A pre-cooler header-capillary joint extreme temperature gradient multi-axis test device and method

Abstract

This invention relates to the field of structural strength evaluation of aero-engine systems, and discloses a multiaxial testing device and method for extreme temperature gradients at a precooler manifold-capillary joint. A cryogenic medium circulation unit provides a cryogenic boundary to the interior of the manifold, and a temperature gradient loading unit locally heats the capillary, thereby constructing an extreme temperature gradient at the brazed joint. The free end of the capillary is fixed to the loading cylinder with potting material, and a multiaxial loading actuator applies the load. An isolation structure is provided at the connection between the capillary and the manifold to prevent media exchange. This invention can simultaneously establish an extreme temperature gradient with both a cryogenic cold end and a high-temperature hot end within a millimeter-scale micro-region of the brazed joint, achieving precise control of the extreme temperature gradient. This more realistically simulates the service thermal environment of the precooler joint, overcoming the shortcomings of existing technologies that cannot reconstruct cryogenic-high-temperature gradients in micro-connection areas, and improving the safety and data reliability of tests on ultra-thin-walled capillary brazed joints.

Description

Technical Field

[0001] This invention relates to the field of structural strength evaluation of aerospace power systems, and discloses a multiaxial test device and method for extreme temperature gradient of precooler main pipe-capillary joint. Background Technology

[0002] Hydrogen-powered aviation propulsion is a crucial direction for future aviation propulsion technology development. Its key lies in the efficient heat exchange of high-temperature airflow through heat exchangers or precoolers to ensure the safe operation of the engine and airframe structure under extreme thermal environments. Precoolers typically employ a structure where a thick-walled main pipe is brazed to an array of ultra-thin-walled capillary tubes. The cryogenic medium flows within the main pipe or heat exchange channel, while the exterior is heated by the high-temperature airflow or combustion gas. This type of structure simultaneously experiences strong heat flow, cryogenic boundaries, and mechanical vibration at millimeter or even sub-millimeter scales, making it a critical weak point affecting the precooler's lifespan and safety.

[0003] The main pipe and capillary tube differ significantly in wall thickness, heat capacity, stiffness, and constraint conditions. When the main pipe is in a cryogenic state (liquid hydrogen temperature: -253℃) while the capillary tube is locally heated to a high temperature (up to 550℃), an extremely steep temperature gradient and significant thermal deformation mismatch will occur near the brazed joint. If mechanical loads such as engine vibration, aerodynamic excitation, pipeline pressure pulsation, and assembly constraints are added, the brazed joint is prone to shear fatigue, bending fatigue, and thermal fatigue coupled damage, which can lead to crack initiation and propagation.

[0004] There are three main difficulties in evaluating the reliability of this type of joint. First, conventional temperature testing equipment is mostly used for macroscopic samples or uniform temperature fields, making it difficult to reconstruct the extreme temperature gradient where the cryogenic cold end and the high-temperature hot end coexist in the tiny connection region between the main tube and the capillary. Second, the outer diameter of the capillary is usually less than a few millimeters, and the wall thickness can be as low as about 0.1 mm. When directly clamped with rigid claws, crushing, tearing, or premature breakage can easily occur at the clamping end, failing to accurately reflect the service damage of the brazed joint. Third, if the cryogenic medium is directly introduced into the micro-capillary and heated externally, the medium inside the tube may boil violently, experience gas blockage, and experience a sudden pressure surge, posing a high testing risk.

[0005] In the prior art, US10627050B1 discloses a low-temperature heating system that achieves wide-range temperature control through inert fluid and heating components, suitable for macroscopic tests such as material friction and wear. However, this solution does not involve the brazed joint between the main tube and capillary tube, nor does it provide multiaxial mechanical loading and fatigue life evaluation functions for the brazed joint. CN102621022B discloses a thermo-mechanical coupled fatigue testing device and method, capable of induction heating, internal cooling, and stress fatigue loading on the specimen; CN114720257A discloses a thermal fatigue testing method for component materials based on scaled-down specimens, used to evaluate the thermal fatigue performance of component materials using scaled-down specimens. Although the above solutions involve thermal fatigue or thermo-mechanical coupled testing, their objects are mainly standard or scaled-down macroscopic specimens, and they do not solve the problems of safe isolation, non-destructive clamping, and multiaxial load transfer of brazed joints between micro-capillaries and thick-walled main tubes under cryogenic-high temperature gradients. CN114383942A discloses an in-situ testing method and in-situ test specimen for the peeling performance of brazed joints, enabling loading and observation of the brazed joints; CN110082040A discloses a thin-walled capillary sealing performance testing device and method; other existing related solutions involve high-temperature alloy capillary brazing equipment, brazing filler metal design, and capillary heat exchanger welding methods. The aforementioned prior art either focuses on brazed joint manufacturing or on single mechanical / sealing tests of brazed joints, and none of them have established an extreme temperature gradient multiaxial fatigue testing platform for the precooler main pipe-capillary joint.

[0006] Therefore, existing technologies cannot simultaneously solve the following problems: safely forming an extreme temperature gradient near the manifold-capillary brazed joint where the cryogenic cold end and the high-temperature hot end coexist; transferring axial, lateral, and torsional loads to the brazed joint without crushing the extremely thin-walled capillary; and preventing cryogenic media from being ejected and leaking through the capillary channel when the brazed joint fails or the joint cracks propagate. Summary of the Invention

[0007] The purpose of this invention is to provide a multiaxial test device and method for extreme temperature gradient of precooler manifold-capillary joint, which can simultaneously establish an extreme temperature gradient with both cryogenic cold end and high-temperature hot end in a tiny area at the millimeter level of the brazed joint. This can more realistically simulate the service thermal environment of the precooler joint and improve the safety and data reliability of the test on ultra-thin-walled capillary brazed joint.

[0008] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows:

[0009] A multiaxial test apparatus for extreme temperature gradients of a precooler manifold-capillary joint includes: A fixed main pipe is used to fix and install a test main pipe with a capillary tube brazed to it. The test main pipe is connected to the fixed main pipe. An isolation structure is provided at the brazed position of the test main pipe and the capillary tube so that the test main pipe and the capillary tube are not connected. A cryogenic medium circulation unit, connected to the fixed manifold, is used to provide a cryogenic boundary to the interior of the test manifold through the fixed manifold. A temperature gradient loading unit is used to locally heat the capillary tube so as to form a temperature gradient at the brazed joint location together with the cryogenic boundary inside the test tube. A multi-axis loading unit includes a loading cylinder, a potting material, and a multi-axis loading actuator. The free end of the capillary is fixed inside the loading cylinder by the potting material. The loading cylinder is connected to the multi-axis loading actuator and is used to apply a test load to the capillary. The test load includes axial tensile and compressive loads, bending loads, or torsional loads around the axis of the capillary.

[0010] Furthermore, the cryogenic medium circulation unit includes a cryogenic medium storage container, a recovery container, a refrigerator, and a circulation drive mechanism connected in sequence by pipelines; the fixed main pipe is installed on the pipeline between the cryogenic medium storage container and the recovery container, and the cryogenic medium forming the cryogenic boundary includes liquid nitrogen, liquid helium, and liquid hydrogen.

[0011] Furthermore, both ends of the test manifold are detachably mounted on the fixed manifold via flanges.

[0012] Furthermore, the isolation structure between the test manifold and the capillary tube includes a blind end and an isolation plug disposed at the brazing end of the capillary tube, or an installation blind hole and a sealing cavity disposed at the brazing position of the test manifold.

[0013] Furthermore, the temperature gradient loading unit includes an induction heating coil arranged around the capillary for local heating of the capillary.

[0014] Furthermore, the induction heating coil is made of hollow copper tube and has a cooling circuit, through which a circulating cooling medium is introduced to cool the induction heating coil.

[0015] Furthermore, it also includes a control acquisition unit, which includes a controller. The controller is connected to the pressure sensor and leakage sensor of the cryogenic medium circulation unit, the temperature sensor of the temperature gradient loading unit, and the force sensor, displacement sensor, torque sensor, and angular displacement sensor of the multi-axis loading unit, respectively, to control the temperature gradient and multi-axis load loading.

[0016] Furthermore, the outer wall of the fixed main pipe is also provided with a heat insulation component to reduce the loss of cold energy.

[0017] To achieve the above-mentioned technical effects, the present invention also provides a multiaxial test method for extreme temperature gradients of the precooler manifold-capillary joint. This method is based on the aforementioned multiaxial test apparatus for extreme temperature gradients of the precooler manifold-capillary joint, and includes: Specimen preparation and potting: Prepare test manifold and capillary specimens, set up an isolation structure at the brazing connection position of the capillary and test manifold, braze one end of the capillary to the test manifold, insert the free end of the capillary into the loading cylinder, inject potting material and cure to form a potting body; Specimen installation and system connection: Connect the test manifold to the fixed manifold, and connect the loading cylinder to the multi-axis loading actuator; Extreme temperature field construction: The cryogenic medium circulation unit is activated to lower the temperature of the test manifold to the first preset temperature value, and the temperature gradient loading unit is activated to raise the temperature of the capillary tube to the second preset temperature value, thus forming an extreme temperature gradient in the brazed joint area. Multi-axis mechanical loading: Start the multi-axis loading unit, apply the corresponding test load to the capillary according to the set load spectrum, and use the sensing component to record the test data.

[0018] Compared with the prior art, the beneficial effects of this invention are: 1. This invention, through a combination of a cryogenic medium circulation unit and a temperature gradient loading unit, establishes an extreme temperature gradient near the brazed joint, where a cryogenic cold end and a high-temperature hot end coexist. This more realistically simulates the service thermal environment of the precooler joint. Compared to the single-temperature cycle test achieved by furnace heating and water cooling in existing technologies, this invention can simultaneously construct cryogenic boundaries and local high temperatures within a millimeter-scale micro-region, achieving precise control of the extreme temperature gradient and overcoming the deficiency of existing technologies in reconstructing cryogenic-high temperature gradients in micro-connection regions.

[0019] 2. This invention isolates the capillary inner bore from the main tube's internal cavity through an isolation structure, reducing the risks of boiling blockage, overpressure, and jet leakage after the cryogenic medium enters the microcapillary. Compared to existing technologies that directly introduce the cryogenic medium into the microcapillary, this invention fundamentally eliminates the channel for the cryogenic medium to enter the capillary inner bore through its isolation structure. When the brazed seam undergoes fatigue fracture under ultimate load, the high-pressure cryogenic medium inside the main tube will not leak outward through the capillary inner bore, fundamentally eliminating the safety hazards of the test and overcoming the risks of boiling blockage, pressure surge, and jet leakage inherent in existing technologies.

[0020] 3. The present invention uses a potting loading cylinder to transform the local clamping of ultra-thin-walled capillary tubes into distributed interface load transfer. While ensuring that the test load is transferred to the brazed joint, it can avoid stress concentration at the capillary clamping end of the rigid claw, which can lead to crushing, tearing or premature breakage. This overcomes the defect of the prior art that cannot apply multiaxial loads to ultra-thin-walled capillary tubes (such as those with a wall thickness of 0.08~0.12mm). Attached Figure Description

[0021] Figure 1 A schematic diagram of the multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint; Figure 2 This is a schematic diagram showing the connection between the test tube and the capillary tube; Figure 3 A schematic diagram showing the positional relationship between the loading cylinder, the temperature gradient loading unit, and the capillary tube; Figure 4 This is a cross-sectional schematic diagram of a multi-axis loading element; Figure 5 A schematic diagram showing the installation position of the main pipe on the main pipe base; Among them, 1. Fixed main pipe; 2. Capillary tube; 3. Test main pipe; 4. Loading cylinder; 5. Potting material; 6. Multi-axis loading actuator; 7. Cryogenic medium storage container; 8. Recovery container; 9. Refrigerator; 10. Cyclic drive mechanism; 11. Induction heating coil; 12. Control and acquisition unit; 13. Thermal insulation component; 1301. Split-type thermal insulation plate; 1302. Main pipe base. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0023] Example 1 like Figures 1 to 5 The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint in this embodiment includes a cryogenic medium circulation unit, a replaceable joint specimen unit, a temperature gradient loading unit, a multiaxial loading unit, and a control and acquisition unit 12. Wherein: The cryogenic medium circulation unit includes a cryogenic medium storage container 7, a circulation drive mechanism 10, a heat exchanger or cooler 9, a recovery container 8, cryogenic piping, a flow control valve, a pressure sensor, and a safety relief valve. The cryogenic medium storage container 7 stores liquid nitrogen or liquid hydrogen. The circulation drive mechanism 10 (such as a compressor or fluid pump) drives the cryogenic medium to circulate in the cryogenic piping, maintaining a set temperature via the heat exchanger or cooler 9. The cryogenic piping is connected to a fixed main pipe 1, and the cryogenic medium enters both the fixed main pipe 1 and the test main pipe 3, forming a cryogenic boundary within the test main pipe 3. The flow control valve controls the cryogenic medium flow rate, the pressure sensor monitors the circulation loop pressure, and the safety relief valve automatically releases pressure when the pressure exceeds a safety threshold.

[0024] like Figure 3 As shown, the replaceable connector test piece unit includes a fixed main pipe 1, a test main pipe 3, and a capillary tube 2. The fixed main pipe 1 is a thick-walled stainless steel or high-temperature alloy pipe, horizontally fixed within the main pipe base 1302. One end of the fixed main pipe 1 is connected to the cryogenic medium storage container 7 via a cryogenic pipeline, and a standard connecting flange is machined onto this pipeline. The test main pipe 3 is a short tubular structure, with mating flanges machined at both ends to mate with the fixed main pipe 1. The fixed main pipe 1 and the test main pipe 3 are connected via flanges, allowing for the placement of metal gaskets. Bolts are tightened gradually in a diagonal sequence to the specified torque to ensure a sealed connection. After the fixed main pipe 1 and the test main pipe 3 are connected, their internal cavities are interconnected, forming a complete cryogenic medium flow channel.

[0025] The fixed main pipe 1 can be installed inside the split main pipe base 1302. The split main pipe base 1302 encloses and fixes the main pipe 1 from the upper and lower halves, and the opening and closing operation of the main pipe base 1302 is realized by the hinge provided on the main pipe base 1302. In this embodiment, a split heat insulation plate 1301 is also provided to cover the outside of the connection area of ​​the fixed main pipe 1. The split heat insulation plate 1301 can serve as a heat insulation component 13 to reduce heat loss.

[0026] The test manifold 3 has mounting holes on its wall. The capillary tube 2 is an ultra-thin-walled stainless steel or high-temperature alloy tube with an outer diameter of 0.5 to 1.0 mm and a wall thickness of 0.08 to 0.12 mm. One end of the capillary tube 2 is pre-sealed by laser welding to form a blind end. This blind end is inserted into the mounting hole of the test manifold 3, leaving a brazing gap of 0.05 to 0.10 mm between them. The brazing filler metal is filled using vacuum brazing or furnace brazing processes to form a ring-shaped brazed seam. Because the insertion end of the capillary tube 2 is pre-sealed, the inner hole of the capillary tube 2 and the internal cavity of the test manifold 3 remain physically isolated and do not communicate with each other. When the brazed seam undergoes fatigue fracture under ultimate load, the high-pressure cryogenic medium inside the test manifold 3 will not leak out through the inner hole of the capillary tube 2, eliminating potential safety hazards during testing.

[0027] The temperature gradient loading unit includes an induction heating coil 11, a high-frequency induction heating power supply, and a temperature sensor. The induction heating coil 11 is a helical coil wound from a hollow copper tube, with circulating cooling water flowing inside to prevent overheating. The induction heating coil 11 is arranged around the outside of the capillary tube 2, located on the tube section between the brazed joint and the loading end. The induction heating coil 11 is connected to the high-frequency induction heating power supply, and the heating temperature is controlled in a closed loop using thermocouples arranged on the surface of the capillary tube 2, with temperature fluctuations controlled within ±5 degrees Celsius. The high-temperature zone of the induction heating and the cryogenic zone of the main tube work together to create an extremely steep temperature gradient in the small brazed joint area, realistically simulating the thermal environment of the precooler during operation.

[0028] like Figure 4 As shown, the multi-axis loading unit includes a loading cylinder 4, a potting material 5, and a multi-axis loading actuator 6. The loading cylinder 4 can be a metal cylinder or a cup-shaped structure with a connecting flange, with the free end of the capillary tube 2 inserted into the center of the loading cylinder 4. The loading cylinder 4 is filled with epoxy resin potting material 5, and the free end of the capillary tube 2 is covered and cured by the potting material 5 to form a potted body. The potting material 5 transforms rigid clamping into distributed interface load transfer, avoiding crushing of the extremely thin-walled capillary tube 2. The loading cylinder 4 is connected to the multi-axis loading actuator 6. The multi-axis loading actuator 6 includes three mutually orthogonal linear actuators and one torsional actuator. The three linear actuators are arranged along the axial direction of the capillary tube 2 and two orthogonal directions perpendicular to the axial direction, respectively, and can independently or collaboratively apply axial tensile and compressive loads and two lateral bending loads. The torsional actuator is arranged coaxially with the loading cylinder 4 and can apply torsional loads around the axis of the capillary tube 2.

[0029] The control and acquisition unit 12 is connected to the pressure and leakage sensors of the cryogenic medium circulation unit, the temperature sensor of the temperature gradient loading unit, and the force, displacement, torque, and angular displacement sensors of the multi-axis loading unit, respectively, to collect various parameters during the test in real time. The control and acquisition unit 12 calculates the dynamic stiffness of the specimen in real time based on the collected load and displacement curves. When the dynamic stiffness drops beyond a set threshold, the cryogenic circulation pressure exceeds a safety threshold, or the leakage sensor alarms, the control and acquisition unit 12 triggers the multi-axis loading actuator 6 to unload to a safe state within a set time, shuts down or reduces the induction heating power, and performs pressure relief or shutdown protection according to the pressure status, improving test safety and data reliability.

[0030] The operating steps of the multiaxial test method for extreme temperature gradients of the precooler main pipe-capillary joint in this embodiment are as follows: Step 1: Specimen preparation and potting Based on the actual structural parameters of the precooler, test manifold 3 and capillary tube 2 were prepared. Test manifold 3 was machined according to the actual material and wall thickness, with mounting holes drilled in the tube wall. Capillary tube 2 was made of the same high-temperature alloy material as the actual precooler. One end of capillary tube 2 was pre-sealed using laser welding to form an isolation structure and inserted into the mounting hole of test manifold 3. A circumferential brazing seam was formed using vacuum brazing. After completion, the airtightness or pressure of the non-communication state between the inner hole of capillary tube 2 and the inner cavity of the manifold was checked. The free end of capillary tube 2 was inserted into loading cylinder 4, and potting material 5 was injected. After static curing, a potting body was formed.

[0031] Step 2: Specimen Installation and System Connection The prepared test manifold 3 is connected to the flange of the fixed manifold 1 via a mating flange. A sealing gasket is placed, and the bolts are tightened to complete the sealing connection. The split heat insulation plates 1301 of the split manifold base 1302 are closed and locked, so that the manifold is covered and fixed inside the base. The loading cylinder 4 is connected to the actuating end of the multi-axis loading actuator 6 via bolts, and the actuator position is adjusted to make the capillary tube 2 in a natural stress-free state. The induction heating coil 11 is installed around the capillary tube 2, and the coil position and spacing are adjusted. Temperature sensors, pressure sensors, leakage sensors, and force / displacement / torque sensors are installed, and the protective chamber is closed.

[0032] Step 3: Construction of Extreme Temperature Field The cryogenic medium circulation unit is activated, and the compressor and refrigerator 9 are turned on. Liquid helium, liquid nitrogen, liquid hydrogen, or other media used to simulate the cryogenic boundary of the precooler are introduced into the fixed main pipe 1 and the test main pipe 3, gradually reducing the main pipe temperature to the set cold end temperature. The cooling rate is controlled by adjusting the medium flow rate. After the cold end temperature stabilizes, the induction heating system is activated, and the heating power is gradually increased to raise the capillary tube 2 temperature to the set hot end temperature (maximum 550℃). Closed-loop control of the cold and hot end temperatures is achieved through thermocouple feedback, establishing a stable extreme temperature gradient in the brazed joint area.

[0033] Step 4: Multi-axis mechanical loading and testing After the temperature field stabilizes, the multi-axis loading unit is activated. A small preload is first applied to eliminate mechanical backlash, then the load is reduced to zero. A load spectrum is compiled based on the actual service conditions of the precooler, setting the amplitude, waveform, frequency, and phase relationship of the loads in each direction. The formal multi-axis loading test is then initiated, continuously applying multi-axis alternating loads according to the set load spectrum while maintaining extreme temperature field stability. During the test, the control and acquisition unit 12 records the load-displacement curves in real time, monitoring changes in the stiffness of the test specimen.

[0034] Step 5: Failure Detection and Uninstallation Protection The control and acquisition unit 12 calculates the dynamic stiffness of the specimen in real time and monitors the pressure and leakage status. When the dynamic stiffness drops beyond a set threshold, the leakage sensor alarms, or the cryogenic cycle pressure is abnormal, the control and acquisition unit 12 unloads the multi-axis loading actuator 6 to a safe state within a set time, shuts down or reduces the induction heating power, and performs pressure relief or shutdown protection according to the pressure status. The number of fatigue cycles at this time is recorded as the life of the specimen.

[0035] Step Six: Cooling and Disassembly and Result Analysis After the test, the induction heating system was first shut down, while the cryogenic circulation continued to run, allowing the specimen to cool down naturally. Once the temperature of capillary tube 2 dropped below room temperature, the flow rate of the cryogenic medium was gradually reduced, allowing the temperature of the main pipe to slowly rise back to room temperature. After the temperature recovered, the circulation system was shut down, the bolts connecting the split-type main pipe base 1302 and the flange were loosened, and the test main pipe 3 and the failed capillary tube 2 specimen were disassembled. Macroscopic and microscopic analyses were performed on the fracture surface of the brazed joint. Combined with the recorded load-displacement data and the number of fatigue cycles, the fatigue performance of the brazed joint under thermomechanical coupled loads was evaluated. After replacing the test main pipe 3 and capillary tube 2 specimens, the next set of tests could be repeated.

[0036] Example 2 The difference between this embodiment and Embodiment 1 lies in the use of an isolation plug in the isolation structure. One end of the capillary tube 2 is not pre-sealed. After inserting the capillary tube 2 into the mounting hole of the test manifold 3, a metal or ceramic isolation plug is inserted into the inner hole of the capillary tube 2. The isolation plug is interference-fitted to the inner wall of the capillary tube 2 or fixed by high-temperature adhesive bonding. The outer side of the isolation plug is brazed to the mounting hole of the test manifold 3, forming a double-sealed structure. The isolation plug blocks the fluid communication between the inner hole of the capillary tube 2 and the internal cavity of the test manifold 3. When the brazed joint fails, the cryogenic medium first encounters the obstruction of the isolation plug and will not leak outward through the inner hole of the capillary tube 2. Other structures and operating methods in this embodiment are the same as in Embodiment 1.

[0037] Example 3 The difference between this embodiment and Embodiment 1 lies in the use of a non-through mounting hole scheme for the isolation structure. The mounting hole of the test manifold 3 is only machined to a portion of the pipe wall thickness without penetrating into the inner cavity of the manifold. One end of the capillary tube 2 is pre-sealed by laser welding to form a blind end, which is then inserted into the non-through mounting hole and brazed. The blind end of the capillary tube 2 is located at the bottom of the mounting hole, thereby structurally isolating the inner hole of the capillary tube 2 from the inner cavity of the manifold. The non-through mounting hole provides an additional structural isolation layer, preventing the cryogenic medium from directly entering the inner hole of the capillary tube 2 even if the brazed seam fails. Other structures and operating methods in this embodiment are the same as in Embodiment 1.

[0038] It should be noted that other isolation structures that can achieve physical isolation and non-communication between the inner hole of the capillary tube 2 and the internal cavity of the test tube 3 are also applicable to this invention.

[0039] Example 4 The difference between this embodiment and Embodiment 1 lies in the type and temperature range of the cryogenic medium. When simulating a liquid hydrogen precooler, liquid hydrogen is used as the cryogenic medium, and the main pipe temperature can be reduced to -253 degrees Celsius. When conducting material screening or preliminary verification, liquid nitrogen is used as the cryogenic medium, and the main pipe temperature is reduced to -196 degrees Celsius to reduce testing costs and safety risks. The induction heating system raises the temperature of capillary 2 to 550 degrees Celsius, creating an extreme temperature gradient in the brazed joint area. Different cryogenic media correspond to different temperature gradient ranges, simulating the service conditions of different types of precoolers. Other structures and operating methods in this embodiment are the same as in Embodiment 1.

[0040] Understandably, the potting material 5 can be replaced with a high-temperature resistant polymer resin or a ceramic-based potting material 5 to accommodate higher capillary heating temperatures or longer high-temperature holding tests. The loading cylinder 4 can be cylindrical or cup-shaped, depending on the test requirements.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A pre-cooler manifold-capillary joint extreme temperature gradient multi-axial test device characterized by, include: A fixed main pipe (1) is used to fix and install a test main pipe (3) with a capillary tube (2) brazed on it. The test main pipe (3) is connected to the fixed main pipe (1). An isolation structure is provided at the brazed position of the test main pipe (3) and the capillary tube (2) so that the test main pipe (3) and the capillary tube (2) are not connected. The cryogenic medium circulation unit is connected to the fixed main pipe (1) and is used to provide a cryogenic boundary to the interior of the test main pipe (3) through the fixed main pipe (1); Temperature gradient loading unit is used to locally heat the capillary (2) so as to form a temperature gradient at the brazing joint position together with the cryogenic boundary inside the test tube (3); The multi-axis loading unit includes a loading cylinder (4), a potting material (5), and a multi-axis loading actuator (6). The free end of the capillary (2) is fixed inside the loading cylinder (4) by the potting material (5). The loading cylinder (4) is connected to the multi-axis loading actuator (6) and is used to apply a test load to the capillary (2). The test load includes axial tensile and compressive loads, bending loads, or torsional loads around the axis of the capillary (2).

2. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, The cryogenic medium circulation unit includes a cryogenic medium storage container (7), a recovery container (8), a refrigerator (9), and a circulation drive mechanism (10) connected in sequence by pipelines; the fixed main pipe (1) is installed on the pipeline between the cryogenic medium storage container (7) and the recovery container (8), and the cryogenic medium forming the cryogenic boundary includes liquid nitrogen, liquid helium, and liquid hydrogen.

3. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, The two ends of the test manifold (3) are detachably mounted on the fixed manifold (1) via flanges.

4. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, The isolation structure between the test manifold (3) and the capillary tube (2) includes a blind end and an isolation plug provided at the brazing end of the capillary tube (2), or a blind hole and a sealing cavity provided at the brazing position of the test manifold (3).

5. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, The temperature gradient loading unit includes an induction heating coil (11) arranged around the capillary (2) for local heating of the capillary (2).

6. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 5, characterized in that, The induction heating coil (11) is made of hollow copper tube and has a cooling circuit. A circulating cooling medium is introduced to cool the induction heating coil (11).

7. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, It also includes a control acquisition unit (12), which includes a controller. The controller is connected to the pressure sensor and leakage sensor of the cryogenic medium circulation unit, the temperature sensor of the temperature gradient loading unit, and the force sensor, displacement sensor, torque sensor and angular displacement sensor of the multi-axis loading unit, respectively, to control the temperature gradient and multi-axis load loading.

8. The multiaxial test apparatus for extreme temperature gradients of the precooler main pipe-capillary joint according to claim 1, characterized in that, The outer wall of the fixed main pipe (1) is also provided with a heat insulation component (13) to reduce the loss of cold energy.

9. A multiaxial test method for extreme temperature gradients of a precooler manifold-capillary joint, the method being based on the multiaxial test apparatus for extreme temperature gradients of a precooler manifold-capillary joint as described in any one of claims 1 to 8, characterized in that, include: Specimen preparation and potting: Prepare test tube (3) and capillary tube (2) specimens. Set up an isolation structure at the brazing connection position of capillary tube (2) and test tube (3). Braze one end of capillary tube (2) to test tube (3). Insert the free end of capillary tube (2) into loading cylinder (4) and inject potting material (5) to solidify and form potting body; Specimen installation and system connection: Connect the test manifold (3) to the fixed manifold (1), and connect the loading cylinder (4) to the multi-axis loading actuator (6); Extreme temperature field construction: Start the cryogenic medium circulation unit to reduce the temperature of the test manifold (3) to the first preset temperature value, start the temperature gradient loading unit to increase the temperature of the capillary (2) to the second preset temperature value, and form an extreme temperature gradient in the brazing joint area; Multi-axis mechanical loading: Start the multi-axis loading unit, apply the corresponding test load to the capillary (2) according to the set load spectrum, and use the sensing component to record the test data.

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