Evaluation and optimization method for connection performance of reusable metal sealing flange

Abstract

The invention relates to an evaluation and optimization method for a metal sealing flange, in particular to an evaluation and optimization method for the connection performance of a reusable metal sealing flange, and solves the technical problem that a finite element analysis model adopted by an existing analysis method for the connection performance of the metal sealing flange is poor in accuracy or the calculation amount of iterative analysis is large. According to the method, four stages of finite element analysis models with different complexity degrees are established, then four stages of numerical simulation analysis are carried out by utilizing the four stages of finite element analysis models, and an optimization iteration sequence of'single pre-tightening cyclic compression-resilience performance-repeated use compression-resilience performance-contact performance-fastener and flange strength / fatigue life 'is formulated. The structure with the connection performance and the repeated service life meeting the design requirements is obtained through step-by-step optimization iteration, the contradiction between the calculation precision and the analysis cost is balanced, and the problem that numerical calculation is difficult due to the scale difference between the sealing ring coating and the flange structure is solved.

Description

Technical Field

[0001] The invention relates to a method for evaluating and optimizing a metal sealing flange, and in particular to a method for evaluating and optimizing the connection performance of a reusable metal sealing flange. Background Art

[0002] The oxygen-rich gas channel of a liquid rocket engine is characterized by high temperature, high pressure and large diameter. Self-tightening metal seal-flange-fasteners (i.e. metal sealing flange) are usually used to achieve detachable connection. The harsh working conditions and long-life and high-reliability service requirements pose extremely high challenges to the optimal design of the metal sealing flange.

[0003] The metal sealing flange uses a high-temperature alloy as the base, and is plated with a soft metal layer such as copper or silver on the surface. The sealing ring is compressed through the flange with the help of fasteners, causing the sealing ring to undergo elastic and plastic deformation to compensate for the deformation and separation of the flange under high temperature and high pressure, and the soft coating on the surface fills the gaps or defects between the compression surfaces of the flange, thereby achieving the purpose of sealing.

[0004] During repeated use, the metal sealing flange is subjected to the cyclic action of assembly load and working load. On the one hand, the sealing ring matrix alloy produces ratchet strain accumulation under the action of asymmetric cyclic plastic strain, causing the sealing ring's resilience to degrade and displacement compensation ability to decrease. On the other hand, the soft metal coating on the surface of the sealing ring is continuously squeezed and accumulated, and wears and thins, causing the contact performance of the sealing ring coating to degrade and the ability to fill the defects in the sealing channel to decrease. These two problems together lead to the main failure mode of metal sealing flanges - sealing leakage. In addition, there are also failure forms such as fatigue failure and insufficient strength of flange and fastener structures during repeated use.

[0005] Therefore, when using the finite element model to analyze the connection performance of metal sealing flanges during the design phase, the following should be considered:

[0006] ① Study the cyclic hardening / softening law and ratchet strain accumulation law of the sealing ring matrix alloy, and use the appropriate cyclic plastic constitutive model to carry out nonlinear finite element analysis to obtain the cyclic compression and rebound response of the sealing ring;

[0007] ② Establish a soft metal coating in the finite element model and introduce the influence of the mechanical properties and thickness of the coating to accurately calculate the contact pressure and contact width of the sealing ring during repeated use;

[0008] ③ Consider other failure modes such as the strength and fatigue life of sealing rings, flanges and fasteners.

[0009] However, there are two sets of contradictions when using finite element analysis:

[0010] ① The two-dimensional axisymmetric model cannot reflect the periodic distribution of the preload along the circumferential direction, and cannot evaluate the strength and fatigue life of the flange and fasteners; while the three-dimensional periodic symmetric model has a large calculation scale and high iterative analysis cost due to the complex structural contact relationship and the scale difference between the sealing ring and the flange;

[0011] ② The coating thickness is usually tens of microns, which is significantly different from the flange structure in scale. It is impossible to simultaneously characterize the sealing ring coating performance and the boundary load properties of the metal sealing flange structure in one model. Summary of the invention

[0012] The purpose of the present invention is to solve the technical problems that the finite element analysis model used in the existing metal sealing flange connection performance analysis method has poor accuracy or large iterative analysis calculation amount, and to provide a method for evaluating and optimizing the connection performance of a reusable metal sealing flange.

[0013] To achieve the above object, the technical solution adopted by the present invention is:

[0014] A method for evaluating and optimizing the connection performance of a reusable metal sealing flange is characterized in that it includes the following steps:

[0015] Step 1, establishing a level I finite element model, wherein the level I finite element model is a two-dimensional axisymmetric cyclic compression-rebound performance analysis model of a sealing ring, wherein the sealing ring is an uncoated sealing ring and is cyclically compressed by a pair of rigid surfaces;

[0016] Step 2: Use the level I finite element model to carry out the single preload cycle compression-rebound characteristic analysis of the sealing ring, evaluate and optimize the single preload cycle compression-rebound performance of the level I finite element model, and obtain the level I optimization model;

[0017] Step 3: Establish a level III finite element model according to the level I optimization model, wherein the level III finite element model is a two-dimensional axisymmetric sealing ring-flange model, wherein the sealing ring is a non-coated sealing ring;

[0018] Step 4: Use the level III finite element model to carry out mechanical performance analysis of the seal-flange joint under repeated use load, evaluate and optimize the repeated use compression-rebound performance, and obtain a level III optimization model;

[0019] Step 5: Establish a level II finite element model based on the level III optimization model, wherein the level II finite element model is a two-dimensional axisymmetric contact performance analysis model of a sealing ring, wherein the sealing ring is a coated sealing ring and is cyclically compressed by a pair of rigid surfaces;

[0020] Step 6: Based on the mechanical properties analysis results of step 4, the contact state of the sealing ring during the Nth repeated use is analyzed using the level II finite element model, and the contact performance is evaluated and optimized to obtain a level II optimization model in which the sealing performance during repeated use and the strength and fatigue life of the sealing ring meet the design requirements; wherein N is the number of repeated use cycles of the metal sealing flange;

[0021] Step 7: Establish a level IV finite element model based on the level II optimization model; the level IV finite element model is a three-dimensional periodic symmetrical sealing ring-flange-fastener model, and the sealing ring is a non-coated sealing ring;

[0022] Step 8. Use the Level IV finite element model to conduct a mechanical performance analysis of the seal-flange-fastener joint, evaluate and optimize the strength and fatigue life of the fasteners and flanges, and obtain a metal seal flange structure whose sealing performance during repeated use, the strength and fatigue life of the sealing ring, the strength and fatigue life of the fasteners, and the strength and fatigue life of the flange all meet the design requirements.

[0023] Furthermore, the step 2 is specifically as follows:

[0024] 2.1. Apply cyclic compression load to the rigid surface in the level I finite element model, compress the sealing ring to the initial design compression amount and then completely unload it, and repeat the cycle in sequence; the initial design compression amount is the compression amount of the sealing ring when the metal sealing flange is started up for a single time;

[0025] 2.2. Draw the axial load-displacement curve of the sealing ring under a single preload cycle and the cumulative plastic strain-preload times curve of the dangerous parts of the sealing ring;

[0026] 2.3. A springback amount-preload times curve is obtained according to the axial load-displacement curve of the sealing ring under a single preload cycle, and then the springback amount of the sealing ring after being loaded-unloaded 2N times by the preload load cycle is obtained according to the springback amount-preload times curve; the preload load is the preload force of the fastener, which is given by the design parameters of the fastener;

[0027] 2.4. According to the cumulative plastic strain-preload times curve of the dangerous part of the sealing ring, the cumulative plastic strain of the sealing ring after being loaded and unloaded 2N times by the preload cycle is determined;

[0028] 2.5. If the springback amount of the sealing ring after 2N cycles of preload loading and unloading is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after 2N cycles of preload loading and unloading is less than the true fracture strain of the sealing ring matrix material / FoS, then the I-level optimization model is obtained and step 3 is executed; otherwise, the initial design compression amount is reduced or the sealing ring structure is optimized, and then return to step 1;

[0029] Among them, FoS is the safety factor;

[0030] The opening amount of the metal sealing flange in the working state refers to the deformation of the sealing lip of the sealing ring relative to the pre-tightened state when the metal sealing flange is in the working state;

[0031] The true fracture strain of the sealing ring base material is a property of the sealing ring base material.

[0032] Furthermore, the step 4 is specifically as follows:

[0033] 4.1. Use the level III finite element model to calculate the axial load-displacement curve and axial contact force-loading history curve of the sealing ring under repeated use conditions, as well as the cumulative plastic strain-loading history curve of the dangerous parts of the sealing ring;

[0034] 4.2. Obtain a rebound amount-repeated use number curve according to the axial load-displacement curve of the sealing ring under repeated use conditions, and then obtain the rebound amount of the sealing ring after repeated use N times according to the rebound amount-repeated use number curve;

[0035] 4.3. The cumulative plastic strain of the sealing ring after repeated use for N times is obtained according to the cumulative plastic strain-loading history curve of the dangerous part of the sealing ring under repeated use conditions;

[0036] 4.4. If the springback amount of the sealing ring after repeated use for N times is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after repeated use for N times is less than the true fracture strain of the sealing ring matrix material / FoS, then a level III optimization model is obtained and step 5 is executed;

[0037] Otherwise, optimize the sealing ring structure and return to step 1; alternatively, increase the preload of the fastener or increase the flange stiffness, and then return to step 3.

[0038] Furthermore, the step 6 is specifically as follows:

[0039] 6.1. According to the sealing ring axial contact force-loading history curve under the repeated use condition obtained in step 4.1, the contact force is applied to the level II finite element model;

[0040] 6.2. Calculate the contact stress mean evolution curve and contact width evolution curve of the sealing ring during the Nth repeated use of the Level II finite element model;

[0041] 6.3. According to the evolution curve of the mean contact stress of the sealing ring during the Nth repeated use, the mean contact stress f of the sealing ring during the N1th startup operation is obtained: N1 and the average contact stress f0 of the sealing ring during the first start-up; where N1 is the number of times the engine is repeatedly started during a single use;

[0042] According to the evolution curve of the contact width of the sealing ring during the Nth repeated use, the contact width d of the sealing ring during the N1th startup operation is obtained. N1 The contact width d0 of the sealing ring during the first startup process;

[0043] 6.4 If f N1 / f0>f1, and d N1 / d0>f2, then a level II optimization model is obtained, and step 7 is executed; when the level II optimization model is repeatedly used, the sealing performance and the strength and fatigue life of the sealing ring all meet the design requirements;

[0044] Otherwise: optimize the sealing ring coating and return to step 5; or, increase the flange stiffness and return to step 3; or, optimize the sealing ring structure and return to step 1;

[0045] Among them, f1 is a coefficient less than 1, reflecting the degree of allowable degradation of contact pressure; f2 is a coefficient less than 1, reflecting the degree of allowable degradation of contact width.

[0046] Furthermore, the step 8 is specifically as follows:

[0047] 8.1. Using the Level IV finite element model, calculate the axial force, stress and strain response of the fasteners and the stress and strain response of the flanges in the preloaded and working states;

[0048] 8.2. According to the stress and strain response of the fastener and the stress and strain response of the flange in the preloaded state and the working state, the cyclic strain amplitude of the fastener and the flange during repeated use is obtained respectively;

[0049] 8.3. Determine whether the strength of the fastener meets the design requirements based on the axial force, stress and strain response of the fastener in the preloaded state and working state, and determine whether the fatigue life of the fastener meets the design requirements based on the cyclic strain amplitude of the fastener during repeated use;

[0050] If the strength and fatigue life of the fastener meet the design requirements, proceed to step 8.4; otherwise, increase the fastener diameter or optimize the flange structure and return to step 3;

[0051] 8.4. Determine whether the strength of the flange meets the design requirements based on the stress and strain response of the flange in the preloaded state and the working state, and determine whether the fatigue life of the flange meets the design requirements based on the cyclic strain amplitude of the flange during repeated use;

[0052] If the strength and fatigue life of the flange meet the design requirements, the evaluation and optimization of the metal sealing flange connection performance are completed, and a metal sealing flange is obtained whose sealing, sealing ring strength and fatigue life, fastener strength, and flange strength and fatigue life all meet the design requirements;

[0053] Otherwise, optimize the flange structure and return to step 3.

[0054] Furthermore, in step 1, the substrate of the uncoated sealing ring in the two-dimensional axisymmetric cyclic compression-rebound performance analysis model of the sealing ring adopts a cyclic plastic constitutive model with a combined hardening model.

[0055] Furthermore, in step 3, the uncoated sealing ring in the two-dimensional axisymmetric sealing ring-flange model adopts a time-dependent ratchet constitutive model based on unified viscoplastic theory, and the flange adopts a linear follow-up cyclic plastic constitutive model.

[0056] Furthermore, in step 5, the substrate and the coating of the coated sealing ring in the two-dimensional axisymmetric contact performance analysis model of the sealing ring both adopt a linear kinematic elastic constitutive model.

[0057] Furthermore, in step 1, the establishment of the level I finite element model is specifically as follows:

[0058] Extract the sealing ring cross section;

[0059] In step 3, the establishment of a level III finite element model based on the level I optimization model is specifically as follows:

[0060] Extract flange section and sealing ring section in level I optimization model;

[0061] In step 5, the level II finite element model is established based on the level III optimization model as follows:

[0062] Extract the seal ring cross section in the Level III optimization model.

[0063] Further, in step 7, the establishment of the level IV finite element model is specifically as follows:

[0064] The sealing ring section in the level II optimization model is extracted, and the flange section in the level III optimization model is extracted at the same time. Then, the sector-shaped area containing a fastener is cut out from the sealing ring section and the flange section respectively.

[0065] Compared with the prior art, the present invention has the following beneficial technical effects:

[0066] The evaluation and optimization method for the connection performance of reusable metal sealing flanges provided by the present invention grades finite element models and repeated mechanical performance evaluations, obtains a structure whose connection performance and repeated service life meet the design requirements through step-by-step optimization iterations, establishes four-level finite element analysis models with different complexities, carries out four-level numerical simulation analysis, and formulates an optimization iteration sequence of "single preload cycle compression-rebound performance → repeated use compression-rebound performance → contact performance → fastener and flange strength / fatigue life", balances the contradiction between calculation accuracy and analysis cost, and overcomes the problem of numerical calculation difficulties caused by the scale difference between the sealing ring plating and the flange structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The figure is a flow chart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0068] The following is a further detailed description of the evaluation and optimization method of the connection performance of the reusable metal sealing flange proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0069] The reuse conditions and the number of operations are determined according to the design requirements of the metal sealing flange. The reuse conditions considered in this embodiment are (pre-tightening→(pressurization→heating→pressure relief→cooling)×N1→disassembly)×N, where N is the number of cycles of reuse and N1 is the number of times the engine is repeatedly started during a single use. The optimization object of this embodiment is a metal seal-flange-fastener structure whose connection performance has met the requirements under a single start-up condition (referring to a single "pre-tightening→(pressurization→heating→pressure relief→cooling)→disassembly" process). After each N use, a new fastener will be replaced and the sealing ring coating will be de-plated and re-plated.

[0070] A method for evaluating and optimizing the performance of reusable metal sealing flange connections, such as Figure 1 As shown, the following steps are included:

[0071] Step 1. Establish a level I finite element model. The level I finite element model is a two-dimensional axisymmetric cyclic compression-rebound performance analysis model of the sealing ring. Specifically: extract the sealing ring cross section, ignore the soft metal coating of the sealing ring, adopt a cyclic plastic constitutive model with a combined hardening model for the sealing ring matrix, and establish a two-dimensional axisymmetric cyclic compression-rebound performance analysis model of the sealing ring cyclically compressed by a pair of rigid surfaces. Among them, the cyclic plastic constitutive model with a combined hardening model can characterize the ratcheting behavior and cyclic softening / hardening behavior of the matrix alloy, so as to accurately describe the cyclic mechanical response of the material and accurately calculate the axial load-displacement curve and ratchet strain-preload times curve under the required cyclic load.

[0072] Step 2: Use the level I finite element model to carry out the single preload cycle compression-rebound characteristics analysis of the sealing ring, evaluate and optimize the single preload cycle compression-rebound performance of the level I finite element model, and obtain the level I optimization model.

[0073] Specifically:

[0074] 2.1. Apply cyclic compression load to the rigid surface in the level I finite element model, compress the sealing ring to the initial design compression amount and then completely unload it, and repeat the cycle. The initial design compression amount is the compression amount of the sealing ring when the metal sealing flange is started up once.

[0075] 2.2. Draw the axial load-displacement curve of the sealing ring under a single preload cycle and the cumulative plastic strain-preload times curve of the dangerous parts of the sealing ring.

[0076] 2.3. The springback amount-preload times curve is obtained based on the axial load-displacement curve of the sealing ring under a single preload cycle, and then the springback amount of the sealing ring after being loaded-unloaded 2N times by the preload load cycle is obtained based on the springback amount-preload times curve. Among them, the preload refers to the preload force of the fastener, which is given by the design parameters of the fastener.

[0077] 2.4. According to the cumulative plastic strain-preload times curve of the dangerous part of the sealing ring, the cumulative plastic strain of the sealing ring after being loaded and unloaded 2N times by the preload cycle is determined.

[0078] 2.5. If the springback amount of the sealing ring after 2N cycles of loading and unloading under the preload is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after 2N cycles of loading and unloading under the preload is less than the true fracture strain of the sealing ring matrix material / FoS, then a level I optimization model is obtained and step 3 is executed; otherwise, the initial design compression amount is reduced or the sealing ring structure is optimized, and then return to step 1.

[0079] Among them, FoS is the safety factor;

[0080] The opening amount of the metal sealing flange in the working state refers to the deformation of the sealing lip of the sealing ring relative to the pre-tightened state when the metal sealing flange is in the working state;

[0081] The true fracture strain of the sealing ring matrix material is a property of the sealing ring matrix material and can be obtained according to specific parameters of the material.

[0082] Step 3: Use the level I optimization model to establish a level III finite element model, which is a two-dimensional axisymmetric sealing ring-flange model. Specifically: extract the sealing ring section and the flange section in the level I optimization model to establish a two-dimensional axisymmetric model, ignore the geometric details such as the flange weight reduction hole and the fastener installation hole, and simulate the preload of the fastener with a pair of equal distributed forces. The flange adopts a linear follow-up cyclic plastic constitutive model. The sealing ring does not consider the soft metal coating, and adopts a time-dependent ratchet constitutive model based on the unified viscoplastic theory.

[0083] Since the flange's response is mainly elastic, only a few stress concentration sites will enter plasticity, and the yield is also very small. Therefore, in order to simplify the model, the flange only needs to use a simple linear follow-up cyclic plastic constitutive model. The analysis of the level III finite element model takes into account the entire service process. For example, the engine will work stably for hundreds of seconds after boosting and heating. The sealing ring will show a certain creep-ratchet interaction effect under the action of high temperature holding load. Therefore, the sealing ring needs to adopt a more complex time-dependent ratchet constitutive model.

[0084] Step 4: Use the level III finite element model to carry out mechanical performance analysis of the seal-flange joint under repeated use conditions, evaluate and optimize the repeated use compression-rebound performance, and obtain the level III optimization model. Specifically:

[0085] 4.1. The axial load-displacement curve and axial contact force-loading history curve of the sealing ring under repeated use conditions, as well as the cumulative plastic strain-loading history curve of the dangerous parts of the sealing ring, are calculated using the level III finite element model.

[0086] 4.2. A springback amount-repeated use number curve is obtained according to the axial load-displacement curve of the sealing ring under repeated use conditions, and then the springback amount of the sealing ring after repeated use N times is obtained according to the springback amount-repeated use number curve.

[0087] 4.3. Based on the cumulative plastic strain-loading history curve of the dangerous parts of the sealing ring under repeated use conditions, the cumulative plastic strain of the sealing ring after repeated use for N times is obtained.

[0088] 4.4. If the springback amount of the sealing ring after repeated use for N times is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after repeated use for N times is less than the true fracture strain of the sealing ring matrix material / FoS, then a level III optimization model is obtained and step 5 is executed;

[0089] Otherwise, optimize the sealing ring structure and return to step 1; alternatively, increase the preload of the fastener or increase the flange stiffness, and then return to step 3.

[0090] Step 5: Use the level III optimization model to establish a level II finite element model. The level II finite element model is a two-dimensional axisymmetric sealing ring model of the sealing ring. Specifically, extract the sealing ring section in the level III optimization model. The sealing ring is a coated sealing ring. The sealing ring is a coated sealing ring and is cyclically compressed by a pair of rigid surfaces. The substrate and coating of the coated sealing ring both adopt linear dynamic elastic constitutive model.

[0091] Taking into account that the level II finite element model mainly focuses on the contact wear mechanical properties of the coating, the sealing ring substrate only focuses on its overall response, that is, the contact force generated at the sealing lip. Therefore, the substrate of the coated sealing ring adopts a simplified linear kinematic elastic constitutive model; and for the coating, it is more necessary to consider the wear caused by radial sliding during the service of the coating and its influence on the contact state of the coating, so the simplified linear kinematic elastic constitutive model is also adopted.

[0092] Step 6: Based on the mechanical properties analysis results of step 4, use the level II finite element model to analyze the contact state of the sealing ring during the Nth repeated use, evaluate and optimize the contact performance, and obtain a level II optimization model. Specifically:

[0093] 6.1. According to the sealing ring axial contact force-loading history curve obtained in step 4.1, apply contact force to the level II finite element model.

[0094] 6.2. Calculate the contact stress mean evolution curve and contact width evolution curve of the Level II finite element model during the Nth repeated use process (referring to the process of “pretightening → (pressurization → heating → pressure relief → cooling) × N1 → disassembly”).

[0095] 6.3. According to the evolution curve of the mean contact stress during the Nth repeated use, the mean contact stress f during the N1th start-up operation is obtained. N1 and the mean contact stress f0 during the first startup process;

[0096] According to the contact width evolution curve during the Nth repeated use, the contact width d during the N1th startup operation is obtained. N1 And the contact width d0 during the first startup operation.

[0097] 6.4 If f N1 / f0>f1, and d N1 / d0>f2, then a level II optimization model is obtained, and step 7 is executed; when the level II optimization model is repeatedly used, the sealing performance and the strength and fatigue life of the sealing ring all meet the design requirements;

[0098] Otherwise: optimize the sealing ring coating and return to step 5; or, increase the flange stiffness and return to step 3; or, optimize the sealing ring structure and return to step 1;

[0099] Among them, f1 is a coefficient less than 1, reflecting the degree of allowable degradation of contact pressure; f2 is a coefficient less than 1, reflecting the degree of allowable degradation of contact width.

[0100] Step 7: Establish a level IV finite element model, which is a three-dimensional periodic symmetrical sealing ring-flange-fastener model, in which the sealing ring is an uncoated sealing ring. Specifically, extract the sealing ring section in the level II optimization model, and extract the flange section in the level III optimization model, and then cut out the sector area containing a fastener in the sealing ring section and the flange section respectively.

[0101] Step 8: Use the IV level finite element model to carry out mechanical performance analysis of the seal-flange-fastener joint, evaluate and optimize the fatigue life of the fasteners and flanges, and obtain a metal seal flange structure whose sealing performance, strength and fatigue life of the seal ring, strength of the fasteners, and strength and fatigue life of the flange all meet the design requirements. Specifically:

[0102] 8.1. Using the Level IV finite element model, calculate the axial force, stress and strain response of the fastener and the stress and strain response of the flange in the preloaded state and working state.

[0103] 8.2. Based on the stress and strain response of the fastener in the preloaded state and the working state and the stress and strain response of the flange, the cyclic strain amplitude of the fastener and the flange during repeated use is obtained respectively.

[0104] 8.3. Determine whether the strength of the fastener meets the design requirements based on the axial force, stress and strain response of the fastener in the preloaded state and working state, and determine whether the fatigue life of the fastener meets the design requirements based on the cyclic strain amplitude of the fastener during repeated use;

[0105] If the strength and fatigue life of the fastener meet the design requirements, proceed to step 8.4; otherwise, increase the fastener diameter or optimize the flange structure and return to step 3.

[0106] 8.4. Determine whether the strength of the flange meets the design requirements based on the stress and strain response of the flange in the preloaded state and the working state, and determine whether the fatigue life of the flange meets the design requirements based on the cyclic strain amplitude of the flange during repeated use;

[0107] If the strength and fatigue life of the flange meet the design requirements, the evaluation and optimization of the metal sealing flange connection performance are completed, and a metal sealing flange is obtained whose sealing, sealing ring strength and fatigue life, fastener strength, and flange strength and fatigue life all meet the design requirements;

[0108] Otherwise, optimize the flange structure and return to step 3.

[0109] It should be noted that, in the above steps, the parameters for optimizing the sealing ring structure, optimizing the sealing ring coating and optimizing the flange structure can be adjusted according to actual conditions as long as the optimization purpose can be achieved.

[0110] In this embodiment, four finite element analysis models with different levels of complexity are first established, and then four levels of numerical simulation analysis are carried out using the four-level finite element analysis models. Among them, the level I finite element model does not consider the coating, and the sealing ring is cyclically compressed by a pair of rigid surfaces; the level II finite element model considers the coating, and the sealing ring is cyclically compressed by a pair of rigid surfaces; the level III finite element model includes an uncoated sealing ring and a flange, and the level IV finite element model includes an uncoated sealing ring, a flange, and fasteners.

[0111] Since the main failure mode of the seal-flange-fastener structure is seal leakage, and the secondary failure mode is insufficient fatigue life and strength, and considering that the seal pressure ratio and contact width need to be guaranteed by a certain residual compression (compression in the pre-tightening state - opening in the working state) or contact stress, an optimized iterative sequence of "single pre-tightening cycle compression-rebound performance → cyclic use compression-rebound performance → contact performance → fatigue life / strength" was formulated, which balanced the contradiction between calculation accuracy and analysis cost and overcame the numerical calculation difficulties caused by the scale difference between the sealing ring coating and the flange structure.

[0112] During the iterative analysis, a two-dimensional axisymmetric model is used to obtain a seal-flange joint structure whose sealing basically meets the design requirements, and then a three-dimensional periodic model is used to analyze the stress and strain response of the seal-flange-fastener joint in detail to evaluate the strength and fatigue life. Since the calculation time of two-dimensional analysis is calculated in minutes and the calculation time of three-dimensional analysis is calculated in hours or days, the use of a two-dimensional axisymmetric model can minimize the number of iterations and improve the optimization efficiency.

Claims

1. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange, characterized in that: The following steps are involved: Step 1, establishing a level I finite element model, wherein the level I finite element model is a two-dimensional axisymmetric cyclic compression-rebound performance analysis model of a sealing ring, wherein the sealing ring is an uncoated sealing ring and is cyclically compressed by a pair of rigid surfaces; Step 2: Use the level I finite element model to carry out the single preload cycle compression-rebound characteristic analysis of the sealing ring, evaluate and optimize the single preload cycle compression-rebound performance of the level I finite element model, and obtain the level I optimization model; Step 3: Establish a level III finite element model according to the level I optimization model, wherein the level III finite element model is a two-dimensional axisymmetric sealing ring-flange model, wherein the sealing ring is a non-coated sealing ring; Step 4: Use the level III finite element model to carry out mechanical performance analysis of the seal-flange joint under repeated use load, evaluate and optimize the repeated use compression-rebound performance, and obtain a level III optimization model; Step 5: Establish a level II finite element model based on the level III optimization model, wherein the level II finite element model is a two-dimensional axisymmetric contact performance analysis model of a sealing ring, wherein the sealing ring is a coated sealing ring and is cyclically compressed by a pair of rigid surfaces; Step 6: Based on the mechanical properties analysis results of step 4, the contact state of the sealing ring during the Nth reuse is analyzed using the level II finite element model, and the contact performance is evaluated and optimized to obtain a level II optimization model; wherein N is the number of reuse cycles of the metal sealing flange; Step 7: Establish a level IV finite element model based on the level II optimization model; the level IV finite element model is a three-dimensional periodic symmetrical sealing ring-flange-fastener model, and the sealing ring is a non-coated sealing ring; Step 8. Use the Level IV finite element model to conduct a mechanical performance analysis of the seal-flange-fastener joint, evaluate and optimize the strength and fatigue life of the fasteners and flanges, and obtain a metal seal flange structure that meets the design requirements when reused.

2. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 1, characterized in that: The step 2 is specifically as follows: 2.

1. Apply cyclic compression load to the rigid surface in the level I finite element model, compress the sealing ring to the initial design compression amount and then completely unload it, and repeat the cycle in sequence; the initial design compression amount is the compression amount of the sealing ring when the metal sealing flange is started up for a single time; 2.

2. Draw the axial load-displacement curve of the sealing ring under a single preload cycle and the cumulative plastic strain-preload times curve of the dangerous parts of the sealing ring; 2.

3. A springback amount-preload times curve is obtained according to the axial load-displacement curve of the sealing ring under a single preload cycle, and then the springback amount of the sealing ring after being loaded-unloaded 2N times by the preload load cycle is obtained according to the springback amount-preload times curve; the preload load is the preload force of the fastener, which is given by the design parameters of the fastener; 2.

4. According to the cumulative plastic strain-preload times curve of the dangerous part of the sealing ring, the cumulative plastic strain of the sealing ring after being loaded and unloaded 2N times by the preload cycle is determined; 2.

5. If the springback amount of the sealing ring after 2N cycles of preload loading and unloading is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after 2N cycles of preload loading and unloading is less than the true fracture strain of the sealing ring matrix material / FoS, then the I-level optimization model is obtained and step 3 is executed; Otherwise, reduce the initial design compression or optimize the sealing ring structure, and then return to step 1; Among them, FoS is the safety factor; The opening amount of the metal sealing flange in the working state refers to the deformation of the sealing lip of the sealing ring relative to the pre-tightened state when the metal sealing flange is in the working state; The true fracture strain of the sealing ring base material is a property of the sealing ring base material and is given by the material parameters.

3. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 2, characterized in that: The step 4 is specifically as follows: 4.

1. Use the level III finite element model to calculate the axial load-displacement curve and axial contact force-loading history curve of the sealing ring under repeated use conditions, as well as the cumulative plastic strain-loading history curve of the dangerous parts of the sealing ring; 4.

2. Obtain a rebound amount-repeated use number curve according to the axial load-displacement curve of the sealing ring under repeated use conditions, and then obtain the rebound amount of the sealing ring after repeated use N times according to the rebound amount-repeated use number curve; 4.

3. The cumulative plastic strain of the sealing ring after repeated use for N times is obtained according to the cumulative plastic strain-loading history curve of the dangerous part of the sealing ring under repeated use conditions; 4.

4. If the springback amount of the sealing ring after repeated use for N times is greater than the opening amount of the metal sealing flange in the working state × FoS, and the cumulative plastic strain of the sealing ring after repeated use for N times is less than the true fracture strain of the sealing ring matrix material / FoS, then a level III optimization model is obtained and step 5 is executed; Otherwise, optimize the sealing ring structure and return to step 1; Alternatively, increase the fastener preload or increase the flange stiffness and return to step 3.

4. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 3, characterized in that: The step 6 is specifically as follows: 6.

1. According to the sealing ring axial contact force-loading history curve under the repeated use condition obtained in step 4.1, the contact force is applied to the level II finite element model; 6.

2. Calculate the contact stress mean evolution curve and contact width evolution curve of the sealing ring during the Nth repeated use of the Level II finite element model; 6.

3. According to the evolution curve of the mean contact stress of the sealing ring during the Nth repeated use, the mean contact stress f of the sealing ring during the N1th startup operation is obtained: N1 and the average contact stress f0 of the sealing ring during the first start-up; where N1 is the number of times the engine is repeatedly started during a single use; According to the evolution curve of the contact width of the sealing ring during the Nth repeated use, the contact width d of the sealing ring during the N1th startup operation is obtained. N1 The contact width d0 of the sealing ring during the first startup process; 6.4 If f N1 / f0>f1, and d N1 / d0>f2, then a level II optimization model is obtained, and step 7 is executed; when the level II optimization model is repeatedly used, the sealing performance and the strength and fatigue life of the sealing ring all meet the design requirements; Otherwise: optimize the sealing ring coating and return to step 5; or, increase the flange stiffness and return to step 3; or, optimize the sealing ring structure and return to step 1; Among them, f1 is a coefficient less than 1, reflecting the degree of allowable degradation of contact pressure; f2 is a coefficient less than 1, reflecting the degree of allowable degradation of contact width.

5. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 4, characterized in that: The step 8 is specifically as follows: 8.

1. Using the Level IV finite element model, calculate the axial force, stress and strain response of the fasteners and the stress and strain response of the flanges in the preloaded and working states; 8.

2. According to the stress and strain response of the fastener and the stress and strain response of the flange in the preloaded state and the working state, the cyclic strain amplitude of the fastener and the flange during repeated use is obtained respectively; 8.

3. Determine whether the strength of the fastener meets the design requirements based on the axial force, stress and strain response of the fastener in the preloaded state and working state, and determine whether the fatigue life of the fastener meets the design requirements based on the cyclic strain amplitude of the fastener during repeated use; If the strength and fatigue life of the fastener meet the design requirements, proceed to step 8.4; Otherwise, increase the fastener diameter or optimize the flange structure and return to step 3; 8.

4. Determine whether the strength of the flange meets the design requirements based on the stress and strain response of the flange in the preloaded state and the working state, and determine whether the fatigue life of the flange meets the design requirements based on the cyclic strain amplitude of the flange during repeated use; If the strength and fatigue life of the flange meet the design requirements, the evaluation and optimization of the metal sealing flange connection performance are completed, and a metal sealing flange is obtained whose sealing, sealing ring strength and fatigue life, fastener strength, and flange strength and fatigue life all meet the design requirements; Otherwise, optimize the flange structure and return to step 3.

6. A method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to any one of claims 1 to 5, characterized in that: In step 1, the substrate of the uncoated sealing ring in the two-dimensional axisymmetric cyclic compression-rebound performance analysis model of the sealing ring adopts a cyclic plastic constitutive model with a combined hardening model.

7. The method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 6, characterized in that: In step 3, the uncoated sealing ring in the two-dimensional axisymmetric sealing ring-flange model adopts a time-dependent ratchet constitutive model based on unified viscoplastic theory, and the flange adopts a linear follow-up cyclic plastic constitutive model.

8. The method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 7, characterized in that: In step 5, the substrate and the coating of the coated sealing ring in the two-dimensional axisymmetric contact performance analysis model of the sealing ring adopt a linear kinematic elastic constitutive model.

9. The method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 8, characterized in that: In step 1, the establishment of the level I finite element model is specifically as follows: Extract the sealing ring cross section; In step 3, the establishment of a level III finite element model based on the level I optimization model is specifically as follows: Extract flange section and sealing ring section in level I optimization model; In step 5, the level II finite element model is established based on the level III optimization model as follows: Extract the seal ring cross section in the Level III optimization model.

10. The method for evaluating and optimizing the connection performance of a reusable metal sealing flange according to claim 9, characterized in that: In step 7, the establishment of the level IV finite element model is specifically as follows: The sealing ring section in the level II optimization model is extracted, and the flange section in the level III optimization model is extracted at the same time. Then, the sector-shaped area containing a fastener is cut out from the sealing ring section and the flange section respectively.

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