A fastener loosening test device

Abstract

The application discloses a fastener loosening test device, and relates to the technical field of fastener testing, which comprises a support and a swing arm. The support is used for supporting the swing arm, and the support is fixed to a vibration test table. The vibration test table is used for applying a transverse vibration load to the support and the swing arm. One end of the swing arm is connected to the support through a connecting piece and a fastener, and the other end is connected with a counterweight, so that the swing arm and the support are in contact in a sliding friction mode, and the swing arm is used for swinging relative to the support around the axis of the connecting piece when the transverse vibration load applied by the vibration test table reaches a critical value. The fastener loosening test device solves the problem that the existing fastener loosening test device cannot carry out the anti-loosening performance test with the bolt pretightening force as a variable.

Description

Technical Field

[0001] This application relates to the field of fastener testing technology, and in particular to a fastener loosening test device. Background Technology

[0002] Currently, bolted connections are widely used in rail transit, aerospace, and mechanical equipment due to their high reliability and ease of disassembly. Under static loads, bolted connections rely on frictional self-locking to maintain stability; however, under dynamic loads (especially lateral alternating loads), the sliding displacement between the connected parts overcomes frictional resistance, leading to a decrease in bolt preload or even complete loosening. Statistics show that bolt loosening failure is one of the main types of fastener failures in rail transit vehicles, becoming a core risk source threatening structural safety.

[0003] In existing systems, bolt loosening tests mainly rely on lateral loads to simulate working conditions, as represented by GB / T10431 and GJB715.3A, but both have significant drawbacks:

[0004] The inherent limitation of the GB / T10431 method is that, to promote lateral displacement, it adds rolling bearings to the connection interface, converting sliding friction into near-zero friction coefficient rolling friction. While this improves displacement sensitivity, it completely eliminates the influence mechanism of bolt preload on anti-loosening performance (such as the friction locking effect), making it unsuitable for effectively assessing the role of axial preload. Therefore, this method is only suitable for evaluating the performance of additional components such as washers and locking plates, and cannot reflect the overall anti-loosening capability of the fastening system.

[0005] The applicability of the GJB715.3A method is insufficient: While this method uses impact loading and retains the effect of preload, its load characteristics do not match the continuous vibration loads in fields such as rail transit and wind power. Furthermore, limited by the marking line comparison method, it cannot quantify the preload attenuation value, only qualitatively determining the loosening state. In addition, the testing accuracy of this method drops sharply for large-diameter bolts (M20 and above), limiting its engineering applicability.

[0006] Therefore, how to avoid the inability of existing fastener loosening test devices to conduct anti-loosening performance tests with bolt preload as a variable is a technical problem that needs to be solved by those skilled in the art. Utility Model Content

[0007] The purpose of this application is to provide a fastener loosening test device that solves the problem that existing fastener loosening test devices cannot conduct anti-loosening performance tests with bolt preload as a variable.

[0008] To achieve the above objectives, this application provides a fastener loosening test apparatus, comprising:

[0009] Supports are used to fix the test bench to which lateral vibration loads are applied.

[0010] The swing arm is connected to the support at one end by a connector and fasteners, and a counterweight is connected to the other end, so that the swing arm and the support are in contact by sliding friction. The swing arm is used to swing relative to the support about the axis of the connector when the transverse vibration load applied by the vibration test bench reaches the critical value.

[0011] In some embodiments, the support is provided with a first groove, and the swing arm is provided with a second groove on the side near the support. Both the first groove and the second groove are fitted with first pads, and a pad with double-sided lubricant is provided between the two first pads. The two first pads are in contact with the pad in a sliding friction manner.

[0012] In some embodiments, a third groove is provided on the side of the swing arm away from the support, and a second pad is embedded in the third groove. The connector passes through the support from the side away from the swing arm to the side closer to the swing arm, and passes through the first pad on the support, the pad, the first pad on the swing arm, the swing arm and the second pad in sequence.

[0013] In some embodiments, the first pad on the support protrudes from the support, and the first pad and the second pad on the swing arm both protrude from the swing arm.

[0014] In some embodiments, the support includes:

[0015] The support body includes a connecting part and a hollow structure located below the connecting part. The connecting part is used to connect the swing arm, and the hollow structure is used to accommodate the swing arm and the counterweight.

[0016] The fixing part is integrally set at the bottom of the support body and located on both sides of the hollow structure along the horizontal direction, and is used to fix the support body to the vibration test bench.

[0017] In some embodiments, the sum of the longitudinal dimensions of the connecting part and the swing arm is less than the longitudinal dimension of the support.

[0018] In some embodiments, the fastener loosening test apparatus further includes:

[0019] An ultrasonic probe is mounted on a fastener.

[0020] An ultrasonic axial force testing mechanism, connected to an ultrasonic probe signal, is used to monitor the axial force of fasteners.

[0021] In some embodiments, the counterweight is a detachable multi-layer structure, the counterweight includes at least three quality grades, the detachable multi-layer structure is connected by threads or stacked by snaps, the counterweight has a through hole in the center, the swing arm has external threads, and the counterweight is fixed to the swing arm by locking bolts.

[0022] In some embodiments, the fastener loosening test apparatus further includes:

[0023] An angle sensor is located at the connection between the swing arm and the support to monitor the swing angle of the swing arm relative to the support in real time.

[0024] The data acquisition system is connected to the angle sensor signal and is used to trigger an alarm when the swing angle of the swing arm relative to the support exceeds a preset threshold.

[0025] In some embodiments, the connector is a pin, or the connector is a ring-shaped adjustable resistor structure. The movable end of the ring-shaped adjustable resistor structure is fixed to the swing arm, and the fixed end of the ring-shaped adjustable resistor structure is fixed to the support. The ring-shaped adjustable resistor structure is connected to the control system. The change in the resistance value of the ring-shaped adjustable resistor structure is used to correspond to the displacement of the swing arm. The control system calculates the loosening rate of the fastener based on the resistance change rate of the ring-shaped adjustable resistor structure.

[0026] Compared to the aforementioned background technology, the fastener loosening test device provided in this application includes a support and a swing arm. The support is used to support the swing arm and is fixed to a vibration test bench, which applies a lateral vibration load to the support and the swing arm. One end of the swing arm is connected to the support via a connector and a fastener, and the other end is connected to a counterweight, allowing the swing arm to contact the support through sliding friction. The swing arm is used to swing relative to the support around the axis of the connector when the lateral vibration load applied by the vibration test bench reaches a critical value.

[0027] During the test, the test device was connected to a vibration test bench, which applied vibration acceleration to the entire device to apply a lateral load, thereby evaluating the overall anti-loosening performance of the fastening system. It can be seen that, compared to the traditional rolling friction contact method at the interface of the fastener connection structure, this device uses a sliding friction contact method at the interface of the fastener connection structure. Maintaining an appropriate coefficient of friction at the contact surface between the swing arm and the support ensures that changes in the fastener preload are reflected in the overall anti-loosening performance of the structure, solving the problem that existing fastener loosening test devices cannot conduct anti-loosening performance tests with bolt preload as a variable. Furthermore, this device utilizes the lever principle, employing a pendulum structure with the swing arm as the lever and the connecting piece as the fulcrum. A counterweight is added to the swing arm, amplifying the lateral load at the fastener location, thereby reducing the required counterweight of the test device and the thrust level requirement of the vibration test bench, improving the device's lightweight design and ease of use. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the fastener loosening test device in the embodiments of this application.

[0030] Figure 2 for Figure 1 The main view.

[0031] Figure 3 for Figure 2 Sectional view of AA.

[0032] Figure 4 for Figure 3 Enlarged view of part B in the middle.

[0033] Figure 5 for Figure 1 The front view of the support in the fastener loosening test device shown.

[0034] Figure 6 for Figure 5 A sectional view of CC.

[0035] Figure 7 for Figure 1 The front view of the swing arm in the fastener loosening test device shown.

[0036] Figure 8 for Figure 7 Top view.

[0037] Figure 9 This is a graph of acceleration data from the elevation method test.

[0038] Figure 10 This is a graph showing the attenuation curve of clamping force of bolts under different preloads using the GB / T 10431 method.

[0039] Figure 11 This is a test data diagram of the fastener loosening test device used in the embodiments of this application.

[0040] Figure 12 This is a graph showing the relationship between the preload of the bolt and the critical loosening acceleration when using the fastener loosening test device in the embodiments of this application.

[0041] in:

[0042] 10-Support, 11-Support body, 111-Connecting part, 1111-First groove, 112-Hollow structure, 12-Fixing part;

[0043] 20 - Swing arm, 21 - Second groove, 22 - Third groove;

[0044] 30 - Connector;

[0045] 40-Fasteners;

[0046] 50-Counterweight;

[0047] 60 - First pad;

[0048] 70-Gasket;

[0049] 80 - Second pad;

[0050] 90 - Locking bolt. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] It should be noted that the directional terms such as "upper end," "lower end," "left side," and "right side" mentioned below are defined based on the accompanying drawings in the instruction manual.

[0054] Please refer to Figures 1 to 12 , Figure 1 This is a schematic diagram of the fastener loosening test device in the embodiments of this application. Figure 2 for Figure 1 The main view. Figure 3 for Figure 2 Sectional view of AA. Figure 4 for Figure 3 Enlarged view of part B in the middle. Figure 5 for Figure 1 The front view of the support in the fastener loosening test device shown. Figure 6 for Figure 5 A sectional view of CC. Figure 7 for Figure 1 The front view of the swing arm in the fastener loosening test device shown. Figure 8 for Figure 7 Top view. Figure 9 This is a graph of acceleration data from the elevation method test. Figure 10 This is a graph showing the attenuation curve of clamping force of bolts under different preloads using the GB / T 10431 method. Figure 11 This is a test data diagram of the fastener loosening test device used in the embodiments of this application. Figure 12 This is a graph showing the relationship between the preload of the bolt and the critical loosening acceleration when using the fastener loosening test device in the embodiments of this application.

[0055] The fastener loosening test device provided in this application includes a support 10 and a swing arm 20.

[0056] Support 10 is used to support swing arm 20. Support 10 is fixed to vibration test bench. Vibration test bench is used to apply lateral vibration load to support 10 and swing arm 20.

[0057] One end of the swing arm 20 is connected to the support 10 via a connector 30 and a fastener 40, and the other end is connected to a counterweight 50, so that the swing arm 20 and the support 10 are in contact by sliding friction, and the swing arm 20 is used to swing relative to the support 10 about the axis of the connector 30 when the transverse vibration load applied by the vibration test bench reaches a critical value. The fastener 40 can be a bolt.

[0058] During the test, the test device was connected to a vibration test bench, and the vibration test bench was used to apply vibration acceleration to the entire device to apply a lateral load, thereby evaluating the overall anti-loosening performance of the fastening system.

[0059] This device abandons the traditional rolling friction contact method at the interface of the fastener 40 connection structure and creatively adopts a sliding friction contact method at the interface of the fastener 40 connection structure. It maintains an appropriate coefficient of friction on the contact surface between the swing arm 20 and the support 10, so that the change in the preload of the fastener 40 can be reflected in the anti-loosening performance of the overall structure. This solves the problem that existing fastener loosening test devices cannot carry out anti-loosening performance tests with bolt preload as a variable.

[0060] Because this device uses sliding friction, the requirements for lateral test loads are increased. To ensure the device's lightweight design and ease of use, while also reducing the thrust performance requirements of the vibration test bench, this device utilizes the lever principle and adopts a pendulum structure. The pendulum arm 20 acts as the lever, and the connecting piece 30 as the fulcrum. A counterweight 50 is added to the pendulum arm 20, amplifying the lateral load at the fastener 40 position. This reduces the required counterweight of the test device and the thrust level requirements of the vibration test bench, improving the device's lightweight design and ease of use.

[0061] In some embodiments, the support 10 is provided with a first groove 1111, and the swing arm 20 is provided with a second groove 21 on the side near the support 10. The first groove 1111 and the second groove 21 are both fitted with a first pad 60, and a pad 70 with double-sided lubricating grease is provided between the two first pads 60. The two first pads 60 are in contact with the pad 70 by sliding friction.

[0062] Of course, depending on actual needs, the aforementioned gasket 70 can be a thin copper sheet.

[0063] It should be noted that the reason why traditional vibration methods commonly employ rolling friction is largely due to the high and unstable coefficient of friction of sliding friction, which requires a large test load and makes it difficult to guarantee the repeatability of test results. In contrast, this device addresses this problem by adding a thin copper sheet between the connected parts 30 and applying grease or lubricant to both sides. This utilizes the friction-reducing effect of the copper alloy and the lubricant to reduce friction-induced heat generation and wear. Simultaneously, it ensures that the interfacial friction coefficient remains stable after multiple tests, thus solving the problem of unstable friction coefficient in traditional sliding friction.

[0064] In addition, a pad design is adopted at the interface of the fastener 40 connection structure. The pad is replaceable, which can ensure the repeatability of test results and extend the service life of the tooling.

[0065] In some embodiments, the side of the swing arm 20 away from the support 10 is further provided with a third groove 22, in which a second pad 80 is embedded. The first pad 60 on the support 10 protrudes from the support 10, and both the first pad 60 and the second pad 80 on the swing arm 20 protrude from the swing arm 20. The connector 30 is inserted into the support 10 from the side away from the swing arm 20 toward the side closer to the swing arm 20, and passes sequentially through the first pad 60 on the support 10, the pad 70, the first pad 60 on the swing arm 20, the swing arm 20, and the second pad 80.

[0066] In some embodiments, the support 10 includes a support body 11 and a fixing part 12. The support body 11 includes a connecting part 111 and a hollow structure 112 located below the connecting part 111. The connecting part 111 is used to connect the swing arm 20, and the hollow structure 112 is used to accommodate the swing arm 20 and the counterweight 50. The fixing part 12 is integrally disposed at the bottom of the support body 11 and is located on both sides of the hollow structure 112 in the lateral direction. The fixing part 12 is used to fix the support body 11 to the vibration test bench.

[0067] Of course, the fixing part 12 can be a fixing hole provided on the left and right sides of the support body 11.

[0068] In this embodiment, the sum of the longitudinal dimensions of the connecting portion 111 and the swing arm 20 is less than the longitudinal dimension of the support 11. The sum of the longitudinal dimensions of the connecting portion 111 and the swing arm 20 refers to the longitudinal dimension being perpendicular to the transverse or vibration direction after the thickness of the connecting portion 111 and the swing arm 20.

[0069] Specifically, the support 10 is fastened to the vibration test bench through fixing holes (bolt through holes) on the left and right sides of the bottom. The connecting part 111 has a groove and a first pad 60 is embedded therein. The first pad 60 fits tightly with the groove of the support 10 without gaps. The upper end of the swing arm 20 has grooves on both the front and rear sides, and pads are embedded therein. The pads fit tightly with the groove of the swing arm 20 without gaps. The support 10 and the swing arm 20 with embedded pads have thin copper pads / sheets with double-sided grease applied to the contact surfaces, and are fastened together by the connector 30 and the fastener 40. The connector 30 is a pin, and the diameter of the pin rod is the same as the diameter of the through hole of the part, and they fit tightly with each other without gaps. The fastener 40 is a test bolt. The test bolt does not fit tightly with the through hole of the assembly position. The diameter of the through hole is determined according to GB / T 5277-85, and a gap is left between the through hole and the test bolt.

[0070] It should be noted that the swing arm 20 is mainly fastened to the support 10 through the fastener 40. The connector 30 does not provide additional preload. The swing arm 20 is rotatably connected to the support 10 through the connector 30.

[0071] In addition, the counterweight 50 is a detachable multi-layer structure. The counterweight 50 includes at least three quality grades. The detachable multi-layer structure is connected by threads or stacked by snaps. The counterweight 50 has a through hole in the center. The swing arm 20 has external threads. The counterweight 50 is fixed to the swing arm 20 by locking bolts 90.

[0072] For example, the lower end of the swing arm 20 has three bolt through holes for connecting to the counterweight 50 by fastening bolts. The number of counterweights 50 can be adjusted according to the test requirements.

[0073] To obtain the change in axial preload of the bolts during the test, ultrasonic axial force testing was used to track and detect the change in axial force of the tested bolts during vibration, and to evaluate the anti-loosening performance of the structure.

[0074] Specifically, the fastener loosening test device also includes an ultrasonic probe and an ultrasonic axial force testing mechanism. The ultrasonic probe is mounted on the fastener 40, and the ultrasonic axial force testing mechanism is connected to the ultrasonic probe for signal monitoring.

[0075] In this way, compared with the force measurement method of using pressure sensors connected in series inside the connection structure, the ultrasonic axial force testing method does not change the original connection structure and interface friction performance, and the test results are more meaningful for engineering guidance.

[0076] The working principle of this device is as follows: A vibration test bench drives the fastener loosening test device to undergo reciprocating constant acceleration vibration. Under the action of acceleration, due to the cooperation between the connecting part 30 and the swing arm 20, the swing arm 20 will generate a reciprocating swing tendency with the connecting part 30 as the axis. At this time, since the length of the power arm in the lever of the swing arm 20 is several times that of the resistance arm, only a small counterweight and acceleration are needed to subject the test bolt to a large lateral force, achieving the device's lightweight and ease of use. During the test, the acceleration is gradually increased. When the acceleration increases to a certain critical value, the frictional force between the interface of the swing arm 20 and the support 10 will be insufficient to overcome the swing tendency generated by the acceleration. The swing arm 20 will then swing, which is reflected in the test bolt as an approximately lateral alternating displacement along a small arc, thus causing the bolt to loosen. By testing and comparing the critical loosening acceleration values ​​under different anti-loosening measures and tightening processes, as well as the axial force loss rate measured by the axial force tester (ultrasonic axial force testing mechanism), the anti-loosening effect of the bolt under different anti-loosening measures and tightening processes can be evaluated. Furthermore, since the device simulates the contact form of sliding friction at the interface of a bolt connection, the frictional force between the interfaces will change with the change of bolt preload (i.e., interface positive pressure), thus reflecting the influence of different bolt preload conditions on the test results.

[0077] In some embodiments, the fastener loosening test apparatus further includes an angle sensor and a data acquisition system. The angle sensor is located at the connection between the swing arm 20 and the support 10, and is used to monitor the swing angle of the swing arm 20 relative to the support 10 in real time. The angle sensor can be a rotary encoder or a potentiometer-type angle sensor. The data acquisition system is connected to the angle sensor signal and is used to trigger an alarm when the swing angle of the swing arm 20 relative to the support 10 exceeds a preset threshold.

[0078] Traditional testing methods (such as GB / T 10431 relying on rolling bearings and GJB 715.3A relying on impact loading) cannot capture the preload decay process in real time. They can only make qualitative judgments through visual markings or statistics of loosening turns, with an error rate as high as 15-30%. In contrast, this design adopts high-precision dynamic monitoring: an angle sensor (such as a rotary encoder with an accuracy of ±0.1°) collects the 20° deflection angle θ of the swing arm in real time. The preload decay of the bolt is directly correlated with the formula ΔF=k·θ (where k is the system stiffness coefficient), forming a preload-angle decay curve. This accurately locates the loosening initiation point (such as the inflection point of θ sudden change). At the same time, combined with angular velocity analysis (dθ / dt), it can distinguish between rotational loosening (θ continuously increases, angular velocity is stable) and non-rotational loosening (θ changes step, angular velocity changes abruptly), providing a differentiated optimization basis for anti-loosening design.

[0079] In addition, compared to traditional methods that require manual inspection to determine looseness and have a delayed response that can easily lead to chain failures (such as derailment caused by bolt failure in rail transit), this device can also trigger audible and visual alarms and push them to remote terminals by setting preset angle thresholds (such as θ>2° for early warning maintenance and θ>5° for emergency shutdown), thus avoiding overload damage or accidents to the test equipment.

[0080] In some embodiments, in addition to using a pin, the connector 30 can also be a ring-shaped adjustable resistor structure. The movable end of the ring-shaped adjustable resistor structure is fixed to the swing arm 20, and the fixed end of the ring-shaped adjustable resistor structure is fixed to the support 10. The ring-shaped adjustable resistor structure is connected to the control system. The change in the resistance value of the ring-shaped adjustable resistor structure is used to correspond to the displacement of the swing arm 20. The control system calculates the loosening rate of the fastener 40 based on the resistance change rate of the ring-shaped adjustable resistor structure.

[0081] Traditional testing methods (such as GB / T 10431, which relies on rolling bearings to eliminate preload, and GJB 715.3A, which relies on impact loading) cannot capture the continuous process of preload decay in real time, and can only make qualitative judgments through visual markings or statistical counting of loose turns. However, the ring-shaped adjustable resistor design used in this device offers the following advantages:

[0082] Firstly, the resistance-displacement linear mapping: the displacement of the swing arm 20 drives the moving end of the ring resistor to rotate, and the change in resistance value ΔR ∝ Δθ (θ is the deflection angle of the swing arm 20) is directly related to the bolt preload attenuation through the calibration curve Δθ = k·ΔR (k is the system calibration coefficient).

[0083] Secondly, the loosening rate is calculated in real time: the control system calculates the loosening rate v=k·(dR / dt) based on the resistance change rate dR / dt, dynamically generates the loosening rate-time curve, and accurately locates the inflection point of loosening acceleration (such as the vibration fatigue critical point).

[0084] Third, micron-level displacement sensitivity: the contact point displacement resolution of the ring resistor reaches 0.01mm (corresponding to an angular resolution of ±0.05°), which can detect the micro-rotation of the bolt by 0.1°, overcoming the defect of the traditional marking line method (GJB 715.3A) which can only identify more than 5°.

[0085] Fourth, millisecond-level dynamic response: The resistance signal is transmitted to the control system through a high-speed ADC (≥1kHz sampling rate) to track the instantaneous slip under vibration load in real time (such as the 5-200Hz vibration spectrum of rail transit), while the response of traditional manual inspection is delayed by more than 10 minutes.

[0086] The working process of this device is as follows:

[0087] 1) Secure the support 10 to the vibration test bench through the fixing holes (bolt through holes) on the left and right sides of the bottom. The installation direction of the support 10 must ensure that the vibration direction of the test bench is parallel to the direction of the contact surface between the swing arm 20 and the support 10.

[0088] 2) Secure the two counterweights 50 to the lower ends of the swing arm 20 using fastening bolts;

[0089] 3) Insert the pin from back to front into the uppermost through hole of the support 10, then pass it sequentially through the first pad 60 on the support 10, the first pad 60 on the swing arm 20, the swing arm 20, and the second pad 80, and press them tightly together. The pad 70 should be evenly coated with grease on both sides to reduce the problem of unstable friction coefficient caused by interfacial frictional heat, ensuring the repeatability of the test results. The pads and pads 70 are test consumables and should be replaced when significant surface wear affects the test results. Newly replaced pads should undergo three vibration loosening tests to allow for interfacial running-in; the formal test can only begin after the results are stable.

[0090] 4) Screw the nut into the pin until it is in the correct position to prevent the pin from coming out of the structure during vibration; no additional torque is required.

[0091] 5) Apply an ultrasonic probe to the test bolt and connect it to an ultrasonic axial force testing mechanism to monitor the bolt axial force. Tighten test bolt 4 according to different set test conditions (different preload axial force or different anti-loosening elements);

[0092] 6) Start the vibration test bench and apply a reciprocating acceleration load along the transverse direction of the test bolt. Gradually increase the vibration acceleration. When the swing arm 20 causes the bolt to loosen, record the vibration acceleration value at this time as the critical loosening acceleration of the bolt connection structure. By comparing the magnitude of the critical loosening acceleration, the effectiveness of the anti-loosening measures can be evaluated. The larger the critical loosening acceleration value, the better the anti-loosening performance of the measures.

[0093] Furthermore, considering the critical loosening acceleration value (a -1 The magnitude of the critical loosening acceleration varies to some extent. To accurately determine the critical loosening acceleration value of the structure, this application employs the lifting-lowering method for testing. The lifting-lowering method involves testing multiple sets of test samples with different vibration accelerations under the same tightening conditions to determine the critical loosening acceleration value. The specific implementation method is as follows:

[0094] During the test, the acceleration load a0 was started at a level higher than the loosening limit, and then the test acceleration load was gradually reduced to... Figure 9For example: If specimen 1 does not loosen within 1 minute under an acceleration load of a0, then specimen 2 will be tested under a lower acceleration load of a1. This process continues until specimen 4. If the structure does not loosen after a 1-minute vibration test, then the next specimen 5 will be tested under a higher acceleration load of a2. Following this pattern, if the previous specimen loosens or experiences a preload reduction of more than 60% within a 1-minute vibration test, then the subsequent test will be conducted at a lower acceleration load level. If the previous specimen passes the test without loosening, then the subsequent test will be conducted at a higher acceleration load level, until all tests are completed.

[0095] The difference Δa between two adjacent acceleration loads is called the "acceleration increment," which can be taken as (3%~5%)a. -1 If the critical loosening acceleration value a -1 If it's unclear, you can first conduct preliminary tests using a small number of samples to estimate a. -1 The values, and the results of the preliminary test can be used to draw the rise and fall graphs later.

[0096] When processing experimental results, data prior to the occurrence of the first pair of opposing results should be discarded, such as... Figure 9 Points 3 and 4 represent the first pair of opposite results, therefore points 1 and 2 should be discarded. Points 3 and 4 are then paired as the first pair, and the average acceleration of points 3 and 4 (a2+a3) / 2 is used as the critical loosening acceleration value for this pair. This process continues, pairing points with opposite results sequentially, skipping those that cannot be paired. The pairs are: points 5 and 6, 7 and 8, 10 and 11, 12 and 13, 14 and 15, and 16 and 9, for a total of 7 pairs. These pairs formed using the "pairing method" and their average accelerations are then statistically processed according to the following formula to obtain the average critical loosening acceleration value a. -1 and standard deviation s a-1 .

[0097] (1)

[0098] (2)

[0099] In the formula: k — the number of pairs formed;

[0100] n—Number of valid samples;

[0101] m—the horizontal level of acceleration;

[0102] a j —The j-th critical loosening acceleration value obtained by the pairing method;

[0103] a i—The acceleration value at the i-th acceleration level;

[0104] v i — The number of samples at the i-th acceleration level.

[0105] The number of valid test specimens should generally be more than 13. At the same time, efforts should be made to ensure that the test acceleration level of the specimen following the last valid data point is at the same stress level as the first valid data point. For example... Figure 9 As shown, the next test acceleration at point 16 is a2, which is the same as the test acceleration at the first valid data point 3.

[0106] Using the lifting method for testing and data processing solves the problem of large dispersion in single test results, making the statistical results more reliable. Furthermore, the test acceleration level can be dynamically adjusted during the testing process, eliminating the need to preset the loosening threshold value and enabling rapid focusing on the critical loosening acceleration range, resulting in higher testing efficiency.

[0107] In summary, the above-mentioned technical solution adopted by this device has the following beneficial effects:

[0108] 1) This device solves the problem that existing test methods cannot effectively carry out comparative tests on anti-loosening performance with bolt preload as a variable. It also creatively adopts a sliding friction contact method at the interface of the fastener 40 connection structure, and maintains an appropriate coefficient of friction on the contact surface between the swing arm 20 and the support 10, so that changes in the preload of the fastener 40 can be reflected in the anti-loosening performance of the overall structure.

[0109] To illustrate the improvement of this device in evaluating axial preload factors compared to GB / T10431 and related test types, we took the experiment of the effect of different preloads on the anti-loosening performance of the joint using two different methods as an example, and conducted the experiment with the target preload of bolts of 10kN, 20kN, 30kN and 40kN respectively.

[0110] Figure 10 To obtain the test curves after conducting tests using the 40 transverse vibration test bench specified in GB / T 10431-2008 standard for fasteners, GB / T 10431 evaluates the anti-loosening performance by assessing the rate of decrease in bolt clamping force. Figure 10 As can be seen, there is no significant difference in the rate of decrease of bolt clamping force under different preload levels, therefore it is impossible to evaluate the anti-loosening performance of the joint under different preloads. In fact, the loosening speed is even faster when the clamping force is greater, which is inconsistent with the common sense that the greater the bolt preload, the better the anti-loosening ability.

[0111] The test was conducted using this device, where the bolt clamping force was monitored in real time by an ultrasonic axial force testing mechanism, and the bolts were tightened to the target preload. The vibration acceleration experienced by the structure was then gradually increased in increments of 1g. The test was stopped when the swing arm 20 began to loosen and the bolt clamping force significantly decreased. The vibration acceleration value at this point was recorded as the critical loosening acceleration of the structure. The test data are as follows: Figure 11 As shown, the data is plotted as follows. Figure 12 It can be observed that the magnitude of the preload is approximately proportional to the critical loosening acceleration of the structure, meaning that increasing the bolt preload can proportionally improve the joint's anti-loosening ability. The test results are more consistent with actual conditions.

[0112] 2) This device reduces friction-induced heat and wear by adding thin copper sheets between the connected parts 30 and applying grease or lubricant to both sides. This utilizes the friction-reducing properties of the copper alloy and the lubricant. Simultaneously, it ensures that the interfacial friction coefficient remains stable after multiple tests, solving the problem of unstable friction coefficients in traditional sliding friction. Furthermore, a pad design is used at the interface of the fastener 40 connection structure. The replaceable pad design ensures the repeatability of test results and extends the service life of the tooling.

[0113] 3) This device provides vibration acceleration through a vibration test bench. Combined with the counterweight design of lever arm 20, it amplifies the lateral load at the test bolt position, thereby reducing the counterweight required for the test device. It also reduces the requirements for the thrust level of the vibration test bench, improving the device's lightweight nature and ease of use.

[0114] 4) This application addresses the issue of dispersion in critical loosening acceleration value testing by using an elevation-increase method for testing and data processing, resulting in more reliable statistical data. The testing process allows for dynamic adjustment of the test acceleration level, eliminating the need to preset the loosening threshold value and enabling rapid focusing on the critical loosening acceleration range, thus improving testing efficiency.

[0115] 5) This device effectively acquires the axial force change of the tested bolt during vibration through ultrasonic axial force testing, and quantitatively evaluates the anti-loosening performance of the structure. Compared with the force measurement method of series pressure sensors inside the connection structure, the ultrasonic axial force testing method does not change the original connection structure and interface friction performance, and the test results are more in line with engineering guidance significance.

[0116] It should be noted that in this specification, relational terms such as first and second are used only to distinguish one entity from several other entities, and do not necessarily require or imply any such actual relationship or order between these entities.

[0117] The fastener loosening test device provided in this application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the solution and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. A fastener looseness testing apparatus characterized by, include: Supports are used to fix the test bench to which lateral vibration loads are applied. A swing arm, one end of which is connected to the support via a connector and fastener, and the other end of which is connected to a counterweight, so that the swing arm and the support are in contact by sliding friction, and the swing arm is used to swing relative to the support about the axis of the connector when the transverse vibration load applied by the vibration test bench reaches a critical value.

2. The fastener loosening test device as described in claim 1, characterized in that, The support is provided with a first groove, and the swing arm is provided with a second groove on the side near the support. Both the first groove and the second groove are fitted with first pads, and a pad with double-sided lubricant is provided between the two first pads. The two first pads are in contact with the pad by sliding friction.

3. The fastener loosening test device as described in claim 2, characterized in that, The swing arm is provided with a third groove on the side away from the support. The third groove is fitted with a second pad. The connector passes through the support from the side away from the swing arm to the side closer to the swing arm, and passes through the first pad on the support, the pad, the first pad on the swing arm, the swing arm and the second pad in sequence.

4. The fastener loosening test device as described in claim 3, characterized in that, The first pad on the support protrudes from the support, and both the first pad and the second pad on the swing arm protrude from the swing arm.

5. The fastener loosening test device as described in claim 1, characterized in that, The support includes: The support body includes a connecting part and a hollow structure located below the connecting part. The connecting part is used to connect the swing arm, and the hollow structure is used to accommodate the swing arm and the counterweight. The fixing part is integrally set at the bottom of the support body and located on both sides of the hollow structure along the lateral direction, and is used to fix the support body to the vibration test bench.

6. The fastener loosening test device as described in claim 5, characterized in that, The sum of the longitudinal dimensions of the connecting part and the swing arm is less than the longitudinal dimension of the support.

7. The fastener loosening test apparatus as described in any one of claims 1-6, characterized in that, The fastener loosening test device also includes: An ultrasonic probe is mounted on the fastener; An ultrasonic axial force testing mechanism is connected to the ultrasonic probe for monitoring the axial force of the fastener.

8. The fastener loosening test apparatus according to any one of claims 1-6, characterized in that, The counterweight is a detachable multi-layer structure, which includes at least three quality grades. The detachable multi-layer structure is connected by threads or stacked by snaps. The counterweight has a through hole in the center, the swing arm has external threads, and the counterweight is fixed to the swing arm by locking bolts.

9. The fastener loosening test apparatus according to any one of claims 1-6, characterized in that, The fastener loosening test device also includes: An angle sensor is located at the connection between the swing arm and the support to monitor the swing angle of the swing arm relative to the support in real time. The data acquisition system is connected to the angle sensor signal and is used to trigger an alarm when the swing angle of the swing arm relative to the support exceeds a preset threshold.

10. The fastener loosening test apparatus according to any one of claims 1-6, characterized in that, The connector is a pin, or the connector is a ring-shaped adjustable resistor structure. The movable end of the ring-shaped adjustable resistor structure is fixed to the swing arm, and the fixed end of the ring-shaped adjustable resistor structure is fixed to the support. The ring-shaped adjustable resistor structure is connected to the control system. The change in the resistance value of the ring-shaped adjustable resistor structure corresponds to the displacement of the swing arm. The control system calculates the loosening rate of the fastener based on the resistance change rate of the ring-shaped adjustable resistor structure.

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