A method and device for testing and processing data of strain rate of a material

Abstract

This invention provides a method and apparatus for performance testing and data processing of strain rate in materials, relating to the field of material testing or analysis technology. The method includes: bringing the cryogenic insulation chamber to a uniform low temperature and applying a load to the sample; acquiring performance test data in real time during the load application process; calculating the displacement field and strain field of the entire field, and calculating the thermo-mechanical conversion coefficient; plotting the original stress-strain curve; using whether the adiabatic temperature rise component exceeds a preset threshold as a segmentation condition, segmenting the engineering stress-strain data based on the segmentation condition, applying a thermal correction factor based on the thermo-mechanical conversion coefficient to the segmented temperature rise influence segment, and obtaining a corrected stress-strain curve; outputting the original stress-strain curve, the corrected stress-strain curve, the temperature field visualization result, and the spatial distribution map of the thermo-mechanical conversion coefficient. This improves the accuracy of mechanical property testing of materials under low-temperature dynamic service conditions.

Description

Technical Field

[0001] This invention relates to the field of materials testing or analysis technology, specifically to a method and apparatus for testing and processing the performance of strain rate in materials. Background Technology

[0002] Materials are facing increasingly harsh operating environments in modern industrial development. For example, materials used in critical components such as those for collision safety in high-altitude, low-temperature, or cold-region aircraft, protection of cryogenic battery structures in new energy vehicles, sealing of cryogenic fuel systems, and ice-collision protection for polar research vessels not only withstand dynamic medium-strain rate impact loads during operation but also need to maintain their mechanical integrity in cryogenic environments. The mechanical properties of materials (especially yield strength and failure modes) are extremely sensitive to temperature and strain rate. Therefore, accurate mechanical property testing of materials under coupled medium-strain rate and cryogenic conditions is crucial for advanced product design, safety assessment, and reliability analysis.

[0003] Currently, some techniques have been reported for testing materials at medium strain rates at room temperature or quasi-static cryogenic conditions, but the coupled mechanical property testing at medium strain rates at low temperatures is not yet mature. Existing technologies mainly suffer from the following shortcomings:

[0004] (I) Device integration and temperature control Existing cryogenic chamber equipment suffers from poor compatibility and insufficient adaptability with medium strain rate testing machines. Its rigid chamber design prevents flexible adjustment of the chamber's position to accommodate tensile and compressive specimens of varying sizes. Traditional cryogenic chambers exhibit slow cooling rates, with a temperature change rate of only about 3°C / min, requiring over 30 minutes to cool from room temperature to -100°C, resulting in low testing efficiency. Furthermore, the uneven temperature distribution within the chamber and the significant temperature gradients in different regions of the specimen lead to deviations in the strain response under stress and deformation.

[0005] (ii) Compatibility of optical measurements In low-temperature environments, liquid nitrogen vaporization causes fogging and frosting on the optical observation window, severely interfering with the optical path of digital image correlation (DIC) and preventing DIC from obtaining clear speckle images. Some existing technologies employ heating for defrosting or post-processing deep learning image restoration, but heating interferes with the low-temperature environment, and restoration algorithms introduce additional errors and cannot be used for real-time, high-frame-rate dynamic acquisition of medium strain rates. Simultaneously, the observation window glass itself undergoes thermal contraction or deformation at low temperatures, leading to distortion in light refraction. Existing DIC correction methods are mostly based on static calibration using calibration plates, which cannot compensate for the variable refractive index distortion caused by real-time dynamic temperature gradients.

[0006] (III) Measurement and Data Processing of Multiple Physical Quantities Existing testing methods typically only record the applied force and macroscopic displacement, neglecting the adiabatic temperature rise effect inside the specimen during high-speed deformation. Under medium strain rate loading, plastic work is converted into heat, and the local temperature of the specimen may be significantly higher than the set ambient low temperature. However, traditional methods still assume that the specimen temperature is uniform and constant, causing the calculated stress-strain curve to deviate from the true value. In addition, existing technologies lack temperature drift compensation for force sensors at low temperatures, and lack the ability to conduct real-time quality assessment and feedback adjustment of multi-source data such as DIC image quality and infrared signal-to-noise ratio, making it difficult to guarantee the validity of data from long-term low-temperature dynamic tests.

[0007] (iv) Security and intelligence aspects Existing low-temperature testing equipment lacks clear status indicators and interlock prompts, making it easy for operators to accidentally open the door at low temperatures, resulting in frostbite or pinching injuries; the testing process relies on manual judgment of the insulation time, which is inefficient and cannot achieve continuous automatic testing of multiple samples.

[0008] Many materials need to operate in extreme environments with medium strain rates and low temperatures. Their mechanical properties directly determine the overall load-bearing capacity and operational safety of the structure. Therefore, accurately measuring the mechanical properties of materials under medium strain rate and low temperature conditions has become one of the core requirements of materials mechanical property research. However, existing medium strain rate and low temperature testing devices and data processing methods cannot simultaneously meet the requirements of rapid establishment of low temperature environments, frost-free high-precision DIC measurement, adiabatic temperature rise identification and correction, multi-physics field data fusion, and efficient and safe operation. This results in inaccurate and incomplete mechanical property data of materials under extreme environments, making it difficult to support the design, reliability assessment, and life prediction of high-end equipment. Summary of the Invention

[0009] In view of this, embodiments of this specification provide a method and apparatus for performance testing and data processing of strain rate in materials, so as to achieve high-precision full-field deformation measurement of DIC, adiabatic temperature rise identification and thermal correction of mechanical property data while dynamically loading medium strain rate on materials in a low-temperature environment.

[0010] The embodiments in this specification provide the following technical solutions: A method for testing and processing the performance of strain rate in a material, comprising the following steps: The sample is installed in the medium strain rate loading device. The liquid nitrogen delivery system and circulating fan are controlled by the feedback of the temperature measuring thermocouple to make the low temperature insulation box reach a uniform low temperature. During the insulation process, continuous anti-frost is carried out through the viewing window. After the insulation is completed, the load is applied to the sample. During the application of load, performance test data is collected in real time. The performance test data includes DIC speckle image sequence collected by high-speed camera system, temperature field sequence collected by infrared thermal imager, loading force signal collected by force sensor and multi-point temperature signal inside the chamber collected by thermocouple. Dynamic background noise removal and windowed thermal-optical distortion correction were performed sequentially on the DIC speckle image sequence, and the displacement field and strain field of the whole field were calculated. Emissivity compensation and spatial registration were performed on the temperature field sequence. The temperature field of the temperature field sequence was decomposed into adiabatic temperature rise components, and the thermo-mechanical conversion coefficient was calculated. Engineering stress-strain data were obtained by applying the force signal and strain field. An animation of the deformation evolution of the specimen surface is generated using displacement and strain fields, and strain concentration areas are identified. The original stress-strain curve is plotted using engineering stress-strain data. The adiabatic temperature rise component is used as a segmentation condition. Based on the segmentation condition, the engineering stress-strain data is segmented. A thermal correction factor based on the thermal-mechanical conversion coefficient is applied to the temperature rise influence segment obtained after segmentation to obtain the corrected stress-strain curve. Output the original stress-strain curve, the corrected stress-strain curve, the temperature field visualization results, and the spatial distribution map of the thermo-mechanical conversion coefficient.

[0011] Furthermore, the sample is installed in a medium strain rate loading device. Feedback from the thermocouple is used to control the liquid nitrogen delivery system and the circulating fan, ensuring the cryogenic insulation chamber reaches a uniform low temperature. During the insulation process, continuous frost prevention is implemented through a viewing window. After the insulation is completed, a load is applied to the sample, including: Place the sample between the upper and lower pressure heads of the medium strain rate loading device and close the insulation door. The liquid nitrogen delivery system is started. Using the PID controller of the temperature control module, the output pressure of the electric air pump and the opening and closing of the solenoid valve are controlled according to the feedback signal of the thermocouple. Liquid nitrogen is delivered into the low temperature insulation box made of double-walled vacuum polyurethane foam. At the same time, the circulating fan is started to make the temperature inside the box uniform until the target low temperature is reached. During the heat preservation stage and subsequent loading process, dry gas is continuously purged under positive pressure through the dry gas purging port of the visible window; The high-speed camera system of the high-precision optical DIC measurement system is activated, and the speckle pattern on the sample surface is aligned through the viewing window. Once the insulation time reaches the set value, the indicator light will turn green and the speaker will emit a prompt sound. Then, the insulation door will be unlocked, and the operator will start the medium strain rate loading device to apply a load to the sample.

[0012] Furthermore, dynamic background noise removal and viewport thermo-optical distortion correction are sequentially performed on the DIC speckle image sequence, and the full-field displacement field and strain field are calculated, including: In the absence of a sample, a set of pure background DIC image sequences were acquired during the liquid nitrogen transport process. The pure background DIC image sequences were decomposed into low-rank sparse components, and the extracted sparse components were used as dynamic stripe noise. Subtract the noise component projected onto the dynamic stripe noise from each frame of the original image in the DIC speckle image sequence to obtain the denoised image sequence; Real-time acquisition of the temperature distribution of the viewing window glass, and calculation of the deflection displacement field Δ(x,y)=t·(dn / dT)· T window (x,y) / n0, where t is the glass thickness, n is the refractive index of the glass material, T is the temperature, d is the differential, dn / dT is the temperature coefficient of refractive index, and n0 is the refractive index at room temperature. T window The temperature gradient on the glass surface; The denoised image sequence is corrected by inverse mapping according to the deflection displacement field to obtain the corrected image sequence. The first frame of the corrected image sequence before load application is used as the reference corrected image, and each frame of the corrected image sequence during load application is used as the deformed image. The reference correction image is divided into several sub-regions. Sub-region matching is performed in the deformed image using a zero-mean normalized cross-correlation function to obtain the integer pixel displacement of each sub-region. The subpixel displacement is calculated based on the grayscale interpolation information of each sub-region using a subpixel interpolation algorithm. The displacement field of the whole field is obtained based on the subpixel displacement of each sub-region, and the strain field of the whole field is calculated by performing point-by-point least squares fitting on the displacement field.

[0013] Furthermore, the temperature field sequence is decomposed into an adiabatic temperature rise component, and the thermo-mechanical conversion coefficient is calculated. Engineering stress-strain data are then obtained by calculating the applied force signal and strain field, including: Spatially register the temperature field and strain field of each frame in the temperature field sequence so that the coordinate systems of the temperature field and strain field are consistent with the global coordinate system of the sample. The adiabatic temperature rise component generated by plastic work is separated from the spatially registered temperature field. Each spatial point is obtained by calculating the adiabatic temperature rise component. At every moment t Thermo-mechanical conversion coefficient ,in, For equivalent stress, For the equivalent change increment, The adiabatic temperature rise component is represented by x and y, where x and y are spatial coordinates within the gauge length plane of the sample. t Let τ be the current time, and let τ be the integral variable.

[0014] Furthermore, engineering stress-strain data are obtained through calculations using the applied force signal and strain field, including: The engineering stress σ is calculated using the applied force signal and the initial cross-sectional area of ​​the specimen. eng (t)=F(t) / A0, where F(t) is the applied force signal at the current time t, and A0 is the initial cross-sectional area; Calculate the axial strain at the center point of the gauge length section of the specimen in the strain field and use it as the engineering strain; By constructing engineering stress-strain data pairs at the same moment using engineering stress and engineering strain, engineering stress-strain data at all moments are generated.

[0015] Furthermore, whether the adiabatic temperature rise component exceeds a preset threshold is used as a segmentation condition. Based on this condition, the engineering stress-strain data is segmented. A thermal correction factor based on the thermo-mechanical conversion coefficient is applied to the segmented temperature rise influence segment to obtain the corrected stress-strain curve, including: Set a preset threshold for the adiabatic temperature rise component, and obtain the corresponding adiabatic temperature rise component for each data point in the engineering stress-strain data. If the adiabatic temperature rise component is greater than the preset threshold, the current data point is assigned to the temperature rise affected segment; if the adiabatic temperature rise component is less than or equal to the preset threshold, the current data point is assigned to the non-affected segment. For each data point in the temperature rise influence range, the thermal correction factor α is calculated. T =1 / (1+β·ΔT adi ·( E / T) / E0), where β is the thermo-mechanical conversion coefficient, ΔT adi Here, E represents the adiabatic temperature rise component, E is the elastic modulus of the sample material, and T is the temperature. The sign for the derivative is E0, where E0 is the elastic modulus at the reference temperature. The corrected engineering stress σ is obtained by using the engineering stress and thermal correction factor of the data points. corr =σ raw ·α T , where σ raw For engineering stress; The corrected engineering stress and the corresponding engineering strain in the temperature rise influence section are recombined to generate the corrected stress-strain curve. The engineering stress-strain data in the unaffected section remains unchanged, and is then recombined with the corrected stress-strain curve before being output.

[0016] Furthermore, it also includes: When calculating the displacement and strain fields of the entire field and decomposing the temperature field sequence into adiabatic temperature rise components, real-time data quality assessment and feedback adjustment are performed, including the following steps: Calculate the mean local contrast of the moving region in the DIC speckle image sequence, the instantaneous signal-to-noise ratio of the temperature field sequence, and the standard deviation of the temperature signals at multiple points inside the chamber collected by the thermocouple. Use the mean local contrast, instantaneous signal-to-noise ratio, and standard deviation as quality indicators. When any quality indicator falls below the corresponding preset threshold, adjust the exposure time, light source intensity, and camera gain of the high-speed camera system, and / or adjust the integration time or emissivity compensation parameters of the infrared thermal imager.

[0017] A performance testing and data processing apparatus for strain rate in a material, the apparatus being used to perform performance testing and data processing methods, comprising: Medium strain rate loading device, used to apply medium strain rate load to the specimen; The low-temperature environment simulation chamber includes a low-temperature insulated chamber, a viewing window set on the low-temperature insulated chamber, and temperature measuring thermocouples. The temperature measuring thermocouples are spaced in the horizontal and vertical directions of the gauge length of the sample. The viewing window is hollow vacuum glass with a low-emissivity film coated on the inner surface. Liquid nitrogen delivery system, used to deliver liquid nitrogen into cryogenic insulation boxes; The temperature control module is used to adjust the flow rate of the liquid nitrogen delivery system so that the cryogenic insulation box reaches and maintains the set uniform low temperature. The anti-frost module includes dry gas purging ports located on the front and rear sides of the viewing window, which are used to blow dry gas onto the glass surface of the viewing window. An infrared thermal imager is installed on the cavity of a low-temperature environment simulation chamber with its optical axis aligned with the surface of the gauge length section of the sample, and is used to acquire temperature field sequences. The high-precision optical DIC measurement system includes a high-speed camera system that acquires speckle images of the sample surface through a viewing window.

[0018] Furthermore, the outer surface of the hollow vacuum glass of the viewing window is coated with a hydrophobic and oleophobic nano-coating. The low-temperature insulation chamber is equipped with a pressure sensor and an automatic exhaust valve. The pressure sensor and automatic exhaust valve are used to maintain a slight positive pressure inside the chamber. The low-temperature insulation chamber is made of double-walled vacuum polyurethane foam. The medium strain rate loading device includes an upper pressure head, a lower pressure head, and a force sensor. A low thermal conductivity material pad is provided at the end face of the upper pressure head and / or the lower pressure head that contacts the specimen. A micro heater is embedded inside the low thermal conductivity material pad, the upper pressure head, or the lower pressure head. The micro heater makes the temperature of the clamping end of the medium strain rate loading device consistent with the temperature of the gauge length of the specimen.

[0019] Furthermore, the performance testing and data processing apparatus also includes: The safety warning module includes indicator lights and a speaker. The indicator lights are used to display different colors during the cooling, heat preservation, and heat preservation end stages, and the speaker is used to emit a warning sound when the heat preservation ends. The low-temperature environment simulation chamber also includes an insulated door installed on the low-temperature insulation chamber body and a circulating fan installed inside the low-temperature insulation chamber body; The liquid nitrogen delivery system includes a liquid nitrogen cylinder, an electric air pump, and a solenoid valve. The outlet of the electric air pump is connected to the pressurization port of the liquid nitrogen cylinder, and the outlet of the liquid nitrogen cylinder is connected to the solenoid valve and the interior of the cryogenic insulation box through pipelines. The temperature control module includes a PID controller. The input terminal of the PID controller is electrically connected to the signal output terminal of the temperature measuring thermocouple, and the output terminal of the PID controller is electrically connected to the control terminal of the electric air pump and the control terminal of the solenoid valve, respectively.

[0020] Compared with the prior art, the beneficial effects that at least one technical solution adopted in the embodiments of this specification can achieve include at least: By integrating low-temperature environment establishment, active anti-frost, simultaneous acquisition of multiple physical quantities, DIC image correction, and adaptive thermal correction based on adiabatic temperature rise components, frost-free acquisition of DIC images and automatic thermal correction of stress-strain data under strain rate loading at low temperatures were achieved, improving the accuracy of mechanical property testing of materials under low-temperature dynamic service conditions. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the performance testing and data processing method for strain rate in materials according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a performance testing and data processing device for strain rate in materials according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the strain rate loading device in an embodiment of the present invention; Figure 4 This is a first schematic diagram of a low-temperature environment simulation chamber according to an embodiment of the present invention; Figure 5 This is a second schematic diagram of a low-temperature environment simulation chamber according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the liquid nitrogen delivery system and the high-precision optical DIC measurement system according to an embodiment of the present invention.

[0023] The attached figures are labeled as follows: 1. Medium strain rate loading device; 11. Upper indenter; 12. Lower indenter; 13. Force sensor; 14. Sample; 15. Testing machine support; 16. Actuating cylinder; 2. Low temperature environment simulation chamber; 21. Temperature setting module; 22. Cooling / heat preservation button; 23. Ventilation plate; 24. Control box support; 25. Speaker; 26. Indicator light; 27. Low temperature insulation chamber; 28. Viewing window; 29. ​​Door opening / closing knob; 210. 211. Insulated door body; 212. Dry gas purge port; 213. Low temperature white LED light; 214. Circulating fan; 215. Solenoid valve; 216. Temperature measuring thermocouple; 3. Liquid nitrogen delivery system; 31. Low temperature conduit; 32. Liquid nitrogen atomizing device; 33. Gas pipe; 34. Electric air pump; 35. Liquid nitrogen cylinder; 4. High-precision optical DIC measurement system; 41. High-speed camera system; 42. Auxiliary light source; 43. Network cable; 44. DIC module. Detailed Implementation

[0024] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Example 1: A device for testing and processing the performance of strain rate in materials.

[0027] like Figures 2 to 6 As shown. This embodiment provides a device for testing and processing the performance of strain rate in a material, which is used to execute the method of the present invention. Figure 2 As shown, the device mainly includes: a medium strain rate loading device 1, a low temperature environment simulation chamber 2, a liquid nitrogen delivery system 3, a temperature control module, a safety warning module, an anti-frost module, an infrared thermal imager, and a high-precision optical DIC measurement system 4.

[0028] I. Medium strain rate loading device.

[0029] like Figure 3 As shown, the medium strain rate loading device 1 is used to apply a medium strain rate load (strain rate range 10) to the specimen 14. - 2s -1 ~10 2 s -1 It includes: an upper pressure head 11, a lower pressure head 12, a force sensor 13, a testing machine support 15, and an actuator cylinder 16. The piston rod end of the actuator cylinder 16 is fixedly connected to the upper pressure head 11, the lower pressure head 12 is fixedly mounted on the testing machine support 15, and the force sensor 13 is connected between the lower pressure head 12 and the testing machine support 15. The sample 14 is placed between the upper pressure head 11 and the lower pressure head 12. When the testing machine receives a loading command, the actuator cylinder 16 drives the upper pressure head 11 to move downward at a constant speed to compress the sample 14, while the lower pressure head 12 remains stationary. The force sensor 13 measures the load during the compression process in real time. Both the upper pressure head 11 and the lower pressure head 12 are made of low thermal conductivity, high strength materials (such as titanium alloy) to reduce the influence of heat conduction on the sample temperature.

[0030] To eliminate the axial temperature gradient caused by heat conduction between the sample clamping end and the metal indenter, a low thermal conductivity material gasket (e.g., polyetheretherketone, ceramic, or aerogel) is provided at the end face of the upper indenter 11 and / or the lower indenter 12 that contacts the sample. A micro heater is embedded inside the low thermal conductivity material gasket, the upper indenter 11, or the lower indenter 12. An independent PID controller ensures that the temperature of the clamping end is consistent with the temperature of the gauge section of the sample 14, thereby ensuring the temperature uniformity of the sample gauge section.

[0031] II. Low-temperature environment simulation chamber.

[0032] like Figure 4 and Figure 5 As shown, the low-temperature environment simulation chamber 2 includes a low-temperature insulated chamber 27, a viewing window 28 mounted on the chamber 27, an insulated door 210, a circulating fan 213, and multiple temperature-measuring thermocouples 215. The low-temperature insulated chamber 27 is made of double-walled vacuum polyurethane foam, which has excellent thermal insulation performance and can greatly suppress heat exchange between the chamber interior and the external environment. The low-temperature insulated chamber 27 is also equipped with a pressure sensor and an automatic exhaust valve to maintain a slight positive pressure inside the chamber (e.g., 20–100 Pa) to prevent external moisture from entering and further reduce the risk of frost formation.

[0033] Six thermocouples 215 are used for temperature measurement, with three positioned horizontally and three vertically along the gauge length of the sample 14, to collect real-time temperature data near the sample. The signal output terminals of the six thermocouples are electrically connected to the PID controller of the temperature control module. A circulating fan 213 is installed inside the low-temperature insulation chamber 27 to force convection when liquid nitrogen enters, ensuring a highly uniform temperature field within the chamber.

[0034] The viewing window 28 uses hollow vacuum glass (two layers of glass with a vacuum layer in between), and its inner surface is coated with a low-emissivity film to suppress heat radiation and reduce heat transfer while ensuring high light transmittance. The outer surface of the viewing window 28 is also coated with a hydrophobic and oleophobic nano-coating to further enhance its anti-frost capability. The insulated door 210 is opened or closed via a door knob 29 and is locked during the experiment to prevent accidental operation that could lead to frostbite or crush injuries.

[0035] The low-temperature environment simulation chamber 2 also includes a temperature setting module 21, a cooling / heat preservation button 22, a ventilation plate 23, and a control box bracket 24. The cooling / heat preservation button 22 is electrically connected to the temperature control module and allows the operator to manually initiate the cooling or heat preservation program, sending corresponding commands to the PID controller. The ventilation plate 23 is mounted on the temperature setting module 21 or the control box bracket 24 to dissipate heat and prevent condensation, ensuring the safe operation of the control system. The control box bracket 24 supports the low-temperature environment simulation chamber 2, and its height is adjustable to accommodate samples 14 of different specifications.

[0036] III. Liquid nitrogen delivery system.

[0037] like Figure 6 As shown, the liquid nitrogen delivery system 3 includes a liquid nitrogen cylinder 35, an electric air pump 34, and a solenoid valve 214. The outlet of the electric air pump 34 is connected to the pressurization port of the liquid nitrogen cylinder 35, and the outlet of the liquid nitrogen cylinder 35 is connected to the solenoid valve 214 and the interior of the cryogenic insulation chamber 27 via pipelines. The liquid nitrogen delivery system 3 also preferably includes a liquid nitrogen atomizing device 32, a cryogenic conduit 31, and a gas pipe 33. When cooling is required, the electric air pump 34 pressurizes the liquid nitrogen cylinder 35, pushing the liquid nitrogen sequentially through the liquid nitrogen atomizing device 32, the cryogenic conduit 31, and the solenoid valve 214 into the cryogenic insulation chamber 27. The solenoid valve 214 controls the on / off state and flow rate of the liquid nitrogen delivery.

[0038] IV. Temperature Control Module.

[0039] The temperature control module includes a PID controller (proportional-integral-derivative controller). The input of the PID controller is electrically connected to the signal outputs of six thermocouples 215, and its outputs are electrically connected to the control terminals of the electric air pump 34 and the solenoid valve 214. Based on the deviation between the average temperature fed back by the six thermocouples and the user-set target temperature, the PID controller dynamically adjusts the output pressure of the electric air pump and the duty cycle of the solenoid valve, thereby precisely controlling the liquid nitrogen delivery flow rate and enabling the cryogenic insulation chamber 27 to quickly reach and maintain the set uniform low temperature. Combined with the circulating fan 213, the temperature uniformity within the chamber can reach ΔT. max ≤1.5℃, cooling rate can reach more than 10℃ / min, and can achieve a minimum low temperature environment of -180℃.

[0040] V. Safety Prompt Module.

[0041] The safety warning module includes an indicator light 26 and a speaker 25. The indicator light 26 displays different colors during the cooling, heat preservation, and heat preservation completion stages (e.g., red during cooling and the experiment, blue during heat preservation, and green when the experiment can begin after heat preservation). The speaker 25 emits a warning sound when heat preservation ends. The heat preservation door 210 is locked and cannot be opened during the experiment until heat preservation ends and the warning sound is emitted, thus preventing personnel from accidentally opening the door at low temperatures and suffering frostbite.

[0042] VI. Anti-frost module.

[0043] The anti-frost module includes dry gas purging ports 211 located on both the front and rear sides of the viewing window 28. The dry gas purging ports 211 are used to continuously purge dry gas (e.g., dry nitrogen) onto the surface of the viewing window glass under positive pressure. This continuous purging of dry gas prevents external moisture from condensing on the glass surface. Combined with the low-emissivity film and hydrophobic coating of the insulated vacuum glass, the problems of frost and fogging on the viewing window can be completely solved, ensuring clear optical imaging.

[0044] 7. Infrared thermal imager.

[0045] An infrared thermal imager is positioned outside an infrared temperature measurement window located on the cavity of the low-temperature environment simulation chamber 2, corresponding to the observation position of the sample. This infrared temperature measurement window is made of low-temperature radiation-resistant infrared-transmitting glass. The optical axis of the infrared thermal imager is aligned with the gauge length surface of the sample 14 to acquire the full-field temperature field sequence of the sample surface in real time. Multiple miniature low-temperature thermocouples are also arranged on the surface of the sample 14 as calibration points for cross-calibration with the temperature field measured by the infrared thermal imager.

[0046] 8. High-precision optical DIC measurement system.

[0047] The high-precision optical DIC measurement system 4 includes a high-speed camera system 41, an auxiliary light source 42, a grid cable 43, and a DIC module 44. The high-speed camera system 41 acquires speckle images of the sample 14 surface through a viewing window 28. A low-temperature white LED lamp 212 is arranged on the top of the low-temperature insulation chamber 27 to provide illumination for the high-speed camera system. The auxiliary light source 42 supplements the field-of-view illumination. The captured speckle images are transmitted to the DIC module 44 for analysis via the grid cable 43. The high-speed camera system 41 is independently fixed to the ground or optical platform and has no rigid connection to the main body of the medium strain rate loading device 1. A flexible light shield is installed between the front end of the high-speed camera system 41 and the viewing window 28, allowing relative displacement but isolating external light, thereby effectively isolating the vibration generated by the medium strain rate loading from interfering with the optical measurement.

[0048] Example 2: Performance testing and data processing method for strain rate in materials.

[0049] This embodiment provides a method for testing and processing data on the low-temperature mechanical properties of materials based on the aforementioned device. For example... Figure 1 As shown, the method includes the following steps.

[0050] Step 1: Low temperature environment establishment, active frost prevention and safe start-up.

[0051] The sample 14 is installed between the upper pressure head 11 and the lower pressure head 12 of the medium strain rate loading device 1, and the insulation door 210 is closed. The operator sets the target low temperature (e.g., -120℃) and insulation time through the touch screen of the temperature setting module 21. The liquid nitrogen delivery system 3 is started. The PID controller of the temperature control module calculates the deviation from the target temperature based on the average temperature signal fed back by the six thermocouples 215, and then controls the output pressure of the electric air pump 34 and the opening and closing duty cycle of the solenoid valve 214 to deliver liquid nitrogen into the low temperature insulation chamber 27 made of double-walled vacuum polyurethane foam. At the same time, the circulating fan 213 is started to force the gas in the chamber to convect until the temperature in the chamber drops rapidly to the target low temperature (cooling rate ≥10℃ / min), and the maximum temperature difference ΔT_max of the six temperature measuring points ≤1.5℃.

[0052] During the heat preservation stage and subsequent loading process, dry nitrogen gas is continuously purged under positive pressure through the dry gas purging ports 211 on both sides of the viewing window 28 (flow rate, for example, 0.2–0.5 L / min). Simultaneously, the viewing window 28 is made of hollow vacuum glass with a low-emissivity film coated on the inner surface and a hydrophobic and oleophobic nano-coating on the outer surface, effectively preventing frost and fogging. The high-speed camera system 41 of the high-precision optical DIC measurement system 4 is activated, and the speckle pattern on the surface of the sample 14 is aligned through the viewing window 28.

[0053] Once the insulation time reaches the set value, indicator light 26 turns green and speaker 25 emits a warning sound, then the insulated door 210 is unlocked. The operator then activates the medium strain rate loading device 1, which, driven by actuator 16, propels the upper pressure head 11 to a preset strain rate (e.g., 50 seconds). -1 A load was applied to specimen 14.

[0054] Step 2: Simultaneous acquisition of multiple physical quantities.

[0055] During the loading process, the following performance test data was collected in real time using synchronous trigger mode: A sequence of DIC speckle images acquired by a high-speed camera system 41 (frame rate ≥ 1000fps, which can be automatically increased to ≥ 5000fps when strain concentration is detected). Temperature field sequence acquired by infrared thermal imager (frame rate ≥ 100Hz); The applied force signal (sampling rate ≥ 1MHz) is collected by force sensor 13. Temperature signals at multiple points inside the chamber were collected by six thermocouples 215.

[0056] All data is synchronously transmitted to the CNC storage system via a high-speed channel (e.g., NIPXIe-5172 acquisition card).

[0057] Step 3: Data calculation and processing.

[0058] 3.1: DIC image preprocessing and displacement and strain field calculation.

[0059] First, without sample 14, a series of pure background DIC image sequences were acquired during the liquid nitrogen transport process. This pure background DIC image sequence was then subjected to low-rank sparse decomposition (e.g., using Robust Principal Component Analysis (RPCA) or the GoDec algorithm). The extracted sparse components were used as dynamic stripe noise (sparseness set to 10%–20%), and the low-rank components were used as the static background.

[0060] Then, the noise component projected onto the dynamic stripe noise is subtracted from each original image in the DIC speckle image sequence acquired during the actual loading process to obtain a denoised image sequence, thereby removing the flow stripe interference generated by liquid nitrogen vaporization.

[0061] Next, the temperature distribution T of the viewing window glass was collected in real time. window (x,y). Based on the pre-determined temperature coefficient of refractive index of the glass material dn / dT and the glass thickness t, the deflection displacement field of light passing through the glass is calculated using the following formula: Δ(x,y)=t·(dn / dT)· T window (x,y) / n0, where n0 is the refractive index at room temperature. T window Let be the temperature gradient on the glass surface. The denoised image sequence is then reverse-mapped and corrected according to Δ(x,y) to obtain the corrected image sequence.

[0062] The first frame of the calibration image sequence before load application is used as the reference calibration image, and each frame of the calibration image during load application is used as the deformed image. The reference calibration image is divided into several sub-regions (e.g., 15×15 pixels). Sub-region matching is performed in the deformed image using the zero-mean normalized cross-correlation function (ZNCC) to obtain the integer pixel displacement of each sub-region. Then, a sub-pixel interpolation algorithm (e.g., bicubic spline interpolation or the Newton-Raphson iterative method based on gray-level gradients) is used to calculate the sub-pixel displacement based on the gray-level interpolation information of each sub-region, obtaining the displacement field (u,v) of the entire field. Finally, point-by-point least squares fitting is performed on the displacement field to calculate the strain field (ε) of the entire field. xx ,ε yy ,ε xy ).

[0063] 3.2: Temperature field treatment and adiabatic temperature rise decomposition.

[0064] Each frame of the temperature field T in the temperature field sequence acquired by the infrared thermal imager IR The coordinates (x, y, t) are spatially registered with the strain field described above, aligning their coordinate systems to the global coordinate system of the specimen. The adiabatic temperature rise component ΔT generated by the plastic work is then separated from the spatially registered temperature field. adi (x,y,t). Specifically, an inverse problem model of heat conduction is established, where the temperature field T... IR Assuming the initial temperature T initial Adiabatic temperature rise ΔT adi With environmental heat conduction T cond Sum of: T IR =T initial +ΔT adi +T cond Using the internal temperature measured by six thermocouples 215 and the miniature thermocouples on the sample surface as boundary conditions, the thermal diffusion equation was solved using the finite difference method, and the ΔT was iteratively separated. adi .

[0065] 3.3: Calculation of the heat-to-mechanical conversion coefficient.

[0066] Using the separated adiabatic temperature rise component ΔT adi The thermo-mechanical conversion coefficient β(x,y,t) of each spatial point (x,y) at each time t is calculated using the following formula: ,in, For equivalent stress, Let τ be the equivalent variable increment, and τ be the integral variable.

[0067] 3.4: Calculation of engineering stress-strain data.

[0068] The engineering stress σ is calculated using the applied force signal F(t) and the initial cross-sectional area A0 of specimen 14. eng (t) = F(t) / A0. Calculate the axial strain ε at the center point of the gauge length of the specimen in the strain field. yy (t), representing engineering strain. By constructing engineering stress-strain data pairs at the same moment using engineering stress and engineering strain, engineering stress-strain data for all moments are generated.

[0069] Step 4: Data quality assessment and feedback adjustment.

[0070] During the calculation of displacement field, strain field, and separation of adiabatic temperature rise, real-time data quality assessment and feedback adjustment are performed. Specifically, the mean local contrast of the moving region in the DIC speckle image sequence, the instantaneous signal-to-noise ratio of the infrared temperature field sequence, and the standard deviation of the temperature signals at multiple points inside the chamber collected by six thermocouples are calculated and used as quality indicators. When any quality indicator falls below the corresponding preset threshold (e.g., mean local contrast < 0.3), at least one of the following feedback adjustment operations is automatically executed: adjusting the exposure time, light source intensity, or camera gain of the high-speed camera system 41; adjusting the integration time or emissivity compensation parameters of the infrared thermal imager; re-performing low-rank sparse decomposition; or triggering automatic system recalibration.

[0071] Step 5: Application and output of results.

[0072] The calculated displacement and strain fields are used to generate an animation of the deformation evolution of the specimen surface and to identify strain concentration regions. The original stress-strain curves are then plotted using engineering stress-strain data.

[0073] The adiabatic temperature rise component is used as a segmentation condition to determine whether it exceeds a preset threshold (e.g., 5℃ or 10℃). Based on this segmentation condition, the engineering stress-strain data is segmented: if the ΔT of a certain data point exceeds a preset threshold (e.g., 5℃ or 10℃), the segmentation is determined. adi If the value exceeds the threshold, it is classified into the temperature rise-affected segment; otherwise, it is classified into the non-affected segment. For each data point in the temperature rise-affected segment, the thermal correction factor α is calculated using the following formula. T : α T =1 / (1+β·ΔT adi ·( E / T) / E0), where β is the thermo-mechanical conversion coefficient calculated in the above steps, ΔT adi Here, E represents the adiabatic temperature rise component, E is the elastic modulus of the sample material, and T is the temperature. E / T is the temperature derivative of the elastic modulus, and E0 is the elastic modulus at the reference temperature. The original engineering stress σ at this data point... raw Multiply by α T The corrected engineering stress σ is obtained. corr =σ raw ·α T The corrected engineering stress and corresponding engineering strain in the temperature rise-affected section are recombined to generate a corrected stress-strain curve. The engineering stress-strain data in the unaffected section remain unchanged.

[0074] Finally, the output includes the original stress-strain curve, the corrected stress-strain curve, temperature field visualization results (e.g., temperature field contour map sequence on the sample surface, temperature-time curves at typical points), and spatial distribution map of the thermo-mechanical conversion coefficient. All output results can be displayed on a screen or exported as data files.

[0075] Example 3: Calibration of temperature field measurement system, simultaneous acquisition of multiple physical quantities and visualization of temperature field.

[0076] An infrared thermography window, made of low-temperature radiation-resistant infrared-transmitting glass, is opened on the cavity of the low-temperature environment simulation chamber 2 at the corresponding observation position of the sample. An infrared thermal imager is positioned outside this window, with its optical axis aligned with the surface of the gauge section of the sample. Miniature low-temperature thermocouples (e.g., 3-6, located at the center, edge, and transition arc of the clamping end) are pre-embedded on the sample surface for cross-calibration with the temperature field of the infrared thermal imager. Before testing, the sample is placed inside the device, initial confining pressure is applied, and initial reference images are acquired.

[0077] After the medium strain rate loading device is started, the system simultaneously acquires the loading force, displacement, stress, strain, full-field temperature field of the sample (infrared thermal imager), instantaneous temperature at key points (miniature thermocouples), and ambient temperature of the cavity (6 temperature-measuring thermocouples) in synchronous trigger mode. Synchronous triggering is implemented by a multi-device synchronous controller based on FPGA to ensure that all data timestamps are aligned.

[0078] During loading, the real-time algorithm identifies the peak temperature rise in the deformation concentration zone, necking zone, and shear band region of the sample, and records the temperature rise start time, temperature rise rate, and the location of the highest temperature rise point. When the instantaneous temperature rise at any location exceeds a set threshold (e.g., 5℃ or 10℃), the system automatically marks the corresponding data segment as the temperature rise influence segment for subsequent mechanical behavior analysis.

[0079] After the test, the system automatically outputs a sequence of temperature field cloud maps on the sample surface (output in time frames to show the temperature rise and diffusion process) and temperature-time curves for typical points (sample center, hot spot, clamping end). These visualizations, along with the stress-strain curves, facilitate users' comprehensive evaluation of the thermo-mechanical coupling behavior of materials under medium strain rate and low temperature conditions.

[0080] Example 4: Liquid nitrogen pipeline precooling and rapid response control To further improve cooling speed and control accuracy, this embodiment provides a liquid nitrogen pipeline pre-cooling method. Before the formal cooling command is issued, the solenoid valve 214 is opened with a duty cycle of 5% to 10%, and the electric air pump 34 is started, allowing a small amount of liquid nitrogen to flow through the liquid nitrogen delivery pipeline. The pipeline is pre-cooled by absorbing heat through liquid nitrogen vaporization. When the temperature sensor on the pipeline detects the set low temperature (e.g., -150°C), liquid nitrogen is then delivered normally according to the requirements of the PID controller. This ensures that the delay time from the opening of the solenoid valve to the entry of liquid nitrogen into the low-temperature insulation chamber 27 is ≤0.5 seconds, eliminating air blockage and achieving millisecond-level response.

[0081] Example 5: Continuous automatic testing of multiple samples.

[0082] This embodiment provides an automatic sample changing device for continuous multi-sample testing. A rotating sample magazine, capable of holding 4 to 8 samples, is installed inside or on the side of the low-temperature insulated chamber 27. Samples are sequentially fed to the loading position (between the upper pressure head 11 and the lower pressure head 12) via an electric push rod or a robotic arm. After each test, the tested sample is automatically retrieved and the next sample is picked up. The entire process is completed in a low-temperature environment without opening the insulated door 210, thus significantly improving testing efficiency, and is particularly suitable for batch material screening.

[0083] Example 6: Low-temperature compensation for force sensors.

[0084] Because strain gauge force sensors exhibit zero-point drift and sensitivity variations at low temperatures, this embodiment provides a method for force sensor temperature compensation. A compensating thermocouple is placed at a distance ≤10mm from the force sensor 13. The force sensor output as a function of temperature is measured beforehand under no-load conditions to establish a compensation function f(T). In actual testing, the temperature T of the compensating thermocouple is collected in real time. comp The original output value F of the force sensor raw Substituting into the compensation function, we obtain the corrected force value F. corr =F raw -f(T comp This improves the accuracy of load measurement.

[0085] Beneficial effects of the embodiments of the present invention: This invention efficiently integrates a medium strain rate loading system with a low-temperature environment simulation chamber. The low-temperature insulated chamber is made of double-walled vacuum polyurethane foam, which greatly suppresses heat exchange between the chamber and the external environment, providing excellent thermal insulation performance. The control box bracket is height-adjustable, allowing for flexible adaptation to samples of different specifications, thus solving the problems of poor compatibility and insufficient adaptability between existing low-temperature chambers and medium strain rate testing machines.

[0086] This invention utilizes a PID controller to dynamically adjust the output pressure of the electric gas pump and the opening and closing of the solenoid valve based on the feedback signals from six thermocouples, precisely controlling the liquid nitrogen delivery flow rate. Combined with the forced convection of the internal circulating fan, the temperature inside the chamber can be reduced from room temperature to -180℃ at a rate of ≥10℃ / min, with a maximum temperature difference of ≤1.5℃ between the six measuring points. This is significantly better than the cooling rate of approximately 3℃ / min and the large temperature gradient of traditional low-temperature chambers, greatly improving testing efficiency and temperature uniformity.

[0087] This invention employs a hollow vacuum glass viewing window with a low-emissivity film coated on the inner surface and a hydrophobic and oleophobic coating that can be applied to the outer surface. Dry gas positive pressure purge ports are set on both the front and back sides of the glass. This provides synergistic anti-frost protection from three dimensions: blocking heat conduction, suppressing heat radiation, and driving away moisture. Compared with existing heating defrosting or post-processing algorithm repair solutions, this invention does not introduce additional heat sources, does not affect the low-temperature stability inside the chamber, ensures the high definition of the original DIC image, and achieves high-quality optical full-field deformation measurement in low-temperature environments.

[0088] This invention features multi-color indicator lights and speaker prompts to clearly distinguish between cooling, heat preservation, and loading states. The heat preservation door is locked during the experiment to prevent frostbite or crush injuries caused by accidental operation. It automatically alerts and unlocks when heat preservation is complete. The clear operation process reduces waiting time and improves experimental efficiency.

[0089] This invention simultaneously acquires DIC speckle images, infrared temperature fields, applied forces, and multi-point temperature signals, and separates the adiabatic temperature rise caused by plastic work. It can identify the temperature rise characteristics of the deformation concentration area, necking area, and shear band of the sample in real time, overcoming the defect of ignoring the adiabatic temperature rise of high-speed deformation in traditional tests, and providing more accurate experimental data for the construction of constitutive models of materials at medium strain rates and low temperatures.

[0090] This invention effectively eliminates optical distortion caused by thermal deformation of the viewing window under low-temperature conditions by arranging temperature sensors on the surface of the viewing window to measure the glass temperature gradient in real time, calculating the light deflection displacement field based on the glass's refractive index temperature coefficient, and then back-mapping to correct the DIC image, thereby further improving the accuracy of DIC strain measurement.

[0091] This invention calculates quality indicators such as speckle contrast, infrared signal-to-noise ratio, and multi-point temperature standard deviation in real time during the testing process. When the indicators are lower than the threshold, the imaging parameters are automatically adjusted or recalibration is triggered, forming a closed-loop control of "acquisition-evaluation-adjustment" to ensure the data validity of the entire testing process.

[0092] This invention performs dynamic background noise removal, distortion correction, digital image correlation calculation, temperature field decomposition, thermo-mechanical conversion coefficient calculation, engineering stress-strain calculation, adaptive segmentation, and thermal correction factor correction on the collected multi-physical quantity data. Finally, it outputs the original stress-strain curve, the corrected stress-strain curve, the temperature field cloud map, and the thermo-mechanical conversion coefficient distribution map, providing comprehensive and reliable data support for the analysis of the mechanical behavior of materials under strain rate at low temperatures.

[0093] This invention provides interfaces for extended functions such as infrared thermal imager, liquid nitrogen pipeline precooling, force sensor low temperature compensation, automatic replacement of multiple samples, and clamping end temperature compensation. These interfaces can be flexibly configured according to actual needs to meet the requirements of different materials and different testing standards.

[0094] In summary, this invention effectively solves the problems in the prior art, such as the difficulty in implementing low-temperature coupling testing at medium strain rates, interference from frost in DIC optical measurements, uneven temperature field, low testing efficiency, and rough data post-processing. It provides a high-precision, high-efficiency, and high-safety technical solution for evaluating the mechanical properties of materials under low-temperature dynamic service environments.

[0095] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of protection of the present invention, should still fall within the scope of the present invention. Furthermore, the technical features, technical features and technical solutions, and technical solutions in the present invention can be freely combined and used.

Claims

1. A method for performance testing and data processing of strain rate in a material, characterized in that, Includes the following steps: The sample (14) is installed in the medium strain rate loading device (1). The liquid nitrogen delivery system (3) and the circulating fan (213) are controlled by the feedback of the temperature measuring thermocouple (215) so that the low temperature insulation box (27) reaches a uniform low temperature. During the insulation process, continuous anti-frost is carried out through the viewing window (28). After the insulation is completed, the load is applied to the sample (14). During the application of load, performance test data is collected in real time, including DIC speckle image sequence collected by high-speed camera system (41), temperature field sequence collected by infrared thermal imager, loading force signal collected by force sensor (13) and multi-point temperature signal inside the box collected by thermocouple (215). The DIC speckle image sequence is subjected to dynamic background noise removal and viewable thermal-optical distortion correction in sequence, and the displacement field and strain field of the whole field are calculated. The temperature field sequence is subjected to emissivity compensation and spatial registration. The temperature field of the temperature field sequence is decomposed into adiabatic temperature rise component and the thermo-mechanical conversion coefficient is calculated. The engineering stress-strain data is calculated by the loading force signal and the strain field. The displacement field and the strain field are used to generate a deformation evolution animation of the sample surface, and strain concentration areas are identified. The original stress-strain curve is plotted using the engineering stress-strain data. The adiabatic temperature rise component is used as a segmentation condition. Based on the segmentation condition, the engineering stress-strain data is segmented. A thermal correction factor based on the thermal-mechanical conversion coefficient is applied to the segmented temperature rise influence segment to obtain the corrected stress-strain curve. Output the original stress-strain curve, the corrected stress-strain curve, the temperature field visualization results, and the spatial distribution map of the thermo-mechanical conversion coefficient.

2. The performance testing and data processing method according to claim 1, characterized in that, The sample (14) is installed in the medium strain rate loading device (1). Through the feedback of the temperature measuring thermocouple (215), the liquid nitrogen delivery system (3) and the circulating fan (213) are controlled to make the low temperature insulation box (27) reach a uniform low temperature. During the insulation process, continuous anti-frost is carried out through the viewing window (28). After the insulation is completed, a load is applied to the sample (14), including: The sample (14) is installed between the upper pressure head (11) and the lower pressure head (12) of the medium strain rate loading device (1), and the heat insulation door (210) is closed. Start the liquid nitrogen delivery system (3), and use the PID controller of the temperature control module to control the output pressure of the electric air pump (34) and the opening and closing of the solenoid valve (214) according to the feedback signal of the temperature measuring thermocouple (215) to deliver liquid nitrogen into the low temperature insulation box (27) made of double-walled vacuum polyurethane foam. At the same time, start the circulating fan (213) to make the temperature inside the box uniform until the target low temperature is reached. During the heat preservation stage and subsequent loading process, dry gas is continuously purged under positive pressure through the dry gas purging port (211) of the viewing window (28); The high-speed camera system (41) of the high-precision optical DIC measurement system (4) is activated, and the speckle pattern on the surface of the sample (14) is aligned through the viewing window (28); When the heat preservation time reaches the set value, the indicator light (26) is switched to green and the speaker (25) emits a prompt sound. Then, the heat preservation door (210) is unlocked and the operator starts the medium strain rate loading device (1) to apply load to the sample (14).

3. The performance testing and data processing method according to claim 1, characterized in that, The DIC speckle image sequence is subjected to dynamic background noise removal and viewport thermo-optical distortion correction in sequence, and the full-field displacement field and strain field are calculated, including: In the absence of a sample (14), a set of pure background DIC image sequences during the liquid nitrogen transport process were acquired. The pure background DIC image sequences were subjected to low-rank sparse decomposition, and the extracted sparse components were used as dynamic stripe noise. Subtract the noise component projected onto the dynamic stripe noise from each original image frame in the DIC speckle image sequence to obtain a denoised image sequence; The temperature distribution of the viewing window glass is collected in real time, and the deflection displacement field Δ(x,y)=t·(dn / dT)· is calculated from the temperature distribution as light passes through the glass. T window (x,y) / n0, where t is the glass thickness, n is the refractive index of the glass material, T is the temperature, d is the differential, dn / dT is the temperature coefficient of refractive index, and n0 is the refractive index at room temperature. T window The temperature gradient on the glass surface; The denoised image sequence is reverse mapped and corrected according to the deflection displacement field to obtain the corrected image sequence; The first frame of the corrected image sequence before the load is applied is used as the reference corrected image, and each frame of the corrected image sequence during the load application process is used as the deformed image. The reference correction image is divided into several sub-regions, and sub-region matching is performed in the deformed image using a zero-mean normalized cross-correlation function to obtain the integer pixel displacement of each sub-region. The subpixel displacement is calculated based on the grayscale interpolation information of each sub-region using a subpixel interpolation algorithm. The displacement field of the whole field is obtained based on the subpixel displacement of each sub-region, and the strain field of the whole field is calculated by performing point-by-point least squares fitting on the displacement field.

4. The performance testing and data processing method according to claim 1, characterized in that, The temperature field sequence is decomposed into an adiabatic temperature rise component, and the thermo-mechanical conversion coefficient is calculated. Engineering stress-strain data is then calculated using the applied force signal and the strain field, including: Spatially register the temperature field of each frame in the temperature field sequence with the strain field, so that the coordinate systems of the temperature field and the strain field are aligned with the global coordinate system of the sample. The adiabatic temperature rise component generated by plastic work is separated from the temperature field after spatial registration. Each spatial point is calculated using the adiabatic temperature rise component. At every moment t Thermo-mechanical conversion coefficient ,in, For equivalent stress, For the equivalent change increment, The adiabatic temperature rise component is represented by x and y, where x and y are spatial coordinates within the gauge length plane of the sample. t Let τ be the current time, and let τ be the integral variable.

5. The performance testing and data processing method according to claim 1, characterized in that, Engineering stress-strain data are obtained by calculating the applied force signal and the strain field, including: The engineering stress σ is calculated using the applied force signal and the initial cross-sectional area of ​​the specimen (14). eng (t)=F(t) / A0, where F(t) is the applied force signal at the current time t, and A0 is the initial cross-sectional area; Calculate the axial strain at the center point of the gauge length section of the specimen in the strain field and use it as the engineering strain; By constructing engineering stress-strain data pairs at the same moment using the engineering stress and the engineering strain, engineering stress-strain data at all moments are generated.

6. The performance testing and data processing method according to claim 1, characterized in that, Using whether the adiabatic temperature rise component exceeds a preset threshold as a segmentation condition, the engineering stress-strain data is segmented based on the segmentation condition. A thermal correction factor based on the thermo-mechanical conversion coefficient is applied to the segmented temperature rise influence segment to obtain the corrected stress-strain curve, including: Set a preset threshold for the adiabatic temperature rise component, and obtain the corresponding adiabatic temperature rise component for each data point in the engineering stress-strain data. If the adiabatic temperature rise component is greater than the preset threshold, the current data point is assigned to the temperature rise affected segment; if the adiabatic temperature rise component is less than or equal to the preset threshold, the current data point is assigned to the non-affected segment. For each data point in the temperature rise influence range, the thermal correction factor α is calculated. T =1 / (1+β·ΔT adi ·( E / T) / E0), where β is the thermo-mechanical conversion coefficient, ΔT adi Here, E represents the adiabatic temperature rise component, E is the elastic modulus of the sample material, and T is the temperature. The sign for the derivative is E0, where E0 is the elastic modulus at the reference temperature. The corrected engineering stress σ is obtained by using the engineering stress at the data points and the thermal correction factor. corr =σ raw ·α T , where σ raw For engineering stress; The corrected engineering stress and the corresponding engineering strain in the temperature rise influence section are recombined to generate a corrected stress-strain curve. The engineering stress-strain data in the unaffected section remains unchanged, and is then recombined with the corrected stress-strain curve before being output.

7. The performance testing and data processing method according to claim 6, characterized in that, Also includes: When calculating the displacement and strain fields of the entire field and decomposing the temperature field sequence into adiabatic temperature rise components, real-time data quality assessment and feedback adjustment are performed, including the following steps: Calculate the mean local contrast of the moving region in the DIC speckle image sequence, the instantaneous signal-to-noise ratio of the temperature field sequence, and the standard deviation of the temperature signals at multiple points inside the box collected by the thermocouple (215), and use the mean local contrast, the instantaneous signal-to-noise ratio, and the standard deviation as quality indicators. When any quality index is lower than the corresponding preset threshold, adjust the exposure time, light source intensity, camera gain of the high-speed camera system (41), and / or adjust the integration time or emissivity compensation parameter of the infrared thermal imager.

8. A device for testing and processing the performance of strain rate in a material, used to execute the performance testing and data processing method according to any one of claims 1 to 7, characterized in that, include: Medium strain rate loading device (1) is used to apply medium strain rate load to specimen (14); The low-temperature environment simulation chamber (2) includes a low-temperature insulation chamber (27), a viewing window (28) and a temperature measuring thermocouple (215) set on the low-temperature insulation chamber (27). The temperature measuring thermocouple (215) is set at intervals in the horizontal and vertical directions of the gauge length section of the sample (14). The viewing window (28) is hollow vacuum glass and its inner surface is coated with a low-emissivity film. Liquid nitrogen delivery system (3), the liquid nitrogen delivery system (3) is used to deliver liquid nitrogen into the cryogenic insulation box (27); Temperature control module, used to adjust the flow rate of liquid nitrogen delivery system (3) so that the low temperature insulation box (27) reaches and maintains a set uniform low temperature; The anti-frost module includes dry gas purge ports (211) disposed on the front and rear sides of the viewing window (28), the dry gas purge ports (211) being used to purge dry gas onto the glass surface of the viewing window; An infrared thermal imager is installed on the cavity of the low-temperature environment simulation chamber (2) and the optical axis of the infrared thermal imager is aligned with the surface of the gauge length section of the sample (14) and used to collect temperature field sequences. A high-precision optical DIC measurement system (4) includes a high-speed camera system (41) that acquires speckle images of the surface of the sample (14) through the viewing window (28).

9. The performance testing and data processing apparatus according to claim 8, characterized in that, The outer surface of the hollow vacuum glass of the viewing window (28) is coated with a hydrophobic and oleophobic nano-coating. The low-temperature insulation box (27) is equipped with a pressure sensor and an automatic exhaust valve. The pressure sensor and the automatic exhaust valve are used to maintain a slight positive pressure inside the box. The low-temperature insulation box (27) is made of double-walled vacuum polyurethane foam. The medium strain rate loading device (1) includes an upper pressure head (11), a lower pressure head (12), and a force sensor (13). A low thermal conductivity material pad is provided at the end face of the upper pressure head (11) and / or the lower pressure head (12) that contacts the sample. A micro heater is embedded inside the low thermal conductivity material pad, the upper pressure head (11), or the lower pressure head (12). The micro heater makes the temperature of the clamping end of the medium strain rate loading device (1) consistent with the temperature of the gauge length section of the sample (14).

10. The performance testing and data processing apparatus according to claim 8, characterized in that, The performance testing and data processing device also includes: The safety prompt module includes an indicator light (26) and a speaker (25). The indicator light (26) is used to display different colors during the cooling, heat preservation and heat preservation end stages, and the speaker (25) is used to emit a prompt sound when the heat preservation ends. The low-temperature environment simulation chamber (2) also includes an insulated door (210) installed on the low-temperature insulation chamber (27) and a circulating fan (213) installed inside the low-temperature insulation chamber (27). The liquid nitrogen delivery system (3) includes a liquid nitrogen cylinder (35), an electric air pump (34) and a solenoid valve (214). The outlet of the electric air pump (34) is connected to the pressurization port of the liquid nitrogen cylinder (35). The outlet of the liquid nitrogen cylinder (35) is connected to the solenoid valve (214) and the interior of the low-temperature insulation box (27) in sequence through a pipeline. The temperature control module includes a PID controller. The input terminal of the PID controller is electrically connected to the signal output terminal of the temperature measuring thermocouple (215). The output terminal of the PID controller is electrically connected to the control terminal of the electric air pump (34) and the control terminal of the solenoid valve (214).

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