Method for evaluating strength-leakage coupling reliability of metal c-type seal structure based on l-m method

Abstract

This invention provides a strength-leakage coupling reliability assessment method for metal C-type sealing structures based on the L-M method, comprising the following steps: establishing a three-dimensional finite element model of the metal C-type sealing structure to obtain the compressive stress value under the target compression ratio; designing a stress relaxation test for the metal C-type sealing structure to obtain sample data of structural strength and calculate the reliability of structural strength; conducting a helium detection test on each sample to obtain the helium leakage rate of each sample over its entire life cycle, and correcting the actual medium leakage rate according to the actual working medium; performing probability distribution hypothesis testing based on the actual medium leakage rate to determine the most suitable distribution type; calculating the leakage reliability based on the distribution type and the actual medium leakage rate; converting the aforementioned data into success-failure data, constructing a structural strength-leakage coupling model, and calculating the system reliability. The method of this invention significantly improves the engineering rationality and credibility of the assessment results.

Description

Technical Field

[0001] This invention relates to the field of sealing structure evaluation, and in particular to a method for evaluating the strength-leakage coupling reliability of metal C-type sealing structures based on the LM method. Background Technology

[0002] Sealed structures are prone to strength degradation and leakage failure under long-term storage and cyclic loading. Traditional reliability assessment methods are mostly based on stress-strength models, which only consider the structural strength as a single factor and fail to fully couple the influence of leakage life. This leads to optimistic assessment results that cannot accurately reflect the reliability level under actual operating conditions. Existing reliability models for metal C-type seal structures are overly conservative in their reliability analysis results because they do not simultaneously consider leakage failure and structural strength failure. Summary of the Invention

[0003] The purpose of this invention is to provide a strength-leakage coupled reliability assessment method for metal C-type sealing structures based on the LM method, in order to solve the technical problems in existing assessment methods, such as ignoring leakage failure, unknown leakage lifetime distribution, difficulty in systematic assessment under limited sample data, lack of correction for real gas leakage rate, and lack of time degradation characteristics in assessment results. This invention aims to achieve high confidence and high engineering applicability reliability assessment of sealing structures under long-term storage and complex operating conditions.

[0004] To achieve the above objectives, this invention provides a strength-leakage coupling reliability assessment method for metal C-type seal structures based on the LM method, comprising the following steps: A three-dimensional finite element model of the metal C-type sealing structure is established. By solving the finite element model, the compressive stress value under the target compression ratio is obtained. A stress relaxation test is designed for the metal C-type sealing structure to obtain sample data of structural strength. Based on the sample data of structural strength and the compressive stress value under the target compression ratio, the reliability of structural strength is calculated. Helium leak tests were performed on each sample to obtain the helium leak rate of each sample over its entire life cycle. The actual medium leak rate was then corrected based on the actual working medium. Probability distribution hypothesis testing was performed based on the actual medium leak rate to determine the most suitable distribution type. The leak reliability was calculated based on the distribution type and the actual medium leak rate. The sample data of structural strength, the helium leakage rate of each sample throughout its entire life cycle, the reliability of structural strength and the reliability of leakage are converted into success-failure data to construct structural strength-leakage coupling and calculate system reliability.

[0005] Preferably, the mean and standard deviation are calculated based on structural strength sample data; Using the compressive stress value at the target compression ratio as the lower limit of performance, a normal distribution model is used to calculate the reliability point estimate. For small sample sizes, the lower confidence limit of reliability at a given confidence level can be obtained by using the classical second-order approximation limit method or the lookup table method.

[0006] Preferably, the actual medium leakage rate is corrected as follows: If the actual working medium is not helium, the helium leakage rate is converted into the leakage rate of the actual working medium using the molecular weight square root ratio correction method and viscosity correction method. Further calculations were performed on the volumetric flow rate, mass flow rate, and equivalent linear velocity of the actual medium under standard conditions. If the actual medium is in a supercritical state, the compressibility factor Z is calculated by introducing the real gas law, and the nonlinear equation is solved by Newton's iteration method to correct the volumetric flow rate. Finally, the leakage rate was obtained, and a cumulative model of leakage amount with storage time t was established.

[0007] Preferably, the upper limit of the allowable leakage rate is used as the performance upper limit u, and the leakage reliability is calculated after determining that the leakage lifetime follows a normal distribution; Based on different leakage reliability levels, leakage reliability at different confidence levels and different storage times is obtained.

[0008] The preferred criteria for converting success or failure data are: ; In the formula, For reliability point estimation, For success / failure data, the number of successful attempts. The total number of success-or-failure data experiments. is the regularized incomplete Beta function, and c is the confidence level.

[0009] Preferably, based on the leakage velocity data of each sample, it is assumed that they follow a normal distribution, an exponential distribution, and a Weibull distribution, respectively, and hypothesis tests are performed for each: The normal distribution is analyzed using the Kolmogorov-Smirnov test. The exponential distribution uses order statistics as a basis. Statistical tests; The Weibull distribution is tested using the W statistic, which is based on the order statistic of the extreme value distribution. Compare the statistics and critical values ​​of each distribution to determine the best-fit distribution type.

[0010] Preferably, the system reliability is calculated for different storage times, specifically as follows: The one-sided tolerance coefficient in the leakage reliability calculation is different under different storage time requirements; the reliability and reliability confidence limit of structural strength and leakage are calculated separately, and the equivalent test number and equivalent success number of the system are calculated by integrating them through the LM method. Finally, the system reliability is calculated according to the required confidence level of the system.

[0011] Therefore, the present invention employs the above-mentioned reliability assessment method for the strength-leakage coupling of metal C-type seal structures based on the LM method, and the technical effects are as follows: The system reliability obtained by the strength-leakage coupling model constructed by the LM method is significantly lower than that of the traditional single strength model, which confirms that ignoring leakage degradation will lead to an overly optimistic reliability prediction.

[0012] The proposed reliability assessment method for the strength-leakage coupling of sealing structures based on the LM method effectively improves the engineering applicability and accuracy of reliability analysis, and provides more comprehensive theoretical support for the design of complex sealing structures. Attached Figure Description

[0013] Figure 1 A photograph of the actual experimental equipment; Figure 2 A photograph of the actual test sample; Figure 3 This is a physical image of the test platform; Figure 4 This is a physical image of the test interface. Detailed Implementation

[0014] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0016] Example 1 The reliability assessment method for the strength-leakage coupling of metal C-type seal structures based on the LM method includes the following steps: Step 1: Obtain strength and reliability data for the metal C-type seal structure 1.1 Establishing a finite element simulation model A three-dimensional finite element model of the metal C-type sealing structure is established, including the end groove of the casing, the rupture disc, and the metal C-type sealing ring. Material mechanical property parameters (such as elastic modulus, Poisson's ratio, and yield strength) are defined, contact pairs are set (inner surface of the jacket and outer surface of the spring, outer surface of the jacket and rupture disc and groove), displacement loading method is adopted, and the compression rate is set (e.g., 20%).

[0017] Solve the finite element model to obtain the compressive stress value of the sealed structure at the target compression rate (e.g., 12.67 MPa), which serves as the lower limit of the design allowable strength of the structure.

[0018] 1.2 Conduct stress relaxation tests Using a stress relaxation testing machine, multiple (e.g., 3) metal C-type sealing structure samples were subjected to the same compression rate, and the actual compressive stress values ​​(e.g., 14.46 MPa, 14.84 MPa, 15.25 MPa) when the target compression displacement was reached were recorded.

[0019] These actual compressive stress values ​​constitute sample data for structural strength.

[0020] 1.3 Calculation of the reliability of structural strength Based on the structural strength sample data, the mean and standard deviation are calculated using the following formulas: (1); (2); In the formula, The intensity sample mean, For the number of intensity samples, For the i-th structural strength sample data, The standard deviation of the intensity sample; Design allowable lower limit (i.e., the compressive stress obtained from finite element simulation) is used as the lower limit of performance, and a normal distribution model is used to calculate the reliability point estimate of the structural strength. : (3); in, It is the standard normal distribution function.

[0021] For small sample sizes, the lower confidence limit of reliability at a given confidence level (e.g., 0.8) can be obtained using the classical second-order approximation limit method or a lookup table method. .

[0022] (4); In the formula, The quantiles of the standard normal distribution f For correction factor, K is the sample size, and K is the statistic. (5); (6); In the formula, This is a point estimate of the mean structural strength for a small sample size. This is a point estimate of the standard deviation of structural strength in the case of a small sample size.

[0023] Function and Principle: This step quantifies the mechanical integrity (strength) of the sealed structure into a probabilistic index, providing basic data for subsequent coupled evaluation. Finite element simulation provides theoretical design values, while stress relaxation tests provide measured values ​​under actual manufacturing and assembly deviations. The combination of the two can reflect the uncertainty of structural strength.

[0024] Step 2: Obtain leakage life reliability data for the metal C-type seal structure 2.1 Conduct helium detection tests The metal tube samples (e.g., 24) with the sealed structure installed are placed into the helium detection test container to build the helium detection platform.

[0025] Measure the helium leakage rate of each sample over its entire lifespan. (Unit: Pa·m) 3 / s).

[0026] 2.2 Correcting the actual medium leakage rate If the actual working medium is not helium (e.g., carbon dioxide), the helium leak rate can be converted to the leak rate of the actual medium (e.g., carbon dioxide) using the molecular weight square root ratio correction method and viscosity correction method: (7); in, The leakage rate of helium gas. Here is the molar mass of helium. For actual working medium The leakage rate, For actual working medium molar mass, The dynamic viscosity of the actual working medium He. for The dynamic viscosity.

[0027] Further calculations were performed on the volumetric flow rate, mass flow rate, and equivalent linear velocity of the actual medium under standard conditions.

[0028] If the actual medium is in a supercritical state (such as carbon dioxide), the real gas law should be introduced to calculate the compressibility factor. Z The volumetric flow rate was corrected by solving the nonlinear equations using Newton's iteration method. (8); In the formula, For the corrected medium volumetric flow rate, The volumetric flow rate of the medium; The leakage rate was finally obtained (unit: g / day), and a cumulative model of leakage amount with storage time t was established: (9); Where d is the diameter of the leak and L is the crack length. This represents the amount of carbon dioxide leakage. This is the corrected carbon dioxide leakage rate. This is the atmospheric pressure under standard conditions, with a value of 101325 Pa.

[0029] 2.3 Hypothesis Testing for Probability Distributions Based on the leakage velocity data of each sample, it is assumed that they follow a normal distribution, an exponential distribution, and a Weibull distribution, respectively, and hypothesis tests are performed for each: The normal distribution is analyzed using the Kolmogorov-Smirnov test. The exponential distribution uses order statistics as a basis. Statistical tests; The Weibull distribution is tested using the W statistic, which is based on the order statistic of the extreme value distribution (approximately following the F distribution).

[0030] By comparing the statistics and critical values ​​of each distribution, the most suitable distribution type is determined. Experimental verification in this application shows that the leakage life of the metal C-type sealing structure follows a normal distribution.

[0031] 2.4 Calculate leakage reliability The performance limit is set at the upper limit of the allowable leakage rate (failure threshold, e.g., 0.0276 g / day). After determining that the leakage lifetime follows a normal distribution, the leakage reliability is calculated. : (10); In the formula, It is the standard normal distribution function. For the mean point estimation of leakage velocity, For the standard deviation point estimation of leakage rate, This represents the performance limit for leakage speed; Function and Principle: This step, for the first time, determines the probability distribution of leakage life through experimental data and hypothesis testing, solving the engineering problem of unknown distribution types. Simultaneously, the introduction of the real gas equation of state significantly improves the accuracy of leakage rate prediction under supercritical conditions. The resulting leakage reliability can quantify the risk of sealing function degradation.

[0032] Step 3: Comprehensive reliability assessment of strength-leakage coupling based on the LM method 3.1 Data Transformation: Non-Success / Failure Data → Success / Failure Data Both structural strength and leakage data are non-success / failure data (following a normal distribution, providing reliability point estimates and confidence lower limits). To facilitate system-level cascade assessment, the LM method is used to transform them into equivalent success / failure data. .

[0033] The basis for the transformation is: (11); For reliability point estimation, For success / failure data, the number of successful attempts. The total number of success-or-failure data experiments. is the regularized incomplete Beta function, and c is the confidence level.

[0034] 3.2 System Reliability Synthesis: Series Model The metal C-type sealing structure is considered as a system composed of "structural strength units" and "sealing leakage units" connected in series. The failure of any unit results in the failure of the entire system.

[0035] Using the equivalent formula for series systems in the LM method, the equivalent success and failure data of the system are calculated. .

[0036] (12); In the formula, For the equivalent system equivalent test sample size, The equivalent number of failures for the equivalent system. Let i be the number of successful units. The test sample size is the number of units 1, 2, ..., p in the series system, where p is the number of units (in this application). p =2).

[0037] 3.3 Calculation System Reliability Perform the above steps for different storage times (e.g., 5 years, 10 years, 15 years) to obtain the system reliability degradation curve over time.

[0038] To compare the advantages and disadvantages of traditional sealing structure reliability assessment methods and the strength-leakage coupled reliability assessment method based on the LM method, structural strength and leakage data of a metal C-type sealing structure were obtained through finite element simulation, stress relaxation test, and helium detection test, respectively. The reliability of both methods was then calculated. The calculation steps are as follows: The reliability of the sealing structure strength is calculated. For a metal C-type sealing structure, the maximum stress of the structure is obtained through finite element simulation. Then, a stress relaxation test is performed on it, and the compressive stress of different samples is substituted into formula (3) to calculate the reliability of the sealing structure strength.

[0039] The reliability of the sealing structure's leakage life was calculated. Helium detection tests were conducted on the metal C-type sealing structure to obtain the leakage amount of each sample over its entire life cycle. First, based on the leakage amount of each sample, a probability distribution hypothesis test was performed on the sealing unit failure, and the probability distribution type of sealing failure was determined according to formulas (20) to (27). Second, the reliability of sealing failure was calculated according to formulas (13) to (19).

[0040] Calculate system reliability. The actual storage time of the samples varies, resulting in different test data, sample mean, and the given confidence level may also differ. Therefore, based on leakage reliability and structural strength reliability, leakage reliability can be obtained under different system confidence levels (e.g., 0.8, 0.9) and different storage times (e.g., 5 years, 10 years, 15 years).

[0041] First, the LM method is used to convert the reliability data of each subsystem into success-failure reliability data using formula (11). Second, the reliability of the system is calculated according to formula (12).

[0042] Following the steps outlined above, the reliability of a metal C-type sealing structure can be evaluated based on limited sample data. Table 1 presents the reliability calculation content, data acquisition methods, and calculation models for different analysis objects.

[0043] Table 1. Reliability calculation content, data acquisition methods, and calculation models for different analysis objects.

[0044] Function and Principle: The core idea of ​​the LM method is based on the fact that the reliability of a series system depends on its weakest link. By unifying unit data with different distribution types and sample sizes into success-failure data, it achieves a confidence assessment of system reliability under limited experimental data. This method does not require the same sample size for each unit, nor does it require consistent data distribution, making it highly applicable in engineering.

[0045] Specific case analysis using the above scheme 1. Stress relaxation test of sealed structure To obtain the compressive stress under actual working conditions, the following methods are used: Figure 1 The testing machine shown is used for stress relaxation tests. The maximum compressive load of this testing equipment is 30 kN, and it is equipped with a 1 kN small-range pressure sensor with a load measurement accuracy of +0.5%. The displacement loading speed is set to 0.1 mm / min, and the test stops when the metal C-ring seal reaches the target compressive displacement.

[0046] Stress relaxation tests were conducted on three metal C-type sealing structures. The pressures at which the compression ratio was reached were 14.46 MPa, 14.84 MPa, and 15.25 MPa, respectively. The design pressure of the sealing structure was 12.67 MPa. The reliability of the structural strength can be calculated according to formulas (13) to (19). The calculation process is as follows.

[0047] The product's performance parameter X follows the mean value. The standard deviation is normal distribution .

[0048] A random sample of n products was taken from a batch, and their performance parameters were measured to be as follows: ,but and The point estimate is: (13); (14); and The interval estimate is: (15); (16); In the formula, γ is the confidence level, γ = 1 - α, and α is the significance level; It is a λ-distribution with n-1 degrees of freedom. The horizontal quantiles can be found in the λ-distribution quantile table. It has n-1 degrees of freedom Distribution Horizontal quantiles can be found Distribution quantile table.

[0049] If the lower limit is allowed l ,but (17); In the formula, It is the standard normal distribution function.

[0050] If the upper limit is u, then (18); If the lower limit is allowed l If the upper limit is u, then (19); First, the mean and standard deviation of the strength of the metal C-type sealing structure are calculated according to formulas (13) and (14). The mean is 14.85 and the standard deviation is 0.395. Second, the allowable lower limit in the reliability assessment can be obtained from the design pressure. According to formula (17), the normal one-sided allowable limit coefficient is calculated to be 5.518. Next, based on the number of test samples and the confidence level, the reliability of the phase change system structural unit is obtained by looking up the table, using linear interpolation, and by calculating formula (19). Finally, the reliability obtained under the condition of a confidence level of 0.80 is 99.48%.

[0051] 2. Helium leak detection test for sealed surfaces To obtain sealing leakage data of the metal C-type sealing structure, a helium detection test was conducted. The leakage rate obtained from the test can be calculated using formula (7) to obtain the leakage velocity of the test sample, and then the sealing leakage reliability of the sealing structure can be calculated.

[0052] The test sample is a metal tube with a sealed structure installed, such as... Figure 2 As shown. The test sample is placed into a sealed helium detection container, completing the setup of the helium detection platform, as follows. Figure 3 As shown, the test interface for the helium detection test is as follows: Figure 4 As shown.

[0053] Based on the sealing reliability test data, the statistics for hypothesis testing of different probability distributions were calculated and are shown in Table 2.

[0054] Normal distribution function for: (20); In the formula, T is the integration variable.

[0055] Common parameters and Unknown, at this time it can be obtained through subsamples Give an unbiased estimator , If we replace it with [something else], then the hypothesis to be tested is actually: ; in, , The mean of the leakage rate samples. This is the leakage speed sample data for the i-th time.

[0056] Its test statistic is .

[0057] Its testing rule is: when At that time, refuse ;when At that time, accept To find the critical value K, we need to know the statistical statistic. The distribution function. This distribution is clearly different from the statistic. The distribution function. According to the testing rules, when the sample is calculated to be... The observed value is greater than the critical value When the normal distribution hypothesis is rejected, the hypothesis is rejected.

[0058] When it is necessary to pass through subsamples To test whether the population distribution follows a one-parameter exponential distribution, while the parameter... When the information is unknown, such as using Maximum likelihood estimation: (twenty one); In the formula, For parameters The maximum likelihood estimate.

[0059] replace Then the hypothesis being tested is actually: (twenty two); Similar to the Kirkpatrick test, its test statistic can be taken as: (twenty three); Let be the extreme value of the deviation of the i-th order statistic.

[0060] In equation (23), , For example The order statistic. To improve the power of the test, the test... The statistic is: (twenty four); To test the statistic, This is the critical value of the test statistic at the significance level.

[0061] And on The result was found The critical value table can be found in Appendix 14 of the "Methods for Reliability Assessment of Weapons and Equipment". Clearly, Large value , The value is also large, at which point the distribution function... The curve and the empirical distribution function If the fit is poor, the null hypothesis should be rejected. Therefore, the test rule is: when... At that time, refuse ;when At that time, accept For a given significance level The critical value can be obtained by referring to Appendix 14 of the "Methods for Reliability Assessment of Weapons and Equipment". When calculated from the sample The observed value is greater than At that time, refuse .

[0062] Assume the product's lifespan distribution is as follows: To test the hypothesis: (25); In the formula, The parameter is unknown.

[0063] To test this hypothesis, n products are randomly selected for life testing, and the testing stops when r products fail. If the failure time is... Then let , , , Then, under the null hypothesis Under the establishment, It is an extreme value distribution The first r order statistics, It is a standard extreme value distribution The first r order statistics, and The value of r1 can be found in the table of values ​​for the best linear unbiased estimate as [r / 2].

[0064] make (26) Pick Then the test statistic W of the Weibull distribution is: (27); Under the original hypothesis Under this condition, the degree of freedom for progressive obedience is... , The F-distribution; its value cannot be too large or too small. Therefore, for a given significance level... The inspection rule is: when or At that time, refuse ; when At that time, accept .

[0065] Table 2. Probability Distribution Hypothesis Test Results

[0066] As shown in Table 1, the statistic of the normal distribution is less than the critical value, satisfying the acceptance condition. Therefore, the probabilistic statistical characteristics of the sealing unit in the phase change system follow a normal distribution. Furthermore, Table 1 also shows that the statistic of the exponential distribution is greater than the critical value, failing to satisfy the acceptance condition. This indicates that exponential distributions are not suitable for characterizing the probabilistic uncertainty of the sealing unit. Although the hypothesis test results of the Weibull distribution satisfy the acceptance condition, the normal distribution is more suitable for assessing the reliability of seal leakage. In conclusion, this paper uses the normal distribution to describe the probabilistic uncertainty of seal leakage.

[0067] Once the probability distribution of seal leakage is determined to be a normal distribution, the reliability of the phase change system under different confidence levels can be calculated according to formulas (13) to (19). The leakage failure threshold of the sealing unit in the phase change system is 0.0276 g / day. The calculation results are shown in Table 3.

[0068] Table 3. Reliability of Sealing Leakage under Normal Distribution

[0069] Finally, the reliability of the traditional sealing structure was calculated according to formulas (1) to (6). The results were compared with the strength-leakage coupling reliability assessment results of the sealing structure based on the LM method under limited experimental data proposed in this paper. The comparison results are shown in Table 4.

[0070] Table 4 Reliability under different methods

[0071] Comparing the data in Table 3, it is evident that reliability assessments based solely on structural strength data yield simplistic and less convincing results. The proposed LM-based reliability assessment method for sealed structures, using limited experimental data, provides a more reasonable assessment result that aligns with actual reliability design levels while also considering the risk of leakage failure to some extent.

[0072] Traditional reliability assessment methods for sealing structures yield a reliability of 0.9948 at a confidence level of 0.8. Using this proposed method, we find that the leakage life of the metal C-type sealing structure follows a normal distribution; at a confidence level of 0.8 and a storage time of 15 years, its reliability is 0.9674. Compared to traditional assessment methods based solely on strength data, this proposed method provides a more reasonable and comprehensive reflection of the sealing structure's reliability under actual operating conditions. Therefore, when assessing the reliability of metal C-type sealing structures, it is necessary to consider the impact of both structural strength failure and leakage failure on seal reliability.

[0073] Therefore, this invention adopts the above-mentioned strength-leakage coupling reliability assessment method for metal C-type sealing structures based on the LM method. By combining strength-leakage coupling modeling, probability distribution hypothesis testing, LM method small sample data fusion, and real gas leakage rate correction, it systematically solves the five core problems in the existing reliability assessment of metal C-type sealing structures, which only consider strength, ignore leakage, have unknown distribution, have limited samples, and lack time effects. This significantly improves the engineering rationality and credibility of the assessment results.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A reliability assessment method for the strength-leakage coupling of metal C-type seal structures based on the LM method, characterized in that, Includes the following steps: A three-dimensional finite element model of the metal C-type sealing structure is established. By solving the finite element model, the compressive stress value under the target compression ratio is obtained. A stress relaxation test is designed for the metal C-type sealing structure to obtain sample data of structural strength. Based on the sample data of structural strength and the compressive stress value under the target compression ratio, the reliability of structural strength is calculated. Each sample is subjected to a helium test to obtain the helium leakage rate of each sample over its entire life cycle, and the actual medium leakage rate is corrected according to the actual working medium. Perform probability distribution hypothesis testing based on the actual medium leakage rate to determine the best-fit distribution type; calculate the leakage reliability based on the distribution type and the actual medium leakage rate. The sample data of structural strength, the helium leakage rate of each sample throughout its entire life cycle, the reliability of structural strength and the reliability of leakage are converted into success-failure data to construct structural strength-leakage coupling and calculate system reliability.

2. The method for strength-leakage coupling reliability assessment of metal C-type seal structures based on the LM method according to claim 1, characterized in that, Calculate the mean and standard deviation based on structural strength sample data; Using the compressive stress value at the target compression ratio as the lower limit of performance, a normal distribution model is used to calculate the reliability point estimate. For small sample sizes, the lower confidence limit of reliability at a given confidence level can be obtained by using the classical second-order approximation limit method or the lookup table method.

3. The method for evaluating the strength-leakage coupling reliability of metal C-type seal structures based on the LM method according to claim 1, characterized in that, The actual media leakage rate is corrected as follows: If the actual working medium is not helium, the helium leakage rate is converted into the leakage rate of the actual working medium using the molecular weight square root ratio correction method and viscosity correction method. Further calculations were performed on the volumetric flow rate, mass flow rate, and equivalent linear velocity of the actual medium under standard conditions. If the actual medium is in a supercritical state, the compressibility factor Z is calculated by introducing the real gas law, and the nonlinear equation is solved by Newton's iteration method to correct the volumetric flow rate. Finally, the leakage rate was obtained, and a cumulative model of leakage amount with storage time t was established.

4. The method for strength-leakage coupling reliability assessment of metal C-type seal structures based on the LM method according to claim 1, characterized in that, Using the upper limit of the allowable leakage rate as the upper limit of performance u, and after determining that the leakage lifetime follows a normal distribution, the leakage reliability is calculated. Based on different leakage reliability levels, leakage reliability at different confidence levels and different storage times is obtained.

5. The method for evaluating the strength-leakage coupling reliability of metal C-type seal structures based on the LM method according to claim 1, characterized in that, The basis for transforming success and failure data is: ； In the formula, For reliability point estimation, For success / failure data, the number of successful attempts. The total number of success-or-failure data experiments. is the regularized incomplete Beta function, and c is the confidence level.

6. The method for evaluating the strength-leakage coupling reliability of metal C-type seal structures based on the LM method according to claim 1, characterized in that, Based on the leakage velocity data of each sample, it is assumed that they follow a normal distribution, an exponential distribution, and a Weibull distribution, respectively, and hypothesis tests are performed for each: The normal distribution is analyzed using the Kolmogorov-Smirnov test. The exponential distribution uses order statistics as a basis. Statistical tests; The Weibull distribution is tested using the W statistic, which is based on the order statistic of the extreme value distribution. Compare the statistics and critical values ​​of each distribution to determine the best-fit distribution type.

7. The method for strength-leakage coupling reliability assessment of metal C-type seal structures based on the LM method according to claim 1, characterized in that, The system reliability is calculated for different storage times, specifically as follows: The one-sided tolerance coefficient in the leakage reliability calculation is different under different storage time requirements; the reliability and reliability confidence limit of structural strength and leakage are calculated separately, and the equivalent test number and equivalent success number of the system are calculated by integrating them through the LM method. Finally, the system reliability is calculated according to the required confidence level of the system.

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