A stainless steel flange reinforcing structure for a launch vehicle propellant tank and a design method thereof

Abstract

The present application relates to a kind of stainless steel flange reinforcement structure for launch vehicle tank and design method, which comprises: collecting tank whole structure parameter to establish integral finite element model and construct load working condition system;Each working condition simulation and the stress gradient distribution data of flange welding joint area are extracted;Locking stress concentration core area and peak stress position;Set initial parameters of reinforcing plate and establish local refinement finite element model;According to pre-set optimization target and constraint condition, carry out reinforcing plate laying position, profile shape and size parameter linkage simulation iterative optimization, determine optimal reinforcement structure parameter;The optimal parameter is substituted into integral model to carry out full working condition re-simulation and fatigue life simulation verification;Water pressure, static tensile and fatigue test are carried out to processing test piece, and the stress suppression effect is verified by comparing test and simulation results, and it is returned to iteration if it does not meet the standard.The present application can make reinforcement design match tank real stress, avoid stress concentration, meet the requirements of long life and light weight.

Description

Technical Field

[0001] This invention relates to the field of rocket propellant tank technology, and in particular to a stainless steel flange reinforcement structure and design method for launch vehicle propellant tanks. Background Technology

[0002] The rocket propellant tank is the core load-bearing and media storage component of the rocket body structure, and its structural reliability directly determines the success or failure of the rocket flight mission. With the continuous development of large-diameter launch vehicles and stainless steel rocket material systems, rocket propellant tanks, compared to those of traditional small-diameter launch vehicles, need to provide greater load-bearing capacity with lower mass. Among these components, stainless steel flanges serve as the core connection structure for components such as manholes, pipeline interfaces, and pressure testing ports. Therefore, they operate under extremely harsh conditions, subjected to a combination of loads including internal pressure, axial overload, vibration and impact, and alternating low-temperature (approximately -181°C or -163°C).

[0003] Due to the inherent characteristics of flange structures, stainless steel flanges used in launch vehicle propellant tanks exhibit areas of abrupt changes in stiffness and thickness. Furthermore, the welded joints between the flanges and the launch vehicle propellant tank shell are highly susceptible to severe stress concentration. These are the most frequent sites for fatigue cracking and media leakage in the propellant tank structure, and represent a core risk control point in the tank structure design. Therefore, effective reinforcement measures are necessary to strengthen the connection between the launch vehicle propellant tank and the stainless steel flanges.

[0004] However, the existing design of stainless steel flange reinforcement structures for launch vehicle propellant tanks has at least the following technical defects: 1. Experience-based design leads to a disconnect from the overall stress characteristics of the launch vehicle's propellant tank: Existing reinforcement schemes often employ uniform-thickness annular or rectangular reinforcement plates, relying solely on engineering experience to determine reinforcement locations and dimensions without considering overall simulation analysis of the entire launch vehicle propellant tank structure under multi-condition composite loads. This results in a mismatch between the reinforcement structure and the actual stress state of the launch vehicle's propellant tank, commonly exhibiting the contradiction of "insufficient reinforcement leading to stress suppression failure, and excessive reinforcement leading to excessive redundant weight," directly compressing the launch vehicle's payload capacity margin.

[0005] 2. Lack of a systematic multi-parameter optimization system, which easily leads to secondary failures: Existing designs do not conduct linked optimization of the reinforcement plate's placement, outline shape, and size parameters based on the stress gradient distribution characteristics of the flange welded joint, making it impossible to accurately suppress stress concentration. Furthermore, existing reinforcement plates typically use right-angled or straight-edged plates with severe stiffness abrupt changes, which easily induce new secondary stress concentrations at the reinforcement plate edges, thus creating new failure risk points.

[0006] 3. Lack of closed-loop design and insufficient engineering reliability verification: Most existing technologies only complete preliminary verification through local simulation of a single operating condition, without conducting overall simulation of the tank's extreme operating conditions throughout its entire life cycle and fatigue life simulation, nor establishing a complete closed loop of "simulation iteration - experimental verification - scheme solidification". The design results are inconsistent with the measured engineering data, making it difficult to meet the stringent requirements of high reliability, long life, and lightweight launch vehicles.

[0007] 4. Poor versatility of the solution and inability to adapt to iterative optimization needs: The relatively fixed reinforcement structure in the existing technology can only be adapted to a single flange specification and specific working conditions. It is difficult to quickly respond to the design change requirements brought about by the iteration of tank structure or adjustment of load conditions, and its engineering promotion and adaptability are insufficient.

[0008] Therefore, to address the aforementioned technical challenges, there is an urgent need for a stainless steel flange reinforcement structure for launch vehicle propellant tanks and a systematic design method for it. Summary of the Invention

[0009] The purpose of this invention is to provide a stainless steel flange reinforcement structure and design method for launch vehicle propellant tanks, so as to solve at least some of the technical problems existing in the prior art.

[0010] To achieve the above objectives, the present invention provides the following solution: In a first aspect, the present invention provides a design method for a stainless steel flange reinforcement structure for a launch vehicle propellant tank, comprising the following steps: S1. Collect all structural parameters of the launch vehicle propellant tank and establish a finite element model of the overall structure of the launch vehicle propellant tank, and at the same time construct the load condition system of the launch vehicle propellant tank; S2. Perform simulation calculations on the finite element model under various working conditions and extract the simulation results. Based on the simulation results, accurately extract the stress gradient distribution data of the welded joint area between the stainless steel flange and the shell of the launch vehicle tank. S3. Based on the stress gradient distribution data, determine at least one of the following: the core region of stress concentration, the location of peak stress, the stress concentration factor, and the circumferential or axial coverage of the region where stress exceeds the standard. S4. Based on the stress concentration core area, set at least one of the initial laying range, initial outline shape and initial thickness of the reinforcing plate, and establish a finite element model of the stainless steel flange with the reinforcing structure and the shell of the launch vehicle tank. S5. Based on the preset optimization objectives and constraints, conduct multi-parameter linkage simulation iterative optimization including the laying position, outline shape and size of the reinforcing plate, and determine the optimal reinforcement structure parameters of the reinforcing plate. S6. Substitute the optimal reinforcement structure parameters into the finite element model to perform full-condition simulation calculation and fatigue life simulation calculation, and verify whether the design requirements are met. If not, return to step S5 to iterate and optimize again. S7. Fabricate test specimens with reinforcement structures according to the optimal reinforcement structure parameters that meet the design requirements, and conduct at least one of the following tests: hydrostatic test, axial static tensile test, and fatigue alternating load test. S8. Compare the experimental results in S7 with the simulation results, and verify whether the stress suppression effect of the optimal reinforcement structure parameters meets the standard. If it does not meet the standard, return to step S5 to iterate and optimize again.

[0011] According to one embodiment of the present invention, the overall structural parameters include: the cylinder diameter, cylinder wall thickness, and end cap type of the launch vehicle propellant tank; The full structural parameters also include: the installation position, specifications, and welding method of the stainless steel flange, as well as the full range of mechanical properties of the stainless steel material of the launch vehicle propellant tank. The load condition system includes: ground hydrostatic test condition, flight segment internal pressure and axial overload combined condition, takeoff or interstage separation vibration and shock condition, and on-orbit temperature-load coupling condition.

[0012] According to an embodiment of the present invention, the simulation calculation of the finite element model under various working conditions includes: performing full-scene static, dynamic and thermodynamic coupled simulation calculation of the finite element model; The extracted simulation results include: the distribution results of stress field, displacement field and vibration response of the overall structure of the launch vehicle tank under various working conditions.

[0013] According to one embodiment of the present invention, in step S4, when a finite element model of a local part of the shell of the launch vehicle tank is established, the mesh size of its weld area is less than 0.5 mm, so as to accurately restore the real structure of the weld contour, fusion line and weld toe area.

[0014] According to an embodiment of the present invention, in step S5, the preset optimization objective includes: a. The peak stress in the welded joint area is reduced to below the material's yield strength; b. The stress concentration factor decreases by more than or equal to 20%; c. Minimize the added weight of the reinforcement structure; In step S5, the preset constraints include: ① The distance between the inner edge of the reinforcing plate and the fusion line of the weld joint is greater than or equal to twice the weld width; ② The welding process of the reinforcing plate is fully compatible with the original flange welding process; ③ The natural frequency of the reinforced structure should not be lower than that of the original structure to ensure no risk of resonance; ④ The reinforcing plate has no secondary stress concentration at the edge, and the peak stress at the edge is less than or equal to 60% of the yield strength of the base material.

[0015] According to an embodiment of the present invention, in step S5, the linkage simulation iterative optimization of the reinforcing plate laying position, contour shape, and size parameters further includes: Optimization of laying position: Taking the stress concentration core area as the center, the laying position is adjusted in both directions along the circumference and axial direction of the shell of the launch vehicle tank to ensure that the reinforcing plate completely covers all areas with excessive stress and avoids locations where the structural stiffness changes abruptly. Contour shape optimization: Based on the stress gradient distribution data of the welded joint, the contour shape of the reinforcing plate is optimized from the initial rectangular or ring shape to an irregular contour shape that matches the stress gradient, and all edges of the reinforcing plate are provided with rounded corners to eliminate abrupt changes in stiffness. Dimensional parameter optimization: Based on the optimal reinforcement structure parameters, multi-parameter sweep simulations are performed on the axial length, circumferential width, thickness, and edge fillet radius of the reinforcement plate to clarify the influence of each parameter on stress suppression effect and structural weight, and to determine the optimal dimensional combination that balances stress suppression effect and lightweight.

[0016] According to one embodiment of the present invention, in step S7, three or more sets of test pieces with reinforcing structures are processed; wherein the material grade, heat treatment state, welding process and processing accuracy of the test pieces are completely consistent with the products used in the actual launch vehicle propellant tanks.

[0017] According to an embodiment of the present invention, in step S7, conducting the hydrostatic test and the axial static tensile test includes: Strain measurement points are pre-arranged in the core area of ​​the welded joint and the reinforcing plate, and load-strain data are collected synchronously.

[0018] Secondly, the present invention provides a stainless steel flange reinforcement structure for a launch vehicle propellant tank, which is obtained according to the design method described in any one of the above contents; Preferably, the stainless steel flange reinforcement structure for the launch vehicle propellant tank includes: a stainless steel flange disposed on the shell of the launch vehicle propellant tank and a reinforcing plate disposed on the outer wall of the shell of the launch vehicle propellant tank; The reinforcing plate is laid in the stress concentration core area at the welded joint between the stainless steel flange and the launch vehicle tank shell. The outline shape of the reinforcing plate is an irregular outline shape with rounded corners that matches the stress gradient distribution at the welded joint. The distance between the inner edge of the reinforcing plate and the fusion line of the welded joint is 2-5 times the weld width. The thickness of the reinforcing plate is 0.8-1.2 times the wall thickness of the launch vehicle tank shell. The radius of all rounded corners of the reinforcing plate is greater than or equal to twice its thickness.

[0019] According to one embodiment of the present invention, the irregular profile shape of the reinforcing plate includes one of an ellipse, a teardrop shape, or a variable width profile with a gradual transition.

[0020] Thirdly, the present invention provides a launch vehicle propellant tank, which includes the stainless steel flange reinforcement structure described in any one of the second aspects.

[0021] Beneficial effects This invention has at least the following technical effects: 1. By establishing an overall parametric finite element model and constructing a full-scenario load condition system, this invention can overcome the problem in the prior art where empirical design leads to a disconnect between the reinforcement structure and the overall stress characteristics of the launch vehicle's propellant tank, thereby enabling the reinforcement design to accurately match the actual stress state of the launch vehicle's propellant tank.

[0022] 2. This invention optimizes the reinforcing plate's placement, outline shape, and size parameters through iterative optimization and uses a rounded corner transition to solve the problem of secondary stress concentration caused by the lack of a systematic multi-parameter optimization system in the prior art, thus making it less likely to create new failure risk points.

[0023] 3. By performing full-condition simulation, fatigue life simulation and physical test closed-loop verification of the optimized reinforcement structure, this invention can make up for the problems of lack of design closed loop and insufficient engineering reliability verification in the prior art, thereby ensuring that the design results meet the stringent requirements of high reliability, long life and lightweight of launch vehicles.

[0024] 4. By adopting a parametric modeling and simulation-driven design method, this invention can improve the problems of poor universality and inability to adapt to iterative optimization requirements of existing reinforcement schemes. In this way, it can achieve rapid response to design changes in the structure and load conditions of launch vehicle tanks and improve engineering scalability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1This is a cloud map showing the initial stress concentration area distribution of the stainless steel flange welded joint in Embodiment 2 of the present invention. Figure 2 This is a stress distribution cloud map of the reinforced stainless steel flange area in Embodiment 2 of the present invention. Detailed Implementation

[0027] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and to exemplify the principles of the present invention, and are not configured to limit the present invention. In addition, the structural components in the drawings are not necessarily drawn to scale. For example, the dimensions of some structural components or regions in the drawings may be enlarged for other structural components or regions to aid in the understanding of the embodiments of the present invention.

[0028] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of the embodiments of the present invention. In the description of the present invention, it should be noted that, unless otherwise stated, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0029] Furthermore, the terms "comprising," "including," "having," or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure or component that includes a list of elements includes not only those elements but also other structural elements that are not expressly listed or inherent to the structure or component. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the article or apparatus that includes the element.

[0030] Spatial relation terms such as "below," "under," "under," "low," "above," "on," and "high" are used for descriptive convenience to explain the positioning of one element relative to a second element, indicating that these terms are intended to cover different orientations of the device, in addition to those different from those shown in the figure. Furthermore, phrases such as "one element on / below another element" can indicate that two elements are in direct contact, or that there are other elements between the two elements. In addition, terms such as "first" and "second" are also used to describe individual elements, areas, parts, etc., without specifically indicating order or sequence, and should not be considered restrictive. Similar terms are used throughout the description to represent similar elements.

[0031] It will be apparent to those skilled in the art that the present invention can be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention.

[0032] Example 1 In a first aspect, this embodiment provides a design method for a stainless steel flange reinforcement structure for a launch vehicle propellant tank, the design method including at least the following steps: S1. Collect all structural parameters of the launch vehicle propellant tank and establish a finite element model of the overall structure of the launch vehicle propellant tank. At the same time, construct a full-scenario load condition system for the launch vehicle propellant tank to clarify the load amplitude, constraint boundary conditions and design limit thresholds for each condition.

[0033] S2. Perform simulation calculations on the finite element model under various working conditions and extract the simulation results. Based on the simulation results, accurately extract the stress gradient distribution data of the welded joint area between the stainless steel flange and the shell of the launch vehicle tank.

[0034] S3. Based on the stress gradient distribution data, lock (i.e. determine, the same below) at least one of the following: the core area of ​​stress concentration, the location of peak stress, the stress concentration factor, and the circumferential or axial coverage of the area of ​​stress exceeding the standard, preferably all of them, so as to clarify the core target area and optimization benchmark of the reinforcement design.

[0035] S4. Based on the locked stress concentration core area, set at least one of the initial laying range, initial outline shape and initial thickness of the reinforcing plate, preferably all of them, and establish a refined finite element model of the stainless steel flange with the reinforcing structure and the shell of the launch vehicle tank.

[0036] S5. Based on the preset optimization objectives and constraints, conduct multi-parameter linkage simulation iterative optimization including the laying position, outline shape and size of the reinforcing plate, and determine the optimal reinforcement structure parameters of the reinforcing plate.

[0037] In step S5, the optimal reinforcement structure parameters of the reinforcement plate are: the optimal laying position of the reinforcement plate, the irregular contour shape matching the stress gradient, and the optimal combination of size parameters.

[0038] S6. Substitute the optimal reinforcement structure parameters into the finite element model to perform full-condition simulation calculation and fatigue life simulation calculation, and verify whether the design requirements are met. If not, return to step S5 to iterate and optimize again. If all performance indicators meet the design requirements, proceed to the subsequent experimental verification stage.

[0039] In step S6, the verification of whether the design requirements are met includes: verifying whether the stress distribution, displacement response and natural frequency of the reinforced structure under each extreme working condition fully meet the design requirements.

[0040] In step S6, the fatigue life simulation calculation can be based on the full life cycle load spectrum of the launch vehicle tank to calculate the cumulative fatigue damage and fatigue life of the reinforced area and verify whether it meets the design life requirements.

[0041] S7. Fabricate test specimens with reinforcing structures according to the optimal reinforcing structure parameters that meet the design requirements, and conduct at least one of the following tests, preferably all of them: hydrostatic test, axial static tensile test, and fatigue alternating load test.

[0042] In step S7, the fatigue alternating load test can simulate the alternating load throughout the entire life cycle of the launch vehicle's propellant tank and can verify the fatigue resistance of the reinforced structure.

[0043] S8. Compare the experimental results in S7 with the simulation results, and verify whether the stress suppression effect of the optimal reinforcement structure parameters meets the standard. If it does not meet the standard, return to step S5 to iterate and optimize again. If it meets the standard, solidify (i.e. determine, the same below) all parameters of the reinforcement scheme to form a stainless steel flange reinforcement structure that can be applied in engineering.

[0044] In this embodiment, the total structural parameters include at least the following: the cylinder diameter, cylinder wall thickness, and end cap type of the launch vehicle propellant tank.

[0045] The complete structural parameters also include: the installation position, specifications, and welding method of the stainless steel flange, as well as the full range of mechanical properties of the stainless steel material of the launch vehicle propellant tank.

[0046] The load condition system includes: ground hydrostatic test condition, flight segment internal pressure and axial overload combined condition, takeoff or interstage separation vibration and shock condition, and on-orbit temperature-load coupling condition.

[0047] In this embodiment, the simulation calculation of the finite element model under various working conditions includes: performing full-scene static, dynamic and thermodynamic coupled simulation calculations on the finite element model.

[0048] The extracted simulation results include: the distribution results of stress field, displacement field and vibration response of the overall structure of the launch vehicle tank under various working conditions.

[0049] In this embodiment, in step S4, when establishing a local finite element model of the shell of the launch vehicle tank, the mesh size of its weld area is less than 0.5 mm, so as to accurately restore the real structure of the weld contour, fusion line and weld toe area, thereby ensuring the accuracy of simulation calculation.

[0050] In this embodiment, in step S5, the preset optimization objective includes: a. The peak stress in the welded joint area is reduced to below the material's yield strength; b. The stress concentration factor decreases by more than or equal to 20%; c. Minimize the added weight of the reinforcement structure.

[0051] Meanwhile, in step S5, the preset constraints include: ① The distance between the inner edge of the reinforcing plate and the fusion line of the weld joint is greater than or equal to twice the weld width; ② The welding process of the reinforcing plate is fully compatible with the original flange welding process; ③ The natural frequency of the reinforced structure should not be lower than that of the original structure to ensure no risk of resonance; ④ The reinforcing plate has no secondary stress concentration at the edge, and the peak stress at the edge is less than or equal to 60% of the yield strength of the base material.

[0052] In this embodiment, step S5, the linkage simulation iterative optimization of the reinforcing plate laying position, contour shape, and size parameters, further includes: Optimization of installation location: Taking the stress concentration core area as the center, the installation location is adjusted in both directions along the circumference and axial direction of the launch vehicle tank shell to ensure that the reinforcing plate completely covers all areas with excessive stress and avoids locations where the structural stiffness changes abruptly.

[0053] Contour shape optimization: Based on the stress gradient distribution data of the welded joint, the contour shape of the reinforcing plate is optimized from the initial rectangular or ring shape to an irregular contour shape that matches the stress gradient, and all edges of the reinforcing plate are provided with rounded corners to eliminate abrupt changes in stiffness and thus avoid secondary stress concentration.

[0054] Dimensional parameter optimization: Based on the optimal reinforcement structure parameters, multi-parameter sweep simulations are performed on the axial length, circumferential width, thickness, and edge fillet radius of the reinforcement plate to clarify the influence of each parameter on stress suppression effect and structural weight, and to determine the optimal dimensional combination that balances stress suppression effect and lightweight.

[0055] In this embodiment, in step S7, three or more sets of test pieces with reinforcing structures are processed, preferably three sets of test pieces with reinforcing structures. The material grade, heat treatment state, welding process, and processing precision of the test pieces are completely consistent with those used in actual launch vehicle propellant tanks.

[0056] In this embodiment, step S7, conducting the hydrostatic test and the axial static tensile test, includes: Strain measurement points are pre-arranged in the core area of ​​the welded joint and the reinforcing plate, and load-strain data are collected synchronously.

[0057] Secondly, this embodiment provides a stainless steel flange reinforcement structure for a launch vehicle propellant tank, which is obtained according to the design method of the stainless steel flange reinforcement structure for a launch vehicle propellant tank described in any of the above contents.

[0058] Preferably, the stainless steel flange reinforcement structure for the launch vehicle propellant tank includes at least: The stainless steel flanges installed on the launch vehicle propellant tank shell and the reinforcing plates installed on the outer wall of the launch vehicle propellant tank shell, wherein: More preferably, the stainless steel flange is welded to the launch vehicle tank shell, and the reinforcing plate is welded to the outer wall of the launch vehicle tank shell.

[0059] The reinforcing plate is laid in the stress concentration core area at the welded joint between the stainless steel flange and the launch vehicle tank shell. The outline shape of the reinforcing plate is an irregular outline shape with rounded corners that matches the stress gradient distribution at the welded joint.

[0060] The distance between the inner edge of the reinforcing plate and the fusion line of the welded joint is 2 to 5 times the weld width. The thickness of the reinforcing plate is 0.8 to 1.2 times the wall thickness of the launch vehicle tank shell. The radius of all rounded corners of the reinforcing plate is greater than or equal to twice its thickness.

[0061] In this embodiment, the irregular contour shape of the reinforcing plate includes one of the following: ellipse, teardrop shape, or variable width contour with a gradual transition, preferably ellipse.

[0062] Thirdly, this embodiment provides a launch vehicle propellant tank, which includes the stainless steel flange reinforcement structure described in any one of the second aspects.

[0063] It should be understood that all rocket propellant tanks that use the above-mentioned stainless steel flange reinforcement structure should be included within the scope of protection of this invention.

[0064] Example 2 This embodiment provides another design method for a stainless steel flange reinforcement structure for a launch vehicle propellant tank. This design method uses a liquid oxygen tank and stainless steel flange of a certain type of launch vehicle as the design optimization objects, and includes the following steps: Step 1: Local parametric modeling of the storage tank and construction of the load condition system: 1.1 In this embodiment, the diameter of the liquid oxygen storage tank of the launch vehicle is 4500mm, and the wall thickness is 3mm. The stainless steel flanges on the side walls are made of 304 stainless steel and are welded to the outer wall of the liquid oxygen storage tank of the launch vehicle by fillet welding. The initial reinforcing plate is set as a rectangular outline with a thickness of 1.5mm, and is laid around the stainless steel flanges, with a weld width of 2mm.

[0065] 1.2 The full range of mechanical properties of 304 stainless steel were collected: elastic modulus of 180 GPa, Poisson's ratio of 0.3, yield strength of 205 MPa, and tensile strength of 515 MPa. Based on the above geometric parameters and material properties, a local parametric finite element model of the liquid oxygen tank and stainless steel flange area of ​​the launch vehicle was established. The overall mesh size of the liquid oxygen tank cylinder was controlled at 5 mm, and for the critical area of ​​the weld joint, the mesh size of the weld area was refined to 0.5 mm to accurately capture the stress gradient changes near the weld toe and fusion line. The model element type adopted a coupled modeling of shell elements and solid elements, thus balancing computational efficiency and local detail accuracy.

[0066] 1.3 Construct a full-scenario load condition system for this embodiment: Set the ground internal pressure test condition with an internal pressure load of 0.7MPa; set the constraint boundary conditions as symmetrical boundary conditions to simulate the actual load and deformation state of the liquid oxygen storage tank section of the launch vehicle.

[0067] Step 2: Local multi-condition simulation of the storage tank and precise location of stress concentration areas: 2.1. Static simulation calculations under internal pressure conditions were performed on the locally parametric finite element model of the liquid oxygen storage tank and stainless steel flange area of ​​the launch vehicle, and the stress field distribution results of the structure were extracted.

[0068] 2.2 Simulation results show that under the design internal pressure condition, significant stress concentration occurs in the weld toe area of ​​the fusion line at the weld joint between the stainless steel flange and the liquid oxygen tank shell of the launch vehicle. At this point, the basic stress of the launch vehicle tank skin far from the weld area is approximately 530 MPa, while the peak stress in the core stress concentration area reaches as high as 948.9 MPa. This peak stress significantly exceeds the yield strength of 304 stainless steel (205 MPa), and the calculated stress concentration factor is approximately 1.8. This area has been precisely identified as the core target area for reinforcement design.

[0069] Step 3: Multi-parameter linkage simulation and iterative optimization of the reinforcement plate: 3.1 Based on the core target area precisely identified as the reinforcement design area, a locally refined finite element model was established, including the skin of the liquid oxygen tank section of the launch vehicle, the stainless steel flange, and the opening area of ​​the reinforcement plate. The mesh size of the weld area in the model was maintained at a high density of 0.5mm to accurately reproduce the real geometry of the weld contour, fusion line, and weld toe.

[0070] 3.2 Setting optimization objectives and constraints: Optimization objective: Reduce the stress concentration factor in the welded joint area to below 1.5, i.e., reduce the stress concentration factor by no less than 20%. Constraints: The natural frequency of the reinforced structure must not be lower than that of the original structure to ensure there is no risk of resonance.

[0071] 3.3 Conduct iterative simulation optimization of the three-level parameters of the reinforcement plate: "layout location, outline shape, and dimensional parameters": Optimization of installation location and scope: Centered on the core weld toe area of ​​stress concentration identified by simulation, the coverage and relative position of the reinforcing plate are adjusted in both the circumferential and axial directions along the liquid oxygen storage tank cylinder of the launch vehicle to ensure that the reinforcing plate can completely cover all areas with excessive stress and avoid causing new stress concentration at the point of abrupt change in structural stiffness.

[0072] Opening profile optimization: Abandoning the initial rectangular profile, and based on the stress gradient distribution characteristics of the welded joint in the circumferential and axial directions, the inner and outer profiles of the reinforcing plate were customized and optimized. The reinforcing plate profile was optimized into an elliptical irregular profile with rounded corners, with its major axis arranged along the axial direction of the launch vehicle's liquid oxygen tank cylinder and its minor axis arranged along the circumference of the launch vehicle's liquid oxygen tank. Simultaneously, all edges of the reinforcing plate were rounded to completely eliminate the abrupt change in stiffness caused by the geometric abruptness and avoid the generation of secondary stress concentration.

[0073] Dimensional parameter optimization: Through multi-parameter sweep simulation calculations, the influence of the axial length, circumferential width, plate thickness and edge fillet radius of the reinforcing plate on the stress suppression effect and the added weight is comprehensively analyzed, and the optimal combination of dimensional parameters that balances lightweighting and stress suppression effect is finally determined.

[0074] Step 4: Full-condition simulation verification of the optimized reinforcement structure: The optimal reinforcement structure parameters obtained in step three were substituted into the finite element model of the liquid oxygen tank and stainless steel flange of the launch vehicle, and full-condition simulation calculations were performed. Simulation results show that under the same extreme internal pressure conditions, the peak stress in the welded joint area after optimization and reinforcement significantly decreased from 948.9 MPa to 772.6 MPa; the stress concentration factor decreased from 1.8 to 1.45, a reduction of 24%, meeting the preset optimization target. Simultaneously, modal simulation results show that the natural frequencies of the local structure of the tank after adding the reinforcement structure do not change substantially compared to the original structure, and there is no risk of introducing resonance. All performance indicators meet the design requirements.

[0075] Step 5: Closed-loop verification and scheme solidification of the reinforcement structure: 5.1. Based on the optimized reinforcement structure parameters, three sets of identical stainless steel flange-liquid oxygen tank section welding test pieces were fabricated. The material grade, heat treatment state, welding process parameters, and machining accuracy of these test pieces were completely consistent with those used in actual launch vehicle liquid oxygen tanks.

[0076] 5.2 Hydraulic pressure test verification under design load: 24 strain measurement points were arranged in the critical weld toe area of ​​the welded joint and the core stress area of ​​the reinforcing plate, and load-strain data were collected simultaneously. The experimental results show that under the design internal pressure hydraulic load, the relative deviation between the measured strain value of the welded joint area and the finite element simulation calculation result is controlled within 10%, verifying the accuracy of the simulation model. The test specimen remained structurally intact during loading, with significant stress suppression effect, and no form of damage or leakage occurred.

[0077] Reference Figure 1 and Figure 2 Based on the simulation optimization and experimental closed-loop verification results in the above design method, it can be seen that in this embodiment, all the reinforcement structure parameters obtained in the above content can be solidified into a final solution that can be engineered, so as to form an engineerable stainless steel flange reinforcement structure.

[0078] It should be understood that the above-described embodiments or examples of the present invention can be combined with each other and have corresponding technical effects.

[0079] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A design method for a stainless steel flange reinforcement structure for a launch vehicle propellant tank, characterized in that, Includes the following steps: S1. Collect all structural parameters of the launch vehicle propellant tank and establish a finite element model of the overall structure of the launch vehicle propellant tank, and at the same time construct the load condition system of the launch vehicle propellant tank; S2. Perform simulation calculations on the finite element model under various working conditions and extract the simulation results. Based on the simulation results, accurately extract the stress gradient distribution data of the welded joint area between the stainless steel flange and the shell of the launch vehicle tank. S3. Based on the stress gradient distribution data, determine at least one of the following: the core region of stress concentration, the location of peak stress, the stress concentration factor, and the circumferential or axial coverage of the region where stress exceeds the standard. S4. Based on the stress concentration core area, set at least one of the initial laying range, initial outline shape and initial thickness of the reinforcing plate, and establish a finite element model of the stainless steel flange with the reinforcing structure and the shell of the launch vehicle tank. S5. Based on the preset optimization objectives and constraints, conduct multi-parameter linkage simulation iterative optimization including the laying position, outline shape and size of the reinforcing plate, and determine the optimal reinforcement structure parameters of the reinforcing plate. S6. Substitute the optimal reinforcement structure parameters into the finite element model to perform full-condition simulation calculation and fatigue life simulation calculation, and verify whether the design requirements are met. If not, return to step S5 to iterate and optimize again. S7. Fabricate test specimens with reinforcement structures according to the optimal reinforcement structure parameters that meet the design requirements, and conduct at least one of the following tests: hydrostatic test, axial static tensile test, and fatigue alternating load test. S8. Compare the experimental results in S7 with the simulation results, and verify whether the stress suppression effect of the optimal reinforcement structure parameters meets the standard. If it does not meet the standard, return to step S5 to iterate and optimize again.

2. The design method according to claim 1, characterized in that, The overall structural parameters include: the cylinder diameter, cylinder wall thickness, and end cap type of the launch vehicle propellant tank; The full structural parameters also include: the installation position, specifications, and welding method of the stainless steel flange, as well as the full range of mechanical properties of the stainless steel material of the launch vehicle propellant tank. The load condition system includes: ground hydrostatic test condition, flight segment internal pressure and axial overload combined condition, takeoff or interstage separation vibration and shock condition, and on-orbit temperature-load coupling condition.

3. The design method according to claim 1, characterized in that, The simulation calculations of the finite element model under various working conditions include: performing full-scene static, dynamic and thermodynamic coupled simulation calculations of the finite element model; The extracted simulation results include: the distribution results of stress field, displacement field and vibration response of the overall structure of the launch vehicle tank under various working conditions.

4. The design method according to claim 1, characterized in that, In step S4, when establishing a local finite element model of the launch vehicle tank shell, the mesh size of its weld area is less than 0.5 mm to accurately reproduce the real structure of the weld contour, fusion line and weld toe area.

5. The design method according to claim 1, characterized in that, In step S5, the preset optimization objectives include: a. The peak stress in the welded joint area is reduced to below the material's yield strength; b. The stress concentration factor decreases by more than or equal to 20%; c. Minimize the added weight of the reinforcement structure; In step S5, the preset constraints include: ① The distance between the inner edge of the reinforcing plate and the fusion line of the weld joint is greater than or equal to twice the weld width; ② The welding process of the reinforcing plate is fully compatible with the original flange welding process; ③ The natural frequency of the reinforced structure is not lower than that of the original structure; ④ The reinforcing plate has no secondary stress concentration at the edge, and the peak stress at the edge is less than or equal to 60% of the yield strength of the parent material.

6. The design method according to claim 1, characterized in that, In step S5, the linkage simulation iterative optimization of the reinforcing plate laying position, contour shape, and size parameters further includes: Optimization of laying position: Taking the stress concentration core area as the center, the laying position is adjusted in both directions along the circumference and axial direction of the shell of the launch vehicle tank to ensure that the reinforcing plate completely covers all areas with excessive stress and avoids locations where the structural stiffness changes abruptly. Contour shape optimization: Based on the stress gradient distribution data of the welded joint, the contour shape of the reinforcing plate is optimized from the initial rectangular or ring shape to an irregular contour shape that matches the stress gradient, and all edges of the reinforcing plate are provided with rounded corners to eliminate abrupt changes in stiffness. Dimensional parameter optimization: Based on the optimal reinforcement structure parameters, multi-parameter sweep simulations are performed on the axial length, circumferential width, thickness, and edge fillet radius of the reinforcement plate to clarify the influence of each parameter on stress suppression effect and structural weight, and to determine the optimal dimensional combination that balances stress suppression effect and lightweight.

7. The design method according to claim 1, characterized in that, In step S7, three or more sets of test pieces with reinforcing structures are processed; wherein the material grade, heat treatment state, welding process and processing accuracy of the test pieces are consistent with those of the products used in the actual launch vehicle propellant tanks; In step S7, conducting the hydrostatic test and the axial static tensile test includes: Strain measurement points are pre-arranged in the core area of ​​the welded joint and the reinforcing plate, and load-strain data are collected synchronously.

8. A stainless steel flange reinforcement structure for a launch vehicle propellant tank, characterized in that, The design method according to any one of claims 1-7 is obtained; The stainless steel flange reinforcement structure for the launch vehicle propellant tank includes: a stainless steel flange disposed on the shell of the launch vehicle propellant tank and a reinforcing plate disposed on the outer wall of the shell of the launch vehicle propellant tank. The reinforcing plate is laid in the stress concentration core area at the welded joint between the stainless steel flange and the launch vehicle tank shell. The outline shape of the reinforcing plate is an irregular outline shape with rounded corners that matches the stress gradient distribution at the welded joint. The distance between the inner edge of the reinforcing plate and the fusion line of the welded joint is 2-5 times the weld width. The thickness of the reinforcing plate is 0.8-1.2 times the wall thickness of the launch vehicle tank shell. The radius of all rounded corners of the reinforcing plate is greater than or equal to twice its thickness.

9. The stainless steel flange reinforcement structure for a launch vehicle propellant tank according to claim 8, characterized in that, The irregular profile shape of the reinforcing plate includes one of the following: elliptical, teardrop-shaped, or variable width profile with a gradual transition.

10. A launch vehicle propellant tank, characterized in that, Includes the stainless steel flange reinforcement structure as described in claim 8 or 9.

Images