, so that the timing error is less than 1 millisecond, so as to output the stress and strain test results of the metal sample.

[0141] It should be noted that the technical principle of obtaining stress-strain test results of metal samples based on stress and strain test results can be found in [reference needed]. Figure 1 The description of the illustrated embodiments will not be repeated here.

[0142] For ease of understanding, the following complete implementation example is provided:

[0143] S501, spray speckle pattern onto the gauge length of the metal sample, mount the metal sample using a support, and adjust the metal sample to align the metal sample and the support coaxially.

[0144] S502: Install the fiber optic imaging module on the guide rail, adjust the imaging fiber so that one end of the imaging fiber is aligned with the speckle and the other end is connected to the bidirectional adapter, place the bracket inside the Dewar cavity, and seal the bidirectional adapter to ensure the airtightness between the flange and the bidirectional adapter.

[0145] S503 transmits analog image signals to the display screen via an imaging fiber. Based on the image displayed on the screen, the imaging fiber is adjusted to ensure that the display screen's image completely covers the gauge length and that the image is distortion-free.

[0146] S504 connects the image acquisition module to the bidirectional adapter and the image processing device, activates the visible light supplementary light source and the infrared light source, and adjusts the light intensity of the visible light supplementary light source and the infrared light source to maximize the contrast of the speckle.

[0147] S505, start the strain testing device for metallic materials in the liquid hydrogen temperature range, and adjust the imaging fiber to ensure that the image simulation signal acquired by the imaging fiber is normal.

[0148] S506, start the strain testing device for metal materials in the liquid hydrogen temperature zone, put the metal sample, support and fiber optic imaging module into the Dewar cavity, seal the Dewar cavity through the flange, and perform vacuuming and helium filling operations in sequence, using helium as the cooling medium to control the internal temperature of the Dewar cavity to drop to the liquid hydrogen temperature zone.

[0149] S507. When the internal temperature of the Dewar cavity drops to the liquid hydrogen temperature range, the universal tensile testing machine and fiber optic imaging module are started. During the strain test of the metal sample by the universal tensile testing machine, the imaging fiber acquires the image simulation signal of speckle, which includes visible light simulation signal and infrared light simulation signal.

[0150] S508: The imaging fiber transmits the image analog signal to the image acquisition module through a bidirectional adapter. The CMOS sensor acquires the image analog signal and performs photoelectric conversion on the image analog signal to obtain visible light image and infrared radiation image.

[0151] S509, the CMOS sensor performs infrared conversion on the infrared radiation image to obtain an infrared image, performs multispectral image fusion based on the visible light image and the infrared image to obtain a fused image, and sends the fused image to the image processing device;

[0152] S510, the image processing device acquires the fused image, performs noise reduction processing on the fused image, and obtains the noise-reduced image;

[0153] S511, Based on the denoised image, determine the speckle center and speckle coordinates to obtain a calibration image, which includes the speckle center, speckle coordinates and a first timestamp;

[0154] S512, sort the multi-frame calibration images based on the first timestamp, determine the speckle center displacement of adjacent frames based on the sorted multi-frame calibration images, and determine the strain test results of the metal sample based on the displacement.

[0155] S513, after starting the universal tensile testing machine, the loading signal of the servo motor on the metal sample is acquired in real time. The loading signal includes a second timestamp. Multiple loading signals are sorted based on the second timestamp, and stress test results are generated based on the sorted multiple loading signals.

[0156] S514, the image processing device acquires stress test results and strain test results in real time, and generates stress and strain test results of metal samples in real time.

[0157] The strain testing device for metallic materials in the liquid hydrogen temperature range described in this application separates the imaging fiber and the image acquisition module. The imaging fiber acquires a simulated image signal of the gauge length of the metallic sample inside the Dewar cavity. This simulated image signal is then transmitted to the image acquisition module via a bidirectional adapter, preventing damage to the image acquisition module due to the low temperature of the liquid hydrogen range and maintaining the ambient temperature during strain testing, thus improving the reliability of the strain test results for the metallic samples. The imaging fiber can be flexibly arranged and adjusted to measure the strain of metallic samples of different sizes. Simultaneously, visible light compensation light and infrared light sources are used to provide visible and infrared illumination to the imaging fiber, obtaining visible and infrared images. Multispectral fusion is then performed to eliminate reflection interference from surface condensates on the metallic sample in the liquid hydrogen temperature range, improving the signal-to-noise ratio of the calibration image and ensuring the accuracy of speckle center or feature point identification, resulting in more reliable strain test results for the metallic samples.

[0158] The above provides a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

Claims

1. A method for testing the strain of metallic materials in the liquid hydrogen temperature range, characterized in that, An application for strain testing of metallic materials includes a universal tensile testing machine, a Dewar cavity, and a support. The support is used to hold the metal sample. The device further includes: a fiber optic imaging module located inside the Dewar cavity, comprising an imaging fiber and a transmission fiber. The imaging fiber is aligned with the gauge length of the metal sample and is used to acquire analog image signals, while the transmission fiber provides illumination; a flange detachably sealed to the top of the Dewar cavity, and the flange is equipped with a bidirectional adapter; an image acquisition module located outside the Dewar cavity, connected to the imaging fiber via the bidirectional adapter, and used to generate digital image signals based on the analog image signals; and an image processing device. The device is communicatively connected to the image acquisition module. The image processing device is used to determine the strain test results of the metal sample based on the image digital signal. The gauge length is provided with speckle patterns. A guide post and a guide rail are vertically arranged inside the support. The guide rail is mounted on the guide post, and the fiber optic imaging module is mounted on the guide rail. The fiber optic imaging module can move along the guide rail and is aligned with the speckle patterns. The image acquisition module includes a visible light compensation light source, an infrared light source, and a hybrid image transcribing unit. The visible light compensation light source and the infrared light source are connected to the optical fiber. The hybrid image transcribing unit includes a CMOS sensor. The image analog signal includes a visible light analog signal and an infrared light analog signal. The CMOS sensor is used to generate the image digital signal based on the visible light analog signal and the infrared light analog signal. The method includes: After the metal sample is mounted on the support, it is placed in the Dewar cavity, and the fiber optic imaging module is adjusted to align with the gauge length of the metal sample. The Dewar cavity is sealed by a flange. After evacuating and filling the Dewar cavity with helium in sequence, the internal temperature of the Dewar cavity is reduced to the liquid hydrogen temperature range. The fiber optic imaging module and the universal tensile testing machine are activated to acquire the image simulation signal of the gauge length segment through the imaging fiber while the optical fiber provides illumination to the Dewar cavity. The image acquisition module acquires the image analog signal, generates the image digital signal based on the image analog signal, and sends the image digital signal to the image processing device so that the image processing device can determine the strain test result of the metal sample based on the image digital signal; The process includes acquiring the analog image signal through an image acquisition module and generating a digital image signal based on the analog image signal, comprising: When the optical fiber provides visible light illumination and infrared light illumination to the imaging fiber, the imaging fiber acquires the image simulation signal, which includes a visible light simulation signal and an infrared light simulation signal. The CMOS sensor acquires the visible light analog signal and the infrared light analog signal, and performs photoelectric conversion on the visible light analog signal and the infrared light analog signal respectively to obtain a visible light image and an infrared radiation image respectively; The CMOS sensor performs infrared image transcription on the infrared radiation image to obtain an infrared image; The CMOS sensor performs multispectral image fusion on the visible light image and the infrared image to obtain a fused image.

2. The method for testing the strain of metallic materials in the liquid hydrogen temperature range according to claim 1, characterized in that, After mounting the metal sample onto the support, it is placed inside the Dewar cavity. The fiber optic imaging module is then adjusted to align with the gauge length of the metal sample, including: The metal sample is installed onto the support, the metal sample is adjusted to align the coaxiality of the metal sample and the support, and the support is placed into the Dewar cavity; The fiber optic imaging module is mounted on the guide rail, and the imaging fiber is aligned with the speckle pattern. The imaging fiber is connected to the bidirectional adapter, the bidirectional adapter is sealed, and the imaging fiber is calibrated to ensure that the image analog signal is distortion-free and the gauge length segment is fully imaged.

3. The method for testing the strain of metallic materials in the liquid hydrogen temperature range according to claim 1, characterized in that, The image digital signal is then sent to an image processing device, which determines the strain test result of the metal sample based on the image digital signal, including: The fused image is acquired, and the fused image is filtered and denoised to obtain a denoised image; Based on the denoised image, the speckle center and speckle coordinates are determined, and a calibration image is generated, wherein the calibration image includes the speckle center, the speckle coordinates, and a first timestamp; Acquire multiple frames of the calibration images, and sort the multiple frames of the calibration images based on the first timestamp; The displacement of the speckle center in adjacent frames is determined based on multiple speckle coordinates, and the strain test results of the metal sample are generated in real time based on the displacement.

4. The method for testing the strain of metallic materials in the liquid hydrogen temperature range according to claim 3, characterized in that, The universal tensile testing machine includes a servo motor, which is connected to the support frame and is used to load the metal sample. After activating the fiber optic imaging module and the universal tensile testing machine, the following is also included: A loading signal is generated by the servo motor, wherein the loading signal includes a second timestamp and loading data of the servo motor on the metal sample; The multiple loading signals are sorted based on the second timestamp, and the stress test results of the metal sample are generated in real time based on the sorted multiple loading signals.

5. The method for testing the strain of metallic materials in the liquid hydrogen temperature range according to claim 4, characterized in that, After generating the stress test results of the metal sample in real time, the method further includes: The strain test results and the stress test results are obtained, wherein the strain test results include the first timestamp and the stress test results include the second timestamp; By matching the first timestamp and the second timestamp, the stress-strain test results of the metal sample are generated in real time.

Images