Method for rapidly comparing bending fatigue characteristics of gears made of two materials

Abstract

The invention discloses a method for rapidly comparing bending fatigue characteristics of gears made of two materials, and belongs to the technical field of mechanical part material performance testing. The method comprises the following steps: synchronously testing bending fatigue limit stresses (under a set service life) of gears made of two materials through a step load increasing method, taking 1.2 times of a larger value of the limit stresses as dead load stresses, and testing respective service lives by adopting a dead load method; and finally, through stress comparison under the same service life or service life comparison under the same stress, quantitative evaluation of the material performance is realized. According to the method, the test period can be shortened by 30%-50%, a unified comparison reference is established, and an efficient basis is provided for gear material type selection.

Description

Technical Field

[0001] This invention belongs to the field of mechanical parts material performance testing technology, specifically involving a method for rapidly comparing the bending fatigue characteristics of gears made of two different materials. Background Technology

[0002] As a core component of mechanical transmission systems, the bending fatigue performance of gears directly affects the reliability and lifespan of the transmission system. Accurately comparing the bending fatigue characteristics of gears made of different materials is a key basis for gear material selection and structural optimization.

[0003] Existing methods for testing the bending fatigue performance of gears have the following limitations:

[0004] The testing methods are limited and the data dimensions are insufficient: Traditional methods (such as conventional group methods and variable load methods) can only obtain fatigue limit or life data separately, and cannot provide two core indicators at the same time, resulting in a lack of comprehensiveness in the comparison of material properties. For example, conventional group methods require testing life under fixed stress, making it difficult to obtain fatigue limit at the same time; variable load methods can obtain fatigue limit, but cannot directly output life data under specific stress.

[0005] The comparison is inefficient and costly: different materials need to be tested separately and the testing process is independent (e.g., material A is tested before material B is tested), which leads to a long test cycle (usually 2-3 months). In addition, due to differences in test environment, equipment status, etc., the comparability of data decreases.

[0006] Lack of a unified comparison framework: Existing technologies do not clearly define quantitative standards for "stress comparison under the same lifespan" or "lifespan comparison under the same stress," and cannot directly answer the question "at 3×10 6 Core engineering questions include "Which material can withstand higher stress under the next lifespan?" or "Which material has a longer lifespan under 600MPa stress?"

[0007] Therefore, there is an urgent need for a method that can simultaneously acquire fatigue limit and life data, establish a unified comparison benchmark, and shorten the testing cycle, so as to achieve rapid and accurate comparison of the bending fatigue characteristics of gears made of different materials. Summary of the Invention

[0008] This invention aims to solve the problems of long comparison cycles, single data dimensions, and lack of unified benchmarks in the existing technology for comparing the bending fatigue characteristics of gears. It provides a composite testing method that combines the stepped loading method and the constant load method to achieve rapid and quantitative comparison of the bending fatigue characteristics of gears made of two different materials.

[0009] The technical solution adopted by this invention to solve the above problems is as follows: a method for rapidly comparing the bending fatigue characteristics of gears made of two materials. This method employs a composite testing process of "stepped loading method to determine fatigue limit + constant load method to obtain life data," combined with a two-dimensional comparison framework, to achieve rapid comparison of material properties. The specific steps are as follows:

[0010] Step 1: Bending fatigue limit test based on the stepped loading method

[0011] Test objects: Gears made of two different materials to be compared (e.g., material A: 20CrMnTi; material B: 20CrMoH).

[0012] Stress parameter setting

[0013] Initial stress: set to 80%-90% of the preset bending fatigue limit stress (the preset value is based on the recommended value in GB / T3480.5-2021).

[0014] Stress increment: The stress increment Δσ for each level is 3%-5% of the preset bending fatigue limit stress, the total number of levels is ≥8, and the final stress must exceed the preset fatigue limit;

[0015] Number of cycles per level: 5 × 10 4 Second-rate.

[0016] Test procedure: Apply stepped stress synchronously to gears made of two materials (i.e., test materials A and B in parallel under the same test environment), with each stress level applied at 5 × 10⁻⁶. 4 Next, check the condition of the tooth root:

[0017] If the tooth root is not broken and has no cracks (not failed), then it enters the next level of stress (increases Δσ).

[0018] If the tooth root breaks or cracks (failure) occur, record the current stress as the bending fatigue limit stress of the material (material A: σFlimA; material B: σFlimB).

[0019] Termination condition: Tooth root fracture or crack formation.

[0020] Step 2: Bending fatigue life test based on constant load method

[0021] Setting the constant load stress: Take 1.2 times the larger value of σFlimA and σFlimB in step 1 as the constant load stress σFc (i.e., σFc=1.2×max (σFlimA,σFlimB)).

[0022] Test procedure: Apply constant stress σFc simultaneously to gears made of both materials, and record the number of cycles at failure.

[0023] If one or two of the gear materials are used in a cycle exceeding 3 × 10 6 If the failure does not occur after the second cycle, σFc is increased by 50% (i.e., σFc' = 1.5 × σFc), the load is reloaded, and the number of failure cycles is recorded (material A: NA; material B: NB).

[0024] Step 3: Two-dimensional comparative analysis

[0025] Stress comparison under the same lifespan: based on a set lifespan NL (e.g., 3×10). 6 Using (times) as a benchmark, compare σFlimA and σFlimB. If σFlimA > σFlimB, then material A has better bending fatigue performance at NL life.

[0026] Life comparison under the same stress: Using the constant load stress σFc as the benchmark, compare NA and NB. If NA > NB, then material A has better bending fatigue performance under σFc stress.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] Efficiency improvement: The stepped loading method and the constant load method are tested in parallel (two materials are tested simultaneously). After the fatigue limit is quickly located by the stepped method, the constant load test can be started directly, shortening the total cycle by 30%-50% (from the traditional 2-3 months to 1-1.5 months).

[0029] Data comprehensiveness: Simultaneous acquisition of fatigue limit (σFlim) and life (N) data, covering core material performance indicators.

[0030] Comparative Quantification: Establishing dual benchmarks of "same life-stress" and "same stress-life" allows for direct quantification of differences (e.g., "material B at 3×10..."). 6 "The stress at the next life is 15.6% higher than that of material A." "The life of material B at a stress of 649.56 MPa is 3.2 times that of material A."

[0031] Engineering applicability: Test parameters (such as initial stress and stress increment) are set based on national standards (GB / T3480.5-2021, GB / T14230-2021), and the results can be directly used for engineering selection.

[0032] Instruction manual illustrations

[0033] Figure 1: Test method flowchart - including the process logic of the stepped load method, the constant load method, and comparative analysis;

[0034] Figure 2: Comparison of SN curves for stepped loading test of material A and material B - the horizontal axis represents the number of cycles, the vertical axis represents the bending stress, and the fatigue limits of both are marked;

[0035] Figure 3: Comparison of life under constant load test – The bar chart shows the number of failure cycles for the two materials under a stress of 649.56 MPa. Detailed Implementation

[0036] The technical solution of the present invention will be described in more detail with reference to preferred embodiments. However, these embodiments are merely descriptions of preferred implementations of the present invention and should not be construed as limiting the scope of the invention.

[0037] I. Test Preparation

[0038] Test samples: Gear of material A (20CrMnTi) and gear of material B (20CrMoH), both of which are standard spur gears (module 3mm, number of teeth 20).

[0039] Equipment: Gear bending fatigue testing machine (compliant with GB / T3480.5-2021 requirements), equipped with stress loading module and tooth root crack detection device (accuracy 0.1mm).

[0040] Preset parameters: Lifespan setting NL = 3 × 10 6 The preset bending fatigue limit stress is based on the recommended value of 500 MPa in GB / T3480.5-2021.

[0041] II. Step 1: Step-by-step load increase method test (fatigue limit acquisition)

[0042] Stress parameters:

[0043] Initial stress: 500MPa × 90% = 450MPa; The initial stress of the first gear corresponding to material A is 450MPa (preset bending fatigue limit stress). =90% of 500MPa), the initial stress of the second gear corresponding to the second material B is 450MPa (preset bending fatigue limit stress). =90% of 500 MPa)

[0044] Stress increment Δσ: 500MPa × 5% = 22.5MPa; Stress increment Δσ per stage corresponding to the first gear A =22.5MPa (the first gear corresponding to the first material A), the stress increment Δσ per stage corresponding to the first gear. B =22.5MPa (the second gear corresponding to the second material B).

[0045] Number of cycles per level: 5 × 10 4 Second-rate;

[0046] Total number of levels: ≥8 levels (in actual testing, material A was level 10 and material B was level 14).

[0047] Testing process:

[0048] Material A, Gear (No. A-01): Loading started at 450 MPa, with stress increasing by 22.5 MPa per stage. No damage was observed in the first 9 stages (5 × 10 cycles per stage). 4 (times); Level 10 (652.5MPa) cycle 3.5×10 4 The tooth root developed a crack, so the test was stopped.

[0049] Table 1. Test data of stepped load increase for the first gear corresponding to material A.

[0050] Material B, gear (No. B-01): Under the same stress gradient loading, no damage was observed in the first 13 stages; the 14th stage (742.5 MPa) underwent 4 × 10 cycles. 4 The tooth root developed a crack, so the test was stopped.

[0051] Table 2. Test data of the stepped load increase test for the second gear corresponding to the second material B.

[0052] Data processing (based on GB / T14230-2021) Material A: According to the stepped loading method test method of standard GB / T14230-2021, three reference SN curves were selected (their bending fatigue limit stresses are 450MPa, 470MPa, and 490MPa, respectively). Based on the Miner criterion, the corresponding damage values ​​were calculated as 1.3458, 0.9204, and 0.6395, respectively. Using the polynomial difference method, the bending fatigue limit stress of gear A-01 was obtained as σ. limA =468.2MPa; Table 3. Material A Gear Step Loading Data Processing

[0053] Material B: Similarly, according to the stepped loading method test method of standard GB / T14230-2021, three reference SN curves were selected (their bending fatigue limit stresses are 530MPa, 550MPa, and 570MPa, respectively); based on the Miner criterion, the corresponding damage values ​​were calculated as 1.1706, 0.8469, and 0.6198, respectively. Using the polynomial difference method, the bending fatigue limit stress of gear B-01 was obtained as σ. limB =541.3MPa.

[0054] Table 4. Material B Gear Step Loading Data Processing

[0055] 3. Step 2: Constant Load Test (Lifetime Acquisition) Dead load stress setting: σFc=1.2×max(468.2MPa,541.3MPa)=1.2×541.3MPa=649.56MPa.

[0056] Testing process Material A, Gear (No. A-02): 1×10 cyclic pressures at 649.56 MPa 5 Subsequently, a crack appeared at the tooth root, and NA was recorded as 1 × 10. 5 Second-rate; Table 5. Test data of gears under constant load for material A

[0057] Material B, Gear (No. B-02): 3.2 × 10⁻⁶ cycles at 649.56 MPa. 5 A crack appeared at the tooth root after that, and NB was recorded as 3.2 × 10⁻⁶. 5 Second-rate.

[0058] Table 6. Test data of gear B under constant load

[0059] IV. Comparison Results Same lifespan (3×10) 6 Comparison of stresses under different stress levels: σFlimB (541.3MPa) > σFlimA (468.2MPa), material B has a better bending fatigue limit; Lifetime comparison under the same stress (649.56MPa): NB (3.2×10 5 times)>NA (1×10 5 Material B has a longer lifespan (times).

[0060] Conclusion: Under the test conditions, the bending fatigue characteristics of 20CrMoH gears are superior to those of 20CrMnTi gears.

[0061] Although preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapidly comparing the bending fatigue properties of gears made of two different materials, characterized in that, The method includes the following steps: Step 1: The two types of gears were tested using the stepped loading method to obtain their respective bending fatigue limit stresses σFlimA and σFlimB under a set life NL. Step 2: Determine the constant load stress σFc based on σFlimA and σFlimB, and use the constant load method to test the gears of the two materials respectively to obtain their bending fatigue life NA and NB under σFc; Step 3: Compare the stress under the same lifetime based on σFlimA and σFlimB, or compare the lifetime under the same stress based on NA and NB; Step 1 and Step 2 are carried out in parallel within the same testing cycle.

2. The method for rapidly comparing the bending fatigue properties of gears made of two materials according to claim 1, characterized in that: The parameters for the stepped loading method in step 1 are set as follows: the initial stress is 80%-90% of the preset bending fatigue limit stress; the stress increment Δσ for each step is 3%-5% of the preset bending fatigue limit stress; and the number of cycles for each stress level is 5×10. 4 The stress level must be at least 8 levels in total, and the final stress must be greater than the preset bending fatigue limit stress.

3. The method for rapidly comparing the bending fatigue properties of gears made of two materials according to claim 1, characterized in that: In step 1, the lifetime NL is set to 3 × 10. 6 The bending fatigue limit stress needs to be obtained based on the stepped loading method test standard of GB / T14230-2021, combined with the Miner criterion and polynomial interpolation method.

4. The method for predicting rotational bending fatigue life based on the gradient characteristics of the seepage layer according to claim 1, characterized in that: In step 2, the constant load stress σFc = 1.2 × max (σFlimA, σFlimB); if the number of cycles for the gears made of the two materials under σFc exceeds 3 × 10 6 If the test still fails, adjust σFc to 1.5×σFc and retest.

5. The method for predicting rotational bending fatigue life based on the gradient characteristics of the seepage layer according to claim 1, characterized in that: In step 3, "stress comparison under the same life" specifically means: under a set life NL, if σFlimA>σFlimB, then the bending fatigue performance of material A is better than that of material B; "life comparison under the same stress" specifically means: under constant load stress σFc, if NA>NB, then the bending fatigue performance of material A is better than that of material B.

6. The method for predicting rotational bending fatigue life based on the gradient characteristics of the seepage layer according to claim 2, characterized in that: The preset bending fatigue limit stress is determined based on the recommended value in the national standard GB / T3480.5-2021.

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