A bolt durability test device and method

Abstract

The application discloses a bolt durability test device and method, which comprises a connecting piece, a connected piece, a bolt connecting the connecting piece and the connected piece, an installation part of a pressure sensor arranged between the connecting piece and the connected piece, a displacement measuring device connected to the connecting piece or the connected piece, an external cyclic load applying device connected to the connecting piece, and a video shooting device recording multiple time points and corresponding load values applied by the cyclic load applying device at each time point. The application can obtain multiple corresponding displacement values of the connecting piece at multiple time points under the action of the cyclic load. The multiple corresponding displacement values can track the slippage change process of the bolt durability failure, lock the time of the bolt connecting pair failure, and provide a basis for selecting a bolt fastener process.

Description

Technical Field

[0001] This invention belongs to the field of bolt quality control, specifically relating to a method and apparatus for testing the durability of suspended bolts. Background Technology

[0002] If automotive mounting bolts fail due to bolt fatigue, a fastener durability test bench must be built for verification.

[0003] When two connectors are connected by suspension bolts and the threaded connection is subjected to cyclic loads, it is necessary to assess whether there is slippage between the contact surfaces of the two connectors. Once slippage occurs between the contact surfaces of the two connectors, under the action of lateral loads, the suspension bolt will experience fretting wear and loss of preload, leading to loosening of the bolt.

[0004] With current technology, it is difficult to track the slip change process of bolt durability failure during bench verification, and it is difficult to accurately pinpoint the number of load cycles when the bolt begins to fail. At the same time, existing bolt durability testing equipment and methods are too complex, and it is difficult to determine the optimal bolt size or material parameters through simple testing equipment and methods while meeting durability requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for testing the durability of suspension bolts, so as to track the slip change process of bolt durability failure and provide a basis for the selection of bolt fastener processes in automobiles.

[0006] To achieve the above objectives, the technical solution of this invention is as follows:

[0007] A bolt durability testing device includes a connector, a connected component, and a bolt connecting the connector and the connected component. The connected component is placed on a workbench, and the connector is located above the connected component. A pressure sensor mounting portion is provided between the connector and the connected component. The bolt connects the connector, the pressure sensor mounting portion, and the connected component together. A displacement measuring device is connected to the connector or the connected component. The connector is connected to an external cyclic load application device. The device also includes a video recording device that records the load values ​​applied by the cyclic load application device at multiple time points.

[0008] Furthermore, the mounting part of the pressure sensor is a flange, which is located at the connection surface between the connector and the connected part, and the pressure sensor is mounted on the side of the flange.

[0009] Furthermore, the displacement measuring device is a dial indicator, with one end of the dial indicator mounted on the workbench and the other end of the dial indicator being a telescopic end. In the initial state, the telescopic end of the dial indicator is compressed and rests against the connector or the surface of the connector.

[0010] Furthermore, there are two dial indicators, namely a first dial indicator and a second dial indicator. One end of the first dial indicator and the second dial indicator are mounted on the worktable, the other end of the first dial indicator rests against the surface of the connector, and the other end of the second dial indicator rests against the surface of the connector.

[0011] Furthermore, the first dial indicator and the device for applying cyclic loads externally are located on opposite sides of the connector.

[0012] Furthermore, the displacement measuring device is a displacement sensor installed on the connector or the connected component.

[0013] Furthermore, the connector is connected to an external load-applying device via a tooling, with one side of the tooling connected to one side of the connector and the opposite side of the tooling connected to the external cyclic load-applying device.

[0014] A method for conducting bolt durability tests using the aforementioned bolt durability testing apparatus, the method comprising:

[0015] A cyclic load is applied to the connector, and when the cyclic load is continuously applied to the connector, the connector slips.

[0016] Multiple sets of test data are recorded in real time at preset time intervals. Each set of data includes a time point, the cyclic load value applied at the time point, the displacement value of the connector relative to the initial position, the clamping force of the bolt connection pair, and the load amplitude with the number of load cycles. When the displacement value of the connector relative to the initial position exceeds the preset slippage safety threshold, the bolt connection pair fails.

[0017] By recording the multiple sets of test data, the slip change process of the connector in the bolt durability failure test is obtained, the moment of failure of the bolt connection pair is determined, and the number of load cycles at the time of bolt failure is determined.

[0018] By repeating the above steps with bolts of different materials and sizes, the failure time of the bolt connection pair under the same cyclic load can be obtained, thus obtaining the durability of bolts of different materials and sizes.

[0019] Furthermore, the method for obtaining the displacement value of the connector relative to its initial position is as follows: when a cyclic load is applied to the connector, the rotation amplitude of the first dial indicator pointer is read, and the displacement value of the connector is obtained through the rotation amplitude.

[0020] Furthermore, the method for recording the applied cyclic load value and the displacement value of the connector relative to its initial position at the aforementioned time point is as follows: simultaneously capture the force value data on the display screen of the cyclic load application device and the rotation amplitude of the dial indicator pointer using a video recording device to obtain the load value and displacement value at the same time. Through continuous video recording, the load value and the displacement value corresponding to the load value at multiple times are obtained.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention records multiple sets of data in real time, each set including the displacement value of the connector at a certain time point. Thus, it can obtain multiple corresponding displacement values ​​of the connector at multiple time points under cyclic loading. Through the multiple corresponding displacement values ​​at multiple time points, the slip change process of bolt durability failure can be tracked.

[0023] 2. By recording multiple sets of data in real time, this invention obtains the number of load cycles in which the displacement value of the connector exceeds a preset threshold, thus determining the number of load cycles in which the bolt fails, thereby accurately locking the number of load cycles at which the bolt begins to fail.

[0024] 3. This invention records the cyclic load values ​​and corresponding displacement changes of the connectors at multiple time points, and plots the test data at multiple time points to obtain the hysteresis curve of the connector displacement change. The abrupt change region of the connector displacement value in the hysteresis curve indicates that the bolt connection may begin to fail. By determining the abrupt change region of the displacement value, it is helpful to lock the time of failure of the bolt connection and determine the number of load cycles when the bolt fails.

[0025] 4. The experimental apparatus and method of the present invention are simple, and the optimal bolt size or material parameters can be determined through a simple experimental apparatus and method. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the bolt loosening stage during the test of this invention.

[0027] Figure 2 This is a schematic diagram of the experimental apparatus of the present invention.

[0028] Figure 3 This is a hysteresis curve showing the load value borne by the connector of the present invention and the displacement.

[0029] In the diagram: 1. Connector; 2. Connected part; 3. Bolt; 4. Workbench; 5. Flange; 6. Pressure sensor; 7. First dial indicator; 8. Second dial indicator; 9. Tooling; 10. Cyclic load application device. Detailed Implementation

[0030] To make the purpose, technical solution, and advantages of the invention clearer, the invention will be further described below with reference to the accompanying drawings.

[0031] When a threaded connection is subjected to a lateral working load, it is necessary to assess whether slippage exists between the contact surfaces. Once slippage occurs, fretting wear and loss of preload will occur under the lateral load, leading to bolt loosening. Factors affecting the loosening rate include bolt preload, working load, connection type and size, etc. In this invention, different bolt connection types include different sizes of the connection surfaces between the two connecting parts. For example, the connection types of the two connecting parts include single-point connection, double-point connection, etc.

[0032] A typical test loosening curve divides the loosening process into two stages. For example... Figure 1 As shown, in the first stage, the preload decreases mainly due to deformation, without bolt unscrewing; in the second stage, the preload decreases significantly due to bolt unscrewing. When the preload is small or the relative sliding of the contact parts is large, loosening will begin in the second stage, and slippage between the bolt and the bearing surface is a necessary condition for the failure of the bolted connection.

[0033] Cyclic loading refers to loads that act on a structure repeatedly during its design and use. Cyclic loads are generally periodic, such as vibration loads from mechanical equipment and traffic loads from vehicles, all of which can have a cyclical impact on a structure. The generation of cyclic loads can lead to fatigue damage and deformation of structural materials, thereby affecting the stability and safety of the structure. Under certain operating conditions, vehicle components are subjected to cyclic loads. This invention simulates the fatigue failure of bolts under cyclic loads.

[0034] like Figure 2 As shown, a bolt durability testing device includes a connector 1 and a connected component 2. The connector 1 is located above the connected component 2. Both the connector 1 and the connected component 2 have threaded holes. The connector 1 and the connected component 2 are connected together by bolts 3. The connected component 2 is mounted on a workbench 4. A flange 5 is provided at the connection surface between the connector 1 and the connected component 2. The flange 5 is located between the connector 1 and the connected component 2. The bolts 3 pass through the bolt holes on the connector 1 and the flange 5 in sequence, and then extend into the bolt hole on the connected component 2, connecting the connector 1, the flange 5, and the connected component 2 together. A pressure sensor 6 is installed at the end of the flange 5. The pressure sensor 6 is mounted on the flange 5 via a mounting base. The size of the flange 5 can be slightly larger than the size of the connection surface between the connector 1 and the connected component 2. The flange 5 can protrude from the connection surface between the connector 1 and the connected component 2 to facilitate the installation of the pressure sensor 6. The pressure sensor 6 can be installed at the end or side of the upper surface of the flange 5. The force value measured by the pressure sensor 6 serves as a reference value for the clamping force of the bolt connection pair.

[0035] A first dial indicator 7 and a second dial indicator 8 are mounted on the workbench 4. The dial indicator body includes two ends. One end of the first dial indicator 7 and the second dial indicator 8 is fixed to the workbench 4 by bolts through a base. The other end of the first dial indicator 7 and the second dial indicator 8 is a telescopic end. The telescopic end of the first dial indicator 7 abuts against the surface of the connecting member 1, and the telescopic end of the second dial indicator 8 abuts against the surface of the connected member 2. In the initial state, the telescopic end of the dial indicator body abuts against the surface of the connecting member 1 or the connecting member 2 in a compressed state.

[0036] The fixture 9 is used to install the device for applying external cyclic load. One side of the fixture 9 is connected to one side of the connector 1, and the other side of the fixture 9 is connected to the cyclic load application device 10. The cyclic load application device 10 can be a hydraulic cylinder, a vibrator, etc. The device for applying external load is used to apply cyclic load to the connector 1. The device for applying cyclic load applies a lateral thrust or tension to the connector 1 at a set frequency.

[0037] The first dial indicator 7 and the second dial indicator 8 are located on the same side of the connector 1 or the connected part 2. The first dial indicator 7 and the tooling 9 are located on opposite sides of the connector 1. When a lateral thrust or pull force is continuously applied to the connector 1 at a set frequency, the connector 1 or the connected part 2 will be displaced. The telescopic end of the dial indicator body will extend or shorten, and the dial indicator pointer will rotate forward or reverse synchronously. The displacement of the connector 1 or the connected part 2 can be obtained by the rotation amplitude of the dial indicator pointer.

[0038] During the experiment of this invention, the displacement of the connector 1 is used to determine whether the bolt has failed, and the displacement value of the connector 2 is recorded as a reference.

[0039] A video recording device is set up at the test site. The video recording device can be a camera. The video recording device is used to simultaneously record the load value applied by the cyclic load application device and the rotation amplitude of the two dial gauges, i.e. the displacement value of the connecting parts 1 and 2. Through the video recording device, the load value applied by the cyclic load application device at a certain moment and the displacement value of the connecting parts 1 and 2 at the same moment can be obtained.

[0040] The present invention also discloses a method for conducting bolt durability tests using the aforementioned testing apparatus, the method comprising:

[0041] Step 1: Apply a cyclic load to connector 1. When a cyclic load is continuously applied to connector 1, connector 1 will slip.

[0042] Start the cyclic load application device. The device applies lateral thrust or tension to the connector 1 at a set frequency. The displacement value of the connector 1 caused by slippage can be read by a dial indicator.

[0043] Step 2: Record multiple sets of test data in real time. Each set of data includes a time point, the load value at the same time point, the displacement value of the connector 1 relative to the initial position corresponding to the load value, the clamping force of the bolt connection pair, and the load amplitude with the number of load cycles.

[0044] In this invention, multiple sets of data can be recorded at set intervals. Each set of data includes a time point, the load value applied to the connector 1 at the time point, the displacement value of the connector 1 relative to the initial position corresponding to the load value, the clamping force of the bolt connection pair, and the load amplitude with the number of load cycles. When the displacement value of the connector 1 relative to the initial position exceeds a preset threshold, the bolt fails. The preset threshold is a slippage safety threshold.

[0045] This invention obtains the displacement of connector 1 at different times under cyclic load by recording multiple sets of data in real time, thus enabling the tracking of the slippage process of bolt durability failure.

[0046] This invention obtains, through real-time continuous recording of multiple sets of data, the displacement value of connector 1 exceeds a preset threshold when the load amplitude changes several times with the load cycle. Thus, it is determined that the bolt fails when the load amplitude changes several times with the load cycle, thereby accurately locking the number of load cycles when the bolt begins to fail.

[0047] In this invention, the display screen of the device applying cyclic load shows the applied force value in real time, and the dial of the dial indicator shows the rotation amplitude. A video recording device simultaneously captures the applied force value and the rotation amplitude of the dial indicator pointer, recording the video at time points to obtain the load value and displacement of the connector at the same moment. Through continuous video recording, the load values ​​and displacement of the connector at multiple moment points can be obtained, and the number of load cycles can be recorded simultaneously. The pressure sensor 6 transmits the measured force value to the computer at set time intervals. The load value at the same moment, the displacement value of the connector 1 relative to the initial position corresponding to the load value, the clamping force of the bolt connection pair, and the load amplitude with the number of load cycles are manually recorded to form a set of test data. Multiple sets of test data are recorded to track the slippage change process of the connector during the bolt durability failure test and accurately lock the number of load cycles when the bolt begins to fail.

[0048] Regarding the set slip safety threshold, it can be obtained from slip simulation experiments during the part design process, or it can be determined empirically. The maximum slip of the connector under operating load is obtained through simulation, and the empirical value is generally required to be less than 100 μm. When the displacement change of connector 1 or connected component 2 exceeds the slip safety threshold, the bolt connection fails. In this invention, the displacement data of connector 1 recorded by the first dial gauge 7 is compared with the slip safety threshold to determine whether the bolt connection has failed. The displacement data of connected component 2 recorded by the second dial gauge 8 is used as a reference.

[0049] In this invention, the cyclic load value and the corresponding displacement change value of connector 1 are recorded in real time at the same moment, and the cyclic load value and the corresponding displacement change value of connector 1 at multiple time points are also recorded, which can be manually depicted as follows. Figure 3 The displacement hysteresis curve shown is as follows. Figure 3 The shear load is the cyclic load value applied to connector 1, with tensile force recorded as negative and thrust as positive. The lateral displacement of connector 1 relative to its initial position under tensile force is recorded as negative, and the lateral displacement of connector 1 relative to its initial position under thrust is recorded as positive. During the test, attention should be paid to abrupt changes in the displacement and shear force curves over time. Abrupt changes in displacement values ​​may indicate the beginning of bolt failure. The displacement value of connector 1 at this point should be compared with the slip safety threshold. If the displacement value of connector 1 is less than the slip safety threshold, the experiment continues; if the displacement value of connector 1 is greater than the slip safety threshold, the experiment is stopped, and the number of load cycles is recorded.

[0050] Step 3: Repeat Step 1 and Step 2 multiple times using bolts of different materials and sizes to determine the failure time of bolted connections under the same cyclic load. This will provide the durability of bolts of different materials and sizes and provide a basis for selecting bolt fasteners in automobiles based on the test results.

[0051] This invention incorporates a pressure sensor 6, whose measured force value serves as a reference for the clamping force of the bolt connection pair. This ensures that multiple durability tests are conducted under the same clamping force, thereby guaranteeing the accuracy of the test results. Furthermore, by employing different clamping forces during the experiment, the impact of varying clamping forces on bolt durability can be verified.

[0052] Under the same load, different bolt materials or sizes result in different displacement changes between connector 1 and connected part 2. By changing the size, material properties, and friction coefficient, the anti-slip performance of bolted connections can be compared. Based on the test results, the selection of bolt fasteners for automobiles can be based on the anti-slip performance of different bolted connections.

[0053] In this invention, the dial indicator can also be replaced with a displacement sensor installed on the connector 1 or the connected component 2. The displacement sensor is installed on the connector 1 or the connected component 2 with adhesive. The displacement sensor transmits the displacement data of the connector 1 and the connector 2 to the computer for storage according to a set frequency.

[0054] In the description of this invention, it should be understood that the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

Claims

1. A method for conducting bolt durability tests using a bolt durability testing device, the bolt durability testing device comprising a connector (1), a connected component (2), and a bolt (3) connecting the connector (1) and the connected component (2), the connected component (2) being disposed on a workbench (4), characterized in that: The connector (1) is located on top of the connected part (2). The mounting part of the pressure sensor (6) is provided between the connector (1) and the connected part (2). The bolt (3) connects the connector (1), the mounting part of the pressure sensor (6) and the connected part (2) together. The connector (1) or the connected part (2) is connected to a displacement measuring device. The connector (1) is connected to an external cyclic load applying device (10). It also includes a video shooting device. The video shooting device records multiple time points and the load value applied by the cyclic load applying device (10) at each time point. The method includes: A cyclic load is applied to the connector (1). When the cyclic load is continuously applied to the connector (1), the connector (1) slips. Multiple sets of test data are recorded in real time. Each set of data includes a time point, the value of the cyclic load applied at the time point, the displacement value of the connector (1) relative to the initial position, and the load amplitude with the number of load cycles. When the displacement value of the connector (1) relative to the initial position exceeds the preset slip safety threshold, the bolt connection pair fails. The slip change process of the connector in the bolt durability failure test is obtained by recording the multiple sets of test data, the moment of bolt connection pair failure is determined, and the number of load cycles when the bolt fails is determined. By repeating the above steps with bolts of different materials and sizes, the failure time of the bolt connection pair under the same cyclic load can be obtained, thus obtaining the durability of bolts of different materials and sizes.

2. The method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that: The pressure sensor (6) is mounted on a flange (5), which is located at the connection surface between the connector (1) and the connected component (2). The pressure sensor (6) is mounted on the side of the flange (5).

3. The method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that: The displacement measuring device is a dial indicator, with one end of the dial indicator mounted on the workbench (4) and the other end of the dial indicator resting against the surface of the connector (1) or connector (2).

4. A method for conducting bolt durability tests using a bolt durability testing device according to claim 3, characterized in that: There are two dial indicators, namely a first dial indicator (7) and a second dial indicator (8). One end of the first dial indicator (7) and the second dial indicator (8) is mounted on the workbench (4). The other end of the first dial indicator (7) rests against the surface of the connector (1), and the other end of the second dial indicator (8) rests against the surface of the connected component (2).

5. A method for conducting bolt durability tests using a bolt durability testing device according to claim 4, characterized in that: The first dial gauge (7) and the device for applying cyclic load externally are located on opposite sides of the connector (1).

6. A method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that: The displacement measuring device is a displacement sensor installed on the connector (1) or the connected component (2).

7. A method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that: The connector (1) is connected to the external load-applying device via a fixture (9). One side of the fixture (9) is connected to one side of the connector (1), and the other side of the fixture (9) is connected to the external cyclic load-applying device.

8. A method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that, The method for obtaining the displacement value of the connector (1) relative to the initial position is as follows: when a cyclic load is applied to the connector (1), the rotation amplitude of the pointer of the first dial indicator (7) is read, and the displacement value of the connector (1) is obtained through the rotation amplitude.

9. A method for conducting bolt durability tests using a bolt durability testing device according to claim 1, characterized in that, The method for recording the applied cyclic load value and the displacement value of the connector (1) relative to the initial position at the time point is as follows: the force value data on the display screen of the cyclic load application device and the rotation amplitude of the dial indicator pointer are captured simultaneously by a video shooting device to obtain the load value and displacement value at the same time. Through continuous video shooting, the load value and the displacement value corresponding to the load value at multiple times are obtained.

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