The bending fatigue test was designed and completed according to GB / T 14230-1993. In the bending fatigue test, according to the different settings of the test point, the usual test methods can be divided into the following.
In the S-N curve test with few specimens, more than six stress levels are usually taken, and only two pairs of gear specimens are selected corresponding to each stress level. The bending fatigue strength test starts from the high stress level, because the high stress level has less cycles, and then the bottom stress level is carried out in sequence. Due to the small number of test pieces and the large dispersion of fatigue life of gears, the accuracy of the curve is very limited.
In practical engineering application, more accurate S-N curve is often needed than the method of few specimens. The solution to this problem is to increase the number of specimens, which is the S-N curve test of group specimens. The group test can meet the requirements. The S-N curve test of group specimen method is to select 4-6 stress levels, select 4-6 test gears under each stress level for data collection test, finally get each stress level and the corresponding fatigue life, and then fit the data to get the S-N curve.
The above two methods have the same characteristic, that is, they both take the force exerted on the gear as the fixed value, and treat the fatigue life as a random variable. If the value of fatigue life is determined and the force exerted on the gear is regarded as a random variable, the probability distribution of fatigue limit of the gear can be obtained, and the limit stress with statistical characteristics can be obtained. The above-mentioned method is the test principle of measuring gear fatigue by up-down method.
By comparing the advantages and disadvantages of the above test methods, for the less specimen method, because the test times are less, it has larger error and is not suitable to be used; When using the up-down method, it is necessary to get a S-N curve of a few specimens before measuring the gear fatigue bending test, which is used to lay a certain foundation for the fatigue limit value under a given fatigue life. Therefore, the final test method adopted in this test is group specimen S-N test.