Fatigue limit load test method for high-strength bolt of vehicle engine

Abstract

The invention provides a vehicle engine high-strength bolt fatigue limit load test method which comprises the following steps: determining bolt test parameters which at least comprise a test minimum load, an initial load amplitude and a load amplitude increment; according to the determined test parameters, carrying out a load test on the bolt by virtue of a preset constant minimum load method, so as to obtain an extreme working additional load which can be borne by the bolt under the fatigue test; and according to the bolt load factor and the limit work additional load, evaluating the limit load which can be borne by the bolt. According to the invention, the measurement of the bearable limit work additional load of the high-strength bolt of the vehicle engine under the specified installation specification can be completed, and the bearable limit load of the bolt can be accurately evaluated.

Description

Technical Field

[0001] The present application belongs to the technical field of engine bolt fatigue testing, and in particular relates to a fatigue limit load testing method for high-strength bolts of vehicle engines. Background Art

[0002] The existing bolt axial load fatigue limit test method uses an asymmetric tensile load and is conducted under a constant average load or constant load ratio until the specimen fails or exceeds the specified number of stress cycles. Specimens are tested sequentially, and the load level for the next specimen is determined (either lower or higher) based on the test result (failure or pass) of the previous specimen. The ultimate load that the bolt can withstand under a constant average load or constant load ratio is analyzed based on the test data.

[0003] The disadvantages of this test method are as follows: (1) The method for selecting a constant average load or a constant load ratio is not clearly specified, which may result in the selection of an average load or a load ratio being significantly different from the actual situation.

[0004] (2) There is no specified method for selecting the initial load, and the test process may generate a lot of invalid data.

[0005] (3) GB / T 13682-92 Axial Fatigue Test Method for Threaded Fasteners stipulates that the specimen should be mounted on the test nut or threaded bushing so that the distance from the end of the specimen thread to the support surface of the fixture is at least 4 times the pitch, and the length of the end exposed to the test nut or threaded bushing is at least 1 time the pitch. Figure 1 shown.

[0006] When installed in this way, the reliability of the threads near the junction of the nut and the supporting surface is mainly assessed. This is different from the thread position that mainly bears the load during actual use of high-strength bolt threads in automotive engines. This installation method ignores the possible state differences in different areas of the threads.

[0007] (4) The existing test method stipulates that the test should be carried out under constant average stress (load) or constant stress ratio (load ratio). However, for most high-strength engine bolts, the minimum load of the bolt remains basically unchanged when the external load changes, and it is the maximum load of the bolt that changes. There is a difference between the load simulation and the actual state of the existing test method, which will reduce the assessment accuracy of the ultimate load that the automotive engine bolts can withstand. Summary of the Invention

[0008] In view of this, the present application aims to propose a fatigue limit load test method for high-strength bolts of vehicle engines to solve at least one of the above problems.

[0009] To achieve the above objectives, the technical solution of this application is implemented as follows: The present application provides a fatigue limit load test method for high-strength bolts for vehicle engines, comprising: Determining bolt test parameters, wherein the test parameters include at least a minimum test load, an initial load amplitude, and a load amplitude increment; According to the determined test parameters, and relying on the preset constant minimum load method, the bolt is subjected to a load test to obtain the ultimate working additional load that the bolt can withstand under the fatigue test; The ultimate load that the bolt can withstand is evaluated based on the bolt load factor and the stated ultimate working additional load.

[0010] Furthermore, the bolt installation preload force is measured in batches, and the preload force distribution parameters are analyzed to obtain the mean and standard deviation of the preload force of the bolts under the prescribed installation specifications, and determine the minimum test load.

[0011] Furthermore, the test minimum load formula is: ; Where, Indicates the bolt installation preload, represents the standard deviation, Indicates the minimum test load.

[0012] Furthermore, the initial load amplitude is set to 80 ~90 , Indicates the stress cross-sectional area of ​​the thread.

[0013] Furthermore, 4% to 6% of the initial load amplitude was used as the load amplitude increment during the test.

[0014] Furthermore, the bolt specimens are tested sequentially according to the lifting method, and the load amplitude of the next bolt specimen is determined based on the test result of the previous bolt specimen; During the test, the minimum test load was set as a fixed value and only the load amplitude was adjusted; After completing the specified number of tests, the test results are analyzed based on the amplitude of the bolt working additional load to obtain the ultimate working additional load that the bolt can withstand under fatigue test.

[0015] Furthermore, the maximum working load that the bolt can withstand is evaluated based on the bolt load factor and the ultimate working additional load, wherein the evaluation formula is: ; Where, Indicates the ultimate working additional load, represents the bolt load factor, Indicates the maximum working load that the bolt can withstand.

[0016] Compared with the prior art, the fatigue limit load test method for high-strength bolts for vehicle engines described in this application has the following beneficial effects: The fatigue limit load test method for high-strength bolts for automotive engines described in this application is mainly used to measure the ultimate load that high-strength bolts such as automotive engine cylinder head bolts, connecting rod bolts, and main bearing bolts can withstand, and can more accurately evaluate the ultimate load that the bolts can withstand under the specified installation state. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings: Figure 1 This is a schematic diagram of the bolt specimen installation requirements described in the embodiment of this application; Figure 2 This is a schematic diagram of the coordinated deformation principle of the bolt and the connected body described in the embodiment of the present application; Figure 3 This is a schematic diagram of the bolt installation depth requirements described in the embodiment of the present application; Figure 4 This is a flow chart of a fatigue limit load test method for high-strength bolts for automotive engines described in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of this application more clear, this application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0019] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should have the usual meanings understood by people with ordinary skills in the field to which this application belongs. The "first", "second" and similar words used in the embodiments of the present application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] This application is mainly used to measure the ultimate load that high-strength bolts such as cylinder head bolts, connecting rod bolts, and main bearing bolts can withstand. After the installation of high-strength bolts such as cylinder head bolts, connecting rod bolts, and main bearing bolts, the bolt preload is When the bolt is subjected to dynamic working load, the working load The load is borne by the bolts and the connected parts. ,in The additional working load of the bolt. The minimum additional working load of the bolt is the preload , the maximum value is If the dynamic working load Increase, the minimum value of the additional working load of the bolt remains unchanged, that is: the minimum value of the additional working load of the bolt is constant, Added. The principle of coordinated deformation of bolts and connected bodies is as follows: Figure 2 shown.

[0021] In addition, a special test base for high-strength bolts for automotive engines is designed, and the bolt installation method is specified. The test base material and thread size are designed according to the material and technical requirements of the actual bolt screw-in position. The length L of the bolt installed in the base is the same as the actual screw-in depth of the bolt, ensuring that the bolt test area is the dangerous area during actual work. The state differences of the bolts at different positions can be considered, such as Figure 3 shown.

[0022] Based on the additional load characteristics of high-strength bolts used in automotive engines, such as cylinder head bolts, connecting rod bolts, and main bearing bolts, a fatigue limit load test method for high-strength bolts used in automotive engines was determined. This method can accurately evaluate the ultimate load that the bolts can withstand under the specified installation state.

[0023] Please refer to Figure 4 As shown, this embodiment provides a fatigue limit load test method for high-strength bolts for vehicle engines, which specifically includes the following methods: Step S101: Determine bolt test parameters, wherein the test parameters at least include a minimum test load, an initial load amplitude, and a load amplitude increment.

[0024] Specifically, in this embodiment, the bolt test parameters are determined before the test, as follows: (1) Determination of the minimum test load. Pre-tighten the bolts Carry out batch measurement, analyze the preload distribution parameters, and obtain the average preload value of the bolt under the specified installation specifications and standard deviation S, determine the minimum test load as , the test is carried out under the maximum possible preload force to improve the safety margin of the bolt reliability assessment results.

[0025] (2) Determination of the initial load amplitude. Based on the test inventory data statistics, for 10.9 and 12.9 grade high strength bolts, the initial load amplitude in this embodiment is In the 80s ~90 (Unit is N) range, The stress cross-sectional area of ​​the thread can improve test efficiency and reduce sample waste.

[0026] (3) Load amplitude increment This embodiment is based on 4%~6% is the load amplitude increment during the test , is a more appropriate range in the lifting method. If the value is too large, the evaluation accuracy will be reduced, and if it is too small, the test efficiency will be reduced.

[0027] Step S102: Perform a load test on the bolt according to the determined test parameters and by relying on a preset constant minimum load method to obtain the ultimate working additional load that the bolt can withstand under the fatigue test.

[0028] Specifically, in this embodiment, if the first bolt does not fail after completing the specified number of cycles, the load amplitude is increased by , the test times are reset to zero and the test is continued until the bolt fails under a certain load level.

[0029] Subsequent bolt specimens are tested in sequence according to the lifting method. The load amplitude of the next specimen is determined (lowered or raised) based on the test result (failure or pass) of the previous specimen. ).

[0030] When increasing or decreasing the load amplitude, ensure the minimum test load Fixed, only the load amplitude changes , that is, the minimum test load is , the maximum load is .

[0031] After completing the required number of tests, The test results are analyzed for the object, and the ultimate working additional load that the bolt can withstand under the specified installation specifications is obtained, that is, limit.

[0032] Step S103: Evaluate the ultimate load that the bolt can withstand based on the bolt load factor and the ultimate working additional load.

[0033] Specifically, in this embodiment, according to the bolt load factor Φ and the ultimate working additional load The maximum working load that the bolt can withstand Conduct an assessment, namely: , the bolt load factor Ф can be obtained through simulation analysis, theoretical calculation and experiment.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

[0035] The embodiments of the present application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of this application.

Claims

1. A fatigue limit load test method for high-strength bolts for vehicle engines, characterized in that: include: Determining bolt test parameters, wherein the test parameters include at least a minimum test load, an initial load amplitude, and a load amplitude increment; According to the determined test parameters, and relying on the preset constant minimum load method, the bolt is subjected to a load test to obtain the ultimate working additional load that the bolt can withstand under the fatigue test; The ultimate load that the bolt can withstand is evaluated based on the bolt load factor and the stated ultimate working additional load.

2. A fatigue limit load test method for high-strength bolts for automotive engines according to claim 1, characterized in that: The bolt installation preload force is measured in batches, and the preload force distribution parameters are analyzed to obtain the mean and standard deviation of the preload force of the bolts under the specified installation specifications, and determine the minimum test load.

3. A fatigue limit load test method for high-strength bolts for vehicle engines according to claim 2, characterized in that: The minimum load formula for the test is: ； Where, Indicates the bolt installation preload, represents the standard deviation, Indicates the minimum test load.

4. The fatigue limit load test method for high-strength bolts for automotive engines according to claim 1, characterized in that: The initial load amplitude is set to 80 ~90 , Indicates the stress cross-sectional area of ​​the thread.

5. The fatigue limit load test method for high-strength bolts for automotive engines according to claim 1, characterized in that: The load amplitude increment during the test is 4% to 6% of the initial load amplitude.

6. The fatigue limit load test method for high-strength bolts for automotive engines according to claim 1, characterized in that: The bolt specimens are tested in sequence according to the lifting method, and the load amplitude of the next bolt specimen is determined based on the test result of the previous bolt specimen; During the test, the minimum test load was set as a fixed value and only the load amplitude was adjusted; After completing the specified number of tests, the test results are analyzed based on the amplitude of the bolt working additional load to obtain the ultimate working additional load that the bolt can withstand under fatigue test.

7. The fatigue limit load test method for high-strength bolts for automotive engines according to claim 1, characterized in that: The maximum working load that the bolt can withstand is evaluated based on the bolt load factor and the ultimate working additional load, wherein the evaluation formula is: ； Where, Indicates the ultimate working additional load, represents the bolt load factor, Indicates the maximum working load that the bolt can withstand.

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