Fastener system verification method

Abstract

The application discloses a fastener system verification method, and realizes performance verification process formulation of a fastener in different application environments of a space vehicle. Through a verification method, a pass judgment, a processing method for unqualified products and a position of a rollback process in each step in the process, the problem of inequality between the performance of the fastener itself and the requirements of the fastener applied to the space vehicle is solved, and it is ensured that the fastener can meet different use environments experienced by the space vehicle.

Description

TECHNICAL FIELD

[0001] The application relates to a fastener system verification method and belongs to the technical field of spacecraft structures. BACKGROUND

[0002] Threaded connection is the most widely used connection form in aerospace vehicles, and its connection reliability has an important influence on the success or failure of launch missions. However, aerospace vehicles face complex flight environments and have great differences in application scenarios, and high requirements are placed on fastener technology. For different application scenarios, the application environment that aerospace fasteners need to adapt to includes high load environment, high corrosion environment, strong vibration environment, high and low temperature alternating environment, high impact environment, 10 years or more storage environment, repeated disassembly and repeated flight environment, which brings great challenges to the performance and quality stability of fasteners.

[0003] However, most of the fasteners currently used in aerospace fasteners only perform strength single-factor index checking in the performance verification process, and do not strictly verify dynamic and static strength, environmental adaptability, installation process, etc., which cannot meet the requirements of new generation aerospace vehicles in extreme service environments such as deep low temperature, ultrahigh temperature and repeated use, and in existing application processes, there are often problems such as frequent application of fasteners themselves, which brings great hidden dangers to the reliability of spacecraft.

[0004] CN202311136615.2 "A Corrosion Resistant Systematic Design Method for Space Fastening Connection System" gives the corrosion rate test and judgment criteria of fasteners in contact with liquid propellants of aerospace vehicles, which has guiding significance for the determination method of fastener corrosion resistance, but the corrosion resistance test time involved is not explicitly corresponding to the storage time after the fastener is installed, and the relationship between the test time and the storage time is not established, so the bearing capacity of the fastener under the storage environment of 10 years or more cannot be effectively verified; and the test time in the method does not match the common time from the propellant filling of the aerospace vehicle to the launch, and the qualification of the fastener in contact with the propellant medium cannot be effectively revealed.

[0005] CN202410601382.7 "A Fastener Detection System and Method Based on a Directional Target" uses a material transfer turntable to automatically drive fasteners for two-step detection to detect the size of the fasteners and improve the detection efficiency. However, only the a size of the fastener size is verified, which lacks universality and generality, and cannot serve as a reference for the fastener verification process.

[0006] CN202123196579.8, "A Carbon-Carbon Fastener Storage Device for Easy Classification and Storage," discloses a carbon-carbon fastener storage device for easy classification and storage, relating to the field of fastener storage. It includes a storage box, box body, storage mechanism, air blowing assembly, and protective mechanism, facilitating quick and practical retrieval of fasteners and increasing work efficiency. However, it describes the unused state of fasteners and does not specify the storage time. Since the long-term storage environment experienced by spacecraft is the state after installation, it cannot serve as a reference for the long-term storage performance of fasteners.

[0007] Currently, while individual verification items for fasteners are relatively well-established both domestically and internationally, there are still no effective verification methods for two common operating conditions encountered by spacecraft: storage environments lasting over 10 years and application environments involving contact with propellant media. Furthermore, no verification process has been established domestically or internationally. There is no clear approach to defining which verification items are required for different application scenarios or how to develop a systematic verification process for fasteners. This leads to a mismatch between the performance of the fasteners themselves and the requirements of spacecraft, resulting in fasteners passing production inspection but failing in actual application.

[0008] Therefore, there is an urgent need to propose a fastener system verification method that can meet the requirements of various application environments during spacecraft use. Summary of the Invention

[0009] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a fastener system verification method to ensure that the fasteners can meet the different operating environments experienced by spacecraft.

[0010] The technical solution of this invention is:

[0011] This invention discloses a fastener system verification method, comprising:

[0012] S1. Perform a general test on the fastener; if it passes, proceed to step S2; if it fails, correct the fastener and repeat step S1.

[0013] S2. Determine whether the fastener is in contact with the medium. If so, perform a medium compatibility test and then a tensile failure hydrogen embrittlement metallographic test. If the test is passed, proceed to step S3. If not, directly perform a tensile failure hydrogen embrittlement metallographic test. If the test is passed, proceed to step S3.

[0014] S3. Determine whether the stress of the fastener exceeds 50% of the minimum allowable tensile strength; if yes, conduct a stress comprehensive test, and proceed to step S4 if the test is passed; otherwise, proceed to step S4.

[0015] S4. Determine whether the fastener is subjected to instantaneous impact load during use. If so, conduct an impact toughness test. If the test is qualified, proceed to step S5. If not, proceed to step S5.

[0016] S5. Determine whether the operating temperature of the fastener is lower than the low temperature threshold; if so, conduct a low temperature tensile failure test; if the test is passed, proceed to step S6; otherwise, proceed directly to step S6.

[0017] S6. Determine whether the operating temperature of the fastener is higher than the high temperature threshold; if so, conduct a high temperature tensile failure test and a high temperature locking test; if the test is passed, proceed to step S7; if not, proceed directly to step S7.

[0018] S7. Determine whether the fastener's operating environment is subjected to large shear loads; if so, conduct a double shear test; if the test is passed, proceed to step S8; if not, proceed directly to step S8.

[0019] S8. Determine whether the fastener is used in a humid or salt spray environment; if so, conduct a comprehensive corrosion environment test; if the test is passed, proceed to step S9; otherwise, proceed directly to step S9.

[0020] S9. Determine whether the fastener is required to be stored for more than 10 years after installation; if so, conduct a long-term storage test; if the test is successful, proceed to step S10; if not, proceed directly to step S10.

[0021] S10. Determine whether the fastener needs to be disassembled and reassembled more than 5 times. If so, conduct a repeated disassembly and reassembly test. If the test is successful, proceed to step S11. If not, proceed directly to step S11.

[0022] S11. Determine whether the fastener has undergone repeated use. If so, conduct a fatigue test. If the test is successful, the fastener passes system verification. If not, the fastener passes system verification.

[0023] Furthermore, in the above method, the general testing and verification of the fasteners specifically includes:

[0024] S21. Verify the dimensions of the fasteners; if they are qualified, proceed to step S22; if they are not qualified, correct the dimensions of the fasteners and repeat step S21.

[0025] S22. Perform surface treatment thickness and bonding force tests on the fasteners; if qualified, proceed to step S23; if unqualified, correct the thickness of the fasteners and repeat step S22.

[0026] S23. Perform a wedge load test on the fastener; if it passes, proceed to step S24; if it fails, reduce the load on the fastener or increase the lower radius of the head, and then re-enter step S21.

[0027] S24. Perform a tightening test on the fastener; if it passes, proceed to step S25; if it fails, modify the tightening structure dimensions of the fastener and then re-enter step S21.

[0028] S25. Perform a hardness test on the fastener; if it passes, proceed to step S26; if it fails, modify the heat treatment method or improve the stability of the raw material, and then re-enter step S23.

[0029] S26. Conduct a vibration test on the fastener; if it passes, proceed to step S27; if it fails, modify the self-locking nut's closing amount and self-locking torque, then re-enter step S21.

[0030] S27. Perform an axial load test on the fastener; if it passes, proceed to step S28; if it fails, modify the load-bearing structure dimensions of the fastener or improve the stability of the raw material, and then re-enter step S21.

[0031] S28. Perform a loosening test on the fasteners; if they pass, proceed to step S29; if they fail, modify the load-bearing structure and dimensions of the support plate nut, and then re-enter step S21.

[0032] S29. Perform a push-out test on the fastener; if it passes, proceed to step S30; if it fails, modify the load-bearing structure dimensions of the support plate nut and then re-enter step S21.

[0033] S30. Perform a permanent deformation test on the fastener; if it passes, the general test is passed; if it fails, modify the self-locking nut's closing amount or the self-locking torque, and then re-enter step S21.

[0034] Furthermore, in the above method, the stress comprehensive test includes stress corrosion test, stress endurance test, stress relaxation test and stress fracture test.

[0035] Furthermore, in the above methods, the stress endurance test, after applying 75-83% of the minimum breaking tensile force and holding for more than 24 hours, should not result in cracks or breakage of the fastener; the stress fracture test, after applying 50-55% of the minimum breaking tensile force, and depending on the material, applying a high temperature of 100-660℃ and holding for more than 25 hours, should not result in breakage of the fastener; the stress corrosion test, after applying 70-75% of the minimum breaking tensile force and immersing in a corrosive solution for more than 1000 hours, should not result in cracks in the fastener under fluorescent flaw detection; the stress relaxation test, after applying 58-62% of the minimum breaking tensile force, and depending on the material, applying a high temperature of 100-660℃ and holding for more than 200 hours, should not result in a reduction of more than 60% in the axial force of the fastener.

[0036] Further, in the above method, for the high-temperature locking test, the test method is as follows: Place the fastener under the condition of the service temperature ±5°C for heat preservation for 6h ± 15min. After cooling to room temperature, conduct the self-locking nut locking force test without applying additional lubrication during the test process.

[0037] Further, in the above method, for the medium compatibility test, the specific test method is as follows: Install the fastener on the clamping test piece according to the tightening torque required by the service condition, and immerse the fastener and the clamping test piece together in the corresponding medium. After maintaining for 100 - 120h, take them out. After the temperature returns to 15 - 30°C, conduct the room-temperature tensile failure test, hydrogen embrittlement test, and metallographic test.

[0038] Further, in the above method, the tensile failure hydrogen embrittlement metallographic test is specifically as follows:

[0039] S71. Conduct the room-temperature tensile failure test on the fastener; if it is qualified, proceed to step S72; if it is unqualified, conduct load reduction treatment, modify the head size, or improve the stability of the fastener raw material for the fastener, and then re-enter step S21;

[0040] S72. Conduct the hydrogen embrittlement test on the fastener, and the test duration is not less than 200h; if it is qualified, proceed to step S73; if it is unqualified, conduct dehydrogenation treatment on the fastener and then re-enter step S23;

[0041] S73. Conduct the metallographic test on the fastener; if it is qualified, proceed to step S3; if it is unqualified, modify the surface treatment method, heat treatment method, or improve the stability of the fastener raw material, and then re-enter step S21.

[0042] Further, in the above method, for the long-term storage test, the test method is as follows:

[0043] Determine the maintenance time of the fastener in the oxygen-rich humid and hot environment;

[0044] Install multiple groups of test fasteners and conduct the long-term storage test of the fasteners in the oxygen-rich humid and hot environment simultaneously;

[0045] Take out a group of test fasteners every 2 - 3 days of the test and conduct the vibration test;

[0046] Continue the test until the test time reaches the maintenance time;

[0047] If in all the vibration tests, the relative rotation of the fastener does not exceed 360°, it is qualified; otherwise, it is unqualified;

[0048] If it is unqualified, modify the surface treatment method or material type of the fastener and re-enter step S1.

[0049] Furthermore, in the above method, the vibration test specifically includes:

[0050] After the fasteners are installed, the system will vibrate for more than 30,000 cycles.

[0051] If the fastener rotates no more than 360° relative to the other, and there is no structural damage, cracks, breakage, or loss of locking performance, it is considered qualified; otherwise, it is considered unqualified.

[0052] Furthermore, in the above method, the impact toughness test specifically involves: conducting an impact toughness test using the Charpy pendulum method. If the impact energy meets the index requirements, it is considered qualified; otherwise, it is considered unqualified, and the heat treatment method is modified, the stability of the fastener raw materials is improved, or the materials are replaced, proceeding to step S3.

[0053] The advantages of this invention over the prior art are as follows:

[0054] (1) This invention adopts a systematic fastener verification method, realizing the formulation of fastener performance verification process under different application environments of spacecraft. By defining the verification method, pass / fail criteria, non-compliance handling method, and the location where the process needs to be rolled back in each step of the process, it solves the problem of the mismatch between the fastener's own performance and the spacecraft's requirements for fasteners caused by the single and unprocessed fastener verification method in the existing fastener verification technology, ensuring that the fastener can meet the different usage environments experienced by the spacecraft.

[0055] (2) The present invention adopts a long-term storage test method to conduct accelerated aging tests on fasteners used in spacecraft that need to be stored for more than 10 years, thereby realizing the confirmation of test conditions for fasteners with different storage years and solving the technical problem that spacecraft models cannot determine whether fasteners are loose under long-term storage conditions.

[0056] (3) The present invention adopts a medium compatibility test to realize the test and evaluation of fasteners that need to be in contact with the propellant medium of the spacecraft. The fasteners are immersed in the medium and maintained for the time common between the spacecraft refueling medium and flight. Three tests are performed on the fasteners to verify the fasteners and solve the problem that the fastener performance does not degrade after the spacecraft refueling medium and flight. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the fastener system verification method of the present invention;

[0058] Figure 2 This is a flowchart of the fastener system verification method of the present invention;

[0059] Figure 3 This is a flowchart of the general testing and verification method for fasteners according to the present invention;

[0060] Figure 4 This invention relates to a method for long-term storage testing of fasteners. Detailed Implementation

[0061] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] like Figure 1 As shown, the present invention provides a fastener system verification method, including a verification process, verification items for different application environments, and a method for handling verification failures.

[0063] Each step requires a pass / fail assessment. If a step fails, targeted modifications are made, the process is rolled back, and selective re-verification of the verification items is performed. If a step passes, the verification for this step is complete, and subsequent verifications proceed. Steps one through ten are general verification items for fasteners, and the process is as follows: Figure 3 As shown, steps eleven through twenty-four require selective determination of whether verification should be performed based on the application environment and requirements of the fasteners. The process is as follows: Figure 2 As shown.

[0064] The method includes the following steps:

[0065] Step 1: Size Verification

[0066] Standard measuring tools were used to verify the key dimensions and tolerances of fastener head and shank structures, nut self-locking structures, etc.

[0067] If the fastener fails to meet the requirements, rework the corresponding dimensions, correct the dimensions, and then re-verify this step.

[0068] Step 2: Surface treatment thickness and adhesion

[0069] The thickness of the surface treatment is checked by metallographic method; the surface treatment adhesion is verified by sticking strong adhesive tape to the surface of the fastener, and the coating of the fastener should be continuous after the tape is removed, or by using thermal shock method.

[0070] If it fails to meet the requirements, the process should be reworked and corrected before re-verifying the step; there is no need to roll back the process.

[0071] Step 3: Wedge Load Test

[0072] A tensile testing machine is used to install wedge-shaped washers at different angles under the bolt head to conduct a tensile test. Tensile force is applied until the bolt breaks, and the breaking force should be within the specified range.

[0073] If the test fails, the failure mode needs to be determined. If the thread fails, the load needs to be reduced. If the head fails, the head size needs to be changed or the lower fillet of the head needs to be increased. Then, the process should be rolled back to step one and the verification should be restarted.

[0074] Step 4: Tightening Test

[0075] Bolts and screws with internal wrenching structures and nuts without support plates should undergo a wrenching test. After applying the specified torque, the fasteners should not show cracks, slippage, or deformation that hinders installation.

[0076] If it fails to meet the requirements, the slot number of the wrench and the dimensions of the nut wrench structure need to be modified, and the process needs to be rolled back to step one to start the verification again.

[0077] Step 5: Hardness Test

[0078] Verify by conducting Rockwell hardness, Brinell hardness, or Vickers hardness tests.

[0079] If the test fails, the heat treatment method must be modified or the stability of the fastener raw materials must be improved through quality control measures such as re-inspection of raw materials upon arrival at the factory. The process should then be rolled back to step three and the verification process should be restarted.

[0080] Step Six: Vibration Test

[0081] Self-locking nut matching combinations require vibration testing. After installing the fasteners, determine the loading method and cyclically vibrate for more than 30,000 times. The relative rotation of the fasteners should not exceed 360°, and there should be no structural damage, cracks, breakage, or loss of locking performance.

[0082] If it fails to meet the requirements, the amount of self-locking nut tightening or the self-locking torque needs to be modified, and the process needs to be rolled back to step one to start the verification again.

[0083] Step 7: Axial Load Test

[0084] The test is conducted using a bolt with a strength greater than that of the nut being tested. After determining the loading speed, a tensile testing machine is used to apply the load. After the specified load is applied, the nut should not fail.

[0085] If it fails to meet the requirements, the structural dimensions of the fasteners need to be modified, or the stability of the fastener raw materials needs to be improved through quality control measures such as re-inspection of raw materials upon arrival at the factory, and the process needs to be rolled back to step one to start the verification process again.

[0086] Step 8: Unscrewing test

[0087] For the sliding plate nut, a loosening test should be performed. The test bolt should be loaded with the specified tightening torque and should not separate from the bracket. Cracks or deformations that would affect the reuse of the nut are not allowed.

[0088] If it fails to meet the requirements, the dimensions, molding process, or materials of the floating support plate nut spring and bracket need to be modified, and the process needs to be rolled back to step one to start the verification again.

[0089] Step Nine: Launch the Trial

[0090] For sliding plate nuts, an ejection test should be conducted. After applying a specified ejection force with a mandrel, the nut should not crack.

[0091] If it fails to meet the requirements, the load-bearing structure dimensions of the pallet nut need to be modified, and the process needs to be rolled back to step one to start the verification process again.

[0092] Step 10: Permanent Deformation Test

[0093] To conduct a permanent deformation test on the self-locking nut, the largest and smallest mandrels were used to repeatedly screw the self-locking nut in and out, and the tightening torque and loosening torque were measured. No grease was applied during the test.

[0094] If it fails to meet the requirements, the amount of self-locking nut tightening or the self-locking torque needs to be modified, and the process needs to be rolled back to step one to start the verification again.

[0095] Step 11: Medium Compatibility Test

[0096] Determine whether the fastener is in contact with a medium, including but not limited to liquid hydrogen, liquid oxygen, nitrogen tetroxide, unsymmetrical dimethylhydrazine, kerosene, and methane. If it is not in contact with a medium, proceed directly to steps twelve through fourteen; if it is in contact with a medium, conduct a medium compatibility test.

[0097] Install the fasteners on the clamping test piece according to the tightening torque required for the operating conditions, and immerse the fasteners and clamping test piece together in the corresponding medium. After maintaining this for 100-120 hours, remove the fasteners and wait for the temperature to recover to 15-30℃ before performing the room temperature tensile failure test, hydrogen content test, and metallographic test in steps twelve to fourteen.

[0098] Step 12: Room temperature tensile failure test

[0099] A load is applied on a tensile testing machine until fracture, and the fracture tensile force must meet the requirements of minimum breaking tensile force and maximum breaking tensile force.

[0100] If it fails to meet the requirements, it is necessary to reduce the load (without rolling back the process), modify the head size, or improve the stability of the fastener raw materials through quality control measures such as re-inspection of raw materials upon arrival at the factory, and roll back the process to step one to start the verification again.

[0101] Step Thirteen: Hydrogen Embrittlement Test

[0102] The test duration shall be no less than 200 hours, and the fasteners shall not break.

[0103] If the product fails to meet the requirements, it must undergo hydrogen removal treatment, and the process must be rolled back to step three to restart the verification.

[0104] Step Fourteen: Metallographic Test

[0105] Inspect the fasteners for surface discontinuities, microstructure, intergranular corrosion, grain flow at the head, and grain flow at the threaded parts.

[0106] If it fails to meet the requirements, the surface treatment method, heat treatment method, or quality control measures such as re-inspection of raw materials upon arrival at the factory must be modified to improve the stability of the fastener raw materials, and the process must be rolled back to step one to start the verification again.

[0107] Step 15: Stress Synthesis Test

[0108] Determine whether the applied stress exceeds 50% of the tensile strength. If not, skip step 15; if so, conduct a comprehensive stress test, including stress corrosion test, stress endurance test, stress relaxation test, and stress fracture test.

[0109] Among them, in the stress endurance test, after applying 75-83% of the minimum breaking tensile force and maintaining it for more than 24 hours, the fastener should not show cracks or breakage; in the stress fracture test, after applying 50-55% of the minimum breaking tensile force, after applying the temperature shown in the table below and maintaining it for more than 25 hours, the fastener should not break; in the stress corrosion test, after applying 70-75% of the minimum breaking tensile force and immersing it in a corrosive solution for more than 1000 hours, the fastener should not show cracks when subjected to fluorescent flaw detection; in the stress relaxation test, after applying 58-62% of the minimum breaking tensile force, after applying the temperature shown in the table below and maintaining it for more than 200 hours, the axial force of the fastener should not decrease by more than 60%.

[0110] Material Test temperature / °C High temperature alloy 630-660 Stainless steel 220-240 Titanium alloy 350-420 Aluminum alloy 100-140

[0111] If the test fails, the heat treatment method, hydrogen removal treatment, and quality control measures such as re-inspection of raw materials upon arrival at the factory must be modified to improve the stability of the fastener raw materials or replace the raw materials. The process must then be rolled back to step three and the verification must be restarted.

[0112] Step Sixteen: Impact Toughness Test

[0113] Determine whether the device is subjected to instantaneous impact load during use. If not, skip step sixteen. If so, conduct an impact toughness test using the Charpy pendulum method. The impact energy should meet the required specifications.

[0114] If the test fails, the heat treatment method must be modified, the stability of the fastener raw materials must be improved through quality control measures such as re-inspection of raw materials upon arrival at the factory, or the materials must be replaced, and the process must be rolled back to step three to start the verification process again.

[0115] Step 17: Low-Temperature Tensile Failure Test

[0116] Determine if the operating temperature is below -150℃. If not, skip step seventeen. If so, conduct a low-temperature tensile failure test. Insulate the fastener to the lowest operating ambient temperature and apply a load at that temperature until it breaks. The calculated tensile strength must meet the requirements.

[0117] If it fails to meet the requirements, it is necessary to reduce the load (without rolling back the process), modify the head size, or improve the stability of the fastener raw materials through quality control measures such as re-inspection of raw materials upon arrival at the factory, and roll back the process to step one to start the verification again.

[0118] Step 18: High-Temperature Tensile Failure Test

[0119] Determine if the operating temperature is higher than 300℃. If not, skip step 18. If so, conduct a high-temperature tensile failure test. Insulate the fastener to the highest operating ambient temperature and apply a load at that temperature until it breaks. The calculated tensile strength must meet the requirements.

[0120] If it fails to meet the requirements, it is necessary to reduce the load (without rolling back the process), modify the head size, or improve the stability of the fastener raw materials through quality control measures such as re-inspection of raw materials upon arrival at the factory, and roll back the process to step one to start the verification again.

[0121] Step 19: High-Temperature Locking Test

[0122] Determine if the operating temperature is higher than 300℃. If not, skip step nineteen. If so, a high-temperature locking test is required. The test method is as follows: Place the fastener at an operating temperature of ±5℃ for 6 hours ±15 minutes. After cooling to room temperature, perform a self-locking nut locking force test. No additional lubrication is applied during the test.

[0123] If it fails to meet the requirements, the amount of self-locking nut tightening or the self-locking torque needs to be modified, and the process needs to be rolled back to step one to start the verification again.

[0124] Step 20: Double Shear Test

[0125] Determine whether the operating environment is subjected to large shear loads. If not, skip step 20. If so, conduct a double shear test on a shear testing machine, applying loads until failure, and the calculated shear strength must meet the index requirements.

[0126] If it fails to meet the requirements, the diameter of the bolt shank needs to be modified or the stability of the fastener raw materials needs to be improved through quality control measures such as re-inspection of raw materials upon arrival at the factory. The process should then be rolled back to step one and the verification should be restarted.

[0127] Step 21: Comprehensive Corrosion Environment Test

[0128] Determine whether the usage environment is exposed to humid or salty environments such as near the ocean. If not, skip step twenty-one; if so, conduct a comprehensive corrosion environment test, including salt spray test, mold test and humidity test.

[0129] Among them, the fastener substrate should not show rust after the salt spray test is carried out for the time shown in the table below, the fastener surface should not be allowed to grow mold within 28 days of the mold test, and the fastener surface should be free of rust within 30 days of the humidity test.

[0130]

[0131] If it fails to meet the requirements, the surface treatment method must be modified or the material replaced, and the process must be rolled back to step one to start the verification process again.

[0132] Step 22: Long-term storage test

[0133] Determine whether a storage period exceeding 10 years is required after installation. If not, skip step twenty-two; otherwise, conduct a long-term storage test. Use an oxygen-rich, humid, and hot environment to accelerate the aging of the fasteners. By increasing the water vapor concentration in the test environment, the rate of water vapor adsorption and diffusion by the material is accelerated, thereby accelerating material failure. The test method is as follows:

[0134] 1) Determine the lifespan of the fasteners in an oxygen-rich, humid, and hot environment. Evaluate the storage period using the GLWeleh model, with the calculation formula shown below:

[0135]

[0136] in Let τ be the damp heat aging rate constant, τ be the material life, [H2O] be the water vapor molar concentration, T be the test temperature, and A and B be the damp heat aging rate fitting constants. The test time corresponding to the required storage time of the aircraft is calculated according to the formula.

[0137] 2) Install multiple sets of test fasteners using the same tooling as in step six vibration test, and conduct long-term storage test of the fasteners in an oxygen-rich, humid and hot environment.

[0138] 3) Take out a set of test fasteners every 2 days and conduct vibration tests according to step six.

[0139] 4) Continue the test until the test time specified in 1) is reached. During the test, the relative rotation of the fasteners should not exceed 360° in all vibration tests.

[0140] If it fails to meet the requirements, the surface treatment method or material type must be modified, and the process must be rolled back to step one to start the verification process again.

[0141] Step 23: Repeated disassembly and reassembly test

[0142] Determine whether the fastener needs to be disassembled and reassembled more than 5 times. If not, skip step 23. If so, conduct 15 repeated disassembly and reassembly tests. No additional lubrication is applied during the test. Apply a tightening torque that matches its own strength for each tightening and loosening cycle. After the test, the test piece should not seize up.

[0143] If it fails to meet the requirements, the surface treatment and lubrication methods need to be modified (return the process to step two), the nut end size needs to be modified (return the process to step one), and the verification process needs to be restarted.

[0144] Step 24: Fatigue Test

[0145] Determine whether the fastener has undergone repeated use. If not, skip step 24; if so, conduct the test according to GJB715.30A. The average fatigue life of the fastener should not be less than 65,000 cycles, and the fatigue life of a single piece should not be less than 45,000 cycles.

[0146] If it fails to meet the requirements, the fillet radius of the head needs to be corrected by rework (no need to roll back the process, just re-evaluate this item), the heat treatment method needs to be modified, or the stability of the fastener raw materials needs to be improved through quality control measures such as re-inspection of raw materials upon arrival at the factory. The process needs to be rolled back to step three to start the verification again.

[0147] If the result is satisfactory after step twenty-four, the fastener system verification is considered successful.

[0148] Example

[0149] The requirements or environmental conditions that the interstage docking structure of a certain spacecraft must meet or experience throughout its entire life cycle are as follows:

[0150] 1. A clamping force of 40kN needs to be applied;

[0151] 2. Storage time must reach 17 years;

[0152] 3. The product must be used in a marine environment and must withstand salt spray for at least 300 hours.

[0153] 4. Operating temperature range: -100℃ to 200℃;

[0154] 5. Contact with kerosene medium;

[0155] 6. The aircraft needs to be reusable;

[0156] 7. Fasteners need to be disassembled and reassembled more than 10 times.

[0157] The structure here uses MJ8 specification 0Cr13Ni8Mo2Al precipitation hardening stainless steel hexagonal head bolts and MJ8 specification GH4169 hexagonal self-locking nuts for connection. The bolt surface treatment is chemical passivation, and the nut surface treatment is chemical passivation + molybdenum disulfide coating. Detailed specifications are explained in the following steps.

[0158] Step 1: Size Verification

[0159] The critical dimensions and tolerances of the threads, bolt head and shank structure, and nut self-locking structure were verified using standard measuring tools. The results were satisfactory, and the process continued.

[0160] Step 2: Surface treatment thickness and adhesion test

[0161] The surface treatment thickness requirement for bolts and nuts is 5-15μm, and the actual measured thickness is 8-11μm, which meets the requirements.

[0162] Apply 3M 250 tape to the surface of the fastener, remove the tape and observe the fastener coating. If the coating is continuous, the result is acceptable, and the process continues.

[0163] Step 3: Wedge Load Test

[0164] The test was conducted according to the method described in GB / T 3098.1. A 10° wedge washer was installed under the bolt head. Three fasteners were selected for testing. The allowable range and measured value of the tensile force are shown below. The tensile force meets the requirements and is greater than 40kN. The fasteners are qualified and can withstand the aforementioned stress environment. The process continues.

[0165] Bolt Force value / kN Pass or fail Tensile force allowable range 58.97-67.93 / No. 1 63.35 Yes No. 2 62.14 Yes No. 3 64.52 Yes

[0166] Step 4: Tightening Test

[0167] The bolts are hexagonal head bolts and do not require a tightening test; the nuts are subject to a tightening test, designed according to HB 7596. Three sets of fasteners are selected for testing. The lower limit of the applied torque and the measured value are shown below. The results are qualified, and the process continues.

[0168] Assembly Torque value / Nm Pass or fail Torque allowable range ≥41.0 / No. 1 58.2 Yes No. 2 57.9 Yes No. 3 58.6 Yes

[0169] Step 5: Hardness Test

[0170] Bolts were tested for Rockwell hardness according to GJB 715.2, and nuts were tested for Vickers hardness according to GB 4340.1. Three fasteners of each type were selected for testing. The allowable range of hardness and the measured value are shown below. The results are qualified, and the process continues.

[0171]

[0172]

[0173] Step Six: Vibration Test

[0174] Five sets of the aforementioned selected bolts and self-locking nuts were used to conduct the test according to the method described in GJB 715.3A. After the fasteners were installed, the loading method was determined and the cyclic vibration was repeated more than 30,000 times. The allowable value of relative rotation of the bolts and nuts after the test and the measured value are shown below. No structural damage, cracks, fractures or loss of locking performance were observed after the test. The result was qualified and the process continued.

[0175] Assembly Relative angle / ° Pass or fail Relative angle allowable range ≤360 / No. 1 0 Yes No. 2 0 Yes No. 3 25 Yes No. 4 0 Yes No. 5 72 Yes

[0176] Step 7: Axial Load Test

[0177] After selecting three matching bolts and nuts, the test was conducted according to the method described in GJB715.23A. The load was applied according to a sine curve. After applying a load of 58.3kN, none of the three nuts showed any damage, and the result was qualified. The process continued.

[0178] Step 8: Unscrewing test

[0179] Skip this step if a floating support plate nut is not used.

[0180] Step Nine: Launch the Trial

[0181] Skip this step if a plate-type nut is not used.

[0182] Step 10: Permanent Deformation Test

[0183] The self-locking nut was subjected to a permanent deformation test according to the method described in QJ 3079.1A. The self-locking nut was repeatedly screwed in and out using the largest and smallest mandrels. No grease was applied during the test. The allowable and measured values ​​of the locking torque and loosening torque were measured as follows. The results were qualified, and the process continued.

[0184]

[0185] Step 11: Medium Compatibility Test

[0186] The process requires contact with kerosene medium. After installing bolts and nuts and applying torque until a clamping force of 30kN is generated, the device is immersed in kerosene medium for 112 hours and then removed. Subsequently, steps twelve to fourteen are performed using the immersed fasteners.

[0187] Step 12: Room temperature tensile failure test

[0188] Take three bolts and apply loads to them on a tensile testing machine according to the method described in GJB 715.23A until they break. The allowable range of tensile force and the measured value are shown below. The tensile force meets the requirements and is greater than 40kN. The fasteners are qualified and can withstand the aforementioned stress environment. Continue the process.

[0189] Bolt Force value / kN Pass or fail Tensile force allowable range 58.97-67.93 / No. 1 59.53 Yes No. 2 59.77 Yes No. 3 60.21 Yes

[0190] Step Thirteen: Hydrogen Embrittlement Test

[0191] After the three sets of bolts and nuts were matched and installed, a hydrogen embrittlement test was conducted according to the method described in HB 5067.1. The test was maintained for 200 hours. After the test, none of the three sets of fasteners showed any fracture, and the result was qualified. The process continued.

[0192] Step Fourteen: Metallographic Test

[0193] Metallographic tests were performed on the fasteners according to the method described in GJB 8618, including surface discontinuity, microstructure, intergranular corrosion, grain line flow at the head, and grain line flow at the threaded part. All results were qualified, and the process continued.

[0194] Step 15: Stress Synthesis Test

[0195] Calculations show that the maximum stress generated by the fastener during use is 956 MPa, which is greater than 50% of the tensile strength, and a comprehensive stress test is required.

[0196] 1) The stress endurance test shall be performed in accordance with the method described in GJB 715.12. After applying 80% of the minimum breaking tensile force, i.e. 47.18kN, it shall be maintained for 24h. If no cracks or fractures appear in the fastener, the result is qualified.

[0197] 2) The stress fracture test was performed according to the method described in GJB 715.29. After applying 55% of the minimum breaking tensile force, i.e. 32.43kN, the fastener was kept in a temperature environment of 300℃ for 25h. If the fastener did not break, the result was qualified.

[0198] 3) The stress corrosion test was performed according to the method described in GJB 715.7. After applying 75% of the minimum breaking tensile force, i.e. 44.23kN, the fastener was immersed in the corrosion solution for 1000h. No cracks were found in the fastener by fluorescent flaw detection, and the result was qualified.

[0199] 4) The stress relaxation test was performed according to the method described in GJB 715.8. After applying 60% of the minimum breaking tensile force, i.e. 35.38kN, the fastener was kept in a temperature environment of 300℃ for 200h. The average axial force of the fastener was 26.35kN, which was reduced by 25.5%, and the result was qualified.

[0200] The stress comprehensive test results were satisfactory, and the process continues.

[0201] Step 16: Impact toughness test: Skip this step if the device will not be subjected to instantaneous impact loads during use.

[0202] Step 17: Low-temperature tensile failure test: If the operating temperature is not lower than -150℃, skip this step.

[0203] Step 18: High-temperature tensile failure test: If the operating temperature is not higher than 300℃, skip this step.

[0204] Step 19: High-temperature locking test: If the operating temperature is not higher than 300℃, skip this step.

[0205] Step 20: Double Shear Test: Skip this step if the device is not subjected to shear load during use.

[0206] Step 21: Comprehensive Corrosion Environment Test

[0207] For applications in environments exposed to the ocean or near other marine environments, a comprehensive corrosion environment test is required.

[0208] The salt spray test results are shown below. The bolt's salt spray resistance time does not meet the model requirements, and the fastener does not meet the model requirements. The surface treatment method for the bolts is modified as follows: the bolts undergo chemical passivation followed by coating with a nano-coating, and the process is rolled back to process one.

[0209] Bolt Salt spray resistance time / h Pass or fail Fastener salt spray resistance time requirement ≥192 / Model salt spray resistance time requirement ≥300 / No. 1 201 No No. 2 197 No No. 3 199 No Nut Salt spray resistance time / h Pass or fail Fastener salt spray resistance time requirement ≥480 / Model salt spray resistance time requirement ≥300 / No. 1 495 Yes No. 2 487 Yes No. 3 495 Yes

[0210] After changing the surface treatment of the bolts, steps one, two, eleven, thirteen, fourteen, and fifteen (stress corrosion) need to be re-verified. Other steps do not need to be re-verified. After all previous procedures have passed, return to this step. The re-verification results are as follows: Salt spray test passed.

[0211] Bolt Salt spray resistance time / h Pass or fail Fastener salt spray resistance time requirement ≥720 / Model salt spray resistance time requirement ≥300 / No. 1 735 Yes No. 2 725 Yes No. 3 724 Yes

[0212] No mold was found on the fasteners within 28 days of the mold test.

[0213] The fasteners showed no signs of rust within 30 days of the humidity test.

[0214] The comprehensive corrosion environment test was deemed satisfactory, and the process continued.

[0215] Step 22: Long-term storage test

[0216] like Figure 4 As shown, the required storage time after installation is 17 years. If it exceeds 10 years, a long-term storage test is required.

[0217] 1) The test time of fasteners in an oxygen-rich, humid, and hot environment was calculated according to the GLWeleh model. and According to the formula, calculations show that under environmental conditions of 80℃×75%RH, a 21-day test is equivalent to the effect of long-term storage for 17 years.

[0218] 2) Install 11 sets of test fasteners using the same tooling as in step six vibration test, and conduct long-term storage test of the fasteners in an oxygen-rich, humid and hot environment.

[0219] 3) Take out a set of test fasteners every 2 days and conduct vibration tests according to step six until the 21-day test is completed.

[0220] The test results are shown below. The fastener assembly can withstand 17 years of long-term storage conditions. The results are satisfactory, and the process continues.

[0221] Test time Relative angle / ° Pass or fail Allowable range ≤360 / 2nd day 0 Yes 4th day 0 Yes 6th day 15 Yes 8th day 0 Yes 10th day 60 Yes 12th day 45 Yes 14th day 75 Yes 16th day 50 Yes 18th day 130 Yes 20th day 145 Yes 21st day 170 Yes

[0222] Step 23: Repeated disassembly and reassembly test

[0223] Fasteners that require repeated disassembly and assembly more than 10 times must undergo a repeated disassembly and assembly test. Self-locking nuts are tested using the equipment described in HB 7596. No additional lubrication is applied during the test. A tightening torque of 35.6 Nm is applied for each tightening and loosening cycle. After the test, the test piece did not seize up, and the result is qualified, so the process continues.

[0224] Step 24: Fatigue Test

[0225] The spacecraft is a reusable type, and the fasteners need to undergo repeated use environments and fatigue tests are required. Three sets of bolt and nut combinations were selected and fatigue tests were conducted according to the method described in GJB 715.30A. The high load was set to 27.12kN and the low load was set to 2.71kN. All three sets of fasteners did not break after 65,000 cycles, and no cracks appeared on the surface. They were deemed qualified.

[0226] In the fastener system verification process, the salt spray test in step twenty-one of the comprehensive corrosion environment test failed to meet the model requirements and was deemed unqualified. After changing the surface treatment of the bolts from chemical passivation to nano-coating, the verification was restarted from step one. Finally, all steps were qualified, and it was determined that the modified fasteners could be reliably applied to the entire life cycle of the inter-stage docking structure of the spacecraft. The fastener system verification was passed.

[0227] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

[0228] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A fastener system verification method, characterized in that, include: S1. Conduct general testing and verification of fasteners; If it passes, proceed to step S2; if it fails, correct the fastener and repeat step S1. S2. Determine whether the fastener is in contact with the medium. If so, conduct a medium compatibility test and then a tensile failure hydrogen embrittlement metallographic test. If the test is passed, proceed to step S3. If not, directly conduct a tensile failure hydrogen embrittlement metallographic test. If the test is passed, proceed to step S3. S3. Determine whether the stress of the fastener exceeds 50% of the minimum allowable tensile strength; if yes, conduct a stress comprehensive test, and proceed to step S4 if the test is passed; otherwise, proceed to step S4. S4. Determine whether the fastener is subjected to instantaneous impact load during use. If so, conduct an impact toughness test. If the test is qualified, proceed to step S5. If not, proceed to step S5. S5. Determine whether the operating temperature of the fastener is lower than the low temperature threshold; if so, conduct a low temperature tensile failure test; if the test is passed, proceed to step S6; otherwise, proceed directly to step S6. S6. Determine whether the operating temperature of the fastener is higher than the high temperature threshold; if so, conduct a high temperature tensile failure test and a high temperature locking test; if the test is passed, proceed to step S7; if not, proceed directly to step S7. S7. Determine whether the fastener's operating environment is subjected to large shear loads; if so, conduct a double shear test; if the test is passed, proceed to step S8; if not, proceed directly to step S8. S8. Determine whether the fastener is used in a humid or salt spray environment; if so, conduct a comprehensive corrosion environment test; if the test is passed, proceed to step S9; otherwise, proceed directly to step S9. S9. Determine whether the fastener is required to be stored for more than 10 years after installation; if so, conduct a long-term storage test; if the test is successful, proceed to step S10; if not, proceed directly to step S10. S10. Determine whether the fastener needs to be disassembled and reassembled more than 5 times. If so, conduct a repeated disassembly and reassembly test. If the test is successful, proceed to step S11. If not, proceed directly to step S11. S11. Determine whether the fastener has undergone repeated use. If so, conduct a fatigue test. If the test is passed, the fastener passes system verification. If not, the fastener passes system verification. The general testing and verification of the fasteners specifically includes: S21. Verify the dimensions of the fasteners; if they are qualified, proceed to step S22; if they are not qualified, correct the dimensions of the fasteners and repeat step S21. S22. Conduct surface treatment thickness and bonding force tests on fasteners; If it passes, proceed to step S23; if it fails, correct the thickness of the fastener and repeat step S22. S23. Perform a wedge load test on the fasteners; If it passes, proceed to step S24; if it fails, reduce the load on the fastener or increase the radius of the head before re-entering step S21. S24. Perform a tightening test on the fasteners; If it passes, proceed to step S25; if it fails, modify the fastener's wrench structure dimensions and then re-enter step S21. S25. Perform a hardness test on the fasteners; If it passes the test, proceed to step S26; if it fails the test, modify the heat treatment method or improve the stability of the raw materials, and then re-enter step S23. S26. Conduct vibration tests on the fasteners; If it passes, proceed to step S27; if it fails, modify the self-locking nut closing amount and self-locking torque, and then re-enter step S21. S27. Perform an axial load test on the fasteners; If it passes, proceed to step S28; if it fails, modify the load-bearing structure dimensions of the fastener or improve the stability of the raw material, and then re-enter step S21. S28. Conduct a loosening test on the fasteners; If it passes, proceed to step S29; if it fails, modify the load-bearing structure and dimensions of the support plate nut and then re-enter step S21. S29. Conduct a push-out test on the fastener; If it passes, proceed to step S30; if it fails, modify the load-bearing structure dimensions of the support plate nut and then re-enter step S21. S30. Conduct a permanent deformation test on the fasteners; If it passes the test, the general test is passed; if it fails, the self-locking nut's closing amount or the self-locking torque is modified before re-entering step S21.

2. The fastener system verification method according to claim 1, characterized in that: The stress comprehensive test includes stress corrosion test, stress endurance test, stress relaxation test and stress fracture test.

3. The fastener system verification method according to claim 2, characterized in that: The stress endurance test involves applying 75-83% of the minimum breaking tensile force and maintaining it for at least 24 hours; the fastener should not show cracks or breakage. The stress fracture test involves applying 50-55% of the minimum breaking tensile force, then applying a high temperature of 100-660℃ and maintaining it for at least 25 hours, depending on the material; the fastener should not break. The stress corrosion test involves applying 70-75% of the minimum breaking tensile force and immersing the fastener in a corrosive solution for at least 1000 hours; the fastener should not show cracks when subjected to fluorescent testing. The stress relaxation test involves applying 58-62% of the minimum breaking tensile force, then applying a high temperature of 100-660℃ and maintaining it for at least 200 hours, depending on the material; the axial force of the fastener should not decrease by more than 60%.

4. The fastener system verification method according to claim 1, characterized in that: The high-temperature locking test is conducted by placing the fastener at a temperature of ±5℃ for 6 hours ±15 minutes, cooling it to room temperature, and then performing a self-locking nut locking force test. No additional lubrication is applied during the test.

5. The fastener system verification method according to claim 1, characterized in that: The specific test method for the medium compatibility test is as follows: the fastener is installed on the clamping test piece according to the tightening torque required by the operating conditions, and the fastener and the clamping test piece are immersed together in the corresponding medium. After maintaining for 100-120 hours, they are taken out and after the temperature recovers to 15-30℃, the room temperature tensile failure test, hydrogen embrittlement test and metallographic test are carried out.

6. The fastener system verification method according to claim 1, characterized in that: The tensile fracture hydrogen embrittlement metallographic test is specifically as follows: S71. Conduct a room temperature tensile failure test on the fastener; if it passes, proceed to step S72; if it fails, reduce the load on the fastener, modify the head size, or improve the stability of the fastener raw material before re-entering step S21. S72. Perform a hydrogen embrittlement test on the fasteners for a duration of not less than 200 hours. If the test is successful, proceed to step S73. If the test fails, perform hydrogen removal treatment on the fasteners and then proceed to step S23. S73. Perform metallographic testing on the fasteners; If it is qualified, proceed to step S3; if it is unqualified, after modifying the surface treatment method, heat treatment method or improving the stability of the fastener raw material, re-enter step S21.

7. The fastener system verification method according to claim 1, characterized in that: For the long-term storage test, the test method is as follows: Determine the maintenance time of the fastener in an oxygen-rich humid environment; Install multiple groups of test fasteners and conduct the long-term storage test of the fasteners in an oxygen-rich humid environment at the same time; Take out a group of test fasteners every 2 - 3 days of the test and conduct a vibration test; Continue the test until the test time reaches the maintenance time; If in all vibration tests, the relative rotation of the fastener does not exceed 360°, it is qualified; otherwise, it is unqualified; If it is unqualified, modify the surface treatment method or material type of the fastener and re-enter step S1.

8. The fastener system verification method according to claim 7, characterized in that: For the vibration test, specifically: After installing the fastener, vibrate it cyclically for more than 30,000 times; If the relative rotation of the fastener does not exceed 360° and there is no structural damage, crack, fracture or loss of locking performance, it is qualified; otherwise, it is unqualified.

9. The fastener system verification method according to claim 1, characterized in that: For the impact toughness test, specifically: Conduct the impact toughness test using the Charpy pendulum method. If the impact energy meets the index requirements, it is qualified; otherwise, it is unqualified. Modify the heat treatment method, improve the stability of the fastener raw material or replace the material, and proceed to step S3.

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