In-situ test method and system for impact toughness of liquid hydrogen temperature zone materials

Abstract

This invention discloses an in-situ testing method and system for the impact toughness of materials in the liquid hydrogen temperature range. The method involves placing the sample on a sample support inside a constant temperature chamber, which contains an impact module comprising an impact hammer and a spring. The temperature inside the chamber is adjusted and stabilized at a preset test temperature. The spring is compressed, moving the impact hammer from its initial position to a preset initial impact position, and the initial and compressed lengths of the spring are recorded. The compressed spring is released, driving the impact hammer to impact the sample in a straight line. After the impact hammer completes its impact, the spring's rebound length when the impact hammer returns to zero is recorded. Based on the spring's initial length, compressed length, and rebound length, as well as the spring constant at the test temperature, the impact energy absorbed by the sample is calculated using the impact energy calculation formula, yielding the sample's impact toughness. The impact energy of the material is calibrated based on the change in the spring's elastic potential energy, enabling in-situ impact testing and ensuring the accuracy and repeatability of impact energy measurement.

Description

Technical Field

[0001] This invention relates to the field of mechanical property testing technology for materials in the liquid hydrogen temperature range, and particularly to an in-situ testing method and system for impact toughness of materials in the liquid hydrogen temperature range. Background Technology

[0002] Impact toughness refers to a material's ability to absorb plastic deformation work and fracture work under impact loads, and is usually determined through impact testing. Existing low-temperature impact testing machines for materials are typically pendulum-type. The working principle of a pendulum impact testing machine is as follows: a pendulum with a certain mass is raised to a specified height, giving it a certain gravitational potential energy; then the pendulum is released, and it moves in an arc around a fixed axis, impacting the specimen placed on a support at its lowest point; after breaking the specimen, the pendulum continues to swing to its highest point on the other side; by measuring the height difference of the pendulum before and after impact, the energy consumed in breaking the specimen, i.e., the impact work, is calculated. Dividing the impact work by the cross-sectional area at the notch of the specimen yields the impact toughness value of the material.

[0003] Because the toughness of materials decreases at low temperatures, increasing the risk of brittle fracture, the impact toughness of metallic materials used in cryogenic pressure vessels must be determined. In principle, the specimens are required to undergo impact testing at a set temperature. However, existing pendulum impact testing machines, due to the large swing amplitude of the pendulum, make it impossible to complete the impact test within a temperature-controlled chamber. To conduct cryogenic impact testing of materials at a specific temperature, the material must be temperature-treated in a constant-temperature chamber before being placed in the testing machine. During this process, the temperature of the tested sample changes, especially in cryogenic environments (such as liquid hydrogen at -253°C). Metallic material samples have high thermal conductivity, and the test temperature differs significantly from the ambient temperature, leading to severe material rewarming. It is difficult to control the temperature of the material during the experiment to the initially set temperature and obtain an acceptable temperature range.

[0004] In existing technologies, some methods employ electromagnetic pulse force to drive a punch for linear impact, replacing the traditional pendulum's circular swing impact, thus miniaturizing the equipment. A high-voltage pulse capacitor bank discharges a coil to generate a pulsed magnetic field, inducing eddy currents on the drive plate. The interaction between these two forces generates pulsed magnetic pressure, propelling the drive plate and the connected punch at high speed to impact the sample. While this reduces the equipment size to some extent, it has several drawbacks: First, the electromagnetic pulse drive system is complex, requiring high-voltage pulse capacitor banks, charging circuits, discharging circuits, and high-voltage switches, resulting in high system costs and safety risks associated with high-voltage operation. Second, accurate measurement of impact energy depends on the precise acquisition of the punch's velocity before and after impact, requiring expensive imaging equipment such as high-speed cameras. Furthermore, in cryogenic, enclosed environments, high-speed imaging through optical windows faces challenges such as frost formation, field-of-view obstruction, and insufficient light, making technical implementation difficult. Third, it is applicable to material impact testing at room temperature, not cryogenic environments, and does not provide a technical solution for in-situ impact testing in cryogenic environments, failing to address the technical challenges of in-situ testing of material impact toughness in the liquid hydrogen temperature range. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes an in-situ testing method and system for the impact toughness of materials in the liquid hydrogen temperature range. The impact module and the sample are placed together in a constant temperature chamber to eliminate the retemperature phenomenon during the sample transfer process. The impact energy of the material is calibrated based on the change of the elastic potential energy of the spring, realizing in-situ impact testing and ensuring the accuracy and repeatability of impact energy measurement.

[0006] On one hand, embodiments of the present invention provide an in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range, comprising: The sample is placed on a sample support inside a constant temperature chamber. The constant temperature chamber is equipped with an impact module, which includes an impact hammer and a spring. The spring is made of austenitic stainless steel or nickel-based alloy and has undergone cryogenic pretreatment. Adjust the temperature inside the constant temperature chamber and stabilize it at the preset test temperature; Compress the spring to move the impact hammer from its initial position to a preset initial impact position, and record the initial length and the length of the spring after compression. Release the compressed spring and drive the impact hammer to impact the sample in a straight line; After the impact hammer completes its impact, the spring rebound length is recorded when the impact hammer rebounds to zero speed. Based on the initial length, compressed length, and rebound length of the spring, as well as the spring constant at the test temperature, the impact energy absorbed by the sample is calculated using the impact energy calculation formula, thus obtaining the impact toughness of the sample.

[0007] According to some embodiments of the present invention, the cryogenic pretreatment includes immersing the spring in liquid nitrogen or liquid hydrogen for 4 to 8 hours to fully stabilize its structure and eliminate residual austenite, so as to ensure the repeatability of the elastic modulus at low temperature.

[0008] According to some embodiments of the present invention, adjusting the temperature inside the constant temperature chamber and stabilizing it at a preset test temperature includes: The temperature inside the constant temperature chamber was lowered to below -253°C and kept stable. Simultaneously, helium gas is introduced into the constant temperature chamber as a cooling medium.

[0009] According to some embodiments of the present invention, the formula for calculating the impact energy is as follows: E' = ½K((x0- x1)² - (x0- x2) 2 ) ; In the formula, K is the spring constant, x0 is the initial length of the spring, x1 is the length of the spring after compression, and x2 is the spring rebound length when the impact hammer rebounds to zero velocity after the impact.

[0010] According to some embodiments of the present invention, the spring stiffness coefficient is obtained through no-load calibration: At the test temperature, and with no sample placed on the sample support, the impact hammer is released from the initial impact position to complete the impact-rebound process without impact. Record the spring rebound length when the impact hammer rebounds to zero velocity; Based on the principle that the impact energy is equal under frictionless loss, the spring stiffness coefficient at the test temperature is determined by multiple measurements and verifications.

[0011] In another aspect, embodiments of the present invention provide an in-situ testing system for the impact toughness of materials in the liquid hydrogen temperature range, used to implement the aforementioned in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range. The system includes: A constant temperature chamber, wherein a sample support is provided inside the constant temperature chamber; A temperature control module is used to adjust and stabilize the temperature inside the constant temperature chamber at a preset test temperature. An impact module is disposed inside the constant temperature chamber. The impact module includes an impact hammer, a spring, and a spring compression unit. The impact hammer moves in a linear direction to impact the sample. The spring is connected to the impact hammer and is used to drive the impact hammer to impact and rebound. The spring compression unit is used to compress the impact hammer from its initial position to the initial impact position and then release it. A displacement recording module is used to record the initial length, compressed length, and rebound length of the spring. The data processing module is used to calculate the impact energy absorbed by the sample based on the spring stiffness coefficient at the test temperature and according to the impact energy calculation formula.

[0012] According to some embodiments of the present invention, the constant temperature chamber has a double-layer structure, with the outer layer being a vacuum insulation layer and the inner layer being a sample chamber filled with helium cooling medium. The impact module is placed in the sample chamber, and the spring compression unit is connected to the spring after passing through the vacuum insulation layer via a drive rod.

[0013] According to some embodiments of the present invention, the displacement recording module includes a laser displacement sensor, which is disposed outside the constant temperature chamber. An optical window is provided on the wall of the constant temperature chamber, and the laser displacement sensor performs non-contact measurement of the position of the impact hammer or the spring through the optical window.

[0014] According to some embodiments of the present invention, the impact module further includes a one-way locking mechanism and a guide cylinder. The one-way locking mechanism is a ratchet mechanism or a spring-driven wedge locking mechanism disposed on the inner wall of the guide cylinder, used to lock the impact hammer after the impact hammer completes the impact and rebounds.

[0015] According to some embodiments of the present invention, a linear bearing sleeve is provided on the outside of the impact hammer, and the linear bearing sleeve is precisely fitted with the inner wall of the guide cylinder to form a self-guiding structure.

[0016] The in-situ testing method and system for impact toughness of materials in the liquid hydrogen temperature range according to embodiments of the present invention have at least the following beneficial effects: This method fundamentally revolutionizes the impact testing principle by replacing the traditional gravitational potential energy difference method with the spring elastic potential energy difference method. It utilizes the spring's elastic potential energy to drive the impact hammer for short-range linear impacts, reducing the overall impact module size to a size that can be placed entirely within a cryogenic chamber. This enables in-situ impact testing in the liquid hydrogen and even liquid helium temperature ranges, completely eliminating the temperature rise problem caused by sample transfer and ensuring that the measured data accurately reflects the impact toughness of the material at the set cryogenic temperature. Low-temperature, no-load dynamic calibration allows for in-situ self-calibration of the spring stiffness coefficient at the test temperature, eliminating the influence of temperature and strain rate effects on the elastic element's performance and ensuring measurement accuracy. The use of austenitic stainless steel or nickel-based alloy springs addresses the cryogenic brittleness problem, and precise signal acquisition is achieved through laser non-contact displacement measurement, ensuring the accuracy and reliability of the test. This method is simple in principle, compact in structure, and highly automated, enabling in-situ impact testing and guaranteeing the accuracy and repeatability of impact energy measurement. It provides a new and reliable solution for evaluating the impact performance of cryogenic materials.

[0017] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of the in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the in-situ testing system for the impact toughness of materials in the liquid hydrogen temperature range according to an embodiment of the present invention. Figure 3 This is a schematic diagram of the thermostat chamber and impact module of the in-situ testing system for the impact toughness of liquid hydrogen temperature zone materials according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the impact and rebound process of the in-situ test method for the impact toughness of materials in the liquid hydrogen temperature range according to an embodiment of the present invention. Figure 5 This is a schematic diagram comparing the sample temperature-time curves during the in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range, as described in this embodiment of the invention.

[0019] Figure label: Incubator 100, sample support 110, sample chamber 120; Temperature control module 200, helium refrigeration unit 210, temperature control unit 220; Impact module 300, impact hammer 310, spring 320, spring compression unit 330; Displacement recording module 400, data processing module 500, sample 600. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," "exceeding," etc. are understood to exclude the stated number, and "above," "below," "within," etc. are understood to include the stated number. If "first," "second," etc. are used in the description, they are only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0023] Currently, no method or system can accurately test the impact toughness of materials in situ under liquid hydrogen temperature conditions. "In-situ" means that the sample remains in a constant temperature environment throughout the entire testing process—from cooling and holding to impact fracture—without undergoing any transfer from a low-temperature environment to room temperature. This problem severely restricts the selection of materials and design for advanced equipment such as liquid hydrogen storage and transportation systems and deep space probes, becoming a pressing technical challenge that needs to be solved.

[0024] To address the shortcomings of the existing technologies, it is necessary to fundamentally change the testing principle and implementation method of traditional impact testing. By innovating the testing principle from the "gravitational potential energy difference method" to the "spring elastic potential energy difference method," the impact module can be miniaturized and linearized, allowing the entire impact module to be completely placed inside the constant temperature chamber, thereby truly realizing cryogenic in-situ impact testing.

[0025] The following core technical challenges need to be addressed: First, how to reduce the size of the impact testing device from the current meter-level to the sub-meter or even decimeter-level, large enough to fit entirely into a constant temperature chamber, while maintaining the accuracy of impact energy measurement, thereby eliminating the need for sample transfer; second, how to establish a new principle for impact energy testing suitable for cryogenic environments that does not rely on precise measurement of impact velocity; third, how to overcome a series of secondary technical difficulties caused by cryogenic temperatures (-253℃ and below) on the elastic elements, moving parts, and measurement system in the impact module, such as material property degradation, thermal deformation, and thermal conduction interference, to ensure that the system can operate stably and reliably for a long time in extreme environments; and fourth, how to prevent the influence of secondary impacts and other interference factors during the impact testing process on the measurement results, ensuring that only one effective impact fracture event occurs in each test, making the energy calculation clear and accurate.

[0026] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This embodiment provides an in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range. Please refer to [link to relevant documentation]. Figure 1 The in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range mainly includes steps S101~S106: S101. Place the sample 600 on the sample support 110 inside the constant temperature chamber 100. The constant temperature chamber 100 is equipped with an impact module 300, which includes an impact hammer 310 and a spring 320. The spring 320 is made of austenitic stainless steel or nickel-based alloy and has undergone deep cryogenic pretreatment.

[0028] S102. Adjust the temperature inside the constant temperature chamber 100 and stabilize it at the preset test temperature.

[0029] S103, compress the spring 320, move the impact hammer 310 from the initial position to the preset initial impact position, and record the initial length and compressed length of the spring 320.

[0030] S104. Release the compressed spring 320 and drive the impact hammer 310 to impact the sample 600 in a straight line.

[0031] S105. After the impact hammer 310 completes the impact, record the rebound length of the spring 320 when the impact hammer 310 rebounds to zero speed.

[0032] S106. Based on the initial length, compressed length, and rebound length of spring 320, and the spring constant at the test temperature, calculate the impact energy absorbed by sample 600 using the impact energy calculation formula, and obtain the impact toughness of sample 600.

[0033] It should be noted that by taking advantage of the small size and linear motion of the spring-type impact module 300, the impact module 300 and the sample 600 are placed together in the constant temperature chamber 100. This ensures that the sample 600 remains in a set low temperature environment throughout the entire process from cooling to the completion of the impact, eliminating the reheating phenomenon during the transfer of the sample 600. The impact energy of the material is calibrated based on the change in the elastic potential energy of the spring, realizing in-situ impact testing and ensuring the accuracy and repeatability of the impact energy measurement.

[0034] In step S101 above, the cryogenic pretreatment includes immersing the spring 320 in liquid nitrogen or liquid hydrogen for 4 to 8 hours to fully stabilize its structure and eliminate residual austenite, so as to ensure the repeatability of the elastic modulus at low temperature.

[0035] In step S102 above, adjusting the temperature inside the constant temperature chamber 100 and stabilizing it at the preset test temperature includes: The temperature inside the constant temperature chamber 100 was lowered to below -253℃ and kept stable; At the same time, helium gas is introduced into the constant temperature chamber 100 as a cooling medium.

[0036] In step S106 above, the formula for calculating the impact energy is: E' = ½K((x0- x1)² - (x0- x2) 2 ) ; In the formula, K is the spring constant, x0 is the initial length of the spring, x1 is the length of the spring after compression, and x2 is the spring rebound length when the impact hammer 310 rebounds to zero speed after the impact.

[0037] In step S106 above, the spring stiffness coefficient is obtained through no-load calibration: At the test temperature, and without placing the sample 600 on the sample support, the impact hammer 310 is released from the initial impact position to complete the impact-rebound process without impact. Record the rebound length of spring 320 when the impact hammer 310 rebounds to zero velocity; Based on the principle that the impact energy is equal under frictionless loss, the spring stiffness coefficient at the test temperature was determined through multiple measurements and verifications.

[0038] Please see Figure 2 and Figure 3 This embodiment also provides an in-situ testing system for the impact toughness of materials in the liquid hydrogen temperature range, used to implement the above-described in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range. The system includes: The constant temperature chamber 100 has a sample support 110 inside; Temperature control module 200 is used to adjust and stabilize the temperature inside the constant temperature chamber 100 at the preset test temperature. Impact module 300 is disposed inside constant temperature chamber 100. Impact module 300 includes impact hammer 310, spring 320 and spring compression unit 330. Impact hammer 310 moves in a linear direction to impact sample 600. Spring 320 is connected to impact hammer 310 to drive impact hammer 310 to impact and rebound. Spring compression unit 330 is used to compress impact hammer 310 from initial position to initial impact position and then release it. Displacement recording module 400 is used to record the length of spring 320 when impact hammer 310 is in different positions; The data processing module 500 is used to calculate the impact energy based on the spring stiffness coefficient K of the spring 320 at the test temperature and the recorded spring length, according to the impact energy calculation formula.

[0039] The constant temperature chamber 100 has a double-layer structure, with an outer layer being a vacuum insulation layer and an inner layer being a sample chamber 120 filled with helium cooling medium. The impact module 300 is placed inside the sample chamber 120, and the spring compression unit 330 is connected to the spring 320 after passing through the vacuum insulation layer via a drive rod.

[0040] The displacement recording module includes a laser displacement sensor placed outside the constant temperature chamber 100; an optical window is provided on the wall of the constant temperature chamber 100; the laser displacement sensor performs non-contact measurement of the position of the impact hammer 310 or the spring 320 through the optical window.

[0041] The incubator 100 is the core container of the system, providing a completely sealed experimental space isolated from the external environment. The incubator 100 employs a double-layered cylindrical structure. For example, the outer layer is a vacuum insulation layer, welded from a stainless steel cylinder with an inner diameter of 300mm and an outer diameter of 400mm, with a sandwich thickness of 50mm. The sandwich layer is evacuated to a vacuum level of 1×10⁻⁶. -4 The heat exchange module 600 is in the Pa range and is lined with five layers of double-sided aluminum-coated polyester film as a multi-layered heat insulation radiation shield to minimize radiative heat transfer. The inner layer is the sample chamber 120, with an effective space of approximately 200 mm in diameter and 400 mm in length, sufficient to accommodate the impact hammer 310, spring 320, and sample support 110. The sample chamber 120 is filled with high-purity helium gas with a purity of over 99.999%, and the pressure is maintained at approximately 0.11 MPa (absolute pressure, slightly higher than the external atmospheric pressure) to prevent the infiltration of external air and moisture. Helium was chosen as the cooling and heat transfer medium because it has the highest liquefaction temperature of all gases (liquefying only at approximately -269°C), and remains gaseous in the liquid hydrogen temperature range (-253°C), preventing pressure drops due to condensation or affecting the mechanical operation of the impact module 300. Simultaneously, helium has excellent thermal conductivity, which facilitates heat exchange between the sample 600 and the impact module 300 and the cold source, ensuring uniform temperature distribution.

[0042] The sample support 110 is installed at the bottom center of the sample chamber 120. The sample support 110 consists of a pair of left and right anvils spaced 40 mm apart. The upper surface of the anvils is machined with V-grooves to support both ends of the sample 600. The anvils are made of high-strength low-temperature steel and have an adjustable limiting block on one side to ensure that the sample 600 is in a simply supported beam stress state during impact and to ensure that the sample notch is precisely aligned with the head of the impact hammer 310.

[0043] The temperature control module 200 includes a helium refrigeration unit 210 and a temperature control unit 220. The helium refrigeration unit 210 uses a two-stage closed-loop refrigerator as the cold source, featuring a primary cold head and a secondary cold head. The secondary cold head is connected to a copper heat sink within the sample chamber 120. Cooling is conducted from the heat sink to the helium gas within the sample chamber 120, and then transferred to the sample 600 and the impact module 300 via convection and radiation. An electric heating film is uniformly adhered to the outer wall of the sample chamber 120 as a heating element. Temperature sensors in the temperature control unit 220 are strategically placed at key locations such as the secondary cold head, the heat sink, near the sample 600, and on the surface of the spring 320, collecting real-time temperature data. Based on feedback from thermometers near the sample 600, the temperature control unit 220 dynamically adjusts the heating power of the electric heating film to precisely match the cooling power at the set temperature point, achieving long-term temperature stability; the temperature control accuracy at -253℃ can reach ±0.2℃.

[0044] Please see Figure 3 The impact module 300 includes an impact hammer 310, a spring 320, a spring compression unit 330, and a guide cylinder. The impact hammer 310 is the core component performing the impact action; its head shape and dimensions are designed according to national standards for pendulum cutting edges. The hammer body of the impact hammer 310 is cylindrical and machined from high-strength stainless steel. A self-lubricating graphite-copper alloy linear bearing sleeve is fitted onto the outer cylindrical surface of the hammer body. This linear bearing sleeve forms a precise clearance fit with the inner wall of the guide cylinder (e.g., a clearance of approximately 0.01-0.02 mm), creating a self-guiding structure. The guide cylinder is installed inside the sample chamber 120, and its axis is strictly aligned with the impact direction, ensuring that the impact hammer 310 maintains linear motion throughout its entire stroke, with low and uniform friction. The spring 320 is the power source driving the impact hammer 310. The spring 320 is a cylindrical helical compression spring wound from nickel-based high-temperature alloy wire.

[0045] The function of the spring compression unit 330 is to compress and store energy in the spring 320 and release it rapidly. For example, a precision ball screw mechanism driven by a stepper motor can be used, with the screw nut connected to the upper end of the spring 320 (or the rear end of the impact hammer 310) via a drive rod. The drive rod passes through the top of the constant temperature chamber 100, entering the cryogenic environment of the sample chamber 120 from room temperature. To minimize heat conduction through this passage, the drive rod is made of a thin-walled titanium alloy tube with a wall thickness of only 0.5 mm. Titanium alloy not only has good mechanical strength at low temperatures but also has a thermal conductivity only about one-quarter to one-sixth that of stainless steel. At the point where the drive rod passes through the wall of the constant temperature chamber 100, multiple sealing and heat insulation structures are installed, forming a cascaded heat-insulating sealing assembly distributed along the axial direction of the drive rod. The stepper motor at the top of the screw is connected to the screw via a coupling, enabling precise control of the spring compression.

[0046] The impact module 300 also includes a one-way locking mechanism, which locks the impact hammer 310 after it completes one impact and rebounds, preventing it from moving forward again. The one-way locking mechanism is either a ratchet mechanism or a spring-driven wedge-type locking mechanism located on the inner wall of the guide cylinder. A linear bearing sleeve is fitted around the impact hammer 310, and the linear bearing sleeve fits precisely with the inner wall of the guide cylinder to form a self-guiding structure.

[0047] The one-way locking mechanism is integrated into the inner wall of the guide cylinder and employs a spring-driven wedge-type locking mechanism. For example, a wedge hole is drilled in the side wall of the guide cylinder at an angle of approximately 30° to the axis, and a wedge block is placed inside the hole, with the upper part of the wedge block's inclined surface facing the front of the impact hammer 310. The rear end of the wedge block abuts against a pre-compression spring made of stainless steel, which pushes the wedge block with a tendency to extend into the cylinder. When the impact hammer 310 moves forward (towards the sample 600) through the mechanism under the drive of the spring force, its side surface presses down on the upper inclined surface of the wedge block, pushing the wedge block outward and compressing the spring 320, thus allowing it to pass smoothly. When the impact hammer 310 rebounds after impact and passes through the mechanism, since the rear end face of the wedge block is a vertical surface, the rear end face of the impact hammer 310 will engage with it. The wedge block cannot retract under the action of the pre-compression spring, thus locking the impact hammer in this position and preventing it from moving forward again. This mechanism is purely mechanical, reliable in operation, requires no electricity or hydraulic drive, and is fully adaptable to cryogenic environments.

[0048] The displacement recording module 400 includes a laser Doppler vibrometer, which is installed outside the constant temperature chamber 100. A circular optical window with a diameter of 25mm is opened on the side wall of the constant temperature chamber 100 at a position corresponding to the middle of the stroke of the impact hammer 310. The optical window is made of optical-grade fused silica glass, with anti-reflection coatings of 1064nm wavelength on both sides to improve laser transmittance. The quartz glass is welded and sealed to the stainless steel chamber via a Kovar alloy (an iron-nickel-cobalt constant expansion alloy) transition ring. The thermal expansion coefficient of the Kovar alloy matches well with both the quartz glass and the metal chamber, effectively preventing window glass breakage or leakage due to uneven thermal contraction stress at cryogenic temperatures. A small retroreflective target is attached to the side of the impact hammer 310. This target is made of microsphere glass microsphere reflective film, which has high reflectivity and large angular tolerance. The helium-neon laser beam emitted by the laser Doppler vibrometer is projected onto a reflective target through a quartz window. The reflected beam is received, and the real-time displacement and velocity of the target point (i.e., the impact hammer 310) are calculated using the principle of interference. The entire measurement chain is non-contact, not interfering with the free movement of the impact hammer 310. Its displacement measurement resolution can reach the nanometer level, and its frequency response can reach the MHz level, fully meeting the accuracy and dynamic requirements for spring compression and impact rebound displacement measurement.

[0049] The data processing module 500, for example, uses an industrial computer to synchronously acquire displacement signals output by a laser Doppler vibration meter and temperature signals output by a temperature sensor at a high sampling rate (e.g., 1MHz); it filters and extracts features from the displacement signals, automatically identifies key values ​​such as spring lengths x0, x1, and x2, calculates the impact energy in combination with the preset spring stiffness coefficient K, generates a test report, and saves it to the database.

[0050] The following section uses the in-situ impact toughness test of an austenitic stainless steel S30408 ​​sample as an example to provide a detailed description of the in-situ impact toughness test method and system for materials in the liquid hydrogen temperature range provided in this embodiment of the invention.

[0051] 1. Sample preparation and installation According to the testing standard, a V-notch standard specimen 600 was cut and machined from the S30408 ​​stainless steel sheet to be tested. The specimen dimensions were 55mm × 10mm × 10mm, the notch depth was 2mm, the notch root radius was 0.25mm, and the notch angle was 45°. The machined specimen 600 was inspected under a microscope to ensure that there were no burrs or cracks at the notch root.

[0052] Open the side door of the constant temperature chamber 100, place the sample 600 on the sample support 110, ensuring the notch of the sample faces away from the direction of the impact hammer 310, i.e., the notch is located on the tensile side of the sample 600. Adjust the position of the sample along its length using the limiting block to ensure the center line of the notch is aligned with the center line of the hammer blade of the impact hammer 310. After confirming that the sample 600 is securely installed, close the side door and lock it tightly.

[0053] 2. Vacuuming and cooling First, the vacuum insulation layer of the constant temperature chamber 100 was evacuated until the vacuum level reached 1×10⁻⁶. -3 Once the pressure drops below Pa, start the ion pump to maintain the vacuum level.

[0054] Then, high-purity helium is introduced into the sample chamber 120 and flushed three times (inflated to 0.12 MPa, then evacuated to a slightly positive pressure, repeated three times) to replace the residual air inside, so that the sample chamber 120 is filled with pure helium and the pressure is stabilized at about 0.11 MPa (absolute pressure).

[0055] The helium cooling unit 210 is activated, and the temperature control unit 220 monitors the temperature near the sample 600 in real time. When the temperature drops to approximately -250℃, the target temperature is set to -253℃. The power of the electric heating film is automatically adjusted to precisely stabilize the temperature at the set point. After the temperature stabilizes within the range of -253℃ ± 0.2℃ and is maintained for at least 45 minutes, both the sample 600 and the impact module 300 have reached complete thermal equilibrium, and the next step can be performed.

[0056] 3. No-load dynamic calibration of spring stiffness coefficient K Before conducting the formal impact test of the sample 600, the no-load dynamic calibration of the spring stiffness coefficient K was performed to verify and determine the actual spring stiffness coefficient of spring 320 at the operating temperature of -253℃.

[0057] (1) Confirm that no sample 600 is placed on the sample support 110 at this time and it is in an unloaded state.

[0058] (2) The spring 320 is compressed by the spring compression unit 330, which pushes the impact hammer 310 from the initial equilibrium position O to the preset initial impact position A; at this time, the compression of the spring 320 is x0-x1. The laser Doppler vibration meter monitors the displacement in real time and automatically records the precise values ​​of the spring lengths x0 and x1 corresponding to points O and A.

[0059] (3) The spring compression unit 330 is released, and the constraint of the spring 320 is removed; the spring 320 is rapidly stretched under the drive of the stored elastic potential energy, pushing the impact hammer 310 to accelerate forward along the guide cylinder.

[0060] (4) Since there is no sample 600 blocking the sample support 110, the impact hammer 310 does not stop after passing point O, but continues to move forward under inertia. After passing the free length of spring 320, it begins to stretch spring 320, converting its kinetic energy into the tensile elastic potential energy of spring 320, until the instantaneous velocity of impact hammer 310 drops to zero. At this time, spring 320 is in the maximum stretched state, and this position is recorded as the maximum stroke position. Subsequently, the restoring force of spring 320 drives impact hammer 310 to move in the opposite direction, and after passing point O again, it compresses spring 320, converting its kinetic energy into compressive elastic potential energy, until the velocity drops to zero again. This process repeats, forming a damped oscillation. After several oscillations, impact hammer 310 tends to come to rest.

[0061] (5) Record the displacement-time curve of the impact hammer 310 throughout the process, and extract the spring length x2' corresponding to the position where the impact hammer 310 rebounds to zero velocity for the first time (marked as point B') from the displacement-time curve.

[0062] (6) In an ideal frictionless system, the spring compression potential energy of the impact hammer 310 at point A should be exactly equal to the spring stretching (or compression) potential energy at point B', i.e., ½K(x0-x1). 2 = ½K(x0-x2') 2However, in actual systems, there is unavoidable energy dissipation due to minute friction and air resistance. By repeating the above operations (2) to (5) at least 5 times, the obtained x1 and x2' data sequences are statistically analyzed. If the standard deviation is extremely small, for example, below the measurement accuracy of 0.01 mm, it indicates that the system energy loss is extremely small and stable, and the spring K value is stable. At this time, the spring stiffness coefficient previously measured by static tensile method at -253℃ for this batch of materials is used as the effective K value.

[0063] If there is a identifiable small systematic deviation between x1 and x2', i.e. x1 is systematically slightly larger or slightly smaller than x2', then the effective spring constant K at that temperature can be deduced from the energy balance relationship: ½K(x0-x1). 2 - ½K(x0-x2') 2 = W loss If W loss If the value can be estimated to be a very small amount through no-load friction testing, then we can approximate it as K = K static ;where K static The static stiffness coefficient of the spring is obtained in advance through standardized spring characteristic tests. For higher precision, K can be set to the average of (x0-x1) and (x0-x2') from multiple no-load tests, such that ∑[½K((x0-x1)] = ... 2 -(x0-x2') 2 )] 2 Minimize the value of K to fit the optimal value.

[0064] The effective spring stiffness coefficient of the nickel-based high-temperature alloy spring at -253℃ was confirmed to be K = 85.0 N / mm, or 85000 N / m, through the no-load dynamic calibration procedure.

[0065] (7) The final determined spring stiffness coefficient K and its applicable temperature range are stored in the data processing module 500 for subsequent formal impact testing. Although this calibration step increases the operation time, it provides a reliable metrological traceability guarantee for impact energy measurement, thereby achieving high-precision in-situ measurement.

[0066] 4. Formal impact test After completing the spring K-value calibration, turn off the helium refrigeration unit 210 and the temperature control unit 220, or set them to maintain a temperature of -253℃. Open the side door of the constant temperature chamber 100, quickly place the pre-prepared S30408 ​​sample 600 (placed at room temperature) onto the sample support 110 and align it. Then close the side door of the constant temperature chamber 100 again. Start the helium refrigeration unit 210 to cool the sample chamber 120 again and stabilize it at -253℃.

[0067] Please see Figure 4After the temperature stabilizes again, drive the spring compression unit 330 to compress the impact hammer 310 from point O to the same initial impact position A as when it was calibrated under no-load conditions (the spring compression is the same), and record x0 and x1.

[0068] The spring compression unit 330 performs a release operation, and the spring 320 is released instantaneously, driving the impact hammer 310 to accelerate linearly along the guide cylinder, violently impacting the notch root of the specimen 600 with a predetermined initial kinetic energy. The complete displacement-time history curve of the impact hammer 310 is recorded in detail; from the displacement-time history curve, one can see the acceleration segment before impact and the sharp drop in velocity at the moment of impact, corresponding to the deformation and fracture process of the specimen 600, as well as complete information on the rebound segment after impact.

[0069] The system automatically identifies point B, the position where the impact hammer 310 first reaches zero velocity after rebounding, and records the spring length x2 at that point. The one-way locking mechanism immediately locks the impact hammer 310 as it rebounds, preventing any secondary impact and ensuring the clarity and uniqueness of the rebound information in the displacement curve.

[0070] The following key location data were obtained through automatic identification and extraction: The spring length (initial length) corresponding to the initial equilibrium position O is: x0 = 120.00 mm The spring length (compressed length) corresponding to the initial impact position A: x1 = 75.00 mm The spring length corresponding to point B, where the initial velocity is zero after the impact rebound, is: x2 = 108.50 mm All three length values ​​mentioned above have been corrected for ambient temperature compensation.

[0071] 5. Calculation of impact energy The data processing module 500 calls the calibrated spring stiffness coefficient K, as well as the values ​​of x0, x1, and x2, and automatically calculates the impact energy according to the formula.

[0072] (1) Calculate the elastic potential energy E1' of the spring at the initial impact position A. The compression of spring 320 at point A is: Δx1= x0- x1= 120.00 - 75.00 = 45.00 mm = 0.0450 m The elastic potential energy E1' is: E1' = ½ × K × (Δx1)² = ½ × 85000 × (0.0450)² = ½ × 85000 × 0.002025= 86.0625 J This energy is the total input energy that the impact hammer 310 receives at the moment of release.

[0073] (2) Calculate the elastic potential energy E2' of the spring at point B, the limit of its rebound. The compression of spring 320 at point B is: Δx2= x0- x2= 120.00 - 108.50 = 11.50 mm = 0.0115 m The elastic potential energy E2' is: E2' = ½ × K × (Δx2)² = ½ × 85000 × (0.0115)² = ½ × 85000 × 0.00013225= 5.6206 J This energy is the elastic potential energy remaining in the spring-impact hammer system after the impact. The impact hammer 310 is locked at point B by the secondary impact prevention module 300, and this part of the energy does not participate in the fracture process of the sample 600.

[0074] (3) Calculate the impact energy E' absorbed by the sample. According to the principle of conservation of energy, the energy absorbed by sample 600 during the impact fracture process (impact work) is equal to the decrease in elastic potential energy of spring 320 before and after the impact: E' = E1' - E2' = 86.0625 - 5.6206 = 80.4419 J ≈ 80.5 J (4) Calculate the impact toughness value The nominal cross-sectional area S of the S30408V-notched standard specimen is 0.80 cm², then the impact toughness value a k for: a k = E' / S = 80.5 / 0.80 = 100.6 J / cm² This value is consistent with the impact energy range reported in the literature for S30408 ​​austenitic stainless steel in the liquid hydrogen temperature range of -253℃, verifying the accuracy and reliability of the measurement results of the spring elastic potential energy difference method.

[0075] It should be noted that the measurement uncertainty mainly stems from the following factors: First, the calibration uncertainty of the spring stiffness coefficient K: after five repeated no-load dynamic calibrations, the relative standard deviation of the measured K value was 0.3%, corresponding to a combined standard uncertainty of approximately 0.26 N / mm; Second, the displacement measurement uncertainty: the displacement measurement resolution of the laser Doppler vibration meter is better than 0.001 mm, and within a 45 mm range, the relative uncertainty introduced by displacement measurement is far less than 0.01%; Third, friction and air resistance losses: verified by no-load calibration, the energy loss caused by mechanical friction and helium resistance accounts for approximately 0.2%-0.5% of the total input energy, which has been indirectly compensated for in the dynamic calibration of the K value. In summary, the expanded uncertainty of the impact energy measurement is approximately ±1.5 J (coverage factor k=2), fully meeting the national standard requirements for the measurement accuracy of impact testing machines.

[0076] The test data and curves are stored in the database together to generate a test report.

[0077] 6. Reheating and sampling after testing After the test is completed, the helium refrigeration unit 210 is turned off, and the sample chamber 120 is gradually restored to room temperature at a rate not exceeding 5°C / min via the temperature control unit 220. During the rewarming process, helium gas is continuously introduced to maintain a slight positive pressure to prevent the backflow of outside air. After the temperature rises to room temperature, the side door is opened, and the broken sample 600 is removed. The sample chamber 120 is cleaned in preparation for the next test.

[0078] Please see Figure 5 This paper proposes a method that replaces the traditional gravitational potential energy difference method with the spring elastic potential energy difference method. By utilizing the spring's elastic potential energy to drive an impact hammer for short-range linear impacts, in-situ impact testing at liquid hydrogen and even liquid helium temperatures is achieved. This completely eliminates the problem of temperature rise caused by sample transfer, ensuring that the measured data accurately reflects the impact toughness of the material at the set cryogenic temperature. Only two length values ​​of the spring 320 before and after the impact (e.g., x1 and x2) need to be measured. Combined with a pre-calibrated spring constant K, the impact energy is obtained through simple algebraic calculations. The entire process does not require a high-speed camera to measure the impact velocity or complex electromagnetic field calculations, demonstrating the method's simplicity in principle, ease of operation, and high adaptability to cryogenic environments. Obtaining in-situ impact toughness data of materials at liquid hydrogen temperatures provides crucial material performance support for cryogenic engineering such as superconducting magnets and deep space probes.

[0079] The embodiments of the present invention have the following beneficial effects: 1. Innovation in Testing Principle: Abandoning the traditional approach of using gravitational potential energy difference as the measurement principle in pendulum impact testing machines, this invention proposes and implements a measurement principle based on the elastic potential energy difference of a spring for cryogenic impact toughness. This results in a significant reduction in equipment size, allowing the entire impact module 300 to be placed inside the constant temperature chamber 100, fundamentally solving the industry problem of test distortion caused by sample reheating in cryogenic environments.

[0080] 2. Truly Achieves Cryogenic In-situ Testing: Since the entire impact mechanism is placed inside a constant temperature chamber of 100°C, the cooling and impact of the sample 600 are completed in the same identical environment, requiring no transfer operations. The temperature fluctuation of the sample 600 is minimal throughout the entire testing process, enabling precise in-situ measurement of the material's impact toughness in the liquid hydrogen and even liquid helium temperature ranges, filling a technological gap.

[0081] 3. Unique self-calibration measurement mechanism: Through low-temperature no-load dynamic calibration, the spring stiffness coefficient of spring 320 at the test temperature can be checked in situ before each test, effectively eliminating the influence of temperature change on the spring elastic modulus and the high strain rate effect during the impact process, ensuring high accuracy and high reliability of the impact energy calculation results.

[0082] 4. Strong adaptability to extreme environments: The spring 320 is made of austenitic stainless steel or nickel-based alloy, which solves the problems of brittle fracture and austenitic phase transformation of conventional spring materials at cryogenic temperatures; the graded vacuum insulation structure and helium cooling medium are used to ensure uniform and stable temperature in the sample chamber 120; the laser non-contact displacement measurement is used, and high-precision measurement can be performed outside the sealed constant temperature chamber 100 equipped with the impact module 300 through the optical window, avoiding the failure risk of contact sensors under huge temperature differences.

[0083] 5. Compact structure and high practicality: By setting a one-way locking mechanism, it ensures that only one effective impact occurs in each test, avoiding the energy calculation confusion caused by the impact hammer 310 rebounding and hitting the sample 600 a second time; by setting a self-guiding structure, it ensures that the impact hammer 310 always hits the root of the sample notch accurately along a straight line, ensuring that the test meets the standard requirements. It has the characteristics of advanced principle, stability and reliability, and is easy to promote and implement.

[0084] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An in-situ testing method for the impact toughness of materials in the liquid hydrogen temperature range, characterized in that, include: The sample is placed on a sample support inside a constant temperature chamber. The constant temperature chamber is equipped with an impact module, which includes an impact hammer and a spring. The spring is made of austenitic stainless steel or nickel-based alloy and has undergone cryogenic pretreatment. Adjust the temperature inside the constant temperature chamber and stabilize it at the preset test temperature; Compress the spring to move the impact hammer from its initial position to a preset initial impact position, and record the initial length and the length of the spring after compression. Release the compressed spring and drive the impact hammer to impact the sample in a straight line; After the impact hammer completes its impact, the spring rebound length is recorded when the impact hammer rebounds to zero speed. Based on the initial length, compressed length, and rebound length of the spring, as well as the spring constant at the test temperature, the impact energy absorbed by the sample is calculated using the impact energy calculation formula, thus obtaining the impact toughness of the sample.

2. The in-situ testing method for impact toughness of materials in the liquid hydrogen temperature range according to claim 1, characterized in that, The cryogenic pretreatment includes immersing the spring in liquid nitrogen or liquid hydrogen for 4 to 8 hours to fully stabilize its structure and eliminate residual austenite, thereby ensuring the repeatability of the elastic modulus at low temperatures.

3. The in-situ testing method for impact toughness of materials in the liquid hydrogen temperature range according to claim 1, characterized in that, The process of adjusting and stabilizing the temperature inside the constant temperature chamber at a preset test temperature includes: The temperature inside the constant temperature chamber was lowered to below -253°C and kept stable. Simultaneously, helium gas is introduced into the constant temperature chamber as a cooling medium.

4. The in-situ testing method for impact toughness of materials in the liquid hydrogen temperature range according to claim 1, characterized in that, The formula for calculating the impact energy is: E' = ½K((x0- x1)² - (x0 - x2) 2 ); In the formula, K is the spring constant, x0 is the initial length of the spring, x1 is the length of the spring after compression, and x2 is the spring rebound length when the impact hammer rebounds to zero velocity after the impact.

5. The in-situ testing method for impact toughness of materials in the liquid hydrogen temperature range according to claim 4, characterized in that, The spring constant is obtained through no-load calibration: At the test temperature, and with no sample placed on the sample support, the impact hammer is released from the initial impact position to complete the impact-rebound process without impact. Record the spring rebound length when the impact hammer rebounds to zero velocity; Based on the principle that the impact energy is equal under frictionless loss, the spring stiffness coefficient at the test temperature is determined by multiple measurements and verifications.

6. An in-situ testing system for the impact toughness of materials in the liquid hydrogen temperature range, characterized in that, The method for in-situ testing of impact toughness of materials in the liquid hydrogen temperature range as described in any one of claims 1 to 5 includes: A constant temperature chamber, wherein a sample support is provided inside the constant temperature chamber; A temperature control module is used to adjust and stabilize the temperature inside the constant temperature chamber at a preset test temperature. An impact module is disposed inside the constant temperature chamber. The impact module includes an impact hammer, a spring, and a spring compression unit. The impact hammer moves in a linear direction to impact the sample. The spring is connected to the impact hammer and is used to drive the impact hammer to impact and rebound. The spring compression unit is used to compress the impact hammer from its initial position to the initial impact position and then release it. A displacement recording module is used to record the initial length, compressed length, and rebound length of the spring. The data processing module is used to calculate the impact energy absorbed by the sample based on the spring stiffness coefficient at the test temperature and according to the impact energy calculation formula.

7. The in-situ testing system for impact toughness of materials in the liquid hydrogen temperature range according to claim 6, characterized in that, The constant temperature chamber has a double-layer structure, with an outer layer being a vacuum insulation layer and an inner layer being a sample chamber filled with helium cooling medium. The impact module is placed in the sample chamber, and the spring compression unit is connected to the spring after passing through the vacuum insulation layer via a drive rod.

8. The in-situ testing system for impact toughness of materials in the liquid hydrogen temperature range according to claim 6, characterized in that, The displacement recording module includes a laser displacement sensor, which is located outside the constant temperature chamber. An optical window is provided on the wall of the constant temperature chamber, and the laser displacement sensor performs non-contact measurement of the position of the impact hammer or the spring through the optical window.

9. The in-situ testing system for impact toughness of materials in the liquid hydrogen temperature range according to claim 7, characterized in that, The impact module also includes a one-way locking mechanism and a guide cylinder. The one-way locking mechanism is a ratchet mechanism or a spring-driven wedge locking mechanism installed on the inner wall of the guide cylinder, used to lock the impact hammer after it completes the impact and rebounds.

10. The in-situ testing system for impact toughness of materials in the liquid hydrogen temperature range according to claim 9, characterized in that, The impact hammer is fitted with a linear bearing sleeve, which cooperates with the inner wall of the guide cylinder to form a self-guiding structure.

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