O-shaped ring service life prediction method suitable for extremely low temperature environment

Abstract

The invention relates to the technical field of hydraulic sealing, in particular to an O-shaped ring service life prediction method suitable for an extremely low temperature environment, and the method comprises the steps: carrying out the uniaxial tensile test of an O-shaped ring material in the extremely low temperature environment, and obtaining a stress-strain curve; establishing an O-shaped ring sealing structure model, and simulating and analyzing the mechanical properties of the O-shaped ring at extremely low temperature to obtain the relationship between the maximum contact stress and the compression ratio of the sealing surface of the O-shaped ring; and a dynamic seal friction wear hydraulic test bed is built, and the relation between the quality of the O-shaped ring and time is obtained. And based on a maximum contact stress criterion, coupling simulation and friction wear test results, and obtaining a life prediction result of the O-shaped ring. The method comprehensively considers the influence of temperature, pressure and medium on the O-shaped ring in the extremely low temperature environment, effectively improves the problem that the existing life prediction method cannot accurately reflect the failure mode of the O-shaped ring material under the extremely low temperature condition, and improves the accuracy of life prediction.

Description

Technical Field

[0001] This invention relates to the field of hydraulic sealing technology, specifically to a method for predicting the lifespan of O-rings suitable for extremely low temperature environments. Background Technology

[0002] In extremely low-temperature environments, external hydraulic systems are indispensable key components in research vessels, station machinery, and marine engineering equipment. O-rings, as the most commonly used sealing element in hydraulic systems, are crucial for ensuring the long-term stability of these systems. While O-rings exhibit high elasticity at room temperature, in extremely low temperatures, the elasticity of the O-ring material decreases and its hardness increases. The working pressure of the hydraulic system often causes significant deformation of the O-ring, and excessive deformation can even lead to brittleness of the sealing material, resulting in a loss of elasticity. O-rings in extremely low-temperature environments are more prone to damage and failure than those at room temperature, requiring more frequent replacements. Therefore, accurately predicting the service life of O-rings under extremely low-temperature conditions is an urgent problem to be solved.

[0003] Currently, most O-ring life prediction methods rely on experimental approaches, primarily natural aging and artificially accelerated aging. The core mechanism is the chemical aging of the O-ring material: oxidation, chain segment breakage, and changes in crosslinking density lead to a gradual degradation of the sealing performance. However, for O-rings operating in extremely low-temperature environments, these methods have significant limitations. Under extremely low-temperature conditions, the movement of molecular chain segments in the O-ring material is hindered, and the material approaches or falls below its glass transition temperature, resulting in decreased elasticity. Furthermore, under extremely low-temperature sealing conditions, the increased hardness of the O-ring makes the sealing contact area more prone to stress concentration and micro-slippage. At this point, the primary cause of O-ring failure is no longer the gradual decline in sealing performance due to chemical aging, but rather mechanical damage and wear caused by embrittlement. The main failure mode of O-rings in extremely low-temperature environments is wear failure.

[0004] Therefore, it is necessary to strengthen research on O-ring life prediction under extremely low temperature conditions. Based on understanding the failure mechanism of O-rings under extremely low temperature conditions, exploring new methods for life prediction is of great significance for ensuring the normal operation of external hydraulic platforms. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of inaccurate prediction of O-ring lifespan under extremely low temperature conditions. By combining simulation and friction and wear testing, and considering the combined effects of temperature, pressure, and oil immersion on O-rings under actual operating conditions, this invention provides an O-ring lifespan prediction method suitable for extremely low temperature environments. Compared with existing lifespan prediction methods, this method can more accurately reflect the failure mechanism of O-rings under extremely low temperature conditions, thus providing a more accurate prediction of O-ring lifespan under these conditions.

[0006] This invention provides a method for predicting the lifetime of O-rings in extremely low temperature environments, comprising the following steps:

[0007] S1. A uniaxial tensile test was conducted on the O-ring material under extremely low temperature conditions to obtain the stress-strain curve.

[0008] Furthermore, the specific method of step S1 is as follows:

[0009] S1.1: Prepare tensile specimens. Select specimens of appropriate size and shape according to standard specifications and actual needs, and ensure that the specimen surface is flat and free of defects.

[0010] S1.2: Install the specimen. Install the specimen on the tensile testing machine, ensuring that both ends of the specimen are parallel and perpendicular to the direction of movement of the testing machine.

[0011] S1.3: Perform a uniaxial tensile test. Start the tensile testing machine and gradually increase the tensile force applied to the specimen until the predetermined tensile degree is reached or failure occurs.

[0012] S1.4: Record data, record the stress-strain curve of the specimen in real time during the test.

[0013] S2. Input the stress-strain curve into the fitting software to fit the stress-strain curve and the hyperelastic constitutive model to obtain the hyperelastic constitutive model that best describes the mechanical behavior of the O-ring in an extremely low temperature environment.

[0014] Furthermore, the specific method for step S2 is as follows:

[0015] S2.1: Data import, import the stress-strain curves obtained from uniaxial tensile tests into the fitting software.

[0016] S2.2: Select the hyperelastic constitutive model to be fitted and set the initial parameter range.

[0017] S2.3: Fit the hyperelastic constitutive model to obtain the parameters of each model and generate the fitting curve.

[0018] S2.4: Fitting and screening: Compare the fitting accuracy of different hyperelastic constitutive models and select the most suitable hyperelastic constitutive model to describe the O-ring under extremely low temperature conditions.

[0019] S3. Establish an O-ring sealing structure model in simulation software and simulate the relationship between the maximum contact stress and the compressibility on the O-ring sealing surface.

[0020] Furthermore, the specific method for step S3 is as follows:

[0021] S3.1: Establish a model. Establish a two-dimensional axisymmetric model of the O-ring sealing structure. The model dimensions refer to the actual dimensions of the sealing structure.

[0022] S3.2: Material parameter input. The parameters of the hyperelastic constitutive model selected by stress-strain curve fitting are input into the simulation software as material properties.

[0023] S3.3: Boundary conditions and load settings: In the simulation model, the groove is constrained as a fixed boundary, and the upper flange is only allowed to have radial displacement; the pre-compression process of the O-ring is realized by displacement loading, the contact between the O-ring and the sealing surface is defined and the friction coefficient is set; medium pressure is applied to one side of the O-ring to simulate the single-sided pressure condition.

[0024] S3.4: Run the simulation and output the results. Change the O-ring compression ratio and output the change in the maximum contact stress on the sealing surface. Plot the maximum contact stress-compression ratio curve of the O-ring.

[0025] S4. Set up a hydraulic test bench for O-ring friction and wear, conduct O-ring friction and wear tests, and obtain the relationship between O-ring mass and time.

[0026] Furthermore, the specific method for step S4 is as follows:

[0027] S4.1: Test bench construction. An O-ring friction and wear hydraulic test bench is constructed within a low-temperature test chamber. The test bench consists of a hydraulic pump, an O-ring friction and wear carrier device, related control valve assemblies, and testing equipment.

[0028] S4.2: Specimen installation: Install the O-ring in the sealing groove of the friction and wear carrier device cavity, ensuring that the O-ring is pre-compressed and forms a dynamic sealing contact with the sealing surface.

[0029] S4.3: Under load, the temperature inside the low-temperature test chamber is adjusted to the predetermined temperature and maintained stable for a period of time. Then, the hydraulic pump is started, and the system working pressure is adjusted to the predetermined pressure through the relevant control valve group to maintain system operation. The system pressure and temperature are monitored in real time by the testing equipment.

[0030] S4.4: Record data. Run the test bench continuously under the set working conditions, stop the machine at regular intervals to remove the O-ring specimens, and measure the mass of the O-rings. During this process, consider the swelling effect of the O-rings in the working medium and record the data at the corresponding time points.

[0031] S5. By combining simulation results of the O-ring sealing structure with O-ring friction and wear test results, the relationship between the maximum contact stress of the O-ring and time is obtained. Based on the maximum contact stress criterion, the O-ring life is predicted.

[0032] Furthermore, the specific method for step S5 is as follows:

[0033] S5.1: Fit the maximum contact stress-compression ratio curve of the O-ring sealing surface obtained in step S3, calculate the fitting formula for the curve, and calculate the compression ratio of the O-ring when the maximum contact stress equals the predetermined working pressure using the fitting formula. According to the maximum contact stress criterion, this compression ratio is regarded as the compression ratio when the O-ring fails. Fit the O-ring mass-time curve obtained in step S4, and calculate the fitting formula for the curve.

[0034] S5.2: Calculate the O-ring's failure mass by combining its density at this extremely low temperature with the O-ring's compression ratio when the maximum contact stress equals the predetermined working pressure. Based on the fitted O-ring mass-time formula during the friction and wear test, obtain the time it takes for the O-ring to reach its failure mass. According to the maximum contact stress criterion, this time is considered the O-ring's seal failure life.

[0035] Preferably, the extreme low temperature range is −60°C to −40°C.

[0036] Hyperelastic constitutive models include the Ogden (N=3) model, Mooney-Rivlin model, Polynomial (N=2) model, Yeoh model, or Neo-Hookean model. The hyperelastic constitutive model that best describes the mechanical behavior of O-rings in extremely low temperature environments is selected based on the fitting accuracy.

[0037] Finite element modeling methods include: when performing finite element analysis on O-rings, establishing a two-dimensional axisymmetric model of the O-ring and the upper and lower flanges based on the axisymmetric structure and stress form of the O-ring; or establishing a three-dimensional solid model to reflect the more complex stress and contact conditions of the O-ring sealing structure.

[0038] In light of the dimensional shrinkage phenomenon of O-rings caused by low temperature and high pressure in practical applications, the simulation is modeled with the O-ring cross-sectional dimensional shrinkage of 1%-5% as the standard.

[0039] In step S4, the O-ring friction and wear pressure is 25MPa–35MPa.

[0040] Consider the effect of the swelling effect of the O-ring in the working medium on the measurement quality.

[0041] Based on the maximum contact stress criterion, O-ring seal failure is judged as follows: by using coupled simulation and O-ring friction and wear test results, the relationship between the maximum contact stress and time is obtained, and the time when the calculated maximum contact stress equals the medium pressure is regarded as the life of the O-ring when predicted to fail.

[0042] Beneficial effects:

[0043] This invention provides a method for predicting the lifespan of O-rings in extremely low-temperature environments. By conducting uniaxial tensile tests on O-ring materials under extremely low-temperature conditions and using the fitting results of a hyperelastic constitutive model, the most suitable parametric model for describing the mechanical behavior of O-rings is selected, improving the accuracy of simulation of O-ring sealing structures. Considering the combined effects of temperature, pressure, and oil immersion on O-rings in actual working conditions, scientific failure criteria are selected. O-ring lifespan prediction is performed through a combination of simulation and experimentation, overcoming the limitations of traditional prediction methods that rely solely on single experiments or simulation models and cannot accurately reflect the failure behavior of O-rings under extreme conditions. This improves the accuracy and scientific rigor of O-ring lifespan prediction in extremely low-temperature environments. Attached Figure Description

[0044] Figure 1 This is a flowchart of the method in an embodiment of the present invention;

[0045] Figure 2 The stress-strain curves of the nitrile rubber O-ring material in the examples are fitted to the hyperelastic constitutive model.

[0046] Figure 3 The stress-strain curve of the silicone rubber O-ring material in the embodiment is a graph showing the fitting curve of the hyperelastic constitutive model.

[0047] Figure 4 The stress-strain curve of the ethylene propylene rubber O-ring material in the embodiment is a graph showing the fitting curve of the hyperelastic constitutive model.

[0048] Figure 5 The graph shows the maximum contact stress and compressibility of the O-ring sealing surface in the embodiment.

[0049] Figure 6 This is a schematic diagram illustrating the O-ring friction and wear test principle in the embodiment.

[0050] Figure 7 This is a schematic diagram of the hydraulic cylinder for the O-ring carrier in the O-ring friction and wear test of the embodiment.

[0051] Figure 8 The graph shows the mass and time curves of the O-ring friction and wear test in the example. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this invention clearer, the following description will be provided in conjunction with the appendix. Figure 1-6 The present invention provides a clear and complete description of its technical solutions through specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] like Figure 1 As shown, this embodiment of the invention provides a method for predicting the lifespan of O-rings suitable for extremely low temperature environments. This embodiment selects three O-ring materials: nitrile rubber, silicone rubber, and ethylene propylene rubber. The main steps include:

[0054] S1. A uniaxial tensile test was conducted on the O-ring material under extremely low temperature conditions to obtain the stress-strain curve.

[0055] In this embodiment, the stress-strain curve acquisition process is as follows: Following the requirements of national standards GB / T 528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber" and GB / T 6031-2017 "Determination of Hardness of Vulcanized Rubber or Thermoplastic Rubber," a standard dumbbell-shaped specimen was used for uniaxial tensile testing. The specimen had a total length of 75 mm, a thickness of 2 mm, an initial test length of 20 mm, and a tensile speed of 500 mm / min. An electronic tensile testing machine was used. The uniaxial tensile test was conducted in a low-temperature chamber. The low-temperature chamber was started, and the temperature was adjusted to −54℃. After the temperature stabilized for 30 minutes, the specimen and testing equipment were placed in the low-temperature chamber and allowed to stand for 2 hours.

[0056] Clamp the specimen in the upper and lower fixtures at -54℃, ensuring that both ends of the specimen are parallel and perpendicular to the direction of movement of the testing machine. Record the stress-strain curve of the specimen in real time until the specimen fails. Repeat the test 5 times for each type of specimen to ensure that there are no less than 3 valid curves for each type of specimen.

[0057] S2. Input the stress-strain curve into the fitting software to fit the stress-strain curve and the hyperelastic constitutive model to obtain the hyperelastic constitutive model that best describes the mechanical behavior of the O-ring in an extremely low temperature environment.

[0058] In this embodiment, the fitting process of the hyperelastic constitutive model is as follows: The stress-strain curve data of the three types of specimens are imported into the fitting software. The stress-strain curve data input into the fitting software are the nominal stress and nominal strain. The expression for nominal strain is:

[0059]

[0060] In the formula: For nominal response; The original length of the rubber is in mm; The value represents the elongation of the rubber, in mm.

[0061] The expression for nominal stress is:

[0062]

[0063] In the formula: Nominal stress (MPa); F is load (N); A0 is the original cross-sectional area of ​​the rubber specimen (mm²). 2 H is the width of the rubber specimen, mm; T is the thickness of the rubber specimen, mm.

[0064] The testing machine typically outputs force-displacement curve data, so a preprocessing step is required before importing the data into the fitting software. In this embodiment, the data has already been converted during the real-time recording of stress-strain data, so no further processing is needed before direct import into the fitting software. The hyperelastic constitutive models used for fitting the stress-strain curve of the O-ring material are the Ogden (N=3) model, the Mooney-Rivlin model, the Polynomial (N=2) model, the Yeoh model, and the Neo-Hookean model. The fitting results for the three types of specimens are as follows: Figure 2 , Figure 3 and Figure 4 As shown. The coefficient of determination R is used. 2 The accuracy of the fit is quantified by two statistics: root mean square error (RMSE). For silicone rubber, the R² of the Ogden (N=3) model is... 2 The highest value indicates the lowest RMSE, resulting in higher fitting accuracy; for nitrile rubber and ethylene propylene rubber, the R-value of the Polynomial (N=2) model is [value missing]. 2 The larger the value, the smaller the RMSE, and the higher the fitting accuracy.

[0065] S3. Establish an O-ring sealing structure model in simulation software and simulate the relationship between the maximum contact stress and the compressibility on the O-ring sealing surface.

[0066] In this embodiment, the simulation process of the O-ring sealing structure is as follows: Considering that the O-ring will shrink in size under the combined effects of temperature and pressure in actual working conditions, this embodiment uses a 2% shrinkage of the O-ring size as the standard for modeling. The parameters of the hyperelastic constitutive model with the best fit of the three O-ring materials are input into the simulation software as material properties to simulate the actual mechanical properties of the O-ring at −54℃. In the boundary conditions and load settings, the groove in the two-dimensional axisymmetric model is constrained as a fixed boundary, and the upper flange is only allowed to move radially. The pre-compression process is simulated by the movement of the upper flange to achieve the purpose of controlling the compression ratio of the O-ring. The friction coefficient between the groove and the wall is set to 0.1. The pressure loading method is consistent with the actual working conditions, with unilateral pressure applied to the O-ring, and the applied medium pressure is 31.5 MPa.

[0067] By gradually changing the compression ratio of the O-ring, the change in the maximum contact stress on the O-ring sealing surface is output. The results are as follows: Figure 5As shown, the results indicate that under ambient temperature of -54℃ and high pressure conditions, the maximum contact stress of the O-rings of all three materials increases with increasing compression ratio. The fitting formulas for the maximum contact stress-compression ratio of the O-rings of nitrile rubber, silicone rubber, and ethylene propylene rubber are shown in Equations (3), (4), and (5), respectively.

[0068]

[0069]

[0070]

[0071] S4. Set up a hydraulic test bench for O-ring friction and wear, conduct O-ring friction and wear tests, and obtain the relationship between O-ring mass and time.

[0072] In this embodiment, the O-ring friction and wear test process is as follows: First, a test setup is constructed as follows: Figure 6 The friction and wear test bench shown includes a hydraulic cylinder 3 with an inner diameter of 63 mm and a stroke of 100 mm. The hydraulic cylinder 3 is housed in a low-temperature test chamber capable of maintaining a constant temperature of −54℃. The hydraulic cylinder 3 is connected to an electromagnetic directional valve 4, which is also connected to a hydraulic pump 1 and a throttle valve 5. A branch line is provided on the connecting pipeline between the electromagnetic directional valve 4 and the hydraulic pump 1, and an overflow valve 2 is installed on this branch line. The overflow valve 2, hydraulic pump 1, and throttle valve 5 are all connected to an oil tank. A first pressure gauge 6-1 and a second pressure gauge 6-2 are respectively installed at the throttle valve 5 and the overflow valve 2. During the test, the electromagnetic directional valve 4 switches 3 times per second. Figure 7 As shown, hydraulic cylinder 3 serves as the O-ring carrier, with the O-ring installed in the groove of the moving piston and a cylinder stroke of 100 mm. The experiment makes the following assumptions: the wear of the rubber material is uniform, and the change in the O-ring's diameter due to wear is also uniform.

[0073] All three rubber materials exhibit a certain degree of swelling in the working medium. Since the swelling rate is related to the contact time between the rubber and the working medium, to avoid the swelling affecting the O-ring quality measurement, the tested O-rings were immersed in oil at −54℃ for 6 hours before the test. During the test, other O-rings of the same material were kept in an oil-immersed state as a control group. This indirectly predicts the rubber swelling of the test group and prevents unlimited expansion. If the swelling change rate is less than 1%, the test group data is considered reliable. The initial average mass of nitrile rubber was 5.329 g (variance 1.6 × 10⁻⁶). -7 The average mass of the sample after low-temperature oil immersion at −54℃ for 6 hours was 5.598 g (variance 3.64 × 10⁻⁶). -6 The swelling rate is approximately 5.05%; the initial average mass of the silicone rubber is 4.926 g (variance 5.76 × 10⁻⁶). -7The average mass of the sample after low-temperature oil immersion at −54℃ for 6 hours was 5.311 g (variance 4.12 × 10⁻⁶). -7 The swelling rate is approximately 7.81%; the initial average mass of ethylene propylene rubber is 4.940 g (variance 6.2 × 10⁻⁶). -7 The average mass of the sample after low-temperature oil immersion at −54℃ for 6 hours was 5.367 g (variance 2.44 × 10⁻⁶). -7 The swelling rate is approximately 8.65%.

[0074] The temperature inside the low-temperature test chamber was adjusted to −54℃ and maintained for 30 minutes. The friction and wear test bench with the O-ring installed was placed in the low-temperature test chamber and allowed to stand for 2 hours. Then, the hydraulic pump was started, and the system working pressure was adjusted to 31.5 MPa through the relevant control valve group. The system pressure and temperature were monitored in real time using testing equipment. The test bench was continuously run under the set conditions, and stopped every 6 hours to disassemble the hydraulic cylinder, measure the mass of the O-ring, and record the data at the corresponding time points. The test results are shown in Table 1.

[0075] Table 1. Test Results

[0076]

[0077] The extreme mass change in the nitrile rubber control group was 0.004g, with a swelling rate of less than 1%, indicating reliable data. The extreme mass change in the silicone rubber control group was 0.003g, with a swelling rate of less than 1%, also indicating reliable data. The extreme mass change in the ethylene propylene rubber control group was also 0.003g, with a swelling rate of less than 1%, indicating reliable data. The data shows that silicone rubber had the slowest wear rate, with a wear mass change of only 10.1% relative to its initial mass. Nitrile rubber's wear mass changed by 12.3% relative to its initial mass, and ethylene propylene rubber's wear mass changed by 16.1% relative to its initial mass. Silicone rubber maintains better elasticity and resilience at low temperatures, resulting in a lower wear rate than nitrile rubber and ethylene propylene rubber, thus extending its lifespan. Figure 8 As shown, the wear of the three types of rubber per unit time tends to decrease gradually with the increase of working time.

[0078] The mass-time fitting formulas for the friction and wear tests of nitrile rubber, silicone rubber and ethylene propylene rubber O-rings are shown in Equations (6), (7) and (8), respectively.

[0079]

[0080]

[0081]

[0082] S5. By combining simulation results of the O-ring sealing structure with O-ring friction and wear test results, the relationship between the maximum contact stress of the O-ring and time is obtained. Based on the maximum contact stress criterion, the O-ring life is predicted.

[0083] In this embodiment, the coupling process between the simulation of the O-ring sealing structure and the O-ring friction and wear test results is as follows: According to the maximum contact stress criterion, when the maximum contact stress on the O-ring sealing surface is less than or equal to the medium pressure of 31.5 MPa, the O-ring seal is judged to have failed. Based on the maximum contact stress-compression ratio fitting formula, the compression ratio at which the maximum contact stress of the O-rings of the three materials equals the medium pressure of 31.5 MPa can be calculated, i.e., the compression ratio at which the seal fails. Among them, silicone rubber requires the highest compression ratio at the maximum contact stress equal to the medium pressure, which is 12.67%, ethylene propylene rubber requires the lowest compression ratio, which is 7.31%, and nitrile rubber requires 11.2%. Combining the density of the O-rings of the three materials at −54℃ with the compression ratio of the O-rings at failure, the mass of the O-rings of the three materials at failure can be calculated. The mass of nitrile rubber is 4.756 g, silicone rubber is 4.546 g, and ethylene propylene rubber is 4.283 g. Based on the O-ring mass-time fitting formulas for the three materials, the calculated lifespans under this working condition are 210h for nitrile rubber, 320h for silicone rubber, and 222h for ethylene propylene rubber.

[0084] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for predicting the lifespan of O-rings in extremely low temperature environments, characterized in that, Includes the following steps: S1. Uniaxial tensile test was performed on the O-ring material under extremely low temperature environment to obtain the stress-strain curve; S2. Input the stress-strain curve into the fitting software to fit the stress-strain curve and the hyperelastic constitutive model to obtain the hyperelastic constitutive model that best describes the mechanical behavior of the O-ring in an extremely low temperature environment. S3. Establish an O-ring sealing structure model in simulation software and simulate the relationship between the maximum contact stress and the compressibility on the O-ring sealing surface. S4. Set up a hydraulic test bench for O-ring friction and wear, conduct O-ring friction and wear tests, and obtain the relationship between O-ring mass and time. S5. By combining the simulation results of the O-ring sealing structure with the O-ring friction and wear test results, the relationship between the maximum contact stress of the O-ring and time is obtained; Based on the maximum contact stress criterion, the life of O-rings is predicted.

2. The method for predicting the lifespan of O-rings in extremely low temperature environments according to claim 1, characterized in that, The specific method for step S1 is as follows: S1.1: Prepare tensile specimens. According to standard specifications and actual needs, select specimens of appropriate size and shape to ensure that the specimen surface is flat and free of defects. S1.2: Install the specimen. Install the specimen on the tensile testing machine, ensuring that both ends of the specimen are parallel and perpendicular to the direction of movement of the testing machine. S1.3: Perform a uniaxial tensile test. Start the tensile testing machine and gradually increase the tensile force applied to the specimen until the predetermined tensile degree is reached or failure occurs. S1.4: Record data, record the stress-strain curve of the specimen in real time during the test.

3. The method for predicting the lifespan of O-rings in extremely low temperature environments according to claim 2, characterized in that, The specific method for step S2 is as follows: S2.1: Data import, import the stress-strain curves obtained from uniaxial tensile tests into the fitting software; S2.2: Select the hyperelastic constitutive model to be fitted and set the initial parameter range; S2.3: Fit the hyperelastic constitutive model to obtain the parameters of each model and generate the fitting curve; S2.4: Fitting and screening: Compare the fitting accuracy of different hyperelastic constitutive models and select the most suitable hyperelastic constitutive model to describe the O-ring under extremely low temperature conditions.

4. The method for predicting the lifespan of O-rings in extremely low temperature environments according to claim 3, characterized in that, The specific method for step S3 is as follows: S3.1: Establish a model. Establish a two-dimensional axisymmetric model of the O-ring sealing structure. The model dimensions refer to the actual dimensions of the sealing structure. S3.2: Material parameter input. Input the parameters of the hyperelastic constitutive model selected by stress-strain curve fitting into the simulation software as material properties. S3.3: Boundary conditions and load settings: In the simulation model, the groove is constrained as a fixed boundary, and the upper flange is only allowed to have radial displacement; the pre-compression process of the O-ring is realized by displacement loading, the contact between the O-ring and the sealing surface is defined and the friction coefficient is set; medium pressure is applied to one side of the O-ring to simulate the single-sided pressure condition; S3.4: Run the simulation and output the results. Change the O-ring compression ratio and output the change in the maximum contact stress on the sealing surface; plot the maximum contact stress-compression ratio curve of the O-ring.

5. The method for predicting the lifespan of O-rings in extremely low temperature environments according to claim 4, characterized in that, The specific method for step S4 is as follows: S4.1: Test bench construction: An O-ring friction and wear hydraulic test bench is constructed in a low-temperature test chamber; the test bench consists of a hydraulic pump, an O-ring friction and wear carrier device, related control valve groups, and testing equipment; S4.2: Specimen installation: Install the O-ring in the sealing groove of the friction and wear carrier device cavity, ensuring that the O-ring is pre-compressed and forms a dynamic sealing contact with the sealing surface; S4.3: Loading the test chamber, adjusting the temperature to the predetermined temperature and maintaining it for a period of time, then starting the hydraulic pump and adjusting the system working pressure to the predetermined pressure through the relevant control valve group to maintain system operation; the system pressure and temperature are monitored in real time by the detection equipment. S4.4: Record data. Run the test bench continuously under the set working conditions, stop the machine at regular intervals to remove the O-ring specimens, and measure the mass of the O-rings. During this process, consider the swelling effect of the O-rings in the working medium and record the data at the corresponding time points.

6. The method for predicting the lifespan of O-rings in extremely low temperature environments according to claim 5, characterized in that, The specific method for step S5 is as follows: S5.1: Fit the maximum contact stress-compression ratio curve of the O-ring sealing surface obtained in step S3, calculate the fitting formula of the curve, and calculate the compression ratio of the O-ring when the maximum contact stress is equal to the predetermined working pressure through the fitting formula. According to the maximum contact stress criterion, this compression ratio is regarded as the compression ratio when the O-ring fails; Fit the O-ring mass-time curve obtained in step S4, and calculate the fitting formula of the curve. S5.2: Calculate the mass of the O-ring at failure by combining the density of the O-ring at this extremely low temperature with the compression ratio of the O-ring when the maximum contact stress equals the predetermined working pressure; according to the fitted O-ring mass-time formula during the friction and wear test, obtain the time when the O-ring reaches the failure mass. Based on the maximum contact stress criterion, this time is regarded as the lifespan of the O-ring seal failure.

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