High-reliability gear fatigue limit rapid test method based on reliability conversion coefficient

Abstract

The invention relates to a high-reliability gear fatigue limit rapid test method based on a reliability conversion coefficient, and the method specifically comprises the steps: carrying out a gear fatigue strength lifting method test, and obtaining the reliability conversion coefficient based on a mathematical statistical method; carrying out a Locati method fatigue test to obtain a fatigue test point; processing a test result of the Locati method based on a reference fatigue S-N curve, and obtaining a gear fatigue limit under 50% reliability; and according to the gear fatigue limit under the reliability of 50%, evaluating the gear fatigue limit under the high reliability by applying the reliability conversion coefficient. The problems of large test sample size, high cost and long test period required for obtaining the high-reliability gear fatigue limit are solved, and a high-precision evaluation result can be kept while the test quantity is reduced; the method can be conveniently applied to engineering practice, and efficient method support is provided for gear anti-fatigue and high-power-density design.

Description

Technical Field

[0001] The present invention belongs to the field of mechanical anti-fatigue design, and relates to a high-reliability gear fatigue limit rapid test method based on a reliability conversion coefficient. Background Art

[0002] As a key component in a mechanical transmission system, the fatigue performance of gears directly affects the reliability and lifespan of the entire system. In engineering practice, failures such as pitting and tooth root fractures caused by gear fatigue often occur, endangering the safety of humans and machines. Therefore, the accurate evaluation of the gear fatigue limit is very important for the high-performance design and safe use of gear transmissions.

[0003] The gear fatigue limit under high reliability can usually be obtained through the up-and-down method fatigue test. However, it requires a large number of test samples and a long test cycle. Taking the gear contact fatigue strength as an example, it takes more than one year to carry out the up-and-down method test to obtain the gear contact fatigue limit under 99% reliability, seriously restricting the process of fatigue data construction. Therefore, there is an urgent need for a test method with short time and low cost to evaluate the gear fatigue limit value under high reliability.

[0004] The Locati method can quickly obtain the fatigue strength limit by stepwise incremental loading on one sample, which can greatly save costs and time. However, it can only obtain the fatigue limit under 50% reliability and cannot obtain the fatigue limit under high reliability. Summary of the Invention

[0005] In view of this, in order to solve the problems of large number of test samples, high cost, long test cycle required for the existing evaluation of the gear fatigue limit under high reliability and the inability to obtain the fatigue limit under high reliability, the present invention provides a high-reliability gear fatigue limit rapid test method based on a reliability conversion coefficient. The reliability conversion coefficient is obtained by statistically analyzing the gear fatigue limits under different reliabilities obtained from the up-and-down method test. The Locati method fatigue test is carried out and the test results of the Locati method are processed based on the reference S-N curve to obtain the gear fatigue limit under 50% reliability, and the reliability conversion coefficient is applied to evaluate the gear fatigue limit under high reliability. This method can evaluate the gear fatigue limit under high reliability with less test cost and cycle, and can be conveniently applied to engineering practice, providing an efficient method support for gear anti-fatigue and high power density design. To achieve the above object, the present invention provides the following technical solutions:

[0006] A high-reliability gear fatigue limit rapid test method based on a reliability conversion coefficient, comprising the following steps:

[0007] S1. Obtain the reliability conversion coefficient: Carry out the up-and-down method test for the gear fatigue strength, and obtain the reliability conversion coefficient based on mathematical statistics methods;

[0008] S2, Gear Fatigue Test by Locati Method: Conduct the gear fatigue test by Locati method to obtain fatigue test points;

[0009] S3, Obtain the Gear Fatigue Limit at 50% Reliability: Based on the reference S-N curve and the test results of the Locati method in Step S2, obtain the gear fatigue limit at 50% reliability;

[0010] S4, Evaluate the Gear Fatigue Limit at High Reliability: According to the gear fatigue limit at 50% reliability in Step S3, apply the reliability conversion coefficient in Step S1 to evaluate the gear fatigue limit at high reliability.

[0011] Furthermore, in Step S1, carry out the up-and-down method test of the gear with reference to the national standards GB / T 14229-2021 or GB / T 14230-2021 to obtain the gear bending fatigue limit at different reliabilities, and divide the results at high reliability by those at 50% reliability to obtain the reliability conversion coefficient.

[0012] Furthermore, in Step S2, formulate the test plan according to the national standards GB / T 14229-2021 or GB / T 14230-2021 and conduct the gear fatigue test by Locati method.

[0013] Furthermore, in Step S3, obtain the reference fatigue S-N curve according to the literature, translate the obtained reference fatigue S-N curve and the limits up and down to obtain 3 reference curves, and process the test results of the Locati method based on the 3 reference curves to obtain the gear fatigue limit at 50% reliability.

[0014] Furthermore, the specific process of obtaining the gear fatigue limit at 50% reliability is as follows: Process the test results of the Locati method based on the above 3 reference curves, calculate and values respectively, plot the corresponding curve, and find out the fatigue limit value corresponding to where is the Miner linear cumulative damage rule, and represents the gear fatigue limit.

[0015] The beneficial effects of the present invention are as follows:

[0016] 1. The present invention proposes a rapid test method for the fatigue limit of high-reliability gears based on a reliability conversion coefficient. By statistically analyzing the gear fatigue limits at different reliabilities obtained from the up-and-down method tests, the reliability conversion coefficient is obtained, and the Locati method fatigue test is carried out, significantly reducing the required test sample size, thereby reducing the gear fatigue test cost and cycle. And based on the reference fatigue S-N curve, the test results of the Locati method are processed to obtain the gear fatigue limit at 50% reliability. The reliability conversion coefficient is applied in combination with the gear fatigue limit at 50% reliability to evaluate the gear fatigue limit at high reliability, which can obtain the fatigue limit at high precision and high reliability while reducing the test volume.

[0017] 2. The present invention proposes a rapid test method for the fatigue limit of high-reliability gears based on a reliability conversion coefficient. This method not only has important scientific value but also provides an efficient and economical means for evaluating the gear fatigue limit in engineering practice, with broad application prospects.

[0018] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0019] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where:

[0020] Figure 1 is a flow chart of a rapid test method for the fatigue limit of high-reliability gears based on a reliability conversion coefficient according to the present invention;

[0021] Figure 2 are the test points and results of the up-and-down method tests for 8 groups of gears in the embodiment, where 2a are the test points and results of the up-and-down method test for gear A1, 2b are the test points and results of the up-and-down method test for gear A2, 2c are the test points and results of the up-and-down method test for gear A3, 2d are the test points and results of the up-and-down method test for gear A4, 2e are the test points and results of the up-and-down method test for gear A5, 2f are the test points and results of the up-and-down method test for gear A6, 2g are the test points and results of the up-and-down method test for gear A7, and 2h are the test points and results of the up-and-down method test for gear A8;

[0022] Figure 3 are the reliability conversion coefficients obtained from the up-and-down method tests for 8 groups of gears in the embodiment;

[0023] Figure 4They are the 3 test points of the gear bending fatigue Locati method in the embodiment, where 4a is the Locati test point I, 4b is the Locati test point II, and 4c is the Locati test point III;

[0024] Figure 5 They are the 3 reference curves of the gear bending fatigue Locati method test in the embodiment;

[0025] Figure 6 They are the fatigue limits corresponding to the 3 test points of the gear bending fatigue Locati method in the embodiment. Specific implementation manners

[0026] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0027] As Figure 1 shown, a rapid test method for gear fatigue limit under high reliability based on a reliability conversion coefficient includes the following steps:

[0028] S1. Obtain the reliability conversion coefficient: Conduct a gear fatigue strength up-and-down method test to obtain the reliability conversion coefficient.

[0029] Refer to the national standard GB / T 14229-2021 or GB / T 14230-2021 to conduct the up-and-down method test of the gear, obtain the gear bending fatigue limits under different reliabilities, and divide the result under high reliability by the result under 50% reliability to obtain the reliability conversion coefficient.

[0030] S2. Gear fatigue test by the Locati method: Conduct a gear fatigue test by the Locati method to obtain fatigue test points.

[0031] Formulate a test plan according to the national standard GB / T 14229-2021 or GB / T 14230-2021, and conduct a gear fatigue test by the Locati method.

[0032] S3. Obtain the gear fatigue limit under 50% reliability: Based on the reference fatigue S-N curve, process the test results of the Locati method in step S2 to obtain the gear fatigue limit under 50% reliability.

[0033] Obtain the reference fatigue S-N curve according to the literature, and obtain three reference curves by translating the obtained reference fatigue S-N curve up and down by the limit. Process the test results of the Locati method based on the three reference curves, and calculate and values, and make the corresponding curve, and find out the fatigue limit value corresponding to , where is the Miner linear cumulative damage rule, represents the fatigue limit of the gear, and obtain the gear fatigue limit under 50% reliability.

[0034] S4. Evaluate the gear fatigue limit under high reliability: According to the gear fatigue limit under 50% reliability in step S3, apply the reliability conversion coefficient in step S1 to evaluate the gear fatigue limit under high reliability.

[0035] Example:

[0036] In this example, taking the acquisition of the gear bending fatigue limit as an example, the up-and-down method test is carried out on 8 groups of gear specimens with different materials, processes and module numbers to obtain the gear bending fatigue limits under 50% and 99% reliability, and divide the results under 99% reliability and 50% reliability to obtain the reliability conversion coefficient. Carry out the Locati method test on the 18CrNiMo7-6 carburized and ground gear with a module of 5 mm, process the test results of the Locati method based on the reference fatigue S-N curve, obtain the gear bending fatigue limit under 50% reliability, and apply the reliability conversion coefficient to evaluate the gear bending fatigue limit under 99% reliability. The specific steps are as follows:

[0037] S1. Carry out the up-and-down method test on the gear fatigue strength to obtain the gear bending fatigue limits under different reliabilities, and divide the results under high reliability by those under 50% reliability to obtain the reliability conversion coefficient.

[0038] In the up-and-down method test case, the materials of the test gears include 18CrNiMo7-6, 20Cr2Ni4A, 20CrMnMo and 42CrMo, covering the process states of carburizing, quenching and tempering, carburizing + shot peening and quenching and tempering + shot peening. The basic parameters of the test gears are shown in Table 1.

[0039] Table 1: Basic parameters and process states of the case gears

[0040]

[0041] The gear bending fatigue up-and-down method test is carried out in accordance with "GB / T 14230-2021 Test Method for Gear Bending Fatigue Strength". First, before the test starts, obtain the gear tooth profile and dangerous section parameters, and determine the clamping position to ensure accurate loading. The initial load is determined through pre-tests or experience, and the load interval is selected as 0.04 - 0.06 times the material's tensile strength according to the national standard GB / T 14230-2021. The failure criteria are a 5% decrease in the test loading frequency and the appearance of visible cracks or tooth breakage at the tooth root. Taking 3 million cycles as the cycle base number, exceeding the cycle base number is judged as exceeding the limit. The total number of test points is not less than 20 and meets the closing requirement (the predicted point after the last test point has the same stress level as the first test point).

[0042] Figure 2 The bending fatigue up-and-down method test points and results of 8 groups of case gears (Gear A1, Gear A2, Gear A3, Gear A4, Gear A5, Gear A6, Gear A7, and Gear A8) are shown. According to the data processing method in GB / T 14230-2021, taking "failure" as the "analysis event", statistically analyze the up-and-down method test results to obtain the gear bending fatigue limits at 50% and 99% reliability. Divide the results at 99% reliability by the results at 50% reliability to obtain the reliability conversion coefficient for each group of test gears. Figure 3 The reliability conversion coefficients obtained from the up-and-down method test of the case gears are shown. The average value of the 8 groups of case reliability conversion coefficients obtained is 0.924, and the obtained average value of 0.924 is used for the subsequent evaluation of the gear fatigue limit at 99% reliability.

[0043] S2. Conduct the Locati method gear fatigue test to obtain fatigue test points.

[0044] The test gear material for the Locati method test case is 18CrNiMo7-6, and the processing technology is carburizing and grinding. The geometric parameters of the test gears are shown in Table 2.

[0045] Table 2: Geometric parameters of the implementation case gears

[0046]

[0047] For the carburized and ground gears of 18CrNiMo7-6, the reference S-N curve and the predicted bending fatigue limit can be obtained from the reference "Chen D, Zhu J, Liu H, et al. Experimental investigation of the relation between the surface integrity and bending fatigue strength of carburized gears[J]. Science China Technological Sciences, 2022, 66(1): 33-46". Its slope is -0.1144 and the intercept is 3.4402, as shown in Equation (1).

[0048]

[0049] As Figure 2 shown, according to the national standard "GB / T 14230-2021 Test method for gear bending fatigue strength", the Locati method gear bending fatigue test is carried out. The case gear is subjected to stepped incremental loading, and the number of cycles for each load level is set to 30,000. Stepped loading is carried out until gear bending failure occurs. Figure 4 The figure shows the test points obtained by the Locati method in the case. A total of 3 test points of the Locati method are obtained, namely: Locati test point I, Locati test point II, and Locati test point III. The total number of cycles of the 3 test points are 144,998, 172,047, and 176,118 respectively.

[0050] S3. Process the test results of the Locati method in step S2 to obtain the gear fatigue limit under 50% reliability.

[0051] As Figure 5 shown, translate the reference fatigue S-N curve up and down to obtain 3 reference curves. Process the test results of the Locati method according to the national standard "GB / T 14230-2021 Test method for gear bending fatigue strength". Substitute each stress level σ i of each test point into the equations of the 3 reference curves respectively to solve the corresponding life value N ij . According to the number of cycles n i of each stress level, calculate the damage value n i / N ij of the corresponding stress level, and calculate the total damage value ∑n i / N ij of each reference curve according to Equation (3). Fit the ∑n / N-σ limThe curve equation, solve for σ when ∑n / N = 1 lim The value, which is the fatigue limit value at 50% reliability. As Figure 6 shown, for the implementation case, the fatigue limit values at 50% reliability of the 3 groups of Locati method test points are 604.95 MPa, 649.42 MPa, and 654.24 MPa respectively, and the average value is 636.20 MPa. This average value can be considered as the bending fatigue limit of the final test gear at 50% reliability.

[0052]

[0053]

[0054] In the formula: σ i is the stress level of the test point, MPa; i is the serial number of the stress level; N ij is the corresponding life value of each stress level on each reference curve; j is the number of reference curves. In this implementation case, j is 3.

[0055] S4. According to the gear fatigue limit at 50% reliability in step S3, apply the reliability conversion coefficient in step S1 to evaluate the gear fatigue limit at high reliability.

[0056] Carry out the Locati method test to obtain the bending fatigue limit of the carburized and ground 18CrNiMo7-6 gear with a module of 5 mm at 50% reliability as 636.20 MPa. Multiply it by the reliability conversion coefficient of 0.924 to get the bending fatigue limit at 99% reliability as 587.85 MPa. Compared with the bending fatigue limit of 607.52 MPa obtained by the staircase method test at 99% reliability, the error is 3.24%, which proves the accuracy of applying the reliability conversion coefficient to evaluate the gear fatigue limit at high reliability. The total number of test points decreased by 85% compared with 20 of the staircase method. The total number of test cycles of the Locati method test is 493,163 times, which is reduced by 98% compared with the total number of cycles of 32,511,828 times of the staircase method.

[0057] In this embodiment, the up-and-down method tests are carried out using carburized gears and quenched and tempered gears with different module numbers and process states as examples. Based on mathematical statistics methods, reliable conversion coefficients are obtained. The Locati method tests are carried out and the test results of the Locati method are processed according to the reference S-N curve to obtain the gear bending fatigue limit at 50% reliability. The reliable conversion coefficient is applied to evaluate the gear bending fatigue limit at 99% reliability. The obtained bending fatigue limit at 99% reliability is 587.85 MPa, and the error compared with 607.52 MPa obtained by the up-and-down method test is 3.24%. Using the high-reliability gear fatigue limit rapid test method based on the reliable conversion coefficient proposed in the present invention, the number of test points is reduced by 85% compared with 20 of the up-and-down method; the total number of cycles of the Locati method is 493,163 times, which is reduced by 98% compared with the total number of cycles of the up-and-down method, which is 32,511,828 times. It can be seen that the present invention can significantly reduce the sample size and cost of gear fatigue tests and provide an efficient method support for gear anti-fatigue and high-power density designs.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A high reliability gear fatigue limit rapid test method based on reliability conversion coefficient, characterized in that: The steps include: S1. Obtaining reliability conversion coefficient: Conduct gear fatigue strength lifting and lowering test and obtain reliability conversion coefficient based on mathematical statistics method; S2. Locati gear fatigue test: Carry out Locati gear fatigue test and obtain fatigue test points; S3, obtaining the gear fatigue limit at 50% reliability: processing the Locati method test result in step S2 based on the reference SN curve to obtain the gear fatigue limit at 50% reliability; S4. Evaluate the gear fatigue limit under high reliability: Based on the gear fatigue limit under 50% reliability in step S3, apply the reliability conversion coefficient in step S1 to evaluate the gear fatigue limit under high reliability.

2. A high reliability gear fatigue limit rapid test method based on reliability conversion coefficient as claimed in claim 1, characterized in that: In the step S1, a gear fatigue lifting method test is carried out with reference to the national standard GB / T 14229-2021 or GB / T 14230-2021 to obtain the gear bending fatigue limit under different reliabilities, and the result under high reliability is divided by the result under 50% reliability to obtain the reliability conversion coefficient.

3. A high reliability gear fatigue limit rapid test method based on reliability conversion coefficient as claimed in claim 1, characterized in that: In step S2, a test plan is formulated according to the national standard GB / T 14229-2021 or GB / T 14230-2021, and a Locati method gear fatigue test is carried out.

4. A high reliability gear fatigue limit rapid test method based on reliability conversion coefficient as claimed in claim 1, characterized in that: In step S3, a reference fatigue SN curve is obtained according to literature data, and three reference curves are obtained by translating the obtained reference fatigue SN curve and the limit up and down. The Locati method test results are processed based on the three reference curves to obtain the gear fatigue limit at 50% reliability.

5. A high reliability gear fatigue limit rapid test method based on reliability conversion coefficient as claimed in claim 4, characterized in that: The specific process of obtaining the gear fatigue limit under 50% reliability is as follows: based on the three reference curves, the Locati method test results are processed and the calculation is performed respectively. and numerical value, make corresponding curve, find the corresponding The fatigue limit value of is Miner's linear cumulative damage law, Indicates the fatigue limit of the gear.

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