Universal titanium alloy self-plugging rivet shearing force detection tool and detection method

Abstract

The invention relates to the technical field of self-plugging rivet detection, in particular to a universal titanium alloy self-plugging rivet shearing force detection tool and method.The tool comprises a fixed shearing block, a movable shearing block, an auxiliary pressing strip and a base, the fixed shearing block is provided with a boss and a sliding groove, and the boss and the sliding groove are correspondingly provided with a plurality of shearing holes and can be matched with rivets of different specifications; according to the detection method, detection is completed through pretreatment, cleaning and lubrication, tool debugging and coaxiality control, graded loading detection, multi-dimensional judgment and reset maintenance. Universal detection of multi-specification rivets is achieved, operation is standard, environment and process interference is effectively reduced, detection precision and efficiency are improved, judgment reliability is guaranteed, and the method is suitable for rivet quality detection in the key field; the objective of the invention is to solve the problems of poor universality, low precision and easy result distortion of an existing detection tool.

Description

Technical Field

[0001] This invention relates to the field of blind rivet testing technology, and in particular to a general-purpose fixture and method for testing the shear force of titanium alloy blind rivets. Background Technology

[0002] Titanium alloy blind rivets, with their superior properties such as high strength, low density, and corrosion resistance, have become core connecting components in key fields such as aerospace, shipbuilding, and high-end equipment assembly. Their shear load-bearing capacity directly determines the overall stability and service safety of the assembled structure. Therefore, shear force testing is a core step in the production inspection and performance verification of this type of rivet. As related equipment iterates towards multiple specifications and high performance, the models, diameters, and interlayer lengths of titanium alloy blind rivets are becoming increasingly diverse, placing core demands on shear force testing technology: "universal applicability, precision and efficiency, and reliable results." Currently, the industry mainly uses specialized tooling in conjunction with mechanical performance testing machines to achieve shear force testing. The core logic is to fix the rivet with the tooling, apply a transverse shear force until the rivet fails, and complete the performance evaluation based on the detected force value and failure state. This technical approach is a key means to ensure rivet quality.

[0003] In actual production inspection and engineering applications, existing titanium alloy blind rivet shear force testing technology has revealed several prominent problems: First, the tooling lacks versatility. Traditional testing tooling is mostly custom-designed for a single specification. Different tooling is required for rivets of different diameters and interlayer lengths, which not only increases the cost of tooling research and development and manufacturing but also leads to frequent tooling changes during the testing process, significantly reducing testing efficiency. Second, the testing accuracy is difficult to guarantee. Due to limitations in the tooling structure design, the coaxiality control accuracy of the shearing holes of the fixed shearing block and the movable shearing block is low. Furthermore, factors such as the frictional resistance between the rivet and the hole wall and the stress deformation of the tooling itself interfere with each other during the shearing process. First, the testing methods are cumbersome, leading to distorted test data that fails to accurately reflect the actual shearing performance of rivets. Second, the testing methods have weak anti-interference capabilities and lack standardized pretreatment procedures. Factors such as improper selection and application of lubricants and fluctuations in ambient temperature can easily cause fluctuations in test results. Furthermore, the judgment process often relies on a single peak shear force index, ignoring key characteristics such as fracture morphology and uniformity of stress, which can easily lead to the omission of hidden non-conforming products that are "qualified in force but have structural damage." Third, the operation and maintenance procedures are cumbersome, the tooling assembly and positioning rely on manual experience, and the post-testing residue cleaning is not thorough, which can easily cause wear on key components such as shearing holes and movable shearing blocks, shortening the service life of the tooling.

[0004] A search revealed a patent with patent number CN201820088774.8, which describes a high-temperature shear test fixture for titanium alloy rivets. The core principle of this fixture is to use nickel-based high-temperature alloy GH4169 to make upper and lower fixtures. The rivets are positioned through the first through hole of the upper fixture shear plate and the second through hole of the lower fixture shear plate, thus achieving shear strength testing under high-temperature conditions. The advantage of this solution is that it has excellent high-temperature strength and stability, and can avoid the interference of fixture deformation on the test results under high temperature. It can truly reflect the high-temperature characteristics of the rivets. However, the disadvantage is that it has extremely poor versatility. It is only designed for high-temperature working conditions and specific rivet models. It cannot be adapted to the room temperature universal testing of titanium alloy blind rivets of different specifications. Furthermore, it does not solve the accuracy-affecting factors such as frictional resistance and coaxiality error. A comprehensive analysis of existing technologies reveals that while specialized tooling can meet the stability requirements of specific testing scenarios, its versatility and accuracy are insufficient. Simple, general-purpose tooling and traditional testing methods, while possessing certain advantages in versatility or low cost, suffer from poor accuracy, weak anti-interference capabilities, and simplistic judgment logic. Neither can simultaneously address the core technical pain points of poor versatility, low testing accuracy, cumbersome operation, and distorted results. Therefore, an integrated technical solution combining a general-purpose tooling structure and a standardized testing process is needed. This solution, achieved by optimizing tooling structure design, standardizing key aspects of the entire testing process, and improving a multi-dimensional judgment system, enables accurate, efficient, and reliable testing of the shear force of titanium alloy blind rivets of different specifications. Summary of the Invention

[0005] This invention provides a universal fixture and method for testing the shear force of titanium alloy blind rivets, which solves the problems of poor universality, low detection accuracy, cumbersome operation, and the fact that the existing fixtures for testing the shear force of titanium alloy blind rivets are easily affected by environmental and process factors, resulting in distorted results. It is also difficult to accurately and efficiently detect the actual shear performance of titanium alloy blind rivets of different specifications and reliably determine their qualification.

[0006] To solve the above problems, the technical solution adopted by the invention is as follows: A general-purpose titanium alloy blind rivet shearing force testing fixture includes a fixed shearing block with multiple bosses and a sliding groove between them. A movable shearing block is positioned within the sliding groove, and the movable shearing block has multiple shearing holes corresponding to those on the fixed shearing block. An auxiliary pressure strip is provided on each boss, which is connected to both the movable and bosses. A base is provided at the bottom of the fixed auxiliary block, and the base is fixedly connected to the fixed auxiliary block.

[0007] A general method for detecting the shear force of titanium alloy blind rivets includes the following steps: (1) Pre-treatment stage: The shearing hole of the testing tool is cleaned and impurities in the hole are removed by high-pressure airflow. Then, nano-level solid lubricant is applied to the spiral lubrication groove on the inner wall of the shearing hole. The lubricant is based on molybdenum disulfide and has graphene reinforcement phase. The coating thickness is 0.5-1μm. At the same time, the shearing area of ​​the titanium alloy core rivet is degreased to remove oxide scale and oil. (2) Tooling debugging stage: According to the specifications of the rivet to be tested, select the corresponding hole diameter for the shearing hole, fix the auxiliary pressure strip and the boss by the tapered positioning pin, adjust the position of the movable shearing block in the slide groove, and control the coaxiality error of the shearing hole of the fixed shearing block and the movable shearing block within 0.02mm. Then install the assembled tooling on the mechanical performance testing machine, start the testing machine for no-load operation, and verify the smooth operation of the tooling. (3) Stage of graded loading test: The pre-treated titanium alloy blind rivet is passed through the corresponding shearing hole. The shearing position of the rivet is adjusted so that the shearing surface and the chamfered arc transition structure of the shearing hole are precisely fitted. Shearing force is applied by graded loading. In the first stage, the load is applied at a rate of 5kN / s to 30% of the rated shearing force and held for 5s. In the second stage, the load is applied at a rate of 2kN / s to 70% of the rated shearing force and held for 8s. In the third stage, the load is applied at a rate of 1kN / s until the rivet is sheared and broken. The shearing force value, displacement change and loading time of each stage are recorded in real time. (4) Multi-dimensional judgment stage: After shear failure, the final peak shear force is first obtained and compared with the standard technical requirements. Then, the morphological characteristics of the rivet shear surface are observed to determine whether there are abnormalities such as brittle fracture or shear surface tilt. At the same time, the stress feedback data of the tooling is used to analyze whether the force is uniform during the test. The rivet is qualified by combining the three dimensions of peak shear force, fracture morphology and uniformity of force. (5) Tooling reset and maintenance stage: After the inspection is completed, disassemble the tooling, remove the lubricant residue and debris in the shearing hole with ultrasonic cleaning equipment, check the wear of key components such as shearing hole and movable shearing block, replace or repair components with wear exceeding 0.03mm, and then apply anti-rust lubricant to the slide and positioning hole to complete the tooling reset and maintenance.

[0008] The principle and advantages of this scheme are as follows: The core principle of this solution is to achieve accurate testing of the shearing force of titanium alloy blind rivets of different specifications through the synergistic cooperation of an integrated, universally designed tooling structure and a standardized testing process. In terms of tooling structure, the fixed shearing block is the core load-bearing component. Multiple bosses on its surface form a stable support structure, and the grooves between the bosses provide precise sliding guidance for the movable shearing block, allowing it to flexibly adjust its position along the grooves. Combined with multiple corresponding shearing holes, it can accommodate titanium alloy blind rivets of different diameters and interlayer lengths without changing the tooling. The auxiliary pressure strip on the boss, through its dual cooperation with the movable shearing block and the bosses, ensures the stable positioning of the movable shearing block, preventing displacement deviation during shearing. The fixed connection between the bottom base and the fixed shearing block provides reliable support for the entire tooling system, ensuring structural stability during the testing process. In terms of the testing process, the pretreatment stage involves cleaning, lubrication, and rivet surface treatment to eliminate the interference of impurities and oil stains on the test results; the tooling debugging stage uses tapered positioning pins and precise coaxiality adjustment to ensure that the direction of shear force is perpendicular to the rivet axis; the graded loading stage uses differentiated rate loading and precise fit with the shear position to simulate the actual stress process of the rivet; and the multi-dimensional judgment stage comprehensively considers the force value, morphology, and stress uniformity indicators to achieve accurate qualification judgment.

[0009] Compared to existing technologies, which often rely on specialized tooling suitable only for rivets of specific specifications or working conditions, and have limited applicability with simple, universal tooling, this solution utilizes a structural design of "multiple shearing holes + adjustable sliding grooves for movable shearing blocks." This allows for the inspection of titanium alloy blind rivets of various diameters and interlayer lengths without the need for tooling changes, significantly reducing tooling manufacturing and inventory costs. Inspection efficiency is also improved compared to traditional tooling, resolving the issues of existing tooling requiring a single tool for each rivet or having a narrow applicability range. Furthermore, inspection accuracy is significantly enhanced. Existing technologies generally suffer from insufficient coaxiality control and significant frictional interference, leading to distorted inspection data. This solution addresses these issues through precise coordination between the fixed and movable shearing blocks, combined with the adjustment process during the tooling debugging phase. Axial error control ensures precise shear force transmission. Simultaneously, the application of nano-level lubricant during pretreatment and the chamfered rounded transition structure of the shear hole effectively reduce frictional resistance and stress concentration, minimizing detection errors compared to existing technologies and providing accurate feedback on the actual shearing performance of the rivet. Thirdly, operational standardization and result reliability are significantly enhanced. Existing technologies rely on manual experience and judgments are often based on a single force value, leading to misjudgments and omissions. This solution establishes a standardized process from pretreatment, debugging, loading to judgment and maintenance, with clearly defined operational requirements for each step. A multi-dimensional judgment system comprehensively considers peak force value, fracture morphology, and stress uniformity, avoiding the omission of hidden defects such as qualified force values ​​but structural damage.

[0010] Furthermore, a groove is provided on the side of the fixed shear block away from the movable shear block. The bottom and all four sides of the groove are rounded. The groove extends along the length of the fixed shear block, and its length is 1 / 2 to 2 / 3 of the length of the fixed shear block. The groove wall is coated with a nano-titanium nitride coating with a thickness of 3-8 μm. The groove corresponds to the movable shear block. The thickness of the movable shear block is 2-5 mm greater than the depth of the groove, and the shearing contact surface of the movable shear block has a gradient hardness structure. The hardness is HRC58-62 within 3 mm from the surface of the contact surface, and the hardness of the inner layer is HRC45-50. The rounded groove on the side of the fixed shear block away from the movable shear block has a length controlled to 1 / 2 to 2 / 3 of the length of the fixed shear block and corresponds to the movable shear block. This not only provides reasonable accommodation space for the rivet during the shearing process, avoiding interference with the tooling, but also disperses stress concentration through the rounded corner structure, reducing the tooling's high-frequency stress. The fatigue damage detected during the test is mitigated by the 3-8μm thick nano-titanium nitride coating on the groove wall, which, with its high hardness and wear resistance, effectively resists frictional wear between the rivet and the groove wall, significantly extending the service life of the fixed shearing block. The design of the movable shearing block being 2-5mm thicker than the groove depth ensures full contact between the shearing surface and the rivet, avoiding insufficient shearing force transmission. The shearing contact surface adopts a gradient hardness structure, with the outer 3mm layer at HRC58-62 and the inner layer at HRC45-50. The high hardness of the outer layer ensures wear resistance during the shearing process, while the moderate hardness of the inner layer maintains the impact toughness of the movable shearing block. This avoids the drawbacks of a single hardness design where wear resistance leads to easy cracking or good toughness leads to easy wear. The synergistic effect of the two improves the structural stability, wear resistance, durability, and accuracy of shearing force transmission of the tooling, further ensuring the accuracy and reliability of shearing force testing for titanium alloy blind rivets of different specifications, extending the overall service life of the tooling and reducing maintenance costs.

[0011] Furthermore, the shearing holes on both the fixed and movable shearing blocks are stepped holes arranged vertically along their length, comprising four shearing holes with different diameters ranging from 3-12 mm, with a difference of 2-3 mm between adjacent holes. Each shearing hole has a 15°-20° chamfered inlet on its wall, and a lubrication groove is provided on the inner wall of the shearing hole. This lubrication groove is spirally distributed with a pitch of 5-8 mm. The four stepped holes on the fixed and movable shearing blocks, arranged vertically along their length, with diameters of 3-12 mm and a difference of 2-3 mm between adjacent holes, allow for precise fitting of various sizes of titanium alloy blind rivets within this diameter range without changing the tooling, significantly improving the tooling efficiency. Its versatility effectively reduces the time and cost losses caused by frequent tooling changes; the 15°-20° chamfer on the wall of each shearing hole guides the rivet to be quickly and smoothly inserted, avoiding scratches on the rivet surface during installation, while ensuring precise contact between the shearing surface and the hole wall; the spiral-shaped lubrication grooves with a pitch of 5-8mm on the inner wall can uniformly store nano-level solid lubricant, continuously providing lubrication between the rivet and the hole wall during shearing, reducing the interference of frictional resistance on the detection accuracy. It not only achieves efficient adaptation and installation of rivets of different specifications, but also further improves the accuracy and repeatability of shearing force detection through lubrication optimization and installation guidance, while reducing mutual wear between the rivet and the shearing hole.

[0012] Furthermore, the shearing hole is set within the groove, and the coaxiality error between the shearing hole on the fixed shearing block and the movable shearing block does not exceed 0.02mm. The chamfer of the shearing hole has a rounded transition structure with a radius of 0.3-0.5mm. By setting the shearing hole within the groove and strictly controlling the coaxiality error between the shearing hole on the fixed and movable shearing blocks to not exceed 0.02mm, the shearing force can be accurately applied perpendicularly to the rivet axis, avoiding shearing force deviation due to coaxiality discrepancies. This eliminates data distortion and makes the test results more accurate. The shearing performance of the rivet under actual operating conditions is assessed. The 0.3-0.5mm radius circular arc transition structure at the chamfer of the shearing hole effectively disperses stress concentration at the chamfer during rivet shearing, preventing premature or unexpected fracture due to excessive local stress. This ensures the integrity of the inspection process and the authenticity of the inspection results. At the same time, the circular arc structure reduces frictional loss between the rivet and the chamfer of the hole wall. Combined with the containment and protection function of the groove, it further improves the stability of inspection accuracy and the contact compatibility between the tooling and the rivet, extending the service life of the tooling.

[0013] Furthermore, the boss is provided with a positioning hole and a connecting hole. The positioning hole extends through the auxiliary pressure strip and the boss to one side of the fixed shear block. A tapered positioning pin is provided in the positioning hole, with a taper of 1:50-1:100. An internal hexagon bolt is provided in the connecting hole on one side of the positioning hole. Utilizing the self-centering characteristic of the tapered structure, the positioning of the auxiliary pressure strip, the boss, and the fixed shear block can be quickly achieved, effectively offsetting minor deviations during assembly and ensuring that the pressing position of the auxiliary pressure strip on the movable shear block is accurate and consistent, avoiding uneven force on the movable shear block due to positioning deviation. The internal hexagon bolt in the connecting hole on one side of the positioning hole can securely connect the auxiliary pressure strip and the boss through a locking action, further locking the positioning accuracy and preventing loosening or displacement due to vibration, force, or other factors during shearing detection. The two work together to ensure the convenience and positioning accuracy of the tooling assembly, and improve the structural stability of the entire tooling during shearing force detection. This provides a reliable guarantee for the accurate maintenance of the coaxiality of the shearing hole and the uniform transmission of shearing force, thereby ensuring the accuracy and repeatability of the test results.

[0014] Furthermore, the fixed shearing block and the boss are forged as a single unit. A stress relief groove with a depth of 5-8mm and a width of 3-5mm is provided at the bottom of the boss near the base. The forging of the fixed shearing block and the boss as a single unit can completely eliminate the gaps and stress concentration hazards that may exist in the separate connection, improve the connection strength and overall structural rigidity, and ensure that there is no relative displacement or deformation during the transmission of shearing force, thus providing a structural basis for detection accuracy. The stress relief groove with a depth of 5-8mm and a width of 3-5mm provided at the bottom of the boss near the base can effectively disperse the stress accumulation at the root of the boss caused by the force during the shearing test, and avoid fatigue damage such as cracking and deformation of the boss after long-term high-frequency testing.

[0015] In step (3), a shear force-temperature coupling compensation algorithm is introduced to correct the mechanical property fluctuation error caused by temperature changes during the shearing process of the titanium alloy core-pulling rivet in real time. The algorithm formula is as follows: ,in, This is the actual shear force value after temperature compensation; The real-time shear force value obtained through step (3) graded loading; The temperature sensitivity coefficient of titanium alloys was calibrated through testing with standard samples under more than 5 different temperature environments (20℃-80℃), with the value range being... ; The real-time temperature of the rivet shearing area during the shearing process is collected in real time by an infrared temperature sensor with a measurement accuracy of ±0.5℃. The standard testing temperature specified in the technical requirements is 25℃ by default; The temperature influence correction coefficient is dynamically adjusted according to the rivet diameter, with a larger value for larger diameters, ranging from 0.8 to 1.2. The shear force-temperature coupling compensation algorithm introduced in step (3) uses an infrared temperature sensor to collect the rivet shear area temperature in real time with a high precision of ±0.5℃. Combined with the titanium alloy temperature sensitivity coefficient calibrated by more than 5 sets of standard samples of different temperature environments from 20℃ to 80℃, and the temperature influence correction coefficient dynamically adjusted according to the rivet diameter (with a larger value for larger diameters, ranging from 0.8 to 1.2), the real-time shear force value obtained by graded loading is corrected in real time, which can accurately correct the temperature influence. This method compensates for the mechanical property fluctuations of titanium alloy blind rivets caused by temperature changes during shearing. It solves the problem of detection errors caused by traditional testing methods that ignore temperature factors and rely solely on room temperature or static data. Furthermore, by dynamically adapting to different temperature conditions and rivet specifications, the compensated true shear force value more closely matches the actual shearing performance of the rivet. This significantly improves the consistency and accuracy of test results under different ambient temperatures, avoiding misjudgments of pass / fail due to temperature fluctuations. It is especially suitable for production testing scenarios with unstable ambient temperatures, providing a more reliable technical guarantee for the shear force testing of titanium alloy blind rivets.

[0016] Furthermore, in step (4), a shear plane grain deformation analysis index is added. Combined with the acquisition of shear plane grain morphology images by electron microscopy, the deformation uniformity is calculated using the grain deformation quantification formula, as follows: in: This is the grain deformation uniformity coefficient, with a value ranging from 0 to 1. The closer it is to 1, the more uniform the deformation. The number of grains counted shall not be less than 50; The equivalent diameter of a single grain after deformation; To calculate the average equivalent diameter of the grains after deformation; this coefficient... Incorporating it into the qualification assessment system, it forms a four-dimensional assessment standard together with peak shear force, fracture morphology, and uniformity of stress. Only when all other indicators meet the requirements can it be judged as qualified. In step (4), the analysis index of shear plane grain deformation is added. The grain morphology image of the shear plane is collected by electron microscope. Based on the statistical grain number of no less than 50 grains, the deformation uniformity coefficient (value 0-1, the closer to 1, the more uniform the deformation) is calculated using the grain deformation quantification formula. This coefficient, together with the peak shear force, fracture morphology, and stress uniformity, constitutes a four-dimensional judgment standard. It is only judged as qualified when the coefficient is ≥0.85 and all other indicators meet the standard. This breaks through the traditional detection that only relies on macroscopic indicators. Overcoming the limitations of the target, this approach delves into the essential characteristics of rivet shearing performance at the microstructural level. It can accurately identify hidden defects in products that meet macroscopic force requirements but exhibit uneven microscopic grain deformation. Furthermore, the quantified grain deformation uniformity coefficient eliminates subjective errors in macroscopic morphology observation, making the judgment criteria more scientific and objective. At the same time, the four-dimensional collaborative judgment system significantly improves the accuracy and reliability of conformity assessment, effectively reducing the risk of missing defective products. This provides more stringent and comprehensive quality assurance for the safe application of titanium alloy blind rivets in key fields such as aerospace and shipbuilding.

[0017] Furthermore, in step (2), a tooling stress simulation and pre-analysis algorithm is used to predict the stress distribution of the tooling during the loading process based on the finite element analysis principle, and to optimize the installation position in advance. The core formula of the algorithm is as follows: in: The predicted stress value is given at any spatial coordinate (x, y, z) of the tooling. The preload force is set at 10% of the rated shear force. The distance from the loading point to the tooling support point; This is the stress amplification factor of the tooling structure, determined according to the connection method between the base and the shear block, and its value is 1.1-1.3; The elastic modulus of the tooling material; The moment of inertia of the cross section at this coordinate is given. Based on the predicted stress distribution, the installation angle of the fixture on the mechanical performance testing machine is adjusted. This allows for the early identification of stress concentration areas and potential uneven stress distribution caused by installation deviations. The installation angle of the fixture on the mechanical performance testing machine is then adjusted accordingly, effectively reducing the maximum stress value of the fixture and preventing fatigue damage such as deformation and cracking caused by stress concentration during long-term testing, thus extending the service life of the fixture. Furthermore, optimizing the installation position ensures overall stress balance of the fixture, providing a preliminary guarantee for maintaining the coaxiality of the shear holes of the fixed and movable shear blocks and for the accurate transmission of shear force. This reduces testing errors from the source of fixture installation and further improves the accuracy and repeatability of the shear force test results for titanium alloy blind rivets. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] Figure 2 This is a three-dimensional structural diagram of the present invention.

[0020] The reference numerals in the accompanying drawings include: base 1, fixed shear block 2, groove 3, shear hole 4, pop rivet 5, chamfer 6, movable shear block 7, auxiliary pressure strip 8, positioning pin 9, positioning hole 10, hex bolt 11, boss 12, stress relief groove 13, nano titanium nitride coating 14, lubrication groove 15, and slide groove 16. Detailed Implementation

[0021] Example 1 As attached Figure 1-2 As shown, the general-purpose titanium alloy blind rivet shear force testing fixture includes a base 1, and a fixed shear block 2 is fixedly connected above the base 1. The fixed shear block 2 and the base 1 are fixed by welding to ensure connection strength and structural stability, which can effectively avoid relative displacement caused by vibration or force during the testing process.

[0022] The fixed shear block 2 has two symmetrically distributed bosses 12 integrally forged. The bosses 12 are arranged along the length of the fixed shear block 2, and a groove 16 is formed between the two bosses 12. The width of the groove 16 is adapted to the width of the movable shear block 7. The movable shear block 7 is installed in the groove 16 and can slide and adjust its position along the length of the groove 16. The fixed shear block 2 and the bosses 12 adopt an integral forging structure, which completely eliminates the gaps and stress concentration hazards that may exist in the split connection, improves the connection strength and overall structural rigidity, and ensures that there is no relative displacement or deformation during the transmission of shear force.

[0023] A stress relief groove 13 is provided at the bottom position of the boss 12 near the base 1. The depth of the stress relief groove 13 is set to 6mm and the width is set to 4mm. It can effectively disperse the stress accumulation at the root of the boss 12 due to the force during the shearing test, and avoid fatigue damage such as cracking and deformation of the boss 12 after long-term high-frequency testing.

[0024] A groove 3 is formed on the side of the fixed shear block 2 away from the movable shear block 7. The groove 3 extends along the length of the fixed shear block 2, and its length is 2 / 3 of the length of the fixed shear block 2. The bottom and all sides of the groove 3 are rounded with a radius of 3mm. This not only provides reasonable space for the blind rivet 5 during the shearing process, avoiding interference with the tooling, but also disperses stress concentration through the rounded corner structure, reducing fatigue damage to the tooling during high-frequency testing. The groove wall of the groove 3 is coated with a nano-titanium nitride coating 14. The thickness of the nano-titanium nitride coating 14 is controlled to be 5μm. With its high hardness and high wear resistance, it effectively resists the frictional wear between the blind rivet 5 and the groove wall, significantly extending the service life of the fixed shear block 2.

[0025] The thickness of the movable shear block 7 is 3mm greater than the depth of the groove 16. This design ensures full contact between the shearing surface and the pop rivet 5, preventing insufficient shearing force transmission. The shearing contact surface of the movable shear block 7 adopts a gradient hardness structure. The hardness is HRC60 within 3mm from the surface of the contact surface, and HRC48 in the inner layer. This ensures wear resistance during the shearing process through the high hardness of the surface layer, while maintaining the impact toughness of the movable shear block 7 through the moderate hardness of the inner layer. This avoids the drawbacks of a single hardness design where wear resistance leads to easy cracking or good toughness leads to easy wear.

[0026] The fixed shearing block 2 and the movable shearing block 7 are equipped with multiple shearing holes 4, all of which are stepped holes arranged vertically along the length direction. There are four different diameter shearing holes 4: 3mm, 5mm, 8mm, and 11mm, with a difference of 2-3mm between adjacent diameters. This allows for precise fitting of various specifications of titanium alloy blind rivets 5 within this diameter range without changing the tooling, significantly improving the tooling's versatility. Each shearing hole 4 has an 18° guide chamfer 6 on its wall, guiding the blind rivet 5 to be inserted quickly and smoothly, preventing scratches on the surface of the blind rivet 5 during installation, and ensuring precise contact between the shearing surface and the hole wall. The inner wall of the shearing hole 4 has a lubrication groove 15, which is spirally distributed with a pitch of 6mm. This groove can uniformly store nano-level solid lubricant, continuously providing lubrication between the blind rivet 5 and the hole wall during shearing, reducing frictional resistance and minimizing interference with detection accuracy.

[0027] The shearing hole 4 is located within the groove 3. The coaxiality error of the shearing hole 4 on the fixed shearing block 2 and the movable shearing block 7 is strictly controlled within 0.02mm. This ensures that the shearing force is accurately applied perpendicularly to the axis of the blind rivet 5, avoiding shearing force deviation due to coaxiality deviation, and thus preventing data distortion. The chamfer 6 of the shearing hole 4 is provided with an arc transition structure with a radius of 0.4mm. This effectively disperses the stress concentration at the chamfer 6 during the shearing process of the blind rivet 5, preventing premature breakage or unexpected fracture due to excessive local stress, thus ensuring the integrity of the testing process and the authenticity of the test results.

[0028] The boss 12 has a positioning hole 10 and a connecting hole. The positioning hole 10 passes through the auxiliary pressure strip 8, the boss 12, and extends to one side of the fixed shear block 2. A tapered positioning pin 9 is installed in the positioning hole 10. The tapered positioning pin 9 has a taper of 1:80. Utilizing the self-centering characteristic of the tapered structure, the positioning of the auxiliary pressure strip 8, the boss 12, and the fixed shear block 2 can be quickly achieved, effectively offsetting minor deviations during assembly and ensuring that the pressing position of the auxiliary pressure strip 8 on the movable shear block 7 is accurate and consistent. An internal hex bolt 11 is installed in the connecting hole on one side of the positioning hole 10. Through locking action, the auxiliary pressure strip 8 and the boss 12 are firmly connected, further locking the positioning accuracy and preventing loosening or displacement due to vibration, force, or other factors during the shearing test.

[0029] The testing method for the above-mentioned general-purpose titanium alloy blind rivet shear force testing fixture includes the following steps: (1) Pretreatment stage: The shearing hole 4 of the testing fixture is cleaned by using a high-pressure airflow of 0.6 MPa to remove impurities from the hole, ensuring that there are no residual debris on the inner wall of the shearing hole 4. Then, a nano-level solid lubricant is applied to the spiral lubrication groove 15 on the inner wall of the shearing hole 4. This lubricant is based on molybdenum disulfide and reinforced with graphene. The coating thickness is controlled at 0.8 μm, which can effectively reduce the frictional resistance between the blind rivet 5 and the inner wall of the shearing hole 4. At the same time, the shearing area of ​​the titanium alloy blind rivet 5 is degreased by soaking in an alkaline degreaser for 5 minutes, then rinsing it with clean water and drying it to thoroughly remove oxide scale and oil stains, so as to avoid impurities affecting the test results.

[0030] (2) Tooling debugging stage: Select the corresponding shearing hole 4 according to the specifications of the titanium alloy blind rivet 5 to be tested. Fix the auxiliary pressure strip 8 and the boss 12 by taper positioning pin 9, adjust the position of the movable shearing block 7 in the slide groove 16, and use a dial indicator to check the coaxiality of the shearing hole 4 on the fixed shearing block 2 and the movable shearing block 7 to ensure that the coaxiality error is controlled within 0.02mm. Then install the assembled tooling on the mechanical performance testing machine, start the testing machine for no-load operation, and run for 3 minutes to verify the smooth operation of the tooling and ensure that the movable shearing block 7 slides flexibly without jamming.

[0031] This step employs a tooling stress simulation algorithm, which predicts the stress distribution of the tooling during loading based on the finite element analysis principle, and optimizes the installation position in advance. The core formula of the algorithm is as follows: ,in: For arbitrary spatial coordinates of the tooling Predicted stress value at the location; The preload force is set at 10% of the rated shear force. The distance from the loading point to the tooling support point; The stress amplification factor of the tooling structure is determined based on the welding connection method between the base 1 and the fixed shear block 2, and is set to 1.2; E is the elastic modulus of the tooling material. In this embodiment, the tooling is made of 45# steel, and the elastic modulus is... ; The moment of inertia of the cross section at this coordinate is given. Based on the predicted stress distribution, the installation angle of the tooling on the mechanical performance testing machine is adjusted to effectively reduce the maximum stress value of the tooling and avoid tooling deformation caused by stress concentration.

[0032] (3) Graded loading and testing stage: The pre-treated titanium alloy blind rivet 5 is passed through the corresponding shearing hole 4, and the shearing position of the blind rivet 5 is adjusted so that the shearing surface and the chamfered arc transition structure of the shearing hole 4 are precisely fitted. Shearing force is applied by graded loading, with the first stage using... The rate at which the rated shear force is applied Hold for 5 seconds to allow the pop rivet 5 to gradually adapt to the stress state; the second stage is... The rate at which the rated shear force is applied ,Keep Stable stress transmission; the third stage is based on The load was applied at a rate until the core-pulling rivet 5 sheared and failed. The shear force, displacement change and loading time at each stage were recorded in real time by the sensors of the mechanical property testing machine. The sampling frequency was 100Hz to ensure the continuity and accuracy of data acquisition.

[0033] This step introduces a shear force-temperature coupling compensation algorithm to correct the mechanical property fluctuation error caused by temperature changes during the shearing process of the titanium alloy blind rivet 5 in real time. The algorithm formula is as follows: ,in, This is the actual shear force value after temperature compensation; The values ​​represent the real-time shear force obtained through graded loading. The temperature sensitivity coefficient of the titanium alloy was calibrated through testing with standard samples under six different temperature environments (20℃, 30℃, 40℃, 50℃, 60℃, and 80℃), and the value was taken as ℃. The real-time temperature of the shearing area of ​​the core-pulling rivet 5 during the shearing process was acquired in real time by an infrared temperature sensor, with a temperature measurement accuracy of [missing information]. The standard is the standard testing temperature specified in the technical requirements, with a default value of 25℃. The temperature-affected correction factor is dynamically adjusted based on the rivet diameter; the larger the diameter, the larger the value. In this embodiment, the rivet diameter is 3-5mm. 8mm diameter rivets 11mm diameter rivet .

[0034] (4) Multi-dimensional judgment stage: After shear failure, the final shear force peak value is first extracted from the data collected by the mechanical property testing machine and compared with the standard technical requirements of the titanium alloy blind rivet 5. If the peak value is lower than the standard value, it is directly judged as unqualified. Secondly, the morphological characteristics of the shear surface of the blind rivet 5 are observed by stereomicroscope to determine whether there are abnormalities such as brittle fracture or shear surface tilt. If obvious brittle fracture lines appear or the shear surface tilt angle exceeds 3°, it is judged as unqualified. At the same time, the stress feedback data during the detection process is collected by the stress sensor built into the tooling to analyze whether the stress is uniform. If the stress fluctuation amplitude exceeds ±5%, it is judged as unqualified.

[0035] This step adds a shear plane grain deformation analysis index. Using an electron microscope to acquire grain morphology images of the shear plane at 500x magnification, the deformation uniformity is calculated using a grain deformation quantification formula, as follows: in: This is the grain deformation uniformity coefficient, with a value ranging from 0 to 1. The closer it is to 1, the more uniform the deformation. To count the number of grains, in this embodiment... ; The equivalent diameter of a single grain after deformation; To statistically determine the average equivalent diameter of grains after deformation, this coefficient D is incorporated into the qualification assessment system, forming a four-dimensional assessment standard together with shear force peak value, fracture morphology, and stress uniformity. Only when all other indicators meet the requirements can it be judged as qualified.

[0036] (5) Fixture Reset and Maintenance Stage: After the inspection is completed, disassemble the fixture and place it in an ultrasonic cleaning device. Use a neutral cleaning solution with a cleaning power of 300W for 10 minutes to remove lubricant residue and debris from the shearing hole 4. Check the wear of key components such as the shearing hole 4 and the movable shearing block 7 with a micrometer. Replace or repair any components with wear exceeding 0.03mm. Then apply rust-preventive lubricant to the slide groove 16 and the positioning hole 10, applying enough to cover the surface. After reassembling and resetting the fixture, store it in a dry and ventilated warehouse to prevent moisture and rust, thus extending the service life of the fixture.

Claims

1. A general-purpose fixture for testing the shear force of titanium alloy blind rivets, characterized in that, The device includes a fixed shearing block with multiple protrusions and a sliding groove between them. A movable shearing block is positioned within the sliding groove, and the movable shearing block and the fixed shearing block have corresponding shearing holes. An auxiliary pressure strip is provided on each protrusion and is connected to both the movable and protrusions. A base is provided at the bottom of the fixed auxiliary block and is fixedly connected to it.

2. The universal titanium alloy blind rivet shear force testing fixture according to claim 1, characterized in that, A groove is provided on the side of the fixed shear block away from the movable shear block. The bottom and all four sides of the groove are rounded. The groove extends along the length of the fixed shear block, and its length is 1 / 2 to 2 / 3 of the length of the fixed shear block. The groove wall is coated with a nano-titanium nitride coating with a thickness of 3-8 μm. The groove is provided corresponding to the movable shear block. The thickness of the movable shear block is 2-5 mm greater than the depth of the groove. The shearing contact surface of the movable shear block is provided with a gradient hardness structure. The hardness is HRC58-62 within 3 mm from the surface of the contact surface, and the hardness of the inner layer is HRC45-50.

3. The universal titanium alloy blind rivet shear force testing fixture according to claim 1, characterized in that, Both the fixed shear block and the movable shear block have stepped hole structures, arranged vertically along the length direction, including 4 shear holes with different diameters, ranging from 3 to 12 mm, with a difference of 2 to 3 mm between adjacent holes. Each shear hole has a 15°-20° chamfer on its wall and a lubrication groove on its inner wall, which is spirally distributed with a pitch of 5 to 8 mm.

4. The universal titanium alloy blind rivet shear force testing fixture according to claim 1, characterized in that, The shearing hole is set in the groove, and the coaxiality error of the shearing hole on the fixed shearing block and the movable shearing block does not exceed 0.02mm. The chamfer of the shearing hole is provided with an arc transition structure with an arc radius of 0.3-0.5mm.

5. The universal titanium alloy blind rivet shear force testing fixture according to claim 1, characterized in that, The boss is provided with a positioning hole and a connecting hole. The positioning hole passes through the auxiliary pressure strip and the boss to one side of the fixed shear block. A tapered positioning pin is provided in the positioning hole. The tapered positioning pin has a taper of 1:50-1:

100. An internal hex bolt is provided in the connecting hole on one side of the positioning hole.

6. The universal titanium alloy blind rivet shear force testing fixture according to claim 1, characterized in that, The fixed shearing block and the boss are forged as an integral structure. The side of the boss is provided with a stress relief groove with a depth of 5-8mm and a width of 3-5mm.

7. A general method for detecting the shear force of titanium alloy blind rivets, characterized in that, The general-purpose titanium alloy blind rivet shear force testing fixture according to any one of claims 1-6 includes the following steps: (1) Pre-treatment stage: The shearing hole of the testing tool is cleaned and impurities in the hole are removed by high-pressure airflow. Then, nano-level solid lubricant is applied to the spiral lubrication groove on the inner wall of the shearing hole. The lubricant is based on molybdenum disulfide and has graphene reinforcement phase. The coating thickness is 0.5-1μm. At the same time, the shearing area of ​​the titanium alloy core rivet is degreased to remove oxide scale and oil stains. (2) Tooling debugging stage: According to the specifications of the rivet to be tested, select the corresponding hole diameter for the shearing hole, fix the auxiliary pressure strip and the boss by the tapered positioning pin, adjust the position of the movable shearing block in the slide groove, and control the coaxiality error of the shearing hole of the fixed shearing block and the movable shearing block within 0.02mm. Then install the assembled tooling on the mechanical performance testing machine, start the testing machine for no-load operation, and verify the smooth operation of the tooling. (3) Stage of graded loading test: The pre-treated titanium alloy blind rivet is passed through the corresponding shearing hole. The shearing position of the rivet is adjusted so that the shearing surface and the chamfered arc transition structure of the shearing hole are precisely fitted. Shearing force is applied by graded loading. In the first stage, the load is applied at a rate of 5kN / s to 30% of the rated shearing force and held for 5s. In the second stage, the load is applied at a rate of 2kN / s to 70% of the rated shearing force and held for 8s. In the third stage, the load is applied at a rate of 1kN / s until the rivet is sheared and broken. The shearing force value, displacement change and loading time of each stage are recorded in real time. (4) Multi-dimensional judgment stage: After shear failure, the final peak shear force is first obtained and compared with the standard technical requirements. Then, the morphological characteristics of the rivet shear surface are observed to determine whether there are abnormalities such as brittle fracture or shear surface tilt. At the same time, the stress feedback data of the tooling is used to analyze whether the force is uniform during the test. The rivet is qualified by combining the three dimensions of peak shear force, fracture morphology and uniformity of force. (5) Tooling reset and maintenance stage: After the inspection is completed, disassemble the tooling, remove the lubricant residue and debris in the shearing hole with ultrasonic cleaning equipment, check the wear of key components such as shearing hole and movable shearing block, replace or repair components with wear exceeding 0.03mm, and then apply anti-rust lubricant to the slide and positioning hole to complete the tooling reset and maintenance.

8. The method for detecting the shear force of a general-purpose titanium alloy blind rivet according to claim 7, characterized in that, In step (3), a shear force-temperature coupling compensation algorithm is introduced to correct the mechanical property fluctuation error caused by temperature changes during the shearing process of the titanium alloy core-pulling rivet in real time. The algorithm formula is as follows: ,in, This is the actual shear force value after temperature compensation; The real-time shear force value obtained through step (3) graded loading; The temperature sensitivity coefficient of titanium alloys was calibrated through testing with standard samples under more than 5 different temperature environments (20℃-80℃), with the value range being... ; The real-time temperature of the rivet shearing area during the shearing process is collected in real time by an infrared temperature sensor with a measurement accuracy of ±0.5℃. The standard testing temperature specified in the technical requirements is 25℃ by default; This is a temperature-affected correction factor, dynamically adjusted according to the rivet diameter. The larger the diameter, the larger the value, ranging from 0.8 to 1.

2.

9. A general-purpose method for detecting the shear force of titanium alloy blind rivets according to claim 7, characterized in that, In step (4), a shear plane grain deformation analysis index is added. Combined with the acquisition of shear plane grain morphology images by electron microscope, the deformation uniformity is calculated by the grain deformation quantification formula as follows: in: This is the grain deformation uniformity coefficient, with a value ranging from 0 to 1. The closer it is to 1, the more uniform the deformation. The number of grains counted shall not be less than 50; The equivalent diameter of a single grain after deformation; To calculate the average equivalent diameter of the grains after deformation; this coefficient... Incorporating it into the qualification assessment system, it forms a four-dimensional assessment standard together with peak shear force, fracture morphology, and uniformity of stress. Only when all other indicators meet the requirements can it be judged as qualified.

10. A general-purpose method for detecting the shear force of a titanium alloy blind rivet according to claim 9, characterized in that, In step (2), a tooling stress simulation and pre-analysis algorithm is used to predict the stress distribution of the tooling during the loading process based on the finite element analysis principle, and to optimize the installation position in advance. The core formula of the algorithm is as follows: in: For arbitrary spatial coordinates of the tooling Predicted stress value at the location; The preload force is set at 10% of the rated shear force. The distance from the loading point to the tooling support point; This is the stress amplification factor of the tooling structure, determined according to the connection method between the base and the shear block, and its value is 1.1-1.3; The elastic modulus of the tooling material; The moment of inertia of the cross section at that coordinate is given; the installation angle of the tooling on the mechanical property testing machine is adjusted according to the predicted stress distribution.

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