Forward design method of fastening system

Abstract

The invention discloses a forward design method of a fastening system. The fastener and the connected piece are designed and verified as a system, a global optimization algorithm is adopted, the size, weight, layout and stress of the connected piece and the fastener are optimized from the system level, accurate selection, improvement and verification of the fastener are achieved, the system weight is reduced, and the service reliability is improved. According to the method, the problem that design methods of the spaceflight fastening system are lacked can be solved, the whole life cycle of the spaceflight fastening system is covered, the fastener can adapt to the more and more complex service environment of spaceflight equipment, and faults caused by failure of the fastener are reduced.

Description

Technical Field

[0001] The invention relates to a fastening system forward design method and belongs to the technical field of spacecraft structures. Background Art

[0002] Fasteners are mechanical components used in aerospace equipment structures, payloads, engines, electrical, control, pressurization and transportation systems to fasten connections. Aerospace fasteners have high strength and high reliability requirements, and must also adapt to extreme environments such as ultra-high temperature, deep low temperature, strong vibration, and high impact, and have extremely high requirements for product performance and quality stability. The connection performance of fasteners is not only related to the fastener products themselves, but also closely related to the connected structure. Especially for the complex service environment of aerospace equipment, the fasteners and the connected structures are severely coupled. The strength test items of fasteners themselves generally include axial tension, shear, wedge load, etc., which cannot characterize the complex load state of the connection parts of aerospace equipment. In the past, aerospace fasteners mainly adopted the methods of inherited design and empirical design, with low design efficiency, and the design level varies from person to person. A systematic fastening system design method has not yet been formed. There have been many abnormal breakage and loosening of fasteners, which cannot support the high-quality development of aerospace equipment. In order to solve the above problems, it is necessary to establish a forward design method for fastening systems to improve the reliability of aerospace fasteners.

[0003] At present, there are some design methods for fastening systems at home and abroad, but they all have shortcomings.

[0004] The Practical Handbook of Aerospace Fasteners, page 202, proposes a formula for calculating the maximum axial load of a bolt based on equivalent axial pressure:

[0005]

[0006] Where M is the bending moment of the shell segment, R is the center radius of the bolts at the butt joint, and F s is the maximum tensile force that the bolt can withstand during operation, and Z is the number of bolts.

[0007] The residual strength factor of the butt-jointed bolts is:

[0008]

[0009] In the formula, F bL is the minimum tensile breaking load of the bolt, which is given by the corresponding bolt standard; n is the safety factor.

[0010] When η≥1, the tensile strength of the bolt meets the design requirements.

[0011] This method uses safety factors to represent the stiffness, thread structure, friction characteristics and other factors of the shell and bolts. To ensure the load-bearing performance of the bolts, a larger safety factor n needs to be set based on engineering experience, resulting in heavy weight and affecting the carrying capacity. In weight-sensitive parts of the structure, the number and size of fasteners need to be reduced, resulting in abnormal fastener breakage problems in large-scale ground tests of launch vehicles.

[0012] The "Research on Digital Technology of Forward Design of Rocket Body Fastening Connection System" proposed a digital technology for forward design of rocket body fastening connection system. This method is based on fastener database, fastener inventory information, and fastener selection requirements. It converts input information such as "environmental requirements", "load requirements", and "functional requirements" into output information of fastener product standards, and realizes fastener optimization push and report statistics functions. Develop simulation calculation software and use the method in VDI2230 to check bolt strength. The forward design process established by this method lacks steps such as demand analysis, system technical indicator establishment, single machine test, and system test verification.

[0013] 202410118792.6 "Threaded fastener design method and system" relates to the field of mechanical parameter technology, and in particular to a threaded fastener design method and system. A threaded fastener design method includes: obtaining characteristic parameters and dimensional parameters of the threaded fastener; based on the characteristic parameters, selecting a specific area in the first component for grinding to form a solder groove; determining the through hole diameter of the second component based on the dimensional parameters, and opening a solder hole on the second component; determining whether to weld based on the overlap between the solder groove and the solder hole; performing fatigue testing on the welded threaded fasteners; adjusting the area of ​​the specific area based on the test results of the fatigue testing; the main purpose of this invention is limited to the welding design, processing and testing of threaded fasteners to ensure the integrity and firmness of the threaded fasteners.

[0014] 202011596374.6 "Threaded Fastener Design Method and System" discloses a threaded fastener design method and system, which includes: calculating the threaded fastener model, extracting the external load of the connection station through CAE, and preliminarily selecting the model of the threaded fastener through the external load; performing dynamic torque / clamping force and angle destructive experiments on the selected model of threaded fasteners, and testing the surface treatment, part size, processing method, assembly relationship status of the threaded fasteners and the consistency of the installed part status; based on the experimental data, analyzing the yield point torque and fitting torque on the test curve to obtain the installation torque or torque + angle process. It can be seen that the purpose of this method is to obtain the installation torque or torque + angle process, formulate a reasonable installation torque, reduce the risk of loosening, and cannot complete the forward design of the fastening system.

[0015] 202310173057.0《Reliability forward design method for fastening connection system based on multiple competing failure modes》 provides a reliability forward design method for fastening connection system based on multiple competing failure modes, including the following steps: failure mode and mechanism analysis of fastening connection system; reliability model of a single threaded connection under a single failure mode; reliability model of fastening connection system based on multiple competing failure modes; forward design of connection system. It can be seen that this method provides a reliability forward design method for fastening connection system based on multiple competing failure modes, and the object of forward design is the reliability of the fastening connection system.

[0016] 202410001458.2 "Forward design method for fastening connection based on integrated design verification" provides a forward design method for fastening connection based on integrated design verification, including: creating a corresponding three-dimensional simulation model based on the physical structure and material information of the fastener and the connection structure; obtaining an initial connection design scheme that meets the load form and connection requirements between the fastener and the connection structure through calculation; using a three-dimensional simulation model to simulate and analyze multiple initial connection design schemes, and performing cyclic simulation judgment on the initial connection design schemes to screen out connection design schemes that meet reliability requirements; using safety verification conditions constructed according to the safety needs of fasteners to verify the safety of connection design schemes that meet reliability requirements under different connection forms. It can be seen that this method is a simulation verification for a variety of fastening connection schemes.

[0017] 201611269889.9 "A Fastener Design System and Method" proposes a fastener design method, which includes five steps: Step 1, automatically complete the fastener diameter, fastener end distance, fastener operation space and fastener spacing; Step 2, automatically generate fasteners according to the fastener diameter, fastener end distance, fastener operation space and fastener spacing; Step 3, check the fastener diameter, shear strength, and pull-off strength, and generate the verification results; Step 4, check the nail hole extrusion strength of the connector and generate the verification results; Step 5, generate the EBOM table of the fastener according to the verification results generated in Steps 3 and 4. It can be seen that this method can only realize the strength verification of fasteners and the nail hole extrusion strength verification of connectors, and cannot realize the forward design of the fastening system. Summary of the invention

[0018] The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, to provide a forward design method for a fastening system, to achieve accurate design, selection and verification of fasteners, and to reduce the weight of the system.

[0019] The technical solution of the present invention is:

[0020] The present invention discloses a fastening system forward design method, comprising the following steps:

[0021] S1. Conduct aerospace equipment demand analysis;

[0022] S2. Establish technical indicators of the fastening system based on the results of demand analysis;

[0023] S3. Design the fastening system according to the technical indicators;

[0024] S4. Determine the product index of fasteners according to the design results;

[0025] S5, determine whether the fastener meets the requirements, if so, select existing fastener products and go to step S7; otherwise, go to step S6;

[0026] S6. Improve the design of the fastener product to obtain the fastener product;

[0027] S7. Carry out the manufacturing and single-machine test verification of fastener products and obtain the single-machine test verification results;

[0028] S8, judging whether the single machine test verification result meets the requirements, if so, performing the fastening system test verification to obtain the fastening system test verification result; if not, returning to step S6;

[0029] S9, judging whether the fastening system test verification result meets the requirements, if so, performing flight verification to obtain the flight verification result; if not, returning to step S3;

[0030] S10, judging whether the flight verification result meets the requirements, if so, performing equipment confirmation to obtain the equipment confirmation result; if not, returning to step S2;

[0031] S11. If the equipment confirmation result meets the requirements, then end; otherwise, return to step S1.

[0032] Furthermore, in the above method, the aerospace equipment demand analysis is specifically: sorting out the input conditions of the aerospace equipment to obtain the requirements related to the fastening system, including load-bearing capacity, service environment, and lifespan.

[0033] Furthermore, in the above method, the bearing capacity is the load requirement of the connection part, including the loads under lifting, ejection, transonic speed, maximum Qα condition and maximum Q condition, wherein Q is the dynamic pressure during flight and α is the aerodynamic composite angle of attack; the service environment includes factory environment, transportation environment, marine environment, flight mechanics environment and flight thermal environment; the life is the storage life of aerospace equipment.

[0034] Furthermore, in the above method, the technical indicators of the fastening system include structure and size, quality, strength grade, preload force, installation conditions, mechanical environment, thermal environment, natural environment and propellant medium environment.

[0035] Furthermore, in the above method, the structure and size are the structural form and size requirements of the fastener and the connected parts; the mass is the total weight of all parts in the fastening system, including the weight of the connected parts and the fasteners; the strength grade is the required value of the tensile load or shear load of the fastener; the preload is the required value of the installation preload of the fastener; the installation condition is the number of times the fastener is installed and disassembled; the mechanical environment includes vibration, impact and acceleration; the thermal environment includes high temperature environment and low temperature environment; the natural environment includes high temperature, low temperature, humidity, mold and salt spray; the propellant medium environment includes unsymmetrical dimethyl hydrazine, nitrogen tetroxide, liquid hydrogen, liquid oxygen, kerosene and methane environment.

[0036] Furthermore, in the above method, the fastening system design is performed by:

[0037] Determine the material category and strength grade of fasteners based on mass and thermal environment;

[0038] The finite element method is used to optimize the design of fasteners. The mathematical model for the optimization design of the fastening system is:

[0039]

[0040] Among them, T α is the lower limit constraint value of the structural size, T β is the upper limit constraint value of the structure size, F δ is the upper limit constraint value of stress of the part at service temperature, m i is the mass of the ith part, W α is the lower limit constraint value of the fastener preload, W β is the upper limit constraint value of the fastener preload.

[0041] Furthermore, in the above method, the manufacturing of the fastener product includes: process simulation, cutting, upsetting, thread rolling, heat treatment and surface treatment; the single-machine test verification of the fastener includes tensile test, shear test, vibration test, salt spray test, mold test, humidity test and stress corrosion test.

[0042] Furthermore, in the above method, the fastening system test verification includes static test, separation test, modal test and environmental test.

[0043] Furthermore, in the above method, the flight test verification includes a one-time flight or repeated flight after returning.

[0044] The beneficial effects of the present invention and the prior art are:

[0045] (1) The present invention can solve the problem of lack of design methods for aerospace fastening systems, cover the entire life cycle of aerospace fastening systems, enable fasteners to adapt to the increasingly complex service environment of aerospace equipment, significantly reduce failures caused by fastener failure, and support the high-quality development of aerospace equipment.

[0046] (2) The present invention designs and verifies fasteners and connected parts as a system, and adopts a global optimization algorithm to optimize the size, weight, layout, and force of connected parts and fasteners from a system level, thereby achieving accurate selection, improvement, and verification of fasteners, reducing system weight, and improving service reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the forward design process of the fastening system of the present invention;

[0048] Figure 2 It is a schematic diagram of the segment axial connection and fastening system of the present invention;

[0049] Figure 3 It is a partial enlarged view of the segment axial connection and fastening system of the present invention;

[0050] Figure 4 This is a dimension diagram to be optimized for the segment axial connection and fastening system of the present invention;

[0051] Figure 5 It is a schematic diagram of a dumbbell-shaped finite element model of a fastener of the present invention;

[0052] Figure 6 It is a schematic diagram of a fastener including a thread refinement finite element model of the present invention;

[0053] In the figure, 1. upper shell section, 2. lower shell section, 3. bolt, 4. nut, 5. simplified bolt model, 6. simplified nut model, 7. modified polished rod, 8. thread. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0055] like Figure 1 As shown, the present invention provides a fastening system forward design method, comprising the following steps:

[0056] Step 1: Conduct aerospace equipment demand analysis;

[0057] Sort out the input conditions of aerospace equipment and obtain the requirements related to the fastening system, including load-bearing capacity, service environment, and lifespan.

[0058] Among them, the carrying capacity is the load requirement of the connection part, including lifting, ejection, transonic speed, maximum Qα condition, and load under maximum Q condition, where Q is the dynamic pressure during flight and α is the aerodynamic composite angle of attack; the service environment includes factory environment, transportation environment, marine environment, flight mechanics environment, flight thermal environment, etc.; the life is the storage period of aerospace equipment.

[0059] Step 2: Establish technical indicators of fastening system;

[0060] The technical indicators of the fastening system include structure and size, quality, strength grade, preload, installation conditions, mechanical environment, thermal environment, natural environment, and propellant medium environment. Among them, structure and size refer to the structural form and size requirements; quality refers to the total weight of all parts of the fastening system, including the weight of the connected parts and fasteners; strength grade refers to the required value of the tensile load or shear load of the bolts; preload refers to the required value of the installation preload of the bolts, and preload is only required when sealing and installing key equipment; installation conditions refer to the number of times the fasteners are installed and disassembled; mechanical environment includes vibration, impact, acceleration, etc.; thermal environment includes high temperature environment and low temperature environment; natural environment includes high temperature, low temperature, humidity, mold, and salt spray; propellant medium environment includes unsymmetrical dimethyl hydrazine, nitrogen tetroxide, liquid hydrogen, liquid oxygen, kerosene, methane and other environments.

[0061] Step 3: Design the fastening system;

[0062] Includes material category, strength grade, layout and lightweight design of fasteners.

[0063] 1) Based on the shell material, lightweight requirements, and thermal environment requirements, preliminarily determine the material category and strength grade of the fasteners. Titanium alloy or aluminum alloy fasteners are used for parts with high lightweight requirements, and high-temperature alloy fasteners or composite material fasteners are used when the temperature environment is higher than 300°C;

[0064] 2) The finite element method is used to design and optimize the fastener layout. The optimized design variables include the size of the connected parts and the fasteners T = {t1, t2, ..., t n}, mass M = {m1,m2,…,m y}, stress F={f1,f2,……,f z}, the number of fasteners N, the size of the fasteners d, and the preload force W of the fasteners (as required).

[0065] Taking the quality of the fastening system as the objective function and the size, stress, and preload (as required) as the constraints, the mathematical model for fastening system optimization is:

[0066]

[0067] Among them, T αis the lower limit constraint value of the structural size, T β is the upper limit constraint value of the structure size, F δ is the upper limit constraint value of stress of the part at service temperature, m i is the mass of the ith part, W α is the lower limit constraint value of the fastener preload, W β is the upper limit constraint value of the fastener preload. The efficient global optimization (EGO) algorithm based on the Kriging model is used to calculate the design variables with the minimum mass of the fastening system.

[0068] Through the above fastening system design, the product indicators of the fasteners are determined, including material category, size and strength indicators.

[0069] Step 4: Analyze whether the existing fasteners meet the requirements. If they do, select the existing fastener products; if they do not, improve the design of the fastener products;

[0070] 1) Determine the fastener material based on the fastener performance characteristics, manufacturing process and use requirements;

[0071] 2) For the fastener with the highest stress in step 3, perform detailed finite element modeling including threads, apply preload to the bolts and nuts, check the strength of the bolts, and confirm whether the specifications, dimensions and strength meet the requirements.

[0072] 3) Design the coating of fasteners according to the natural environment such as high temperature, low temperature, humidity, mold, salt spray, etc., the propellant medium environment such as unsymmetrical dimethyl hydrazine, nitrogen tetroxide, liquid hydrogen, liquid oxygen, kerosene, methane, and the number of repeated disassembly and assembly. Among them, all fasteners are equipped with anti-corrosion coatings, such as chemical passivation for stainless steel and high-temperature alloy fasteners, sulfuric acid anodizing for aluminum alloy fasteners, and pulse anodizing for titanium alloy fasteners. Fasteners used in propellant media are not coated with lubricating coatings to avoid contaminating the propellant; the lubricating layer uses lubricating materials such as molybdenum disulfide, hexadecanol, and silver plating.

[0073] 4) Based on the above design results, analyze whether the existing fasteners meet the requirements. If they do, select existing fastener products and proceed to step five. If they do not meet the requirements, improve the design of fastener products for the unsatisfactory items and then proceed to step five.

[0074] Step 5: Carry out fastener manufacturing and single machine test verification;

[0075] If the existing fasteners meet the requirements, the product manufacturing will be carried out directly; if they do not meet the requirements, process research and product manufacturing will be carried out, including process simulation, cutting, upsetting, thread rolling, heat treatment, and surface treatment. Among them, the bolt head is upsetting, the fillet under the head is rolled to strengthen, and the thread is rolled after heat treatment.

[0076] Carry out single-machine test verification of fasteners, including tensile test, shear test, vibration test, salt spray test, mold test, humidity test, stress corrosion test, etc.

[0077] After the fastener is tested and verified, determine whether it meets the requirements. If it does, proceed to step 6; if not, return to step 4.

[0078] Step 6: Conduct fastening system test verification;

[0079] Carry out test verification of fastening system, including static test, separation test, modal test and environmental test.

[0080] After the fastening system test is verified, determine whether it meets the requirements. If it does, proceed to step 7; if not, return to step 3.

[0081] Step 7: Conduct flight verification.

[0082] Conduct flight test verification, including one-time flight or repeated flight after return.

[0083] After flight test verification, determine whether the requirements are met. If yes, proceed to step eight; if not, return to step two.

[0084] Step 8: Equipment confirmation.

[0085] After step 1 to step 7, make a final judgment on whether the fastening system meets the equipment requirements. If it does, complete the entire forward design process; if not, return to step 1.

[0086] Example

[0087] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0088] Taking a launch vehicle segment axial docking and fastening system as an example, the specific implementation of the present invention is as follows:

[0089] Step 1: Conduct aerospace equipment demand analysis;

[0090] Sorting out the input conditions of the launch vehicle, including carrying capacity, service environment, and lifespan, specifically including:

[0091] 1) Load-bearing capacity: The service conditions include lifting, ejection, transonic speed, maximum Qα condition, and maximum Q condition. Among them, the maximum Qα condition has the largest load, with a bending moment of 24.9 kN.m at the butt joint and an axial tension of 250.0 kN.

[0092] 2) Service environment: The temperature in the factory environment and transportation environment is -30℃~+40℃, the relative humidity is not more than 98% (25℃), there is an ocean salt spray environment, the rainfall is not more than 8.0mm / h, and the flight temperature does not exceed 107℃;

[0093] 3) Lifespan: not less than 5 years.

[0094] Step 2: Establish technical indicators of fastening system;

[0095] Establish the technical indicators of the segment axial butt fastening system, including:

[0096] 1) Structure and size: Both connected parts are in the form of inverted frames, with an outer diameter of φ1200mm and a height of 500mm. The width of the upper shell section is t2≤80mm, and the width of the lower shell section is t5≤80mm;

[0097] 2) Quality: The quality of the fastening system is ≤ 20kg;

[0098] 3) Strength grade: The material of the connected part is aluminum alloy 2A14, the heat treatment state is T6, the tensile strength is ≥335MPa, and the yield strength is ≥280MPa; the fastener material is steel, and the tensile strength should be ≥1100MPa;

[0099] 4) Preload: no requirement;

[0100] 5) Installation conditions: During the service life of fasteners, it is expected that they will be disassembled and assembled 5 to 10 times;

[0101] 6) Mechanical environment: including vibration, impact, and acceleration;

[0102] The random vibration test conditions are shown in the following table:

[0103]

[0104] The impact test conditions are shown in the following table:

[0105]

[0106] The acceleration shall not be less than 22g, along the product axis in both positive and negative directions and in the horizontal direction, once in each direction, and the time shall not be less than 3 minutes.

[0107] 7) Thermal environment: -30℃~+107℃;

[0108] 8) Natural environment: including humidity, mold, and salt spray.

[0109] Carry out humidity test according to GJB 715.10- "Fastener Test Method Humidity" and no rust should appear on the product surface within 30 days.

[0110] The mold test shall be carried out according to GJB 150.10A- "Military Equipment Laboratory Environmental Test Methods Part 10: Mold Test". Mold is not allowed to form on the product surface within 28 days.

[0111] Carry out salt spray test according to GJB 150.11A- "Military Equipment Laboratory Environmental Test Method Part 11: Salt Spray Test". The product substrate should not rust within 480 hours.

[0112] 9) Propellant medium environment: None.

[0113] Step 3: Design the fastening system;

[0114] 1) According to the shell material, lightweight requirements, and thermal environment requirements, it is preliminarily determined that the material of the bolt is 0Cr13Ni8Mo2Al precipitation hardened stainless steel, with a tensile strength of ≥1410MPa, a yield strength of ≥1310MPa, and a structure of MJ threaded hexagonal head bolts; the material of the nut is GH4169 high-temperature alloy, with a tensile strength of ≥1300MPa, a yield strength of ≥1100MPa, and a structure of MJ threaded hexagonal self-locking nuts; the temperature resistance range of the bolts and nuts is -50℃~+300℃, meeting the requirements of -30℃~+107℃;

[0115] 2) The finite element method is used to design and optimize the fastener layout. The optimized design variables include the size of the upper shell section, the lower shell section and the fasteners T = {t1, t2, ..., t8}, the mass M = {m1, m2, ..., m y}, stress F={f1,f2,……,f z}.

[0116] In the formula, the meaning, initial value, lower limit and upper limit of each symbol are as follows:

[0117]

[0118]

[0119] A finite element model was established, and the bolts and nuts were simplified into dumbbell-shaped structures, that is, the bolts were replaced by simplified bolt model 5, the nuts were replaced by simplified nut model 6, and the bolt threads were replaced by modified polished rod 7. The diameter of the modified polished rod 7 was converted according to the thread stress cross-sectional area, as shown in the table below.

[0120] Thread specification <![CDATA[Thread stress cross-sectional area (mm 2 )]]> Diameter of corrected polished rod 7 (mm) MJ6×1 21.75 5.26 MJ8×1 41.68 7.29 MJ10×1.25 65.14 9.11

[0121] Taking the quality of the fastening system as the objective function and the size and stress as the constraints, the mathematical model for fastening system optimization is:

[0122]

[0123] Among them, Fβ is the upper limit constraint value of the stress of the part at the service temperature, and the failure criterion is the vonMises yield criterion. The bending moment applied to the upper and lower shell segments is 24.9 kN.m, and the axial tension is 250.0 kN. The efficient global optimization (EGO) algorithm based on the Kriging model is used to calculate the design variables with the minimum mass of the fastening system. The optimized solution is as follows:

[0124]

[0125]

[0126] Through the above fastening system design, the design parameters of the fastening system are determined. The minimum mass of the fastening system is 13.21kg, the fastener specification is MJ6, the material of the bolt is 0Cr13Ni8Mo2Al precipitation hardened stainless steel, the tensile strength is ≥1410MPa, the yield strength is ≥1310MPa, and the structure is MJ threaded hexagonal head bolt; the material of the nut is GH4169 high temperature alloy, the tensile strength is ≥1300MPa, the yield strength is ≥1100MPa, and the structure is MJ threaded hexagonal self-locking nut.

[0127] Step 4: Analyze whether the existing fasteners meet the requirements. If they do, select the existing fastener products; if they do not, improve the design of the fastener products;

[0128] 1) Determine the material of the fastener according to the performance characteristics, manufacturing process and use requirements of the fastener; the existing MJ thread hexagonal head bolt is made of 0Cr13Ni8Mo2Al precipitation hardening stainless steel, the smelting method is "vacuum induction + vacuum consumable remelting", the specifications are MJ3-MJ24, and the surface treatment is chemical passivation, chemical passivation + molybdenum disulfide coating; MJ thread hexagonal self-locking nut is made of GH4169 high-temperature alloy, the smelting method is "vacuum induction + electroslag remelting or vacuum induction + vacuum consumable remelting", the specifications are MJ3-MJ24, and the surface treatment is chemical passivation + molybdenum disulfide coating, copper plating + molybdenum disulfide coating.

[0129] 2) For the fasteners with the highest stress in step 3, a refined finite element modeling with threads is performed. Both the bolt and nut models contain threads, and a preload is applied to the bolts and nuts, with the preload being 35% of the yield tension of the bolts. The strength of the bolts and nuts is checked, and the material does not yield, and the strength meets the requirements.

[0130] 3) According to the requirements of the fastening system for installation conditions, mechanical environment, natural environment, and propellant medium environment, analyze whether the existing fasteners meet the requirements:

[0131] a) Installation conditions: During the service life of fasteners, it is expected that they will be repeatedly disassembled and assembled 5 to 10 times. The existing MJ threaded hexagonal head bolts and MJ threaded hexagonal self-locking nuts can meet 15 times of repeated disassembly and assembly, which meets the requirements;

[0132] b) Mechanical environment: including vibration, impact, acceleration, MJ threaded hexagonal head bolts and hexagonal self-locking nuts can meet the requirements;

[0133] c) Thermal environment: -30℃~+107℃, the temperature resistance range of fasteners is -50℃~+300℃, which meets the requirements;

[0134] d) Natural environment:

[0135] The bolts and nuts are subjected to humidity test according to GJB 715.10- "Fastener Test Method Humidity". No rust will appear on the product surface within 30 days, which meets the requirements. The bolts and nuts are subjected to mold test according to GJB 150.10A- "Military Equipment Laboratory Environmental Test Method Part 10: Mold Test". No mold will appear on the product surface within 28 days, which meets the requirements.

[0136] The bolts and nuts were subjected to salt spray test according to GJB 150.11A- "Military Equipment Laboratory Environmental Test Method Part 11: Salt Spray Test". After more than 192 hours, the bolts with chemical passivation or chemical passivation + molybdenum disulfide coating would show rust on the product substrate, which did not meet the requirements; the nuts with chemical passivation + molybdenum disulfide coating would not show rust on the product substrate within 480 hours, which met the requirements; the nuts with copper plating + molybdenum disulfide coating would show rust on the product substrate after 192 hours, which did not meet the requirements.

[0137] 4) The fastening system of this embodiment does not have a propellant medium environment and does not need to be analyzed.

[0138] Through the above analysis, the existing nuts meet the requirements, but the bolts do not meet the salt spray test requirements. It is necessary to improve the design of bolt products from the perspective of improving salt spray resistance. Organic silicon nano-coating is sprayed on the outer surface of the bolt, and the coating thickness is 5μm to 15μm.

[0139] Step 5: Carry out fastener manufacturing and single machine test verification;

[0140] Spray the organic silicon nano coating on the bolts, and solidify it after spraying. The curing temperature does not exceed 250℃, which will not affect the strength of the bolts.

[0141] After the bolts are sprayed with silicone nano-coating, a salt spray test is carried out according to GJB 150.11A-"Military Equipment Laboratory Environmental Test Method Part 11: Salt Spray Test". The product substrate will not rust within 720 hours, meeting the requirements; a mold test is carried out according to GJB150.10A-"Military Equipment Laboratory Environmental Test Method Part 10: Mold Test". No mold will be produced on the product surface within 28 days; a humidity test is carried out according to GJB 715.10-"Fastener Test Method Humidity". No rust will appear on the product surface within 30 days.

[0142] The bolts and nuts are assembled as a whole and subjected to vibration test according to GJB 715.3A- "Fastener Test Method Vibration", and no structural damage, cracks, fractures or nut loosening are found. The bolts are subjected to room temperature destructive tensile test according to GJB 715.23A- "Fastener Test Method Tensile Strength", and the breaking force is 30.77kN~35.45kN. The bolts are subjected to stress corrosion test according to GJB 715.7- "Fastener Test Method Stress Corrosion", and no fracture is found after 1000h. After the test, 100% of the products are inspected, and no defects such as cracks are found.

[0143] After the fastener is tested and verified on a stand-alone basis, it is determined that the requirements are met and the process proceeds to step six.

[0144] Step 6: Conduct fastening system test verification;

[0145] Carry out fastening system test verification, including:

[0146] 1) Static test: The fastening system, as a whole, participates in the static test of the launch vehicle. Loads are applied according to the lifting, ejection, transonic speed, maximum Qα condition, and maximum Q condition. The strength of the fastening system meets the requirements.

[0147] 2) Separation test: The fastening system participated in the interstage separation test of the launch vehicle. The separation energy was a flexible detonating cord assembly with a charge line density of 2.2g / m. During the separation process, the fastening system structure was intact and met the requirements.

[0148] 3) Modal test: The fastening system participates in the modal test of the launch vehicle and meets the requirements.

[0149] 4) Environmental test: According to the mechanical environment and thermal environment in step 2, random vibration test, impact test, acceleration test and high and low temperature test are carried out respectively. The fastening system is not damaged or loosened, and meets the requirements.

[0150] After completing the above tests, it is proved that the fastening system meets the requirements and proceed to step seven.

[0151] Step 7: Conduct flight test verification of aerospace equipment.

[0152] The flight test verification was carried out and was a complete success, with all performance of the fastening system meeting the requirements.

[0153] Step 8: Equipment confirmation.

[0154] After steps 1 to 7, it is determined that the fastening system meets the equipment requirements and the entire forward design process is completed.

[0155] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

[0156] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. The fastening system forward design method is characterized by: The following steps are involved: S1. Conduct aerospace equipment demand analysis; S2. Establish technical indicators of the fastening system based on the results of demand analysis; S3. Design the fastening system according to the technical indicators; S4. Determine the product index of fasteners according to the design results; S5, determine whether the fastener meets the requirements, if so, select existing fastener products and enter step S7; Otherwise, proceed to step S6; S6. Improve the design of the fastener product to obtain the fastener product; S7. Carry out the manufacturing and single-machine test verification of fastener products and obtain the single-machine test verification results; S8, judging whether the single machine test verification result meets the requirements, if so, performing the fastening system test verification to obtain the fastening system test verification result; if not, returning to step S6; S9, judging whether the fastening system test verification result meets the requirements, if so, performing flight verification to obtain the flight verification result; if not, returning to step S3; S10, judging whether the flight verification result meets the requirements, if so, performing equipment confirmation to obtain the equipment confirmation result; if not, returning to step S2; S11. If the equipment confirmation result meets the requirements, then end; otherwise, return to step S1.

2. The fastening system forward design method according to claim 1, characterized in that: The aerospace equipment demand analysis is specifically: sorting out the input conditions of the aerospace equipment, and obtaining the requirements related to the fastening system, including load-bearing capacity, service environment, and lifespan.

3. The fastening system forward design method according to claim 2, characterized in that: The bearing capacity refers to the load requirement of the connection parts, including the loads under lifting, ejection, transonic speed, maximum Qα condition and maximum Q condition, where Q is the dynamic pressure during flight and α is the aerodynamic composite angle of attack; the service environment includes factory environment, transportation environment, marine environment, flight mechanics environment and flight thermal environment; the lifespan refers to the storage period of aerospace equipment.

4. The fastening system forward design method according to claim 1, characterized in that: The technical indicators of the fastening system include structure and size, quality, strength grade, preload force, installation conditions, mechanical environment, thermal environment, natural environment and propellant medium environment.

5. The fastening system forward design method according to claim 4, characterized in that: The structure and size are the structural form and size requirements of the fasteners and connected parts; the mass is the total weight of all parts in the fastening system, including the weight of the connected parts and the fasteners; the strength grade is the required value of the tensile load or shear load of the fastener; the preload is the required value of the installation preload of the fastener; the installation condition is the number of times the fastener is installed and disassembled; the mechanical environment includes vibration, impact and acceleration; the thermal environment includes high temperature environment and low temperature environment; the natural environment includes high temperature, low temperature, humidity, mold and salt spray; the propellant medium environment includes unsymmetrical dimethyl hydrazine, nitrogen tetroxide, liquid hydrogen, liquid oxygen, kerosene and methane environment.

6. The fastening system forward design method according to claim 1, characterized in that: The specific method for designing the fastening system is as follows: Determine the material category and strength grade of fasteners based on mass and thermal environment; The finite element method is used to optimize the design of fasteners. The mathematical model for the optimization design of the fastening system is: Among them, T α is the lower limit constraint value of the structure size, T β is the upper limit constraint value of the structure size, F δ is the upper limit constraint value of stress of the part at service temperature, m i is the mass of the ith part, W α is the lower limit constraint value of the fastener preload, W β is the upper limit constraint value of the fastener preload.

7. The fastening system forward design method according to claim 1, characterized in that: The manufacturing of the fastener products includes: process simulation, cutting, upsetting, thread rolling, heat treatment and surface treatment; the single-machine test verification of the fasteners includes tensile test, shear test, vibration test, salt spray test, mold test, humidity test and stress corrosion test.

8. The fastening system forward design method according to claim 1, characterized in that: Fastening system test verification, including static test, separation test, modal test and environmental test.

9. The fastening system forward design method according to claim 1, characterized in that: The flight test verification includes a one-time flight or repeated flight after return.

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